Page 11 - HVAC Pump Handbook

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Digital Electronics and HVAC Pumps

8 The Basic Tools

can be set up for calculations by the computer. After all the programs
have been run, the designer can select the one that provides the op-
timal system conditions that meet the specifications of the client.
The designer now has time to play “what if” to achieve the best pos-
sible design for a water system. In the past, the engineer was often
time driven and forced to utilize much of a past design to reach a
deadline for a current project. Now the engineer can model pumping
system performance under a number of different load conditions and
secure a much more complete document on the energy consumption
of proposed pumping systems.
The designer can compute the diversity of an HVAC system with
much greater accuracy. Diversity is merely the actual maximal heat-
ing or cooling load on an HVAC system divided by the capacity of the
installed equipment. For example, assume that the total cooling load
on a chilled water system is 800 tons, but there are 1000 tons of cool-
ing equipment installed on the system to provide cooling to all parts of
that system. This disparity is caused by changing some loads or differ-
ences in occupancy. The diversity in this case would be 800/1000, or
0.80 (80 percent).
This is a simpler and easier definition of diversity than a more
technical definition that states that diversity is the maximal heating
or cooling load divided by the sum of all the individual peak loads. For
example, a 10-ton air handler might have a peak load of only 9.2 ton.
The true diversity might be slightly less than that acquired by using
the installed load.

1.4.1 Equation solution by computer
A number of equations are provided herein for the accurate solution
of pressures, flows, and energy consumptions of HVAC water systems.
These equations have been kept to the algebraic level of mathematics
to aid the HVAC water system designer in the application of them to
computer programs. Computer software is now available commercially
to assist in the manipulation of these equations. Typical of them is
the EES—Engineering Equation Solver program, available from F-
Chart Software, Middleton, Wis.

1.5 Databasing
After the designer has completed the overall evaluation of a water
system, databasing can be used to search elements of past designs for
use on a current project. Databasing is a compilation of information
on completed designs in computer memory that can be recalled for

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