The selection of an air cooled condenser is based on the heat rejection capacity at the condenser rather than net refrigeration eefect at the evaporator because the referigerant gas absorbs additional energy in the compressor. This additional energy, the heat of compression, varies appreciably with the operating conditions of the system and with compressor design, whether open or suction colled hermetic type.
OPEN COMPRESSORS - TABLE A
EVAPORATOR TEMP. (�C)
CONDENSING TEMPERATURE �C
30
35
40
45
50
55
60
-35
1.37
1.4
1.44
1.50
*
*
*
-30
1.327
1.36
1.40
1.44
1.50
*
*
-25
1.28
1.31
1.35
1.39
1.44
1.49
*
-20
1.24
1.27
1.31
1.35
1.39
1.44
1.49
-15
1.21
1.24
1.28
1.31
1.35
1.39
1.44
-10
1.18
1.21
1.24
1.27
1.31
1.35
1.39
-5
1.15
1.18
1.21
1.24
1.28
1.31
1.35
0
1.12
1.15
1.18
1.20
1.24
1.27
1.31
5
1.10
1.13
1.15
1.17
1.20
1.24
1.27
10
1.08
1.11
1.13
1.15
1.18
1.20
1.24
* Outside of normal limits for single stage compression application.
SUCTION COOLED HERMETIC COMPRESSORS - TABLE B
EVAPORATOR TEMP. (�C)
CONDENSING TEMPERATURE �C
30
35
40
45
50
55
60
-35
1.56
1.60
1.65
1.71
*
8
*
-30
1.49
1.52
1.56
1.62
1.68
8
*
-25
1.43
1.46
1.49
1.54
1.60
1.68
*
-20
1.37
1.40
1.45
1.48
1.54
1.60
1.65
-15
1.32
1.35
1.39
1.43
1.47
1.53
1.58
-10
1.28
1.31
1.33
1.37
1.42
1.47
1.52
-5
1.24
1.26
1.29
1.33
1.37
1.41
1.46
0
1.20
1.22
1.25
1.28
1.32
1.36
1.41
5
1.16
1.19
1.22
1.24
1.27
1.31
1.35
10
1.13
1.15
1.18
1.21
1.24
1.26
1.29
Some compressor manufacturers publish heat rejection feagures as part of their compressor ratings. Since heat rejection varies with compressor designs, it is recommended that the compressor manufacturer's data be used whenever available in selecting an air cooled condenser. If the compressor manufacturer does not publish heat rejection ratings, factors from Table A and B may be used to estimate total heat rejection - THR.
SELECTION EXAMPLE
GIVEN:
Compressor Capacity
38600W
Evaporator Temperature
5�C
Referigerant
R-22
Ambient Air
35�C
Maximum Condensing Temperature Suction Cooled Hermetic Compressor
50�C
PROCEDURE
1.
Assuming the compressor manufacturers heat rejection data is not available, determine the heat rejection factors for the specified conditions from Table B
2.
Multiply the compressor capacity by the heat rejection factor to estimate the required condenser capacity.
3.
Divide by the specified temperture difference between condensing referigerant and the ambient air (TD).
4.
Since R-22 is specified, select from Table No. 5 - based on 1 KTD.
SELECTION: Using the heat rejection factor from Table B, the required condenser capacity is:
1.27 x 38600 = 49022 W THR Divide the condenser capacity by the T.D. 49022 � 15�K = 3268 W/K
From Table No. 5 for 1 KTD, the proper selection is the Model MAC 357D with a capacity of 3800W; In this instance the condenser is oversized and the condenser will balance the compressor heat rejection at less than maximum condensing temperature of 50�C.
