UFC 3-420-01
25 October 2004
Including changes 1 and 2, October 2006
(3) Solution:
(a) Peak Domestic Hot Water Demand:
⎞ ⎛ T d - Tc ⎞
⎛
90
V p = h occ ⎜ occupant ⎟ ⎜ - Tc ⎟
⎜
⎟⎜
⎟
⎠⎝Ts
⎝
⎠
⎛ 2occupants ⎞⎛ 90L ⎞⎛ 43C - 4.4C ⎞
⎟⎜
⎜ occupant ⎟⎜ 60C - 4.4C ⎟
Vp
= (36heads)⎜
⎟
head
⎝
⎠⎝
⎠⎝
⎠
V
= 4499 L(1188 gal )
p
(b) Initial Storage Tank Size:
⎛ 2occupants ⎞⎛ 50L ⎞
⎟⎜
⎟
St
= (36heads)⎜
head ⎠⎜ occupant ⎟
⎝
⎝
⎠
S
= 3600L(951gal)
t
Use 2 tanks of 1893 L (500.0 gal) each to fit into the available space.
(c) \Initial Recovery Rate:
⎛ 9.5 min ⎞
⎛ 60 sec ⎞
d= ⎜
⎟(2occupants)⎜
⎟ = 1140 sec
⎜ occupant ⎟
⎝ min ⎠
⎝
⎠
4499 L - (75% x2eachx1893L)
R=
= 1.46 Lps (1388 gph or 23 gpm)
1140 sec
(d) Flow rate for domestic hot water /2/circulation pump (heat loss through piping is
0.629 kW):
E-8
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