18
CG-SVX01C-E4
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
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.
Installation
4
5
6
1.5
4
5
6
200
10
20
2.0
2.5
3.0
1.5
3.5
4.0
4.5
250
15
25
2.4
3.0
3.6
1.5
3.9
4.5
5.1
300
15
30
2.0
2.5
3.0
1.5
3.5
4.0
4.5
400
25
40
2.5
3.1
3.8
1.5
4.0
4.6
5.3
450
25
45
2.2
2.8
3.3
1.5
3.7
4.3
4.8
490
25
50
2.0
2.5
3.0
1.5
3.5
4.0
4.5
500
15
50
1.2
1.5
1.8
1.5
2.7
3.0
3.3
600
15
60
1.0
1.3
1.5
1.5
2.5
2.8
3.0
700
20
70
1.1
1.4
1.7
1.5
2.6
2.9
3.2
800
25
80
1.3
1.6
1.9
1.5
2.8
3.1
3.4
900
30
90
1.3
1.7
2.0
1.5
2.8
3.2
3.5
925
25
100
1.0
1.3
1.5
1.5
2.5
2.8
3.0
Unit
size
Bigger
Compressor
tonnage
step
Total unit
Tonnage
Compressor step
temperature fall
versus Delta T water
loop
Minimum
recommended
water loop
temperature
fall
Dead Band
minimum versus
delta T water
loop
