UFC 3-420-01
25 October 2004
(3) Normally if a central energy plant is available it will be life cycle cost
effective (an analysis must be performed) to generate domestic hot water
using distributed media as the heat source. If there is no central plant or if the
plant does not operate during the nonheating season provide a separate
domestic hot water source. If the site consists of several barracks buildings,
evaluate the life cycle cost of these alternatives:
(a) A single boiler to provide low temperature hot water, 94C (200F) to
heat exchangers in each barracks for domestic hot water generation.
(b) A single heating source for domestic hot water in each individual
barracks separately.
If the barracks building is not part of a building complex and there is no
central plant or distribution system available then a single heating source
must be provided.
b. Calculations: The following information applies to all types of domestic
water heating systems for barracks.
(1) Peak Demand: Design for the case where all occupants are taking
showers at essentially the same time. Public law limits the maximum flow
from of each showerhead and lavatory faucet to 0.16 Lps (2.5 gpm). It is
assumed during peak demand that the shower requires 7.5 minutes and the
lavatory requires 2 minutes of full hot water flow. As a result, the peak
domestic hot water demand can be found using equation (1) below:
= (h)(occ)(P) T d
V p
(1)
T s
where:
VP = volume of domestic hot water required at peak, L (gal).
h = number of shower heads, ea.
Occ = number of occupants using each shower, ea.
Td = temperature of water delivered to shower valve = 43C (110F)
Ts = temperature of water in storage tank, degrees C (degrees F)
P = amount of water used per occupant during peak demand, 90.0
L/occupant (23.75 gal/occupant)
Note that there is no diversity in the number of occupants in the building.
The peak volume of domestic hot water is calculated assuming 100%
building occupancy. Also note that equation (1) does not take laundry or
dining facilities into account. Add additional hot water requirements if
laundry or dining facilities will be requiring hot water during the peak
demand period.
(2) Tank Size: Once the peak demand is known, the tank capacity and
E-2
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