Carrier XRV Especificações descarregar pdf (Página 70)

Maximum Load T2:

54 – 44 = 10º F (12.2 – 6.7 = 5.5º C)

Maximum Load P2:

120 – 37 = 83 psid (827 – 255 = 572 kPad)

To avoid unnecessary surge prevention, add about 10 psid

(70 kPad) to P2 from these conditions:

T2 = 10º F (5.5º C)

P2 = 93 psid (642 kPad)

Calculate Minimum Load

— To calculate the minimum load

conditions, estimate the temperature difference the cooler will

have at 10% load, then estimate what the suction and condens-

ing temperatures will be at this point. Use the proper saturated

pressure and temperature for the particular refrigerant used.

Suction Temperature:

43 F (6.1 C) = 38 psig (262 kPa) saturated

refrigerant pressure (HFC-134a)

Condensing Temperature:

70 F (21.1 C) = 71 psig (490 kPa) saturated

refrigerant pressure (HFC-134a)

Minimum Load T1 (at 20% Load): 2 F (1.1 C)

Minimum Load P1:

71 – 38 = 33 psid (490 – 262 = 228 kPad)

Again, to avoid unnecessary surge prevention, add 20 psid

(140 kPad) at P1 from these conditions:

T1 = 2 F (1.1 C)

P1 = 53 psid (368 kPad)

Calculate Surge/ HGBP Delta Tsmin

— Convert design suc-

tion temp to pressure using an R-134a pressure/temperature

chart.

Min. Cond. Pressure = (suction pressure) + (ΔP minimum)

Convert Min. Cond. Pressure to Min. Cond. Temperature

using a saturation pressure/temperature chart for R-134a.

Surge / HGBP Tsmin = (Min. Cond. Temp.) – (design suc-

tion temperature)

Calculate Surge/ HGBP Delta Tsmax

Max. Cond. Pressure = (suction pressure) + (ΔP maximum)

Convert Max. Cond. Pressure to Max. Cond. Temperature

using a saturation pressure/temperature chart for R-134a.

Surge / HGBP Tsmax = (Max. Cond. Temp) – (design suc-

tion temperature)

VPF Surge Prevention Configurations are defined as

follows:

• Surge/HGBP Delta Tsmin is the minimum difference

between cooler and condenser saturation temperatures.

(See Fig. 36.)

• Surge/HGBP IGVmin is the lowest position of the guide

vanes that affects Surge prevention. This is not likely to

require adjustment at the jobsite other than to ensure that

it matches the value supplied with the machine selection.

These values produce the minimum load point of the Surge

Prevention line:

• Surge/HGBP Delta Tsmax is the maximum difference

between cooler and condenser saturation temperatures.

(See Fig. 37.)

• Surge/HGBP IGVmax is the highest position of the

guide vanes that affects Surge prevention. This is not

likely to require adjustment at the jobsite other than to

ensure that it matches the value supplied with the

machine selection.

NOTE: The preceding two values produce the full load point

of the surge prevention line.

• Surge Line Shape Factor determines the curvature of the

line mainly in the low load zone. (See Fig. 38.)

• Surge Line Speed Factor determines how much the surge

line moves to accommodate lower compressor speed. As

compressor speed drops the ΔT values on the surge pre-

vention line decrease. Increasing the Speed Factor causes

Surge Prevention to activate sooner as the compressor

speed drops. (See Fig. 39.)

• Surge Line High Offset determines the ΔT increase

beyond the surge prevention line where the high stage of

Surge Prevention takes effect. The high stage produces

larger RPM increase steps. This is not likely to require

adjustment at the jobsite other than to ensure that it

matches the value supplied with the machine selection

• Surge/HGBP Deadband controls the amount the ACTIVE

DELTA TSAT must drop below the Surge Prevention to

de-activate Surge Prevention.

0 102030405060708090100110

Tsmin=30

Tsmin=40

Tsmin=50

GV_POS

Delta Tsat

Fig. 36 — Effect of SURGE/HGBP DELTA TSMIN

on Surge Prevention

a19-1959

0 102030405060708090100110

Tsmax=60

Tsmax=70

Tsmax=80

GV_POS

Delta Tsat

Fig. 37 — Effect of SURGE/HGBP DELTA TSMAX

on Surge Prevention

a19-1960

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