Heating Schematic, what have I missed? Any advice or or thoughts.

[Just David]

A little background, we have gas warm air heating fitted in the 60's when the house was built. It was just replaced with a newer model that has a built-in water heater that can put out about 3.3Kw/h.
On the roof we have grid tied 7kw/h PV panels along with batteries. I would like to put a further 1.5Kw/h worth of panels on the only other piece of the roof where they would be viable, this would be used solely for heating water via immersion heating. (I did look at air source but it wasn't going to be possible).I did look at solar thermal panels but for a few reasons I've had to rule them out. I have 2 stainless steel unvented tanks although I won't be using them with mains pressure. My thoughts are the lower tank on the 1st floor is only heated (by gas) only in a few winter months, the higher tank should be sufficient for the rest of the year. Take a look at the drawing, What are your thoughts? I was hoping gravity feed might eliminate the requirement of 2 pumps?


Heating-schematic.jpg

[Mike90250]

Is the gas heater on a lower floor than it's storage tank?

You will most likely, need a pump at the gas heater, thermosiphon is not likely going to be enough - depending on the size of your heat coil. You need the hourly BTU calcs for this.

For thermosiphon to work, all the pipes must have a slope to them, and no reverse pitch.

There's going to be losses each time you transfer from tank-tank-heat ex

I used domestic rated SS tanks at full house pressure, the only heat ex is in the glycol loop on the rooftop heater, and the 1" SS loop in the masonry heater
I've chosen to preheat water for the tankless water heater, winter, the masonry heater boost the 35F water up to at least 80F, so the propane usage is low. Summers,
we get 160F water from the roof and have a mixer valve at the tankless to keep that below 130F
example below - built and running since 2012 fall

1711_HotWaterSchematic_AsBuiltcC.jpg

1711_HotWaterSchematic_AsBuiltcC.jpg

[Just David]

Hi Mike

Yes, the gas boiler is on the floor immediately below the first tank with the second tank on the next floor above the first tank. The water heater within the boiler is rated at 11,340 Btu and the heating coil within Tank 1 is rated at 15,000 Btu. The pipes are vertical ( about 6 feet) with then about 3 feet just slightly uphill from horizontal. Pipe size is 22mm (3/4"). Does that suggest that it may gravity cycle or is it going to come down to try it and see?

[Mike90250]

The cold return has be to lower then the hot inlet. and for thermosiphon, 3/4" is a bit small, I'd go with 1". From your boiler, you may need to use copper, because PEX may not take the heat long term

[Just David]

Hi Mike, the height of the inlet/return to the tanks in the diagram is incorrect, that's a drawing error on my part, thanks for pointing it out, I'd overlooked it. At the actual tank externally they are actually level, obviously internally this isn't the case and it is clearly marked flow and return to prevent error.

The first couple of yards from the boiler I have done in copper before going over to plastic, I looked at the plastic pipe specs and it is well within temp/pressure range and Hepworth also offer a 50 year warrantee on their plastic products, so it should be OK.

I connected up today from the gas boiler to Tank 1 and gravity fed cycling worked fine I'm pleased to say, no pump will be required there. Now need to plumb in the top tank and see what issues that gives.