cooling 45L water tank as cold as possible? (for no more than $200)

novo20 · Apr 23, 2020

Hi,

what is an economical way to cool water in a 45L tank? i want the water to be as cold as possible. now the water temperature is 35c.

- if i get a cheap water cooler like this one: ae01.alicdn.com/kf/HTB1BiiVO9rqK1RjSZK9q6xyypXai.jpg
, then connect the cold outlet to the tank and put a water pump in the tank and send it back to the water cooler? if yes, can you help explain it?

- or, these cheap aquarium coolers aliexpress.com/item/4000462429723.html, are they useful? how low can they get the water

down, if it is 35c ?

- another way?

marconi · Apr 24, 2020

novo20: Greetings from sunny London.

What an interesting question. May I ask why you want to reduce the water temperature? And how quickly do you want this to happen?

The physics is that water is only a liquid until 0C; below this temperature it enters its solid phase ie: ice.

So when you say as 'cold as possible' do you mean 'and still be a liquid'?

Is there anything in the water as it is to be cooled?

Where are you in Saudia Arabia so I can look in my Atlas.

novo20 · Apr 25, 2020

marconi said:
novo20: Greetings from sunny London.

What an interesting question. May I ask why you want to reduce the water temperature? And how quickly do you want this to happen?

The physics is that water is only a liquid until 0C; below this temperature it enters its solid phase ie: ice.

So when you say as 'cold as possible' do you mean 'and still be a liquid'?

Is there anything in the water as it is to be cooled?

Where are you in Saudia Arabia so I can look in my Atlas.

Hi Marconi,

I'm in Riyadh. Yeah it has to be liquid. If it goes down to 20c that would be great, 15c or less would be perfect. It's just water.

Thanks.

Darkwood · Apr 25, 2020

Hi novo,

Could you also give some reasoning here, what is this project/requirement for?

Will it be containing life as in a aquarium etc?
How precise does temp' control need to be?
Is pollution of the water a problem either as a consequence of cooling method or simply long term exposure or stagnation?
Will you be adding anything to the water?
Will you need redundancy.... IE some form of fail safe if the primary method stops working?
Is this water for consumption at any point?

With little background it is hard to advise and some methods may not be appropriate for certain circumstances, so please try address some if not all of the points above as they can have influence on the options you choose thus affecting the overall cost.

marconi · Apr 25, 2020

novo20: Some numbers.

45 L is 45kg of water.

The temperature change T you desire is 45- 15 = 30C.

Water has a specific heat capacity of 4200 Joules per kg per degree C. So, to raise 1kg of water by 1C requires 4200J - assuming the water is insulated from its environment say in a well lagged tank.

Thus the amount of heat energy to be removed to cool 45L from 45C to 15C is

4200 x 45 x 30 = 5670kJ

To cool 45 L by 30C in an hour (3600s) say would require a method of removing heat at a rate of

5670/3600 = 1.5kW or 1500J/s

Heat pumps whether for heating or cooling have a co- efficient of performance COP which is a measure of how well they convert mechanical effort into heating/cooling effect. See:

Coefficient of performance - Wikipedia - https://en.wikipedia.org/wiki/Coefficient_of_performance

The higher the COP the more efficient/economic is the heat pump. So, if the heap pump has a COP for cooling of 2, then 1500W of cooling effect could theoretically be provided from a mechanical effort of 0.75kW ie: for very 750J of mechanical from an electric motor the heat pump would produce 1500J of heat transfer.

A 0.75kW mechanical output electric motor will have an mechanical output to electrical input power efficiency of circa 0.8; thus the required electrical power is 1/0.8 x 0.75 = 1kW electrical power.

A typical chest freezer has an electrical motor consuming circa 300W - depends on its size and cop of the heat pump.

Conceptually then you would need the equivalent of three or four chest freezer heat pumps to cool 45L form 45C to 15C in one hour.

The cost to do this would be 1 kW-hour which in the UK is about 17p.

or you could play tunes and have one 300We motor cop2 45L chest freezer containing the 45L of water and it would cool the water down over a longer period say 3-5 hours.

I am just playing with ball park figures to appreciate the problem for you.

One might be able buy a 45L chest freezer for less than 200 dollars - I don't know.

Hope this helps inform you better.

marconi · Apr 25, 2020

To help you further you now need to answer Darkwood's questions. We are all intrigued by your question.

novo20 · Apr 29, 2020

darkwood said:
Hi novo,

Could you also give some reasoning here, what is this project/requirement for?

Will it be containing life as in a aquarium etc?
How precise does temp' control need to be?
Is pollution of the water a problem either as a consequence of cooling method or simply long term exposure or stagnation?
Will you be adding anything to the water?
Will you need redundancy.... IE some form of fail safe if the primary method stops working?
Is this water for consumption at any point?

With little background it is hard to advise and some methods may not be appropriate for certain circumstances, so please try address some if not all of the points above as they can have influence on the options you choose thus affecting the overall cost.

Hi darkwood, Thanks for the reply.

there is no life inside the tank!
temp control does not have to be precise
pollution is not a problem
i'm not adding anything to the water
fail safe would be nice, as long as it is not costly
the water is not for consumption!

Thanks
[automerge]1588200460[/automerge]

marconi said:
novo20: Some numbers.

45 L is 45kg of water.

The temperature change T you desire is 45- 15 = 30C.

Water has a specific heat capacity of 4200 Joules per kg per degree C. So, to raise 1kg of water by 1C requires 4200J - assuming the water is insulated from its environment say in a well lagged tank.

Thus the amount of heat energy to be removed to cool 45L from 45C to 15C is

4200 x 45 x 30 = 5670kJ

To cool 45 L by 30C in an hour (3600s) say would require a method of removing heat at a rate of

5670/3600 = 1.5kW or 1500J/s

Heat pumps whether for heating or cooling have a co- efficient of performance COP which is a measure of how well they convert mechanical effort into heating/cooling effect. See:

Coefficient of performance - Wikipedia - https://en.wikipedia.org/wiki/Coefficient_of_performance

The higher the COP the more efficient/economic is the heat pump. So, if the heap pump has a COP for cooling of 2, then 1500W of cooling effect could theoretically be provided from a mechanical effort of 0.75kW ie: for very 750J of mechanical from an electric motor the heat pump would produce 1500J of heat transfer.

A 0.75kW mechanical output electric motor will have an mechanical output to electrical input power efficiency of circa 0.8; thus the required electrical power is 1/0.8 x 0.75 = 1kW electrical power.

A typical chest freezer has an electrical motor consuming circa 300W - depends on its size and cop of the heat pump.

Conceptually then you would need the equivalent of three or four chest freezer heat pumps to cool 45L form 45C to 15C in one hour.

The cost to do this would be 1 kW-hour which in the UK is about 17p.

or you could play tunes and have one 300We motor cop2 45L chest freezer containing the 45L of water and it would cool the water down over a longer period say 3-5 hours.

I am just playing with ball park figures to appreciate the problem for you.

One might be able buy a 45L chest freezer for less than 200 dollars - I don't know.

Hope this helps inform you better.

Hi marconi, thanks for the reply.
The electric bill is not a problem, also It does not matter how long it takes to cool the water, even if it take few days, as long as it maintains the new temperature, once the
new temperature is reached.
also there is no way i can move the tank! so the cooling has to be external (mini fridge, cold water dispenser, aquarium chiller, or something else?)
Thanks.

marconi · Apr 30, 2020

novo20: Could you place the 45L inside a chest or upright freezer? One could then arrange a thermostat to sense the water inside the tank or perhaps through the side of the tank if the tank is metal. The thermostat then controls the power to the freezer. The freezer's thermostat is set to -5C say but the tank 'stat is set to 15C so it is this one that determines if the compressor needs to run. Clearly more design effort required but as a concept it could be done without spending much more than $200.

You need to be mindful of the risk of legionella bacteria in water if the body of water is not changed frequently. Even then tests may need to be done and water control measures introduced. It is some years since I had responsibility for legionella control so I direct you to this - note cold water to be less than 20C - but it is not that simple:

Managing legionella in hot and cold water systems - https://www.hse.gov.uk/healthservices/legionella.htm

novo20 · May 5, 2020

marconi said:
novo20: Could you place the 45L inside a chest or upright freezer? One could then arrange a thermostat to sense the water inside the tank or perhaps through the side of the tank if the tank is metal. The thermostat then controls the power to the freezer. The freezer's thermostat is set to -5C say but the tank 'stat is set to 15C so it is this one that determines if the compressor needs to run. Clearly more design effort required but as a concept it could be done without spending much more than $200.

You need to be mindful of the risk of legionella bacteria in water if the body of water is not changed frequently. Even then tests may need to be done and water control measures introduced. It is some years since I had responsibility for legionella control so I direct you to this - note cold water to be less than 20C - but it is not that simple:

Managing legionella in hot and cold water systems - https://www.hse.gov.uk/healthservices/legionella.htm

Hi marconi, many thanks for your replies.

No I can't put the tank inside a freezer. The tank is 85*85*6cm but it is also part of another big machine.
can you rate the following choices
1- cold water dispenser, where the water is circulated between the tank and the cooler.
2- cheap mini fridge and a long garden hose! like this video

View: https://www.youtube.com/watch?v=n5s8Cu59-NM

3- cheap peltier aquarium chiller like in the original post.

Thanks.

Darkwood · May 5, 2020

Are we to assume that this is used for cooling processes on the machine?

If so we would need to account for the extra heating of the water against the background temp' the water would normally sit at thus a higher capacity cooling method would be needed

I know I ask alot of questions but all of these are very valid points in that they change the parameters of what you are asking and thus a possible solution may be different.

novo20 · May 6, 2020

darkwood said:
Are we to assume that this is used for cooling processes on the machine?

If so we would need to account for the extra heating of the water against the background temp' the water would normally sit at thus a higher capacity cooling method would be needed

I know I ask alot of questions but all of these are very valid points in that they change the parameters of what you are asking and thus a possible solution may be different.

Hi darkwood, Thanks for the reply.
There is no heating inside the machine at all. The only heat is the weather, the machine is outdoors. It is covered from the sun, but it gets really hot here in the summer.

Thanks.

Darkwood · May 6, 2020

novo20 said:
Hi darkwood, Thanks for the reply.
There is no heating inside the machine at all. The only heat is the weather, the machine is outdoors. It is covered from the sun, but it gets really hot here in the summer.

Thanks.

You seem to have missed giving me a direct answer, is this water used to keep the machine cool in any way hence it will be inheriting process heat, also when you say there is no heating inside the machine at all do you mean the machine has no heating equipment like electrical elements or does this cover the process of the machine that it produces no heat or that heat production can be classed as negligible.
What does the machine do?

There seems to be a bit of a mystery to why you want to keep that water at that temp' and it could be beneficial to know the reasons as it may change the advice we give here, if the water is for cooling purposes then the solution may not necessarily change but may need to be scaled up to account for the inherited heat from its use.