MIL-HDBK-1003/6
Section 4:
HTW HEATING PLANTS
4.1
General Requirements
a) Design engineers should be selected on the basis of their past
experience with HTW system design.
b) The design engineering firm selected should prepare a detailed
economic analysis of comparable steam and HTW systems before a decision is
made to use either system.
c) One of the main advantages of HTW compared to steam systems is
the smaller pipe sizes and pumps required due to the tremendous thermal
storage of water. Table 5 shows the influence of temperature differentials on
pipe and pump size. The minimum temperature differential recommended is 100
degrees F (55.5 degrees C). The preferred temperature differential range is
120 to 150 degrees F (66.6 to 83.3 degrees C).
d) Refer to Table 6, for information on types of equipment and
their application.
Table 5
Influence of Temperature Differentials on Selection of
Pumps and Pipe Sizes for HTW Systems
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* Temperature difference
NF
*
20
50
100
150
200
*
*
* Discharge temperature
NF
*
270
300
350
400
450
*
*
* Return temperature
NF
*
250
250
250
250
250
*
*
* Mean temperature
NF
*
260
275
300
375
350
*
*
* Flow rate per 20
*
* (Million BTU/hr) MMBH lb/hr 1,000,000 400,000 200,000 133,000 100,000
*
*
*
* Density of returning
*
* water
7.86 *
lbs/gal
7.86
7.86
7.86
7.86
*
*
* Pump capacity
212.5 *
GPM
2,125
850
425
283
*
*
* Assumed pump head
*
ft
100
100
100
100
100
*
*
* Pump HP required
8.4 *
HP
84.0
33.6
16.8
11.2
*
*
* Pump efficiency
*
%
60
60
60
60
60
*
*
* Pump size
*
I.P.S.
8"
6"
4"
3-1/2"
3"
*(Assumed head loss 10'/100')
*
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18
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