Need help designing a solar water heater for radiant floor heat

[WillyP]

Originally Posted by solarhotairpanels

Willy, how is your system build coming along?
I've been sitting here since July tapping my foot waiting for your update.

Take about 2 million pictures ok?
I like looking at pictures with my morning coffee. :-)

Sorry man! I am in the design phase right now. I am asking a million questions and have already realized some serious errors in my plan. I wont begin construction on the house, until spring of next year. But I plan on taking pictures and videos as well.

I retire in April of 2022, once that happens I will begin building the house.

[solarhotairpanels]

Originally Posted by WillyP

Sorry man! I am in the design phase right now. I am asking a million questions and have already realized some serious errors in my plan. I wont begin construction on the house, until spring of next year. But I plan on taking pictures and videos as well.

I retire in April of 2022, once that happens I will begin building the house.

OK Sounds good.

[jeff5may]

Better hurry up before the dollar implodes. Your retirement account might need another zero on it before you can retire. Mr president is already on with the rhetoric: more stimulus, more spending, minimum wage hiking, and we NEED inflation. His plan sounds like your original plan: a hundred square feet of sunlight, to heat pipes, to oil, to glycol, to water, to (I think) slab.

Meanwhile, in my world, I gave away another window heat pump to my buddy. R290 txv heat, original cap tube cool. It was rated for 10kbtu and 10 eer as an air conditioner. It got down to 20 degF here last week, and dude said it kept his workshop as comfy as the propane heater he was feeding a BBQ tank a week to do the job. He keeps asking me how much he owes me for it. I told him happy birthday.

[IamIan]

Originally Posted by WillyP

Jeff:
I am not using it for domestic hot water. I will be using an electric hot water heater, powered by the PV panels (grid tied system).
I will be heating the whole house.
The Evacuated tubes will heat about seventy gallons of water. That water will feed heat exchangers inside the underground tanks and the discharge tank. Each tank will have its own thermal switch, with its own pump. That way I can regulate the temperature of the water that feeds the radiant floor heater.
The heater itself will have its own PV panels with battery backup. It wont be attached to the main system for the house. That way it will work in a power outage.

Conventional resistance electric hot water heater .. or .. heat pump hot water heater ?

Both use electricity .. can be powered by the solar / batteries.

But the heat pump option have 3 benefits over 'old school' resistance electric heaters.

#1> Efficiency
Less wh of electricity input per wh of heat output.

#2> Temperature gradient
Extract wh of heat out of the solar thermal sun room collector .. even when it's cold at the collector .

#3> Reversible
Can provide both heating and cooling

- - - -
The expensive (but easier) route is to buy the heat pump unit as an off the shelf from OEM plug and play unit .. the less expensive (more effort) .. is to convert one of the mass produced heat pumps to do the job.

The window air conditioning unit .. is a common mass produced conversion .. for people wanting temperature regulation for things like gaming CPUs , brewing (beer or wine) , pet enclosures (reptile or aquarium) .. commonly used for the the cooling (aka chiller) side .. but both heating and cooling are options .. do a web or youtube search for DIY 'chiller' and you'll see at least a few DIY conversions.

[jeff5may]

IamIan,
Take a gander on this discussion group. Geothermal forum. Probably half a dozen build threads where members have rolled their own. My favorites are Randy and Jake (randen, memphis). Randy used a smallish window AC unit, Jake built a DX ground loop from scratch. Jake amped his up by adding an indoor dehumidifier loop. Both run off 120 volts and save energy.

https://ecorenovator.org/forum/showthread.php?t=4413

https://ecorenovator.org/forum/showthread.php?t=3247

[randen]

The utilization of solar heated hot water for heating a concrete slab for space heating is Nirvana!! On all accounts its a home run for: saving money, complexity, and comfort.

Here in Canada our winter weather is a little harsh. But I have once described the comfort like this. "On a cold windy morning standing infront of a window with a coffee in hand watching the wind swirl the snow around with my sock feet on a porcelain HEATED floor is the most comfortable feeling know to man!!!"

I have 220 sqft of flat plate solar collector on a south facing wall. with a full day of sunshine from 10:00am til 4:00pm will warm the concrete slab to 28 Deg. C which will store enough heat for 24 hrs. and hopefully the next day more sun!!

Complexity well start with planning!! The concrete slab has to be well insulated a minimum of 4" HD foam insulation under. the slab an 2" around the edge to mitigate any heat losses
Tubing in the floor. There are a few manufactures of this product designed for this application Wirsbo comes to mind. They have a complete system of manifolds valves etc. This tubing is tied to the weld mesh thats in the concrete at a foot apart. There is a lot of information now on lengths required in the loops.
DO NOT over control these loops!! IT is NOT necessary to sense and control the temperature of the zones!!! The liquid heating of the slab is very uniform and thats what you want. KEEP IT SIMPLE!!! Choose a central location in the house and place a thermistor (install a little well for the Thermistor it maybe necessary to replace) in the concrete between the loops to control the slabs temperature/Circ. pump.

DO NOT consider storage tanks, buffer tanks, mass storage (tank with boulders) Phase change materials ETC.! I know I probably made some enemies there. But hear me out: You cannot store enough water and keep it insulated and manage the pumping, heat transfer and the cost for all this is overwhelming. KEEP IT SIMPLE.!!

THE CONCRETE SLAB IS YOUR HEAT STORAGE.

We have experienced power outage (no power for circ. pumps) in a winter storm. The concrete floor maintained enough heat during that event for THREE DAYS.


To heat the floor with solar make a DEDICATED hot water loop in the floor. Hot Water/Glycol (propylene Glycol for freeze protection) Employing a small circulation pump, small expansion tank and Mixing valve on its own manifold. Having a dedicated solar heating loop raises the efficiency doing away with heat exchangers ETC.

KEEP in mind your goal of heating with the sun cost nothing going forward.!! Depending on the amount of sun in the winter SOLAR has provided HALF our homes heat!!

Install a second loop offset the tubes in the concrete in the middle of the dedicated solar loop. You will also need a manifold and small circ. pump and expansion tank. This will be your supplemental heat if you don't receive any sun.!! Your heat source here is your choice Propane boiler Demand heater Wood boiler or the King.... HEAT PUMP

Dedicated loops just saved you costs in both efficiencies and extra costs related to heat exchangers and valving. Plastic tubing is cheap by comparison.

Space heating is the largest energy cost for the home. Solar hot water heating is direct and no energy conversions like using Solar PV. and inverters ETC.

It works, we've being living with solar space heating since 2008 saving energy saving money and very comfortable

Randen

[WillyP]

Thanks for your input. It sounds like you have a system that works for you. I am curious about two things. How do you keep the slab from cracking? If you use deep footers, are they insulted?

[skyking]

concrete cracks. put reinforcing in it to prevent displacement.
I like this idea, but I also like conventional construction with a crawlspace for various reasons. I am *so* on the fence about slab on grade vs frame flooring.

[mwmkravchenko]

Originally Posted by WillyP

Thanks for your input. It sounds like you have a system that works for you. I am curious about two things. How do you keep the slab from cracking? If you use deep footers, are they insulted?

I grew up in Manitoba Canada. The ground freezes solid there to 8 feet deep. If you do not have a basement you have a slap on grade. A floor on a raised bed of aggregate so that it will not stay wet. Properly done this is more than enough to support a house. You do have to use Re-bar. If it is a larger building you can thicken the edges of the slab. As was mentioned the slab has to be insulated from the Ground. When it gets that cold it is a good idea to insulate anyway!

Oh, and if you are wondering, this frozen ground thaws in the spring and you can dig like normal. It's not permafrost. Where I live now near Ottawa Ontario the maximum frost depth is 5 feet. Under snow cover it's more like 18 to 24 inches. Same goes for Manitoba you get 5 or 6 feet if you have good snow cover. Roads are where you will get maximum penetration. Or windswept areas.