MIL-HDBK-1003/3
f) Low temperature hot water heating systems are often
designed for a 20 degree F temperature drop. This makes it easy
to size the pump--divide the Btu's by 10,000 to obtain the pump
gpm.
g) Pumping systems that are open, such as cooling
towers, or systems with hot liquids, such as a deaerator feed
pump, require special attention to ensure proper NSPH. Keep the
pump low enough and close enough to maintain proper NPSH.
h) Calculate pipe and fitting friction drop, the head
loss through the coils, control valves, heat exchanger, etc. To
this add any static head, if the system is not a closed system.
Also add nozzle loss for spray equipment, such as evaporative
condensers, cooling towers with nozzles, or air washers.
I) Arrange pumps in parallel, i.e., one pump for each
boiler, chiller, cooling tower, etc.
7.2.3
Chilled Water
7.2.3.1
Pipe Size. Refer to pars. 7.1 and 7.2.1. For dual
temperature systems, note that the required temperature
difference and the required flow may be different for heating and
for cooling operation.
7.2.3.2
Coils.
Refer to par. 7.2.2.2.
Note the following:
a) Multiple rows may be needed for humidity control.
With cooling coils it is important to specify the entering and
leaving wet bulb temperature and add the latent load of
dehumidification.
b)
Dehumidifying coils will need drip pans and drains.
7.2.3.3
Expansion Tanks. Refer to par. 7.2.2.3. Expansion
tanks are required to provide for change in water volume due to
changes in temperature.
7.2.3.4
Pumps. Refer to par. 7.2.2.6. It is common with large
chilled water systems to check the economics of pumping systems.
Is it lower cost to pump more or less flow on the chilled water
and cooling water circuits? Should colder chilled water, smaller
or larger pipes, a bigger chiller, warmer condenser water, or
smaller cooling towers be used? Evaluate the life cycle
economics on several alternatives to select the most cost
effective solution.
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