pressure can affect compressor power for the same example system as used to
generate the data in Table 1. The far right column in Table 2 shows the
percentage increase in compressor power as discharge pressure and saturated
discharge temperature (Tdsat) is increased.
increases in discharge pressure result in higher energy usage for lower
temperature refrigeration systems. From this data, a second rule of thumb can
"for every 1 psig decrease in discharge pressure, compressor power
be drawn -
is reduced approximately 0.5%."
Table 2: Effect of discharge pressure on compressor power.
Tdsat (F) Pd (Psig) Comp. kW
Calculations done using refrigeration model with following conditions:
- R-22, Sat. Suction Temp=-10 F, Case load = 200,000 Btu/hr
It should be further noted that compressor discharge pressure is always a
function of and higher than condensing pressure, and that other system elements can
substantially elevate discharge pressures above levels enforced by ambient
temperatures and resulting condensing temperatures and pressures alone.
include gas defrost discharge pressure regulators and heat reclaim system valves,
piping, and controls. Whether an increase in discharge pressure is imposed by a rise in
ambient temperature or by the action of refrigeration system elements, the efficiency and
energy penalties are the same.
Having reviewed the parameters that affect compressor power and system
efficiency, we can now explain how E2 controllers are designed to apply these basic
principles to refrigeration systems in order to minimize refrigeration system power
consumption.
HIGH SIDE CONTROL WITH E2.
Most mechanical and electronic control systems cycle condenser cooling fans to
on and off in order to maintain fixed high side condensing and operating pressures and
resulting saturated condensing temperatures (typically 90 degF), even when outdoor
ambient temperatures may permit condensing pressures to drop (float) to lower levels.
E2 controllers include resident control strategies that let one take advantage of lower
ambient temperatures to reduce refrigeration system compressor power.
operated utilizing E2's TD (where TD = the temperature difference between ambient air
temperature and condensing temperature) condenser fan control strategy, E2s permit
refrigeration system operation at the lowest condenser pressure possible with minimum
70
128.1
75
132.3
80
143.7
85
155.7
90
168.5
95
181.9
100
196
105
210.8
110
226.4
115
242.8
It can be also observed that
%kW/psig
20.14
0.65%
20.69
0.62%
22.16
0.57%
23.68
0.51%
25.24
0.48%
26.86
0.44%
28.52
0.41%
30.25
0.38%
32.03
0.35%
33.89
0.34%
These
When
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