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bmxeroh · 08-07-15, 10:29 AM

I think you're going to have trouble pulling enough heat out of the air to really make much of a difference. The 1 gallon ice bucket thing works somewhat well because of latent heat. It takes 144btus to melt 1lb 32 degree F ice to 32 degree F water, and there's about 8 lbs to a gallon, so you end up with around 1150btus. The phase change from ice to water is where the latent heat thing comes in, and it takes a lot of energy in one direction or another to change phases.

HOWEVER, it only takes 1 BTU to raise a lb of water 1 degree, so now that same gallon of water @ 32 degrees F now only takes 384 btus to raise the temp to 80 degrees F. This is the sensible heat part of things. Considering ground water temps are usually at least 50ish degrees or higher, there really aren't alot of BTU's left to do anything effective. Don't get me wrong, technically doing what you're suggesting will cool the air, but I doubt it will cool the air faster than the structure is gaining heat.

Which leads me in to the second question. The reason that opening the windows doesn't have a huge effect immediately is entirely a thermal mass problem. More specifically the difference in how much heat the structure itself can store, vs how much heat the air volume within can store. So you can change out the entire air volume in a hot structure with cooler air, and very quickly the stored heat within the actual structure will reheat that new air, ad nauseam until you have removed enough BTU's from the structure itself, rather than just the hot air. While water does have a higher heat capacity than air, bringing in cold water requires the heat in the structure to conduct into the air, and then conduct into the water. The flip side of this is it provides even more thermal mass to resist the temp change during the day, but I would guess that you don't want a whole bunch of 55 gal drums of water in your apartment. Plus, don't you pay for water there? Even if it's included expect your landlord to get really irritated with you burning through that much water. I'm pretty sure to get 1 ton of cooling for 12 hours at a 30 degree temp rise in the water would require something like 600 gallons of water, but I would love for someone to double check that because I started getting confused going in that direction. If that's the case 600 gallons a day is going to get you evicted quick.

08-07-15, 10:29 AM	#2
bmxeroh Helper EcoRenovator Join Date: Sep 2014 Location: Columbus, OH Posts: 34 Thanks: 1 Thanked 5 Times in 5 Posts	I think you're going to have trouble pulling enough heat out of the air to really make much of a difference. The 1 gallon ice bucket thing works somewhat well because of latent heat. It takes 144btus to melt 1lb 32 degree F ice to 32 degree F water, and there's about 8 lbs to a gallon, so you end up with around 1150btus. The phase change from ice to water is where the latent heat thing comes in, and it takes a lot of energy in one direction or another to change phases. HOWEVER, it only takes 1 BTU to raise a lb of water 1 degree, so now that same gallon of water @ 32 degrees F now only takes 384 btus to raise the temp to 80 degrees F. This is the sensible heat part of things. Considering ground water temps are usually at least 50ish degrees or higher, there really aren't alot of BTU's left to do anything effective. Don't get me wrong, technically doing what you're suggesting will cool the air, but I doubt it will cool the air faster than the structure is gaining heat. Which leads me in to the second question. The reason that opening the windows doesn't have a huge effect immediately is entirely a thermal mass problem. More specifically the difference in how much heat the structure itself can store, vs how much heat the air volume within can store. So you can change out the entire air volume in a hot structure with cooler air, and very quickly the stored heat within the actual structure will reheat that new air, ad nauseam until you have removed enough BTU's from the structure itself, rather than just the hot air. While water does have a higher heat capacity than air, bringing in cold water requires the heat in the structure to conduct into the air, and then conduct into the water. The flip side of this is it provides even more thermal mass to resist the temp change during the day, but I would guess that you don't want a whole bunch of 55 gal drums of water in your apartment. Plus, don't you pay for water there? Even if it's included expect your landlord to get really irritated with you burning through that much water. I'm pretty sure to get 1 ton of cooling for 12 hours at a 30 degree temp rise in the water would require something like 600 gallons of water, but I would love for someone to double check that because I started getting confused going in that direction. If that's the case 600 gallons a day is going to get you evicted quick.