McQuay AVR User Manual

AAF-HermanNelson Classroom Unit Ventilators

Models AVS, AVB, AVV and AVR Floor Units

Catalog UV1600

Contents

Introduction 3

AAF-HermanNelson Classroom Unit Ventilators 3 The Model AV Floor Unit 4

Features & Benefits 5

Quiet Operation With Our GentleFlo Delivery 5 The Right Amount of Fresh Air and Cooling 6 Precise Temperature and Dehumidification Control 7 Low Installation Costs 9 Low Operating Costs 10 Easy To Maintain 11 Built To Last 13

MicroTech II Controls 15

MicroTech II Controls For Superior Performance, Easy Integration 15 Control Modes and Functions 17 Advanced Control Options 19 System Components 21

Accessories 25

Wall Louvers & Grilles 25 Ventimatic™ Shutter Room Exhaust Ventilation 26 Storage Cabinets, Sink & Bubbler 27 End Panels, Filler Sections & Sub-Bases 28

Application Considerations 29

Why Classrooms Overheat 29 Meeting IAQ Requirements 31 Following ASHRAE Control Cycle II 31 Meeting ARI 840 Requirements 32 Meeting IBC Seismic Requirements 33 Face & Bypass Temperature Control 34 Modulating Valve Temperature Control 36 Coil Selection 37 DX Split Systems 38 Window Downdraft Protection 40 Digital Ready Systems 43 Field-Installed Controls By Others & Digital Ready Controls 43 Unit Installation 48 Unit Arrangements: 16-5/8" Deep 51

Unit Arrangements: 21-7/8" Deep 52

Coil Selection 55

Quick Selection Procedure 55 Coil Selection Procedure 56 Chilled Water Selection Example 58 Hot Water Heating Selection 60 Steam Heating Selection 63 Electric Heating Selection 64 Direct Expansion Cooling Coil Selection 65

Valve Selection 66

Face and Bypass End-Of-Cycle Valve Sizing & Piping 66 Modulating Valve Sizing & Piping 68 Steam Valve Sizing & Piping 70

General Data 72

AV General Data 72 Available Unit Ventilator Combinations 73 Available Coil Combinations 75

Details & Dimensions 76

Coil Connections 76 Condensate Drain Connections 79 16-5/8” (422 mm) Deep Unit Arrangements 80 21-7/8" Deep Arrangements 82 End Panels 87 Valve Dimensions 88 Wall Intake Louvers & Grilles 89 Ventimatic Shutter Assembly 90 Sink & Bubbler Cabinet 91 Filler Sections & Utility Compartment 92 Shelf Storage Cabinets 93 Finned Tube Radiation Cabinets 95

Wiring Diagrams 96

Typical MicroTech II Wiring Diagrams 96 Typical Digital Ready Wiring Diagram 99 Typical Controls By Others Wiring Diagram 100

Guide Specifications 101

AAF-HermanNelson Unit Ventilator Model AV Guide Specifications 101

The ventilation rate of AAFHermanNelson unit ventilators is certified and tested per Air Conditioning and Refrigeration Institute (ARI) Standard 840.

McQuay is a registered trademark and MicroTech II, Digital Ready, GentleFlo, ServiceTools,

Microsoft is a registered trademark and Windows is a trademark of Microsoft Corporation.

and Protocol Selectability are trademarks of McQuay International.

Introduction

AAF-HermanNelson Classroom Unit Ventilators

Low Installation Costs

New construction installations are easily accomplished with AAF-HermanNelson unit ventilators because they avoid the added cost and space required for expensive ductwork. Retrofit installations are also economical because new units fit the same space occupied by existing ones. Multiple control options—including MicroTech II controls with Protocol Selectability™, or

For more than 85 years, schools have relied on AAF-HermanNelson unit ventilators to keep classrooms comfortable. Students learn more readily in a quiet, wellventilated environment. That’s why Herman Nelson invented the unit ventilator and why we remain committed to meeting the changing requirements of schools with the highest quality products available.

We realize that keeping expenditures down is a high priority for school administrators and school boards. AAF-HermanNelson unit ventilators are inexpensive to install and operate, and they are designed and built to provide decades of trouble-free service.

Quiet Operation

AAF-HermanNelson unit ventilators are engineered and manufactured to deliver quiet, continuous comfort. We developed our GentleFlo™ air moving system to minimize operating sound levels—even as demands for more fresh air require units to operate longer and work harder.

The Right Amount of Fresh Air and Cooling

AAF-HermanNelson unit ventilators deliver required amounts of fresh air to meet ventilation requirements, and added cooling capacity to maintain consistent comfort for students and teachers. Our Economizer Operation, Demand Control Ventilation (DCV) and Part Load, Variable Air options allow you to closely match comfort requirements and reduce operating costs.

Precise Temperature and Dehumidification Control

AAF-HermanNelson unit ventilators feature precise temperature and dehumidification control to keep students and teachers comfortable while making maximum use of “free” outdoor-air cooling to reduce operating costs. They utilize a draw-thru air design that contributes to even heat transfer and uniform discharge air temperatures into the classroom. Coupled with face and bypass air control and our MicroTech passive dehumidification control strategies, they provide precise control of temperature and humidity levels.

II™ active and

Digital Ready™ features—provide easy, low cost integration into the building automation system of your choice.

Low Operating Costs

When running, AAF-HermanNelson unit ventilators can use as little electricity as two 100-watt light bulbs. They take maximum advantage of “free” cooling opportunities to reduce operating costs. During unoccupied periods and at night, units operate sparingly to conserve energy.

Easy To Maintain, Modular Design

AAF-HermanNelson Unit Ventilators are designed to provide easy access for maintenance and service personnel to all serviceable components. Most tasks are easily handled by a single person.

Built To Last

Our proven institutional design can withstand the rigors of the classroom environment. It features an extra-sturdy chassis and double-wall damper on the inside; scuffresistant finishes and tamper prevention features on the outside. In fact, many units installed over 30 years ago continue to provide quiet, reliable classroom comfort.

MicroTech II Control For Superior Performance, Easy Integration

AAF-HermanNelson unit ventilators can be equipped with MicroTech II™ unit controllers for superior performance. Factory integrated and tested controller, sensor, actuator and unit options promote quick, reliable start-up and minimize costly field commissioning. Our Protocol Selectability feature provides easy, low-cost integration into most building automation systems. Select BACnet communications to communicate control and monitoring information to your BAS, without the need for costly gateways. Unit controllers are L the optional L

, LonTalk® or Metasys® N2 Open

ONWORKS

communication module.

ONMARK

certified with

AAF-HermanNelson Model AV Unit Ventilators 3

Introduction

The Model AV Floor Unit

Our Model AV is a vertical, floor-standing unit that utilizes remotely-supplied chilled water or refrigerant for cooling, and hot water, steam or electric heat for heating. The Model AV also can be supplied as a heating/ventilating unit only or as a cooling/ventilating unit only.

The Model AV is just right for new construction and for retrofit applications. Older buildings with baseboard

Hinged Top Access Doors

Welded OnePiece Chassis

Sampling Chamber

Draw-Thru Air Flow

Quiet, Aerodynamic Fans

radiant heat or other hydronic heating systems can be easily adapted to work efficiently with Model AV units. Chilled-water or refrigerant cooling can be added to provide year-round comfort. The major features of this model are shown below and described in more detail on the following pages.

Fan Motor Out Of Airstream

MicroTech II Controls

Composite Drain Pan

Sectionalized Access Panels

Face And Bypass Damper Design

• Welded One-Piece Chassis offers

superior strength, durability, and vibration reduction.

• Unique Draw-Thru Design provides

uniform air distribution across the coil for even discharge air temperatures.

• Quiet, Aerodynamic Fans utilize

GentleFlo technology for exceptionally quiet unit operation.

• Modular Fan Section improves

balance, alignment and simplifies maintenance.

• Fan Motor Located Out Of Air

Stream and away from heating coil

reduces heat exposure to prolong life.

• Face And Bypass Damper Design

provides superior dehumidification and reduces chance of coil freeze-up

Advanced Heat Transfer Coil

• Certified Ventilation Performance

per ARI-840.

• MicroTech II Controls provide supe-

rior comfort control and easy integration into the building automation system of your choice.

• Advanced Heat Transfer Coil design

provides extra capacity.

• Sturdy Cabinet Construction

includes hidden reinforcement, a nonglare textured surface, and a tough, scuff- and mar-resistant finish to make the top sturdy enough to support maintenance personnel.

• Sectionalized Front Access Panels

provide easy access to unit interior. Panels are easily removed by a single person. Front side panels can be removed while unit is running.

Single Full-Length Air Filter

Sturdy Cabinet

• Two Hinged Top Access Doors pro-

vide easy access to motor and end bearing. Special tamper-resistant fasteners deter unauthorized access.

• Sampling Chamber for unit-mounted

sensor provides accurate sensing of room temperature.

• Indoor Room Air Damper blocks

unwanted gusts of outdoor air on windy days. Its nylon bearings are quiet and maintenance free.

• Insulated Double-Wall Outdoor Air

Damper seals tightly without twisting.

• Single Full-length Air Filter is effi-

cient and easy to replace. All air delivered to classroom is filtered.

• UL/cUL Listed

4 McQuay Catalog 1600

Features & Benefits

Quiet Operation With Our GentleFlo Delivery

• Fan wheels are large, wide and rotate at a low speed to reduce fan sound levels. They are impact-resistant and carefully balanced to provide consistent performance.

• Offset, aerodynamic fan wheel blades move air efficiently (

• Precision tolerances help reduce flow and pressure turbulence, resulting in lower sound levels.

• Fan housings incorporate the latest logarithmicexpansion technology for smoother, quieter air flow (

Figure 2).

Figure 1. GentleFlo Fan Technology

Figure 1).

Expanded discharge air opening

• A large, expanded discharge opening minimizes air resistance, further lowering sound levels.

• Modular fan construction contributes to equal outlet velocities and promotes quiet operation.

• Fan shafts are of ground and polished steel to minimize deflections and provide consistent, long-term operation.

• Fan assemblies are balanced before unit assembly, then tested after assembly (and rebalanced if necessary) to provide stable, quiet operation.

Figure 2. GentleFlo Reduces Turbulence

Minimal

Offset aerodynamic blades

Logarithmic expansion housing

Precision Tolerances

AAF-HermanNelson Model AV Unit Ventilators 5

GentleFlo fan blade design

turbulence

Typical fan blade design

High turbulence

Features & Benefits

The Right Amount of Fresh Air and Cooling

AAF-HermanNelson unit ventilators deliver required amounts of fresh air to meet ventilation requirements and added cooling capacity to maintain consistent comfort for students and teachers. Our Economizer Operation, Demand Control Ventilation (DCV) and Part Load, Variable Air options allow you to match classroom comfort requirements even more closely, and reduce operating costs.

This means that you can be confident that your school is meeting ventilation standards for Indoor Air Quality and that your students are receiving adequate air to be attentive to instruction. At the same time, you are saving money in early morning hours, between classes or after hours when classrooms are heated and cooled but not always fully occupied.

Economizer Operation

It is well recognized that cooling, not heating, is the main thermal challenge in school classrooms. The typical classroom is cooled by outdoor air over half the time, even in cold climates. It is therefore essential that unit ventilators efficiently deliver outdoor air when classroom conditions call for “free” or economizer cooling.

With AAF-HermanNelson unit ventilators, you can have outdoor air whenever it is needed. Economizer operation is facilitated by the outdoor air damper, which automatically adjusts the above-minimum outside air position to provide free cooling when the outdoor air temperature is appropriate ( with MicroTech II controls, three levels of economizer control are available (see

Figure 3. Full Economizer Mode

100% Outdoor Air Into Classroom

Figure 3). On units equipped

page 17).

Part-Load Variable Air Control

Part Load Variable Air control can be used in conjunction with face and bypass damper temperature control to automatically adjust the unit ventilator fan speed based upon the room load and the room temperature. This MicroTech II control option provides higher latent cooling capabilities and quieter operation during non-peak load periods by basing indoor fan speed upon room load. Lower fan speeds in conjunction with our GentleFlo fan technology (see page

page 5) contributes to a very quiet

classroom environment.

Room-temperature PI control loops determine the speed of the fan, which varies according to the room load. It also provides a built-in delay to prevent overshooting for better comfort control. The outdoor air damper’s minimum-air position is adjusted with the fan speed to bring in a constant amount of fresh air.

Demand Control Ventilation

AAF-HermanNelson unit ventilators can be equipped to use input from a CO based on actual occupancy instead of a fixed design occupancy. This Demand Controlled Ventilation (DCV) system monitors the amount of CO outdoor air is introduced to maintain good air quality. The system is designed to achieve a target ventilation rate (e.g., 15 cfm/person) based on actual occupancy.

By using DCV to monitor the actual occupancy pattern in a room, the system can allow code-specific levels of outdoor air to be delivered when needed. Unnecessary over-ventilation is avoided during periods of low or intermittent occupancy, leading to improved energy efficiencies and cost savings.

controller to ventilate the space

so enough fresh

Face &

Bypass

Damper

Room Air

Damper

6 McQuay Catalog 1600

Filter

Outdoor Air Damper

Outdoor Air

Features & Benefits

Precise Temperature and Dehumidification Control

AAF-HermanNelson unit ventilators provide precise temperature and dehumidification control to keep students and teachers comfortable while making maximum use of “free” outdoor-air cooling to reduce operating costs. They utilize a draw-thru fan design that contributes to even heat transfer and provides uniform discharge air temperatures into the classroom. Coupled with face and bypass damper air control and/or our MicroTech

II active and passive dehumidification control strategies, they provide precise control of temperature and humidity levels under both part-load and full-load conditions.

Draw-Thru Design For Even Discharge Temperatures

The AAF-HermanNelson Draw-Thru design sets our unit ventilators apart from most competitive models. With this system, fans draw air through the entire heat transfer element ( concentrated areas of the coil element. The result is more uniform discharge air temperatures into the classroom and more efficient unit ventilator operation.

Figure 4. Draw-Thru Design Provides Even Discharge Air

Figure 4) rather than blowing it through highly

Uniform Discharge Air (Shaded)

Motor

Fans

Condenser

Ta bl e s 1 and 2 below compare the composition of the air streams through the coil and air streams bypassing the coil at various bypass air percentages for draw-thru and blow-thru unit ventilators using 450 cfm of outdoor air. At both 0% bypass air and 100% bypass air, no difference exists in the composition of the air streams. However, at all other bypass air percentages (part load), significant differences are evident.

For instance, compare the 1500 cfm draw-thru (Ta bl e 1) and blow-thru (Tab le 2) units at 70% bypass air. At this point, the draw-thru unit still has all of the outdoor air going through the coil. Meanwhile, the blow-thru unit is bypassing 70% (315 cfm) of the humid outdoor air directly into the classroom.

Table 1: AAF-Herman Nelson 1500 CFM Draw-Thru Unit

Bypass Air Stream CFM Cold Air Stream CFM

Tot al

% Bypass Air

0 1500 0 0 0 1500 1050 450

10 1500 150 150 0 1350 900 450

20 1500 300 300 0 1200 750 450

30 1500 450 450 0 1050 600 450

40 1500 600 600 0 900 450 450

50 1500 750 750 0 750 300 450

60 1500 900 900 0 600 150 450

70 1500 1050 1050 0 450 0 450

80 1500 1200 1050 150 300 0 300

90 1500 1350 1050 300 150 0 150

100 1500 1500 1050 450 0 0 0

Bypass

Total Unit CFM

From

Room

From

Outdoors

Tot al

Coil

From

Room

From

Outdoors

Table 2: 1500 CFM Blow-Thru Unit

Face & Bypass Design For Better Temperature and Humidity Control

When coupled with our draw-thru design, face and bypass damper air control offers maximum dehumidification and optimal temperature control. That’s because indoor and outdoor air streams can be separated until it is optimal to mix them.

During most part-load conditions, humid outdoor air is directed through the cold coil (coil surface below the dew point) where moisture is removed. Room air is bypassed around the coil, since it has already been dehumidified. This arrangement allows for maximum condensate removal. Humid outdoor air is not bypassed around the coil until the total amount of cooling air required is less than the total amount of fresh outdoor air required in the

% Bypass Air

0 1500 0 0 0 1500 1050 450

10 1500 150 105 45 1350 945 405

20 1500 300 210 90 1200 840 360

30 1500 450 315 135 1050 735 315

40 1500 600 600 0 900 450 450

50 1500 750 525 225 750 525

60 1500 900 630 270 600 420 180

70 1500 1050 735 315 450 315 135

80 1500 1200 840 360 300 210 90

90 1500 1350 945 405 150 105 45

100 1500 1500 1050 450 0 0 0

Bypass Air Stream CFM Cold Air Stream CFM

Tot al

Bypass

Total Unit CFM

From

Room

From

Outdoors

Tot al

Coil

From

Room

From

Outdoors

225

room.

AAF-HermanNelson Model AV Unit Ventilators 7

Features & Benefits

This illustrates that the most effective way to maintain an acceptable humidity level with a chilled-water unit ventilator system is to use a face and bypass damper, draw-thru unit.

Why Blow-Thru Designs Don’t Measure Up

Blow-thru designs cannot provide comfort like this. With blow-thru designs, the humid outside air is pre-mixed with the room air before it can go through the coil (

Figure 5). Dehumidification occurs only to the portion of the air that is directed unevenly through the cooling coil. The air that bypasses the coil is largely humid outdoor air, resulting in unconditioned air being bypassed and creating poor comfort conditions.

Figure 5. Draw-Thru Vs. Blow-Thru Design

Coil

Face &

Bypass

Damper

Room Air

Damper

Room Air

AAF-HermanNelson Draw-Thru Design

Outdoor Air Damper

Outdoor Air

With a blow-thru design the positive pressure of the fan discharge can create areas across the coil of varying temperatures and airflow. In addition, blow-thru face and bypass damper construction picks up heat by wiping the coil, creating overheating conditions. The sound level in a blow-thru design also varies based upon the position of the face and bypass damper.

Coil

Filter

RA/OA Divider

Room Air

Outdoor Air

Blow-Thru Design

See “Active Dehumidification Control (Reheat)” on page 20 for more information.

Passive Dehumidification (Optional)

On units with face and bypass damper air control and MicroTech II part-load variable air control, passive dehumidification can be used under high humidity conditions to keep classrooms comfortable. A unitmounted humidity sensor and fan speed changes are utilized to improve latent cooling by keeping the air in closer contact with the cold coil for passive dehumidification.

This occurs in the unoccupied mode as the unit operates to satisfy the unoccupied temperature and humidity set points with the outside damper closed. The face and bypass damper is placed in a minimum face position to promote high latent cooling. The unit fan continues to operate on low speed until the load is satisfied. This is very helpful in high humidity areas where high night time humidity can be absorbed in the building during off hours.

Increased Coil Freeze Protection

AAF-HermanNelson units equipped with face and bypass damper control provide extra protection from coil freeze-up. That’s because there is a constant flow of hot water through the coil, and water that is flowing typically does not freeze. Additionally, all AAF-HermanNelson units feature a double-walled, insulated outdoor air damper with airtight mohair seals to prevent unwanted coil air from entering the unit.

Furthermore, a low-temperature freezestat is factory installed on all units with hydronic coils. Its serpentine capillary tube senses temperatures across the leaving air side of the coil, allowing the unit controller to react quickly to low-temperature conditions.

Active Dehumidification (Reheat)

In high-humidity applications where valve-controlled,

Figure 6. Freezestat

Freezestat

reheat units are used, the Active Dehumidification Control (ADC) sequence should be considered. During excessive humidity conditions, a humidity sensor directs the unit to continue cooling past the room setpoint to remove excess moisture. Hydronic heat or electric heat is then used to reheat the discharge air to maintain acceptable room temperatures.

MicroTech II controls minimize the amount of reheat needed to maintain relative humidity below a preset limit.

Capillary Tube

Reheat is used only when required and in the most energy-efficient manner possible.

8 McQuay Catalog 1600

Features & Benefits

Low Installation Costs

AAF-HermanNelson unit ventilators have many features that make them economical to purchase and to install in both new construction and retrofit applications. It is this attention to detail and understanding of school applications that make them the system of choice.

Perfect For Both New & Retrofit Applications

New construction installations are easily accomplished with AAF-HermanNelson unit ventilators because they avoid the added cost and space required for expensive ductwork. Further savings can be realized because piping installations use less space than duct systems. This is important in existing buildings and also in new construction where floor-to-floor heights can be reduced, saving on overall building costs.

Retrofit installations are also economical because new units fit the same space occupied by existing ones. Using AAF-HermanNelson unit ventilators, central equipment, such as chillers, can be sized smaller using building diversity. This results in a low capital-cost system.

Built In Flexibility

AAF-HermanNelson unit ventilators include features that make them easy to set up and reconfigure as needed to meet special requirements. These features include:

• Reversible Drain Connections All units come with a composite drain pan that has drain connections on either end ( connection is also provided. The drain-side connection can be selected in the field. The direction in which the drain pan slants can also be field-modified.

Figure 7. Composite Drain Pan, Reversible Connections

• Add Cooling At A Later Date Because we recognize that some schools may wish to add cooling at a later date, even heating-only units are shipped standard with a composite drain pan.

Figure 7). A secondary, overflow drain

Secondary Overflow Drain Connection

Primary Drain

Connection

Connect Drains On Either End, Slant Pan To Either End, Can Field-Modify

• Adjustable Leg Levelers Adjustable leg levelers are furnished on the front legs of all floor units to compensate for floor irregularities (

Figure 8. Adjustable Leg Levelers

Leg Leveler

Figure 8).

• Built-in Pipe Tunnel A built-in pipe tunnel allows field crossover of hot-water or chilled-water piping, electrical conduit or refrigeration tubing (see Unit Arrangements beginning on page

51).

• Built-In Wire Race A built-in metal wire race runs from one end of the unit to the other to provide extra protection for wires and protect them from unit air.

Controls Flexibility

Multiple control options—including MicroTech II controls with our Protocol Selectability feature—provide easy, low cost integration of AAF-HermanNelson unit ventilators into the building automation system of your choice (see page 15). You can also operate these units individually or in a master-slave control configuration.

With MicroTech II controls, you select BACnet, LonTalk or Metasys and monitoring information to your BAS, without the need for costly gateways. Unit controllers are L certified with the optional L module.

Controls and communication modules can be factory provided or field-installed by others. Factory integrated and tested controller, sensor, actuator and unit options promote quick, reliable start-up and minimize costly field commissioning.

You can also use our Digital Ready option, where we factory-install and pre-wire control sensors and actuators and the controller is field-installed by others. See Ready Systems” on page 43.

N2 communications to communicate control

ONMARK

ONWORKS communication

“Digital

AAF-HermanNelson Model AV Unit Ventilators 9

Features & Benefits

Low Operating Costs

Schools consume more than 10% of the total energy expended in the United States for comfort heating and cooling of buildings. As energy costs increase, educators are placed in a difficult position: caught between rising costs, lower budgets and the requirements to raise educational standards.

Fortunately, the technology and the system exists for schools to take control of their energy expenditures while providing a comfortable environment for learning. And that system is the AAF-HermanNelson unit ventilator.

Consider these realities of school environments:

• Most heating energy in schools is expended to heat unoccupied spaces. Because lights, computers and students give off considerable heat, occupied spaces require little supplemental heat.

• The removal of heat is usually required in occupied classrooms, even when outside temperatures are moderately cold (i.e., 35-40°F).

Then consider how AAF-HermanNelson unit ventilators, located in each classroom, take advantage of these realities to lower operating costs:

• They provide individual classroom control and comfort.

• They can be cycled on when the room is occupied and

cycled off when it is not.

• They bring in fresh air from directly outside the classroom for high indoor air quality.

• During most of the school year, they use outdoor air to keep classrooms comfortable without the expense of mechanical cooling.

• They have their own air-moving device—a fan and 1/4 hp motor—which uses about as much energy as two 100-watt light bulbs. Compare this to the energy consumed by the 20-plus-hp motors used in centralized systems to cool both occupied and unoccupied spaces (at about 1 hp of energy consumed per room).

MicroTech II Control Options Further Reduce Operating Costs

Many of the MicroTech II control options available with AAF-HermanNelson unit ventilators can further reduce operating costs. For example:

• Economizer Operation Economizer operation automatically adjusts the above-minimum outside air position to provide free cooling when the outdoor air temperature is appropriate.

• Demand Control Ventilation By using CO2 levels to monitor the actual occupancy pattern in a room, the

system can allow code-specific levels of outdoor air to be delivered when needed without costly overventilation during periods of low or intermittent occupancy (

Figure 9. Energy Savings with Demand Control Ventilation

100%

20%

• Occupancy Mode Operation Units can be programmed to operate only sparingly during unoccupied periods and at night to conserve energy.

Figure 9).

Energy Savings

with DCV

Unoccupied

After Hours

DCV's fresh air for indoor air quality

6:00 8:00 10:00 12:00 2:00 4:00 6:00 8:00 10:00

School Hours

Cleaning

Unoccupied

10 McQuay Catalog 1600

Features & Benefits

Easy To Maintain

AAF-HermanNelson Unit Ventilators are designed to provide easy access for maintenance and service personnel to all serviceable components. Most maintenance tasks are easily handled by a single person.

Modular Fan Deck

The entire fan deck is easily removed as a single unit. This provides ready access to fan wheels, motors, bearings and other components for service, cleaning or repair.

The fan deck’s rotating element has one large, selfaligning, oilable end bearing and two oilable motor bearings for smoother operation. The location of these bearings at the ends of the shaft (out of the airstream) enables easy access and long life.

Figure 10. Long-life bearings

Even “permanently” lubricated motors are supplied with recommended lubrication charts calling for lubrication every seven years. Maintenance instructions of the motor manufacturer should be followed closely.

Heavy-Duty Discharge Grille

The discharge grille on the top of the unit is made from extra-strength steel bar stock, promoting long life (

Figure 11). It can be removed to facilitate cleaning of fans and fan housings. A built-in 10-degree angle provides proper air throw to blanket the room for proper air circulation and comfort.

Figure 11. Heavy-Duty Steel Discharge Grille

Easy Motor Removal

Unlike with many competitive models, the motor in AAF-HermanNelson unit ventilators is separate from the fan assembly and is located out of the airstream at the end of the fan shaft—away from the hot coil—for easier maintenance and removal. Locating the motor away from the coil ( motor life. Our direct-coupled motor and self-aligning motor mount facilitate motor change-out. The motor comes with a molex plug that fits all sizes and further simplifies removal.

Figure 12) has the added benefit of extending

Figure 12. Modular Fan Deck

Heavy-Duty Discharge Grille

Modular Fan Deck

AAF-HermanNelson Model AV Unit Ventilators 11

Motor & Bearings Located

Out Of Airstream

Features & Benefits

Tamper-Resistant Fasteners

Front panels and top access doors are held in place by tamper-resistant, positive-positioning fasteners. They are quickly removed or opened with the proper tool, but deter unauthorized access to the unit’s interior (

Figure 13).

Sectionalized Access Panels And Doors

All floor units have three separate front panels and hinged top access doors, sized for convenient handling by a single person (

Figure 13). The result is easy,

targeted access to the component that needs servicing:

• Two 12 inch-wide end panels provide easy access to piping, temperature control components and the fan switch. Unlike units with full-length front panels, these can be removed without disturbing the normal operation of the unit.

• Hinged top access doors provide easy access into the end compartments to facilitate convenient servicing of the motor and shaft bearing.

• A short, center front panel provides easy access to the filter and discharge grille.

Single-Filter Design

With AAF-HermanNelson’s single-filter design, filter change-out takes only seconds. Uneven dust loading is eliminated, which is common to units with separate filters for room and outdoor air, or that use a metal partition to separate filtering of indoor and outdoor air. The result can be longer filter life, which means less maintenance and fewer filters consumed.

Three filter types are offered:

• Single-use filters which feature Amerglas media and are designed to be used once and discarded. These are standard on all but electric heat units.

• Permanent metal filters which may be removed for cleaning and reused numerous times. These are standard on electric heat units.

• Renewable media filters, which consist of a heavyduty, painted-metal structural frame and renewable Amerglas media.

Figure 13. Easy Access With Tamper-Resistant Fasteners

Discharge Grille

Doors

Right Front Access Panel

Discharge Screen

Tamper-Resistant Fasteners

Fan Motor

Ta m pe r -

Resistant

Fasteners

Center Front Access Panel

Tamper-Resistant Fasteners

Top Access

Left Front

Access Panel

Renewable Media Filter

12 McQuay Catalog 1600

Features & Benefits

Built To Last

Our industrial-strength design provides the durability to withstand the rigors of the classroom environment. Its solid construction and rugged finish promotes continued alignment, structural strength and long-lasting beauty decades after the unit is installed. In fact, many units installed over 30 years ago continue to provide quiet, reliable classroom comfort.

Heavy Duty Frame Construction

AAF-HermanNelson’s exclusive, unitized frame (

Figure 14) is far superior to the fastener-type construction used by other manufacturers. Loosened fasteners can cause vibration, rattles and sagging panels. With unitized construction, there are no fasteners (screws or bolts) to come loose.

Other design features that promote trouble-free operation and long life include:

• A corrosion-resistant, galvanized-steel frame.

• Extra-strength, steel-bar discharge grille.

• Heavy-gauge-metal cabinet access panels and doors.

• An extra-strength pipe tunnel that stiffens the structure

while adding aerodynamic air flow within the unit.

• Hidden reinforcement that provides additional built-in

support for the top section as well as better support for the fan deck assembly.

• A rigid exterior that is strong enough to support

maintenance personnel without fear of damaging the unit.

Rugged Exterior Finish

The superior finish of the unit ventilator’s cabinets fosters long-lasting beauty as well as resistance to abuse and corrosion. We apply the very highest standards at every step of the finishing process to provide lasting quality:

• High-quality furniture steel is carefully inspected before painting. Scratches and marks that might show through are removed.

• After fabrication, the metal undergoes a five-stage cleaning and phosphatizing process to provide a good bonding surface and reduce the possibility of peeling or corrosion.

• A specially formulated, environmentally friendly, thermosetting urethane powder is applied electrostatically to the exterior panels. This film is oven-cured to provide correct chemical cross-linking and to obtain maximum scuff- and mar-resistance.

• The top of the unit is finished with a textured, non-glare and scuff-resistant, charcoal bronze electrostatic paint. End and front panels are available in a pleasing array of architectural colors.

• The Oxford brown steel kickplate is coated and baked with a thermosetting urethane powder paint to blend with floor moldings and provide years of trouble-free service.

• Each unit is painstakingly inspected before boxing, then encapsulated in a clear plastic bag, surrounded by an extra-heavy-duty cardboard box and secured to a skid to help provide damage-free shipment.

Figure 14. Heavy-Duty, Welded Chassis

Unitized Frame

Welded Construction

AAF-HermanNelson Model AV Unit Ventilators 13

Energy-Efficient Fan Motor

Features & Benefits

Durable, Energy Efficient Fan Motors

AAF-HermanNelson unit ventilators are equipped with 115/60/1 NEMA motors that feature low operating current and wattage (

Figure 15. Energy-Efficient Fan Motor

Additional features of these motors include:

• Split-capacitor (PSC) design with automatic reset and thermal-overload protection.

• No brushes, contacts or centrifugal starting switches— the most common causes of motor failure.

• A built-in, decoupled isolation system to reduce transmission of vibrations for quieter operation.

• A multi-tap, auto-transformer (Figure 16) provides multiple fan motor speed control through the speed switch. The motor is independent of supply voltage, which allows stocking of one motor (school districtwide) for various voltage applications.

Figure 16. Multi-Tap Auto-Transformer

Figure 15).

Energy Efficient NEMA Motor

Decoupled Isolation System

Additional features include:

• Face and bypass dampers have a twist-free reinforced aluminum construction for durability. Aluminum is used because it is lightweight and noncorrosive, resulting in low torque and easy movement.

• Outdoor air dampers are made of galvanized steel to inhibit corrosion, with double-wall welded construction for rigidity and encapsulated insulation (

Figure 17). Additional insulation is provided on the exterior of the outdoor air damper blade and on the outdoor air entry portion of the unit.

Figure 17. Outdoor Damper Seals Out Cold Weather

Turned Metal

Damper Blade

Turned Metal Damper Stop

Wool Mohair

End Seal

Full-Length Wool Mohair Damper

Additional Insulation

Wool Mohair End Seal

• Room air dampers are free-floating and designed to prevent intermittent gusts of cold air from blowing directly into the classroom on windy days (

Figure 18). They are constructed of aluminum with built-in rigidity. The metal forming technique that is employed resists twisting and incorporates a full-length counter weight for easy rotation. The simple principle of an area exposed to a force is used to automatically close the damper, rather than open it, when gusts of cold air occur.

Figure 18. Room Air Damper Auto-Closed By Wind Gusts

Wind Gust

Durable Damper Design

All dampers in AAF-HermanNelson Unit Ventilators use the turned-metal principle on their long closing edges (

Figure 17). Positive sealing is provided by embedding the edge into wool mohair (no metal to metal contact). There are no plastic gaskets to become brittle with time, sag with heat or age, or require a difficult slot fit to seal. Nylon damper bearings foster quiet, maintenance-free operation.

14 McQuay Catalog 1600

MicroTech II Controls

MicroTech II Controls For Superior Performance, Easy Integration

AAF-HermanNelson unit ventilators equipped with MicroTech provide superior performance and easy integration into your building automation system of choice. MicroTech II benefits include:

• Factory integrated and tested controller, sensor, actuator and unit options promote quick, reliable start-up and minimize costly field commissioning.

• High-performance features and advanced control options can quickly pay for themselves in saved energy costs and more comfortable classrooms.

• Select from three control levels: stand-alone, masterslave or network control.

• For network control applications, our Protocol Selectability feature provides easy, low-cost integration of AAF-HermanNelson unit ventilators into most building automation systems.

• Flexible BAS network communication options guard against controls obsolescence, keeping MicroTech II controls viable for the life of your AAF-HermanNelson equipment.

II unit controllers can

If a school has more than one zone, separate, remote time clocks are used to regulate each zone. In this case, the remote-mounted time clock energizes or deenergizes an external, 24-volt or 120-volt control circuit which operates the unit-mounted day/night relays in that zone.

Master-Slave Control

Designate the master and slave units and we will factory configure and install the controllers so they are set up for a local peer-to-peer network between units (leaving only the network wiring between these units to be field installed).

Slave units can be field-configured to be dependent or independent as follows:

• Dependent slave units follow the master unit completely. They are ideal for large spaces that have even loads across the space (such as some libraries).

• Independent slave units (default) use master setpoints and slave sensors. The slave follows the master unit modes, such as heat or cool, but has the flexibility to provide the conditioning required for its area within the space. Independent slave units perform better in spaces where loads vary from one area of the space to the other (such as stairwells or cafeterias).

Three Control Levels

MicroTech II unit controllers provide the flexibility to operate AAF-HermanNelson unit ventilators on any of three levels:

• As stand-alone units, with control either at the unit or from a wall sensor.

• In a master-slave relationship, where slave units follow the master unit for some or all functions.

• Controlled as part of a network using a centralized building automation system.

Stand-Alone Control

When operating in stand-alone mode, the MicroTech II controller performs complete room temperature and ventilation control. Units can be operated in occupied, unoccupied, stand-by, or bypass (tenant override) modes. Occupied/unoccupied changeover can be accomplished:

• Manually by a unit-mounted day/night switch.

• Automatically by a unit-mounted day/night time clock.

• Automatically by a remote-mounted time clock that

operates unit-mounted day/night relays.

Network Control

MicroTech II unit controllers provide easy integration into your building automation system of choice. All factoryinstalled options are handled by the unit controller. This simplifies the transmission of monitoring and setpoint data to the building automation system.

You select BACnet, LonTalk or Metasys N2 Open communications to communicate control and monitoring information to your BAS, without the need for costly gateways (see page 22). Unit controllers are LONMARK certified with the optional LONWORKS communication module.

Flexible network communication options via our Protocol Selectability feature help you avoid control obsolescence over the life of your AAF-HermanNelson equipment.

“Optional Communication Modules” on

AAF-HermanNelson Model AV Unit Ventilators 15

MicroTech II Controls

A Wide Variety of Input, Output & Alarm Data Points Available

A wide variety of data is available from AAFHermanNelson unit ventilators when equipped with MicroTech II unit controllers in a network situation. They

classroom and notify your building automation system of alarm conditions regardless of the protocol you select. See

"Table 3: Network Operation - Typical Data Points" below for a list of inputs, outputs and alarm functions available.

provide a clear picture of just what's happening in each

Table 3: Network Operation - Typical Data Points

Read/Write Attributes Read Only Attributes

• Application Mode

• Auxiliary Heat

Enable

• Compressor Enable

• Emergency Override

• Energy Hold Off

• Heat/Cool Mode

• Occupancy

Override

• Outdoor Air Humidity

• Reset Alarm

• Reset Filter Alarm

• Setpoint Offset

• Source (Water In)

Temperature

• Space CO2

• Space Humidity

• Space

Temperature

• Binary Input 1 Status

• Binary Output 1 Status

• Binary Output 2 Status

• Compressor Run Time

• Chiller Water Valve

Position

• Discharge Air Temperature

• Discharge Air Temperature Setpoint

• Effective Setpoint

• Effective Space

Temperature

• Fan Speed

• F & BP Damper

Position

• Local Setpoint

• Outdoor Air Damper

Position

• Space Fan Runtime

• Unit Ventilator

Controller State

• Water-out Temperature

• WH or CW/HW Valve

Position

Not all data points or alarms listed will be available in all unit ventilator configurations. Humidity and CO2 points require the use of optional sensors.

Read/Write

Setpoint Attributes

• Econ. IA/OA Enthalpy

Differential Setpoint

• Econ. IA/OA Temp. Differential. Setpoint

• Econ. Outdoor Air Enthalpy Setpoint

• OAD Min. Position Low-Speed Setpoint

• OAD Min. Position Med.-Speed Setpoint

• Occupied Cooling Setpoint

• Occupied Heating Setpoint

• Space CO2 Setpoint

• Space Humidity

Setpoint

• Standby Cooling Setpoint

• Unoccupied Cooling Setpoint

• Unoccupied Heating Setpoint

• UV Software Application Version

Typical Alarms

• Indoor Air Temperature Sensor

Failure

• DX Pressure Fault

• Compressor Envelope Fault

• Condensate Overflow Indication

• Indoor Air Coil DX Temperature

Sensor Failure

• Outdoor Air Temperature Sensor Failure

• Discharge Air Temperature Sensor Failure

• Outdoor Air Coil DX Temperature Sensor Failure (or)

• Water Coil DX Temperature Sensor Failure

• Water-out Temperature Sensor Failure (or)

• Water-in Temperature Sensor Failure

• Space Humidity Sensor Failure

• Outdoor Humidity Sensor Failure

• Space CO2 Sensor Failure

• Source Temperature (Water-in)

Inadequate Indication

• Change Filter Indication

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MicroTech II Controls

Control Modes and Functions

AAF-HermanNelson unit ventilators equipped with MicroTech operate in a variety of modes based on the current situation in the room and the status of the unit ventilator. Changes in mode can be triggered manually, via network signals, by sensor readings, or by date and time. External inputs and outputs can be used to change modes, communicate data to network controls or change the functional operation of the unit.

Occupancy Modes

MicroTech II unit controllers can be set up to change modes based on room occupancy. Four different occupancy modes are provided, as described below.

Occupied Mode

This is the normal daytime operation mode. The controller maintains a room set point using the outside air capability and other functions.

Note: For non-school applications, the unit can also be

Unoccupied Mode

This is the night setback operating mode, in which the unit responds to a new room set point and cycles to maintain the condition. The fan comes on when heating or cooling is needed and runs until the load is satisfied. The outdoor air damper is closed during this mode. When a cooling load is satisfied by a refrigerant system, the compressor is de-energized and the unit ventilator indoor fan continues to run for a fixed period of time to remove coldness from the evaporator coil. This reduces the potential for low refrigerant temperatures to exist on the evaporator coil.

II unit controllers can be programmed to

configured to cycle the fan in response to the room load. In this case, the fan would normally be in the Off Mode until heating or cooling is required. The outside air damper is always closed when the fan is off. When the fan starts, the outside air damper opens to the required position, usually minimum position.

can be made in 1-minute increments from 1 minute to 240 minutes through ServiceTools™ (see network.

page 24) or a

Economizer Modes

Economizer operation is facilitated by the outdoor air damper, which automatically adjusts the above-minimum outside air position to provide free cooling when the outdoor air temperature is appropriate. Three levels of economizer control are available:

Basic Economizer Operation: The MicroTech II

controller compares the inside and outside temperatures. If the temperature comparison is satisfactory, then freeair economizer operation is used to cool the space. Reheat units also come configured with an indoor humidity sensor.

Expanded Economizer Operation: In addition to

comparing inside and outside temperatures, outdoor relative humidity is measured to calculate outside air enthalpy. If the enthalpy set point is not exceeded, and the temperature comparison is satisfactory, then free economizer operation is used to cool the space. This helps to minimize the entrance of humid outside air.

Leading-Edge Economizer Operation: The MicroTech II

controller compares both indoor and outdoor temperatures and indoor and outdoor relative humidities. Then it calculates both inside and outside air enthalpy to determine if free economizer operation can cool the space with non-humid outside air. This is a true enthalpy economizer—a first for unit ventilators.

Night Purge Mode

Under this mode, the unit is configured to purge the room space for one hour for various reasons (odor or fume removal, drying, etc.).During Night Purge the outside air damper is open full and the fan is run on high speed. No “normal” heating or cooling takes place (the emergency heat set point is maintained) and the exhaust fan, if the room is so equipped, is signaled to turn on.

Stand By Mode

In this mode, the unit maintains the occupied mode set point temperature with the outdoor air damper closed. The fan runs continuously unless it is configured to cycle in response to the load.

Bypass Mode

This is a tenant override operating mode in which the unit is placed back into the Occupied Mode for a predetermined time. The default is 120 minutes. Settings

AAF-HermanNelson Model AV Unit Ventilators 17

Freeze Prevention Mode

This mode helps protect the unit ventilator from freezing air conditions. Control functions vary depending on the type of temperature control used by the unit, as follows:

Face and bypass control units: Upon sensing a potential

freezing air temperature condition leaving the heating coil, the unit will automatically protect itself by shutting the outside air damper and opening the EOC valve. The face and bypass damper is allowed to operate normally to control the space. The fan continues to run to remove the cold air. Once accomplished, the freezestat is reset,

MicroTech II Controls

the outside air damper opens to the minimum position and the unit commences its normal mode of operation.

Valve control units: Upon sensing a potential freezing

air temperature condition leaving the heating coil, the unit will automatically protect itself by shutting the outside air damper and opening the hot water valve to a minimum of 50% (more if required to heat the room). The fan speed will be staged down to low speed and then turned off. When the freezestat is reset, the outside air damper opens to the minimum position and the fan runs at low speed for a minimum of 10 minutes. It then will stage up if needed to satisfy the room set point. This reduces the potential to overheat a room recovering from a potential freeze condition.

Note: Valve selection and coil sizing is critical for proper

operation. Face and bypass control is recommended for proper humidity and freeze protection.

Emergency Heat Mode

If the unit is left in a mode that does not normally allow heating (such as Off, Fan Only, Cool, or Night Purge) and the room temperature falls below 55°F, the unit will heat the space to above 55°F and then return to the previously set mode of operation. This mode of operation can be field configured and/or be disabled.

External Input Functions

The unit ventilator controller is provided with three (3) binary inputs that allow a single set of dry contacts to be used as a signal to it. Input signal choices are described below. Multiple units can be connected to a single set of dry contacts.

Note: Not all of the functions listed can be used at the same

time. The unit ventilator controller is provided with configuration parameters that can be adjusted to select which function will be used for these inputs where multiple functions are indicated below. For wiring examples see installation manual IM Unit Ventilator Controller.

Unoccupied Input Signal

This input signals the unit ventilator controller to go into unoccupied or occupied mode. When the contacts close, the unit ventilator controller goes into unoccupied mode; when the contacts open, it goes into occupied mode. Additional variables can affect occupancy mode and override this binary input. See

“Occupancy Modes” on

page 17.

Dewpoint/Humidity Input Signal (Optional)

This input signals the unit ventilator controller to go into active dehumidification mode. When the contacts close

747: MicroTech II

(high humidity) the controller will go into active dehumidification; when the contacts open (low humidity) it will stop active dehumidification.

Remote Shutdown Input Signal

This input signals the unit ventilator controller to go into shutdown mode. When the contacts close, the controller goes into shutdown mode; when the contacts open, it returns to normal operation.

Ventilation Lockout Input Signal

This input signals the unit ventilator controller to close the outdoor air damper. When the contacts close (ventilation lockout signal) the controller closes the outdoor damper; when the contacts open, it returns to normal outdoor damper operation.

Exhaust Interlock Input Signal

This input signals the unit ventilator controller that an exhaust fan within the space has been energized. The controller then repositions the outdoor air damper to a user-adjustable minimum position. When the contacts close (exhaust fan on signal) the controller uses the value defined by the Exhaust Interlock OA Damper Min Position Setpoint as the new minimum outdoor air damper position regardless of the indoor air fan speed. When the contacts open, it returns to normal outdoor damper operation.

External Output Functions

The unit ventilator controller is provided with three (3) binary outputs to perform the functions described below. These are relay type outputs that are intended to be used with signal level voltages only (24 VAC max).

Note: Not all of the functions listed can be used at the same

time. The unit ventilator controller is provided with configuration parameters that can be adjusted to select which function will be used for these outputs when multiple functions are indicated below. For wiring examples, see installation manual IM Unit Ventilator Controller.

Lights On/Off Signal

This relay output provides one set of NO dry contacts that can be used to signal the operation of the room lights. When the unit ventilator controller is in occupied, standby or bypass occupancy modes, the relay output will signal the lights on (contacts closed); when the controller is in unoccupied occupancy mode the relay output will signal the lights off (contacts open).

747: MicroTech II

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MicroTech II Controls

Fault Signal

This relay output provides NO, NC, and Common connections that can be used to signal a fault condition. When a fault exists, the unit ventilator controller energizes this relay output. When the fault or faults are cleared, it de-energizes this relay output.

Exhaust Fan On/Off Signal

This relay output provides one set of NO dry contacts that can be used to signal the operation of an exhaust fan. When the outdoor air damper opens more than the Energize Exhaust Fan OA Damper Setpoint, the relay output will signal the exhaust fan on (contacts closed). When the outdoor damper closes below this setpoint, the relay output will signal the exhaust fan off (contacts open).

Auxiliary Heat Signal

This relay output provides one set of NO dry contacts that can be used to operate an auxiliary heat device. The unit ventilator controller by default is configured to operate a NO auxiliary heat device (de-energize when heat is required) such as a wet heat valve actuator with a spring setup to open upon power failure. However, the Auxiliary Heat Configuration variable can be used to set the controller to use an NC auxiliary heat device (energize when heat is required) such as electric heat.

fan operation under normal operating conditions, in conjunction with our GentleFlo fan technology (see 5page 5) contributes to a very quiet classroom envionment.

page

Demand-Controlled Ventilation (Optional)

AAF-HermanNelson unit ventilators can be equipped to use input from a CO based on actual occupancy instead of a fixed design occupancy. This Demand Controlled Ventilation (DCV) system monitors the amount of CO students and teachers so that enough fresh outdoor air is introduced to maintain good air quality. The system is designed to achieve a target ventilation rate (e.g., 15 cfm/person) based on actual occupancy.

With DCV you can be confident that your school is meeting ventilation standards for Indoor Air Quality and that your students are receiving adequate air to be attentive to instruction. At the same time, you are saving money in early morning hours, in between classes, or after hours when classrooms are heated and cooled but not always fully occupied.

controller to ventilate the space

produced by

Advanced Control Options

MicroTech II controls make possible a number of advanced control options that can quickly pay for themselves in saved energy costs and more comfortable classrooms, as described below.

Part Load Variable Air Control

Part Load Variable Air control can be used in conjunction with face and bypass damper temperature control to automatically adjust the unit ventilator fan speed based upon the room load and the room-temperature PI control loop. This MicroTech II control option provides higher latent cooling capabilities and quieter operation during non-peak load periods by basing indoor fan speed upon room load.

During low-load or normal operation (about 60% of the time) the fan will operate on low speed. When the load increases to an intermediate demand, the fan will automatically shift to the medium-speed setting. Under near-design or design-load conditions, the fan will operate on high speed. A built-in, 10-minute delay helps minimize awareness of fan speed changes. Low-speed

As Simple as a Thermostat

Demand Controlled Ventilation is easy to apply. When DCV is ordered, a CO and configured for operation. The system does the rest. If desired, the ventilation control setpoint can be adjusted through the MicroTech II Controller.

sensor is mounted on the unit

Acceptance By Codes And Standards

ASHRAE Standard 62-2004 Ventilation for Indoor Air Quality recognizes CO controlling ventilation based on occupancy. The ASHRAE standard has been referenced or adopted by most regional and local building codes. This standard references ventilation on a per-person basis.

Using CO2 control will sometimes lower the absolute amount of outside air delivered into a room but will maintain the per-person rate. For example, if a classroom is designed for 30 students, the ventilation rate is 450 cfm (30 students X 15 cfm/student). However, when there are only ten students in the classroom, the CO

control will adjust ventilation to 150 cfm (10 students

X 15 cfm/student). A minimum base ventilation rate (typically 20% of design levels) is provided when in the

based DCV as a means of

AAF-HermanNelson Model AV Unit Ventilators 19

MicroTech II Controls

occupied mode. This provides outdoor air to offset any interior source contamination while allowing for proper space pressurization.

Active Dehumidification Control (Reheat)

In high-humidity applications where valve-controlled, reheat units are used, the Active Dehumidification Control (ADC) sequence should be considered. During excessive humidity conditions, a humidity sensor directs the unit to continue cooling past the room setpoint to remove excess moisture. Hydronic heat or electric heat is then used to reheat the discharge air to maintain acceptable room temperatures.

MicroTech II controls minimize the amount of reheat needed to maintain relative humidity below a preset limit. Reheat is used only when required and in the most energy-efficient manner possible.

Active Dehumidification comes standard on units equipped with MicroTech configuration and valve-control temperature modulation. The MicroTech ADC humidity sensor is unit-mounted. It issues a signal proportional to the classroom’s humidity level (unlike humidistats which issue an open-close signal). This enables a control sequence that manages both the temperature and the relative humidity.

When the relative humidity exceeds a preset value, the modulating chilled-water valve opens fully to dehumidify the mixture of outdoor and return air entering the cooling coil. The reheat modulating water valve then opens, or electric heat is engaged, to reheat the air leaving the cooling coil, as required to maintain the classroom setpoint.

Active dehumidification starts when the indoor relative humidity exceeds the preset relative humidity upper setpoint and continues until the room humidity falls 5% below the endpoint. During active dehumidification, economizer operation is disabled (and the outdoor air damper is reset to its minimum position) unless the outdoor air temperature is below 55°F. It is maintained until dehumidification is completed. When the indoor humidity level is satisfied, the MicroTech II controller reverts to its normal sequences to satisfy the classroom temperature setpoint.

II controls, a reheat

closer contact with the cold coil for passive dehumidification.

This only occurs in the unoccupied mode as the unit operates to satisfy the humidity set point with the outside damper closed. The face and bypass damper is placed in a minimum face position to promote high latent cooling. The unit fan continues to operate on low speed until the load is satisfied. This is very helpful in high humidity areas where high night time humidity can be absorbed in the building during off hours.

DX Split System Control

On unit ventilators equipped with direct-expansion (DX) coils, the unit ventilator controller is configured to operate the compressor as secondary (mechanical) cooling when economizer cooling is available, and as primary cooling when economizer cooling is not available. Addtiional DX control features include:

Compressor Envelope: This helps protect the

compressor from adverse operating conditions that can cause damage and or shortened compressor life. It ends compressor operation if coil temperatures exceed the defined operating envelope.

Compressor Cooling Lockout: The unit ventilator

controller is configured to lock out compressor cooling when the outdoor air temperature falls below the compressor cooling lock out setpoint. Below this temperature setpoint only economizer cooling will be available.

Minimum On And Off Time: The unit ventilator controller

is provided with minimum-on and minimum-off timers to prevent adverse compressor cycling (3-minutes default).

Compressor Start Delay Variable: This variable is

intended to be adjusted as part of the start-up procedure for each unit. It is used to prevent multiple unit compressors from starting at the same time after a power failure or after an unoccupied-to-occupied changeover. Each unit should be configured at start-up with a slightly different (random) delay, or groups of units should be provided with different delays.

Passive Dehumidification Control

On units with face and bypass damper control, a chilledwater coil and MicroTech II part-load variable air control, passive dehumidification can be used under high humidity conditions to keep classrooms comfortable. A unit-mounted humidity sensor and a low fan speed are utilized to improve latent cooling by keeping the air in

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MicroTech II Controls

System Components

The main components of the MicroTech II system are:

• The Unit Ventilator Controller (UVC)

• The Local User Interface (LUI)

• Optional plug-in network communication modules

In addition, unit ventilators equipped with MicroTech II controllers feature factory-mounted sensors and actuators for system control and feedback.

Unit Ventilator Controller

The MicroTech II UVC is a DDC, microprocessor-based controller designed to provide sophisticated comfort control of an economizer-equipped AAF-HermanNelson unit ventilator. In addition to normal operating control, it provides alarm monitoring and alarm-specific component shutdown if critical system conditions occur. Each UVC is factory wired, factory programmed and factory run-tested for the specific unit ventilator model and configuration ordered by the customer.

Figure 19. MicroTech II Control Board

Terminal Connections

Plug-In Control Module

Figure 20. User Interface Touch Pad

The User Interface has individual touch-sensitive printed circuit board mounted buttons, and comes with a built-in menu structure (Hidden Key and Password Protected) to change many of the common operating variables.

Four Operating Mode States

Four different user operating mode states can be chosen on the LUI:

Heat: Heating and economizer operation only.

Cool: Cooling and economizer operation only.

Fan Only: Fan only operation.

Auto: The unit automatically switches between heating,

cooling and economizer operation to satisfy the room load conditions. The current unit state is also displayed.

Local User Interface

A built-in LUI touch pad with digital LED Display is located in the right hand compartment below the top right access door. In addition to the Operating Mode States and Fan Functions, the Touch Pad will digitally display:

• The room set point temperature.

• The current room temperature.

• Any fault code for quick diagnostics at the unit.

Four Fan States

Four fan states are provided on all units: high, medium low and Auto speed modulation. The Auto speed function (part load, variable air) varies the fan speed automatically to meet the room load whether the unit is in heating, cooling or economizer mode.

All this is accomplished with a standard, single-speed NEMA frame motor. A built-in 10-minute delay helps minimize awareness of speed changes. During low-load or normal operation (about 60% of the time) the fan will operate at low speed. The low speed operation, along with GentleFlo fan technology, contributes to a very quiet classroom environment.

When the load increases to an intermediate demand, the fan automatically shifts to the medium speed setting. At near-design or design-load conditions the fan will operate on high speed.

With four fan states and GentleFlo fan technology, there is no need to oversize units or worry about uncomfortable conditions.

AAF-HermanNelson Model AV Unit Ventilators 21

MicroTech II Controls

Optional Communication Modules

Optional communication modules provide control and monitoring information to your building automation system without the need for costly gateways. Available communication protocols include BACnet, LonTalk and Metasys N2 Open. The communication modules for each are described below.

Figure 21. Typical 2" x 4" Communication Module

BACnet MS/TP Communication Module

This module allows the UVC to inter-operate with systems that use the BACnet (MS/TP) protocol with a conformance level of 3. It meets the requirements of the ANSI/ASHRAE 135-1995 standard for BACnet systems.

LonWorks SCC Communication Module

This module supports the LonWorks SCC (Space Comfort Communication) profile number 8500-10. Unit controllers are LonMark certified with this optional LonWorks communication module.

Metasys N2 Communication Module

This module provides N2 Open network communication capability to the UVC for communication with Johnson Metasys systems.

Figure 22. Wall-Mounted Temperature Sensors

Standard Expanded Deluxe

Standard Sensor: This sensor has no remote setpoint

adjustment capability.

Expanded Sensor: This sensor has a remote room

setpoint adjustment of ±3°F (±1.5°C) from the room setpoint established on the unit ventilator’s local user interface touch pad. Five temperature settings are provided on each side of center.

Deluxe Sensor : This sensor has a remote room setpoint

adjustment of from 54°F (12°C) to 82°F (28°C) with a midpoint setting of 68°F (20°C).

Note: McQuay does not recommend using the Deluxe Sensor

with DX systems due to its wide operating range and potential problems with the refrigerant system.

Humidity Sensors

On units equipped with humidity sensors, the UVC is configured to use a 0-100% RH, 0

VDC, capacitive humidity sensor. Humidity sensors are available as unitmounted only. The humidity sensors are used with units capable of passive or active dehumidification, or with units using an outdoor enthalpy economizer or an indoor/ outdoor enthalpy economizer.

Sensors

The UVC is configured to use passive Positive Temperature Coefficient (PTC) unit-mounted and wallmounted sensors. These sensors vary their input resistance to the UVC as the sensed temperature changes.

CO2 Sensor for Demand Controlled Ventilation

On units equipped for Demand Controlled Ventilation (DCV) the UVC is configured to use a 0-2000 PPM, 0-10 VDC, single beam absorption infrared gas sensor. CO

sensors are available as unit mounted only. An air collection probe (pitot tube and filter) is installed in the return air of the unit.

Remote Wall-Mounted Temperature Sensors

MicroTech II unit ventilators offer three choices for

Figure 23. CO2 Sensor For Demand Control Ventilation

remote wall-mounted room sensors (

Figure 22). Each has a tenant override capability and comes with an international, quick-fastening connection capability.

22 McQuay Catalog 1600

MicroTech II Controls

Figure 24. MicroTech II Sensor and Component Locations

Top V i ew

Room Humidity

Sensor (Optional)

Face & Bypass

Damper Actuator

RoomTemp

Outdoor/Return

Air Damper

Actuator

Sensor

Discharge Air Temp S e n s o r

Interface (LUI)

External Signal

Connection Plugs

Freezestat

Low Refrig Temp S n s r

Local User

Time Clock (Stand Alone Unit Option)

Tenant Override Switch

MicroTech II Unit Ventilator Controller

Communication Module (Optional)

Control Transformer

Fuse(s)

Electric Connection Box

Outdoor Air

Temp S e n s o r

Outdoor Humidity Sensor

Front View

Drainpan Condensate Overflow Sensor (Optional)

A sensor can be installed in the drain pan of the unit ventilator to sense high water levels and force the unit to discontinue cooling. This helps prevent the overflow of condensate fwhen the drain is clogged.

Actuators

Face & Bypass Damper Actuator

On units equipped with face & bypass damper control, the UVC is configured to operate a floating-point (tristate), direct-coupled, face & bypass damper actuator. To determine the modulating damper position, the controller uses a separate, factory-preset, configurable setting for each actuator's stroke time. To increase accuracy, the controller has an overdrive feature for the 0% and 100% positions and a periodic (12-hour) auto-zero PI control loop for each modulating actuator.

Figure 25. Face & Bypass Damper Actuator

CO2 Sensor

(Optional)

Main Power

On/Off Switch

Outdoor Air/Return Air Damper (OAD) Actuator

The UVC is configured to operate a floating-point (tristate) direct-coupled actuator for the outdoor air damper. This actuator provides spring-return operation upon loss of power for positive close-off of the outdoor air damper. To determine damper position, the UVC uses a separate, factory-preset, configurable setting for each actuator's stroke time. To increase actuator positioning accuracy, the UVC is provided with an overdrive feature for the 0% and 100% positions and a periodic (12- hour) auto-zero PI control loop for each modulating actuator.

Figure 26. Outdoor Air Damper Actuator

2-Position End-of-Cycle Valve Actuators (Optional)

On units equipped with 2-way or 3-way, end-of-cycle (EOC) valves, the UVC is configured to operate 2position End-Of-Cycle (EOC) valve actuators (

Figure 27). Spring return actuators are used for all End of Cycle (EOC) valves. All wet heat and heat/ cool EOC valves are normally open, and all cooling EOC valves are normally closed.

AAF-HermanNelson Model AV Unit Ventilators 23

MicroTech II Controls

Figure 27. End of Cycle Valve Actuator

Modulating Valve Actuators (Optional)

On units equipped with modulating valves, the UVC is configured to operate floating-point (tri-state) actuators for modulating 2- way and 3-way valves (

Figure 28. Modulating Valve Actuators

2-Way Valve 3-Way Valve

Figure 28).

Spring return actuators are used for all modulating valves. All wet heat and heat/ cool valves are normally open, all cooling valves are normally closed.

To determine modulating valve position the UVC uses a separate factory preset, configurable setting for each actuator's stroke time. For accuracy of actuator positioning, the UVC is provided with an overdrive feature for the 0% and 100% positions and a periodic (12-hour) auto-zero PI control loop for each modulating actuator.

Optional Time Clock For Stand-Alone Operation

As an option, stand-alone, non-slave unit ventilators can be factory-equipped with a unit-mounted, digital, 24-hour/ 7-day time clock with 20 programs ( is factory-wired to automatically place the unit into occupied or unoccupied mode based upon its schedule. Features of this clock include:

Figure 29). The clock

• Large keys with circular programming for easy schedule setup

• An LCD display

• Manual 3-way override (On/Auto/Off)

• Capacitor backup to retain program memory during

power outages.

Figure 29. Optional Time Clock

ServiceTools™

ServiceTools for MicroTech II Unit Ventilators is a CD containing software for operation on a personal computer. This software provides a visual schematic of the unit, a pictorial representation of the sequence of operation and enables the service technician to:

• Monitor equipment operation.

• Configure network communications.

• Diagnose unit operating problems.

• Download application code and configure the unit.

This software is a purchased tool for service technicians and will run on PCs with Windows 2000 (SP2), and NT4.0 (SP6) and XP (SP1) operating systems. This tool provides more capabilities than the unit’s user interface touch pad and is highly recommended for startup and servicing. (It may be required for startup and/or servicing, depending upon unit integration and other requirements.) It has no BAS functions, such as scheduling or trending, and it cannot serve as a Work Station Monitoring package.

ServiceTools comes with a service cable having two interface connections:

• A 12-pin connection to connect to the main control board.

• A 3-pin connection to connect to the optional communication modules.

98 (Second Edition),

24 McQuay Catalog 1600

Accessories

Wall Louvers & Grilles

AAF-HermanNelson wall louvers allow outdoor air to be drawn in while blending with the building architecture. They are sized to match the unit outside air opening and provide maximum air intake. Heavy-gauge, all-aluminum construction is standard, with a decorative grille optional.

Both louvers and grilles are available either painted or unpainted. When painted, a specially formulated, environmentally friendly thermosetting urethane powder is applied electrostatically and baked for long lasting beauty as well as resistance to corrosion. The paint is then oven cured to provide correct chemical crosslinking, which can provide years of service. The alloy used for louvers and grilles, AQ 5005, is suitable for color anodizing by others.

Figure 30. Intake Louvers

Horizontal Blade Louver

Vertical Blade Louver

Weep Holes

Louver Details

Louvers are available in both horizontal and vertical blade configurations (

Figure 30):

• Horizontal blade construction turns the incoming air to keep moisture from entering. Bottom weep holes drain moisture to the outside.

• Vertical-blade construction provides positive water impingement and entrapment. The bottom lip drains moisture to the outside.

Louvers can be supplied with or without flanges:

• Flanged louvers are typically used for a panel wall finish (

Figure 31).

• Unflanged louvers are typically used for recessing into a masonry wall.

A half-inch-square mesh bird screen (Figure 32) located on the leaving air side of the louver prevents birds and other small animals from entering. The screen’s strong aluminum mesh is designed to minimize air pressure drops, unlike expanded metal mesh.

Figure 32. Louver Assembly With Grille

Bird Screen

Louver

Grille

Grille Details

AAF-HermanNelson decorative intake grilles come in either painted or unpainted AQ 5005 aluminum with holes for mounting to building exteriors (

Figure 33). Their square holes are designed to match the blades of the AAF-HermanNelson louver, maximizing the air opening.

Figure 33. Decorative Intake Grille

Weep Holes

Figure 31. Flanged Louver (Indoor View)

Bird Screen

AAF-HermanNelson Model AV Unit Ventilators 25

Accessories

Ventimatic™ Shutter Room Exhaust Ventilation

Outdoor air introduced by the unit ventilator must leave the room in some way. In some states, exhaust vents are required by law or code to accomplish this. The Ventimatic shutter is a more economical solution to the problem.

The Ventimatic shutter is a continuously variable, gravityactuated room exhaust vent (

Figure 34). It operates in direct response to positive static air pressure created when ventilation air is brought into the room by the unit ventilator. It is a “one-way” shutter that opposes any flow of air into the room.

Figure 34. Ventimatic Shutter

Front (Indoor Side)Back (Outdoor Side)

The Ventimatic Shutter’s ability to exhaust only the amount of air required results in considerable energy savings. In the heating mode, the unit ventilator will be able to bring in only the required percent minimum outdoor air. Unlike systems that rely on powered exhaust, no energy will be wasted heating excess outdoor air. In the cooling mode, the unit ventilator will be able to bring in 100% outdoor air for full natural or free cooling when it is energy effective.

Since it is not powered, Ventimatic Shutter’s operation is inherently silent. Unlike other non-powered vents, it opens at an extremely low positive pressure (0.005"). Its shutter flaps are made of temperature-resistant glass fabric impregnated with silicone rubber for flexibility and long life. This fabric retains its original properties down to

-50°F.

Ventimatic Installation

The Ventimatic Shutter should be mounted on the same wall as the unit ventilator. This neutralizes the effect of wind pressure forcing excess air into the room through the unit ventilator louver. That’s because the wind pressure will also keep the Ventimatic Shutter closed and prevent room air from escaping. Since the existing room air cannot leave, excess air from the wind gust will not enter. (In contrast, a powered exhauster would “assist” the wind’s effect.) Same-wall mounting also minimizes “short circuiting” of air flow that could occur with opposite-wall mounting.

The Ventimatic Shutter is generally mounted on an AAFHermanNelson wall louver (ordered separately) which is then used for exhaust (

Figure 35). For large unit ventilators, two Ventimatic Shutters may be mounted side by side on the same wall louver to promote adequate exhaust air capacity. The size and appearance of wall louvers and grilles used for unit ventilators and for Ventimatic Shutters are identical and present an architecturally coordinated and pleasing installation.

An ideal method of integrating the Ventimatic Shutter with the unit ventilator is to locate the shutter behind a matching open-shelf or closed-shelf storage cabinet mounted next to the unit ventilator. For example, 48-inchlength wall louver can be accommodated behind a 4foot-high storage cabinet. The cabinet should be ordered with a slotted-type kick plate to provide a concealed exhaust air path to the shutter. This combination will enable a complete, integrated, energy-efficient HVAC and room exhaust system. For dimensional information, see

“Ventimatic Shutter Assembly” on page 90.

Figure 35. Ventimatic Shutter Installation

Aluminum Exterior Grille (Optional)

Aluminum Louver

Ventimatic Shutter

Louver

Two Shutter Assemblies Mounted On One Louver

Center Cover

Baffle Plate

Steel Interior Grille (Optional)

26 McQuay Catalog 1600

Accessories

Storage Cabinets, Sink & Bubbler

AAF-HermanNelson storage cabinets are designed to complement our classroom unit ventilators. They are made from heavy-gauge steel and finished with environmentally friendly, thermosetting urethane powder paint that is available in a pleasing array of matching architectural colors.

Storage Cabinets

Shelving cabinet tops are furnished with a textured, nonglare and scuff-resistant charcoal bronze electrostatic paint. Optional laminate tops are available for these cabinets and for field-supplied and installed countertops. Other features include:

• Adjustable kick plates with leg levelers are standard on all units and functional accessories. European cabinet design has adjustable leg levellers on each corner that adjust to compensate for variations in the floor.

• Adjustable-height metal shelves for flexible storage space ( tools by repositioning the four concealed shelf holding clips.

• Optional easy sliding doors with bottom glide track for good alignment ( prevents door bottom intrusion into the storage space. Optional door locks.

• Door pulls added for convenience and finished appearance.

Figure 36). Shelves can be adjusted without

Figure 37). Bottom glide track

Figure 37. Cabinet With Sliding Doors

Sink & Bubbler Cabinet

Sink & bubbler cabinets have a one-piece stainless steel top with stainless steel bowls, a raised front lip, and formed back and end splash boards ( have a choice of single or double bowls and optional door locks to conceal storage and piping. The adapter back top, when furnished, has a charcoal textured finish.

Figure 38. Cabinet With Sink And Bubbler

Figure 38). You

Figure 36. Cabinet With Shelves

AAF-HermanNelson Model AV Unit Ventilators 27

Accessories

End Panels, Filler Sections & Sub-Bases

AAF-HermanNelson end panels, filler sections and subbases can be used to match up AAF-HermanNelson unit ventilators with existing furniture or units, or with our storage, sink and bubbler cabinet offerings

End Panels

One-inch end panels are typically used to finish off stand-alone floor units. Six-inch end panels, with kick plates, can be used to provide extra space needed for piping ( wrapped in plastic and boxed to help prevent damage during construction.

Figure 39. End Panels

Figure 39). All end panels are individually

End Panel

Sub-Bases

AAF-HermanNelson sub-bases are used to provide additional height to floor unit ventilators so that they match up with the window sill or with existing cabinets (

Figure 40).

Note: Prior to 1968, unit ventilators came in 28, 30 and 34-inch

heights. The industry then standardized on the 30-inch height of the current AAF-HermanNelson unit.

Sub-bases can also be used to raise the outside air opening above floor level to reduce blockage of outside louvers and reduce louver soiling from rain splash.

They are available in 1, 2, 4, 6 and 12-inch heights with a depth of either 16-5/8" or 21-7/8". The unit ventilator’s leg levelers can also be used to level the entire unit/subbase assembly, compensating for uneven floors.

Sub-bases have an Oxford brown, baked, thermalsetting urethane powder paint finish that matches the unit’s bottom section and withstands cleaning of floors.

Figure 40. Sub-Base

Filler Sections

Filler sections can be used as spacing between cabinets, walls and unit ventilators. They are available with either laminate or painted metal tops and come in 18" and 24" lengths. They may be cut to length, with a minimum length after cutting of 3".

Each filler section includes a top, a front panel and a kick plate. Corner sections are also available which include a top, a corner post and a corner kickplate. For dimensional information and illustrations, see Sections & Utility Compartment” on page 92.

“Filler

Sub Base

28 McQuay Catalog 1600

Application Considerations

Why Classrooms Overheat

Overheated classrooms occur every day in schools in every area of the country. The most serious result is their detrimental effect on students’ ability to concentrate and learn. Research has determined that the ability to learn and retain knowledge decreases rapidly as the temperature exceeds recommendations. Overheated rooms also represent wasted fuel, resulting in excessive operating costs.

Correcting an overheating problem in an existing building is very difficult and expensive. It calls for redesign and alteration of the heating and ventilating system, necessitating considerable renovation. This potential problem should be recognized, understood and planned for when heating and ventilating systems are designed for new and existing buildings.

Schools Have Special Needs

Schools have unique heating and ventilating needs, in large part because of their variable occupancy and usage patterns. Fewer cubic feet of space is provided per student in a school building than in any other type of commercial or public building. School classrooms are typically occupied only six hours a day, five days a week, for only three-fourths of the year, with time out for vacations. All in all, this represents approximately 15% of the hours in a year that a classroom is occupied.

To understand the overheating problem in schools, one must first realize that the excess heat comes from what is commonly termed “uncontrolled heat sources.” To gain some perspective on how this affects heating and cooling decisions, let’s take a look at a typical classroom in the northern section of the midwestern United States.

Suppose we have a classroom that is 24 by 38 feet with 10-foot ceilings and 100 square feet of window area along the outside wall. At an outside temperature of 0°F and a desired room temperature of 72°F, let’s assume the normal amount of heat loss from the room to the outside is 55,000 BTUs per hour.

As the outside temperature changes, so does the amount of heat that the room loses. This is represented in

Figure 41 by Room Heat Loss Line A, which ranges from 55,000 BTUs per hour at 0°F outside air temperature to zero BTUs at 70°F. Obviously, if the heating system were the only source of heat in the classroom, the solution would be simple: The room thermostat would cause the heating system to supply exactly the amount of heat required to maintain the room at the thermostat temperature setting. In reality, the introduction of excess heat from a variety of uncontrolled

sources makes the challenge considerably more complex.

Figure 41. Heat Gain vs. Heat Loss In Occupied Classrooms

60,000

50,000

40,000

30,000

20,000

Room Heat Loss, BTU/HR

10,000

-10 0 10 20 30 40 50 60 70

As this chart illustrates, even in very cold weather an occupied classroom is more likely to require cooling than heating.

ROOM HEAT LOSS LINES

Outside Air Temperature, °F

Temperature On Room Heat Loss Line Above Which Cooling Is Always Required

10,000 BTU/HR

}

Possible Heat Gain From Sun, Direct & Reflected

8,500 BTU/HR

}

Heat Gain From Lights

7,800 BTU/HR

}

Heat Gain From Students

Heat From Students

Body heat generated by students in a classroom is one of the three primary sources of uncontrolled heat. In a typical classroom of 30 students, the amount of heat given off at all times will vary according to factors such as age, activity, gender, etc. A conservative estimate is 260 BTUs per hour per pupil. Multiply this by 30 and you get a total of 7,800 BTUs per hour added to the room by the students alone. This excess heat is noted in Figure 41 as “Heat Gain from Students.”

Heat Gain From Lights

Heat emitted by the lighting system constitutes a second uncontrolled heat source. Artificial lighting is needed in most classrooms even during daylight hours to prevent unbalanced lighting and eye strain. A typical classroom requires approximately 2,500 watts of supplemental lighting to provide properly balanced lighting. Fluorescent lights add heat to the room at the rate of 3.4 BTU per watt per hour, or a total of 8,500 BTU per hour. This extra heat is represented in

Figure 41 as “Heat Gain from

Lights.”

Add the heat gain from lighting to the 7,800 BTUs introduced by student body heat and we now have an extra 16,300 BTU/HR being introduced into the classroom by uncontrolled sources. This heat gain remains constant regardless of the outdoor air temperature.

AAF-HermanNelson Model AV Unit Ventilators 29

Application Considerations

Solar Heat Gain

The sun is a third uncontrolled source of heat. And, because it is neither positive nor constant, calculating its contribution to the overall heat gain is difficult. Solar heat gain can be the worst offender of the three in classrooms with large windows. Indirect or reflected solar radiation is substantial even on cloudy days, even in rooms with north exposure, as a result of what is termed “skyshine.”

To get an idea of the potential effect of the sun, let’s assume that the solar heat gain in our hypothetical classroom will peak at 240 BTU/HR per square foot of glass area. If we then assume a glass area of 100 square feet and at least 100 BTU/HR per square foot of glass for solar heat gain, we can calculate a very conservative estimate of 10,000 BTU/HR heat gain through windows. If we add this to the heat from the lights and body heat, total heat gain adds up to 26,300 BTU/HR from sources other than the heating and ventilating system. This is indicated in top horizontal line, which intersects Room Heat Loss Line A at approximately 37°F. This is a reasonable estimate of the maximum uncontrolled heat gain that can be received in the typical classroom from these common heat sources.

Figure 41 by the

The Analysis

From Figure 41 it is evident that, at an outside temperature of 48°F or higher, the heat given off by 30 students and classroom lighting is sufficient to cause overheating. This is true even if the classroom is occupied at night when solar heat gain is not a factor. But, since classrooms are occupied during the day, solar addition provides heat in varying amounts even in classrooms with north exposures. Consequently, the heating and ventilating system in our typical classroom must provide cooling at all times when the outdoor temperature is above 48°F and at any time during colder weather when the solar heat gain exceeds room heat loss.

If we assume an average winter temperature of approximately 33°F in the region where our typical classroom is located, we know that, half of the time, both night and day, the outside temperature will be above 33°F. However, since it is generally warmer during the day, when school is in session, the heating and ventilating system will be required to provide cooling for this classroom during much of the time that the room is occupied.

In this example, we’ve assumed that our classroom had a room heat loss of 55,000 BTU/HR at a design outdoor air temperature of 0°F (Room Heat Loss Line “A”). Bear in mind, however, that the recent trend in “energy-saving” building design often results in rooms with lower room

heat loss, as indicated by Room Heat Loss Lines “B”, “C” and “D.” At 0°F design outdoor air temperature:

• Room “B” has a room heat loss of 45,000 BTU/HR,

• Room “C” has a room heat loss of 35,000 BTU/HR,

• Room “D” has a room heat loss of 25,000 BTU/HR.

Note the lowering of the temperature above which cooling will always be required as the room heat loss decreases.

We’ve noted that cooling is always required in Classroom “A” when outdoor air temperatures exceed 48°F. In Classroom “B,” “C,” and “D” cooling is always required when outdoor temperatures exceed 44°, 36°and 23°F, respectively (

Now that we understand the reason for classrooms overheating, the solution is simple: The heating and ventilating system must provide cooling to take care of the heat given off in the classroom by uncontrolled heat sources.

Figure 41).

Cooling The Classroom

The AAF-HermanNelson Unit Ventilator has become a standard for heating and ventilating systems in schools because it provides the solution for overheating classrooms. The unit ventilator cools as well as heats. During the heating season the outdoor air temperature is nearly always below the desired room temperature. It stands to reason then that the outside air should be used to provide the cooling necessary to keep classrooms down to thermostat temperature.

The classroom unit ventilator does just that. By incorporating an automatically controlled outdoor air damper, a variable quantity of outdoor air is introduced in the classroom, metered exactly to counteract overheating. Since our problem is more one of cooling than of heating, it is evident that more than just the room heat loss must be determined to design a good heating and ventilating system. The cooling requirements should be assessed as well, and the free-cooling capacity of the equipment specified along with the heating capacity required. If this is done, the optimum learning temperature can be maintained in each classroom.

30 McQuay Catalog 1600

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