McQuay SWP023 User Manual

Self-Contained Air Conditioning Systems

Type SWP Vintage H
with R-410A Refrigerant

Capacity: 20 through 130 tons

Catalog 860-9

Engineered for flexibility and performance™

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Continued Leadership in

Self-Contained Systems Design s . . . . . . . . . . . . . . .3

McQuay Self-Contained Systems . . . . . . . . . . . . . . . 4

SWP 012–130 Features and Options . . . . . . . . . . . . 4

Cabinet, Casing and Frame . . . . . . . . . . . . . . . . . 6

Compressor/ Condensing Section . . . . . . . . . . . . 7

Cooling Coil Section . . . . . . . . . . . . . . . . . . . . . . .8

Supply Fan Section . . . . . . . . . . . . . . . . . . . . . . . .8

Acoustical Discharge Plenum . . . . . . . . . . . . . . . 10

Variable Air Volume Control . . . . . . . . . . . . . . . . 10

Economizer Options . . . . . . . . . . . . . . . . . . . . . .10

Condenser Head Pressure Control . . . . . . . . . . .11

Filter Section . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Blank Sections . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Heating Section . . . . . . . . . . . . . . . . . . . . . . . . . .12

System Flexibility with Unit Options . . . . . . . . . . . . 13

Selection/Application Flexibility . . . . . . . . . . . . . .13

Arrangement Flexibility . . . . . . . . . . . . . . . . . . . .13

Optimal Discharge Air Temperature . . . . . . . . . .13

Controllers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

R-410A Refrigerant . . . . . . . . . . . . . . . . . . . . . . . 14

MicroTech III Unit Controls . . . . . . . . . . . . . . . . . . . . 15

Open Choices Benefits for Easy Integration . . . . 15

Alarm Management and Control . . . . . . . . . . . . . 21

Application Considerations . . . . . . . . . . . . . . . . . . .23

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Unit Location . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Acoustical Considerations . . . . . . . . . . . . . . . . . .24

Equipment Room . . . . . . . . . . . . . . . . . . . . . . . .24

Ductwork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Condenser Water Piping . . . . . . . . . . . . . . . . . . . 25

Head Pressure Control . . . . . . . . . . . . . . . . . . . . 25

Variable Air Volume . . . . . . . . . . . . . . . . . . . . . . 25

Variable Frequency Drives . . . . . . . . . . . . . . . . .26

Duct Static Pressure Sensor Placement . . . . . . .26

Zone Sensor Placement . . . . . . . . . . . . . . . . . . .26

Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

System Operating Limits . . . . . . . . . . . . . . . . . . .27

Airflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Fan Heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Condenser Water Flow . . . . . . . . . . . . . . . . . . . . 27

Coil Freeze Protection . . . . . . . . . . . . . . . . . . . . 28

Air Density Correction . . . . . . . . . . . . . . . . . . . . . 28

Unit Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Terms of Sale . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Selection Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 29

Physical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Performance Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

DX Cooling Capacity Data . . . . . . . . . . . . . . . . . 36

Waterside Economizer Capacity . . . . . . . . . . . . 44

Heating Capacity Data . . . . . . . . . . . . . . . . . . . . 45

Component Pressure Drops . . . . . . . . . . . . . . . 46

Total Unit Water Pressure Drop . . . . . . . . . . . . . 49

Fan Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Dimensional Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Recommended Clearances . . . . . . . . . . . . . . . . 61

Electrical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Supply Power Wiring . . . . . . . . . . . . . . . . . . . . . 65

Unit Weights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

2 McQuay Catalog 860-9

Introduction

Introduction

Continued Leadership in Self-Contained Systems Designs

McQuay SWP self contained air conditioning systems trace
their history to the late 1970s. The first self contained variable
air volume systems with waterside economizer cycle was
developed by us for the prestigious 499 Park Avenue office
building in New York City. McQuay SWP, with decades of
innovation, design flexibility, durable construction, low capitol
and operating cost, make us the leader of self contained system
market and the preferred HVAC solution for thousand of most
prominent building projects.

SWP water cooled self-contained air conditioner is an ideal
option for a job where energy efficiency, reliability, indoor air
quality and acoustic are top priorities. Along with providing
high quality and state-of-the-art technology, SWP self­contained systems offer the following valuable features and
benefits to satisfy a wide range of diverse applications.

• Comfort and Redundancy

– Occupants enjoy individual control over comfort condi-

tions and off-hour system operation.

– Tenants benefit from their indivi dual efforts to control

energy costs.

– Routine service is located where it minimizes tenant

inconvenience.

– Individual or dual systems per floor provide system

redundancy and standby.

• Economical First Cost

– VAV system flexibility uses building diversity to reduce

system tonnage and first cost.

– Factory-packaged concept reduces field labor, installation

time and expense.
– No expensive chilled water piping or chiller room.
– Individually tested, factory-designed systems reduce

startup and installation expense.
– Reduced penthouse and equipment room requirements.
– Centralized condenser water and condensate piping and

streamlined system layout.
– Modular units design make renovation projects easier

since individual section designed for narrow hallways,

elevators and doorways.
– Optional acoustical discharge plenum is an available

option in any height to match your job needs and mini-

mizes supply duct transition losses.

• Energy Efficient System

– Reduces fan kW and operating costs at part load condi-

tions.
– Savings maximized through use of variable speed fan

control.
– Individual zone control.

• Improving Indoor Air Quality

For better filtration filter selection flexibility includes:
– MERV 7, 8, 11, 13, or 14 options with & without pre-fil-

ter. Microbial-resistant filter option is also an available
option.

– Featured Double-wall panel construction that eliminates

fibers in the supply air stream and is easy to clean.

– Provided with double-sloped, galvanized or stainless steel

drain pans eliminate stagnant water and minimizes bacte­rial growth.

• Quiet System Operation

– Provided by structural quality and specialized design.
– Recognized for quiet operation by renowned U.S. acous-

tical consultants.

– Provided with a SWSI airfoil plenum fan for excellent

acoustics and better efficiency

– Unit featured discharge plenum with sound baffles is an

available option for sound sensitive job

• Free Cooling

– Water or air economizer capability for optimized energy

savings.

– Economizer reduces compressor operating hours and

energy costs.

– Year-round “free cooling” capability.

• Efficient Part Load Operation

– System energy at part load operation is more efficient

than to central chilled water systems.

– Multiple systems and compressors versus a single, large

central plant.

– Efficient and reliable system for partial occupancy and

after hours operation.

– Operates only the system(s) on the floor(s) requiring after

hours use.

• Economical Integrated or Stand Alone DDC controls

– Monitoring and diagnostics reduce the potential for

expensive field repairs.

– Industry leading Protocol Selectability™ feature provides

effective BAS selection flexibility.

• Maintenance Costs Reduction

– No complicated central chiller plant to maintain.
– Service and maintenance are performed out of the occu-

pied space.

– Control and product reliability functions designed by the

equipment manufacturer for single source responsibility
and improved reliability.

• System Versatility

– Applicable to schools, offices, shopping centers, manu-

facturing facilities, etc.
– Prime candidate for floor by floor building renovation.
– Retrofit alternative where existing chiller cannot be

ed for replacement.

access

McQuay Catalog 860-9 3

McQuay Self-Contained Systems

McQuay Self-Contained Systems

SWP 012–130 Features and Options

Airfoil Plenum Fans

• SWSI fans more energy efficient and quieter than forward

curved fans

• Premium high efficiency open, drip-proof standard

motors and TEFC motors, an available option

• Seismic control restrained spring isolators are available

• Aerodynamically designed fan also available with 12

blades for even lower sound levels

Coils

• High efficiency enhanced corrugated fin design

• High coil performance and reduced static

pressure losses

• Interlaced and/or row split circuiting to keep

full face of the coil active and to eliminate air
temperature stratification and optimum part
load performance

Durable Construction

• Pre-painted or G90 galvanized steel exterior

cabinet panels

• Standard foam injected panels with R-13

insulation provide superior rigid double wall
construction and minimizes air leakage

• For better acoustics, an additional 2", 1. 5# density

R-8 fiberglass insulation is an available option for
fan and plenum sections

• Double-sloped drain pans help eliminates

standing stagnant water

Blank Sections

• Available to mount air blenders, carbon or

charcoal filters, sound attenuators or other
specialty equipment

• Allow customization for maximum system

performance and efficiency

• Can reduce design and installation costs

Scroll Compressor(s)

• Durable and reliable multiple compressors

• Lower operating cost with High EERs

• Customize selections to match specific

application

• Mounted on resilient rubber isolation for

smooth and quiet operation

Access Panels and Doors

• All panels and access doors shall be sealed

with permanently applied bulb-type gasket

• Access doors are flush mounted to cabinetry,

with hinges, latch and handle assembly

4 McQuay Catalog 860-9

Refrigerant Circuits

• Suction and discharge service valves, an available

option, to isolate each compressor

• Hot gas bypass, an available option, on units with

two refrigerant circuits

McQuay Self-Contained Systems

Shell and Tube Condensers

• Carbon steel Shell and Tube Condenser , non-

ferrous water channels and enhanced tubing for
high performance

• Integral sub-cooling circuit is provided as

standard to maximize efficiency

• Mechanically cleanable condenser and water

piping is rated for standard 300 psig waterside
working pressure & 450 psig is an available
option

• Two-way valve for head pressure control is

available for low condenser water temperatures

Multiple Filter Options

• 2" 30% (MERV7) and 75% (MERV13) filter s

• 4" 30% (MERV8), 65% (MERV1 1), 75% (MERV13)

and 85% (MER V14) longer lasting filters available

• 4" primary filters also available with 2" or 4" with

pre-filter

Economizer Options

• W aterside economizer effectively uses low cooling tower

water temperatures to offload compressor operation

• An airside economizer control package is available for

controlling field installed mixing dampers capable of 100%
outside airflow.

MicroTech® III Control System

• Factory-installed and tested to help minimize costly field

commissioning.

• Open Choices™ feature for easy integration into the BAS of

your choice using open, standard protocols such as BACnet®
or LONTALK®.

• Easily accessed for system diagnostics and adjustments via a

keypad/display on unit.

• Optionally add a remote keypad and display that is identical to

the unit mounted user interface.

Factory-Mounted Variable Frequency Drives

• Controlling fan motor speed can lower fan operating

costs and sound levels

• All VFD selections are plenum rated

• Manually activated bypass contactor is available to

allow system operation in the event of drive service

McQuay Catalog 860-9 5

McQuay Self-Contained Systems

McQuay Self -Contained SWP systems are built to perform,
with features and options that provide for lower installed and
operating costs, good indoor air quality, quiet operation and
longevity.

Cabinet, Casing and Frame

• Unit base constructed of 15-gauge and 10-gauge galvanized

steel for vibration control and rigging strength.

• Heavy-duty lifting brackets strategically placed for balanced

cable or chain hook lifting.

Figure 1: Low Leak Gasketed Frame and Foam Panels

• Unit cabinet constructed with foam insulation standard and

heavy gauge [pre-painted] [galvanized steel] exterior panels
for long equipment life.

• All sections have galvanized steel internal lining.

• 2-inch thick panels and access doors are thermal broke

double wall assembly, with [R-13 foam] [R-8 fiberglass].

• System components strategically located for ease of

inspection, serviceability and maintenance.

• Refrigeration components positioned out of the airstream so

adjustments and readings can be made without disrupting
system operation.

• Access doors flush mounted to cabinetry, with hinges, latch

and handle assembly.

• Doors on positive pressure sections are provided with

secondary latches to relieve pressure and prevent injury
upon access.

Figure 2: Hinged Access Doors with double latches

• Low leak gasketed frame channels minimize air leakage and

eliminates metal-to-metal contact between paneling and
frame work. Air leakage is only 0.5 cfm/square foot at 5"
cabinet pressure.

6 McQuay Catalog 860-9

McQuay Self-Contained Systems

Control Panel

Coil/Access
Section

Supply Fan
Section

Compressor/
Condenser
Section

Base Plates

Modular Design

• Optional modular construction unit shipped with a nitrogen

holding charge.

• Four distinct sections; coil/access section, supply fan

section, compressor/condenser section and the control panel.

Figure 3: SWP Modular Sections

• Insulated and segregated condensing section from the air

handling section to avoid transmission of noise to the
circulated air stream.

• Each refrigerant circuit is furnished with filter-drier, liquid

moisture indicator/sight glass , th erm a l ex pansion valve,
liquid line shutoff valve with charging port, high pressure
relief device and high and low pressure cutouts.

• If any compressor is made inoperable, the remaining

compressors are still allowed to operate.

• Thermal expansion valve capable of modulation from 100-

25% of its rated capacity.

• Hot gas bypass also available on units with two refrigerant

circuits.

Condensers

• All units feature carbon steel mechanically cleanable shell

and tube condenser.

• Includes non-ferrous water channels and enhanced tubing

for high performance.

• Serves an independent refrigerant circuit and includes a

spring loaded high pressure relief valve

• Integral sub-cooling circuit provided as standard to

maximize efficiency.

Compressor/ Condensing Section

Compressors

• All units feature multiple reliable scroll compressors for

• Suction and discharge service valves and gauge ports,

• Individual branch circuit fusing protects each compressor.

• T o prevent compressor short cycling, MicroTech® III

• Compressors mounted on resilient rubber isolation for

Figure 4: Compresors

efficient system part load control, quiet operation and
system redundancy.

available option, on each compressor.

control system incorporates timing functions.

smooth and quiet operation.

Figure 5: Condensers

• All units are leak tested, evacuated and shipped with a [full

operating charge of R-410A] [for modular design nitrogen
holding charge] and POE oil.

• Condenser assembly and all factory water piping rated for a

waterside working pressure of 300 psig as standard [450
psig] tested before shipment.

• Provided with a single supply and return water connections

• Unit available in both right-hand and left-hand piping

locations.

• Optional two-way valve provides accurate head pressure

control for condenser entering water temperatures as low as
40ºF.

McQuay Catalog 860-9 7

McQuay Self-Contained Systems

Refrig. Flow Ckt 1
Refrig. Flow Ckt 2

Ckt 2

Ckt 1

Ckt 1

Ckt 1

Ckt 1

Ckt 1

Ckt 1

Ckt 1

Ckt 1

Ckt 2

Ckt 2

Ckt 2

Ckt 2

Ckt 2

Ckt 2

Ckt 2

Airflow

Cooling Coils

Cooling Coil Section

• Large face area coils with high efficiency , enhanced copper

tubing and ripple corrugated aluminum fins.

• Features interlaced and/or row split circuiting to keep the

full face of the coil active and eliminate air temperature
stratification and optimum part load performance.

Figure 6: Evaporator Coil Circuiting

• 5 or 6 row evaporator coil with 12 fins/ inch spacing and

multiple face areas allows a custom match to specific design
loads.

• Provides low air pressure drop, high full and part load

operating efficiencies.

• Mounted in a [galvanized] [stainless steel ] cross broke and

double sloped drain pan with a full 2 inches of insulation.

• Compressor staging sequenced to take maximum advantage

of available coil surface.

• Each evaporator coil circuit furnished with a wide range

thermostatic expansion valve with an adjustable superheat
setting and external equalizer.

• An intermediate drain pan in the coil bank helps to provide

condensate removal without carryover.

Figure 7: Cooling Coil Section Shown

Supply Fan Section

• Single width, single inlet (SWSI) airfoil supply air fan

selections provide efficient, quiet operation at wide ranging
static pressure and air flow requirements.

• Each fan assembly is dynamically trim balanced at the

factory for quiet operation before shipment.

• All fan drives are factory sized according to job specific

airflow, static pressure, and power requirements.

• For seismic sensitive regions, spring fan isolators are

available with seismic restraints.

• 150% service factor drives extend service life of the fan

belts. Drive components and fan bearings are easily accessed
for periodic maintenance.

• Mounted on 2 inch deflection spring isolators for excellent

isolation effectiveness.

• Solid steel shafts rotating in 200,000 hour pillow block ball

bearings with grease fittings.

• Motor availability includes premium efficiency, open, drip-

proof, and totally enclosed selections; EPACT compliant
premium efficiency selections.

8 McQuay Catalog 860-9

Figure 8: Airfoil Fan

McQuay Self-Contained Systems

McQuay Plenum Fan

Least turbulance

and best acoustics

* Ceiling heights restrict “h” and
increase the problem with housed fans

Competitive Housed Fan

Excessive turbulance

and mediocre acoustics

Competitive Housed Fan

Worst turbulance

and worst acoustics

h*

Acoustical Advantages

McQuay SWP Self-contained units are provided with a high
efficient, SWSI airfoil plenum fan and have several acousti cal
advantages:

• Airfoil fans are more efficient than forward curved fans

contributing to less noise.

• For specific unit sizes, several fan diameters are available,

fan selection provides optimal efficiency.

Figure 9: Supply Fan Comparison

• Competitive supply duct work normally involves

discharging air vertically into a ceiling, then routing it
horizontally, Figure 10. McQuay’s plenum fan discharge has
far less velocity pressure than competitive housed fan
discharge, resulting in:

• 90º duct elbows that generate far less turbulance.

• Air flow that can be routed in any direction.

McQuay Catalog 860-9 9

McQuay Self-Contained Systems

McQuay Optional Plenum

“h” can be varied
to match ceiling height

h

Competition

Expansion Loss

90° Elbow Loss

Standard Exterior
Galvanized Surface

Standard Galvanized Liner

Standard Injected Foam Panel

Optional Fiberglass Insulation

Perforated Liner

Interior Optional

Acoustical Discharge Plenum

McQuay offers an optional acoustical discharge plenum,

Figure 10, that minimizes supply duct transition losses and

noise:

• Plenum fans pressurize the entire cabinet and have no

significant plenum air pressure drop (housed fans have
expansion, contraction and 90º elbow losses).

• Discharge plenums offered in any height to match ceiling

height.

• Custom size duct connections are available on any size

plenum.

Discharge Plenum with Foam Insulation and Sound
Baffles

Optional discharge plenum with foaminjected panels can be
provided with the additional sound attenuating baffle option
consisting of:

• Additional 2" of fiberglass insulation.

• Perforated liners, Figure 11.

Figure 10: Acoustical Discharge Plenum

Variable Air Volume Control

• Energy saving advanced technology variable frequency

drive (VFD), fan speed control is available with the
convenience and cost savings of factory mounting and
testing.

Figure 12: Variable Frequency Drive Controller

Figure 11: Foam Insulation and Sound Baffles

• All VFD selections are plenum rated and are conveniently

mounted within the control panel.

• MicroTech III controls provide advanced duct static pressure

control and controlled by either single or two-duct static
pressure sensors.

• A manually activated bypass contactor is available to allow

system operation even in the event of drive service.

• All VAV systems include an adjustable, duct high-limit

switch to protect duct work from excessive pressure.

Economizer Options

Waterside Economizer

• An energy saving, waterside economizer package, an

available option on all return air unit.

• Includes factory mounted 4-row [chemically cleanable coil]

[mechanically cleanable coil], control valves and piping.

• Rated for 300 psig as standard [450 psig] waterside working

pressure and the entire coil and piping assembly is factory
leak tested.

• Factory integrated MicroTech III controller to control

economizer operation and maximize free cooling potential.

• Unit enables economizer operation whenever cooling tower

water temperature is less than the unit entering air
temperature by a field adjustable value, generally 5-7°F.

10 McQuay Catalog 860-9

McQuay Self-Contained Systems

Mechanically Cleanable

Economizer Coil

• To save energy with a variable pumping system control

valves operation can be selected to maintain full flow
through the unit at all times or to isolate the unit from the
condenser water loop when there is no call for cooling.

• To extend free cooling savings, economizer operation can be

enabled during mechanical cooling.

• Unit enables mechanical cooling only when the economizer

valve is driven 90% open and cooling load is not satisfied.

• Economizer control will maintain full free cooling capability

until disabled by the economizer changeover set point.

• T o help protect against coil freeze-up an optional factory

mounted freeze stat is available.

Figure 13: Mechanically Cleanable Waterside
Economizer Coil

• To extend free cooling savings, economizer operation can be

enabled during mechanical cooling.

• Unit enables mechanical cooling only when the economizer

damper is driven 90% open and cooling load is not satisfied.

• Economizer control will maintain full free cooling capability

until disabled by the economizer changeover set point.

Condenser Head Pressure Control

• Unit requires condenser head pressure control for

applications where a waterside economizer package is not
being used and entering condenser water temperatures can
be less than 55°F.

• Optional two-way valve provides accurate head pressure

control for condenser entering water temperatures as low as
40degree F

Filter Section

• Selection flexibility includes face loaded rack with non-

gasketed frames and filter clips.

• Unit features 2-inch filter option available in 30% (MERV 7)

& 75% (MERV 13) nominal efficiency

• Longer lasting 4-inch filters higher filtration option is

available in 30% (MERV 8) & 65% (MERV 11), 75%
(MER V 13) & 85% (MERV 14) nominal efficiency with and
without 2-inch or 4-inch 30% pre-filter.

Airside Economizer

• A mixing box containing outdoor air, return air and exhaust

air dampers are available using the McQuay Vision™ air
handling unit platform.

• Factory integrated MicroTech III controller controls

economizer operation and maximize free cooling potential.

• Airside economizer control package available to control

field installed mixing dampers capable of 100% outside
airflow.

• Unit enables economizer operation whenever outside air

enthalpy , comparative enthalpy or dry bulb temperature
changeover provides control flexibility to bring in most
amount of outside air for free cooling.

• Economizer damper control actuator modulates in response

to the cooling load.

• MicroTech III controller positions outside air damper to

maintain minimum ventilation requirements when
economizer is not in operation.

Figure 14: 4 Inch Filters

Blank Sections

• Available to mount air blenders, pre-heat coils, sound

attenuators or other specialty equipment using the McQuay
Vision™ air handling unit platform and shipped loose.

• Allow customization for maximum system performance and

efficiency and reduce design and installation costs.

McQuay Catalog 860-9 11

McQuay Self-Contained Systems

Electrical

• Units are completely wired and tested at the factory prior

shipment.

• Wiring complies with NEC requirements and all applicable

UL standards.

• For ease of use, wiring and electrical components are

number coded and labeled according to the electrical
diagram whenever applicable.

• Supply air fan motors, compressor motors and electric heat

all branch circuits have individual short circuit protection.

• Control circuit power is supplied through a factory installed,

low voltage transformer.

• The supply fan motor circuit includes a three phase

contactor and ambient compensated overload protection
with manual reset.

• Each refrigerant circuit includes both a high and low

pressure cutout switch.

• A terminal block is provided for the single, main power

connection and a terminal board is provided for low voltage
control wiring.

• A factory mounted, non-fused main circuit interrupter is

available for disconnecting the main electrical power to the
unit.

• Dual power blocks or disconnect switches are available to

accommodate requirements for standby, emergency power
supplies.

Heating Section

Hot Water Heat

• Multiple coil selections offered to size heating output to

application needs.

• Hot water coils are 5/8-in. O.D. copper tube/ aluminum fin

design with patented HI-F5 fins.

• Rated in accordance with ARI Standard 430.

• Pre-heating control fully integrated into the unit’s

MicroTech III control system is available using the McQuay
Vision™ air handling unit platform.

• Available with factory-mounted freezestat.

Steam Heat

• Steam heating coils are 5/8-in. O.D. copper tube/aluminum

fin jet distributing type with patented HI-F5 fin design.

• Rated in accordance with ARI Standard 430.

• Multiple different steam coil selections offered to size

heating output to application needs.

• Pre-heating control fully integrated into the unit’s

MicroTech III control system is available using the McQuay
Vision™ air handling unit platform.

• Available with factory-mounted freezestat.

Electric Heat

• Factory assembled, installed and tested.

• Two stage capability for application flexibility.

• Durable low watt density nickel chromium elements for

longer life.

• Entire heat bank protected by a linear high limit control with

each heater element protected by an automatic reset high
limit control.

• Fuses provided in each branch circuit.

12 McQuay Catalog 860-9

System Flexibility with Unit Options

Along with providing high quality and state-of-the-art
innovation, SWP self-contained systems offer customized
flexibility to satisfy a wide range of diverse applications.

System Flexibility with Unit Options

discharge orientations. Piping and fan arrangement flexibility
can simplify mechanical equipment room arrangement,
improve installation costs, and total system performance.

Selection/Application Flexibility

Nominal cooling capacities range from 12 to 130 tons. In
addition, all units offer multiple compressor selections to meet
exacting system requirements. The flexibility to optimize the
self-contained system to fit the application is a McQuay SWP
advantage. Available system applications include the
following:

• VAV dischar ge air temperature control with static pres­sure control.

• Discharge air temperature control with constant air vol­ume.

• Constant volume, zone temperature control.

• 100% outside air control.

• Dehumidification control, with or without reheat control.

In addition to compressor/coil flexibility, SWP systems offer
single width, single inlet, air foil fans with factory-mounted
variable frequency drives for maximizing VAV system fan
performance. High efficiency fan capability coupled with
extensive compressor flexibility provide the right system
selection for the application.

Arrangement Flexibility

All SWP systems offer the flexibility of right-hand and left­hand piping and control panel arrangements and multiple fan

Optimal Discharge Air Temperature

More and more system engineers are designing optimal
discharge air temperature systems to improve system
performance and system first cost; the McQuay SWP provides
the flexibility to do it successfully. Optimal discharge air
temperature systems are designed to provide unit leaving air
temperature selections of 52°F to 53°F versus more
conventional systems that supply air at temperatures closer to
58°F . This five to six degree reduction in air temperature to the
room diffusers can subsequently reduce the required supply air
volume to the room by 20% to 25%.

The benefits of optimal discharge air temperature systems
become quite apparent with a look at the advantages offered
with reduced supply air cfm airflow:

• Reduced first cost and installation cost by allowing
smaller duct sizes and a smaller air distribution system.

• Reduced bhp requirements. Depending on changes in
duct size and the resulting total static pressure, a 20%
reduction in supply air cfm can reduce fan bhp require­ments by 25% or more.

• Reduced fan sound power generation and a quieter room
environment.

• Reduced equipment room size may be possible due to
using a physically smaller unit size.

• Filtration Flexibility.

McQuay Catalog 860-9 13

System Flexibility with Unit Options

Controllers

MicroTech III DDC control systems provide constant volume,
variable air volume, 100% outside air, and/or dehumidification
control flexibility . See “MicroTech III Unit Controller” section
for more information.

Summary of Available Options

• Multiple different compressor/coil capacity selections

• Mult ip le control options: VAV, CV, 100% O A, dehumidi­fication

• Nonfused main power disconnect switch

• Dual nonfused main disconnect switches

• Nonaveraging freezestat for hot water or waterside econ­omizer coil protection

• Unit phase failure/under voltage protection

• Premium efficiency fan motors

• TEFC fan motors

• Condenser water flow switch

• 4-row waterside economizer system

• Air cycle economizer system

• Modulating hot water heat control

• Staged electric heat

• Multi direction, acoustic discharge plenum

• Factory-mounted and factory-controlled variable fre­quency drives

• High efficiency filtration options

• Right-hand and left-hand piping se lections

• Multiple fan discharge arrangements

• Head pressure control valve

• Special coil coatings

• Double wall cabinet construction

• Seismic fan isolation

• Independent refrigerant circuit units offer the following
options:

• Five-row or six-row DX coils with enhanced heat trans­fer surfaces

• R-410A refrigerant

• Service and shut off valves on liquid and discharge

Figure 15: MicroTech III DDC Co ntroller

R-410A Refrigerant

McQuay SWP units with independent refrigerant circuits are
available with non-ozone depleting R-410A refrigerant.

Features

• R-410A refrigerant is environmentally friendly with zero
ozone depleting allowance (ODP). Customers have no
phase out and replacement concerns.

• Units are factory engineered for proper cooling perfor­mance using R-410A.

• R-410A efficiency is excellent. McQuay R-410A SWP
units are available with EERs that exceed ASHRAE 90.1-

2010.

• Units are factory charged with R-410A and synthetic oil
(such as POE), and they include components and controls
specifically tailored to R-410A.

• R-410A refrigerant is a blend, but the glide is negligible.
This is not true for R-407C. If R-407C leaks, the remain­ing charge may not have a proper mix of components. R­410A does not have this problem so leaks are easier to
repair.

• Units are factory tested prior to shipment.

14 McQuay Catalog 860-9

MicroTech III Unit Controls

McQuay SWP systems continue to provide industry leading
performance, equipped with a complete MicroTech III control
system. In addition to providing stable, efficient temperature,
and static pressure control, the controller is capable of
providing comprehensive diagnostics, alarm monitoring, and
alarm specific component shutdown if critical equipment
conditions occur. The unit controllers are factory mounted and
configured for stand-alone operation or integration with a
building automation system (BAS) through an optional
communication module with our Open Choices feature.

Open Choices Benefits for Easy Integration

Easy, low cost integration into most building automation
systems without costly gateway panels.

• Flexibility to select either BACnet® or L

communication. Units are LonMark® 3.4 certified with the
appropriate communications module for L
networks.

• Comprehensive unit control and status information is

available at the BAS regardless of communication protocol.

• Long-term choices for equipment adds or replacements, and

for service support.

• Flexible alarm notification and prioritization with Intrinsic

Alarm Management (BACnet).

• Simplified BAS integration with the ability to set network

parameters at the unit controller, reducing installation time
and costs.

• Easy monitoring and troubleshooting of communication

status from the unit controller to the BAS.

ONWORKS®

ONWORKS

MicroTech III Unit Controls

Components

Each SWP self-contained system is equipped with a complete
MicroTech III unit control system that is pre-engineered,
preprogrammed, and factory tested prior to shipment. Each of
the MicroTech III unit control systems is composed of several
components that are individually replaceable for ease of
service. These components include:

• Unit controller with user interface display and navigation
wheel

• Optional expansion modules

• Communication module (optional)

• Pressure transducers

• Unit-mounted temperature sensors

• Zone temperature sensor packages

• Humidity sensor

Main Control Board (MCB)

The main control board (MCB) contains a microprocessor that
is preprogrammed with the software necessary to control the
unit. This provides that schedules, set points and parameters
are not lost, even during a long-term power outage. The
microprocessor board processes system input data and then
determines and controls output responses. An RS-232
communication port is provided as standard to allow for direct
or modem access with a PC-based service tool.

Expansion Modules

These boards are used to expand the input and output
capability of the unit controller. Each board communicates via
serial data communications. These microprocessor based
boards provide independent operation and alarm response even
if communication is lost with the unit controller.

Communication Module

An optional communication module provides the means to
factory or field configure MicroTech III unit controls for
interoperability with an independent BAS. Communication
modules are available to support industry recognized
communication protocols including BACnet MS/TP, BACnet/
IP and L

Figure 16: MicroTech III Keypad Display

McQuay Catalog 860-9 15

ONWORKS.

MicroTech III Unit Controls

Keypad/Display

All MicroTech III unit controllers include a push/pull
navigation wheel and display. The display is a supertwist
nematic type with highly visible black characters on a yellow
background. The 5-line by 22-character format allows for easy
to understand plain English display messages. All operating
conditions, system alarms, control parameters and schedules
can be monitored from the keypad/display. If the correct
password has been entered, any adjustable parameter or
schedule can be modified from the keypad.

Temperature and Humidity Sensors

With the exception of the zone, outside air and return air
sensors, all temperature sensors are factory installed and
tested. Zone sensor packages are available to suit any
application. A humidity sensor is available for field
installation.

Static Pressure Transducers

All pressure transducers are factory installed and tested.
Connection and routing of field-supplied sampling tubes is
done at time of unit installation.

Zone Temperature Sensors

Two optional zone temperature sensors are available:

• Zone sensor with tenant override switch

• Zone sensor with tenant override switch and remote set
point adjustment

Timed tenant override is a standard MicroTech III
control feature.

Zone sensors are required for the controller’s purge cycle,
space reset of supply air set point, and night setback or setup
features. All zone sensors are field installed with field wiring
terminated at a separate, clearly marked terminal strip.

Stand-alone Controller Features

MicroTech III applied rooftop unit controls includ e all of th e
essential features required to make them capable of completely
independent, stand-alone operation.

Internal Time Clock

An internal, battery-backed time clock is included in the
MicroTech III unit controller. Current date and time can be
quickly and easily set at the user interface keypad.

Internal Schedule

Seven daily schedules and one holiday schedule can be entered
at the keypad of all unit controllers. For each of these eight
schedules, one start and one stop time can be entered. Up to 10
holiday periods, of any duration, can be designated. The unit
will automatically run according to the holiday schedule on the
holiday dates. To handle special occasions, an additional ‘one
event’ schedule can also be used.

In lieu of its internal schedule, the unit can be operated
according to a network schedule from a BAS.

External Time Clock or Tenant Override Input

An input is supplied that can be used to accept a field wired
start/stop signal from a remote source. An external time clock,
a tenant override switch, or both may be connected. Whenever
the external circuit is closed, the controller overrides the
internal schedule (if activated) and places the unit into the
occupied mode.

If the internal schedule or a BAS network schedule is used,
field wiring is not required.

Timed Tenant Override

Off-hour operation flexibility is a must in today’s office
environments and even stand-alone MicroTech III controls
handle it with ease. When unit operation is desired during
unoccupied hours, initiate timed tenant override by pressing
the tenant override button on either of the optional zone sensor
packages. The unit then starts and runs in the occupied mode
for a keypad-adjustable length of time (up to five hours ). If th e
button is pressed again while the unit is operating, the timer
resets to the full time allowance without interrupting unit
operation. Tenant override operation also can be initiated by a
BAS.

Three Remote Set Point Adjustment Options

1 Remote user interface option (RUI).
2 Building automation system (BAS). See “Open Choices

Benefits for Easy Integration” on page 15.

3

All constant air volume-zone temperature control (CAV­ZTC) unit controllers include an input that can be used to
remotely adjust the zone cooling and heating set points.
To use this feature, wire the optional zone sensor
package with set point adjustment to the controller. The
remote set point adjustment feature can be enabled or
disabled from the keypad at any time. When enabled,
remote set point adjustment is available even if the return
temperature is selected to be the Control Temperature.

16 McQuay Catalog 860-9

MicroTech III Unit Controls

Auto/Manual Operation Selection

Automatic or manual operation can be controlled either
remotely or at the keypad.

All controllers include three inputs that can be used to enable
or disable cooling, heating, and fan operation from remote
switches. With the “heat enable” and “cool enable” terminals,
the operator can enable cooling, heating, or both as desired.
Using the system “off” terminals, the operator can disable the
fans, and thus the entire unit.

From the keypad, there are a variety of occupancy and auto!
manual control mode selections available to the operator:

• Occupancy modes
– Auto
– Occupied
– Unoccupied
– Bypass (tenant override)

• Control modes
– Off manual
– Auto
– Heat/cool
– Cool only
– Heat only
– Fan only

Compressor Lead-lag Selection

All unit controllers are capable of automatic compressor, lead­lag control.

Waterside Economizer Changeover

On units equipped with a waterside economizer package, the
MicroTech III unit controller includes an internal changeover
strategy that compares entering cooling tower water
temperature to the unit’s mixed air temperature. If the entering
water temperature is less than the mixed air temperature by a
field-adjustable differential (typically 5°F to 7ºF), the
economizer control valve modulates in response to the cooling
load.

Airside Economizer Changeover Selection

On units equipped with an economizer, there are three methods
of determining whether the outdoor air is suitable for free
cooling: two methods sense enthalpy (dry bulb temperature
and humidity) and one senses outdoor air dry bulb
temperature.

The two enthalpy changeover methods use external, factory
installed controls. One compares the outdoor ambient enthalpy
to a set point; the other is a solid state device that compares the
outdoor ambient enthalpy to the return air enthalpy. This

comparative enthalpy control can improve total economizer
performance.

All unit controls include an internal dry bulb changeover
strategy that can be selected at the keypad. When this method
is selected, the controller compares the outdoor air dry-bulb
temperature to a keypad programmable set point. The external
enthalpy control input is then ignored.

Cooling and Heating Lockout Control

All unit controls include separate keypad programmable set
points for locking out mechanical cooling and heating.
Mechanical cooling is locked out when the outdoor
temperature is below the cooling lockout set point; heating is
locked out when the outdoor temperature is above the heating
lockout set point. This feature can save energy cost by
eliminating unnecessary heating and cooling during warm-up
or cool-down periods or when the outdoor ai r tem perature is
mild.

Night Setback and Setup Control

When one of the zone temperature sensors is connected to the
unit controller, night setback heating and night setup cooling
control are available. Separate, keypad programmable night
heating and cooling set points are used to start the unit when
necessary. After the unit starts, night setback and setup control
is similar to normal occupied control except that the minimum
outside air damper position is set to zero. If the outside air is
suitable for free cooling, it is used during night setup
operation.

Except for 100% outside air applications, night setback control
is available even if the unit is not equipped with any heating
equipment. When the space temperature falls to the night
setback set point, the fans simply start and run until the
temperature rises above the differential. This feature might be
useful for applications that use, for example, duct-mounted
reheat coils.

Morning Warm-up Control

If the Control Temperature (space or return) is below set point
when the unit enters the occupied mode, the morning warm-up
control function will keep the outs
heat is supplied to satisfy set point. The outside air damper will
remain closed until either the space temperature rises to the

heating set point or the keypad adjustable morning warm-up
timer expires (default is 90 minutes). The morning warm-up
timer supplies the minimum required amount of outdoor air
after a certain time regardless of the space temperature.

Morning warm-up control is automatically included on all
except 100% outside air units. It is available even if the unit is

ide air dampers closed while

McQuay Catalog 860-9 17

MicroTech III Unit Controls

Condenser Head Pressure Control (units without
waterside economizer only)

Mechanical cooling is allowed whenever the entering cooling
tower water temperature is 55ºF or warmer, without the use of
head pressure control. When the entering water temperature is
below 55ºF , a factory-installed and factory-controlled two-way
modulating head pressure control valve can be utilized. The
regulating valve is controlled by the MicroTech III controller
to maintain refrigerant head pressure.

Outdoor Air Purge Control (units with airside
economizer only)

Purge control is designed to take advantage of cool early
morning outside air conditions. It starts the fans and modulates
the economizer dampers to maintain occupied cooling
requirements during unoccupied periods, if conditions are
appropriate. This provides the opportunity to flush the space
with fresh outdoor air prior to occupancy. Purge operation is
possible only during a keypad-adjustable time window prior to
occupancy (0 to 240 minutes). When the purge-cycle is active,
mechanical cooling is disabled. To use the purge feature,
connect one of the zone temperature sensors to the unit
controller. Below is a description of purge control operation.

During the purge time window, the unit starts and runs
whenever these three requirements are met:

• The space temperature must be warm enough to enable
occupied cooling.

• The outside air enthalpy must be low enough to enable
the economizer.

• The outside air temperature must be at least 3°F less than
the space temperature.

When any one of these conditions is no longer true, the unit
shuts down. As conditions allow, purge cycles the unit in this
manner until it enters the occupied mode.

Proportional Integral (PI) Control

The Proportional Integral (PI) control algorithm controls
modulating actuators to maintain a measured variable
(temperature or pressure) at or near its set point. For example,
it controls economizer dampers to maintain the discharge
cooling set point and it controls the supply fan variable
frequency drives to maintain the duct static pressure set point.
The integral control feature effectively eliminates
“proportional droop” (load dependent offset) resulting in the
tightest possible control.

For each PI loop, four keypad adjustable parameters allow the
control loop to be properly tuned for any application:

•Period

• Dead band

• Proportional band

• Integral time

Appropriate default values for these parameters are loaded into
each controller. These default values will provide proper
control for most applications; therefore, field tuning is usually
not required and thus start-up time is reduced.

Change Algorithm

The PI function is also used to adjust set points instead of
controlling variable speed drives or actuators directly. For
example, in zone control applications, the PI loop
automatically “changes” the discharge temperature set point
(cooling or heating) as the Control Temperature deviates from
the zone set point. Another PI loop then controls the
economizer actuator or heating valve actuator using the current
discharge temperature set point. Unlike a typical
“mastersubmaster” reset strategy, this “cascade control”
continuously adjusts the discharge set point, even if the
Control Temperature’s deviation from set point remains
constant. This means that the unit’s cooling or heating output
is set according to the actual load, not just the current zone
temperature. The tightest possible zone temperature control
results because “proportional droop” (load dependent offset) is
eliminated.

Calibrate

When initiated at the keypad by an operator, the Calibrate
function automatically calibrates all actuator position feedback
inputs and all pressure transducer inputs. It does this by
shutting the unit down and then driving all actuators to the full
closed and full open positions. The controller records the input
voltage values that correspond to these positions. The pressure
transducer input voltages, which are assumed for 0.00-in.
W.C., are also recorded. When Calibrate is finished, enter an
operator command at the keypad to start the unit.

Field Output Signals

All MicroTech III controls include two solid-state relay
outputs that are available for field connection to any

suitable device: the remote alarm output and the occupied
output. These two outputs are used to signal field equipment of
unit status.

Remote Alarm Output: The remote alarm output can be
used to operate a 24 volt relay to provide a remote alarm
signal to a light, audible alarm,
alarm condition exists at the unit.
Fan Operation Output: The fan operation output is used
to operate a 24 volt relay to control field equipment that
depends on fan operation; for instance, to open field
installed isolation dampers or VAV boxes. To allow actua­tors enough time to stroke, the fan operation output is
energized three minutes before the fans start. It then
remains energized until thirty seconds after the unit air­flow switch senses no airflow. The fan operation output is
on whenever the unit airflow switch senses airflow.
Outside Air Damper output: Use to signal an outside air
damper actuator to open whenever the unit is in an occu­pied cooling or heating condition.

or other device when an

18 McQuay Catalog 860-9

MicroTech III Unit Controls

Standard Control Options

SWP Self-Contained systems are available for most any
constant or variable air volume application. MicroTech III
controls offer three basic control configurations that use
sophisticated state change control logic to provide stable,
reliable and efficient control:

• Variable air volume with discharge temperature control
(DAC)

• Constant air volume with zone temperature control (S
CC)

• Constant air volume with discharge temperature control
(DAC)

When combined with MicroTech III’s many available control
capabilities, both factory-installed and keypad-programmable,
these three basic configurations can be customized to meet the
requirements of the most demanding applications.

Variable Air Volume with Discharge Temperature
Control (DTC)

All VAV units provide true discharge temperature control in
addition to duct static pressure control. Cooling only, cooling
with single-stage “morning warm-up” heat, and cooling with
modulating heat configurations are available.

Control Temperature

The Control Temperature make s the heat/cool changeover
decision. It determines whether cooling or heating is enabled;
the discharge temperature then determines whether cooling or
heating is actually supplied. At the keypad, the operator can
choose the source of the Control Temperature from among the
following selections.

• Space temperature sensor

• Return temperature sensor

• Outside air temperature sensor (modulating heat only)

• Network communication

The operator enters separate cool and heat enable set points
and deadbands that the Control Te mperature is compared with
(see Figure 17). When the Control Temperature is greater than
or equal to the cooling set point plus DB/2, cooling is enabled.
When the Control Temperature is less than or equal to the heat
set point minus DB/2, heating is enabled. If desired, these set
points and differentials can be set so that there is a dead band
in which both cooling and heating are disabled. The
controller’s software prevents simultaneous cooling and
heating.

Figure 17: Control Temper a ture Logi c

Constant Air Volume with Zone Temperature Control
(SCC)

SCC units are available in either cooling only or cooling with
modulating heat configurations. Either of these configurations
is available for 100% recirculated, mixed, or 100% outdoor air
applications.

Constant Air Volume with Discharge Temperature
Control (DTC)

DTC units are available in cooling only, cooling with single­stage “morning warm-up” heat, or cooling with modulating
heat configurations. This unit configuration can be used for
applications that have zone controlled terminal heating coils or
for constant volume, 100% outdoor air applications. The
discharge temperature control strategies used with the hybrid
DTC unit are identical to those used with the DTC unit.

Discharge Temperature Control

MicroTech III VAV-DTC and CAV-DTC controls provide
sophisticated and flexible discharge air temperature control
that is only possible with DDC systems. Separate discharge air
temperature set points are used for cooling and modulating
heating control. At the keypad, the operator can either enter the
desired set points or select separate reset methods and
parameters for each set point.

Proportional Integral Modulation

When operating in economizer free cooling or unit heating, the
previously described PI algorithm maintains discharge
temperature control. It provides precise control of the
economizer dampers, modulating gas heat, steam or hot water
valves.

Compressor Staging

Two staging algorithms are available to control a unit’s
multiple steps of capacity control, Degree-Time (also known
as “average”) and Nearest. These control algorithms provide
reliable discharge temperature control while managing
compressor cycling rates. Constraints on compressor staging
are essential for preventing short cycling, which can reduce
compressor life by causing improper oil return and excessive
heat buildup in the motor windings.

The Degree-Time Compressor staging algorithm keeps track
of the discharge temperature and stages cooling up or down to
maintain an average temperature that is equal to the discharge

McQuay Catalog 860-9 19

MicroTech III Unit Controls

cooling set point. A stage change can occur only (1) after the
keypad adjustable inter-stage timer has expired (f ive minute
default setting) and (2) if the discharge temperature is outside a
keypad programmed dead band. After these two conditions
have been met, staging occurs as the controller attempts to
equalize two running totals: degree-time above set point and
degree-time below set point. The result is that the average
discharge temperature is maintained at the cooling set point.

The Nearest Compressor staging algorithm keeps track of the
discharge temperature and stages cooling up or down to
maintain the discharge temperature as close as possible to set
point. A stage change can occur only (1) after the keypad
adjustable inter-stage timer has expired (five minute default
setting) and (2) if the control logic calculates that a stage
change will result in a discharge temperature closer to set point
than the existing condition. The controller logic continually
calculates the expected effect of a stage change and uses this
information before making a change. A change is made only if
it will bring the discharge temperature closer to set point,
resulting in a more consistent discharge temperature, reduced
compressor cycling and more stable control VAV box control.

Supply Air Reset

By automatically varying the discharge air temperature to suit
a building’s cooling or heating needs, supply air temperature
reset can increase the energy efficiency of VAV and CA V-DTC
systems. MicroTech III controllers offer a variety of different
reset strategies that can be selected at the keypad. Because
they are keypad programmable, reset strategies can be changed
or eliminated as desired. Separate strategies can be selected for
both cooling and modulating heat. If reset is not desired, a
fixed discharge cooling or heating set point can be entered.

The following reset methods are available:

• Space temperature

• Return temperature

• Outdoor air temperature

• Supply airflow (VAV, cooling set point only)

• External 0–10 VDC or 0–20 mA signal

• Network communication

For all temperature reset methods, the mini mum and maximum
cooling and heating set points are keypad programmable along
with the corresponding minimum and maximum space, return
or outdoor air temperature parameters. For the supply airflow
method, the discharge set point will be reset as the supply fan
modulates between 30% adjustable and 100% adjustable. For
the external method, the discharge set point will be reset as the
voltage or current signal varies over its entire range. For units

in a BAS network, the discharge set points are reset via the
communication signal.

Zone Temperature Control

MicroTech III CAV-ZTC controls provide the sophisticated
and flexible zone temperature control that is only possible with
DDC systems. Zone temperature sensors are available with or
without a remote set point adjustment. With the remote
adjustment model, the space set point can be set at the keypad
or at the zone sensor package. Even if a zone sensor is
connected, remote set point adjustment can be enabled or
disabled as desired at the keypad.

Control Temperature

The Control Temperature is the representative zone
temperature. When compared with the zone set points, the
Control Temperature determines whether the unit supplies
heating, cooling, or neither. It also determines the amount of
cooling or heating required to satisfy the load. Its source can
be selected at the keypad from among the following selections:

• Zone temperature sensor

• Return temperature sensor

Because it is the representative zone temperature, the Control
Temperature is the primary input to the MicroTech III zone
temperature control algorithms. Control Temperature
parameters are described below. The controller’s software will
prevent cooling and heating from being inadvertently enabled
at the same time.

Change and Proportional Integral Modulation

When economizer “free” cooling or unit heating is required,
the two MicroTech III PI loops combine for cascade-type
control, providing the tightest possible zone temperature
control. By controlling the discharge temperature along with
the zone temperature, these functions eliminate temperature
variations near the diffusers that could otherwise occur as a
result of traditional zone control’s inherent lag effect.

Change: If the Control Temperatur e is above or below the
set point by more than the dead band, the Change PI loop
periodically adjusts the cooling
temperature set point either up or down as necessary. The
amount of this set point change corresponds to the Control
Temperature’s position in the modulation range. The far­ther the Control Temperature is from the set point, the
greater the discharge set point change will be. The
Change-adjusted discharge cooling and heating set points
are limited to ranges defined by keypad programmable
maximum and minimum values.
PI: Using the Change function’s current discharge set
point, the PI function maintains precise discharge temper-

or heating discharge air

20 McQuay Catalog 860-9

MicroTech III Unit Controls

Compressor Staging

Compressor staging is controlled directly by the Control
Temperature. When the Control Temperature is warmer than
the zone cooling set point, cooling is staged up; when the
Control Temperature is cooler than the zone cooling set point,
cooling is staged down. However, a stage change can only
occur when the Control Temperature is outside the dead band
(see Figure 18). Staging is constrained by an inter-stage delay
timer (five minute default setting) and minimum and
maximum discharge air temperature limits (all keypad
programmable). These constraints protect the compressors
from short cycling while eliminating temperature variations
near the diffusers.

Figure 18: Compressorized Logic

Project Ahead Algorithm

Because the inherent lag effect in zone temperature control
applications can cause overshoot during warm-up or cool­down periods, MicroTech III features a “Project Ahead”
control algorithm. Project Ahead calculates the rate at which
the Control Temperature is changing and reduces the unit’s
cooling or heating output as the zone temperature nears its set
point, essentially eliminating overshoot.

Duct Static Pressure Control

On all VAV-DTC units, duct static pressure control is
maintained by the PI algorithm, which provides precise control
of the supply fan variable speed drive. The keypad
programmable set point can be set between 0.20-in. W.C. and

4.00-in. W.C.
On larger buildings with multiple floors, multiple trunk runs or

large shifts in load due to solar effects (east/west building
orientation), an optional second duct static sensor is offered.
The MicroT ech III controller automatically selects and uses the
lower of the two sensed pressures to control fan volume to
provide adequate static pressure to the most demanding space
at all times.

Operating States

Operating states define the current overall status of the self­contained system. At the user interface, the operator can
display the current operating state and thereby quickly assess
the unit’s operating condition.

Alarm Management and Control

MicroTech III unit controllers are capable of sophisticated
alarm management and controlled response functions. Each
alarm is prioritized, indicated, and responded to with the
appropriate action. The active alarm (up to 10 alarms, arranged
by alarm priority) and previous alarm (up to 25 alarms, arrange
by date/time cleared), each with a time and date stamp, can be
displayed at the user interface. Generally speaking, whenever a
current alarm is cleared, it is logged as a previous alarm and
the oldest previous alarm is removed.

Alarm Priority

The various alarms that can occur are prioritized according to
the severity of the problem. See Table 1. Three alarm
categories are used: faults, problems, and warnings.

1 Faults are the highest priority alarms. If a fault condition

occurs, the complete unit shuts down until the alarm
condition is gone and the fault is manually cleared at the
keypad. A fault example is Fan Fail alarm.

2 Problems are the next lower priority to alarms. If a

problem occurs, the complete unit does not shut down,
but its operation is modified to compensate for the alarm
condition. A problem automatically clears when the
alarm condition that caused it is gone. Compressor Fail is
an example of a problem where only the affected
compressor is shut down.

3 Warnings are the lowest priority alarms. No control

action is taken when a warning occurs; it is indicated to
alert the operator that the alarm condition needs
attention. To make sure that they are read, the operator
must manually clear all warnings. Dirty Filter indication
is an example of a warning.

Generally, a specific alarm condition generates an alarm that
falls into only one of these categories. Under different sets of
circumstances, however, the freezestat and most of the sensor
failure alarm conditions can generate alarms that fall into
multiple categories.

McQuay Catalog 860-9 21