Thermodynamic Heating

[extractorfan]

I’m sure this technology must have been discussed on here but after a brief search I can’t find it.

I had a guy round yesterday to sell me a solar pv system, that I will probably go for, it’s the grid connected one where you sell electricity back to the grid at the new lower tariff.

However, I was interested in this Thermodynamic water heating system, it’s not really solar and I pointed this out to the man, it’s like a fridge motor in reverse, takes heat out of the outside and puts it into the water in the panel and it runs of electric. Apparently it costs about the same as running a fridge 24 7 and keeps your water at a very comfortable 55 degrees C. He said it wasn’t suitable for central heating, only for hot water for Baths, Showers and Washing Up.

Has anyone on these forums tried this technology? It costs about 6.5K to install but could easily shave £1000 per year off our gas bill.

This isn't the company selling it to me, but it's exactly this technology.

http://www.thermodynamicssolar.co.uk/ (Edited to correct URL - Ken)

[emordnilap]

So it's a version of an air-source heat pump? I hear they do work but require prodigious amount of electricity to do so. Maybe this is a refinement. Thanks for the info.

[Blue Peter]

Apparently it costs about the same as running a fridge 24 7 and keeps your water at a very comfortable 55 degrees C. He said it wasn’t suitable for central heating, only for hot water for Baths, Showers and Washing Up.

Has anyone on these forums tried this technology? It costs about 6.5K to install but could easily shave £1000 per year off our gas bill.

Are you sure that you spend £1,000 p.a. on hot water? I would suspect that it is closer to 10 - 20% of that,


Peter.

[extractorfan]

Are you sure that you spend £1,000 p.a. on hot water? I would suspect that it is closer to 10 - 20% of that,


Peter.

It may be slightly less, not 10 - 20% though, OH and Son have lots of baths and OH likes to rinse plates under hot water (only when I'm not there, make me really peed off when I see it).

[PS_RalphW]

Air source heat pumps are used for water heating in parts of the USA.

They make sense in hot dry, climates, where heating water by cooling the air in your house is to some extent killing two birds with one stone. In cold, dank, UK they make less sense.

[RenewableCandy]

Personally I wouldn't go for an ASHP to heat water. Its COP (heat energy out / elec energy in, should always be >100%), decreases with increasing temperature difference, that's why HPs (all types) are much better used with under-floor heating where there's a huge area but it only has to go up to 40 degC or so to keep your room nice and warm.

How much are you paying per kWp for solar PV? Should be at or below £2000 by now.

Here at Chateau Renewable we pay about £4 pw (120 kWh) for gas-heated HW, so not much at all. We're 2 adults and 2 teenagers so my guess is that unless you have something extra in your house (public jaccuzzi?) you're prob paying about the same.

[extractorfan]

How much are you paying per kWp for solar PV? Should be at or below £2000 by now.

Here at Chateau Renewable we pay about £4 pw (120 kWh) for gas-heated HW, so not much at all. We're 2 adults and 2 teenagers so my guess is that unless you have something extra in your house (public jaccuzzi?) you're prob paying about the same.

Not exactly sure what you mean, what am I paying per panel? It's 8.5k for 16 panels, installed.

That sounds like really cheap hot water to me, I'll do some more thinking about it.

[kenneal - lagger]

You've still got the running costs which will be between a third and half the cost of heating that water by electricity. It will be about a third the cost in summer and half, if you are lucky, over winter. If you get a long cloudy spell over winter the cost could rise to almost the same as direct electric water heating.

Sounds like a very long payback period to me.

[Tarrel]

My gut feel would be to go for solar thermal for hot water heating, even if it meant cutting back on the number of solar pv panels to make room for it on the roof. Solar thermal requires less equipment than the solar pv plus heat pump set-up. Therefore lower embedded energy in the manufacture and, from your point of view, less to go wrong. Plus, it has the potential to operate off-grid (if you have a solar powered pump), whereas a grid-connected solar pv system will cut out if the grid goes down. AFAIK, solar thermal would do a better job of heating the water in less than ideally sunny conditions as well.

[woodburner]

Solar thermal cangive you fast hot water wthout having to heat the whole tank to do it. A thermosyphon heats the tank from the top down, rather than bottom up. This one looks to have Mike Pepler's approval too. It is connected to your existing tank, so you don't have to buy a new, possibly expensive, solar tank.

I fitted one to mine, one day I will get a panel and a solar pump. East facing is useful as it gives you early hot water in the summer with no FF input needed.

[extractorfan]

Solar thermal cangive you fast hot water wthout having to heat the whole tank to do it. A thermosyphon heats the tank from the top down, rather than bottom up. This one looks to have Mike Pepler's approval too. It is connected to your existing tank, so you don't have to buy a new, possibly expensive, solar tank.

I fitted one to mine, one day I will get a panel and a solar pump. East facing is useful as it gives you early hot water in the summer with no FF input needed.

I wanted solar hot water from the start, and said to the man that I'd have to have fewer solar panels so I could fit solar hot water, he then went on to talk about Thermodynamic heating and that this doesn't need to be in the sun. This is when the discussion led me to pointing out it wasn't solar hot water then. So his sales pitch got me sidetracked onto that.

I'm glad PS is here to discuss these things with . I shall research the solar syphon and concentrate on solar hot water first, pv later (which was the original order in the plan of last year, behind schedule).

[emordnilap]

My gut feel would be to go for solar thermal for hot water heating, even if it meant cutting back on the number of solar pv panels to make room for it on the roof. Solar thermal requires less equipment than the solar pv plus heat pump set-up. Therefore lower embedded energy in the manufacture and, from your point of view, less to go wrong. Plus, it has the potential to operate off-grid (if you have a solar powered pump), whereas a grid-connected solar pv system will cut out if the grid goes down. AFAIK, solar thermal would do a better job of heating the water in less than ideally sunny conditions as well.

I concur with this.

The bit about the solar-powered pump is key - power cuts can be a problem in good weather as well as bad.

A question for people who have solar hot water pumped by grid power: what precautions have you taken in case that power goes down?

[PS_RalphW]

My previous house had a solar powered pump for the solar hot water. It reduced the overall efficiency because you needed stronger sunlight to generate enough electricity to drive the pump, than you needed to marginally heat the water if the pump was operating. We had very few power cuts.

In our new home we have no options for solar h/w or pv, and 3 power cuts in 3 months.

[emordnilap]

My previous house had a solar powered pump for the solar hot water. It reduced the overall efficiency because you needed stronger sunlight to generate enough electricity to drive the pump, than you needed to marginally heat the water if the pump was operating. We had very few power cuts.

Our solar-driven pump kicks in with very little prompting! Obviously, it's controlled by the difference in temperature in the tank and the panel but still.

In our new home we have no options for solar h/w or pv, and 3 power cuts in 3 months.

[Tarrel]

My previous house had a solar powered pump for the solar hot water. It reduced the overall efficiency because you needed stronger sunlight to generate enough electricity to drive the pump, than you needed to marginally heat the water if the pump was operating. We had very few power cuts.

In our new home we have no options for solar h/w or pv, and 3 power cuts in 3 months.

How come no options? Is it a planning issue, or lack of a sunny aspect?