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        ![]() MIL-HDBK-1003/13A 
UA 
Overall heat loss coefficient 
of building times building 
area (Btu/hr deg. F) 
UL 
Collector overall heat loss 
coefficient (Langleys/deg. F-day) 
V 
Net space heat load = R x [eta]w 
W 
Weight of DHW to be 
heated/day (lbm) 
[alpha] 
Absorptance 
[epsilon] 
Emittance 
[epsilon]c 
Effectiveness of the 
collector-tank heat exchanger 
[epsilon]L 
Effectiveness of the space 
heating load heat exchanger 
[eta] 
Collector efficiency 
[eta]collect 
Average collector efficiency 
[eta]delivery 
Delivery efficiency 
[eta]w 
Heater (DHW or space) 
utilization efficiency 
[theta] 
Hours of useful sun/day 
[(tau alpha)] 
Product of cover transmittance 
and plate absorptance account- 
ing for dirt and shading 
[(tau alpha)] 
Average value of [(tau alpha)] over 
one day 
[(tau alpha)]n 
[(tau alpha)] at normal radiation 
incidence 
[phi] 
Utilizability (see 3.12) 
Preparing Activity: 
Navy - YD 
Project FACR-0151 
152 
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