Suggestion for chilled water line.....

[Bashir01219]

We are installing a new Air Handling Unit, and chiller pipeline distance is nearly 50 mtr. The chilled water unit is in 6th floor and the AHU is in ground floor. We are using two chilled water circulation pump max. head 38 mtr. & volumetric flow rate at that head is 20 m3/hr.
My question is what are the probable problems with this scenario, if we run the system.
AHU capacity is 9000 cfm, and chilled water temp required 6.5 to 12 deg. C, no flow rate is mentioned.

[nike123]

We are installing a new Air Handling Unit, and chiller pipeline distance is nearly 50 mtr. The chilled water unit is in 6th floor and the AHU is in ground floor. We are using two chilled water circulation pump max. head 38 mtr. & volumetric flow rate at that head is 20 m3/hr.
My question is what are the probable problems with this scenario, if we run the system.
AHU capacity is 9000 cfm, and chilled water temp required 6.5 to 12 deg. C, no flow rate is mentioned.

What is required cooling capacity of AHU or what is model make and model#?
Whit that flow and delta t capacity of AHU should be around 130 kW

[Bashir01219]

Model: CARYAIRE CDS 100
Pre/Post Cooling Coil: 14 / 22 TR
Power Consumption: 57 Kw

[nike123]

Model: CARYAIRE CDS 100
Pre/Post Cooling Coil: 14 / 22 TR
Power Consumption: 57 Kw

14+22 TR = 126,6 kW
To me, it looks OK, if your actual flow is as it is calculated.

[Bashir01219]

Sir,
Plz make it clear to me.
i undesrstand nothing...

[nike123]

Sir,
Plz make it clear to me.
i undesrstand nothing...

You gave us volumetric flow and temperatures of water. From that we could calculate actual capacity transfered in pipes if they are having that flow and that temperatures at inlet and outlet of chiller.

1 m^3 of water is ~1000 kg of water.

Q=m*c*(T2-T1)
Where
Q= Heating/cooling energy in Wh
m=mass of water in kg
c= specific capacity of water in Wh/(kg*K) => 1,163
T1= Water inlet temperature 6,5°C
T2= Water outlet temperature 12°C

In your case:
Q=20000*1,163*(12-6,5)=127930Wh Or 127,93 KWh of energy transferred thru that pipes in 1 hour.
That require chiller of 127 KW of cooling capacity and same capacity water-to-air coil (if we ignore heat loss/gains in pipes).
Since you mentioned that your AHU has 14 and 22 TR coils, that converted to kW is 49kW and 77kW, witch in sum is 36TR or127kW of cooling capacity and which is matched to that water flow.

Now you only need to ensure that pipeline and pumps are dimensioned right to achieve that water flow, and that you have chiller of required capacity.

Since your pumps have 20m^3 flow at "max" head of 38 meters of water column (although pump max head is when there is no flow at all, but I presumed that you picked some operational point of pump at max speed which correspond to pressure losses in your piping and coils,and chiler HE) that mean that your chilled water lines are OK (if my presumption is right).
Therefore I wrote:

To me, it looks OK, if your actual flow is as it is calculated.

[Bashir01219]

Sir,
i am really greatfull to you.
Lots of questions.......
How can u assume m=20000kg ?
14TR=49kw how?
And AHU required chilled water temperature in between 6.5 to 12 deg C, so is it correct T2=12 and T1=6.5
Last question, if we use a chiller of 46 Ton, is it possible to run the system?
if yes then how?
Again lots of thanks.............

[nike123]

Sir,
i am really greatfull to you.
Lots of questions.......
How can u assume m=20000kg ?

Density of water at 5°C = 1000 kg/m3
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

20m^3= 20*1000 =20000 kg


14TR=49kw how?1TR=> 1 "ton (http://en.wikipedia.org/wiki/Ton) of cooling", a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h. It is the amount of power needed to melt one short ton (http://en.wikipedia.org/wiki/Short_ton) of ice in 24 hours, and is approximately 3,51 kW.

14TR= 14+3,51=49,14 kW





And AHU required chilled water temperature in between 6.5 to 12 deg C, so is it correct T2=12 and T1=6.5It is correct. That temperature is not in between! As cool water of 6,5°C enters heat exchanger of AHU it is heated by heat from air and its temperature rise. When water reach exit of heat exchanger it is heated at 12°C.That is required inlet and outlet temperature for AHU in order that AHU have nominal capacity as stated at nameplate.



Last question, if we use a chiller of 46 Ton, is it possible to run the system?Yes it is!


if yes then how?

Some small portion of power will be lost in pipeline.
You will need chiller tank with properly sized volume to prevent short-cycling.
http://www.mechanicalconceptsllc.com/downloads/Chiller%20Storage%20Tank%20Sizing%20-%202-20-9.xls

[Bashir01219]

Density of water at 5°C = 1000 kg/m3
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

20m^3= 20*1000 =20000 kg

1TR=> 1 "ton (http://en.wikipedia.org/wiki/Ton) of cooling", a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h. It is the amount of power needed to melt one short ton (http://en.wikipedia.org/wiki/Short_ton) of ice in 24 hours, and is approximately 3,51 kW.

14TR= 14+3,51=49,14 kW




It is correct. That temperature is not in between! As cool water of 6,5°C enters heat exchanger of AHU it is heated by heat from air and its temperature rise. When water reach exit of heat exchanger it is heated at 12°C.That is required inlet and outlet temperature for AHU in order that AHU have nominal capacity as stated at nameplate.


Yes it is!



Some small portion of power will be lost in pipeline.
You will need chiller tank with properly sized volume to prevent short-cycling.
http://www.mechanicalconceptsllc.com/downloads/Chiller%20Storage%20Tank%20Sizing%20-%202-20-9.xls
Sir,
Thanks a lot for your informative answer......

I need more clarification.
We have three AHU Cooling load = 39 Kw, 147 Kw, 144 kw (3000+10000+15000 m3/hr)
So total cooling load = 330 kw, if we convert it into TR so it becomes = 330/3.51=94 Ton
So, we need a chiller of 90Ton capacity, am I right?
If I am not right then why?

Another Question:
AHU2 Specification: Air vol.= 10000 m3/h, fan model: KHF - 450, fan total pressure -900 pa, cooling load: 147 kw , heating capacity: 50 kw.
AHU3 Specification: Air vol.= 15000 m3/h, fan model: KHF - 500, fan total pressure -900 pa, cooling load: 144 kw , heating capacity: 100 kw
For AHU3 Air volume is higher then AHU2 but cooling load is low, why? Is it for heating capacity?

[Aik]

Sir,

I need more clarification.
We have three AHU Cooling load = 39 Kw, 147 Kw, 144 kw (3000+10000+15000 m3/hr)
So total cooling load = 330 kw, if we convert it into TR so it becomes = 330/3.51=94 Ton
So, we need a chiller of 90Ton capacity, am I right?
If I am not right then why?

It depends on how much consumers there are in system and how much consumers work at the same time. If I understand correctly you want use one chiller? Or you want use three chillers?
I agree with nike123 that you will need chiller tank in any case.

For AHU3 Air volume is higher then AHU2 but cooling load is low, why?
May be the surface of condenser is smaller.

[Sridhar1312]

20000 x(12-6.5)/3024 = 36.37 TR is the AHU capacity.

Why 38 M head is not clear then the flow may increase in reality as 6th floor means 6 x 4 M per floor 24 meters and From chiller to AHU and ahu to chiller static heights gets nullified in reality only the pressure drop in the AHU, Chiller and Friction loss shall be on the PUMP.
To me the chilled water pump head is over sized.
This pump is from Chiller or from Tank? is it feeding only to this AHU please check and revert.

[Bashir01219]

It depends on how much consumers there are in system and how much consumers work at the same time. If I understand correctly you want use one chiller? Or you want use three chillers?
I agree with nike123 that you will need chiller tank in any case.

May be the surface of condenser is smaller.
All the 03 chillers are for one floor, so we need to run all the system at a time, and we are using one chiler (capacity 90 Ton).
My question is how much surplus we have?

[Bashir01219]

20000 x(12-6.5)/3024 = 36.37 TR is the AHU capacity.

Why 38 M head is not clear then the flow may increase in reality as 6th floor means 6 x 4 M per floor 24 meters and From chiller to AHU and ahu to chiller static heights gets nullified in reality only the pressure drop in the AHU, Chiller and Friction loss shall be on the PUMP.
To me the chilled water pump head is over sized.
This pump is from Chiller or from Tank? is it feeding only to this AHU please check and revert.
If our pump head is over sized what will be the problems?
The pump is only for chilled water circulation, and we have chilled water pump suction and discharge head where the entire pipe is linked and no chilled water Tank!
What are the benefits of chilled water tank?
It’s a closed loop & we provide water make-up tank…

[Bashir01219]

Density of water at 5°C = 1000 kg/m3
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

20m^3= 20*1000 =20000 kg

1TR=> 1 "ton (http://en.wikipedia.org/wiki/Ton) of cooling", a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h. It is the amount of power needed to melt one short ton (http://en.wikipedia.org/wiki/Short_ton) of ice in 24 hours, and is approximately 3,51 kW.

14TR= 14+3,51=49,14 kW




It is correct. That temperature is not in between! As cool water of 6,5°C enters heat exchanger of AHU it is heated by heat from air and its temperature rise. When water reach exit of heat exchanger it is heated at 12°C.That is required inlet and outlet temperature for AHU in order that AHU have nominal capacity as stated at nameplate.


Yes it is!



Some small portion of power will be lost in pipeline.
You will need chiller tank with properly sized volume to prevent short-cycling.
http://www.mechanicalconceptsllc.com/downloads/Chiller%20Storage%20Tank%20Sizing%20-%202-20-9.xls
Sir,
I am still waiting for your answer?

[nike123]

Sir,
Thanks a lot for your informative answer......

I need more clarification.
We have three AHU Cooling load = 39 Kw, 147 Kw, 144 kw (3000+10000+15000 m3/hr)
So total cooling load = 330 kw, if we convert it into TR so it becomes = 330/3.51=94 Ton
So, we need a chiller of 90Ton capacity, am I right?
If I am not right then why?


You are right. Actually, you need chiller of 94 TR or more, if they all work in same time.


Another Question:
AHU2 Specification: Air vol.= 10000 m3/h, fan model: KHF - 450, fan total pressure -900 pa, cooling load: 147 kw , heating capacity: 50 kw.
AHU3 Specification: Air vol.= 15000 m3/h, fan model: KHF - 500, fan total pressure -900 pa, cooling load: 144 kw , heating capacity: 100 kw
For AHU3 Air volume is higher then AHU2 but cooling load is low, why? Is it for heating capacity?Nominal air flow for general purpose of air-conditioning is 350 to 450 CFM per 1 TR (175-215 m^3/h).

If your data about capacity is right, first unit of 10000 m^3/h is probably for dehumidification purpose or your AHU is designed for 100% fresh air of high temperature and humidity.

10000/200=50kW

How did you come to cooling capacities of AHU.

[nike123]

If our pump head is over sized what will be the problems?

If your pump head is over sized you have inefficient pumping (high energy consumption of pump) and flow would be to high. You can limit flow with some gate valve (by adding restriction) but pump will still be inefficient.


The pump is only for chilled water circulation, and we have chilled water pump suction and discharge head where the entire pipe is linked and no chilled water Tank!
If total water volume of system is big enough, you don't need tank. Since that is chiller and AHU setup, I prety much doubt that you have enough volume, and you need chiller with capacity regulation or/and with tank.


What are the benefits of chilled water tank?
It’s a closed loop & we provide water make-up tank…http://www.gorhamschaffler.com/ChillerLoopVolume.html

[Bashir01219]

If your pump head is over sized you have inefficient pumping (high energy consumption of pump) and flow would be to high. You can limit flow with some gate valve (by adding restriction) but pump will still be inefficient.
If total water volume of system is big enough, you don't need tank. Since that is chiller and AHU setup, I prety much doubt that you have enough volume, and you need chiller with capacity regulation or/and with tank.
http://www.gorhamschaffler.com/ChillerLoopVolume.html
That is an amusing attachment, it helped me lot and now its clear to me what were our problem, we fill the problem but without logic!
If we want to installed three or four chiller (total capacity: 180 Ton) all in a row and all the chilled water inlet & outlet pipe is summarized in pump suction and discharge header , is there any problem?
And we want to distributed the chilled water from that discharge header to all the AHU, FCU.

[Aik]

If we want to installed three or four chiller (total capacity: 180 Ton) all in a row and all the chilled water inlet & outlet pipe is summarized in pump suction and discharge header , is there any problem?


The chillers will dress in parallel or in in series?
In any case I suppose it's bad idea even from the point of view of automatic administration.

[Bashir01219]

The chillers will dress in parallel or in in series?
In any case I suppose it's bad idea even from the point of view of automatic administration.
series or parallel same thing.......
main thing is all the chilled water accumulating in the same header and then distribuiting, so what are the problems may occure?
its a closed loop.

[nike123]

series or parallel same thing.......
main thing is all the chilled water accumulating in the same header and then distribuiting, so what are the problems may occure?
its a closed loop.

It is not same thing!
If they are parallel, than flow must be balanced in effort to every chiller has nominal flow.
If they are in series, you will be having same flow on every chiller, which is not good, and you will be having high total temperature difference, because each chiller will be cooling water from previous chiller.

Therefore, they must be parallel.

Regarding balancing (and ensuring proper flow in each element of instalation), you should use dedicated pump for each chiller, and dedicated pump for each AHU, and all circuits connected in one vessel (hydraulic separator and buffer tank) like this one:
http://www.cemline.com/products/steeltank/sebmenu.asp

Similar use as in this project:
http://www.mediafire.com/?zdunyzytjqr

Or, you could use separate chillers of matching sizes to AHU, and separate pump for each AHU/chiller combination, on separate circuits.

[Aik]

Therefore they must be parallel.


And make proper automation: determine when each chiller will start/stop to provide the same working time.

[Sridhar1312]

From the communication it looks like there are three chillers each of 90 TR capacity. Please let us know how many air handling units are connected to the chillers.
If you are talking of only one Air handling units which is of 36 TR and if you are operating one chiller (90 -{36+Line losses) say around 50 TR is surplus.
Even if you have three chillers the pressure drop shall be taken for longest path and the friction drop due to water flow , pressure drop in chiller and pressure drop in AHU cooling Coil.

If your requirement of chilled water is intermittent it is better to have common tank with partition making hot well and cold well. The chilled water from Hotwell to Chiller will return to cold well and secondary pump from cold well to AHU, and other down stream equipments where chilled water is circulated and returns to Hotwell. Normally Hot well Tank is 1/3 and cold well is two third size of the total requirement. The Total tank capacity can be 3 to 5 minutes chilled water circulation.
Your question is not complete and is not giving full details to enable any one to give you the solution or correct lead.

Pump Head- Please go through the Priciples of Rfefrigeration by Roy J. Dossat and understand the sizing of the pumps. 38 meter head is too much and the real head may not be available making the pump operate with high discharge of flow which will increase velocity in the chiller and erosion may take place.

[Bashir01219]

From the communication it looks like there are three chillers each of 90 TR capacity. Please let us know how many air handling units are connected to the chillers.
If you are talking of only one Air handling units which is of 36 TR and if you are operating one chiller (90 -{36+Line losses) say around 50 TR is surplus.
Even if you have three chillers the pressure drop shall be taken for longest path and the friction drop due to water flow , pressure drop in chiller and pressure drop in AHU cooling Coil.

If your requirement of chilled water is intermittent it is better to have common tank with partition making hot well and cold well. The chilled water from Hotwell to Chiller will return to cold well and secondary pump from cold well to AHU, and other down stream equipments where chilled water is circulated and returns to Hotwell. Normally Hot well Tank is 1/3 and cold well is two third size of the total requirement. The Total tank capacity can be 3 to 5 minutes chilled water circulation.
Your question is not complete and is not giving full details to enable any one to give you the solution or correct lead.

Pump Head- Please go through the Priciples of Rfefrigeration by Roy J. Dossat and understand the sizing of the pumps. 38 meter head is too much and the real head may not be available making the pump operate with high discharge of flow which will increase velocity in the chiller and erosion may take place.
Things are become complex to me……..
Let it simple. We have three (3) chillers, capacity: 90+46+40 Ton. One in 6th floor and rest of two are in first floor, and we are facing problem with this 1st floor chiller because chiller position is not good and performance is poor. Evaporator fines become jammed every single day as garments factory is just beside it. Now we have no way to shift this two chillers to 6th floor, it’s a running plant and we have not enough time to think about it. Basically we work for Radiant + Roche Pharmaceuticals, the chilled water installer use three pump in each unit, two for running and one for spare, they run the two pump and objective of this two pump is maintain suction & discharge header, all the supply and return is connected with this.
Previously under 90 ton chiller we have three AHU (total cooling load is 330 kw, but all the AHU is oversized, and RH range is 40 to 60, so we think there is some surplusir because we can control the air volume & air change rate is quite high nearly 25 but we need just 10 to 12!, ). And under 86 ton chillers we have 1 AHU (capacity 9000 cfm & RH 30 to 40 %), 5 FCU (5300 cmh, 3300 cmh, 3300 cmh, 1300 cmh, 2300 cmh).
Now we are trying to place all the chillers in parallels in 6th floor which will operate with two pump, suction & discharge header, single pump unit will control all the AHU, FCU, is their any simple solution for us?
I dont think so!
Thanks all of my Sir for their help.................

[Bashir01219]

i am little confused!
no one is answering, because?
a) my problem is big or
b) my mail is big.

In Bangladesh & many others country use the same way what we are using..............

[nike123]

i am little confused!
no one is answering, because?
a) my problem is big or
b) my mail is big.

In Bangladesh & many others country use the same way what we are using..............
Bashir, you need to learn to be patient! We are not service for your needs. We simply want to help, but after we deal with our jobs and our obligations.:eek:

[Bashir01219]

Bashir, you need to learn to be patient! We are not service for your needs. We simply want to help, but after we deal with our jobs and our obligations.:eek:
Thanks Sir,
I can understand....

[nike123]

There is no simple solution. Chilers are primary side and AHU-s are secondary side. Each chiller need proper flow to operate and AHU-s needs different flows to operate.
As I described, on secondary side, for each AHU you need separate pump or you need common pump with speed regulation or head control and balancing valves for establishing proper flow.

[Bashir01219]

There is no simple solution. Chilers are primary side and AHU-s are secondary side. Each chiller need proper flow to operate and AHU-s needs different flows to operate.
As I described, on secondary side, for each AHU you need separate pump or you need common pump with speed regulation or head control and balancing valves for establishing proper flow.
Sir,
Thanks for your suggestion.
We have separate flow control valve for each unit, and we setup the system with trial and error basis.
How can we calculate how much flow rate and pressure needed for a particular AHU or FCU or chiller unit, I didn’t find anything fro the manuals? If their any calculation?

[nike123]

[
quote=Bashir01219;188973]Sir,
Thanks for your suggestion.
We have separate flow control valve for each unit, and we setup the system with trial and error basis.
How can we calculate how much flow rate

Q=m*c*(T2-T1)
Where
Q= Heating/cooling energy in Wh
m=mass of water in kg
c= specific capacity of water in Wh/(kg*K) => 1,163
T1= Water inlet temperature 6,5°C
T2= Water outlet temperature 12°Cm=Q/(c*(T2-T1))
Flow is:
qv=qm/ρ

Where:
qv= volume flow
qm= mass flow
ρ= density of fluid


and pressure needed for a particular AHU or FCU or chiller unit, I didn’t find anything fro the manuals? If their any calculation? If by pressure you mean pump head than you need to know that when pump circulate fluid, there is friction. Friction mean pressure drop and pump need to overcome that pressure drop to establish required flow rate.
For that calculation you need software like Pipe flow (http://www.pipeflow.co.uk/public/control.php) or simmilar, or you need engineer with knowledge for calculation of pipe diameters and pump characteristics.

http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm

[Bashir01219]

[m=Q/(c*(T2-T1))
Flow is:
qv=qm/ρ

Where:
qv= volume flow
qm= mass flow
ρ= density of fluid

If by pressure you mean pump head than you need to know that when pump circulate fluid, there is friction. Friction mean pressure drop and pump need to overcome that pressure drop to establish required flow rate.
For that calculation you need software like Pipe flow (http://www.pipeflow.co.uk/public/control.php) or simmilar, or you need engineer with knowledge for calculation of pipe diameters and pump characteristics.

http://www.efunda.com/formulae/fluids/calc_pipe_friction.cfm

Sir,
Again thanks a lot.....
But Sir most of the AHU did'nt have any Recommended T1 & T2 value, can we get the value from chilled water inlet & outlet water temp. gauge ?
What is the standerd pressure drop through Chiller HE?
If HE water inlet pressure is too high then what problems may arise?
I observe that when we installd chillers in parallel we found that all the chillers not performing similarly, i mean some are getting more load then others, whats are the reason............

[nike123]

Sir,
Again thanks a lot.....
But Sir most of the AHU did'nt have any Recommended T1 & T2 value, can we get the value from chilled water inlet & outlet water temp. gauge ?

Since air is what gives heat to water in AHU you need first corect air flow which is around 200m^3/hr per 1kW of AHU capacity (if used for normal operation).
Since latent heat is gained also from condensation of moisture in air that flow is not necessary as I mentioned above if coil has function as dehumidifier.
Than you need to ensure proper heat transfer from air/condensed-water-from-air to water in heat exchanger which is present when water leaving temperature is 5K above water entering temperature (for cooling).
Generally, in air conditioning, these temperatures are 7°C and 12°C respectively.
Answer to your question above is:


Recommended T2 and T1 value depend on application but usual T2-T1 value is 5K
You cannot get recommended value by measuring actual T2-T1



What is the standerd pressure drop through Chiller HE?There is no standard pressure drop. Pressure drop is known in manufacturer literature and it depend on water flow thru AHU.
Every manufacturer gives chart or table about recommended, minimum maximum flow and pressure drop-flow relation



If HE water inlet pressure is too high then what problems may arise?To much head mean high flow which mean loss in efectivness of heat ransfer in HE and high pump energy consumption=> Low plant COP, possible cavitation, high pressure loss on components high noise in pipes etc...



Originally Posted by Bashir01219 http://www.refrigeration-engineer.com/forums/images/VA_RE/buttons/viewpost.gif (http://www.refrigeration-engineer.com/forums/showthread.php?p=187918#post187918)
If our pump head is over sized what will be the problems?
If your pump head is over sized you have inefficient pumping (high energy consumption of pump) and flow would be to high. You can limit flow with some gate valve (by adding restriction) but pump will still be inefficient.

I observe that when we installd chillers in parallel we found that all the chillers not performing similarly, i mean some are getting more load then others, whats are the reason............

There is no simple solution. Chilers are primary side and AHU-s are secondary side. Each chiller need proper flow to operate and

[Bashir01219]

Since air is what gives heat to water in AHU you need first corect air flow which is around 200m^3/hr per 1kW of AHU capacity (if used for normal operation).
Since latent heat is gained also from condensation of moisture in air that flow is not necessary as I mentioned above if coil has function as dehumidifier.
Than you need to ensure proper heat transfer from air/condensed-water-from-air to water in heat exchanger which is present when water leaving temperature is 5K above water entering temperature (for cooling).
Generally, in air conditioning, these temperatures are 7°C and 12°C respectively.
Answer to your question above is:


Recommended T2 and T1 value depend on application but usual T2-T1 value is 5K
You cannot get recommended value by measuring actual T2-T1

There is no standard pressure drop. Pressure drop is known in manufacturer literature and it depend on water flow thru AHU.
Every manufacturer gives chart or table about recommended, minimum maximum flow and pressure drop-flow relation


To much head mean high flow which mean loss in efectivness of heat ransfer in HE and high pump energy consumption=> Low plant COP, possible cavitation, high pressure loss on components high noise in pipes etc...
Thanks Sir,
Now i need to sumarized all this thing.!