Page 244 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

The Use of Water in HVAC Systems 241

Low-temperature hot water heating Chap. 20
Medium- and high-temperature hot water Chap. 21

8.8 Suggested Design Rules
Generally, water consumption is not a concern in most HVAC sys-
tems, since most systems are circulatory. The use of energy is impor-
tant! If the recommendations and equations developed herein are
used, efficient pumping procedures will result for these water sys-
tems. Following are some additional recommendations.

1. The prospective water system should be designed to the specific
requirements of the owner, utilizing the following principles to
achieve the most efficient system possible within the first cost bud-
get of the project.
2. The water system should be configured to distribute the water effi-
ciently with a minimum use of energy-wasting devices. These
devices are listed here:
a. Three-way temperature-control valves
b. Balancing valves, manual or automatic
c. Pressure-reducing or pressure-regulating valves
d. Crossover bridges and return valves
3. The piping should be designed without
a. Reducing flanges or threaded reducing couplings
b. Bullhead connections (e.g., two streams connected to the run
connections of a tee with the discharge on the branch of the tee)
4. The friction for the piping should be calculated for all pipe runs,
fittings, and valves.
5. Distribution pumps should be selected for maximum efficiency at
the design condition and within the economic constraints of the
project.
6. Distribution pumps should be added and subtracted to avoid oper-
ation of pumps at points of high thrust and poor efficiency. Pump
sequencing should achieve maximum possible system efficiency.
7. Coil control valves and their actuators should be sized to ensure
that they can operate at all loads on the system without lifting the
valve head off the valve seat.
It is obvious from the preceding section that the design of HVAC
water systems is not a simple task. Much analysis must be done, bal-
ancing many cost factors against operating costs to achieve the eco-
nomically feasible design for each installation. Reiterating, the use of
computers enhances this effort and eliminates much of the drudgery
of this design work.

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