Carrier 48MA User Manual

NumberOne

AirConditbning

Maker

Carrier Parkway • Syracuse, N Y 13201

Packaged Rooftop Multizone Units

DX Cooling/Natural or LP Gas, Electric or Hot Water/Glycol Heat

....

i-x

CONTENTS

INTRODUCTION

PHYSICAL DATA

CONSTRUCTION

General

Electrical -

Refrigeration System

Heating

SYSTEM SELECTION AND OPERATION 7

APPLICATION

Diversity

Limitations

Reheat Applications

Economizer

Economizer and Exhaust Performance

Economizer Economics

Night Setback

MISCELLANEOUS

Sound and Vibration

Thermostat Usage and Control

Return Air Systems

INTRODUCTION

The Carrier 48MA/50ME modular multizone

mmdiffers markedly from the traditional hot deck/ cold deck reheat multizone. Carrier’s packaged rooftop units do not employ the hot deck/cold deck principle or the zoning dampers associated with conventional units.

Page

Carrier’s distinctive design — individual modules

for heating and/or

cooling with

constant module

I

airflow,

is

a

true

innovation

to the

multizone

market.

The

modular

units

heat, cool or de-

2

humidify

in

each

module

simultaneously

and

3

independently

of

all other modules. Modules

can

serve individual

zones or be

grouped

together to

3

serve larger zones.

3

The modular multizones are available in 6 sizes

3

based on cooling capacity.

5

Capacity

No. of

Unit

10

(tons)

Modules

Designation

15

8

48MA/50ME016

10

20

8

48MA/50ME024

25

10

48MA/50ME028

10

28 5

10

48MA/50ME030

11

30

12

48MA/50ME034

11

37

12

48MA/50ME040

14

LP

or

natural

gas,

electric

resistance or

hot

15water/glycol heating options are available to maxi­

16mize efficient use of local energy resources. Econo-

	19	mizers,	power	exhaust,		roll	filters	and
	19 ■;	high-efficiency filters are also available as factory
		installed	options	-	all	providing	a	greater
	20
		flexibility	in applying		the	modular	multizone to
	20
		specific job requirements.

RATING TABLES	30-41
FAN PERFORMANCE	42
Pulley Selection	42
Balancing Dampers	42
Performance Table	43
HEATING PERFORMANCE	46
Electric	46
Gas	46
Hot Water/Glycol	47
ELECTRICAL DATA	48-52
Power Wiring	52

A recent multizone energy study compared the energy usage of the Carrier modular units with 3 competitive designs. The study simulated (by computer) the operation of the units for one year in a typical building in each of 14 major U.S. cities. The cities represented complete coverage of the climatic conditions experienced throughout the country. Study results showed the Carrier multi­ zone consumed less energy than the others in each case considered under all climatic conditions. Details of the energy study are contained in the Carrier brochure, The Modular Multizone Versus the Others.

© Carrier Corporation 1976

Form 50ME-1XA

Table 1 — Physical Data

UNIT 48MA OR SOME				0T6	024		028			030			034	040
	Zone Modules			8	8		10			10			12	12
OPERATING WT (lb)				3385	3805		4075			4080			4800	5700
	Bose Unit 48MA
	Bose Unit SOME (with heat)			2985	3405		3665			3670			4400	5250
	Roof Curb			_506	506		506			506			630	630
REFRIG CHARGE (lb, R-22)				28 "	~~32		43			43			57		"65 “■
COMPRESSOR							Reciprocating Hermetic, 1725 Rpm						06DE537		06EE250
	No. 1 Type			06DE537		06 DE 824		06DE537		06DE537
		Cylinders ... Unloaders		6 2	6 .. 2		6 . 2			6 . . 2			6 . . . 2	4 . . 1
	No. 2 Type					06DA824		06DA824		06DA537			06DA537		06EA250
		Cylinders (has no unloaders)			6		6			6			6	4
	System Oil Charge (pts)				22		22			22			21	31
	Unlaader Settings (psig)					Compressor No. 1 Only
		Left Bank	Loads				71.0 ± 1 5
			Unloads				57.5 ±25
														75.5 ± 1 5
		Right Bank	Loads				76 0 + 1 5
			Unloads				62 5 ± 2.5							58.0 ±25
	Capacity Steps (%)			100,67,33	100,83,67		100,80,60			100,80,60			100,83,67	100,75,
					50,33,17		40,20			40,20			50,33,17	50,25
OUTDOOR AIR FANS								Propeller, Direct Drive
	Mtr Hp ... Rpm ... Frame (NEMA)						1 . 1075			56 (1-phase)
			No. 1
			No. 2				1 ... 1140			56 (3-phase)	I 1		1140 . 56 (3-ph)
			No. 3
INDOOR AIR FANS				2 ... 15x15		2 . 15x15		2 . 15x15		2 . 15x15			3 ... 15x9		3 . 15x9
	No. ... Size (in.)
	Cfm (Norn)			6000		8000		10,000		10,000			12,000		12,000
		Motor Hp ... Rpm Std		5 . . 1725		7/2 ... 1725		10 ... 1725		10 ... 1725			15 ... 1725		15 ... 1725
			Opt	-		-		-		-			20 ... 1725		20 ... 1725
	Fan Pulley			10.6		10.6		8 0		8 0			8 0		8.0
		Outside Diameter (in.)
		Bore (in..)		Р/!б		1 ... 3V630		2 ... 3VS60		P/16			1“/б		1‘Мб
		Fan Belt No. ... Size w/Std Mtr		1 3V630						2 . 3V560			2 3V630		2 ... 3V630
		w/Opt Mtr		-		-		-		-			3 . 3V670		3 . . 3V670
	Motor Pulley A							Factory	Instai led				5 0		5.0
		Outside Diam (in.) w/Std Mtr		5.3		6.0		5 0		'5 0
			w/Opt Mtr	_		-		-		-			6.0		6.0
		Bore (in.)		iVe		1%		1		1%			1%		1%
								%		1095			1095		1095
		Resulting Fan Rpm w/Std Mtr		880		995		1095
			w/Opt Mtr	-		-		-		-			1320		1320
	Motor Pulley B							Shippec		With Unit			5 6	5.6
		Outside Diam (in.) w/Std Mtr		6.0	6 9			5.6		5 6
			w/Opt Mtr	—				-					6.5	6.5
		Resulting Fan Rpm w/Std Mtr		995	1145			1230		1230			1230	1230
			w/Opt Mtr	-				-					1425	1 1425
HEATING SECTION (48MA)						2-Stage Furnace Assembly in Each Zone Module
	Rise Range						25 F to 55 F at 0 75 in. v^g ESP							360-720
		Input (1000 Btuh) Min-Max Total		240-480	240-480		300-600		I	300-600	I		360-720
		Each Module		60	60		60			60			60	60
		Bonnet Cap. (1000 Btuh) Total		360	360		450		I	450	j		540	540
		Stage 1/Stoge 1 ± 2		22.5/45.0	22.5/45.0		22.5/45.0			22.5/45.0			22.5/45.0	22.5/45.0
HEATING SECTION (SOME ELEC)						See Electrical Data Table for Electric Heat Data
	HEATING SECTION (SOME, GLY.)							1 Heating Coil in each Zone Module
	Max allowable inlet temperature							ZOO F
	Max allowable flow, each coil							6 gpm
	Solution mixture							20% glycol
	Max allowable working pressure							30 psig					3 76	3.76
	Total internol volume (gals)			2.61	2.61		3.15		]	3.15	1
	PRESSURE SWITCHES							29 ± 5 psig
,		_	Cutout
	Low-Pressure		r. ^ .					39 ± 5 psig
			Cut-in
	High-Pressure		^ul^n					400 ± 5 psig
								300 ± 5 psig
	Indoor Air Flow Switch (AFS 1)						6000							9000		О
		Factory Setting (cfm)
		Adjustment Range (cfm)			4000-6000								6000-9000
	INDOOR AIR FILTERS
								12 ... 20x25x2
		Std No. ... Size (in.)
	High Efficiency (optional)					Same but with 36.5% efficiency (NBS Dust Spot Test)
		No. ... Size (in.)
								65 ft of 2-in. media
		Roll Media (optionol)

CONSTRUCTION

General — Carrier Modular multizones are sturdy and lightweight. The units are ideal for rooftop applications where low silhouettes are required.

^|p Maximum height of any 48MA/50ME unit mounted on a matching roof curb is less than 5 feet. Each unit is of one-piece design with extruded aluminum frame and 26 ga steel top and side panel construction. Panels are easily removed for access to unit interior. Assembled, the insulated unit will not sweat at 77 E wet-bulb on cooling days. The unit insulation conserves heat energy in the winter, keeping energy costs to a minimum.

The unit roof curb, constructed of 14 ga galvanized steel, is National Roofing Con­ tractors Association (NRCA) approved. A condenser run-off sheet is built into the curb and is insulated to prevent heat transfer. The curb is designed to be flashed to the roof and includes wood nailers to aid installation. All duct and utility connections are inside the curb perimeter.

Service access on side panels is accomplished by removing latches on each side of panel. The side panel gaskets provide complete perimeter sealing when compressed against the base unit frame. Each 48MA/50ME unit has large, waterproof condensate pans to prevent moisture leakage into the con­ ditioned space. Galvanneal steel panel surfaces are bonderized and finished with Carrier Weather Armor, a baked enamel finish.

Enters are 2-in. throwaway fiberglass with an NBS efficiency of 10%. High efficiency (36.5% NBS) throwaway filters are available as a factoryinstalled option. With 41.5 square feet of zone filter area standard, both the lowand highefficiency filters are extremely effective. With this large area, filter velocity is low — 335 fpm in the 48MA/50ME040 and 145 fpm in the 48MA/ 50ME016. A roll filter package is available as a factory-installed option.

The package consists of 65 ft of 2-in. filter media, automatic media advance switch, advance motor and a runout switch. Outside air is drawn into the unit thru louvered side panels and pre­ filtered by cleanable outdoor air filters in the panels.

Electrical — The Carrier Modular multizones include factory-installed power and control circuit breakers which are suitable for use as disconnect switches where local codes permit. A 350-va, 115-volt convenience outlet on the main control panel allows use of a trouble light or small power tools.

Etched solid copper circuit panels with inter­ changeable plug-in relays and marked terminal boards are used in all units to improve reliability and simplify the modular design. Conventional commercial 24-volt, 2-stage heat/2-stage cool

thermostats are	readily	wired	to marked terminals
on the zone	control	board.	Modules combined to

make a single, large zone are controlled by a single

thermostat	by	wiring	the	zone	module	control
terminals	as	illustrated	in	thermostat	usage	section
using factory-supplied jumpers.

Refrigeration System — The modular multizone units incorporate individual zone evaporator coils plus an outdoor air (Humidry®) evaporator coil (see Eig. 1). The zone coils are controlled by room thermostats thru a liquid line solenoid valve. The metering device for the zone evaporators is a capillary tube.

The outdoor air evaporator coil cools and dehumidifies the outside air drawn into the unit. This coil is a “free floating” coil; that is, after the first zone cooling coil is activated by cooling demand, the outdoor air coil is controlled by suction pressure only. Since the outdoor air evap­ orator coil handles a varying load, a thermal expansion valve is used to meter the correct amount of liquid refrigerant to this coil.

The load on unit compressors varies depending on outdoor air coil load and the number of zone coils in operation simultaneously. Compressor unloaders and hot gas bypass valves are employed to compensate for the variation. The 15-ton unit unloads to 1/3 or 5 tons, the 20-ton unit to 1/6 or 3.3 tons, the 25-ton unit to 1/5 or 5 tons, the 28-ton unit to 1/6 or 4.7 tons, the 30-ton unit to 1/6 or 5 tons, and the 37-ton unit to 1/4 or 9.3 tons. The unloaders operate from suction pressure to maintain system suction temperature between 32 and 45 E. If the load is less than the minimum step indicated above, a hot gas bypass valve meters hot gas into the outdoor air coil to provide an additional load to the system. This keeps the compressor on the line and prevents the coils from icing up due to low suction temperature.

Since the outdoor air coil would become a condenser when the ambient temperature is below the suction temperature, a thermostat closes the outdoor air damper if the ambient drops below 32 E and compressors are operating. If there is no airflow across the outdoor coil, there is no heat transfer and the coil becomes an extension of the refrigerant piping.

Head pressure is maintained by cycling one or 2 condenser fans with a condensing pressure switch and modulating the remaining fan with a Motormaster® solid state speed controller, permitting operation of the refrigerant system to -20

ambient. The Carrier modular design is not de­ pendent on an economizer cycle for cooling at low outdoor temperatures. (A factory-installed econo­ mizer option is available.)

All multizone units function satisfactorily in the full cooling or full heating mode. However, at

Fig. 1 — Refrigerant Piping Schematic (10-Zone Units Shown, 8- and 12-Zone Units Similar)

partial load operation, difficulties arise in conven­ tional hot deck/cold deck units. When some zones are at full heat, some at partial heat, some at partial cooling, conventional multizones must operate the hot and cold decks simultaneously at high energy cost. The Carrier Modular design satisfies each zone’s demand by a discrete module(s). There are no hot decks, cold decks or zone air mixing dampers to waste energy. The only energy expended is that required to heat or cool the individual zone. Since there is no mixing, energy is saved and operating costs are significantly lowered. In addition, the control system provides excellent humidity and temperature control. Multi­ stage cooling is available on larger zones where 2 or more modules are used for efficient control of zone space requirements.

The following features and safety devices are provided on the refrigerant cycle:

1.Suction line accumulator

2.Crankcase heaters

3.Highand low-pressure switches

4.Discharge line thermostat

5.Time Guard® circuit

6.Airflow switch for indoor fan motor

7.Internal motor protection thermostats em­ bedded in compressor motor windings

8.Hot gas bypass capability

9.Compressor unloading capability

10. Filter-driers

PSYCHROMETRICS ^ The 48MA/50ME units differ psychrometrically from the conventional multizones due to the operation of the outdoor air coil. The coil in the Carrier units cools and dehumidifies the outdoor air entering the unit thus assuring that raw outdoor air is not passed along to the zones. This air treatment by the outdoor air coil (and also by the zone module evaporator coils) provides excellent low load performance and precise temperature control to the conditioned space. The only large load variation occurs on the outdoor air coil where a thermal expansion valve is used. This allows the use of simple capillary tube expansion devices on the zone coils. The zone coils cool and dehumidify a mixture of return air and outdoor air — outdoor air at the approximate dew point temperature of the return air.

The psychrometric chart (Figure 2) illustrates this air treatment for a typical set of conditions. As an example: 1000 cfm of outdoor air at 95 F/75 F having 99 grains moisture content enters the outdoor air coil and is cooled and treated so that the air leaving the coil has 68 grains of moisture content. The outdoor air coil under these con­ ditions has a capacity of 60,000 Btuh of which 39,000 Btuh is sensible. This is a coil sensible heat factor of 0.65. By examining the room conditions, it is evident that the outdoor air coil is very effective in removing the latent load. At 75 F/50%, the room content is 64 grains of moisture. The percent moisture removed with respect to room conditions is:

% removed	99 - 68	100	=	88.5%
	99 - 64

The 1000 cfm of outdoor air at 68 grains is mixed with 8000 cfm of return air at 75 F/50% room conditions (64 grains). This mixture then enters the zone modules and is cooled and dehumidified by the zone coil.

Heating (General) — The 48MA/50ME modular multizone units offer a wide range of factoryinstalled heating options.

In all cases, the modular design provides a number of small heating steps to maintain very close discharge temperature control without wide variation. Conventional multizones cycle a few large increments to maintain the necessary hot deck temperatures and, thus, cannot control dis­ charge temperature as well as the modular units.

Another feature of the modular design is the reduced impact of heater malfunction. Any unit can have a malfunction — such as an open coil in a relay or contactor or gas valve failure in a gas-fired unit. The Carrier 48MA/50ME units, with 8, 10 or 12 independent heating sections, would experience heat failure in one module only and all others would operate normally. Conventional multizones could lose a large percentage of heating capacity or the entire heat source in the hot deck could become inactive.

GRAINS OF MOISTURE/

LBS OF DRY AIR

The Carrier modular multizone units are de­ signed to provide reliability, serviceability, oper­ ating economy and comfort control — features difficult to match with conventional hot deck/cold deck reheat multizone units.

GAS HEATING SYSTEM (48MA) Each module has a 2-stage burner, with one pilot per pair of modules. The first-stage gas valve (115-v) controls gas flow to the main orifice and to the second-stage valve. A 24-v solenoid valve provides gas to the second stage when open (see Eig. 3). Both heating stages are contained in one valve body.

The gas heating section has standing pilots and continuous forced draft combustion. The pilots have automatic spark relight for dependable ignition.

The 48MA modular multizone has individual 18 ga Chromized steel heat exchangers and stainless steel main burners in each module.

Safety features on the heating system include:

1.A.G.A. certification of the entire unit design as ' well as the furnace section.

2.Airflow switch for indoor fan motor.

3.Airflow switch for forced draft fan motors.

4.Door switch for combustion compartment.

5.Pilot switch to ensure a pilot flame

GV - Gas Vaive (Zone Module)	MGV
MS ~ Main Burner	PS -

MOTSS:

tPirst stage of gas valve is a 115-vott sok-noid; second stage is a 24-voit soienoid with .60% gas bvpess.

Gnits 48MA034 ano 040 fi ave one pilot shotoff valve feeding all pilot burners.

Unit is eouipped with a forced-draft blower and: the foiiowing

- Main Gas Vaive	PV ~ Pilot Valve (shutoff;
Pilot Sorrier

safety devices: forced-draft airfiow switcfi, tiame rcll-oot pro­ tection switch, combustion dtarnbet access door switch, heating lirrtt switches, and soark-ignitecl automatic pilots. Al! of these switches are iccateci in the heating section and rrtust. be in safe condition before tfie inain burners can ignite.

Fig. 3 — Gas Piping Schematic (10-Zone 48MA Unit Shown, 8- and 12-Zone Units Similar)

6.Heating limit switches.

7.Flame rollout protection switch.

In special applications where natural gas supply is limited, units must be modified to operate under derated input/output conditions. The 48MA modu­ lar multizones can be derated by changing the zone module burner spuds and gas valve orifices as follows:

NATURAL GAS FIRED UNITS

T O T A L M O D U L E

D E R A T E D I N P U T ( % ) H i g h F i r e / L o w F i r e

90/45

80/40

70/35

S P U D S I Z E

No 36

No 38

No 41

No 43

G A S V A L V E O R I F I C E S I Z E

No 36

No. 38

No. 41

No 43

(on 2-stage units) and third step of heating is controlled by the outside air thermostat (OAT.) and operates simultaneously with the second stage of the thermostat (on 3-stage units) when the outside air temperatures are below OAT. setpoint. The setpoint on the outside air thermostat is adjustable from 0 to 55 F.

Safety features include:

1.UL certification on entire unit, as well as electric heat section

2.Manual reset circuit breakers

3.Klixon high-temperature protection

4.Airflow safety for indoor fan motor

5.Fusible links in each heater phase

6.Two-pole contactors on each element

Under these conditions, the units still have 2 stages of derated heat input. Derating below these limits is not approved. If single-stage heat is acceptable, disconnect high fire stage to permit each module low fire input only (% as shown under low fire).

Contact Carrier Service Department before de­

rating to the above limits.
ELECTRIC HEATING SYSTEM (SOME) - The
SOME electric heating system contains single-phase
Nichrome wire coils (see Fig. 4), wired and phase
balanced to provide 2 or 3 steps of heat control.
Each zone has 2 or 3 steps of strip heat available,
controlled simultaneously by the zone thermostat
and the outdoor air thermostat. When heat is
required, the first stage of zone thermostat ener­
gizes the first step of zone heating. The second step
(on 3-step units) of heating is controlled by the
second stage of the zone thermostat. The second	Fig. 4 — Electric Heating Unit (50ME)

нот WATER/GLYCOL HEATING SYSTEM -

Hot water is a frequent selection for heating due to simplicity of the piping system, the ease in maintaining uniform temperature control and quieter operation. In addition, when renovating an existing building, a hot water heating plant is usually available.

Carrier’s hot water/glycol heating option (Fig. 5) is ideally suited for these renovations. Each zone module has its own high capacity heating coil. All controls, solenoid operated shutoff valve and balancing valves are included in the option. There is no internal piping or wiring; only one connection is required for supply and return hot water/glycol. The option does not include internal pressure relief for partial load operation. External piping to the unit must be in accordance with existing codes. It must include proper relief for water flow (the maximum allowable hot water/glycol system work­ ing pressure is 30 psi.) or a modulating control to compensate for decrease in water flow rate to zone coils under partial load conditions when some coils are cycled closed. System heater coils are designed for operation with a water/glycol solution of 20% minimum glycol for proper freeze-up protection. Figure 35 located in the Heating Capacity Section, page 47 portrays an example of selecting and rating hot water/glycol heating coils for use with SOME multizone units.

The hot water/glycol option is not intended for use on a steam system. Where steam is the only heating medium available, a steam-to-water con­ verter or a steam-to-water interchanger should be used.

Fig. 5 — Hot Water/Glycol Heating (50ME)

SYSTEM SELECTION AND OPERATION

To better understand the actual operation of the modular multizone, a typical design example is provided.

Refer to Carrier’s Engineering Guide for Multi­ zone Unit Systems and contents of this booklet for

typical multizone design considerations. Using the Engineering Guide, calculate cooling and heating load estimates for the areas to be served by the multizone unit. Divide each area into zones based on the peak load and control requirements within the area.

The resulting loads in a typical building have been calculated as follows:

Cooling
Grand Total Load (GTE)	.................... 275,000 Btuh
Sensible Load (SL) ..............................	215,000 Btuh
Room Design....................................	75 F db/50% Rh
Outdoor Air (OA) Cfm .......................................	1000

OA Ambient Temperature . . . . 95 F db/75 F wb

Electric Power Source ................................. 460/3/60

у XT	Room Total Load* Room Sensible Load
zone JNo.	(RTL)/Zone			(RSL)/Zone
1	19,000		Btuh	16,935Btuh
2	25,000		Btuh	22,505Btuh
3	25,000		Btuh	22,505Btuh
4	70,000		Btuh	59,160Btuh
5	22,000		Btuh	19,720Btuh
6	25,000		Btuh	22,505Btuh
7	40,000		Btuh	33,870Btuh
Total		226,000 Btuh		197,200Btuh

*Loads are peak loads.

Heating (Electric Resistance Heat required)

Zone No	Heating Load/Zone		Electric Resistance/Zone
1	34,000	Btuh	10.0 kw
2	44,000	Btuh	12.9 kw
3	44,000	Btuh	12 9kw
4	111,000	Btuh	32.5 kw
5	42,000	Btuh	12.3 kw
6	44,000	Btuh	12 9kw
7	81,000 Btuh		23 7 kw
Total*	400,000	Btuh	117 2 kw

*Zone Peak Capacities.

Selection:

Due to the many heating options and ranges on each 48MA/50ME unit, multizone unit selection is normally based on cooling load requirements. Enter the 48MA/50ME rating tables in the Per­ formance Data Section and select the unit that meets or exceeds the grand total load at the specified conditions. (Interpolation may be neces­ sary to obtain unit rating at certain conditions; extrapolations are not advised. Contact Carrier Engineering for performance data at points beyond the range of published tables.) The 024 size unit does not have sufficient capacity to meet load requirements at any cfm. The 028 size exceeds load requirements; however, it is the smallest unit that meets specifications. Thus, the 48MA/“' 50ME028 at: 9000 cfm; 1000 cfm OA; 95 F/75 OA temperature; and 75 F/50% Rh room design has a TC of 282,000 Btuh, SHC of 219,000 Btuh, compressor kw of 27.5 and a RSHF of .835. Calculate the RTC and the RSHC by deducting the outdoor air load from the unit capacity.

The outdoor air load with respect to room condias follows:

outdoor ail

total heat (OATH) = 4 5 (hgg:,- Ьго,ошХ (OA cfm)

=4.5 (38.61 - 28.29) (1000)

=46,440 Btuh

Or, a graph, shown 'in Fig. 6, can be used to find the OA load factor, 4.5 (hoa “ hfoom). for all conditions illustrated in the 48MA/50ME rating

<

О

2

u.

\0

1

z>

H

Ш

Q

<

о

<

I-

o

h-

Ш

a

CO

I-

Э

о

tables (Performance Rating Section). Thus,

OATH = (OA load factor) (OA cfm)

=(46.5) (1000)

=46,500 Btuh

which agrees with the above calculation.

Outdoor air

sensible heat (OASH) = 1.09 (toa ■" boom) (OA cfm)

=1.09(95 - 75) (1000)

=21,800 Btuh

OA WET BULB

Fig. 6 — Outdoor Air Load Selection Chart

8

The unit capacity available to offset room loads is.

Room TC = Unit TC — outdoor air TC

=282,000 -46,500

=235,500 Btuh

Room SHC = Unit SHC — outdoor air sensible heat

=219,000 -21,800

=197,200 Btuh

For comparison:

	Load			Unit Capacity
GTL	275.000	Btuh	TC	=	282,000	Btuh
SL	215.000	Btuh	SHC	=	219,000	Btuh
RTL	226.000	Btuh	RTC	=	235,500	Btuh
RSL	197,200 Btuh		RSHC = 197,200 Btuh

The 48MA/50ME size meets or exceeds the total and zone load requirements at the specified conditions. The excess RTC decreases space average relative humidity slightly below the room design of 50%. By increasing air quantity above 9000 cfm, this excess latent capacity can be converted to additional sensible capacity if desired.

Since the modular multizone is a constant volume machine, the selected supply cfm per zone must be proportioned to satisfy each zone’s peak load condition.

Room sensible capacities (RSC) are divided equally among the modules if an equal cfm is going to each. In this example, the 48MA/50ME028 has 10 modules and the nominal cfm is 900 cfm per module.

The cfm to each zone can be varied (with field-supplied manual dampers in zone ducts) to match different zone requirements, but since the original rating was based on 9000 cfm supply air, all variations must total 9000 cfm. The effects of changing cfm quantities on room TC and room SHC in each module are shown in Fig. 7. When the cfm is changed (by some percent) from the nominal in a specific module, then the room capacity multipliers in Fig. 7 are used to correct room TC and room SHC. Capacity versus cfm changes for the example is given in Table 2.

By analyzing each zone’s ratio of deviation from equal sensible heat allocation, the proper cfm change is determined. In the example, if building room SHC is 197,200 Btuh and 10 zones are used, each zone’s normal room SHC is 19,720 Btuh. But

if zone 3 has 22.505 Btuh room SHC, then by ratio of 22,505 : 19,720 or 1.14, the cfm change is +20% (see Fig. 7). Correspondingly, if zone 1 had 16,935 Btuh room SHC, the cfm change is -20%.

In applications where the zone selection is not an increment of the number of unit modules (i.e. one zone requiring 500 cfm in a 48MA/50ME028 with 10,000 cfm), refer to Module Cfm Limits, page 10, for details on using cfm’s below 600 cfm/module.

Formulas required to use ratings are:

Outdoor Air Total Heat (OATH)

OATH = 4.5 (OA cfm) (hoa-hioom)

Outdoor Air Sensible Heat (OASH)

OASH = 1.09 (OA cfm) (toa ~ troom)

Room Total Capacity (RTC)

RTC = Unit TC-OATH

Room Sensible Heat Capacity (RSHC)

RSHC = Unit SHC - OASH

Room Sensible Heat Factor (RSHF)

portp _ RSHC

Leaving Air Temperature (LAT)

LAT = room temperature RSHC

1.09 cfm

Determine Heating Capacity:

The specified requirement for electric heat dictates the selection of a 50ME028 unit with a kw option that meets or exceeds the heating load.

Table 9, page 50 indicates that the 028 unit has heating capacity options of 66, 88 and 132 kw. The 132 kw option is selected as it provides adequate heat for this application. The kw/zone and number of heat stages available are:

	Zone No.		Load	Zone Heating	Stages
				Capacity	of Heat
		1	10.0 kw	13.2 kw	3
	2		12.9 kw	13.2 kw	3
	3		12.9 kw	13.2 kw	3
	4		32.5 kw	39.6 kw	9
	5		12.3 kw	13 2 kw	3
	6		12.9 kw	31.2 kw	3
	7		23.7 kw	26 4 kw	6
		Total	117.2 kw	132.0 kw	30

Stages of heat are controlled individually in the small zones or collectively in large zones to provide flexible and continuous control for each zone.

Table 2 — Capacity vs Cfm Changes

	ZONE	NO. OF	RSL/ZONE	% DEVIATION	% CFM CHANGE		UNIT TOTAL		UNIT	ADJUSTED
						CFM	CAPACITY	X	NOMINAL
	NO.	MODULES	PEAK LOAD	(RSL/NOM UNIT RSHC)	FROM NOMINAL					UNIT RTC
							MULTIPLIER*		RTC/ZONE
	1	1	16,935	16,935/19,720 = 86	-20	720	9	X	23,550	21,195
	2	1	22,505	22,505/19,720 =1.14	+20	1080	1 1	X	23,550	25,905
	3	1	22,505	22,505/19,720 =1.14	+20	1080	1 1	X	23,550	25,905
	4	3	59,160	59,160/3 X 19,720 = 1.00	0	2700	1 0	X	3 X 23,550	70,650
	5	1	19,720	19,720/19,720 =1.00	0	900	1.0	X	23,550	23,550
	6	1	22,505	22,505/19,720 =1.14	+20	1080	1.1	X	23,550	25,905
	7	2	33,870	33,870/2 x19,720 = .86	-20	1440	.9	X	2 X 23,550	42,390
		10	197,200			9000				235,500
	*Unit total capacity multiplier is obtained from Fig. 7. Use % change from nominal and read multiplier from graph.
	RSHC — Room Sensible Heat Capacity			RSL — Room Sensible Load		RTC — Room Total Capacity

a:

LJ

II

a

z>

2

2 O O

I 0
95
90
85	<
	a.
	<
80
75

•% CFM CHANGE ■ FROM NOMINAL

Fig. 7 — 48MA/50ME Room Capacity Multipliers

Power Wiring Data — The 50ME028, 460-3-60 unit with 132 kw of electric resistance heat, has a 75.8 cooling circuit minimum wire ampere and a heating circuit minimum wire ampere of 207.0. If any module is operating on mechanical cooling (com­ pressor operating), one heating stage in each module is locked out and cannot be energized. This, a common feeder can be sized for minimum wire ampere of 221 (see Fig. 37).

APPLICATION

Diversity — The size, shape and orientation of the building — as well as the application and location of zones, influence the degree of diversity that may be applied to a multizone system.

Since the normal application of multizone units involves zones where loads are shifting due to solar energy, people, equipment and lights, diversity will exist.

The Carrier modular multizones will be affected by building diversity only on the refrigeration system. When a particular zone (or zones) thermo­ stats are satisfied, a solenoid shuts off the zone evaporator coil. This enables more refrigerant to flow to other operating zone coils, creating a larger capacity for that zone. However, the diversity will lower the selected unit total capacities.

The 48MA/50ME ratings do not reflect diver­ sity but can be converted to diversity ratings by using the capacity correction factors and formulas in Table 3.

Table 3 — Capacity Correction Factor (CCF)

LOAD		DIVERSITY FACTOR
	1.0		90		.80
TC (Unit)	1 0		97		94
SHC (Unit)	1 0		94		89

[TC (CCF) - OATH]

RTC (with diversity)

(Diversity Factor)

[SHC (CCF) - OASH]

RSHC (with diversity)

Diversity Factor

This is accomplished by rating the unit assum­ ing that no more than 9 of 10 zones would be on at one time, 90% diversity. The same logic applies to other diversity factors on an average basis, such as 85 or 95%.

A rating with a diversity factor results in a lower room SHF; therefore, a reselection at a higher total unit cfm is advisable to take full advantage of the building diversity.

Limitations

MODULE CFM LIMITS AND FAN PER­ FORMANCE — The cfm limits per zone are 1200 cfm maximum and 600 cfm minimum. The

1 0

outboard zones in the 8-, 10and 12-module units are limited to a maximum of 1000 cfm. The maximum limit is necessary to prevent blow-off to the heat exchangers and into the ductwork. The minimum limit prevents burner cycling on limit switches and prevents electric heater cycling. At reduced cfm’s, zone evaporator coils overfeed refrigerant, but there is no liquid flood-back to the compressor as it is protected by a suction line accumulator.

For applications below 600 cfm, it is recom­ mended that the heating controls be modified as follows:

Gas fired (300 to 599 cfm) — Use first-stage heat only, deactivate second stage.

Electric Resistance (450 to 599 cfm) — Use firstand second-stage heat on 3-stage units.

Electric Resistance (300 to 449 cfm) — Use first-stage heat on 2- or 3-stage heat units.

Optimum performance is delivered in the 800 to 1000 cfm range. Extremely low cfm requirements reduce unit cooling capacity. Low zone cfm applications may also be handled by sizing the zone for a higher cfm (to increase unit efficiency) and diverting the extra air into the return air system or a larger interior space. Extra air should not be diverted into spaces with different perimeter wall orientations.

Fan performance data. Table 4 and Fig. 32, 33 and 34, (Fan Curves) are located in the Fan Performance Section and are based on 15% out­ door air. When the outdoor air dampers are closed and there is no outdoor ventilation air into the unit, unit cfm is reduced by 2 to 6%. This reduction is due to the static pressure drops existing in the separate airflows thru the unit. This reduction should be considered in special applica­ tions where little or no ventilation is required and cfm requirements are critically designed.

MAXIMUM VENTILATION LIMITS Under normal mechanical cooling, the amount of ventila­ tion air that can be introduced is a function of the outdoor air damper setting and negative static

pressure at the return air intake of the unit. Figures 8 thru 11 show ventilation air versus negative static pressure at various settings of the outdoor air damper. A 5.5 setting of the ventilation control dial is the maximum opening of the dampers. The ventilation dial can be set in any position from 0 to 5.5 to obtain the desired cfm of outdoor air. The ventilation dial is located on the control panel adjacent to the heating section.

Reheat Applications — A space with a high latent load and a very low sensible load may require reheat capability for dehumidification. Typical spaces of this type are conference rooms or visual aids rooms where people congregate with the lights out.

Reheat control is achieved on the 48MA/50ME unit by wiring a humidistat (Fig. 12) in parallel with the cooling thermostat on any zone requiring reheat capability. This may be done on one module or all modules. When using reheat control on electric resistance heat units, extreme care must be exercised with power wiring as heating and cooling can operate simultaneously in each module.

When the zone’s humidity level reaches the setpoint of the humidistat, mechanical refrigera­ tion is activated for that zone module and the air is dehumidified and then reheated on thermostat demand before being discharged to the zoned space.

The 48MA/50ME Economizer — The 48MA/50ME units can be equipped with an economizer control. The control functions as follows: with ambient temperatures above the economizer changeover point, the outdoor air damper is set at the ventilation position, cooling is accomplished by the compressors when the room thermostat calls for cooling. If the zone is not calling for cooling, the mixed air is circulated thru the space. When the ambient temperature drops below the economizer changeover point, the compressors are locked out and the damper motor is under control of a mixed air thermostat to maintain a mixed air temperature low enough to provide cooling when the room thermostat demands it. (See Fig. 13.)

1 1

3,000

100 I	15	2	25 3	.4	5 .6 7 8 9 10
	NEGATIVE STATIC PRESSURE AT UNIT RETURN

Fig. 8 — Ventilation Air Chart,

48MA/50ME016

Fig. 10 — Ventilation Air Chart,

48MA/50ME028,030

Fig. 9 — Ventilation Air Chart,

48MA/50ME024

Fig. 11 — Ventilation Air Chart,

48MA/50ME034,040

1 2

If a zone	thermostat calls for cooling while in	Г	~l	LI
economizer mode, a set of cooling relay (CR)
contacts close, energizing the economizer relay
(ECR). See Fig. 14. The ECR is a DPDT plug-in
relay. For economizer damper control, the ECR
locks out the outside air damper adjustable poten­
tiometer and shifts the damper control to a Mixed
Air Thermostat (MAT.). The MAT. sensor, located
in the fan section, adjusts the outside air damper to
maintain a	preset mixed air temperature (see
Fig. 15).

The 48MA/50ME economizer operation pro­ vides economic use of outdoor air for low-cost cooling. When all zone cooling thermostats are satisfied, economizer controls are bypassed and the outdoor dampers are modulated to the minimum ventilation position. The mixed air temperature increases, minimizing the amount of reheat re­ quired in other zones that require heating.

LEGEND

Refer to Economizer Economics, page 15 to determine if the addition of an economizer is justified.

SEQUENCE;

HA — Heat Anticipator	S)	Screw Terminal
Hu - H umidistat	-------	Printed Circuit
TC — Thermostat, Cooling	-------------------	Factory Control Wires
TH — Thermostat, Heating	----------------------	Field Wiring

Fig. 12 — Humidistat Connections

1 — Ambient temperature decreases

2 — Compressor is locked out by economizer control thermostat 3 — Outside air damper is regulated by mixed air thermostat

to maintain fixed mixed air temperature

Fig. 13 — Economizer Operation

LEGEND

C — Compressor Contactor

CCP — Capacity Control Pressurestat

CHR — Crankcase Heater Relay

CR — Cooling Relay

DLT — Discharge Line Thermostat

ECR — Economizer Relay

ECT — Economizer Thermostat

EXC — Exhaust Motor Contactor

EXR — Exhaust Relay

FCPS — Ean Cycling Pressurestat

HPS — High Pressure Switch

HR — Holding Relay

IT — Internal Thermostat

LPS — Low-Pressure Switch

MCR — Master Cooling Relay

MHR — Master Heating Relay

OFC — Outdoor Fan Contactor

TM - Ti mer Motor

Fig. 14 — Economizer Condensing Schematic

13

OA DAMPER ADJUST

MIXED AIR THERMOSTAT

MOTOR POT

LEGEND

CHR — Crankcase Heater Relay

ECR — Economizer Relay

LAT — Low Ambient Thermostat

OA — Outside Air

Fig. 15 — Economizer Damper Control Schematic

less, the outdoor air damper begins to close, and return air damper begins to open (see Fig. 13). As this happens, total supply cfm progressively increases from 8500 cfm to 10,000 cfm (design).

An exhaust damper option is also available for use with the economizer. It is located between the return air plenum and the condenser fans. The option consists of a TPDT plug-in relay (EXR), an exhaust damper, and a plug-in jumper. The damper provides a forced exhaust of indoor air during the economizer operation. The exhaust damper opens when the return air damper is 25% closed. With the damper installed, ECR and EXR are energized simultaneously. The EXR locks out outdoor fan motor (OFM) controls (32LT on OFMl and FCPS on OFM2 and OFM3) and outdoor (condensing) fan motors operate at full speed, discharging excess return air to the atmosphere thru the open exhaust damper (see Fig. 16).

Economizer And Exhaust Performance — An economizer can be readily factory installed on the 48MA/50ME since the damper motor and outdoor air damper are standard equipment. The econo­ mizer package consists of a return air damper, linkage, plug-in relays, MAT. wiring, and mixed air thermostat.

When the 48MA/50ME unit is on full econo­ mizer control, the supply cfm to the space drops off slightly since the resistance of the outdoor air intake is generally greater than that of the return air ductwork. To partially offset this, the return air dampers have a built-in bypass.

With the outdoor air dampers fully open and the return air dampers fully closed, the total cfm drops 15%. The total cfm consists of 70% outdoor air and 30% return air thru the built-in bypass. If, for example, the unit normally operates at 10,000 cfm supply air, the minimum supply cfm when the economizer is operational is 8500. This 8500 cfm consists of 6000 cfm outdoor air and 2500 cfm return air. As the ambient temperature drops from 48 F (recommended economizer setpoint), the proportion of outdoor air to the supply air required to maintain mixed air temperature is

The 48MA/50ME exhaust operation is similar in performance to a relief damper except that the exhaust dampers are mechanically linked to the return air dampers and the condenser fans operate to produce a pressure differential which aids the exhaust cycle. At approximately 0 in. wg at the return air opening, the 48MA/50ME units exhaust between 150 to 200 cfm/ton. With positive return static, more air is exhausted. At -0.40 in. wg (.25 in. wg on the 016 unit) return air static, exhaust capabilities of the units drop to zero.

In the example, the 4000 cfm exhausted at 0 in. return static accounts for all but 1100 cfm outdoor air introduced by the economizer outside air section. In practice, this excess cfm is con­ sidered a nominal ventilation rate, slightly pres­ surizing a building to eliminate drafts and unwanted air seepage. This excess air filters out of the building thru doors and window spaces. The ^slight positive pressurization of the building aids the exhaust fans in removing air. If, however, the balance between the building static and exhaust system leaves the building with unacceptably high positive static pressures, a relief ventilator or roof power exhauster may be used. For extensive or

SEQUENCE:

1 — Return damper closes 25%.

2— The exhaust damper opens

3— The OFM (condensing fans) speed controls are bypassed and

fans run full speed, exhausting return air to atmosphere

Fig. 16 — Exhaust Damper Operation

14

complicated return air duct systems with static pressure greater than -0.2 in. wg at the return air plenum, duct mounted return air exhaust fans can be installed for proper airflow. However, return air exhaust fans add to the operating cost and increase

mnoise level. More efficient duct design methods should be investigated to eliminate the need for special return air exhaust fans.

Economizer Economics — Economizer control on a multizone unit does not necessarily reduce operating cost as it would on a single zone unit. A single zone unit either heats or cools; a multizone unit can do both simultaneously. Therefore, in a multizone, the economizer operates to maintain a mixed air temperature low enough to cool a zone with a high internal load. The remaining zones requiring less cooling or heating must have heat added to offset cooling capacity available but not needed. This is true of any multizone with any type of control system.

The amount of heat required to neutralize the overcooling capacity is dependent on:

1.The percent cooling capacity required from the unit, and

2.The mixed air temperature required to satisfy the zone with the highest internal load.

As the ambient temperature drops, the percent of outdoor air needed to maintain a mixed air temperature is less. Since the reheat or wasted heat added is a function of the difference between outdoor air introduced and ventilation rate, operating cost is reduced at lower ambients. A high ventilation rate also reduces the reheat requirement and associated cost. The following example illus­ trates the need for a careful analysis of job requirements before arbitrarily selecting on econo­ mizer control.

Example:

A 48MA/50ME unit is operating with econo­ mizer control and supplying 10,000 cfm of 55 F mixed air. The normal ventilation rate is 2000 cfm. Assuming a realistic cooling load of 50%, 5000 cfm of the 55 F air is used for cooling. Since the ventilation rate is 2000 cfm, half is sent to the cooling zones leaving 4000 cfm of low-cost cool­ ing. The remaining 5000 cfm of 55 F air, including 1000 cfm of ventilation air, is going to zones with either no load or a heating load and must be neutralized.

Although 4000 cfm or low-cost cooling is ob­ tained, an extra 4000 cfm of air must be heated to some degree above and beyond that in a unit without economizer controls.

For an identical unit without economizer con­ trol, only 4000 cfm of the 5000 cfm needed for cooling requires mechanical cooling, since the 1000 cfm of ventilation air is already cooled. Of the other 5000 cfm, 4000 cfm is return air and is

neutral, and 1000 cfm is ventilation air to be heated. In the final analysis, it must be determined if it is more economical to heat 4000 cfm from 55 F to 75 F, or to cool it from 75 F to 55 F. The answer depends on the efficiency of the cooling and heating source.

An example of economizer economics is illus­ trated in Fig. 17. The graph plots percent cooling load versus relative energy cost (electricity to gas) and is based on the following typical assumptions:

48MA028 — 10,000 cfm, 15% outdoor air

48 F outdoor changeover temperature

75 F room design

55 F supply air temperature

Compressor changeover point (COP.) of 3.3 (100 F condensing temperature and unloaded compressor were used to obtain this value)

The relative cost figures are in $/Btu input for gas and $/kwh electric cost converted to Btu.

Example:

$.10/100,000 Btu (input) - gas cost $.015/kwh - electric cost

Convert electric cost-

$.015/kwh X kwh/3413 Btu x |Q5QQQ

= $.44/100,000 Btu

Cost Ratio:

$.44/100,000 Btu _ , ,

.10/100,000 Btu

Therefore, if cooling load is less than 45% (from graph) at the changeover temperature, the economizer is uneconomical for 48MA units.

For 50ME electric heat units, the cooling load break-even point is 70%; the internal load must be greater than 70% to justify economizer control.

Fig. 17 — 48MA/50ME Economizer

Break-Even Point

15

The cooling load for this comparison is the internal load (lights and people) minus the negative transmission at the changeover temperature (48 F). To determine the percent cooling load, compare this value to the unit design cooling capacity.

Night Setback — Niglit setback control can be added to a 48MA/50ME unit using field-supplied components. There are 3 sets of terminals on the accessory section of the unit zone control board (see Fig. 18). The terminals are used in combina­ tion to achieve the system desired. Terminal sets are: cooling lockout (CL), night setback (NS) and “Short To Close Dampers.” Red jumpers are factory wired across CL and NS; “Short To Close Dampers” are bare (see Fig. 19). If the circuit between CL terminals is broken, 115-v power to the compressor control circuit liquid line solenoids and economizer thermostat (if used) is shut off. If the circuit between NS terminals is broken, 115-v power to the zone control transformers is shut off. By replacing both jumpers with appropriate switches and connecting proper switch across “Short To Close Dampers,” NS control is attained. Although many versions of NS are possible, the 3 most common methods are detailed here.

METHOD NO. 1 - HEATING NIGHT SETBACK, COOLING LOCKED OUT, AND CONTINUOUS INDOOR EAN OPERATION

This automatic NS system requires a Honeywell S659A seven-day timer, a Honeywell R8227B fan center (night setback relay) and a Honeywell T822D thermostat (heating type) 24-v service. In this system (see Eig. 20), when the timer reaches the “Night” position, the switches are as shown. CL opens, dampers close and NS opens. The fan continues to operate.

As the temperature falls, the NS thermostat located in the average temperature space energizes the NS relay (fan center) which in turn energizes the zone control transformers. The individual zones then heat until the NS thermostat is satis­ fied. The dampers remain closed and cooling is still locked out. If a day/niglrt switch is used, the NS thermostat is overridden and heating is controlled by the normal thermostats.

Accessory remote panel assembly and/or ac­ cessory economizer may be used with this system if desired. Cycling indoor fans with NS thermostat is possible if the accessory remote panel is not used. Connect the field wiring to the MU terminals instead of the NS and the indoor fan contactor will cycle with the heaters. Although this system does not provide a time off delay for the fans after heater shutdown, test experience indicates that this is not a problem on these units.

METHOD NO. 2 - HEATING NIGHT SETBACK, COOLING LOCKED OUT AND CYCLING IN­ DOOR EANS

This system requires a Carrier remote control panel assembly 48MA900041, Honeywell S659A sevenday timer, Honeywell R8227B fan center (night setback relay) and a Honeywell T822C thermostat (cooling type).

The number of candidate systems for NS increases with the use of the remote accessory panel. A typical system is shown in Eig. 21. The use of the master unit relay (MUR) and the master cooling relay (MCR) requires 24-v wiring only. Installing the timer and the NS relay in proximity to the remote control panel results in all wiring being located inside the building in one area.

1 6

AB — Accessory Board

AFS - AirfI ow Switch

APS — Air Pressure Switch

C — Compressor Contactor

Cap. — Capacitor

CB — Circuit Breaker

CCB — Compressor Circuit Breaker

CCP — Capacity Control Pressurestat

CH — Crankcase Heater

CHR — Crankcase Heater Relay

CL — Switch, Cooling Lockout

CO — Convenience Outlet

Compr — Compressor

CR — Cooling Relay

DLT — Discharge Line Thermostat

ECR — Economizer Relay

ECT — Economizer Thermostat

EXR — Exhaust Relay

FCB — Fan Circuit Breaker

FCPS — Fan Cycling Pressurestat

FL	— Fusible Link
FRS	— Filter Media Runout Switch
Fu	— Fuse
GV	- Gas Valve
Gnd	— Ground
HA	— Heat Anticipator
HC	— Heater Contactor

1

LEGEND

HPS — High Pressure Switch

HR — Holding Relay

Htr — Heater

I — Ignitor

IFC — Indoor Fan Contactor

I FCB — Indoor Fan Circuit Breaker

IFM — Indoor Fan Motor

IP — Internal Protector

LAT — Low Ambient Thermostat

LLS — Liquid Line Solenoid

LPS — Low-Pressure Switch

LS — Limit Switch

MCR

— Master Cooling Relay

(MC)

MHR

— Master Heating Relay

(MH)

MUR

— Master Unit Relay

(MU)

IM.C. — Normally Closed

N.O. — Normally Open

NS — Night Setback Switch

OAT. — Outdoor Air Thermostat

OFC — Outdoor Fan Contactor

OFCB — Outdoor Fan Circuit Breaker

OFM — Outdoor Fan Motor

Pig — Plug

R — Resistor

	RB	Relay Board
	Sw	Switch
	TB	Terminal Block
	TC	Thermostat, Cooling
	TH	Thermostat, Heating
	TM	Timer Motor
	T ran	Transformer
	ZB	Zone Board
	<	Receptacle
	□	Plug
		Terminal Block
	o
		Terminal (marked)
	' o	Terminal (unmarked)
	A	Circuit Board Terminal
		Splice
		Terminal, Circuit Board,
		Factory Connected
	□□ s	Terminal, Circuit Board,
		Field or Accessory
		Factory Wiring
		Accessory or Field Wiring
		Circuit Board Run
		To indicate common potential only, not to
		indicate wire.