Systems & CodeQuestion 37 of 110
A hot-water recirculation loop loses 4,000 BTU/hr to the piping. The pump must circulate enough water so it cools only 20 F while replacing that loss. Using Q (gpm) = BTU/hr / (500 x delta-T), what recirculation flow is required?
a.0.4 gpm
b.0.2 gpm
c.0.8 gpm
d.2.0 gpm
Explanation
Q = 4,000 / (500 x 20) = 4,000 / 10,000 = 0.4 gpm. The 500 factor is the heat capacity of water in BTU per hour per gpm per degree F. A low recirculation flow is enough to offset standby losses and keep hot water instantly available without eroding the piping.
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