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Sharing Domestic Hot water tank with heating system

(6 posts) (4 voices)

Started 8 years ago by middo
Latest reply from cremorne121

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middo
Member

I am working on a design for a self build house, aiming for 8 or 9 NatHERS rating. Given the design and location I have a peak heat requirement of 3kW, and maximum daily heating of 24kWhrs excluding solar gains.

When I add the solar gains, I believe I could provide the bulk of heat from a shared solar collector (sharing domestic hot water and heating, with electric boost for exceptional cases). 60<=>90 evacuated tubes with inclination optimized for July to minimize overheat in Summer. Looking at using a conventional >400L residential hot water tank with electric boost. And 3x in slab hydronic loops for delivering heat.

So here is my question, how do you share a conventional residential boiler?
- Are open systems (sharing heating and domestic hot water circuits) non compliant in Australia? I have seen these designs on some international sites.
- If so I need to separate the heating circuit by insert a heat exchanger and making it a closed loop. Does anyone have recommendations for local suppliers of necessary components? (plate heat exchanger or boiler with internal heat exchanger / expansion tank system for the closed loop)

Posted Thursday 23 Jan 2014 @ 1:28:33 pm from IP #
Morbo
Member

ours is at 30 deg, overheating in summer. Not much going on the last few Melbourne winters, too cloudy. 225L tank, 2 people.
You would have to put your 60-90 tubes at winter angle, maybe even 10 deg steeper, otherwise you will be in serious trouble in summer. 90 tubes will get 400L from 20 to 70 in 2 days max in summer

Posted Thursday 23 Jan 2014 @ 8:34:49 pm from IP #
MaxG
Member

The coil you put in needs to be watermark approved...

AFAIK open systems are allowed in AU.

I am in a similar boat: owner-building, installing hydronic floor heating, hot water, etc. will decide on the heat source when ready; however, the decision on the tank has been made. I will build it myself, by using a 5,000l stainless steel water tank, wrap R5 insulation around it and hang a few coils in... being an open system. One for the heating, one for solar evac tubes, one for the wet back on the wood combustion heater, most likely a fourth as a reserve.

Posted Friday 24 Jan 2014 @ 8:04:09 am from IP #
middo
Member

Morbo, Yes overheat is a concern and will have to build in overheat protection. Apricus offer a product that seems ideal:

http://www.apricus.com/html/solar_heat_dissipator.htm#.UuIyXBA1i9I

Will have to plumb something like that in for safety. (thermostatic valve or solenoid operation will depend on the controller that I use)

Posted Friday 24 Jan 2014 @ 9:33:08 am from IP #
Morbo
Member

actually 60 tubes may just get you by in winter in terms of hot water. Got 30 but facing not exactly north, and last few winters its 20-25 deg in the tank, and we don't use much hot water.
Maybe you are better off extracting heat from the roof space as you are harvesting a way bigger surface area.

Posted Friday 24 Jan 2014 @ 9:56:02 am from IP #
cremorne121
Member

The Enter Shop (Gary Flood) in Melbourme appears to have good knowledge. I'm planning on using a copper ring main with copper convectors to heat the living room. All water is the same, no separate loops. Just one water pump to circulate through the ring main, and an air fan in the convector.

Posted Friday 24 Jan 2014 @ 9:56:58 am from IP #

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