UFC 3-420-01
25 October 2004
Including changes 1 and 2, October 2006
with actual design inlet water and storage temperatures.
Note 2: The tank size may be adjusted up or down to accommodate available tank sizes
or available recovery capacities. A smaller tank size yields a higher recovery rate.
Simply enter the desired tank size into equation 2 and solve for the required recovery rate.
Verify that the combination of tank size and recovery rate is commercially available./2/
(4) Pipe Sizes: The next component to be sized in the system is the
domestic hot water distribution piping. Appendix A of the 1997 National
Standard Plumbing Code, Chapter 45 of the ASHRAE Handbook -
Applications 1995 and Chapter 33 of the ASHRAE Handbook -
Fundamentals 1997 provide an ample set of resources on this topic.
Therefore, this appendix will not discuss this process.
(5) Domestic Hot Water Circulation Pump: After the domestic hot water
distribution piping has been sized, the domestic hot water circulation pump
can be sized. This pump is used to circulate the domestic hot water
through the distribution piping system. Size the pump using equation (3)
below:
q
Q
=
(3)
cρ c p ΔT
p
where:
Qp = pump capacity, Lps (gpm)
q = heat loss in the piping system, kW (BTUH)
kW ⋅ sec
min
c = constant, 1
(60
)
hr
kJ
kg
lb
(8.33
)
ρ = density of water, 0.9971
L
gal
kJ
BTU
cp = specific heat of water, 4.18
(1
)
kg ⋅ K
lb ⋅ F
ΔT = allowable temperature drop through the system, K (F)
Equation (3) can be simplified to:
E-4
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