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Author Topic: Quote for GSHP  (Read 6111 times)
benseb
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« on: May 31, 2019, 09:34:25 PM »

Hi

We have a period house, 1800s construction with rubble filled solid walls. We have ok insulation- walls are insulated internally, ceilings insulated and double glazing. We have solid floors which aren’t insulated and lots of timber double glazed doors. Have done lots of draught proofing and added velux which helps with solar gain.

Our oil boiler is 16 years old and as we have some cash would like to replace it with something more efficient and green.

Oil bills range between £1500 and £2500 per year and we heat to about 19c but only for about 2.5 hours per day to keep costs low.

EPC is C. Energy usage 30,000Kwh. Heat loss calculator by installers estimates as 60,000kwh but they have warned this is overkill as SAP greatly underestimated the U values of stone walls but they have to spec to provide this. (We used about 30,000kwh of oil last year)

We’ve just had a quote for a GSHP with boreholes (trenches would be too disruptive outside, and probably not enough room)

Heat pump is a 3 phase 24Kw Heliotherm

Cost is approx £30k for boreholes,  the heat pump installation, water tanks, ground works etc.

RHI basically covers this cost over 7 years but no extra return. Then we save on fuel

What I’m struggling with is that estimate show our elec cost will be about £2200 compared to oil at £4000

I get that this will be much more comfortable at 21c 24/7 but if we decide to heat to just 19c which we’d be happy with, we won’t see as much benefit from the fuel savings...

Are there likely to be any alternatives?  Was hoping to spend some more on insulation then have a cheaper GSHP install and running costs but I’m struggling to know what we can retrofit without masses of disruption

Thanks


« Last Edit: May 31, 2019, 09:53:10 PM by benseb » Logged
RIT
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« Reply #1 on: May 31, 2019, 10:03:52 PM »

Have you talked to anyone about an ASHP unit? A unit would not be as efficient as a GSHP, but the installation cost would most likely be a lot less.

The RHI payment for ASHP is about half of that for GSHP so it's not a simple choice - you would need to talk to an expert.
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2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

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brackwell
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« Reply #2 on: May 31, 2019, 10:27:16 PM »

that estimate of elec cost to be about £2200 compared to oil at £4000 is based on the 60,000kwh fig. so if you have 30,000kwh then those figs will be 50% (30K kwh with a COP of 4 = 7500kwhx 0.15 kwh leccy = £1125 so about correct). This sounds a little optimistic for a retrofit system compared to your oil system to me.

However has no one mentioned that HP like to run at low water temps in order to get the efficiency and this usually equates to using under floor heating or doubling the size of your rads!
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benseb
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« Reply #3 on: June 01, 2019, 08:15:24 AM »

Hey

Yes considered ASHP but it can get cold and damp here which is their weakness so GS appeals a lot more. Plus the higher RHI!

I replaced our radiators downstairs recently and generally added 50-100% to their output by oversizing and getting higher output column rads. UFH isn’t possible due to floor heights and low ceilings.

Saying that the new heat loss calcs would say our existing rads are massively undersized even for oil, which again points to the heat calcs being on the high side as we have no issues with them now.

So hard to do heat loss on an old building with stone walls, doesn’t tick any boxes!!

Anyone got experience of HelioTherm or MasterTherm heat pumps?
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gnarly
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« Reply #4 on: June 01, 2019, 09:18:34 AM »

Is your oil boiler condensing?  Apparently they only became mandatory in 2007 (12 years ago) so it might not be.

Agree that ASHP would be a concern with that heat load... keeping warm during a super cold spell would be difficult and seems sure to involve expensive electric back up heat.

Another option is an oil / ashp hybrid system, with both oil and ashp feeding the same heating circuit but not at the same time.
  * heat is additive so any ashp heat comes directly off the oil requirements
  * provides backup heating so boiler or ashp going wrong doesn’t leave you totally without any heat
  * ashp gets used more in the shoulder seasons and the radiators won’t need to be super oversized
  * ashp is much more efficient in shoulder seasons too
  * should still get RHI with a heat meter

Anyway just a thought as a half way house.  If more people could do hybrid heating systems it would really reduce fossil fuel use...
 
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benseb
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« Reply #5 on: June 01, 2019, 10:17:22 AM »

That could be a good shout. Although to be honest I'd rather get rid of the nasty dirty oil if possible. It leaves us open to replacing the oil boiler too which I don't really want to spend money on a fossil fuel

I was hoping to find a way of adding more insulation to reduce down the heat load of the house, bu really it's only the floors and that sounds like a horrible job.

We do have lots of barn doors which are double glazed but timber (and thin in places), so perhaps either replacing the doors or getting some hefty curtains might be a big help...
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Tinbum
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« Reply #6 on: June 01, 2019, 12:03:13 PM »

I have an old barn/ Methodist chapel that I have planning to convert to a dwelling but building control is a nightmare and is putting me off. Never use NHBC for conversions- they want everything replaced!!  The walls are really thick stone and they want me to cover them all in insulation! The house I lived in there is the same construction, with no wall insulation, and was the cosiest house ever and the bills weren't at all high. It was a loverly temperature all year round. Calcs for heat loss through stone walls are all wrong.
« Last Edit: June 01, 2019, 12:07:09 PM by Tinbum » Logged

85no 58mm solar thermal tubes, 28.5Kw PV, 3 x Sunny Backup 5048, 3x Sunny Island 5048, 2795 Ah (135kWh) (c20) Rolls batteries 48v, Atmos wood gasification boiler, Brosley wood burner, 2000lt buffer tank and 250lt DHW
benseb
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« Reply #7 on: June 01, 2019, 01:42:51 PM »

Yes agreed. I just double checked the heat loss calcs...

The exterior walls were quoted with a U value of 1.75 - thats for a hefty external limestone wall, cavity, brick inner layer, plus 50mm of EPS internally. Putting this into a calculator myself I got a U of 0.6 - which changes our heat loss by about 20,000Kwh/year!!

Very difficult to trust a quote on those calculations. Makes the difference between an 18Kw and a 30Kw heat pump requirement. It would also mean my radiators would need to be humongous! And I thought 1500mm x 600mm x triple was enough.

I was watching a very interesting talk about GSHP and they guy said his house was full stone, very little insulation. Once he had it up to temperature, the thermal mass kept it very cosy. His thoughts were you either have high thermal mass OR you need lots of insulation, but high thermal mass AND lots of insulation isn't needed.

As long as you don't have lots of draughts!

So draught proofing will be my focus for now I think, and getting another quote on the heat loss as I dont want to be getting a 30Kw GSHP if an 18 will suffice!
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Countrypaul
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« Reply #8 on: June 01, 2019, 02:02:39 PM »

If you are putting in lots of draught proofing and making the whole house much more airtight, then you need to be aware that lack of ventillation can cause problems such as increased dampness and mould. you might want to look at an MVHR system if you go for a high degre of air tightness, but retro-fitting could be a nightmare.

You have another option concerning the GSHP and or ASHP and that is to put a small one in (or even one of each) and keep the oil burner for the time being. As you increase the air tightness and insulation (including fitting big thermal curtains) you should then see a drop in the use of the oil burner, to the point it is no longer used and can be retired, or choose to put in a second heat pump and use two smaller one rather than one large one.  Probably much less popular with installers though as they cant sell you as much.

Thermal mass works well if it is inside the thermal envelope, if outside the thermal envelope then it is much less beneficial - hence one reason why EWI is used.

An older oil burner whilst not as efficient as a modern one is likely to be more reliable and can last much longer than 16yrs. Ours was 25yrs old and still going strong, though we only used about 1500L per year (small house with solid brick walls). We moved house into a larger renovated property where we put in lots of insulation and effort into air tightness (and installed an MVHR system) so left the old boiler behind.  The cost of replacing the old oil boiler with a modern one indicated that we would never get close to recuperating the cost by a long way.

You also don't mention whether you have PV installed which could also help reduce the costs of the HPs during the shoulder seasons.

Several on here have also installed air to air heat pumps to help hea the house - and also cool in in summer, these tend to be much less expensive to install and can make a significant contribution.

Don't think that you have to change from one single source of heating to a single other source, a mixture of different heat sources can make a more efficient solution in some cases.  Also running a heat pump at night and loading a thermal store (or thermal mass in the property) off E7 might be less espensive that running a HP 24/7. With more variable rate electricity tariffs appearing selecting when to run a HP may also give more options.
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brackwell
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« Reply #9 on: June 02, 2019, 07:34:53 AM »

If i understand correctly the decsion is not about whether to have GSHP or not but what size of HP is required.
Well,i think this is a non decision because

1) Tests with modern condensing modulating gas boilers showed that the boilers efficiency had very little correlation with size. This is obvious really because their output modulates up /down to suit and achieve optimum eficiency in nearly all cases. This is also true of the modern inverter type HPs.  So whether you choose 15kw or 30kw is irrelevant except you might need 3ph leccy for 30kw ?  but the cost differential of the heat pump must be small in the total cost ?

2) If you were to choose a system 50% the size of max winter it would still cater for 75% of your heat requirements.

3)  The RHI payment is based on haveing a system which meets the efficiency requirements. This is not based on what you think is necessary but what the calculations deem to be necessary and has to be done by a MCS installer (more expense). This may be a very expensive or impossible requirement to meet.  You would end up gaming the system however as the RHI payments would be based on theoretical requirement not your actual requirements.

4) the very important and essential difference with heat pumps is they are best to leave ticking over for long periods and even 24/7 if necassary to gain max efficiency and therefore least cost. This is a completly different mind set to FF boilers and takes a bit of getting used to but it does make for a very flexible system and so whether its a 15 kw HP working 24/7 in depths of winter or a 30kw working for less hrs is largely irrelevant.

5) trust you have the correct soil/rock conditions

With or without RHI this GSHP would be a great system.
« Last Edit: June 02, 2019, 08:00:55 AM by brackwell » Logged
benseb
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« Reply #10 on: June 02, 2019, 08:52:01 AM »

Thanks for the replies

Yes I guess it depends on how much difference the Hp cost. Initially this was going to be quite a lot as on Single Phase it would mean 2 HPs but luckily we have 3P so the incremental cost for a single larger unit is probably not as big

I like the idea of a bivalent system as the oil boiler still works, but it’s just size restrictions as our current huge  boiler and huuuge 500l tank are in our downstairs toilet. I think we’ll be ok replacing with a smaller DHW tank, buffer and GSHP  but no room for the big 50Kw oil boiler!

I guess what’s thrown me is having the heat loss calcs so wildly different from real life as the walls were t species correctly. I think I’ll get another company to run some too and see what they come back with

I do love the idea of GSHP but the price is stacking up. At £30k there’s not really any RHI return over the cost of the system but at least it will pay that back
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brackwell
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« Reply #11 on: June 02, 2019, 09:05:01 AM »

The bivalent system will make it very difficult with RHI as you would then need to fit measuring equipment on the GSHP and this is all you would get paid for.  I suspect this would get even more uneconomic.
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benseb
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« Reply #12 on: June 02, 2019, 09:48:48 AM »

Ok, so plan then is to get another set of heat loss calcs so I can see what’s realistic and get a couple of ideas on which heat pump we’d need

I have land which I could put a strip of solar PV on (sadly not enough for ground loops!) so that will get some consideration too

I was a bit anti solar since the FIT was removed but I guess with a heat pump it will certainly help in the shoulder months. Although I have quite a cool house in the summer it could power some GsHP cooling too to recharge the borehole if plenty of PV generated.
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Countrypaul
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« Reply #13 on: June 02, 2019, 10:33:08 AM »

Whether it is worthwhile to "recharge" the borehole with the PV will depend significantly on the geology. If there is significant turnover of water in the borehole you might find that the temperature evens out over relatively shot periods of time regardless of how much heat you put in or take out.
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Bodidly
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« Reply #14 on: June 02, 2019, 10:38:45 AM »

Is it a good idea to have a GSHP without UFH? From what you describe of the insulation and the radiators I would expect a poor COP but maybe GSHPs have come on in recent years. Ours has ground loops, we are well insulated all around combined with UFH and it's good but not miraculous.
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