Heat pump to power hydronic heating as well as hot water?

Hi limefroggy

That is the set up we have. We have two heat pumps for our slab hydronic heating and our hot water system. We have a hot water storage tank. You won't need a separate solar hot water system as well. You could still install solar panels to off set the electricity used for the heat pumps. That is what we have done.

We have Sanden Heat pumps which are 70%+ more energy efficient than your normal electric heaters.

You won't be able to put your hot water system onto 'off-peak' electricity though, otherwise your floor won't heat during the day (if that makes sense).

A company in Melbourne sized our complete system (calculated the thermal load I think it was called) based on number of people in the house and the design/ building materials of the house. They were fantastic.

Bare in mind the 'two' lots of hot water don't meet. The in slab hydronic is a closed system. It is a 'heat exchange'. I'm still learning the process. So far so good, no complaints. The in slab is wonderful and the hot water is coming out of the taps

Hi dolphinblu, just jumping onto this older thread to ask who you used please?

Using an integrated space heating and domestic hot water heating system is a good idea, especially if you leverage solar. If done well it is far more efficient and cost effective over its lifetime than two separate conventional systems.

There's no reason why you can't have some thermal solar panels in series with the heat pump heating loop. The solar can pre-heat the water so you only need a smaller heat pump as the delta temp rise required of the heat pump with be much less (or maybe zero on a nice sunny day). If you use integrated PV-T (photovoltaic + thermal) panels, then you're doing even better (plus the PV component is more efficient than conventional PV only panels, as the fluid takes away some of the heat that reduces panel efficiency).

Solar thermal is a far more efficient process than solar photovoltaic (around 3-4 times more efficient), plus the hot water storage tank is basically a big, dumb battery.

Finding suitable product with watermark approvals is difficult I must admit. Good products exist, but the problem is that traditionally Australia is a market that is very slow on the uptake of new technologies (VERY slow - one great analogy of that is the fact that in Germany they have museums about coal mines....we still have coal mines...). Companies like Alfa Laval have some excellent instantaneous heat exchanger products for space heating and domestic hot water (closed loop, open loop, and combination multi-circuit units). They are excellent units, but don't have AU approvals - the manufacturers don't want to spend the money going through the approval process because it is a risky market venture. They might spend $50,000 getting watermark, and sell 20 units a year...

As for PV-T panels, there are a few around that I have no hesitation in using (and have used). Solimpeks is one. I have no concerns about safety (if buying from a quality manufacturer of course) with water running through PV panels. For example, we have been putting 240 and 415 volt heating elements inside hot water tanks all over the world for the best part of a century.... All good pretty much.

Head pressure - I don't have proprietary knowledge of domestic hydronic heat pump units, if you're using a closed loop heat exchanger you'd just have a suitably sized pump to circulate the heating fluid through the closed loop. But if the circulating pump is part of the underfloor loop then yes, pressure drop may be an issue.

I personally don't really do any engineering for domestic, but we are starting to do this sort of thing on a semi-regular basis when designing commercial and multi-residential buildings, hospitals, aged care etc. One example - I recently completed a 4 bedroom disabled care house/hostel where I designed ground source heat pump ducted AC, with the waste heat from the GSHP used to heat domestic hot water via a heat exchange tank. The overall build cost for this system was only about 10% more than an equivalent Daikin ducted VRF system and standalone Rheem solar/electric HWU - but is about twice as efficient. With the 5kWp PV solar system, the building is not far off being energy-neutral (except for basically lighting, power and cooking at night)

I wonder the ease & cost associated with having chilled water pumped through the floor in summer? Does anyone know what would be involved?

Actually I just read where you said you have Sanden heat pumps. I believe these are solely heating units.