Freezer as Ice thermal storage air conditioning

[DrakeTruber]

Here’s an idea for off grid air conditioning. An air conditioner could run directly off solar during the day to cool our small insulated bedroom. Then, at night, it would be awesome to have ice stored from a solar powered freezer outside, that we can use to blow cold air directly onto occupants of the bedroom at night. Thus, no need for expensive batteries for cooling and a good backup in case the bedroom temperature isn’t exactly where we want it. The fancy name we can slap onto this is ice storage air conditioning: https://en.m.wikipedia.org/wiki/Ice_storage_air_conditioning

What are your thoughts/advice on this? I have no experience with HVAC so any feedback on how to handle the details would be invaluable

 

[DThames]

Storing the ice inside the cooled space would make more sense in regard to the heat gain on the ice. If you could move frozen containers of ice from the outside freezer to the inside, then just blow air over them if you want to better cold the room. You could swap out containers from yesterday, putting them back in the freezer to freeze the next day.

 

[DrakeTruber]

I’ve thought of similar ideas. My concern is the daily task becoming an inconvenience, and also the amount of ice weighing down our “RV”. Also, having the freezer inside the structure would heat it slightly. You bring up an excellent concern with heat gain outside. Perhaps thicker insulation, maybe using an ice cream freezer or something with better insulation properties. Was also thinking of drilling two holes in the top of the chest for insulated ducts to connect

 

[stienman]

Here's another thread that discusses this as well:

Solving the climate control crises

I've been diving deep into solving the temp control environment for vanlife. The biggest gripe of van and small space dwellers who want to live off grid is the struggle to keep their space a constant 70 degree temperature in their van or small space. May this be a thread to help solve this...

diysolarforum.com

And searching for "frankencooler" will yield a lot of products along this line.

 

[DrakeTruber]

Yeah looked through that entire thread!

 

[DThames]

I’ve thought of similar ideas. My concern is the daily task becoming an inconvenience, and also the amount of ice weighing down our “RV”. Also, having the freezer inside the structure would heat it slightly. You bring up an excellent concern with heat gain outside. Perhaps thicker insulation, maybe using an ice cream freezer or something with better insulation properties. Was also thinking of drilling two holes in the top of the chest for insulated ducts to connect

Yeah looked through that entire thread!

It would really take a lot of power to do anything meaningful, I am afraid. I have a large chest freezer and it runs for hours per day just holding the contents at a constant temp. Your solar array would need to be in the thousands of watts, I would expect, if you want to daily make ice to later melt.

 

[Koldsimer]

Apart from other concerns, humidity could be a major issue. Of course, i'd much rather be trying to sleep in a cool 72 degree room with 70% humidity than a 90 degree room with 50%.

 

[Cyanlite]

Cheaper to just get an AIO with a cheap battery to power a small 5000btu A/C

 

[RV10flyer]

I'm gonna use my old deep freezer that will hold around 150 gallons of anti-freeze/water solution. I will cool it during the day to around 25-30F. I will run circulating pump at night as needed to circulate fluid through a water coil like those used for an outdoor wood boiler. The pump controlled by a thermostat that also energizes my blower on the air handler. That should dehumidify better than my air source heat pumps that run a 38-40°F evaporator.

 

[DThames]

I'm gonna use my old deep freezer that will hold around 150 gallons of anti-freeze/water solution. I will cool it during the day to around 25-30F. I will run circulating pump at night as needed to circulate fluid through a water coil like those used for an outdoor wood boiler. The pump controlled by a thermostat that also energizes my blower on the air handler. That should dehumidify better than my air source heat pumps that run a 38-40°F evaporator.

Please report when operational.

 

[DrakeTruber]

Please report when operational.

I second this. Flyer, I’m guessing that pumping the coolant as opposed to direct fan with ducts is to avoid humidity? Also what made you decide to go ahead with the freezer as opposed to paying more for more batteries and running a high efficiency mini split. Was anyone’s project an inspiration for you? Got any math to back up your decision making. Best of luck with this

 

[DrakeTruber]

Posted the same question on Reddit for more feedback. I was told that the freezing approach is often used in marine applications. I was also told that the freezing approach is anachronistic due to improved heat pump efficiency. So I’m up in the air

https://www.reddit.com/r/OffGrid/comments/weh6cs

 

[Al D]

This is valid if you isolate the freezer outside of the area being cooled. You are storing energy in a thermal battery instead of a chemical battery. A thermal battery's application is limited to exactly what you are trying to do; displace heat energy.

The picture OP attached will not be an efficient use of the freezer since all of the heat generated will be contained inside the same room to be cooled. Vent the exhaust for a more valid use.

 

[DrakeTruber]

This is valid if you isolate the freezer outside of the area being cooled. You are storing energy in a thermal battery instead of a chemical battery. A thermal battery's application is limited to exactly what you are trying to do; displace heat energy.

The picture OP attached will not be an efficient use of the freezer since all of the heat generated will be contained inside the same room to be cooled. Vent the exhaust for a more valid use.

Thanks for your feedback Al D. Agreed that having the freezer inside is silly; it was the closest image I could find online. So you feel that the idea holds water, even when there are efficient heat pumps on the market? How would you handle the project

 

[RV10flyer]

I second this. Flyer, I’m guessing that pumping the coolant as opposed to direct fan with ducts is to avoid humidity? Also what made you decide to go ahead with the freezer as opposed to paying more for more batteries and running a high efficiency mini split. Was anyone’s project an inspiration for you? Got any math to back up your decision making. Best of luck with this

I'm an hvac guy by trade. So I'm presently running 6.25 tons of capacity with 4 hp systems, varying SEER's from 16-33. I have an old deep freeze that still works and some propylene glycol just begging to be used in a little experiment. I have a ton of unused power from the time my 134 kWh batteries are charged back up at noon-3ish. I consume about 15-25% of my capacity from 6 pm to 9 am. Plus I have to run a dehumidifier a liitle bit every humid day to maintain 45-50% rh inside. One would think these new modern high eff hp's would remove enough, but they don't. Also the outdoor humidity seems to run higher these last few years.

 

[RV10flyer]

Thanks for your feedback Al D. Agreed that having the freezer inside is silly; it was the closest image I could find online. So you feel that the idea holds water, even when there are efficient heat pumps on the market? How would you handle the project

I don't know if it would be more efficient than my 20 Seer American Standard heat pump system for the downstairs, but by the time I get it finished next year with that project, I will have been off grid for over a year and should have some numbers to compare it to. The main reason is to have a 25-30F coil removing more humidity and using less battery capacity at night. Also my inverters would produce less heat at night and my power shed Fujitsu 9K would run less. I'll let everyone know how it works.

 

[RV10flyer]

Please report when operational.

I will.

 

[Al D]

If you're set on not having a lifepo4 battery or equivalent, then this is probably the best way to do it. You are trying to store excess solar energy for the purpose of cooling your room. Before air conditioners, wealthy people could use ice to cool a room. That's where the "1 ton" jargon comes from. It takes 288,000 BTUs to melt 1 ton of ice. If that's accomplished in 24 hrs, you are using 12,000 BTUs per hour to cool.

It is antiquated, but tried and true.

If you have the ability to run a fan and small water pump, I would design the system like a heat exchanger. Fill a container with water that takes up as much of the freezer space as possible. Submerge a coil of 1/2" plastic tubing in the container 90% full of water (water freezes to about 9-10% more volume). Connect it to a small water pump and a radiator. You will prime the system with water and 40% antifreeze. Have the fan blow across the radiator. As the pump cycles the antifreeze solution, heat will be extracted from the air and distributed into the ice block (or, most likely, very cold water).

I should point out that the radiator, fan, container, and plastic tubing will have an up front cost. Also, carrying around that much weight in water will have an ongoing cost against your fuel efficiency. The efficiency of your old freezer also warrants contemplation. And it will take up a lot of room. Is it maybe worth getting an extra battery? Your call.

 

[RV10flyer]

If you're set on not having a lifepo4 battery or equivalent, then this is probably the best way to do it. You are trying to store excess solar energy for the purpose of cooling your room. Before air conditioners, wealthy people could use ice to cool a room. That's where the "1 ton" jargon comes from. It takes 288,000 BTUs to melt 1 ton of ice. If that's accomplished in 24 hrs, you are using 12,000 BTUs per hour to cool.

It is antiquated, but tried and true.

If you have the ability to run a fan and small water pump, I would design the system like a heat exchanger. Fill a container with water that takes up as much of the freezer space as possible. Submerge a coil of 1/2" plastic tubing in the container 90% full of water (water freezes to about 9-10% more volume). Connect it to a small water pump and a radiator. You will prime the system with water and 40% antifreeze. Have the fan blow across the radiator. As the pump cycles the antifreeze solution, heat will be extracted from the air and distributed into the ice block (or, most likely, very cold water).

I should point out that the radiator, fan, container, and plastic tubing will have an up front cost. Also, carrying around that much weight in water will have an ongoing cost against your fuel efficiency. The efficiency of your old freezer also warrants contemplation. And it will take up a lot of room. Is it maybe worth getting an extra battery? Your call.

I'm an HVAC guy, so I have used circulating pumps, tubing, tube in a tube coils, heat exchangers, etc.

I have over 2000 lbs of LFE, so it's really just to see if it makes a difference in my 20-30 kWh nighttime consumption and dehumidifies better.

 

[Hedges]

I'm gonna use my old deep freezer that will hold around 150 gallons of anti-freeze/water solution. I will cool it during the day to around 25-30F. I will run circulating pump at night as needed to circulate fluid through a water coil like those used for an outdoor wood boiler. The pump controlled by a thermostat that also energizes my blower on the air handler. That should dehumidify better than my air source heat pumps that run a 38-40°F evaporator.

My objection to this is you are storing your cold as cold liquid, not as phase change.
The energy absorbed by melting ice is the same amount as required to heat that 0 degree C water to 100 degrees C. (edit: 80 degrees C.)

If your cycle is liquid 25 degree F warming to 75 degree F, that's 50 degree F swing, or 28 degrees C swing.
Barely over 1/4 the storage you could get building ice (and that could keep working up to room temperature, so about 5x the thermal capacity.)

I figure it is easy to recover cold with antifreeze liquid in tubes through ice. What is more difficult is freezing to build ice, because the ice will be thermal insulation, slower transfer than convection.