Page 223 - HVAC Pump Handbook

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The Use of Water in HVAC Systems

220 The HVAC World

TABLE 8.1 Energy Data for an Existing High School

Balance valves Balance valves Percent
Item set traditionally opened completely change
Flow, gal/min 700 750 7
Cooling load, tons 215.8 278.1 29
Supply temperature, °F 45.0 45.4 —
Return temperature, °F 52.4 54.3 4
Differential temperature, °F 7.4 8.9 20
Secondary pump
discharge pressure, psig 67 58 13
Pump speed, rev/min 1232 1032 16
Pumping system kW 18 16 11
Secondary pumping, 0.083 0.058 30
kW/ton

SOURCE: Ben L. Kincaid and Andrew Spradley, Removing Manual Balancing in a High
School, 1995.

The increase in system flow with the balance valves opened was
caused by the addition of the auditorium air-handling units. Some sig-
nificant system changes were achieved, namely, reduction in pump
speed and discharge pressure and an increase in the differential tem-
perature.
Although these are very specific data for a single installation, the
over 30 percent reduction in pumping energy demonstrates that the
use of mechanical devices such as balance valves and any kind of
pressure-regulating valve should be reviewed carefully to determine
their effect energywise on an HVAC water system.

8.1.5 Effect of energy consumption
on chillers and boilers
On chilled and hot water systems, it must be remembered that all the
energy lost through a flow-regulating device such as a balance valve
results in heat in the water. Therefore, on chilled water applications,
this heating effect must be taken into consideration as an additional
load. On hot water systems, it is beneficial and should be deducted
from the energy lost. This is one reason why the energy lost in bal-
ance valves on heating systems was seldom questioned.
Following is a procedure for checking the total energy lost to bal-
ance valves on a particular chilled water system. When the balance
valves are checked or set for a desired flow, the flow and pressure
drops should be recorded for each valve and the preceding equations
used to compute the energy loss for each valve. All the balance-valve
losses can be totaled for an annual energy loss. Table 8.2 can be used
for this computation.

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