Green Building Forum - Heat pump dilemma

Heat pump dilemma

GreenPaddy — Sat, 14 Jan 2012 16:23:43 +0000

In complete ignorance of PV panel operation... if they really do get hot, and thus degrade performance (not withstanding that it may be over egged), would laminating a PV on top of a solar thermal panel not kill 2 birds with one stone - hot water and a more efficient PV?

Heat pump dilemma

JSHarris — Sat, 14 Jan 2012 16:31:39 +0000

Posted By: GreenPaddyIn complete ignorance of PV panel operation... if they really do get hot, and thus degrade performance (not withstanding that it may be over egged), would laminating a PV on top of a solar thermal panel not kill 2 birds with one stone - hot water and a more efficient PV?

Yes, that's just what the PV/T panels that we've mentioned do. At the moment there seem to be three manufacturers, Anaf Solar, Zen Renewables and Volther Hybrid. All claim improvements in PV performance and around two or three times as much energy out as hot fluid than as electricity through the year.

Heat pump dilemma

Gavin_A — Sat, 14 Jan 2012 16:53:38 +0000

personally I only think they really make sense when combined with a heat pump to allow useful heat to be extracted at lower panel temperatures than would be needed for straight solar water heating.

Heat pump dilemma

Gavin_A — Sat, 14 Jan 2012 16:56:27 +0000

also the performance claims for PV on the new form energy site are nonsense. Performance degradation at 100 deg for an average PV panel would be around 30% not 90%, and in the UK at least their maximum operating temperature tends to be more like 60 degrees, certainly nothing like 100 degrees or us solar installers wouldn't be able to install them in the first place for health and safety reasons.

I may have to have words with them about that claim tbh as it's pure misinformation.

Heat pump dilemma

JSHarris — Sat, 14 Jan 2012 17:07:10 +0000

Posted By: Gavin_Aalso the performance claims for PV on the new form energy site are nonsense. Performance degradation at 100 deg for an average PV panel would be around 30% not 90%, and in the UK at least their maximum operating temperature tends to be more like 60 degrees, certainly nothing like 100 degrees or us solar installers wouldn't be able to install them in the first place for health and safety reasons.

I may have to have words with them about that claim tbh as it's pure misinformation.

I guessed 60 deg C was about the max when I posted earlier that the New Form Energy stuff was way off, glad you think it's about right as it was just a guess based on how hot I *think* mine get!

Their own graph on the same page doesn't support the daft 10% claim either.

The heat pump idea is a good one, but as I think we discussed last time this came up I wonder what happens when the panels get really cold in winter? I believe there are two potential issues. The first is getting a working fluid that is OK down to maybe - 20 or -30 deg C to allow useful heat extraction from the surrounding air when it's really cold, the second is the effect that cooling the panels down below dew point might have on PV performance. I can see a situation where the panels frost up more frequently than non-cooled panels, reducing average PV performance in winter.

Heat pump dilemma

borpin — Sat, 14 Jan 2012 17:38:20 +0000

Posted By: JSHarrisYes, that's just what the PV/T panels that we've mentioned do.

The issue I have is this is very new, and the longevity of it has not been proved.

Heat pump dilemma

Gavin_A — Sat, 14 Jan 2012 17:40:02 +0000

I'd either match them up with a small ground loop, or biomass boiler for use when there's no / little solar energy available, as well as a decent size thermal store to store excess day time heat generation for night time use.

Heat pump dilemma

WillInAberdeen — Sat, 14 Jan 2012 21:56:14 +0000

Re: decision process- I did a lot of break-even economics for my ASHP.

Looking back, I rose-tinted the economics at every opportunity - I ignored maintenance costs, ignored cost-of-capital, used the manfr's CoP figs unsceptically, ingnored the value of many hours of my own time to research/tweak/nurse the system, ignored the space it would take up and the noise it makes, took credit for RHi which might never happen...
... now its installed, I got to admit that I could have saved more money and CO2 by spending the money other ways. But I still like having it, its a great toy.

Not trying to put you off, just suggesting that if you want a GSHP then go and buy one, you dont need to justify it to anyone but yourself!

Heat pump dilemma

JSHarris — Sat, 14 Jan 2012 22:16:23 +0000

Thanks, I'm tempted to do this, but don't want to be left with a white elephant. Part of me wants the very most efficient system possible and part of me suggests over-egging things a bit might be safer in terms of always having enough heating capability (in case the heat-loss calcs are in error).

I can fit a 4 kW GSHP easily enough, I think, and could also fit the Ecocent for DHW and to help shift heat out of the upstairs rooms when it's hot. I can't get enough PV on the roof to offset the electricity this will use, though, so the idea of having some solar thermal contribution to reduce the primary energy import seems to make sense.

I still need to know more about the combined PV and ST panels, as they may offer a better solution in terms of giving me much of the annual DHW for free.

In cost terms an electric boiler for the few occasions when the Ecocent can't recover enough heat from upstairs to run the UFH downstairs is without a doubt the cheapest solution, but it would mean using more energy.

There's something like a six or ten to one price ratio between a GSHP and an electric boiler, meaning that I could buy an awful lot of extra heating with the capital cost difference (maybe 10 years worth or more of cost differential). If it turns out that the house needs next to no supplementary heat and that the heat transfer from upstairs solar gain to ground floor heating and DHW is enough, then the GSHP might never be needed, in which case I'd feel happier having a much cheaper electric boiler sitting idle.

Heat pump dilemma

qeipl — Sun, 15 Jan 2012 17:39:20 +0000

Posted By: GreenPaddyQuote from Chris p Bacon - "It really makes me question the viability of using a GSHP for such low energy demands particularly so if a high percentage of the demand is for DHW."

This is exactly the point I'm trying to make on my somewhat maligned "Â£100 heating challenge" thread.

I like the thrust of your Â£100 heating challenge thread, and I like Jeremy discussing his options so openly on this thread.

I've said it before, here and on Navitron: at heart we're a bunch of tinkerers who love fiddling about with technology and are inclined to 'invest' in all sorts of shiny equipment to 'save' a few kWh per annum when both we and the planet might be better off if we directed our effort and investment in more rational ways.

We need more threads like this one - refining our ideas of what makes overall sense.

Heat pump dilemma

JSHarris — Tue, 17 Jan 2012 16:27:06 +0000

I've just received some info by email about a combined MVHR and GSHP system that has been designed for passive houses that might be of interest. On the face of it the unit seems to be quite well suited to my needs, as it can have a 3 kw GSHP, provide DHW and air heating/cooling and does MVHR as well. The brochure is too big to upload and I can't seem to be able to find a link to it, which is a shame.

The unit has an integrated MVHR, 180 litre DHW tank with solar coil and 3 kW GSHP all in one box, which seems neat. I've no idea of the price, but as far as I can see the only shortcoming is the relatively small hot water tank, which isn't going to give much of a buffer I'd have thought.

If anyone want a copy of the pdf brochure by email, just whisper your email and I'll forward it on. I got it from the people that are marketing the PV/T system discussed in another thread, Zen Renewables.

[Edited to add:

I've done some digging around and it seem that this system is the Danish-made Nilan Compact P+JVP, details of which can be found here: http://www.nilan.dk/Frontpage/Solutions/Domestic-solutions/Total-solutions/Compact-P--JVP.aspx ]

Heat pump dilemma

Chris P Bacon — Tue, 17 Jan 2012 20:12:58 +0000

I don't have the figures to hand, Jeremy, but I priced up the Nilan unit from some Danish online seller and from memory the price was horrendous. Not sure how that will translate to UK pricing but I'll see if I can dig up the links again.

If you try on google.dk for the full model name you might get there before me.

Heat pump dilemma

Ed Davies — Tue, 17 Jan 2012 20:32:54 +0000

Integrated thingies make me nervous about having to replace the whole lot one day.

Heat pump dilemma

SteamyTea — Tue, 17 Jan 2012 20:44:06 +0000

Where I am with GreenPaddy, KISS, works for me.

Heat pump dilemma

Chris P Bacon — Tue, 17 Jan 2012 21:04:04 +0000

The list price for the basic unit in Denmark is 58,730DKK discounted to 50,750DKK by an online seller. The smallest GSHP option is an additional 34,900DKK list or 30,995DKK discounted, all prices include VAT. So at the present spot rate that's about Â£9,150 converting from the discounted prices. That of course doesn't include your ground loop and pumps or your ventilation ducts, transport installation and commissioning.

[edit] The solar coil is another Â£365 extra but the tank is only 180 litres so if you have a decent solar thermal array you will need to dock another tank along side it assuming that's possible.

Heat pump dilemma

joe90 — Tue, 17 Jan 2012 21:09:36 +0000

i'm with GreenPaddy and SteamyTea, KISS

Heat pump dilemma

JSHarris — Tue, 17 Jan 2012 21:19:00 +0000

Yeah Gods, that's pricey! Thanks for digging that out, Chris, sometimes it's very useful to be able to discount an option quickly simply because of price......................

Heat pump dilemma

SteamyTea — Tue, 17 Jan 2012 21:22:49 +0000

I go on the theory that unless I can buy the best I get the cheapest. Hence Heinz Tomato soup and a Tesco 14V cordless Drill.
Makes life very easy