Wild idea for free cooling - would this work?

[mperkel]

I have an idea for a home cooling system that I'm designing and I'd like to get some feedback as to if you all think this will work. The idea is to get (nearly) free cooling based on two things.

1) Storing the cool night temperature in water/concrete and using that the next day.

2) Some evaporative cooling.

I live in Gilroy California. Hot dry days and usually cool nights. Generally low humidity. Temps can be in the 100 to 110 range from late june to september. However at night it goes down to 50 to 60.

Here's the idea. I get 180 concrete blocks measuring 6"x8"x16" arranged with holes aligned horizontally and stacked 4 wide, 18 long, and 5 high. About 9000 pounds of concrete. The structure is enclosed in a way so that air can be blown through the structure. Air would travel through the left two vertical columns, turn around at the end, and come back through the right two columns.

The basic simplified idea is to blow the cool night air through at night chilling the blocks down. Then in the day time circulate air through them into the house cooling the home.

Additionally, I'm thinking about a system to wet the concrete blocks (soaker hoses) so that at night evaporative cooling will chill the concrete even further giving me colder and wetter concrete with more thermal mass from the water. Then in the daytime I will get some additional evaporative cooling.

Concrete blocks work like a sponge absorbing water and can then deliver evaporative cooling into the air. It won't be as good as a swamp cooler but will work somewhat.

So - am I nuts or onto something?

[Short Circuit]

How will you prevent the concrete from heating up in the daytime? Your "temperature storage" battery theory breaks down when consideration of heat capture is considered in all that concrete... You'd be better, IMO, with a geothermal system under the ground!!!

[pstu]

I have an idea for a home cooling system that I'm designing and I'd like to get some feedback as to if you all think this will work. The idea is to get (nearly) free cooling based on two things.

1) Storing the cool night temperature in water/concrete and using that the next day.

2) Some evaporative cooling.

I live in Gilroy California. Hot dry days and usually cool nights. Generally low humidity. Temps can be in the 100 to 110 range from late june to september. However at night it goes down to 50 to 60.

Here's the idea. I get 180 concrete blocks measuring 6"x8"x16" arranged with holes aligned horizontally and stacked 4 wide, 18 long, and 5 high. About 9000 pounds of concrete. The structure is enclosed in a way so that air can be blown through the structure. Air would travel through the left two vertical columns, turn around at the end, and come back through the right two columns.

The basic simplified idea is to blow the cool night air through at night chilling the blocks down. Then in the day time circulate air through them into the house cooling the home.

Additionally, I'm thinking about a system to wet the concrete blocks (soaker hoses) so that at night evaporative cooling will chill the concrete even further giving me colder and wetter concrete with more thermal mass from the water. Then in the daytime I will get some additional evaporative cooling.

Concrete blocks work like a sponge absorbing water and can then deliver evaporative cooling into the air. It won't be as good as a swamp cooler but will work somewhat.

So - am I nuts or onto something?
Not crazy at all. What you are describing is a form of "Cool Storage", a well respected method of reducing peak load. Old homes made of stone and adobe did it by means of their sheer mass. What is a question mark is:
1) Will it have enough BTU capacity to make the difference you want, and
2) can you build it cheaply enough that it will be economical.

Just having a basement will deliver some of those benefits.

Living in a region with dry climate and cool nights, gives you unique advantages. I live in S. Texas which is a hot-humid climate, overnight cool-off is trivial compared to yours.

Best of luck -- Pstu

[HAP2]

I would think you would just break even. The blocks would abosorb an equal amount of heat that you will need to get rid of before the blocks could begin to absorb the cooler temp. Perhaps if you buiried them...?

[Realist]

Ice storage has been done for years
I think the Media You want to use not as thermo dynamic as you hope it will be

[5thRoot]

This is very similar, except in reverse, to the electric ETS heating systems that were popular in the past. But if you have ever seen one of those systems, you will understand that this is not an easy undertaking. If it could be done economically and effectively, it would already be in practice. With some more engineering it might work, but you have a long way to go.

[btuhack]

You'd be better, IMO, with a geothermal system under the ground!!!

X2, built in storage,cheaper to do, tax breaks, just pay for the heat transfer at an increased efficiency.

Or, buy a cave and live in it, I think that's what the desert indians did before the white man made them live on reservations.

[tha_dub]

If you could put that concrete 20 feet down in the ground I think it would work perfect!

[pstu]

It is apparent you have been thinking of this idea with some detail: the construction and number of blocks etc. Is there anyone else who has done something like this, or would you be the first person ever to do this?

Perhaps a small-scale model of this could be built, and you could measure the amount of cooling possible. Use it to cool a tiny shed or something. That would tell you more cheaply, whether your plan would work for a whole house.

Best of luck -- Pstu

[trouble time]

Your "Idea" is the source of heating and cooling for one of the Ontario Hydro buildings in downtown Toronto. It was built in the 1970's.

[rickboggs]

I have an idea for a home cooling system that I'm designing.....
So - am I nuts or onto something?Here is a study you might be interested in.
http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1771-08.pdf

I think thermal storage would have helped in the results.

[billygoat22]

you may consider using a mass storage tank instead of block- a big tank of water.

circulate the water through a cooling tower at night to chill the tank down, in the day pump the water through a coil to cool the house.

the amount of cooling effect you'd need during the day would give the amount of thermal mass necessary for storage- the temp differential between morning and evening ( of the water)x the heat capacity of the water x the mass. you'd also need cool enough and dry enough nights to store that amount of cooling overnight.

[billygoat22]

was taking a look at the psychometric chart- at 100 degrees and 27% rh, if the temp drops to 60 at night, the relative humidity would be right at 100%- you cannot get a cooling boost at night using evaporative cooling since it would hardly evaporate.

based on the numbers in the first post, seems an evaporative cooler would work well for daytime cooling.

[paul42]

http://www.coolerado.com/

looks like the idea answer to me

[CraziFuzzy]

This is exactly the reason I with there were more Water/or glycol based home units. The cost of a water tank is minimal, compared to the price different between peak and off-peak energy uses. If one could switch to a TOU rate, run their AC at night, to cool a large water tank (burried, to be even better), and then run just a small pump and fan coil during the day, the savings would be amazing. Get real crazy and run a stratified tank and you gain even more capacity/gallon. a 5000 gallon stratified tank (approx 10ft diameter by 8 ft high) could cool a 3 ton load for 12 hours before becoming depleted. Cool it at night when the electric rates can be as low as a third of daytime rates, AND the condenser can run MUCH more efficiently, and you will see the benefits.

[stonewallred]

I would bury the blocks, and have them arranged around 4 or 6 inch rigid metal pipe and set up a pair of fans, one to pull cool air in at night, and the other to blow air through the pipes and into your home during the day.

There are a ton of books about this subject, passive cooling and heating would be the subject you are looking for.

The old adobe houses used not only the size and mass, but also a pretty sophisticated air movement system via convection. That is what the big room in the center of them that is much higher than the rest of house and had windows was for. Also small or no windows helped.

But I would say a geo system would be comparable in upfront costs, not all that expensive to operate, and do a much better job of cooling and heating your home.

[glennwith2ns]

Guy around here tried something similar to this.

He built a cinder block room (think elevator shaft) in the center of his house, then went and filled it with river rock (like you see on roofs) Had duct into the bottom and one out the top. I go past it everyday and often wonder how it worked out for him. Cant imagine it was worth the expense.

[mperkel]

This isn't new construction. It's a retrofit I'm putting under my deck.

More details. the idea is to use the cool night air to cool down the blocks for the next day. Here in Gilroy California we have cool nights and hot dry days.

Also - I'm thinking about putting soaker hoses through the blocks to get them wet and use some evaporative cooling. At night I'll blow air through the blocks, not through the house, to cool the blocks down to 50 degrees. So on the morning I'll have 9 tons of wet cold concrete blocks. Because the block are damp and hold water they should make good evaporators.

By my calculation between the thermal mass of the concrete blocks, the water, and evaporation, I'll have about 65,000 BTUs of cold to deliver to the house. I think that will do it. If it doesn't I'll just have to use the AC on the hottest days for a short time.

[mperkel]

http://www.coolerado.com/

looks like the idea answer to me

This is very interesting and is giving me more ideas.

[worknfool]

Take heat from here and put it over there...sounds simple enough.

If you're interested in doing more research check out the German standards for passive solar design. Differing latitudes but the base elements are the same. Also take a look at trombe wall construction and the use of earth tubes. The former being typically filled masonry units, concrete or even water filled vessels behind specialized glazings to control seasonal gain relative to the sun's angle of attack. The latter a kind of geothermal air to air heat exchanger using low velocity circulating fans. Often as not the two are used together. All of these ideas share the same premise of thermal mass as a storage medium or battery if you will, and have been implemented with great success all over the world. It seems that somewhere between these ideas and the old city buildings with a basement filled with ice there's room for experimentation.

If you're not a mason and wish to work with the CMU idea something else to look at is a process called dry stack construction. Plain block are simply stacked in a running bond like so many Lego blocks. Over this an 1/8" coating of cementious fiber reinforced parging (also known as Surface Bonding Concrete) is either sprayed or troweled on. The resultant wall, even without fill or steel reinforcement, is actually stronger laterally than a CMU wall built using type "S" mortar in every joint. When steel and grout fill are employed the resultant wall is incredibly strong as well as being a great accumulation of thermal mass. There's also the added benefit of having a water proof wall that's air tight.

By combining elements from above (passive solar design, geothermal tempered air exchange and thermal mass storage) along with super-insulating all six planes of the building envelope from the outside and utilizing a hydronic slab installation, the active heat inputs can be reduced to nill or very close to it. The reverse has been tried for cooling with varying degrees of success, mainly do to issues with humidity control and condensation.

[GT Jets]

If you sit down and do the math this will not work because of many factors. You have not taken into account that it is only in the 50's-60's for 4 or 5 hours at night and it gets hotter than hades for at least twice that time....(I lived in Gilroy for most of my life)

The blocks will not hold nearly the thermal energy you are thinking of because of the low delta-t.

Use water, holds more energy and is a lot easier to take advantage of the effect.

Gotta swimming pool? :yes:


GT

[worknfool]

How deep's the aquifer? ;)

[Rcb2875]

The best design for free heating and cooling was invented about four billion years ago. Sadly the majority of us that can reasonably use it have built our homes on top of it instead of in it.

[mperkel]

I think everyone can agree that this is going to work. The question is if it is going to work well enough to be practical. There have been a number of interesting comments. But this is an existing house. If I were building some new I would have done things differently. So - think retrofit.

My goal is to pay for whatever I build in less that 3 years without artificial tax subsidies and use simple parts and simple building techniques.

Anyhow. I'm doing some experiments tonight. I lined up 8 blocks, 2 tall, 4 long. I wetted them and I'm blowing air through them with a small fan. I'm trying to see how cool I can get them compared to air temperature. I want to see if evaporative cooling of wet block this way will chill significantly below air temperature at night. Trying to get that delta T I need.

It rained yesterday so humidity is higher than usual. This is worst case today. We'll see how it works and test over a few days.

It's all about science and the numbers. I'll either have them or I won't. We'll see.

[Rcb2875]

I don't think you will really see anything significant with your test as described. I believe you may find more favorable results if you were to take the blocks and put them in the ground along with some back yard engineering to have the air circulate through them much like a coil. You should try to take advantage of the geothermal properties you already have in your back yard. You don't have to go deep to find cooler ground, although a decent depth is better. The earth is a great heatsink.

Interesting thread and look forward to what you come up with.

[mperkel]

I have a fan blowing through wet block. Humidity is 68% which is high for this area but it just rained yesterday. Air temp is 64.2. Block temperature is 58.8. Time is 9:00 pm. Looks similar to tests I did last year with swap coolers so I'm getting a similar temp differential. I think in general I'm going to be able to cool to 50-55 at night. 9000 pounds of wet concrete.

I'm also interested in a hot day test. With wet concrete I'm wondering what the outside temp can get up to where I still have 65 degree air coming out.

[pstu]

I have a fan blowing through wet block. Humidity is 68% which is high for this area but it just rained yesterday. Air temp is 64.2. Block temperature is 58.8. Time is 9:00 pm. Looks similar to tests I did last year with swap coolers so I'm getting a similar temp differential. I think in general I'm going to be able to cool to 50-55 at night. 9000 pounds of wet concrete.

I'm also interested in a hot day test. With wet concrete I'm wondering what the outside temp can get up to where I still have 65 degree air coming out.

Thank you for telling us about the results of your experiment.

Best of luck -- Pstu

[mperkel]

It's 6:00 AM. Humidity is 95%. Air temp 55.1. Block temp 53.6.

This is about what I expected. I need to go buy a scale so I can weigh a wet block and a dry block and that way I can tell how much water a wet block absorbs and also see how much water is evaporating.

At this point I'm also losing coolness to the air in the surfaces, or possible evaporating more water on the outside surfaces so I'm going to mentally need to take that into account.

This round of experiments is just to just get a general feel for thermal properties and mechanical properties of concrete cinder blocks. I'm trying to determine how good the thermal conductivity is. I think it's pretty good for something that is not solid concrete but somewhat porous.

Also - I don't know of anyone using concrete block as an evaporative medium before. It's not your typical swam cooler material. Need to understand how much water a block can hold. How well does it conduct water to the surface? I don't think anyone has ever used concrete block in this manner before. If it doesn't work at least I'll be able to document that so others won't waste their time.

[Gunnery Sergeant Hartman]

What is the cost for the water you'll be running over these blocks?

Also, what about minerals and other additives left behind in the pours of the blocks after evaporation? Is there a way to clean the blocks or will they just become full of corrosion after a short time?

[mperkel]

Weather prediction is high of 84 today. Not what I was hoping for for data gathering. And it rained 2 days ago. Will probably be a week before there's a typical 105 degree hot dry day.

[mperkel]

What is the cost for the water you'll be running over these blocks?

Also, what about minerals and other additives left behind in the pours of the blocks after evaporation? Is there a way to clean the blocks or will they just become full of corrosion after a short time?

I haven't thought it through to that level. I don't think I'm going to use a lot of water. The idea is to develop a really good computer control that will get on the Internet and look at the weather forecast and only use water on the really hot days.

I do plan to make it so the back end of the blocks have a panel that I can remove to access them. My plan is to just stack the blocks. Put a layer of landscaping cloth in between each layer to hold them together.

So - I don't think the cost of the water is significant. Cleaning - I dunno.

[mperkel]

It's 1:20 pm. Humidity is 37%. Air temperature is 81.8 Concrete blocks are at 64.3. What I'm really testing here today is how good concrete block work as an evaporative cooling medium and so far it looks really good. Looks like I've created the equivalent of an artificial cave.

In about 30 minutes the sun is going to shine directly on the top of the blocks. It will be interesting to see what occurs then. That's not going to happen in what I'm going to build, but it should produce some interesting data anyhow.

[billygoat22]

you'll not get any cooler than the dew point on those block. you can use a psychometric chart to do a lot of calculations on the water evaporation.

37% during the day- you'll pretty much hit 95%+ if it drops down to the low 60s.

may want to check the heat capacity of block, even wet, as opposed to water.

[billygoat22]

sorry, should have used "specific heat". for water- 1 btu/ lb*F, portland clinker cement- .16, concrete- .156.

someone said 5000 gallon tank for heat storage- 40000 lbs worth. if you didn't get enough evaporation to boost cooling, you may need as much as 6 times the mass of concrete to store energy.

You may try moisture absorbtion of brick and stone in building assemblies in the search engine. data has already been collected on how concrete block absorbs water. (Plays a role in how brick and concrete breaks down in freezing climates)

[mperkel]

you'll not get any cooler than the dew point on those block. you can use a psychometric chart to do a lot of calculations on the water evaporation.

37% during the day- you'll pretty much hit 95%+ if it drops down to the low 60s.

may want to check the heat capacity of block, even wet, as opposed to water.

My plan is to use both the heat capacity of the block and evaporation.

It's 5:11 pm. Humidity is 40%. Air temp is 91.8. Block temp is 70.5. The hot sun is shining directly onto the blocks and has been for the last 2 hours. However the water the blocks soaked up so far is still keeping them cool.

I do understand the dew point limit. But I think I can get a few extra degrees of cool at night using evaporation, and also talking advantage of the thermal mass of the water in the concrete. Also on warm nights the evaporative cooling will make up the difference since warm nights are usually dryer.

[mperkel]

sorry, should have used "specific heat". for water- 1 btu/ lb*F, portland clinker cement- .16, concrete- .156.

someone said 5000 gallon tank for heat storage- 40000 lbs worth. if you didn't get enough evaporation to boost cooling, you may need as much as 6 times the mass of concrete to store energy.

You may try moisture absorbtion of brick and stone in building assemblies in the search engine. data has already been collected on how concrete block absorbs water. (Plays a role in how brick and concrete breaks down in freezing climates)

Granted that concrete blocks aren't the greatest when it comes to thermal mass. I'm thinking that other properties are significant. They have a lot of surface area allowing heat and cold to transfer efficiently in and out. They absorb water like a sponge. And they seem to be a good evaporative medium.

[CraziFuzzy]

I still feel that if you've got the space for this concrete structure, you'll be MUCH better off with water for storage (and a simple fan coil, even a repurposed car radiator would work).

[CraziFuzzy]

I also don't think you are going to gain much in your climate with the evaporative cooling at night. Looking at historical data, rarely does the nightime temp stay much higher than dewpoint, so you really aren't gaining much for the added complications. Evaporative cooling is just not of much use at night except in the deserts. It is certainly of use during the day, where the dry bulb is quite a bit above dewpoint.

Here's something else about soaking the blocks. This will result in a swamp cooler effect during the day, where the warm air is drawn through the blocks, THEN you will get some evaporation from the wet blocks, and that cool moist air will be brought into the house. Though I fail to see how this would really be much different than just using an off-the-shelf swamp cooler.

[mperkel]

A number of you have suggested and I have thought about chilling water instead of concrete block. I'm listening. I have thought about plans to chill water at night and use the stored chilled water to cool the house. That idea is definitely still on the table.

Thermal mass wise 9000 pound of concrete is the same as 225 gallons of water. In tests that I've done using evaporation at night - yes I don't gain much but I do gain some. On cool nights it's maybe 3 degrees but the warmer the night the greater the gain. With evaporative cooling I think I can consistently get 50-55 degree water.

Trying to figure out what is the best way to get the coolness of the water into the house. Something equivalent to a car radiator with a fan in front of it? I'm thinking of a unit under the house that would draw air in - chill it - and then blow it back into the house.

Sine this is low delta T I'd need a really good heat water to air heat exchanger. Looking for suggestions.

[REP]

Well they did stuff like this 3000 years ago in Egypt.
Of course back then they had slaves to take the stone blocks in and out of the bldg,and other slaves to gentlely fan the occupants.
So all you need are 6-10 big guys to hang around all the time.Of course you'd have to feed them and there goes your effiency.

[Rcb2875]

Have you thought about a water well? I think the earths average ground temp is around 55 degrees at certian depths. That may be a nice easy supply of naturally chilled water. I have two wells that I do not use and have been tossing around the idea of trying them out for geothermal cooling. I'll try and get a depth and water temp tomorrow ( South La. ) I am thinking they are somewhere around 1,200 ft or was it 200 ft bah I cant remember.