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        ![]() MIL-HDBK-1003/13A 
. 
(mCp)c 
Heat capacity flow rate 
through collector (Btu/hr deg. F) 
. 
(mCp)min 
The lesser of the two heat 
capacity flow rates in the 
collector-tank heat exchanger 
No 
Number of days in month 
NI 
Number of days in computation 
period 
P 
Degree days 
qc 
Solar heat collected per ft2 
of collector per month 
(Btu/ft2-mo) 
Qd 
DHW heating load (Btu/day) 
Qdt 
Yearly total load (DHW only) 
(Btu/yr) 
QL 
Total heat load (space + DHW) 
per month (Btu/mo) 
QLt 
Yearly total heat load 
(space + DHW) (Btu/yr) 
Qu 
Useful heat collected = 
Acqc (Btu/mo) 
R 
Gross space heat load = 
LxMxP 
S 
Slope factor = ratio of 
direct solar radiation on a 
tilted surface to that on a 
horizontal surface 
Ta 
Average ambient air 
temperature (deg. F) 
Ti 
Collector inlet fluid 
temperature (deg. F) 
To 
Collector outlet fluid 
temperature (deg. F) 
Tref 
212 deg. F, a reference temperature 
151 
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