Ice Bank Cooling

Question

Ice Bank Cooling A century ago when mechanical refrigeration was just coming into use, Ice Banks were a common way to cool large infrequently used areas. Large tanks of water were located in special ice bank rooms in basements and compressors worked 24/7 to remove heat from them and freeze them. Other lines of saline solution were chilled and fed into large radiators where air handlers moved large volumes of air through to cool the occupied areas. I was on the building committee of a large church in St. Louis for several years that was cooled by an ice bank. The compressor was surprisingly small but since most of the church was only used on Sunday and Wednesday evening the system was able to cool the large auditorium with no problems. The church had been built in the 1920’s and the ice bank system was still working normally in the 1990’s when I was there.

I want to implement ice bank cooling at my place in rural Texas south of Houston. I am completely off grid half a mile from the blacktop. I have solar and by 10:00 the battery banks are topped off. I have to use a small generator during the night since my battery banks won’t run the AC all night when it is hot.

Here are some thoughts on how it might be tested and implemented. Use a 250 gallon tote. Enclose it completely in a wooden frame with foam. Insert expansion tubing and tubing for water with anti-freeze to dump heat.

Assuming 200 gallons of water after tubing space, if the whole thing was frozen it would absorb 230,400 BTU before its temperature went up. Latent heat of fusion of water is 144 BTU per lb. At 8 pounds per gallon, 200 gallons is 1600 lbs. 1600x144=230,400.

If ten percent of the water can be frozen around the coils, 23,040 BTU could be absorbed. A 5000 BTU window unit cools my bedroom adequately. If I understand the concepts and numbers dumping heat to the ice in the tote would provide me with 4 plus hours of similar cooling. If 20% could be frozen it would handle an entire night. Water with antifreeze could be used with an automotive radiator and fan to cool the bedroom, dumping the heat to the tote.

If a DC motor could be used to drive the compressor, and if it could be fed directly from the solar panels when the battery bank was full, energy loss should be at the minimum. A microcomputer can monitor the input into the charge controller and the battery voltage and decide when to run the compressor.

Automotive AC compressors can be used to pressurize the freon. Golf cart motors and controllers could handle the control of the DC directly from the solar panels, driving the compressor via a V belt, or a controller could be made using a big mosfet and controlled by the microprocessor.

I am a retired microprocessor programmer so that part is not a problem and I have a machine shop. Is the whole idea practical? What are the problems? Has or is it being done?

Answer 1

From your description the only significant difference from well-established cooling systems is that you’ll be running the compressors directly from the solar panels. The thing to look out for here is that the power available from the panels will vary somewhat with the angle and intensity of the sun. My inclination would be to run the motors from your battery pack and top up the battery continuously from the panels, that way you won’t need to worry about startup load etc. BTW freon is out of favour as a refrigerant these days, pentane is often used, or ammonia for larger installations.

Answer 2

If my memory is close a typical car compressor puts out about 40,000 BTU (3.3 Tons). Each ton requires 1 Hp, so you need 3.3 Hp to drive that compressor. At 746 watts per Hp you need about 2462 watts of power. That is about 21 amps at 120 or at 24V just over 100 amps. You do have an advantage that type of compressor probably has a swash plate which will change the pumping capacity to keep the output constant over a range of RPM. It would definitely be a fun project but some heavy currents will be involved. You might be able to find a smaller compressor to back down part of the load. No doubt your system would work. I do not know what you have available to you in skills etc so I cannot judge if you can do it. If you have a small stream???

Answer 3

It is a good idea, I have thought about it here as an on-grid solution. We have electricity prices that vary with time of day, and overnight prices are about 20% of the peak daytime prices. For hot weather it makes sense to store 'cool' in, for example, a frozen lump of ice. I did some calculations some time ago and a couple of cubic metres of ice would store a significant amount of energy.

There was a company in California that offered these solutions, Ice Energy, but it went broke recently Ice Energy story, but it's still a good idea and may well be used in future houses. It just needs an insulated storage tank and a suitable adapted heat pump. If these can be appropriately engineered for the right price.

Answer 4

your thinking is sound. Storing ice or cold water will likely do exactly what you want, the only problem is just getting it to work, but none of the concepts are difficult. Probably sizing the compressor is the hardest thing.

Answer 5

This is a great old idea that is making a comeback. Trane for example is making commercial systems of icebank storage.

I know that the Manhattan Center for the Performing Arts had one installed about 25years ago. My former boss was the impetus behind that. It not only saves energy as you can run the system off-peak with reduced electric costs (especially demand charges), but with oversized air ducts and low air velocity it greatly reduces the noise and vibration for their state of the art sound, TV recording and performance spaces. The Trane system uses plastic pipes and heat exchangers I believe. Other systems use a conventional ice maker that drops the ice into a water tank to make slurry.
Ammonia is the pretty much the most efficient refrigerant out there, but there are problems - you can’t use copper pipes. As my boss used to say “You can use copper in an ammonia system and it will work, for a while.” The presence of even a small amount of water in the system and the copper is eaten up by the ammonia. As you will be using a secondary refrigeration circuit of brine, this should not be a problem. New ammonia systems use central ammonia refrigeration systems, but all cooling is done with secondary brine circuits. This reduces the amount of ammonia necessary (legal and safety requirement) and keeps it all in one place for containment in case of leaks.
Hydrocarbon refrigerants are being used, but there the danger is explosions as these are highly combustible. Freon is gradually being phased out, but systems are still generally available.
Definitely run the system off your batteries and allow the solar panels to recharge the batteries.
You say your batteries are fully charged by 10am. What about increasing battery storage?
I think your idea is marvelous and should work admirably.