Author Topic: Solar Hydronic Heating Design (Read 9369 times)

shaniac · « **on:** October 16, 2012, 08:27:14 PM »

Hello, I am thinking about heating a new 40 x 28 foot slab with hydronic heating using water from my domestic solar hot water. Attached is my first draft at a schematic for pulling this off. Does anyone have any suggestions or advice? Since my SHW tank has only one heat exchanger that is already in use with my closed solar loop I was planning on using my domestic hot water. I don't plan to have any zones in the slab and plan to have a 6 inch slab for thermal mass. Your thoughts please on my layout? Thank you for all your sagely advice. Past and present.

JW · « **Reply #1 on:** October 16, 2012, 08:31:29 PM »

I can see this PDF will load, takes a minuite thou. I was wondering if PDF files could be attached to the forum. It needs the link to work, but it does work. (takes some notes)

JW

JW · « **Reply #2 on:** October 16, 2012, 08:37:17 PM »

I know this is a stupid question shaniac, but what {Tag} did you use to upload the PDF?

JW

JW · « **Reply #3 on:** October 16, 2012, 08:47:55 PM »

PDF test

SHW_heat_diagram 01.pdf (12.75 kB - downloaded 309 times.)

Ah-ha

shaniac · « **Reply #4 on:** October 16, 2012, 08:51:41 PM »

Thanks, I just uploaded the PDF as an attachment. No tag just used the drop down menu. If there is a better way I am all ears. Just thought the PDF would be easiest for all. (small, flexible, etc.) Thank you.

JW · « **Reply #5 on:** October 16, 2012, 08:57:08 PM »

Yes you are correct, upload PDF file as an attachment, that works. I was wondering how a PDF file would work, I dont think theres a way to make the PDF open as an image.

I think its great that the forum will save/attach a PDF file, since if someone puts a PDF file together, it can be saved as an attachment and the forum will host the file. NEAT

Thanks for your feedback

JW

Frank S · « **Reply #6 on:** October 17, 2012, 12:33:46 PM »

Are you living totally out in the boonies where there will never be an inspector? Otherwise it is not a good Idea to try and use your domestic hot water for anything other than domestic uses IE washing dishes laundry bathing those things . You could install a secondary HWH for the slab as long as there would be an anti siphon check on the cold side preventing any possibility of slab water returning to the house supply

madlabs · « **Reply #7 on:** October 17, 2012, 05:59:52 PM »

As Frank said, don't mix domestic and hydronic water systems.

That said, I would get rid of the tank heater anyway. I helped a friend with his system and we used an electric 11kW on demand style heater to supplement the solar as needed. Works great. We did end up modulating the temp of the heater as it was getting too hot. With a smaller heater (the same company makes a 7kW model) I don't think we would have to do this. We also had a make-up water connection to the main pressure water system, through a check valve, to prevent a leak from ever draining the system.

Been a number of years and the system has done very well. The system is very similar to what you have sketched.

Jonathan

electrondady1 · « **Reply #8 on:** October 17, 2012, 06:18:02 PM »

slab water
yumm !

shaniac · « **Reply #9 on:** October 17, 2012, 08:52:18 PM »

Thanks gents, although I am not excited about the possibility of savoring "slab water" the quotes I am getting on stand alone slab heating options is making my piggy bank run and hide. I was hoping I could utilize the hot water I have and make a more affordable solution. But it sounds like I will need an additional heat exchanger and twin pumps to avoid the dreaded line ... Honey... this tastes like Slab Water!

Frank S · « **Reply #10 on:** October 18, 2012, 05:21:27 AM »

Chris O has an excellent solar heating system although I believe it is possibly a dry system. For your slab heating the in slab plumbing is what should be considered first everything out side of that can be upgraded as needed.
you can start off with a tank-less heater unit and pump then add solar panels or add more tank-less wattage units. But once the slab is poured and the concrete has cured you are stuck with what you have. Spend the most you have available in your budget for the best you can afford on the slab

madlabs · « **Reply #11 on:** October 18, 2012, 10:42:57 AM »

If you buy the panels new, they are pricey. But you can often find those panels for next to nothing if you are a scrounger. In my area anyway, there were a fair number of systems installed some years back and often they weren't properly done. So the home owner decides "solar sucks". I have 8 or so that I got this way.

As Frank said, you can start with the on demand heater and then add solar. Or at least put the PEX in your slab so that when you can it's there. My buddy's place is so nice in the winter.

Jonathan

Frank S · « **Reply #12 on:** October 18, 2012, 12:08:48 PM »

and for you guys who are thinking about pouring a slab but don't like the idea of piping think about this use heat mat tapes or electric resistance heat wires at least near the door ways these can be wired in later and used as your dump loads a few years ago my company built a 100,000 cubic meter cold storage that's over 353,000 cubic feet @ -20 to - 30 degrees to prevent cold soak and possible icing of the slab at the door areas we used heat mats and in some of the rooms the heat mats were laid through out the floor
No reason why this could not be used in homes and shops whether RE/AE or grid
OF course our slabs were 30 cm thick concrete then 25cm foam insulation then 20 cm of concrete with the heat mats in the upper 10 cm of the concrete. I left out the placement of several layers of bitumine and nylon moisture barriers I'm not giving away all of my trade secretes at one time

GaryGary · « **Reply #13 on:** October 18, 2012, 09:54:25 PM »

Hi,
I'm not sure this helps much, since you are a ways down the line, but I use this system for both solar domestic water heating and space heating: http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm

It needs only one heat exchanger and only one pump for the whole deal.
The pump circulates tank water in the collector loop without a heat exchanger (so, no heat exchanger losses).
The one heat exchanger is a single pass heat exchanger that the domestic water goes through on its way to the regular hot water tank. The heat storage tank is simple and non-pressurized and can have large capacity at low cost.

I think that Radiantec may offer some methods to use hot water tanks in combined space and water heating -- I've not looked at them myself, but they may be worth a look: http://www.radiantec.com/installation-manual/index.php

Gary

ghurd · « **Reply #14 on:** October 18, 2012, 10:07:42 PM »

About the PDF: I am worried about the intentional 'slab' angles shown.

And digging some 6~12" down below the slab adds a lot of thermal capacity, even if the 6~12" lines are below the slab on the return. It probably depends on your location.

A guy in Nebraska put some lines 36" below the slab and basically ran solar hot water through them 7 months a year and it worked great for him. Warm dirt = warm house?
G-

MattM · « **Reply #15 on:** October 21, 2012, 01:02:41 AM »

If you have a crawlspace under the house then floor insulation is great. Lay down plastic over the dirt to keep moisture out. The ground temperature isn't always helpful. This also minimizes subterranean termite risk.

SparWeb · « **Reply #16 on:** November 15, 2012, 11:52:40 PM »

You might be interested in reading the HomePower cover story for this month.
The diagram in the article has all of the features yours has (and a few more like a heat exchanger which you don't always need).

bob g · « **Reply #17 on:** November 16, 2012, 06:57:57 AM »

make extra sure to be there when the concrete work is being done

i can't tell you how many folks have had contractors conveniently forget to put the insulation down under the slab!

and putting it down right is very important to the success of the system.

there is a rather famous example of this blunder in an offgrid colorado home, the place being a million dollar proposition, and the contractor didn't insulate the slab! therefore the house never realized its full potential.

bob g

ghurd · « **Reply #18 on:** November 18, 2012, 09:39:33 PM »

Quote from: bob g on November 16, 2012, 06:57:57 AM

make extra sure to be there when the concrete work is being done

i can't tell you how many folks have had contractors conveniently forget to put the insulation down under the slab!

I have seen it too.

Typical?

"Forget" to do something means no parts cost, no labor cost, etc.
Profit is profit for the greedy.
G-

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Author Topic: Solar Hydronic Heating Design (Read 9369 times)