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Author Topic: Nervous about ASHP  (Read 5485 times)
Speltzer
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« on: June 08, 2018, 11:48:14 AM »

Hi.

Cards on the table I am a new homeowner, complete novice when it comes to renewable energy and I've sought this forum out in the hope of getting some impartial advice. We have just bought a new home that is off the grid and we need to put a new heating system in - of course anyone who can advise on whether we should go for bulk heating oil, a heat pump or something else, also sells whatever their preference, and so I've been left wary of everyone!

I know the more info the better with this kind of thing, so our house:

- 3 bed semi
- 1920s built
- no cavity insulation (possibly solid wall, not sure)
- no loft insulation
- double glazing downstairs, single up
- draughty
- internal floor area: 94m2
- Energy Efficiency Rating: F (33)
- EPC heat demand (kWh per year): space - 19,238 water - 2,718
- EPC annual heating cost estimate as stands: 1,737

Currently our house is fully fitted with radiators and a hot water tank but they are powered by a 20kW multifuel stove in the lounge. After trying it this winter, we need to upgrade!

We were originally going to go for a bulk oil tank (like much of the village) as we don't have room for an LPG gas tank. But then I got a letter from a renewable energy company pitching ASHP. I've always thought they'd be a non-starter because of the nature of our house but thought I'd meet them and hear what they had to say.

They talked a good game and with domestic RHI we'd be able to get 9k back over 7 years after a 10k installation outlay (vs 7.5k cost for oil and no RHI).

I'm still nervous - again because our house is poorly insulated - but this company is adamant that doesn't matter and ASHP would be great for us.

Here is their pitch:

- Target internal temp: 21C
- Outdoor ambient assumed: -2C
- Assumed heat loss factor: 90w pm2
- Estimated building heat load: 8.5kW
- Install 11kW Mitsubishi Ecodan ASHP with weather compensation
- The Ecodan will use no external electricity source to provide heating, only what it needs to run its compressor.
- It will achieve its output down to -20C
- ASHP SPF = 3.2
- Fuel price comparison: Oil = 6.5p per unit / LPG = 8.5p / Electricity = 15p divided by 3.2 = 4.68p
- Annual spend comparison: Oil = 1,500 / LPG = 1,900 / ASHP = 1,100

A lot of information there, thanks anyone who has the time to go through it, but what I'm essentially asking is will the above pitch stand true in practice for an old draughty house like ours or am I being misled?
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M
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« Reply #1 on: June 08, 2018, 12:06:48 PM »

Hiya, and welcome.

I'm interested in all aspects of HP's and discussions, but can't provide much info, however, can I ask some questions for further analysis by others?

You've gone to great effort to list poor insulation etc. Do you plan to change this, insulate roof, double glazing upstairs, any plans for wall insulation (internal or external) any restrictions on changing the building aesthetics?

You say you are off the grid, but do you just mean the gas grid, or leccy grid too?

Do you plan, would you consider a PV install too, which might help with some of the ASHP heating during the day?

Is the current wet system suitable for an ASHP, that is, are the radiators large/oversize, are the pipes large enough?

I think you've described a house not suitable for ASHP (so well worth asking for help on here), so I'm very interested to see the thoughts and comments you get too.

Have fun, Mart.
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Speltzer
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« Reply #2 on: June 08, 2018, 12:27:42 PM »

Thanks for the response Mart.

To clarify:

- we are going to look into loft insulation but windows and wall may need to be more long-term and so would like to find a heating solution that works with our current set-up
- we are off the gas grid but we have electricity
- would consider PV but not at this moment, so again want to choose the heating solution based on how it works alone with our current set-up.
- I'd say our radiators are currently normal size but the company says they are relatively cheap to replace if needed, and we would be ok with that.
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RIT
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« Reply #3 on: June 08, 2018, 12:35:55 PM »

Welcome to our little community.

Your starting point is going to have to be insulation in part as the RHI scheme requires that you carry out such work.

Another major reason for needing the insulation is the fact that you have tried to use the current 20kW multifuel solution and its not working out for you. Just putting in another solution with approx. the same heat output will not solve the problem. Also, ASHP solutions work best if they operate at a lower output temp than other systems. So you need to reduce your heat loss, upgrade all your radiators or operate the ASHP at very inefficient level.

One of the key things to consider with ASHP is the quoted output is based on its SPF, which is a seasonal average. The stats you have listed show that the device is an 8.5kW unit with an SPF of 3.2. So it's peak heat output may be quoted at 27.2kW. This will be lowered if you need to produce very hot water to drive the radiators and will be lowered again as the outside temp drops.


So the key things for any of the solutions are

 - research your walls to see if you can insulate.
 - deal with the loft as soon as you can with 270mm+ of insulation
 - chase down all the air gaps and fill them.

Your current EPC report is likely to list all of the above and give some basic figures regarding the energy saving you can expect. Each saving will make it easier to deploy ASHP and as you will have already seen from the quote you have the RHI payments make it something of a no brainer.
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Speltzer
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« Reply #4 on: June 08, 2018, 12:47:19 PM »

Thanks very much for your reply RIT. All understood. Odd thing is that the company selling us this ASHP said insulate after the installation because the RHI payments would be larger for an uninsulated house (the thinking being that they are a bigger environment impact and therefore are in greater need of the funding).

The EPC does indeed say we can reduce our energy needs greatly with loft and wall insulation. I know that the ASHP will not operate at its full efficiency in our current state, but these guarantees have been made by this company for our house as it stands. Should I take them with a pinch of salt?

What I'm worried about mainly is any money saved through the RHI being outstripped by running costs because this company has overstated the ASHP performance in practice.
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TheFairway
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« Reply #5 on: June 08, 2018, 01:21:08 PM »

Oh dear. Sounds a case of lets waste heat and energy in order to get a bigger income rather than fix the wastage and doing the job properly with probably more options as you will know what you are really up against.

tbh if you insulated loft and draft proofed, you could even find that the heating that you have now is adequate enough for you to get through a few more winters in relative comfort. Insulation brings instant results.
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titan
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« Reply #6 on: June 08, 2018, 01:24:36 PM »

If it were me I would get the insulation done as a priority, replace the windows, stop the draughts and see how your existing heating copes. All wet system heat pumps work with low temperature water and I would think all your existing rads would need to be replaced to be used with a heat pump. You may find off peak direct electric is viable with a well insulated house. PV is well worth considering if you have a suitable roof especially when used with an export diverter to heat DHW, It is relativity easy to put a spreadsheet together to calculate your building heat losses and therefore heating requirements and you can also see what effect each change has and set your priorities.
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Speltzer
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« Reply #7 on: June 08, 2018, 01:26:03 PM »

I did wonder whether a bigger RHI payment ultimately meant a bigger job and pay day for them.

Either way, I won't be keeping our current heating solution - I'd rather turn the heating on with a switch that having to go out to get buckets of coal. So insulation or not, we will be going for bulk oil or ASHP before the winter.
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RIT
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« Reply #8 on: June 08, 2018, 01:30:34 PM »

Thanks very much for your reply RIT. All understood. Odd thing is that the company selling us this ASHP said insulate after the installation because the RHI payments would be larger for an uninsulated house (the thinking being that they are a bigger environment impact and therefore are in greater need of the funding).

The EPC does indeed say we can reduce our energy needs greatly with loft and wall insulation. I know that the ASHP will not operate at its full efficiency in our current state, but these guarantees have been made by this company for our house as it stands. Should I take them with a pinch of salt?

What I'm worried about mainly is any money saved through the RHI being outstripped by running costs because this company has overstated the ASHP performance in practice.

All the possible solutions are likely to be 'oversold' one way or another so you just have to make sure that there is free capacity in the solution. Face it, if you spend time talking to the provider of an oil fired solution do you think they will talk about just how costly the oil will be by the end of the system's life. It is also a simple fact that systems can't be sized to meet the worse case scenario you may experience as they would end up oversized for all the rest of the time.

I do not know in detail how the RHI and EPC figures are combined, hopefully, someone else will have more exact info.

As for the running costs, as long as the system is not having to produce very hot water to cope with undersized radiators it should be just about impossible to install an ASHP solution to be more costly to run that oil or gas. The RHI payments just the whole thing even better.

One thing you to consider is keeping an exterior wall free from radiators in your main living room for the installation of a standalone ASHP through wall unit. As all the heating calculations are averages you may want an independent heat source to boost your control over the temperature in your main room. This is nothing odd, just consider how many people in new homes with gas CH also have a separate gas or wood fire in their living room. As you do not have access to gas, a ASHP solution would seem a good option.
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Speltzer
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« Reply #9 on: June 08, 2018, 01:44:09 PM »

We would be keeping our current multi-fuel stove in the lounge, which should have a greater output into the room as it would no longer be heating radiators and a water tank.

Many thanks for all your input to those that have given it so far.
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A.L.
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« Reply #10 on: June 08, 2018, 01:58:06 PM »

hello and welcome,

- if your epc has recommendations for cavity wall insulation and loft insulation then the level of subsidy given by RHI will be calculated as if these items are installed.

- the figure 8.5kW or 11kW is the OUTPUT of the heat pump

- your priorities are therefore loft and cavity wall insulation and a thorough draught-proofing campaign

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Speltzer
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« Reply #11 on: June 08, 2018, 02:11:31 PM »

Cheers A.L. Understood. We will be insulating, but I also need to get the ball rolling on whatever heat solution we're going to be using to have it ready in time for winter.

Based on responses, I get the feeling that ASHP is going to be a bit of a risk/unknown in our situation. I suppose the performance of bulk oil would at least be more predictable.
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A.L.
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« Reply #12 on: June 08, 2018, 02:21:56 PM »

hello again,

We were originally going to go for a bulk oil tank (like much of the village) as we don't have room for an LPG gas tank.

- lpg has an energy density around 7.6kWh/litre and oil around 10kWh/litre so not to much difference in size for similar capacities
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brackwell
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« Reply #13 on: June 08, 2018, 02:32:47 PM »

You will not be able to achieve the pre requirements of RHI for a heat pump in that it has to be able to run with a COP (coefficient of performance) of 3 FOR EVERY ROOM i believe.  In any case ASHP not suitable for your requirements.  So oil its going to be then end of story.   Then when you dont like the bills for the oil you will have to start insulating as people here are telling you.   The common forms of insulations pay for themselves in savings and is immediate.   With proper insulation particularly the draft proofing and even more so preventing heat going up the chimney you could quite easily half your heating and hot water requirement.  Thats not eco warrior stuff just fact.
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todthedog
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« Reply #14 on: June 08, 2018, 02:49:31 PM »

Hello and welcome,

The forums moto 'Insulate insulate insulate'

In my view insulate as your first priority. It will be money quickly recouped whatever decisions you make to say nothing of greatly increased comfort.

Best of luck
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