Combining a heat pump and electric boiler for solar PV powered home

heatpumpsolar

I'm curious if anybody has experience with, or ideas about installing a heat pump/electric boiler hydronic heating and cooling system to maximize efficiency for a solar PV powered home. So far I've found this Nor-Aire system: http://www.electromn.com/gen/nc-fe.htm and envision either Buderus, Ecostyle or Pensotti radiators.

According to technical support at Nor-Aire their heat pump can increase temps to 110 degrees. A couple of things that I'm trying to figure out is whether it's more efficient to run more radiators at a lower heat level and how to size the boiler to get up to the operating temps of the radiators (either low at 140 degrees, or higher up to 180 degrees) with those considerations.

I'm a builder, but not an HVAC person so I'd like to hear from those of you who might be interested in this topic. Thanks!

jumper

Install more PV & forgo heat pumps. More economic & comfortable to use hotter water for heating. Also more economic to store hot water than electric energy.
OTH store hot water does not take care of night time A/C. Easiest is to manually switch between PV daytime and utility nighttime for that. When you're away leave A/C on PV.

heatpumpsolar

I live in the UP of MI. The heat pump is a good way to efficiently get the water to temperature, but it won't get hot enough to supply a radiant heating system. I don't always need to feed the system with Solar PV as grid power is available but I'm hoping to design a system that is very efficient and may be able to provide the heat I need with a combination of wind and solar.

Jamie Hall

Oh dear. These things sound so wonderful and attractive. Until you do the sums.

Do I presume that the intention is to have this building's electrical power come solely from solar photovoltaics? Or is the place going to be grid connected, with a nominal PV array? It makes a huge difference in how you think about it.

Also, where is it to be located? What will work in, say, southern Utah won't even come close in, say Massachusetts.

Yes, the heat pump you mention will raise water to a maximum of 110 F -- but no higher. Perhaps more to the point, therefore, your return temperatures will have to be significantly below 110 -- probably around 80 -- to get anything out of it useful at all. but... even a full-ledged radiant floor system is going to need water at at least that, and unless sized very very carefully will not have low enough return temperatures to get anything much out of the heat pump.

Therefore, even if you were to use an electric boiler to boost the temperature to 140 or 180 to be able to use anything like normal radiation for heating, you'd still have to have an extensive radiant floor system to extract the additional heat from the water to get it down to 80 or so for the heat pump to be useful at all.

You might be able to get away with using the heat pump to heat water for hydronic air handlers, but again they would have to be quite large to essentially cool the water enough for the heat pump to be useful.

If this is to be off-grid, again, do your sums. Yes, you can use an electric boiler, of course. But how big is your PV array going to be? And how much energy storage are you going to have for when the sun isn't shining? Not that it can't be done -- it can. But the arrays in most climates get to be impressively large -- and the storage battery banks begin to look like something from a fleet submarine.

There's also a cost factor involved...

You really need a qualified engineer -- they do exist -- to do the sums on this and specify what is needed, then you need to assess the costs and see whether going this route is even remotely feasible.