An Idea to Save Electricity

[zippetydude]

Hi Perry. Interesting thread. I like the simplicity of your initial design and have thought before that it was amazing that people with pools didn't do something similar (only in reverse) to heat their pools. A simple circulating line through black pipes at low pressure would be almost fool proof and would cost very little to run. Your idea is very reasonable. I think the only reason it isn't employed more is that it doesn't do the complete job in one step and in an affluent society it can end up labeled "just too complicated" even though nothing could be further from the truth.

With regard to the modifications, I think the tank of water to help disperse the accumulating energy might be avoided. Rather than round pipes, which minimize the ratio of surface area to volume, you could easily substitute relatively thin, flat rectangular ducting with corrugations or internal baffles so that it would be a good radiator but still have the strength to avoid being crushed. A further thought...if the unit could be placed just a few feet beneath a lawn that is already regularly watered, you'd get double use from the water at no additional expense. Same thing could be done beneath the leach field of a septic system. Thanks for the interesting post.

z

[Perry]

Re: heating pools...makes too much sense. Amazes me that people heat pools with electricity when we have sunlight.

Affluent society...yes, from there comes waste through convenience, or in some cases waste is deliberate.
https://en.wikipedia.org/wiki/Handicap_principle
https://en.wikipedia.org/wiki/Conspicuous_consumption

I'm hoping that some variation of this idea in some setting can pay for itself in 3 years. That would be equivalent to 26% APR on investment without the risk of the stock market or a startup venture. Any smart business person would be all over that.

I'll look into some other pipe shapes.... Thank you.

Grass...yes the evaporative cooling would lower the surface temp. A cheapskate version, something I would do, is to hook up a misting system near a window AC. Any time a sensor detects movement of the condenser fan, the misting system comes on. It would greatly increase the cooling ability of a cheap AC unit, but unfortunately it would use water. It would not increase humidity inside the house as long as the AC is set to recirculate.

[Perry]

Some more notes about the images. Ideally, the condenser fan should blow upwards because it's better to not have to change the direction of the airflow in a tight space. The pipes also need rounded turns, and cooling pipes need proper tilt angles and a gravel drainage to deal with water condensation.

[Hikin_Jim]

The pool heating thing, if it raises the pool's temp at all significantly, ought to get people's attention. Pools are expensive to heat, as any homeowner will tell you, and there are sometimes restrictions on pool heating.

Any idea how effective this idea would be in heating a pool? Are we talking 5 degrees above what it would otherwise be? 10? Obviously it would vary quite a bit depending on implementation.

HJ

[Perry]

It's been years since I've done thermal/fluids & heat transfer calculations, and at the moment I don't have a lot of free time, but direct solar heating is easy to estimate. In full sun, about 1,000 Watts of energy reaches a square meter that is perpendicular (0 degree incidence) to the direction of the sunlight. If the bottom of a pool and all sides are a dark blue (because black would not match most people's tastes) I think that would absorb about 50% of the sunlight and I'll roughly guess that the sunlight averages about 60 deg incidence over 8 hours. cos(60) = 0.5

A pool of 10' x 20' is about 3m x 6m so

3m x 6m x 8hr/day x 0.5 x 0.5 x 1kW/m^2 = 36kW-hr per day

If you are in a bracket of 15 cents per kW-hr, that's saving $5.40 per day. At 300 sunny days/year that's about $1,620 per year in savings on electrical heating costs.

I'm sure there are other important details, and I may be a bit off on some numbers because I have to go to bed soon, but that shows why it makes no sense to use a bunch of electricity to heat a pool when a can of dark paint can go a long ways. Maybe a special underwater paint is $50-$100 to cover that much area, not sure but I know it's way less than the electricity saved in a year.

[Hikin_Jim]

Hmm. Interesting.

I wonder how dark the paint has to be before it makes much difference. Most people's pool bottoms range from white to a very light blue. Aesthetically, we like light blue water, I think. But a darker color would be so much more efficient in terms of heat absorption. Navy blue would probably work quite well, but I can't see it being adopted any time soon; it's just too dark.

But what about royal blue? Would royal blue offer enough advantage in terms of heat absorption to justify the expense and effort of implementing it?

HJ

[zippetydude]

I agree that a rich royal blue might be very attractive.

With regard to simple recirculating pipes, my thought was to have a low power pump run the water slowly through a series of black pipes, and ideally the pipes would be enclosed by a black bottomed box with clear plastic walls and top. In this way there would be minimal heat lost into the surrounding air so that not only the heat from the sun's rays absorbed directly into the pipes would contribute to the warming but also the ambient temperature of the pipes sitting inside of a stifling hot box. If you've ever gotten into a car on a hot day you will recognize the additional potential here.

BTW Perry, a few years ago we had a problem with our air conditioner in that on hot days over 100 it couldn't keep up in the afternoon. The sun's rays hit the west wall directly making it hot to the touch on the outside and surprisingly warm on the inside. As a temporary measure I strung some misters across the wall. I'd turn them on just before the sun began to strike the wall. Our water bill did not change noticeably and the fix worked instantly. The misters are very effective and the water use is minimal.

z

[Perry]

I think that royal blue and even a regular blue would make a noticeable reduction in electric bills. It's more complicated than my basic math because 45% of the sun's energy is infrared and 5% is ultraviolet. So we can't know the exact albedo just by looking at the color of a paint.
http://solartoday.org/2012/08/white-is- ... est-color/

There's also reflection on the water surface as the light enters and as it leaves the pool.
http://www.physicsclassroom.com/getatta ... /src41.pdf

I think that a darker color will save electricity. People seem to have different opinions on the Internet. There's some people saying the water absorbs IR. It's hard to research these things with a fussy 2-year-old at home.

Zip, your idea makes too much sense. Unfortunately, I suspect that most pool owners in Southern California are not doing this.
http://energy.gov/energysaver/solar-swi ... ol-heaters
http://www.poolsuppliessuperstore.com/h ... aters.html
http://www.builditsolar.com/Projects/Po ... lector.htm

[phydeux]

Here's some examples of geothermal heating/cooling systems that are already available:

https://www.youtube.com/watch?v=2o7vVjth_TU

https://www.youtube.com/watch?v=d5Tbsx3R2T8

I know there was a "This Old House" episode where they did install a system on Nantucket Island (can't find the exact episode on Youtube). The gound provided a constant 60F temperature source, then the air in the house was adjusted with a heater to a desirable temperature.

[Perry]

Nice videos. I'm wondering why people aren't doing this with air? It seems so much simpler and less expensive.

Here's another basic calculation for the pool surface painting. Ignoring the sun's IR and UV, visible light is 50% of the energy. I'll ignore long-wave IR coming off a heated object because direct water contact cools the painted surface. About 85% of the light during the 8-hour period is not reflected back into the air. The internal reflections are complicated. Let's compare 20% absorption after internal pool reflections to 70% absorption after reflections. (The paints absorb less on a single bounce.)

1kW/m^2 x 50% visible x 85% transmission x gain of 50% absorption x cos(60) x 8hours/day x 3m x 6m = 15.3 kW-hour/day

x 15 cents/kW-hr = $2.30/day savings

That's still substantial.