Need constructive critique on my idea for a solar hot water panel , please

[ilbebauck]

Some background : I live alone and want to totally eliminate the need to run my 40 gallon electric water heater, and since i live in sunny Florida I believe I can do so given my low requirement for hot water. Im going to be building my solar collector very soon when all the materials are gathered. My requirement for hot water usage is to take a relatively quick shower of 5-10 minutes using 100 f. hot water and believe the following plan will handle at least that :

I want to use 3/4"x300' coiled red Pex Tubing which measures 32" diameter x 7" high . I will set this in a box which i will construct out of wooden 2x12's with a 1/2" thick plywood on the backside (treated) for a 36"x36" od Box. . I will lay 4" of dense pink Foamboard in the bottom . A 32" square sheetmetal plate painted with flat high temp. low gloss Black paint (primed first) will be layed on top of the bottom Foamboard . The coiled Pex tubing will be wrapped in heavy duty tin foil sheet to prevent UV light from seeing the Pex , and this foil will be pulled tight around the coil of Pex and also painted high temp flat black. ... then the coil will sit inside the box in direct contact with the sheetmetal plate. A double pane window in frame measuring 36" sq. od (without any inside bars) will be fastened on top of the box for a greenhouse effect. The box will sit against the southside of the house on the ground at a 30 degree angle from vertical in a location where where it will recieve full sun. I will cut the hot water CPVC pipe above the water heater and route to the Solar Panel using 3/4" CPVC (insulated) connecting to the 3/4" Pex tubing stubbed out of the side of the Box using Pex compression fittings . The return CPVC pipe (insulated) will run back to the top of the water heaters hot water supply pipe. (Since my hot water reqirements are very minimal, I opted not to heat the entire water heater) .

Since stagnation temps/pressure in the box are of concern, i plan on securing a section of shiny sheetmetal over the face of the Box for capacity control during the summer months.

Specs on the Pex are 100 psi at 200 f. Specs on the CPVC pipe are 100 psi at 180 f. May aim is to deliver hot water in the 100-120 f. range thru experimenting with how much to cover the front of the Box with the shiny sheetmetal plate .

Total estimated cost for this project is $300 ($100 for the Window , $120 for the coiled Pex, and $80 for the wood and CPVC piping with fittings .

If you have tips, considerations, concerns, etc... I would love to hear them. Thanks. Dave.

[.p.jm.]

That is not 'hot' water, that is 'slightly warm' water.

Pex is good to 160 PSI at 200F, I think.

What's going to drive the water to the tank ?

[ilbebauck]

malrescuesite.com/

1. The Pex im using is rated at 200 f. @ 100 psi.

1. Im not sending the solar heated water to the Tank (Water Heater)...im simply putting it back into the hot water supply line above the Water Heater , so no pump is required. It will use the line pressure to force the water thru the Pex Collector once i open the shower hot water faucet.

[.p.jm.]

!!!

Better figure out the gallonage there, skippy. You'll get about enough to wash your hands ( in slightly warm water ).

Not hardly worth the effort.

[ilbebauck]

animalrescuesite.com/

malrescuesite.com/

In 300' of .675 i.d. piping, there is approx. 6.5 gallons. And thats enough for my quick warm shower which i enjoy.

[ilbebauck]

Thanks much. Ill get hold of him.

[.p.jm.]

My grandmother is more help than you, and she's dead.

[Steve]

Here a couple of things you haven't taken into account. first, there is a reason the piping in solar collectors is copper... Start with actual temperatures in the collectors... copper doesn't melt at 200F. Copper is also a lot better conductor than plastic. Plastic makes great insulation. Then there is this little matter of the temperature setting that you want to use. There is a reason that waterheaters are set at 125F or higher... can you say legionella?? As a rule, solar is used to *augment*, not replace waterheaters.

Its you money and your health, you can do what you want.... you can DIY "cheap" or you can get it done right.

[.p.jm.]

that a flow rate of 0.5 to 1 GPM - that's not 'a shower', that's 'a light misting' :-)

And when it runs out, and you get a blast of that 120 - 130 water from the heater that's been pushing it ..... or cold water if the heater's off .....

Now, figure out how much energy it takes to raise 6.5 gallons from your supply temp to your 100F outlet. Say a 50 degree rise. Now look at the cost of electricity to supply that much energy.

~ 50 lbs of water, raising 50 degrees = 2500 BTU.

aka 733 W aka ~ .7 KW.

Multiply by your electric rate - maybe $ 0.10 / KW ? $0.15 ?

So - maybe $ 0.07 to $ 0.10 per shower.

vs How much investment ?

[.p.jm.]

Neither does PEX :-) Not that it will get that hot.

Of course, wondering 'what temperature will it be at THIS time ?' will add excitement to his day .....

Oh, BTW - I just remembered - he CAN't use PEX ! It deteriorates in sunlight ( UV ) !

Oops .....

[PaxPerPoten]

!!!

!!!

Just enough to flush an older toilet. ;-)

[PaxPerPoten]

Also 120°F+ is needed to break down and utilize detergent. Dishwashers have an extra heater to take in 120°F From the Water heater and increase it to 140°F to more efficiently break down detergent. Also Laundromats have Hot water in the 140°F to 160°F to sterilize clothing and to kill bedbug eggs. Never select warm or cold in a public laundromat.

I vote we send Stormy over to straighten this guy our.. :-p

[PaxPerPoten]

Some special types don't..The gas company uses some that can be let victim to old Sol.

[PaxPerPoten]

Why not super insulate that electric heater, put a farm timer on it for one hour in the early morning and one hour in the late afternoon. Of course install thermal breaks or thermal loops at the water heater. The money saved..not buying pex ought to pay for a few electric bills. I did that with a stubby 40 gallon at the Lake a few years ago. The Heater sat on a tinfoil covered stereo foam pad inside a foil faced Stereo home made cabinet. Then stuffed with fiberglass bats. It also had Thermal breaks on the water lines.

[ilbebauck]

I wanted to do this project as cheapily as possible so copper was ruled out otherwise i would have gone with 3/4" id copper. With capacity control the Pex wont melt . So long as theres bleach and the water moves periodically in a water heater, there is no health risk...ive been taking cool showers all my life at 100 f.

[ilbebauck]

malrescuesite.com/

I figure out of my $100 electric bill, $20 of that goes to the electric to heat water ; therefore my project will net a 15 month payback which is outstanding.

[ilbebauck]

malrescuesite.com/

I addressed the UV light problem in my OP , and it wont be a problem the way im going to do it.

[ilbebauck]

When i run the Dishwasher, ill introduce hotter water than `120 f. BUt all i want for a shower is 100 f.

[ilbebauck]

Because you need a pump if youre going to heat a storage tank and i dont want to lay out anymore than $300...that was my budget. It will work fine the way i have it planned out.

[Steve]

I figure out of my $100 electric bill, $20 of that goes to the electric to heat water ; therefore my project will net a 15 month payback which is outstanding.

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Don't forget to add in the cost of the permit and inspection.