Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

GEOTHERMAL heating—using the warmth of the Earth's interior to heat water—is an old idea. Using the planet's natural coolness, though, is something of a novelty. Nevertheless, as cooling and heating are merely two ends of the same process, it could save money and reduce carbon-dioxide emissions. As long, that is, as you can find a suitable source of cold.

Fortunately for Toronto, it sits next to a very large supply of the stuff, in the form of Lake Ontario. Canada's largest city has been pioneering the idea that instead of using electricity to power air conditioning, a useful supply of cold can be directly extracted from the environment.

Three large pipes have been run 5 kilometres (3 miles) into Lake Ontario, to a depth of 83 metres. The water at that depth is a constant 4°C, its temperature protected by a layer of water above it, called a thermocline. The water is piped to a filtration plant and then to a heat-transfer station on the lakeside. Here the chill is "transferred" to another closed loop, consisting of smaller pipes that supply the towers of the city's financial district.

http://www.economist.com/science/tq/displaystory.cfm?story_id=9065015

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

This is an excellent idea. Once built, the operating costs will probably be way less than for conventional air-conditioning. As a bonus, you won't have the heat from the hot-sides of many conventional AC systems actually making the city they're located in hotter.

Now I wonder if a similar idea I had would be feasible. I was thinking of storing enough water cooled during the winter to more or less fill the entire attic, and using it for AC in the summer. The attic is about 42'x22', and the height in the middle is roughly 6.5'. Assuming I could build a tank to fill essentially the entire volume with water, that would be about 3000 cubic feet of water. I wonder how long this could provide AC, assuming I could cool it to just above freezing by March, and insulate it fairly well so higher ambient temperatures don't heat it much?

nope... not nearly enough capacity to store enough cool for long.

but for heating with wood... there's a system out there that uses wood fire's peak nature to heat up water. which is then stored in a 500-1,000+ gal insulated tank.

very efficient use of a wood fire. you'd only have to fire once a week for hot water in summer.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

jtr1962 said:

This is an excellent idea. Once built, the operating costs will probably be way less than for conventional air-conditioning. As a bonus, you won't have the heat from the hot-sides of many conventional AC systems actually making the city they're located in hotter.

Now I wonder if a similar idea I had would be feasible. I was thinking of storing enough water cooled during the winter to more or less fill the entire attic, and using it for AC in the summer. The attic is about 42'x22', and the height in the middle is roughly 6.5'. Assuming I could build a tank to fill essentially the entire volume with water, that would be about 3000 cubic feet of water. I wonder how long this could provide AC, assuming I could cool it to just above freezing by March, and insulate it fairly well so higher ambient temperatures don't heat it much?

Click to expand...

If you had that much water in your attic it would probably fall in to the basement unless you a reinforced structure. The best way would be to build a tank just under the frost line. A tank won't help much either you would need a tank in the shape of a grid pattern to radiate the heat out and in the winter use it to absorb the heat from the ground and put it back in the house.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

Water weighs approximately 5 lbs. per square foot per inch depth. Assuming an average depth of 36" in your attic that would be 180 lbs per square foot, most residential attics are designed to support about 20 or 30 lbs per square foot, and living spaces are designed to hold about 40 or 50 lbs per square foot. If you have a basement though...

If you are serious about doing this, you can calculate how much water it would take to contain the heat load from your home in the summer. I suspect you will need a goodly sized pond. Another alternative would be a ground loop heat pump system.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

What happens to the life in the water when all the cool water is sucked out and replaced with warm water? I think a ground loop heat pump would be a much more environmentally friendly solution.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

You might be able to build a nice watergarden in your yard. Run copper pipes around in it before it gets to your condenser unit...much of the heat would be absorbed by the pond. Have a waterfall or fountain in their to help keep the pond from over heating. That should boost the effeciency of your system and perhaps look nice as well.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

tebore said:

If you had that much water in your attic it would probably fall in to the basement unless you a reinforced structure. The best way would be to build a tank just under the frost line. A tank won't help much either you would need a tank in the shape of a grid pattern to radiate the heat out and in the winter use it to absorb the heat from the ground and put it back in the house.

Click to expand...

Oh well, it was just a thought. I'm guessing my house could probably deal with the weight (it's only about 100 tons by my calculations) since it's brick with a poured concrete foundation but it seems I would need a lot more than the 3000 cubic feet of water I could store in my attic to last the summer. We don't have nearly enough property (the lot is only 40'x100') to even think of putting a big enough water tank in the ground, or making a pond. Probably a geothermal heat pump to take advantage of the cooler ground temps in the summer (and warmer temps in the winter) might be a better answer.

I've thought of using either stored rain water or tap water to cool the hot side of an AC system. Even in mid-summer the tap water is no higher than about 78°F so the end result would be a much more efficient AC system. The "used" tap water could be sent to water the grass.

It is pretty easy to figure out how much cooling you can get from 3,000 cuft of water...

3,000 cuft * 62.427 lbs/cuft [inverted units] = 187,281 lbs. [comma in wrong place]

A typical room AC unit is around 10,000 btu/hour...

your water will change about 19 hours per degree F... From 40F to 80F would be 40 degree F change...

40F * 19 hr/F = 749 hours of cooling at 10,000 BTU per hour

Or, about 62 days of "12 hours per day" of cooling.

All of the above is assuming you have 40F staring water and can get some cooling up to 80F--probably a bit optimistic--but good for a SWAG.

Regarding using a pipe out to the ocean... That is a bit more problematic.

San Francisco used to have the largest heated outdoor pool in the world (1/4 mile long) that used sea water. Also, a major aquarium in the park also uses ocean water for its salt water exhibits. And, I grew up in a town with a sewer outfall...

In all cases, broken pipes from storms (every few years or so) were (are) a constant nightmare. Between the waves and corrosion--it was not a cheap way of getting (or dumping) water.

-Bill

Regarding once use of tap water for the cool side of an AC unit... The City of San Francisco did that for many years (back in the Main Frame Decades).

Issue was that while it was cheap for the city (lower electricity bills, and they do not pay a water bill for city water), it was a tremendous waste of water--and they were shamed into ending the practice because of one of our droughts that we get every so often... So much so that they drilled wells to try and get water that way--in those days (3 decades ago?), the system was not able to handle the sand and other contaminates in the local well water.

I am sure that ground sourced systems are much better today.

-Bill

PS: With where our local water prices are going, 3,000 cuft of water is well over $100 (probably more if all used in one month).

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

Cooling a home, as mentioned is better done by utilizing the temp differential of underground earth. It's stable at around 55 degrees F. Circulating water to heat exchangers at either end to transfer heat from interior air.

Your attic is better utilized to preheat hot water during warm seasons, as attics can hit 160+F in the summer. Circulate water between several radiators and a well insulated storage tank(the original hot water heater tank will do) with a solar powered pump. Flow detectors and diverter valves are used to redirect cold water feed to radiators during demand.
Similar set up can be used to capture the waste heat from a central AC compressor.
Heated waste water from showers and dishwashers can be extracted too.

Although the idea of pumping cold lake or seawater to use in the chillers of AC units is 'cheaper' the waste heat must go back to the source, and that can destroy the eco system that is built around the cold temps.
Look at all the dead marine life caused by nuclear reactor sites using nearby rivers as source of cooling!

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

I've mentioned this before.....

When AT&T split up the new baby telephone companies were free to create new structures. In doing so, Pacific Bell created the San Ramon complex. It housed 10,000 people at it's peak. The building is surrounded on two sides by man made lakes. The lakes were used as heat sinks at night when the air conditioning froze a huge block of ice. During the day the ice blocks were used to cool the building via heat exchangers.

An interesting side effect of the extra heat pumped into the lakes; It attracted migratory birds. The birds left their droppings in the water, fertilizing it. The heat plus nutrient rich water caused intense growth of vegetation in the water.

It was relaxing to watch the floating mowing machine cruise lazily through the water all day, every day. It looked like a flat bottom fishing boat with a paddle wheel on the front to pull the clipped weeds from the water.

Yep, there are always impacts.

Daniel

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

For a while in the late 70s I had a hobby farm in a place where the ground water was 45° F. It was actually cold enough that it made it kind of tricky to water the garden. I contemplated putting an 'A' frame coil in a duct with a fan to dump some of the heat from the house into the water before it hit the garden but I sold the place before I got around to it. I think it would have worked really well with soaker hoses as I would be able to scale the flow match the 'A' frame. Cool the house and make it better for the garden, too.

When AT&T split up the new baby telephone companies were free to create new structures. In doing so, Pacific Bell created the San Ramon complex. It housed 10,000 people at it's peak. The building is surrounded on two sides by man made lakes. The lakes were used as heat sinks at night when the air conditioning froze a huge block of ice. During the day the ice blocks were used to cool the building via heat exchangers.

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IMHO this seems like the best idea for air conditioning to me -- run the air conditioner in the middle of the night in order to make ice. Ice is a much better heatsink than "cooled water" because it takes a huge amount of latent heat to melt ice. Storing an insulated "block" of ice sufficient enough to cool a building for an entire day shoudln't take up a ridiculous amount of space, either.

The fact that a lot of electrical load would be shifted to the night-time is a huge benefit, everyone running AC in the middle of the day time during summer is what causes so much strain on the grid. A lot of places offer off-hours deals too where electricity bought off hours is a lot cheaper (such as $0.18/kWh during the day, $0.05 at night)

cmaylodm said:

What happens to the life in the water when all the cool water is sucked out and replaced with warm water? I think a ground loop heat pump would be a much more environmentally friendly solution.

Click to expand...

Thats what I was thinking.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

You could build an insulated, underground phase change thermal mass.

Use a large tank filled with roughly 10-30% ethylene glycol. In that tank, place several loops of polypropylene pipe. Use these pipes to connect to a heat exchanger exposed to the winter air and circulate 70-80% glycol. In the winter, use the frigid air to circulate the 70% glycol to slowly freeze the water out of the 10-30% glycol. In doing so it will concentrate the glycol in the remaining liquid thus lowering the freezing point of the remaining liquid. The freezing process performs a "mushy zone" distillation using the liquid/solid phase change. Much like distilling with liquid to gas phase change. The tank glycol solution will only freeze to its eutectic point at roughly -85F. As long as your outside temperature doesn't go below -85F you're OK. In the summer, you use the reverse phase change to store heat from your house.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

jtr1962 said:

Oh well, it was just a thought. I'm guessing my house could probably deal with the weight (it's only about 100 tons by my calculations) since it's brick with a poured concrete foundation but it seems I would need a lot more than the 3000 cubic feet of water I could store in my attic to last the summer. We don't have nearly enough property (the lot is only 40'x100') to even think of putting a big enough water tank in the ground, or making a pond. Probably a geothermal heat pump to take advantage of the cooler ground temps in the summer (and warmer temps in the winter) might be a better answer.

I've thought of using either stored rain water or tap water to cool the hot side of an AC system. Even in mid-summer the tap water is no higher than about 78°F so the end result would be a much more efficient AC system. The "used" tap water could be sent to water the grass.

Click to expand...

your best bet would be to dig a well down to the thermal layer where the temp was at least in the mid 60's or lower. With a heat pump you can heat or cool depending in the climate. My moms house has had this system since the early 80's. The heat pump is over 20 years sold and has maintained a SEER of 33. I would love to do this for my house but the city will not approve the permit.. No water wells in the city limits. A well around here cost about $18 per foot to drill with the hardware and I would have to drill about 350 feet to get to my desired temperature. In Austin Texas, about 150 miles north west of me, you need to go down about 800 feet. The problem is that it is all lime stone and the cost is about $20,000 just to drill the hole, casing, pumps and heat pump extra.

In your area, I think you are scewed. I think I remember that New York has some bedrock much harder than limestone that would be problematic.

Re: Hydrothermal cooling: How to use cold water from lakes and oceans for air conditionin

Just FYI, the brick on a typical house is classified as a veneer. It's decorative only. The walls sit on the studs. The brick just sits there.

Also, modern brick is decorative, not structural. Apply a nice load to it and watch it fail.

I noticed an interesting thing from hurricane katrina. When the water surge hit wood-sided homes it punched holes through. When it hit brick homes the brick held the wall together and the whole wall fell over. The mechanism was that the water entered through doors and windows. It then pushed the walls out from the inside. Not that it really matters anyway. All belongings were swept away in either case, but at least the wood sheathing left *some* structure behind to live in (which is what many people had to do).






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Originally Posted by jtr1962
Oh well, it was just a thought. I'm guessing my house could probably deal with the weight (it's only about 100 tons by my calculations) since it's brick with a poured concrete foundation ...

I've got one of the most efficient A/C systems around. it's a smaller version of HUGE water tower systems typically used for commercial complexes.

water tower uses tap water, from deep underground pipes, up to 40 degrees cooler than air temps. then water is pumped to top of tower evaporating and carrying away heat. water is one of the most efficient heat transfer agent known.

chilled water is then routed to heat exchanger using internal loop of R409A. driven by a large semi-hermetic compressor. rest of heat exchange is pretty standard, other than size of air exchange box.

original compressor was made in 50's by chryler air temp. I did the retro-fit to a modern semi-hermetic compressor and changed refrigerant from R12 to R409A. took a engine cherry picker to move compressors in place.

during 100 degree summer days. my monthly electric bill for a 2500sf single level home will be under $100.

A cooling tower augmented condenser coil is a great way to boost efficiency.

It's almost intutive. Is it easier to pump heat into 100F air or 60F water/air?
They work especially well in dry climates. It wouldn't work so well in the jungle.

cy said:

I've got one of the most efficient A/C systems around. it's a smaller version of HUGE water tower systems typically used for commercial complexes.

water tower uses tap water, from deep underground pipes, up to 40 degrees cooler than air temps. then water is pumped to top of tower evaporating and carrying away heat. water is one of the most efficient heat transfer agent known.

Click to expand...