Carrier GTR040-420 Dokumentacja Pobierz pdf (Strona 72)

MINIMUM FLUID LOOP VOLUME — To obtain proper

temperature control, loop fluid volume must be at least 3 gal-

lons per ton (3.25 L per kW) of chiller nominal capacity for air

conditioning and at least 6 gallons per ton (6.5 L per kW) for

process applications or systems that must operate at low ambi-

ent temperatures (below 32 F [0° C]). Refer to application

information in Product Data literature for details.

FLOW RATE REQUIREMENTS — Standard chillers

should be applied with nominal flow rates approximating

those listed in Table 38. Higher or lower flow rates are per-

missible to obtain lower or higher temperature rises. Mini-

mum flow rates must be exceeded to assure turbulent flow

and proper heat transfer in the cooler.

Consult application data section in the Product Data litera-

ture and job design requirements to determine flow rate re-

quirements for a particular installation.

Table 38 — Nominal and Minimum Cooler

Fluid Flow Rates

LEGEND

*Nominal flow rates required at ARI conditions are 44 F (6.7 C) leaving-fluid

temperature, 54 F (12.2 C) entering-fluid temperature, 95 F(35 C) ambient.

Fouling factor is .00001 ft

⋅

F/Btu (.000018 m

⋅

K/W).

NOTES:

1. Minimum flow based on 1.0 fps (0.30 m/s) velocity in cooler without special

cooler baffling.

2. Minimum Loop Volumes:

Gallons = V x ARI Cap. in tons

Liters = N x ARI Cap. in kW

Operation Sequence —

During unit off cycle, crank-

case heaters are energized. If ambient temperature is below

36 F (2 C), cooler heaters (if equipped) are energized.

The unit is started by putting the ENABLE/OFF/REMOTE

CONTACT switch in ENABLE or REMOTE position. When

the unit receives a call for cooling (either from the internal

control or CCN network command or remote contact closure),

the unit stages up in capacity to maintain the cooler fluid set

point. The first compressor starts 1

to 3 minutes after the call

for cooling.

The lead circuit can be specifically designated or randomly

selected by the controls, depending on how the unit is field

configured (for 040-070 sizes, Circuit A leads unless an

accessory unloader is installed on Circuit B). A field configura-

tion is also available to determine if the unit should stage up

both circuits equally or load one circuit completely before

bringing on the other.

When the lead circuit compressor starts, the unit starts with

a pumpout routine. On units with the electronic expansion

valve (EXV), compressor starts and continues to run with the

EXV at minimum position for 10 seconds to purge the refriger-

ant lines and cooler of refrigerant. The EXV then moves to

23% and the compressor superheat control routine takes over,

modulating the valve to feed refrigerant into the cooler.

On units with thermostatic expansion valve (TXV)

(30GTN,R and 30GUN,R 040,045 units with brine option),

head pressure control is based on set point control. When the

lead compressor starts, the liquid line solenoid valve (LLSV) is

kept closed for 15 seconds by a time delay relay. The micropro-

cessor stages fans to maintain the set point temperature speci-

fied by the controller. There is no pumpout sequence during

shutdown of TXV controlled chillers.

On all other units (EXV units), the head pressure is con-

trolled by fan cycling. The desired head pressure set point is

entered, and is controlled by EXV position or saturated con-

densing temperature measurement (T3 and T4). For proper op-

eration, maintain set point of 113 F (45 C) as shipped from fac-

tory. The default head pressure control method is set point con-

trol. The head pressure control can also be set to EXV control

or a combination of the 2 methods between circuits.

For all units, if temperature reset is being used, the unit con-

trols to a higher leaving-fluid temperature as the building load

reduces. If demand limit is used, the unit may temporarily be

unable to maintain the desired leaving-fluid temperature be-

cause of imposed power limitations.

On EXV units, when the occupied period ends, or when the

building load drops low enough, the lag compressors shut

down. The lead compressors continue to run as the EXV clos-

es, and until the conditions of pumpout are satisfied. If a fault

condition is signaled requiring immediate shutdown, pumpout

is omitted.

Loading sequence for compressors is shown in Tables 6A

and 6B.

FIELD WIRING

Field wiring is shown in Fig. 40-45.

Operation below minimum flow rate could subject tubes to

frost pinching in tube sheet, resulting in failure of cooler.

UNIT SIZE

30GTN,R

AND 30GUN,R

NOMINAL

FLOW RATE*

MINIMUM

FLOW RATE

(See Notes)

Gpm L/s Gpm L/s

040 86 5.43 36.8 2.32

045 101 6.37 37.7 2.38

050 123 7.76 37.7 2.38

060 151 9.53 47.5 3.00

070 173 10.91 47.5 3.00

080,230B 192 12.11 66.7 4.20

090,245B 216 13.62 59.5 3.75

100,255B,270B 240 15.14 84.1 5.30

110,290B,315B 264 16.65 84.1 5.30

130 30018.91106.9

150,230A-255A 34821.91106.9

170,270A,330A/B,

360B (50 Hz)

38424.21207.5

190,290A,360A/B (60 Hz),

360A (50 Hz), 390B

43227.21207.5

210,315A,390A,420A/B 48030.21489.3

ARI — Air Conditioning and Refrigeration Institute

Gpm — Gallons per minute (U.S.)

L/s — Liters per second

N — Liters per kW

V — Gallons per ton

APPLICATION V N

Normal Air Conditioning 33.25

Process Type Cooling 6 to 10 6.5 to 10.8

Low Ambient Unit Operation 6 to 10 6.5 to 10.8

1 2 ... 67 68 69 70 71 72 73 74 75 76 77 ... 103 104

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