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Bigger
Compressor
Unit
tonnage
size
step
200
10
250
15
300
15
400
25
450
25
490
25
500
15
600
15
700
20
800
25
900
30
925
25
18
Installation
Minimal installation water
content
The water volume is an important
parameter because it allows a stable
chilled water temperature and avoids
short cycle operation of the
compressors.
Parameters which influence the
water temperature stability
- Water loop volume.
- Load fluctuation.
- Number of capacity steps.
- Compressors rotation.
- Dead band.
- Minimum time between 2 starts of
a compressor.
Minimum water volume for a
comfort application
For comfort application we can allow
water temperature fluctuation at part
load. The parameter to take into
account is the minimum operating
time of the compressor. In order to
avoid lubrication problem on a scroll
or an hermetic reciprocating
compressor it must run at least
2 minutes (120 seconds) before it
stops.
The minimum volume can be
determined by using the following
formula
Compressor step
temperature fall
Total unit
versus Delta T water
Tonnage
4
20
2.0
25
2.4
30
2.0
40
2.5
45
2.2
50
2.0
50
1.2
60
1.0
70
1.1
80
1.3
90
1.3
100
1.0
Minimum
recommended
water loop
temperature
loop
5
6
1.5
2.5
3.0
1.5
3.0
3.6
1.5
2.5
3.0
1.5
3.1
3.8
1.5
2.8
3.3
1.5
2.5
3.0
1.5
1.5
1.8
1.5
1.3
1.5
1.5
1.4
1.7
1.5
1.6
1.9
1.5
1.7
2.0
1.5
1.3
1.5
1.5
Volume = Cooling capacity x Time x
highest capacity step (%) / Specific
heat / Dead band
Minimum operating time =
120 seconds
Specific heat = 4.18 kJ / kg
Dead band recommended = 3°C
Dead band calculation
Dead band = (Biggest compressors
step tonnage / Total tonnage) X
(Water temperature difference
entry/leaving) + allowed water loop
temperature fall
Minimum allowed temperature fall =
1.5°C
Minimum dead band calculation
table versus the targeted water
temperature delta T
It is preferable to have a higher dead
band than the minimum
recommended.
Dead Band
minimum versus
delta T water
fall
loop
4
5
3.5
4.0
3.9
4.5
3.5
4.0
4.0
4.6
3.7
4.3
3.5
4.0
2.7
3.0
2.5
2.8
2.6
2.9
2.8
3.1
2.8
3.2
2.5
2.8
6
4.5
5.1
4.5
5.3
4.8
4.5
3.3
3.0
3.2
3.4
3.5
3.0
CG-SVX01C-E4
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