ASHRAE Journal - December 2019 - 57

COLUMN ENGINEER'S NOTEBOOK

for most projects since
TABLE 1 Example chiller bid summary.
the extra level of effort
OPTIONS
1
2
3
4
5
6
required above the more
PRICING
conventional practice is
Tags CH-1, CH-2 CH-1, CH-2 CH-1, CH-2 CH-1, CH-2 CH-1, CH-2 CH-1, CH-2
minimal.
Price for Both Chillers (Including Freight)
$206,670
$238,210
$201,940
$318,790 $241,950
$232,350
Table 1* shows bid
GENERAL
results from an ofﬁce
Compressor Type
Screw Centrifugal Open Drive
Dual Centrifugal
Screw
Centrifugal Centrifugal
building project with
Refrigerant Type
134a
134a
134a
134a
134a
134a
two chillers and a variBearing Type
Standard
Magnetic
Standard
Magnetic
Magnetic
Standard
able primary ﬂow (VPF)
Operating
Weight
(lbs)
17,881
12,086
19,335
12,580
16,504
15,944
distribution system.
Refrigerant Weight (lbs)
760
552
1,101
950
800
475
Fields marked in green
Variable
Speed
Drive
(Y/N)
Y
Y
Y
Y
Y
Y
are positive features
OPERATING CONSTRAINTS
while those marked in
Capacity (% Of Design Capacity) Below Which
10%
10%
red are negative eleHot-Gas Bypass Operates (If HGBP is Provided)
ments. The most imporCapacity (% of Design Capacity) Below Which
12%
12%
15%
DNL
14%
20%
Chiller Cycles
tant criteria are:
Minimum "Lift" (CWRT-CHWST) at Minimum
20.0
0.0
15.0
0.0
1.0
25.0
* Price
Load °F
* NPLV (non-stanMaximum CHWST Reset Temperature °F
62.0
60.0
60.0
60.0
65.0
65.0
dard part load value),
EVAPORATOR
which is a measure of
Design Capacity (tons)
300
300
300
300
300
300
annual efﬁciency. It is
Design CHW Flow (gpm)
288
288
288
288
288
288
more indicative of anLeaving CHWST °F
42.0
42.0
42.0
42.0
42.0
42.0
nual performance than
Entering CHWRT °F
67.0
67.0
67.0
67.0
67.0
67.0
full-load efﬁciency (kW/
Evaporator Passes
3
3
3
2
2
3
ton) since the chillers
CHW Pressure Drop (ft)
15.9
14.4
12.7
7.4
4.8
3.0
will seldom operate at
Minimum CHW Flow Rate VPF (gpm)
114
111
112
140
184
269
full load.
Minimum CHW Flow Rate VPF (%)
40%
39%
39%
49%
64%
93%
* Unloading capabiliCONDENSER
ty, i.e. at what minimum
Design CW Flow (gpm)
600
600
600
600
600
600
load can the chiller
Entering CWST °F
76.9
76.9
76.9
76.9
76.9
76.9
stably operate?
Leaving CWRT °F
90.8
90.7
90.7
90.8
90.7
91.0
* Evaporator miniCondenser Passes
2
2
2
2
2
2
mum ﬂow rate. With a
CW Pressure Drop (ft)
11.6
10.6
14.5
9.1
4.6
7.8
VPF distribution system,
PERFORMANCE
a lower minimum ﬂow
A-Weighted Sound Power dB(A)
84
75
80
100
79
83
rate will impact chilled
Full Load amps
270
233
230
253
227
313
water pump energy
NPLV
0.34
0.37
0.41
0.38
0.37
0.45
use more than design
Design kW
166.4
178.4
160.3
182.5
174.5
206.7
evaporator pressure
Design kW/ton
0.555
0.533
0.534
0.545
0.521
0.617
drop.
* Condenser water pressure drop. The condenser wa- terion as we move away from refrigerants with high
ter pumps are constant ﬂow so condenser pressure drop Global Warming Potential (GWP). Unfortunately, for
will drive condenser water pump energy.
some chiller types, new generation low GWP refrig* Refrigerant. This is an important selection crierants are not yet an option, as was the case in this
* The

actual bid form includes much more information than shown here. Rows not relevant to this article were eliminated.
D E C E M B E R 2 0 19

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