The expansion tank in the larger mini-chiller unit is connected to the top of the water storage
tank and it has a capacity of 8 litres, with a charged pressure of 1.5 bar.
To calculate the size of a diaphragm expansion tank
, use the following formula:
where
V
t
= V
s
[(v
2
/v
1
) - 1] - 3
α∆
t
1 - (P
1
/P
2
)
in the system
wer temperature
ody
r temperature (t
1
)
the tank for the heating cycle of the mini-chiller unit, use the lower tempe
the largest AC 58A as an example, we calculate as follows:
* 25 litres
°C, the specific volume be read fro e water properties table (App.
volume v
2
= 0.001008
V
t
is the tank volume
V
s
is the water volume
v
1
is the specific volume of water at lo
v
2
is the specific volume of water at higher temperature
α is the linear coefficient of thermal expansion for the b
= 11.7 * 10
-6
m/(m.K) for steel
= 17.1 * 10
-6
m/(m.K) for copper
At is higher temperature (t
2
)
- lowe
P
1
is the pressure at lower temperature
P
2
is the pressure at higher temperature
To size rature (t
1
) as
the design chilled water temperature (e.g. 7°C) and the higher temperature (t
2
) as design hot
water temperature (e.g. 40°C).
Using
Water volume required = (50,000 Btu/hr / 10,000)
= 125 litres
At 7 can m th 11)
v
1
= 0.001 m
3
/kg
At 40°C, the specific
m
3
/kg
Use the pressure P
2
equivalent to the pressure relief valve setting, e.g. 300 kPa.
Use the pressure P
1
as the positive pressure at the point of installation, e.g. 80 kPa.
Therefore,
= 12
= 1.17 litres
taking into account a 20% safety factor)
s, using a 2 litres expansion tank will suffice for the above operation
(0.001008/0.001) - 1] - (3*11.7*10
-6
)(40-7)
t
5
V
[
1-(80/300)
]
(1.4 litres,
Thu
Section 6 Page 91
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