Store temperature in ice?

[OzSolar]

Ice storage is fascinating to me. I've only seen it on a big scale though. Believe or not "The Lawrence Welk Theater" in Branson had it. The challenge with AC is that your equipment has to be sized to meet the biggest loads which in many spaces 8 hours a day or less which means you've paid for equipment you're only getting ~33% utilization from.

Ice Storage allows you to reduce the size of your equipment and rely on the energy you stored ice when your cooling load and energy costs were off peak and still meet your cooling needs.

 

[JLBinTN]

You wouldn't even have to take the ice out of the freezer, just open the freezer. You also wouldn't have to power it to maintain the ice when it's not used, it's just water.. if it's in containers that won't burst, let it change back to water and then freeze it again with excess solar the next day.

Every watt that freezer uses will add heat into your RV when it's running. You will then have to run more AC to remove that heat, which will consume more of your excess solar. How much excess solar do you have? If you haven't removed that excess heat by the time the sun sets it will take away some of the benefits of the melting ice for temp reduction.

I have no idea how much difference a freezer full of frozen water bottles would have on your rv temps if turned off and open. I'm sure somebody here can do the complicated math for a certain volume of frozen water in a certain volume of air (not counting air leakage to the outdoors in the rv).

I like the idea, but I don't know how much difference it will really make with the size of a single freezer that would fit in an RV.

edit..
Maybe if you used the excess solar to freeze some of those frozen neck bands, and kept swapping those out all night long.. it would have more of a noticeable effect.. Turn the freezer off though, or it's just adding heat and wasting battery power at night.

"Before electric air conditioners existed, people used large blocks of ice to cool their homes and businesses. The ice absorbed heat and slowly melted as it warmed up. The use of tons to measure cooling capacity comes from this time. A ton refers to the amount of heat it takes to completely melt a ton of ice."

1 ton AC = 12,000 BTU

Not a complete answer to the question asked, but it's a start.

 

[cs1234]

"Before electric air conditioners existed, people used large blocks of ice to cool their homes and businesses. The ice absorbed heat and slowly melted as it warmed up. The use of tons to measure cooling capacity comes from this time. A ton refers to the amount of heat it takes to completely melt a ton of ice."

1 ton AC = 12,000 BTU

Not a complete answer to the question asked, but it's a start.

I was not aware of that. It makes sense though, and is pretty cool.

Once again, there is too much math involved for me to feel like doing it, but:

How much ice, (in original water gallons), does one need to equal the equivalent hourly output of a 4 ton ac unit at full bore, assuming it's regular cycle times and such?

 

[timselectric]

A bunch

 

[MajicDiver]

100 years ago the large strawberry farms of East Tennessee shipped fresh strawberries to the north east in late April and May in box cars that had walls lined with ice. Then A/C was invented and California put them out of business. In the nuclear industry the Westinghouse designed PWR commercial reactors have an “ice condenser” in the containment building to serve as a backup cooling system in certain types of accidents. It’s relatively expensive to operate and maintain but necessary. You could absolutely do it, but like most things Solar it would probably not pay for itself. But most of us aren’t worried about that too much. Most solar systems “could” eventually pay for themselves if things go well but it would be a long time.

 

[JimJr]

1btu per pound degree F ---- 32 water to 212
144 btu's per pound -- 32F liquid to 32 F frozen
1/2 btu per pound --- 32F frozen and below

A 2000 pound chunk of ice (250 gallons ) if used for 8 hours , that would be equivalent to a 3 ton unit.
A RV wouldn't have a weight problem , but a space problem. A normal AC compressor on the gas motor is @ 3T to 5T capacity.

I had figured out a newer 2400 square ft home with a two car garage 25 x 25 , put a room 10 Ft high under it . In a body of water 8 ft high there
is enough btu's in there to heat the house using a heat pump, the entire heating season.
Guess what you have left , A huge chunk of ice for "AC" in the summer. and repeat

 

[No Idea]

1btu per pound degree F ---- 32 water to 212
144 btu's per pound -- 32F liquid to 32 F frozen
1/2 btu per pound --- 32F frozen and below

A 2000 pound chunk of ice (250 gallons ) if used for 8 hours , that would be equivalent to a 3 ton unit.
A RV wouldn't have a weight problem , but a space problem. A normal AC compressor on the gas motor is @ 3T to 5T capacity.

I had figured out a newer 2400 square ft home with a two car garage 25 x 25 , put a room 10 Ft high under it . In a body of water 8 ft high there
is enough btu's in there to heat the house using a heat pump, the entire heating season.
Guess what you have left , A huge chunk of ice for "AC" in the summer. and repeat

I love building construction rabbit holes so just ignore if you want because it is a big off topic digression. I wrote it because the concept is a really neat (dare I say "cool"?) idea.

A construction design to compensate for internal ice expansion so as not to crack the concrete would be interesting.

Tanking basements is much more effective done on the side that sees the higher hydrostatic pressure, IE the outside in normal basements. In your case it becomes more complex because even though tanking the inside is easier in terms of construction method your tanking material(s) needs a guaranteed leak proof method that has a fair amount of mechanical expansion and contraction ability. If it ever leaks or it fails to expand back to original thickness when the water melts then come the next freeze cycle the foundations will crack. Putting the water in multiple tanks that each can handle the smaller volume of expansion would be easier so you have an air gap but you have to factor in human access for repairing or swapping damaged tanks. Just saying your room will likely need to be oversized to get the volume of water you want.

Next design challenge is freezing and thawing RC concrete walls and floors since even with no direct contact they would eventually reach the same freeze and thaw temperatures. A lot of normal thermal insulation might work to keep the temperature gradient acoss the concrete close to external. Must be doable since such structures exist for permafrost construction (temperature gradient the other way) but have never done it personally.

You could avoid it and pile your house foundation around your room so there is a lot of ground clearance between the piles and your room but whatever room you build needs enough mass to overcome the bouyancy of your room in summer if it rains and you have flotation from normal water hydrostatic on outside and lighter ice on inside. Normally that is just concrete mass but, as previously noted, you need waterproof and thick flexible material to avoid damaging concrete.

Above ground smaller tanks with a volume and shape dictated by the tank material that can handle the expansion and contraction with a s*it load of external insulation would be easier to design and maintain and therefore I expect a lot cheaper because of that. You would avoid involvement of expensive engineers for an above ground solution too.

However the flip side of all this is that thermally heating the water in insulated tanks above ground is a simpler design challenge. So you use the heated water in winter and chilled water in summer. Insulation is insulation.

Not knocking your good idea just enjoying a morning coffee thinking about your good idea.

I feel the need to add a signature to my profile because I actually have a degree in B.S. hence my enjoyment.

 

[JRH]

A bunch

YESSS…..A WHOLE BUNCH….

 

[JimJr]

I love building construction rabbit holes so just ignore if you want because it is a big off topic digression. I wrote it because the concept is a really neat (dare I say "cool"?) idea.

A construction design to compensate for internal ice expansion so as not to crack the concrete would be interesting.

Tanking basements is much more effective done on the side that sees the higher hydrostatic pressure, IE the outside in normal basements. In your case it becomes more complex because even though tanking the inside is easier in terms of construction method your tanking material(s) needs a guaranteed leak proof method that has a fair amount of mechanical expansion and contraction ability. If it ever leaks or it fails to expand back to original thickness when the water melts then come the next freeze cycle the foundations will crack. Putting the water in multiple tanks that each can handle the smaller volume of expansion would be easier so you have an air gap but you have to factor in human access for repairing or swapping damaged tanks. Just saying your room will likely need to be oversized to get the volume of water you want.

Next design challenge is freezing and thawing RC concrete walls and floors since even with no direct contact they would eventually reach the same freeze and thaw temperatures. A lot of normal thermal insulation might work to keep the temperature gradient acoss the concrete close to external. Must be doable since such structures exist for permafrost construction (temperature gradient the other way) but have never done it personally.

You could avoid it and pile your house foundation around your room so there is a lot of ground clearance between the piles and your room but whatever room you build needs enough mass to overcome the bouyancy of your room in summer if it rains and you have flotation from normal water hydrostatic on outside and lighter ice on inside. Normally that is just concrete mass but, as previously noted, you need waterproof and thick flexible material to avoid damaging concrete.

Above ground smaller tanks with a volume and shape dictated by the tank material that can handle the expansion and contraction with a s*it load of external insulation would be easier to design and maintain and therefore I expect a lot cheaper because of that. You would avoid involvement of expensive engineers for an above ground solution too.

However the flip side of all this is that thermally heating the water in insulated tanks above ground is a simpler design challenge. So you use the heated water in winter and chilled water in summer. Insulation is insulation.

Not knocking your good idea just enjoying a morning coffee thinking about your good idea.

I feel the need to add a signature to my profile because I actually have a degree in B.S. hence my enjoyment.

Your looking at this like a refrigerator freezer , water expands 10% in the process . In the freezer you're freezing the water from the outside in .
if you freeze the the water from the inside to the outside , no isn't any outside wall expansion pressure , other than the water itself .
As for buoyancy , do you build your house in a pond or swamp ? As for insulation the ground temp to ice is 20 to 30 degrees difference in most places in the continental USA, don't need much , not exposed to the sun, rain,wind . The old-timers used saw dust in their ice houses .

Sealing the water not escaping , use a vinyl pool liner. Freezing water you get 144 btu per pound, just heating the the water is @ 110btu ( 70 to 180 ) plus more insulation because of the higher temperature difference and needing more volume to get the same btu capacity.

Heat pumps will work very efficiently with this temperature range , Heat pumps normally waste the hot or cold to the outside air or ground, why not save it , The AC would use a small water pump and a heat exchange coil in the furnace

Jim jr

 

[No Idea]

Your looking at this like a refrigerator freezer , water expands 10% in the process . In the freezer you're freezing the water from the outside in .
if you freeze the the water from the inside to the outside , no isn't any outside wall expansion pressure , other than the water itself .
As for buoyancy , do you build your house in a pond or swamp ? As for insulation the ground temp to ice is 20 to 30 degrees difference in most places in the continental USA, don't need much , not exposed to the sun, rain,wind . The old-timers used saw dust in their ice houses .

Sealing the water not escaping , use a vinyl pool liner. Freezing water you get 144 btu per pound, just heating the the water is @ 110btu ( 70 to 180 ) plus more insulation because of the higher temperature difference and needing more volume to get the same btu capacity.

Heat pumps will work very efficiently with this temperature range , Heat pumps normally waste the hot or cold to the outside air or ground, why not save it , The AC would use a small water pump and a heat exchange coil in the furnace

Jim jr

Thanks for taking the time to read and reply. Sounds like your location will have none of those issues.

Only bit I can't get my head around is freezing inside out vs outside in being different expansion. Guess I need to brush up on that one.

 

[RCinFLA]

Freezer evaporator temps are designed to freeze ice. Air conditioner evaporators are designed not to drop below freezing point of water.

Your freezer evaporator will turn into a block of ice from air humidity condensation.

 

[JLBinTN]

Now you guys have me thinking about using excess solar to chill (summer)/heat (winter) a buried water reservoir for use with a high efficiency geothermal heat pump. I would think it would be possible to easily cool/heat a home all night long using just a fraction of the electricity used by a conventional heat pump.

 

[JimJr]

Freezer evaporator temps are designed to freeze ice. Air conditioner evaporators are designed not to drop below freezing point of water.

Your freezer evaporator will turn into a block of ice from air humidity condensation.

You are correct on regular AC units m But heat pumps are designed to go below freezing to get the heat out of the sub 32F air. As long as you don't change what Freon the compressor was came with, It will work. Modifying the unit will void the warranty any how, but I did not specify the modifications nor the level of refrigeration skills needed to do this , I have them .
The operation parameters for the are the same for this setup, just modifying on how it is done , using different valves and exchangers .

Jim jr

 

[RCinFLA]

You are correct on regular AC units m But heat pumps are designed to go below freezing to get the heat out of the sub 32F air. As long as you don't change what Freon the compressor was came with, It will work. Modifying the unit will void the warranty any how, but I did not specify the modifications nor the level of refrigeration skills needed to do this , I have them .
The operation parameters for the are the same for this setup, just modifying on how it is done , using different valves and exchangers .

Jim jr

Actually, reverse cycle heat pump's outside coil is not supposed to go below about 30 degs F. When they hit 30+/-2 degs they go into a defrost mode which just puts the reversing valve back to air conditioner cooling mode to warm up outside coil and turns on auxiliary electric heat strips at the top of inside air handler to keep the inside blower air from getting too cold during defrost. It usually only takes a couple of minutes to get outside coil warm enough to melt off any ice starting to build up. The trick is the unit must do defrosting often enough to prevent any significant amount of ice buildup. The defrost controller often has a timer that prevents unit from jumping back into defrost too soon after completing last defrost cycle even if coil drops below 30 degrees, as it is unlikely much ice has built up in a short time since last defrost cycle.

Depending on outside temp and relative humidity they can get overwhelmed. The outside unit defrost function only has ability to detect outside coil temperature and a not very accurate refrigerant pressure switch on outside coil lines. It cannot directly detect ice. When superheat pressure gets too low on outside coil, indicating likely freeze up, they give up and shut down, turning over inside heating solely to electric heat strips.

Mini-splits reverse cycle heat pumps often do not have auxiliary electric heat strips in inside unit.

A good install design selects the wattage of inside electric heat strips based on typical local weather conditions. Larger wattage electric heat strips should be installed in locations likely to get colder, high relative humidity, outside conditions.

Picture shows a unit that the defroster got overwhelmed. It should have given up long before it got this bad. Maybe the owner had lawn sprinklers programmed to turn on during the night in attempt to protect their plants from freeze damage, putting a lot of local humidity in air.

 

[JLBinTN]

Actually, reverse cycle heat pump's outside coil is not supposed to go below about 30 degs F. When they hit 30+/-2 degs they go into a defrost mode which just puts the reversing valve back to air conditioner cooling mode to warm up outside coil and turns on auxiliary electric heat strips at the top of inside air handler to keep the inside blower air from getting too cold during defrost. It usually only takes a couple of minutes to get outside coil warm enough to melt off any ice starting to build up. The trick is the unit must do defrosting often enough to prevent any significant amount of ice buildup. The defrost controller often has a timer that prevents unit from jumping back into defrost too soon after completing last defrost cycle even if coil drops below 30 degrees, as it is unlikely much ice has built up in a short time since last defrost cycle.

Depending on outside temp and relative humidity they can get overwhelmed. The outside unit defrost function only has ability to detect outside coil temperature and a not very accurate refrigerant pressure switch on outside coil lines. It cannot directly detect ice. When superheat pressure gets too low on outside coil, indicating likely freeze up, they give up and shut down, turning over inside heating solely to electric heat strips.

Mini-splits reverse cycle heat pumps often do not have auxiliary electric heat strips in inside unit.

A good install design selects the wattage of inside electric heat strips based on typical local weather conditions. Larger wattage electric heat strips should be installed in locations likely to get colder, high relative humidity, outside conditions.

Picture shows a unit that the defroster got overwhelmed. It should have given up long before it got this bad. Maybe the owner had lawn sprinklers programmed to turn on during the night in attempt to protect their plants from freeze damage, putting a lot of local humidity in air.

View attachment 105852

If the evaporator coil isn't cooler than the outside temp, then there's no way to extract any energy from the air passing over the coil, so what's the point in running at all?

 

[Roswell Bob]

Why use ice? Because water is inexpensive? Why not use liquid Sodium or parafin?

 

[JimJr]

Actually, reverse cycle heat pump's outside coil is not supposed to go below about 30 degs F. When they hit 30+/-2 degs they go into a defrost mode which just puts the reversing valve back to air conditioner cooling mode to warm up outside coil and turns on auxiliary electric heat strips at the top of inside air handler to keep the inside blower air from getting too cold during defrost. It usually only takes a couple of minutes to get outside coil warm enough to melt off any ice starting to build up. The trick is the unit must do defrosting often enough to prevent any significant amount of ice buildup. The defrost controller often has a timer that prevents unit from jumping back into defrost too soon after completing last defrost cycle even if coil drops below 30 degrees, as it is unlikely much ice has built up in a short time since last defrost cycle.

Depending on outside temp and relative humidity they can get overwhelmed. The outside unit defrost function only has ability to detect outside coil temperature and a not very accurate refrigerant pressure switch on outside coil lines. It cannot directly detect ice. When superheat pressure gets too low on outside coil, indicating likely freeze up, they give up and shut down, turning over inside heating solely to electric heat strips.

Mini-splits reverse cycle heat pumps often do not have auxiliary electric heat strips in inside unit.

A good install design selects the wattage of inside electric heat strips based on typical local weather conditions. Larger wattage electric heat strips should be installed in locations likely to get colder, high relative humidity, outside conditions.

Picture shows a unit that the defroster got overwhelmed. It should have given up long before it got this bad. Maybe the owner had lawn sprinklers programmed to turn on during the night in attempt to protect their plants from freeze damage, putting a lot of local humidity in air.

View attachment 105852

Your only partially correct , the newer units measure the fan speed (load) to determine the defrost cycle . This way it includes all the air temp and the humidity levels . The evaporator temp goes sub zero F degrees . My addition would put another heat ( water) exchanger between the compressor and the evaporator. The unit should never know where the heat came from .

JimJr

 

[Vigo]

I have nothing against doing the math, but i will say that is basically free, if you have excess space in your RV's fridge/freezer, to fill up all the free space with water, and then transfer the actual refrigerated items into a cooler on the floor overnight, and leave the fridge door open all night.

I have a mini fridge in my shop that I use to have cold drinking water. It's got maybe 1 gallon of drinking water and 7 gallons of 'thermal mass' water in it, so that when i turn off the shop at night and come back in the next morning, the water in the fridge is still much colder than if i left just a few water bottles in an otherwise empty fridge.

So, if you don't have anything that actually has to STAY refrigerated overnight, or if you do but you also have a cooler you could transfer it to overnight, just shove a bunch of water in there and give it a go and just see if the result helps you decide whether to invest real effort or not.

I think one of the things to keep in mind is you don't really need the same amount of cooling all night long anyway. The cooling you need to do in the space at night is non-linear, needing the most at the beginning when the sun has not been down for long, and quickly dropping until you need relatively very little by the end of the night. There is also probably a substantial drop in 'required cooling' the second that you the human lose consciousness. So even if a bunch of cooled water doesn't stay cold til morning, if it makes it 2 hours before flatlining it might still be useful (considering it's basically free) if you guesstimate that something like 30+% of the total nightly cooling you need done happens in those first 2 hours.

When i first went off-grid in May and didn't have my whole setup assembled yet, I would stack a bunch of frozen water bottles by my fan or window unit in the bedroom when i went to bed. I don't know how much they helped in real numbers, but they helped by more than what they cost me, and if i had a reason to go back to doing that i would. It's extremely low-cost, low-risk and even if it's mathematically a gimmick, science has shown that the placebo effect is surprisingly powerful anyway.

 

[ArtDeco]

Not all ice is equal though, It can be as low as -100F or as high as 32F.
I am wondering if I had my battery charged at noon, the extra power can be as much as 2KWH, is there any freezer that can convert that much power into temperature? Also, I assume the colder the ice, the more power will be required to maintain it. Unless we do not maintain it, we would need a special algorithm to control the freezer to use maximum output when solar power is available and shut off when we have no extra power

Indeec not all ice is equal. There is a reason the frozen food companies use dry ice ...

 

[cs1234]

@Vigo

Have you seen the latest in active cooling pillow technology? I think that's what we need to be focusing on.

Moona

@Will Prowse , see if you can get one for review!