Understood. I found a couple other, perhaps underemphasized advantages to a tight fitting and motorized pool cover besides reducing required (and more costly) heat input:
1.) Fewer chemicals required.
2.) Less cleaning required ( but duck guano still needs removal from the cover, otherwise the cover becomes a duck crap wrap.
3.) If a dark and opaque cover, the cover has more than some ability to heat the water, reducing required heat addition still further (== less $$)
4.) A lot less PITA of cover removal/storage.
BTW, never store a wrapped/rolled up bubble wrap type cover in the sun, or shade for that matter without covering it with something opaque - otherwise it'll cook in the sun, or at least and still get pretty warm in the diffuse sunlite present in the shade.
Motorized covers are not cheap, and not easily fitted to irregular pool shapes but pretty slick if/where they can be used. The dark brown motorized cover I had in Albuquerque covered the pool whenever to pool was not being used. Water was => 80 F. or so from mid April to mid/end of Oct. w/ no other heat addition, and uncovered more than a few nites following warm/hot days, although that increased required cleaning a bit.
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1500 kWh and a heat pump w/an average C.O.P. of 4 or so will produce ~ (1500)*(3412)*(4) ~ 20,500,000 BTU/yr. to offset pool heat loss. The top heat loss of an uncovered pool that size will be about that same amount as that 20.5 MM BTU per yr. .per deg. deg. F. temp. diff., pool water to air temp. Start with a pool cover. See my 10/12/2016 post to this thread.Leave a comment:
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And, FWIW, some data:
Between 06/14/15 and 08/1515 on 26 sets (days) of measurements under clear skies, among lots of other data, I measured the following average data based on N=26:
GHI irradiance: 942 W/m^2, std. dev. 24.6 W/m^2
POA irradiance: 965 W/m^2, std. dev. 16.2 W/m^2
Ambient temp: 33.0 C. , std. dev. 3.4 C.
Wind speed: 1.8 m/sec. std. dev. 0.38 m/sec.
Cell temp.: 59.6 C. , std. dev. 3.6 C.
Exposed (to irradiance) roof deck temp.: 68.4 C., std. dev., 3.8 C.
Under panel roof deck temp.: 39.0 C., std. dev. 4.2 C.
All temp. data for each of the 26 dates is the average of 32 separate temps., each of which are themselves averages of 4 random location temp. readings across each of 16 panels, taken immediately before and after the time of minimum incidence angle of direct beam irradiance on the array. Or, in the case of the under array roof temps., the same sampling method done at the same time. All temps. taken with IR thermometer I calibrated using an ice, bath, boiling water and my body temp.
Thus the roof deck under the panels was, on average, ~ 29 C. lower than the same roof material exposed to direct sunlight,.
The roof deck under the array was above the ambient temp. due to thermal radiation from the array heating that portion of e roof deck. That cell temp. to roof deck is also some information to corroborate approx. cell temp. with measurements of cell temp., although there are too many variables involved to get very quantitative about it, it can still serve as another quasi independent equation to help cover all the unknowns in getting an energy balance on the array which is the overall goal, as can the roof deck to cell temp. itself.
About half of the array is over a cathedral ceiling in the living room. The other half is over a crawl space. The insulated ceiling temp. over the array (the south portion of the ceiling) in the living room was ~ 1.5 - 2 C. higher than the north portion, but a lot of that can probably be attributed to orientation. I don't have data on the crawl space underoof temp. diff. between those parts under the array and those parts not under the array.
I believe array shading can help lower the temp. of an attic of a crawl space when there is no insulation directly under the roof. How that may influence the temps. in the rest of the dwelling is largely dependent of the level of insulation between an attic or crawlspace and the rest of the building space.Leave a comment:
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And on the same topic, the best way to reduce the attic temperature (other than improving ventilation) is to intercept the solar energy above the roof and keep it out of the attic. That is, among other ways, with solar PV or solar thermal panels. Especially if you provide adequate air space between the PV panels and the roof.Leave a comment:
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i just got an estimate (we r in ny) for a heliocor system- black tubing goes on the roof for a 18x36 inground... price installed ...9,200 bucks- WOW... thats a lot of $$$- but I figure the payback in not using my propane heater is about 4years... not a bad payback period, but a lot of upfront $$$$.... there is also another 'unique' solar heater that they place up in your attic to take advantage of the heat up there- its black tubes that suck in attic heat... and lowers the attic heat .. not sure of the pricing... trying to gather info from an installer.... downside ofcourse is u better not have a leak...Leave a comment:
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I am the opposite - I grew up in a house with an in-ground pool and as soon as I could afford it I bought a house with a property large enough for a pool and put one in. I don't think I will ever own another property without a pool. And that is despite living in Canada where you need to heat the pool and can only use it from June-Sep.
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This makes a ton of sense as many people, or at least me, are using electricity to cool the house and natural gas to heat the pool. Why not transfer the house's excess heat to your pool water?
You probably mean This Old House: https://www.thisoldhouse.com/how-to/...ir-conditioner
I wonder why these aren't more common?Leave a comment:
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If the goal is to heat swimming pool water in the most cost effective way: Use a black piece of plastic over the pool and keep the upper side free of moisture. Cost is low, close to max. amount of solar energy will get to the water, evaporative losses, which usually make up something like half the losses will be low to almost zero. Convective losses will be about the same as an uncovered pool.
However, as a practical matter, keeping the cover in place as well as removal and placement is a real PITA, and mostly unworkable from a practical and aesthetic standpoint. Material service life will be low, probably less than a few months. But it is most likely the cheapest way considering material cost only.
For separate flat plate pool heaters, I'd agree that the best practical of the solar solutions to heating pool H2O is probably the Fafco type heaters. They do cost a bit more, but they are quite efficient and fit for purpose, which is more than can be said for most of the DIY stuff if those characteristics are of any importance. Not knocking DIY'ers, but beyond a hobby and/or a learning expericence, most of it is not an effective use of resources.
If I understand what Tstahoe is writing, (s)he is referring to the solar shower bags that have a clear cover over a black bag. They do work. The clear plastic is there to lower the convective heat loss some and help achieve higher temperatures for comfort.
In most any reasonable climate, pool heaters work best with no covers, and the highest mass flow rates and velocities consistent with reasonable pumping costs and other component requirements.
The idea of clear tubing being better than dark and opaque, and what I'm assuming is some notion that heat is conducted through plastic at the same rate as through metal to a tube of some sort, is not correct, nor is the idea that some black background will reradiate some energy onto some tubing.
Non metallic material is OK for pool heaters but the thermal conduction path lengths need to be kept much shorter and/or with greater section thicknesses than for metals as f(thermal conduction of the material).
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Saw a program where they added on to the pool pump a heat transfer coil to the heat pump. In the summer it acted as a heat sink to the AC and in the winter a heat source for the heat pump. Talk to some HVAC guys.Leave a comment:
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It depends on:
How well the black background will re-radiate it's heat into the tubing.
How much heat is absorbed directly by the water inside the clear tubing vs. black.
What the transmission rate is for heat from outside of the tubing to the water inside.
What difference in flow characteristics are (diameter of the tubing, friction of the water against the walls of the tubing)
How weather conditions will affect things for one vs. the other) (ex. wind; different levels of sun)
My assumption is that simple black tubing like a fafco panel is the most cost effective for most climates.
And that if it were more cost effective to go with what you're describing, you'd see somebody selling it and showing off studies to prove their solution is better.Leave a comment:
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Newbie here. For warmer climates, what about a simple black insulated back with clear tubing for a solar coil? Wouldn't this allow for more of the sun's energy to get into the water faster? My thinking is from camping showers with one black side and one clear side. Also, I've heard clear or lighter colored blankets for pools are better than the darker ones if heating the pool is desired.Leave a comment:
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