Hi all ,

I am new to this site...

Could you please some one help me out to locate 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

I would appreciate the earliest response

Thanks & Regards

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 don't 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

Thanks caibuadday...

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

Any more suggestion...

I would appreciate your reply

Thanks & Regards

this is the formular for sizing expansion tank

Vt =[ (0.00041T - 0.0466) Vs] / [ (Ha/Ht) - (Ha/Ho)]

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

Thanks caibuadday...

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...

Quote:

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Originally Posted by anvarpb

Thanks caibuadday...

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..............

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they are about the same, don't 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

Hi ,
I am following up this topic and intersted to know what is the best location of the pressurization unit in the chilled water loop
Thanks

Quote:

---

Originally Posted by mias3525

Hi ,
I am following up this topic and intersted to know what is the best location of the pressurization unit in the chilled water loop
Thanx

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As high as possible, indoor ,where you could inspect it, not inside ceiling

How can I calculate the expansion tank in the closed loop of chilled water system?

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

You can locate pressurisation unit anywhere you want. If your chiller and pumps are located on level 0 than locating the pressurisation unit at highest level will make it smaller and cheaper than if you locate it on level 0. However bare in mind that it might not be feasible to locate pressurisation unit at highest level (no plantrooms).

Cut in and out points will depend on pressure in piping that you want to keep. When pumps are not operating the pressure in piping should be above atmospheric (positive gauge) at all points of the system to prevent air infiltration. Typically you need around 30 kPa positive pressure.

ASHRAE formulas are OK. For sizing

Chilled water is closed system so pumps should be sized for pressure loss through piping, coils and fittings only!! Not for static head.

Location of the pressurisation unit has nothing to do with pump selection. Pumps will be the same wherever you put your pressurisation unit.


Let me know if you need more help

How to calculate the head and flow for chilled pumps primary & secondary?

Dear kdagencies,

Appreciate your answer.
What about the flow rate capacity of the pressurization pump?

To anvarpb,
What is the Q in your equation above?
Is it the sensible heat you mean?

Hope to hear you soon.
This is a good thread to share ideas.

I was following above questions. Can anybody tell me what will be the pressure at the highest / top level of the building?

I like to add a smole correction for this. If consider the pump head as same as the hight of the building you will never reach to the top. First calculate the head loss of the piping arrangement and add that to this. That is your pump head. But do not forget to keep the safety factor.

Hi
And also for calculating open exp. Tank volume you can use below eq.

V = 1.5 x ( Q / 1000)
Q = boiler heat Capacity, Kcal/hr
V = open exp. Tank volume, Lit.

Salam
This is a common problem in New Dubai
Was sudden District Cooling become the favorite choice for newly developed towers because of more investment advantages?
However
Observations:
* Secondary chilled water pumps are at full speed (VFD) and sometimes even stand-by pump is on.
* Lower floors tenant are paying high energy (BTU Meter) Bills.
* Higher floors are not getting enough cooling.
* When humidity level rise, condensation & fungus will hit the tower.
* DC-Provider is not satisfied of less cooling consumption
Reasons:
* Form of air pockets.
* Wrong location of Chilled Water Pump
* Wrong location of make-up pressurization pumps
* Using bad quality of Air Vent Valves
* Unbalanced chilled water system (Can't be balanced as it is)
* DC-Provider control the flow depending on Temp. Diff, while tower control's flow depending on Pressure, no integration or communication between both systems
For Corrective Action & Solution
Please send me your e-mail so I will send you a presentation
Thanks
Eng. Juma Yousef
Getco-Green Earth Technology Co.
+971-50-4948385
[email protected]

Dear Caibuadday,

In a chilled water system (primary secondary and tertiary pumps with chillers), how to determine the maximum allowable pressure at the pressurozation unit to use in the calculation it is too much confusing and not clear for chilled water system.

And if the pressurization unit is installed at the suction of the pump how it keeps the pressure constant at this point? In other way if we install the pressure unit at the discharge side of the pump why negative pressure will come at the suction?

I wish your supportive answer since no one is able to answer me and even in the BS and ashrae these 2 points not clear.

Thank You so much!

Quote:

---

Originally Posted by dulenz

You can locate pressurisation unit anywhere you want. If your chiller and pumps are located on level 0 than locating the pressurisation unit at highest level will make it smaller and cheaper than if you locate it on level 0. However bare in mind that it might not be feasible to locate pressurisation unit at highest level (no plantrooms).

Cut in and out points will depend on pressure in piping that you want to keep. When pumps are not operating the pressure in piping should be above atmospheric (positive gauge) at all points of the system to prevent air infiltration. Typically you need around 30 kPa positive pressure.

ASHRAE formulas are ok. For sizing

Chilled water is closed system so pumps should be sized for pressure loss through piping, coils and fittings only! Not for static head.

Location of the pressurisation unit has nothing to do with pump selection. Pumps will be the same wherever you put your pressurisation unit.


Let me know if you need more help

---

Dear Dulenz,

In a chilled water system (primary secondary and tertiary pumps with chillers), how to determine the maximum allowable pressure at the pressurozation unit to use in the calculation it is too much confusing and not clear for chilled water system.

And if the pressurization unit is installed at the suction of the pump how it keeps the pressure constant at this point? In other way if we install the pressure unit at the discharge side of the pump why negative pressure will come at the suction?

I wish your supportive answer since no one is able to answer me and even in the BS and ashrae these 2 points not clear.

Thank You so much!