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closed loop Chilled water system - pressurisation units
Hi all ,
I am new to this site...
Could you please some one help me out to locate the the pressurization unit for a chilled water system application in 120m tower building. The heat exchangers/CHW pumps are located at 0.0 level...System volume is about 35-40 m3 and pump head is around 4 bar...
What is the ideal position of pressurization units... and what would be cut in & cut out pressure settings for the unit..I would appreciate if you can give the selections too
you have a building 120m H (~400 ft), pump's head 4 bar ( 1 bar = 1 atmosphere= 14.7 psi)
to pump up 400ft (120M) we need at least 173 psi, 4 bar = 58.8 psi, the pump only pump up 1/3, not enough pressure. where is the heigthest coil; the supply should be at least 10 psi, you need at least 181 psi
you mention the heat exchange. so you dont have a chiller??, you could control temp/ press with combination of pump (VFD) and auto valve..... there is no cutin/out the pump always run ,unless cooling not required...... as with chiller: first you put on the pumps, fan then chiller, shut off chiller then fan and pumps..... if the chiller is running without the pumps on it probadly end up in the dumpster
But.... Since the chilled water system in the question is of closed loop type , to my knowledge, I do not have to worry about the static head...
As you said I need a temperary pump of the capacity 173 psi for the initial filling purpose only ( During filling its an open system )
. Once the system is filled with the chemically treated water and fully closed( to resist the corrossion), only friction losses of pipes, fittings, valves, p.d across the coil of the farthest terminal unit, heat exchanger p.d etc... only exist..
To cater that I require a pump of the capacity( m = Q / Cp * delta T ) where m is the flow rate, Cp specific heat capacity, delta T Temperature change...and head of 4.5 bar (which is the total friction loss+p.d across coil and heat exchanger).
My question was regarding the pressurisation unit/expansion vessel location and its capacities to take care of any water leakages/ volume changes due to the variation of temperature of water in the system...
The system in the question is of district cooling type..so i don't have chillers ........
District cooling incoming temp 4.5 deg C , Return Temp 13.5 deg C
Building side Supply Temp 5.5 deg C Return temp 14.5 deg C
Vt = required tank vol
Vs= total vol of system, gallon
T= design average temp, F degree
Ha= atmospheric press absolute,== 34 ft
Ht= min press at tank, equal to the fill press plus static press at tank , ft of water plus absolute (34)
Ho= max press at tank, ft of plus absolute (34)
re check your total system vol with pump's flow rate formular
a water columne of 120 M heigth would have a press of 173 psi, in order for the water to reach the top of the building your pump need to put out at least 173 psi.
the person did your building peak cooling load calculation and/ or sizing your pump should be able to help you size the tank
I have used this equation for the expansion tank sizing.............
A) Expansion Tank Sizing Based on ASHRAE Systems and Equipment Handbook Chapter 12
Vt=Vs((v2/v1)-1)-3£Λt
1-(P1/P2)
Where :
Vt= Volume of expansion tank, m3
Vs= Volume of water in system, m3
t1= lower temperature, ̊ C, chilled water leaving temp
t1= higher temperature, ̊ C, ambient temperature
Pa= atmospheric pressure , kPa
P1= pressure at lower temperature, kPa (Design Fill Pressure -Static Head+28 kPa)
Pa= pressure at higher temperature, kPa
v1= specific volume at lower temperature, m3/kg
v2= specific volume at higher temperature, m3/kg
£=linear cofficient of thermal expansion of steel
Λt=(t2-t1)
Static Head = in Kpa
Thnaks..............
I have used this equation for the expansion tank sizing.............
A) Expansion Tank Sizing Based on ASHRAE Systems and Equipment Handbook Chapter 12
Vt=Vs((v2/v1)-1)-3£Λt
1-(P1/P2)
Where :
Vt= Volume of expansion tank, m3
Vs= Volume of water in system, m3
t1= lower temperature, ̊ C, chilled water leaving temp
t1= higher temperature, ̊ C, ambient temperature
Pa= atmospheric pressure , kPa
P1= pressure at lower temperature, kPa (Design Fill Pressure -Static Head+28 kPa)
Pa= pressure at higher temperature, kPa
v1= specific volume at lower temperature, m3/kg
v2= specific volume at higher temperature, m3/kg
£=linear cofficient of thermal expansion of steel
Λt=(t2-t1)
Static Head = in Kpa
Thnaks..............
they are about the same, dont forget in the metric system the total absolute press is about 14.4 psi, its actual 14.7....... pick the size of the tank equal to the result or next size Up
guoc luck
Dear All,
I have been seeing the mails on this topic. Following are my suggestions;
If the pressurisation unit is located on the terrace, pump of the pressurisation unit will not have to work against the total static head, resulting in smaller size pump. If you keep the unit at ground level, the pump will have to overcome the static to push water in the circuit. Pump in this case will become multistage & H.P. will go up.
For expansion tank sizing also the static plays important part. If the tank is on terrace, the size would be smaller. If kept of ground level, the size will go up substantially.
Please let me know if anything else is required on this topic.
DILIP DATEY
Linear Mode
