Calculating the kw of a room

[marc5180]

Hi all, i have been asked a question on what kw would be needed for a room of 5m wide x 8 m long and 4m high.

The room would be used as a cold store which would need to be cooled to 10DegC. There would be around 8000 litres of liquid stored in stainless steel vats.

How would i go about calculating would size unit he would need.

I would ask my college tutor but i wont see him for another week.
Thanks

[frank]

Hi Marc

Quite a complicated calculation for the uninitiated.

The following are some of the things you need to know before you can start the calculation.

SHC of the liquid to be cooled
Time scale for the cooling process
Delivery temperature
Final temp (10C you say)
U values of the room materials
Temperatures on other side of the room
External walls or internal walls
Refrigerant to to be used (evaporating temp)
Internal lighting?
Fork trucks?
Personnel?
Infiltration

Can you provide any of these?

[superswill]

try these past links

http://www.refrigeration-engineer.com/forums/showthread.php?t=5691

http://www.refrigeration-engineer.com/forums/showthread.php?t=5469

doesn't cool pack size cold rooms?

[marc5180]

ok, i will try

SHC of the liquid to be cooled.
Not sure what this is?

Time scale for the cooling process..
between 1 - 2 hours

Delivery temperature.
Around the 20degC mark

Final temp (10C you say)
yes needs to be kept around 10degc

U values of the room materials.
The 4 walls will be made of brick so (0.56 W/m·K)??

Temperatures on other side of the room
On the 3 sides of the room there will be offices,
On the fourth side is a brew house which will have variable temperatures max 25DegC

External walls or internal walls
Internal walls

Refrigerant to to be used (evaporating temp)
Again i don't know, possibly R404a?

Internal lighting?
Lights will be off when the room is empty, so no

Fork trucks?
Personnel?
Infiltration

None of the above.

The room is to be used as a cooling room for conditioning beer.

[taz24]

ok, i will try

SHC of the liquid to be cooled.
Not sure what this is?

Time scale for the cooling process..
between 1 - 2 hours

Delivery temperature.
Around the 20degC mark

Final temp (10C you say)
yes needs to be kept around 10degc

U values of the room materials.
The 4 walls will be made of brick so (0.56 W/m·K)??

Temperatures on other side of the room
On the 3 sides of the room there will be offices,
On the fourth side is a brew house which will have variable temperatures max 25DegC

External walls or internal walls
Internal walls

Refrigerant to to be used (evaporating temp)
Again i don't know, possibly R404a?

Internal lighting?
Lights will be off when the room is empty, so no

Fork trucks?
Personnel?
Infiltration

None of the above.

The room is to be used as a cooling room for conditioning beer.


A few other things to know.

What is the floor and ceiling insulation value.

The biggest factor I see is you say the liquid will be cooled by 10 degrees in 2 hours and there is 8000 ltrs.

8000 ltrs is 8000Kg or 8 metric tonne. In 2 hours, 10 degrees of cooling is a colossal amount of heat to be removed and the equipment will be large.

Have you considered a heat exchanger to cool the ilquid directly and then put it in the vats to be kept at 10c in the room.

Cheers taz.

.

[marc5180]

A few other things to know.

What is the floor and ceiling insulation value.

The biggest factor I see is you say the liquid will be cooled by 10 degrees in 2 hours and there is 8000 ltrs.

8000 ltrs is 8000Kg or 8 metric tonne. In 2 hours, 10 degrees of cooling is a colossal amount of heat to be removed and the equipment will be large.

Have you considered a heat exchanger to cool the ilquid directly and then put it in the vats to be kept at 10c in the room.

Cheers taz.

.
Hi Taz, before the beer enters the room where it is 20 degC it will already have been put through a heat exchanger lowering the temp from around 65DegC.

He has been told that there is something that could be designed for him purely for chilling the vats instead of the whole room using glycol and a very small chilled water plant? Surely this will be very expensive though compared to a cellar cooler.

[Toosh]

Hi Mark, SHC is the specific heat of the cooling median

[taz24]

Hi Taz, before the beer enters the room where it is 20 degC it will already have been put through a heat exchanger lowering the temp from around 65DegC.

He has been told that there is something that could be designed for him purely for chilling the vats instead of the whole room using glycol and a very small chilled water plant? Surely this will be very expensive though compared to a cellar cooler.


If the beer is being cooled to 20c why can't it be cooled to 10c?

Beer can be treated as water when cooling and the cooling effect of 8000Kg of water by 10 deg in 2 hours without direct contact will be near impossible or require such a hugh system as to make it unviable.

Just treat the beer as water and do the calcs I bet you will be suprised at the work the system will have to do.

taz.

.

[nike123]

For cooling 8000L of beer at 20°C to 10 °C in two hours it is needed about 60kW of cooling capacity.

[marc5180]

If the beer is being cooled to 20c why can't it be cooled to 10c?

Beer can be treated as water when cooling and the cooling effect of 8000Kg of water by 10 deg in 2 hours without direct contact will be near impossible or require such a hugh system as to make it unviable.

Just treat the beer as water and do the calcs I bet you will be suprised at the work the system will have to do.

taz.

.

So are you suggesting another heat exchanger or larger heat exchanger before the beer goes into the vats, then maybe a smaller fridge unit to maintain the temperatures.

[marc5180]

For cooling 8000L of beer at 20°C to 10 °C in two hours it is needed about 60kW of cooling capacity.


How did you work that out Nike?

He says that the consultant has quoted him around £3500 for a complete system that will do the job. I very much doubt that for 60kw of cooling??

[nike123]

How did you work that out Nike?

He says that the consultant has quoted him around £3500 for a complete system that will do the job. I very much doubt that for 60kw of cooling??


http://farm4.static.flickr.com/3105/3246436845_d7a1649afa_o_d.png

[nike123]

How did you work that out Nike?

He says that the consultant has quoted him around £3500 for a complete system that will do the job. I very much doubt that for 60kw of cooling??

Are you sure that 2 hour pull down time is quoted in that proposal?

[marc5180]

He says that it is but i very much doubt it. Maybe to maintain it once it's at 10°C

[nike123]

He says that it is but i very much doubt it. Maybe to maintain it once it's at 10°C

Probably, that is 4 kw cooling demand.

[marc5180]

That sounds more like it. I'll ring him later and speak to him.

[marc5180]

I've just spoken to him and he says the consulatnt told him the cost would be £3500 to fit a system that would get the beer down to 10°C and maintain it.

He thinks he may have got mixed up with the pull down time and may have got it wrong. If the pull down time was say 24 hours how much of a difference would this make?

[nike123]

I've just spoken to him and he says the consulatnt told him the cost would be £3500 to fit a system that would get the beer down to 10°C and maintain it.

He thinks he may have got mixed up with the pull down time and may have got it wrong. If the pull down time was say 24 hours how much of a difference would this make?
Around 8kW cooling capacity if equipment works 18hr a day!

[marc5180]

He is going to have to speak to the consultant who will advise him of the pull down time for the price that he quoted and then go from there.
thanks

[nike123]

He is going to have to speak to the consultant who will advise him of the pull down time for the price that he quoted and then go from there.
thanks

That is the right way to do things.