JamesP

ASHP v GSHP. ST or PV diverter.

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I need to decide in the next month which system to install. Can anyone give me some pros and cons of either  system. I have space for ground loops.

The other question is solar thermal or solar PV diverter like immersun as I have 3.7Kw PV already.

New self build timber frame, MVHR, UFH, well insulated, about 290sqm, 3 bathrooms, 4 person  occupancy.

 

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12 minutes ago, Alexphd1 said:

1st of. Is there a option of mains gas?

No mains gas.

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If you have a low energy house, close to passiv, then gshp may not be worth it, it is going to cost a lot more to purchase and install and I doubt you would recover the extra outlay. As you already have PV then just get a diverter.

 

In our case we have 330m2 to passiv standards, inc pressure tested, and manage with a 7kW ASHP with 4kWp PV and an Immersun. We manage to use 97% of generated power with a total savings and income of £650 to £750 per year.

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Your circumstances sound similar yo mine. Approx 300 m sq total living area, about 190 of it downstairs. We have a large field area next to the garden and do have space for ground loops and so looked at ground source at the outset but eventually discounted this on the basis that we simply wouldn't need that sort of capacity. The house is 3 bedroom, 2 permanent occupants and up to 6 from time to time.

We are having PV and I was then considering ASHP but wasn't keen on that. It now seems fairly settled that I will be using PV and phase change heat batteries (sunamp) and mains electricity predominantly on E7 or E10 (or something along those lines).

I can't give precise details as the system is being worked on and sized at the moment but it seems like an elegant solution with low on going maintenance needs. MVHR is also going in to the property.

Edited by vivienz
bloody autocorrect

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I chose air source.

 

I just about had enough room for ground loops, and had my own digger at the time so installation costs would have just been time and some diesel, but then I found the pipe for the gtound loops and the antifreeze to go in them would have cost way more than the actual GSHP. Then there is the cost of changing (and disposing of the old) antifreeze every 10 years.

 

So I decided for the much cheaper and easier install I would go air source. It is arguably slightly less eficcient, but that is more than offset by the simplicity and lower cost.

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As above we ruled out gshp pretty early on. We picked up a cheap (western branded) ASHP & solar thermal  on line and plan to fit that to a 500l thermal store. The above material is bought but haven't ruled out ditching the solar thermal and thermal store to PV & sunamp (work with ashp). The ditched material will be used elsewhere. 

I am not really convinced on direct e7 when you can pick up a heat pump so cheap & install diy less than £1000.

Edited by Alexphd1

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Our draft SAP says we have a primary energy demand of 19200 kWh/year. Nuheat have quoted for both heat pumps and say we have a total

building heat requirement of 21913 kWh/year. RHI could pay for most of the pump and install cost.

@ragg987  Do you know what your SAP energy demand was  and how much you use annually ?

A friend just fitted an ASHP and just had a bill for nearly £300 for a months electricity so he's not happy.

@ProDave I have digger but really can"t face digging 500 metres of trench. 

@Alexphd1 A heat pump for less than a grand, how??

@vivienz  Similar issues regarding requirements, I struggle to understand Sunamp?

 

What does it all mean,

 

 

 

 

ASHP1.jpg

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A basic monobloc inverter ASHP, of a good, known and trusted brand, can be had for less than £1000 if you hunt around.

 

Any ASHP that is using £300W of electricity in a month is either absolutely massive or is set up so badly as to not be worth having.  There are a LOT of badly specified/set up/installed heat pump installations around.

 

In this cold weather I've been keeping an eye on the energy used by our ASHP.  It heats the whole house  to around 21 deg C, using UFH,  and pre-heats the hot water.  In the past month of pretty cold weather (nights down as low as -3 deg C around here) the electricity used by the heat pump has totalled 67 kWh over that month, so a cost of under £15, including the standing charge.  That's a daily cost of around £0.50, not taking account of the fact that some days (like right now) the heat pump is being powered entirely by the PV, so is costing nothing at all to run.  At a guess I'd say the true cost in electricity for heating over the past month would be well under £0.50 per day, allowing for those clear and sunny cold days where we've had quite a bit of PV output.

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54 minutes ago, ProDave said:

Then there is the cost of changing (and disposing of the old) antifreeze every 10 years.

I have googled the life out of this and cannot find much to say that antifreeze needs to be changed periodically. Even heat pump manufacturers are playing that down.Do you have reference material / links? @JSHarris, any input please?

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The main problem is that the anti-corrosion inhibitors within the antifreeze used in GSHP brine solutions become less active with time, to the point where they are generally ineffective after around 8 to 10 years.  That's the main reason for changing the antifreeze, and is really unavoidable, as oxygen will find it's way into the system and deplete the ability of the anti-oxidants to function.  They are needed as there are mixed metals in the ground loop side, usually a brazed stainless steel heat exchanger, perhaps copper pipe work internally, a pump that is probably a mix of cast iron and brass, etc. 

 

Yes, the manufacturers do play down the cost of antifreeze replacement, but I've yet to hear of a "sealed for life" system that doesn't need the (pretty expensive) non-toxic, biodegradable, antifreeze replaced during the life of the system.

 

It's a bit like PV, in that the cost of replacing or repairing the inverter around every ten years is rarely factored in either, yet few inverters will run for longer than around 10 years, as that's about the maximum life of the capacitors in them, as a rule.

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This is a example. Ivt is a Swedish based company who I believe is owned by bosch. IVT also make the worcester range of gshp, this ashp unit is maded in Japan and i think is a rebadged version of the Mitsubishi ecodan (which is regarded as best in industry). Also does cooling👍 patience and eBay... I will be honest there is somebody selling a broken one as well on eBay, but that wouldn't put me personally off this unit.

Screenshot_20180215-093416.png

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When I looked into installing a GSHP at our last house, changing the antifreeze was one of the 'service' issues mentioned by both installers that I had approached. 

 

The most interesting piece of information that came out of the exercise was confirming that if your heating requirement was less than 5000 kWh / yr, a GSHP would cost more to run, as the additional electricity usage of the pump used to circulate the ground loops outweighed the  saving from improved CoP (compared to an ASHP).

 

The only real benefit that the installers could offer, and their main sales pitch was look at the money you will make from RHI.

 

 

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I remember boiler manufactures saying the anti freeze in solar thermal panels had to be changed at some point due to loss in efficiency, part of the the "service" was to check anti freeze.

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6 minutes ago, JSHarris said:

Yes, the manufacturers do play down the cost of antifreeze replacement, but I've yet to hear of a "sealed for life" system that doesn't need the (pretty expensive) non-toxic, biodegradable, antifreeze replaced during the life of the system.

If biodegradable then what about disposal to sewer / other & typical costs per say 8 year event if known ? Eg professional disposal with paper trail ?

 

2 minutes ago, Alexphd1 said:

I remember boiler manufactures saying the anti freeze in solar thermal panels had to be changed at some point due to loss in efficiency, part of the the "service" was to check anti freeze.

Most people with ST I've been called out to ( not working ) don't even know it's a sealed and pressurised system with a pressure gauge until I point it out. A quick top up and they're off to go, but some say they haven't bothered with it for ages as they thought it was going to cost for repairs.

Another top day for the "fit and forget" posse. You pay they walk away :/

Bonkers. 

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5 minutes ago, Alexphd1 said:

I remember boiler manufactures saying the anti freeze in solar thermal panels had to be changed at some point due to loss in efficiency, part of the the "service" was to check anti freeze.

 

 

Yes, for the same, or similar, reasons, the anti-corrosion inhibitors become ineffective with time.  The same goes for car antifreeze, too, although at least you can use longer-life products, as you don't have to meet the biodegradability requirement needed for a GSHP.

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10 minutes ago, JSHarris said:

Any ASHP that is using £300W of electricity in a month is either absolutely massive or is set up so badly as to not be worth having.  There are a LOT of badly specified/set up/installed heat pump installations around.

@JSHarris Its a 12kW for a very well insulated 200 sq m new build. I think the set up needs looking at. Your figures are very impressive, is there any point having solar thermal if you have PV with a diverter, can you have both?

Can someone clarify the RHI, is it just based on your EPC rating and an estimate of your energy requirements or do you submit actual units used like the Solar PV tariff with a meter?

Thank you.

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22 minutes ago, Nickfromwales said:

If biodegradable then what about disposal to sewer / other & typical costs per say 8 year event if known ? Eg professional disposal with paper trail ?

 

 

 

I'm pretty sure it's OK to pump biodegradable GSHP antifreeze into a main sewer, but the chances are a packaged treatment plant wouldn't tolerate that volume of the stuff.

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Domestic rhi is projected energy usage from your EPC. This works against you if you build a low energy house!  Commercial rhi is metered. 

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8 minutes ago, JamesP said:

@JSHarris Its a 12kW for a very well insulated 200 sq m new build. I think the set up needs looking at. Your figures are very impressive, is there any point having solar thermal if you have PV with a diverter, can you have both?

 

 

I couldn't see any merit in solar thermal, it's expensive to buy and install, produces very little output in winter, needs regular maintenance and doesn't perform as well as might be expected from the apparent efficiency difference between that and PV.  There are some interesting comparisons of costs etc here (although a bit out of date now):

https://edavies.me.uk/2011/12/pv-heating/

https://edavies.me.uk/2012/01/pv-et-flat/

https://edavies.me.uk/2012/01/solar-per-area/

https://edavies.me.uk/2012/11/pv-dhw/

 

Yes you can have both, but you have to bear in mind that solar thermal can only ever deliver heat energy when the collector on the roof is hotter than the tank or other thermal storage system.  PV can deliver heat into a tank or other thermal storage system no matter what the temperature.

 

 

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8 minutes ago, Alexphd1 said:

Domestic rhi is projected energy usage from your EPC. This works against you if you build a low energy house!  Commercial rhi is metered. 

The draft SAP is 19200kWh/year and SAP value of 91.38, SAP band B. 

Will my EPC be very different, is it worth it?

 

Edited by JamesP

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Our as built SAP shows 6500kWh for space heating. In Dec and Jan I would estimate we used 1600kWh per month, or 400kWh on input of ASHP based on scop of 4 (actual). £50 per month, some of which will have been offset by PV.

 

The trick to keeping scop high is to run the flow as cool as possible. Keep ufh spacing tight, avoid driving the pump for hard and short cycles but rather on all the time and heating gently.

 

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@JamesP - here's a link to a thread specifically on sunamp, but there's plenty more elsewhere on the forum.

 

sunamp heat battery thread

 

The big picture principle is relatively simple, the task of applying those principles to a domestic heat storage system is anything but simple and way beyond my pay grade!  It is, however, a clever and new solution to storing heat energy without the use of a water tank that is certainly gaining popularity amongst members on the BH forum, including me. 

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@JamesP my only additional comment to this thread is that when I did all the leg work on this at the start of my build I found NuHeat (who you mention in your first posts) massively over-specified the requirements, over estimated the likely RHI payments and was obscenely expensive for their solution.

Personally I'd keep shopping. One supplier not mentioned here that seems to have a reasonable reputation is Earth Save Products. When I spoke to them they certainly had a much better grasp of the requirements of a well insulated new build.

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You can pay a LOT for a heat pump. My plumber friend paid in the order of £10K to have a system installed. He was swayed by the rhi payment and the need for installation by an MCS company to claim that.  Given that he is a plumber I am willing to bet he would have done better to just buy one and install it and forget the rhi.  I get the feeling the only people that actually benefit from that scheme are the installers.....

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