Specifications
31
ENVISION COMMERCIAL SPECIFICATION CATALOG
3, 4 & 5. HP Selection:
After making our preliminary selection (NS*022 PSC), we
enter the tables at design water flow and water tempera-
ture and read
Total Cooling, Sens. Cooling and Heat of Rej. capacities:
Total Cooling ...............................................................20,300 BTUH
Sensible Cooling ......................................................... 15,700 BTUH
Heat of Rejection ......................................................25,900 BTUH
6 & 7. Entering Air and Airflow Corrections:
Next, we determine our correction factors. (Refer to Cor-
rection Factor Tables - Air Flow and Entering Air correc-
tion tables — using 755 cfm. or 755÷700 nom. = 108%).
Corrected Total Cooling = 20,300 x 1.007 x 0.897 = 18,337
Corrected Sens Cooling = 15,700 x 1.034 x 0.995 = 16,153
Corrected Heat of Reject = 25,900 x 1.010 x 0.951 = 24,877
8. Water Temperature Rise Calculation & Assessment:
Note: 500 = parameters for water & 485 = parameters for
antifreeze solutions to 30% weight.
When we compare the Corrected Total Cooling and Cor-
rected Sensible Cooling figures with our load requirements
stated in Step 1, we discover that our selection is within
+10% of our sensible load requirement. Further more, we
see that our Corrected Total Cooling figure is within 1,000
Btuh of the actual indicated load.
Selection Example cont.
Antifreeze Corrections
Catalog performance can be corrected for antifreeze use. Please use the following table and note the example given.
Antifreeze Correction Example
Antifreeze solution is Propylene Glycol 20% by weight. Determine the corrected heating and cooling performance at 30°F
and 90°F respectively as well as pressure drop at 30°F for an Envision Series NS*048-PSC.
The corrected cooling capacity at 90°F would be: 46,500 MBtuh x 0.969 = 45,059 MBtuh
The corrected heating capacity at 30°F would be: 38,000 MBtuh x 0.913 = 34,694 MBtuh
The corrected pressure drop at 30°F and 12 GPM would be: 9.0 feet of head x 1.270 = 11.43 feet of head
Antifreeze Type
Antifreeze
% by wt
Cooling
Capacity
Heating
Capacity
Pressure Drop
EWT - degF [DegC] 90 [32.2] 30 [-1.1] 30 [-1.1]
Water 0 1.000 1.000 1.000
10 0.991 0.973 1.075
20 0.979 0.943 1.163
Ethylene Glycol 30 0.965 0.917 1.225
40 0.955 0.890 1.324
50 0.943 0.865 1.419
10 0.981 0.958 1.130
20 0.969 0.913 1.270
Propylene Glycol 30 0.950 0.854 1.433
40 0.937 0.813 1.614
50 0.922 0.770 1.816
10 0.991 0.927 1.242
20 0.972 0.887 1.343
Ethanol 30 0.947 0.856 1.383
40 0.930 0.815 1.523
50 0.911 0.779 1.639
10 0.986 0.957 1.127
20 0.970 0.924 1.197
Methanol 30 0.951 0.895 1.235
40 0.936 0.863 1.323
50 0.920 0.833 1.399
Warning: Gray area represents antifreeze concentrations greater than 35% by weight and
should be avoided due to the extreme performance penalty they represent.
HR = 500 x GPM x (T
in
- T
out
)
HR
= (Tin - Tout) or ∆T Rise
500 x GPM
24,877
= 8.29 °F Rise
500 x 6