Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: Speltzer on June 08, 2018, 11:48:14 AM



Title: Nervous about ASHP
Post by: Speltzer 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?


Title: Re: Nervous about ASHP
Post by: M 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.


Title: Re: Nervous about ASHP
Post by: Speltzer 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.


Title: Re: Nervous about ASHP
Post by: RIT 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.


Title: Re: Nervous about ASHP
Post by: Speltzer 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.


Title: Re: Nervous about ASHP
Post by: TheFairway 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.


Title: Re: Nervous about ASHP
Post by: titan 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.


Title: Re: Nervous about ASHP
Post by: Speltzer 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.


Title: Re: Nervous about ASHP
Post by: RIT 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.


Title: Re: Nervous about ASHP
Post by: Speltzer 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.


Title: Re: Nervous about ASHP
Post by: A.L. 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



Title: Re: Nervous about ASHP
Post by: Speltzer 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.


Title: Re: Nervous about ASHP
Post by: A.L. 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


Title: Re: Nervous about ASHP
Post by: brackwell 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.


Title: Re: Nervous about ASHP
Post by: todthedog 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


Title: Re: Nervous about ASHP
Post by: pdf27 on June 08, 2018, 02:52:12 PM
A couple of additional comments:
  • RHI companies jack the price up something awful - that same heat pump can be bought for £4,500 inc. VAT (https://www.wolseley.co.uk/product/mitsubishi-ecodan-air-source-heat-pump-pack-ftc4-112kw/) and because it is a monobloc unit installation is almost a DIY job (you need an electrician to do the connection, the plumbing is DIYable if you're confident). The remaining ~£5k is for the paperwork to enable you to claim the RHI plus a little bit of plumbing and wiring.
  • As per the Mitsubishi website (https://www.mitsubishi-electric.co.nz/materials/hotwater/brochures/@Ecodan.pdf), the claimed COP is with the water being supplied to the house at 35°C. That absolutely kills the radiator power output - assuming your water is currently flowing through them at 70°C then you need to quadruple the radiator size to give the same level of heat (https://www.castrads.com/frequently-asked-questions/buying-cast-iron-radiators/how-does-delta-t-affect-heat-output/). They're right in that it's pretty easy to do (a DIY job if you're reasonably confident or have access to YouTube - I did two recently), but if you don't do it the COP will fall of a cliff.
  • The fact that they're suggesting an 11kW unit but a 20kW stove isn't keeping the house warm rings all sorts of alarm bells for me - heat is heat no matter where it comes from, and an undersized ASHP is likely to prove horribly expensive to remedy. The RHI is supposed to guarantee that the heat pump can be the sole source of heat - so I'm wondering if they're sizing it based on the heat losses after insulation is fitted and not saying so. They may be assuming it is left on 24/7 rather than firing up as needed - that would let a smaller unit keep the house warm, but the total heat used would be rather larger than if you just left the house to cool down during the day while you were out and heated it again just before you got home.
  • The forum mantra is "insulation, insulation, insulation" - at the very least get yourself down to the nearest DIY shed and pick up a load of rolls of loft insulation and get them in ASAP. It'll make your life a lot more comfortable in both summer and winter, and if you don't have any insulation at present start making a sizeable dent in your heating bills.


Title: Re: Nervous about ASHP
Post by: A.L. on June 08, 2018, 03:17:12 PM
hello again,

- your presumably rural location, total lack of loft insulation and potentially high carbon savings from a non mains gas fuel at the moment could make you a valuable customer under the energy company obligation to the extent that you could possibly get loft & cavity wall insulation (and possibly other things) free!

- contact the Energy Saving trust on 0300 123 1234 for an unbiased assessment of your situation.


Title: Re: Nervous about ASHP
Post by: Speltzer on June 08, 2018, 03:24:47 PM
Many thanks for everyone's input. A.L I'll give them a call thanks.


Title: Re: Nervous about ASHP
Post by: Countrypaul on June 08, 2018, 06:37:57 PM
Can you clarify what the issue is with the current heating system as you say after using it over winter you need to upgrade? Is the sytem not putting out sufficient heat, or is it too much hassle to live with? Your comment about wanting to flick a switch rather than carry buckets of coal makes me wonder whether the hassle is the primary reason for changing as opposed to the actual heat output.
If the hassle factor is the main issue, then some of the advice given may benefit from revision. It would also be worth explaining how you actually use the coal fired stove currently as that can give an insight into other features. For example, if you ran the stove full bore for an hour in the morning and just left it ticking over in the evening. Does the stove heat the radiators directly or does it heat a large tank that is used to heat the radiators?  Are you in most of the day, or out to work office hours or shifts?  Where does the stove get its air supply from? Some can take the air directly from outside, others require that there is a large vent in the room to allow (cold) air in.
Be aware that if you insulate well and also seal all draughts and leaks there is a possibility you may run into other problems as the house may not ventilate enough on its own. If you therefore put double glazed windows in you may need to heave trickle vents in the windows just to provide ventilation.


Title: Re: Nervous about ASHP
Post by: Speltzer on June 08, 2018, 06:52:51 PM
Hi Countrypaul. All good questions...

- issue with the fire is both that it is inconvenient but also that it cannot heat more than two or three radiators at any given time effectively - as well as the lounge that it's in (there is no radiator in there). We can activate or deactivate its feeding of the radiators, but there is no way to stop it from heating the water in the hot water tank - even if we don't want any hot water! So there's quite a bit of wastage there.

- I am in most of the day because I work from home and would need to keep the fire fully stocked throughout the day to keep temperature up for more than say an hour.

- There is an open vent in the lounge wall because of the fire - one that we can't close.



Title: Re: Nervous about ASHP
Post by: desperate on June 08, 2018, 09:41:33 PM

  • The fact that they're suggesting an 11kW unit but a 20kW stove isn't keeping the house warm rings all sorts of alarm bells for me - heat is heat no matter where it comes from, and an undersized ASHP is likely to prove horribly expensive to remedy.
Spot on,

this company say that your heating load is 8.5kW but your 20kW stove wont heat the house!! there is something fundamentally wrong here. TBH for a solid wall house of that size 8.5kW heat load sound pretty low to me.

Go nuts with insulation and draught proofing, keep your present heating system and see how you get on this coming winter, buy a couple of extra jumpers and save your self a shedload of money. Then if you need to upgrade the heating system you will truly know where you stand.

Desp


Title: Re: Nervous about ASHP
Post by: linesrg on June 08, 2018, 09:49:19 PM
Speltzer,

You are in a difficult situation, one not entirely dissimilar to the one we found ourselves in when we moved in to our current property.

We had a single oil burner Stanley range in the kitchen which required a window to be left open as it was not eternally air fed and which didn't really provide heat to all the radiators fitted due to the pipework starting off as 22mm then down to 15mm and then 8mm all of which severely restricted the flow.

Whilst you may not be overly enthusiastic about the prospect of lugging coal around it may pay to find out whether your current system is performing as it should be. Better piping/ pumping/ controls may transform it?

Like you it was clear the house need work doing on the insulation front, the draught front and also the heating front. Now while not everybody on the forum will agree with our decision we too decided, after the first winter, there was no way we were going to tolerate the 'status quo' for the following heating season. After much research and advice we went down the route of an LPG condensing, weather compensated boiler and a major re-piping of the radiator system (the latter alone would have improved the original system to be honest as where 30" walls required to be 'penetrated' they were). We went the LPG route as it was more able to deal with a wide range of heat outputs as we improved the house insulation values as against an oil fired boiler which is less flexible.

Having changed the heating system we then set about ripping out the old lath and plaster upstairs one room at a time and refurbishing using large amounts of Celotex and fibreglass. We've replaced the sealed units in the Velux windows and new glazing goes into each room we refurbish. We went slightly over the top on the last occasion with two triple glazed window units and a triple glazed front door.

We still have some way to go but our energy consumption is way down on what it was. Money for larger scale projects isn't really available at the moment but I do intend putting another 100mm of fibreglass in the roof space before the next heating season.

Regards

Richard


Title: Re: Nervous about ASHP
Post by: regen on June 09, 2018, 07:44:06 AM
A 20kw boiler should be more than enough if the house is adequately insulated and the boiler is running correctly. We heat a 150m2 house at 800 ft with a 21kw unit which burns wood only. There is underfloor wet system covering approx 40% of the ground floor but since installation 3 years ago the rads have never been turned on and the combination of the WBS,UFH and the thermal store keep the whole house at 20 deg plus. The stove is lit for about 12 hours each day in winter and occasionally in summer.

The reason this works and our combined electricity bill and wood cost is less than £600pa is the INSULATION and DRAUGHT PROOFING. We do have oil back up and have used less than 500 litres over the past 4 years.

Regen


Title: Re: Nervous about ASHP
Post by: gnarly on June 09, 2018, 08:23:34 AM
You can combine the ashp with another backup heat, eg. Oil.  That completely avoids any risk of the ashp not coping.  (As a general point ashp’s aren’t great when below zero as they get into a freeze/defrost cycle, and there is typically an auxiliary electric resistance heater).  Ashp would be on when the external temperature is above a ‘bivalent point’ and the oil will be on when it is colder.  It also means you get the best efficiency out of the ashp, the oil boiler will cycle less (a good thing) and you will also use much less oil.


Title: Re: Nervous about ASHP
Post by: Speltzer on June 09, 2018, 11:47:31 AM
Thanks for your responses everyone. Even if the multi-fuel stove were able to heat the house, I still wouldn't want to make a fire every time I want the heating on.

I also understand that insulation will improve the efficiency of any heating system. I'll get around to that but I need to decide on a heating system either way and I need to do it in the next month.

Having read the responses here, I'll go with bulk oil since that is tried and tested and has a better output.


Title: Re: Nervous about ASHP
Post by: brackwell on June 09, 2018, 11:52:10 AM
Do not forget to block up the chimney and the obligatory air vent.


Title: Re: Nervous about ASHP
Post by: Speltzer on June 09, 2018, 11:58:51 AM
We'll be keeping the fire, so think will still need them.


Title: Re: Nervous about ASHP
Post by: brackwell on June 09, 2018, 12:28:15 PM
Well i can understand that but if this is an occasional fire remember it is quite likely more heat is being lost than gained from the fire. Amazing thought that?  Anyway best of look with the change.
Ken


Title: Re: Nervous about ASHP
Post by: Speltzer on June 09, 2018, 02:12:48 PM
Yeah, I know whatever we put in place won't be the ideal. Not really looking for ideal though - just didn't want to install an ASHP and have a cold house and astronomical elec bills.


Title: Re: Nervous about ASHP
Post by: billi on June 09, 2018, 09:02:52 PM
Quote
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!

Hi

I guess the woodstove is not delivering 20 kW  

Do you have  a thermal store ?  how much liters ?  , i guess  i would leave the big  AS heatpump idea out for 10000 GBP  for now ,  maybe  take that monney and  fit solar pannels or PV , for double the RHI  payment  of 20 pennce for solar thermal
or just forget about RHI  

10000 GBP buys me 8-10 kW PV  including a little ashp  that feeds the buffer tank (if you have one )  that can deliver   about  3500 kwh in winter  and plus heatpump then Cop3  brings you  to about 10000 kWh in winter  for heating  and  s!te loads of surplus in summer   , so  brings  your electricity bill down  and hot water for free during summer

I mean   just install something that does not costs running it
Anyway    as all others said,   think about insulation , it has a huge inpact

Billi


Title: Re: Nervous about ASHP
Post by: Countrypaul on June 10, 2018, 09:10:20 AM
Do you have any sort of loading valve on the stove such as a Laddomat or Esme? Using a stove with backboiler that does not make use of a laoding valve can result in very poor stove performance, there are several threads on this subject if you want to read more about it. The usual results due to lack of loading valve appear to be radiators never getting properly warm, excessive tar and soot production and the house always feeling cold!  Two other factors that can contribute to poor stove heating are gunked up pipes, try powerflushing the system (this will apply regardless of whether you reply on the stove, oil boiler or ASHP), and not having the lockshield valves on the radiators set properly (again there is a recent article about that).  Obviously this won't help with your flick a switch and have the heating come on, but might improve the stove and radiator performance significantly.  Are there any pums/valves on the stove circuit to direct the hot water to the DHW tank or central heating?

What make/model of stove is it you have? Some you can take the boiler out of, others you can't is my understanding. Have you thought about combining the stove and oil boiler using either a thermal store or neutraliser etc. That way you could also get a away with a smaller oil burner (less expensive) which would cycle less, but rely on using the stove if the weather came along with a really cold spell.


Title: Re: Nervous about ASHP
Post by: billi on June 10, 2018, 11:16:47 AM
exactly CP  ,  first to have a look at the current install , seems  a good  start  to have a woodburning boiler plumped in and   just find a way tro complete   with an add on  heating idea
Billi


Title: Re: Nervous about ASHP
Post by: Philip R on September 25, 2018, 09:13:47 PM
Just seen this thread.
I would stick with the LPG and go for a Robur K18 Gas absorbtion heat pump. I dont have one as my condensing boiler is working well. But its replacement, wherever I end up living ( if on mains gas or LPG) would be one of these or something similar that enters the market.

Although dearer than electric ASHP, It is a lot more powerful. I also can produce decent hot water output with little decrement to COP, Also electrical load is the air fan and circ pump, not the high powerred compressor. So more realistic chance of powerring it during a possible power cut, using smaller backup power source.

Philip R


Title: Re: Nervous about ASHP
Post by: andrewellis on September 26, 2018, 09:27:27 AM
Most of what I wrote probably doesn't apply as I didn't notice you are running a wood burner but the same principles apply.  The problem with a stove is it isn't putting out much heat overnight.  Therefore you need more power to play catchup in the day.  We had a 22kw oil burner and now have a 12kw GSHP.  It runs 24/7 keeping the house at 19ºC on average.  Its worth doing the calculations very accurately or you will be sad.

We have an old granite smiddy that was converted in the 80's.  I did similar calculations to yourself but also did a room by room calculation.  You can download the mcs spreadsheet which the installers will use.  To convince myself I also did real world calculations last year by placing an iPhone in the boiler recording audio all night and day for a few weeks.  Luckily the temperature was -6 last year.  I turned the boiler down to its minimum which worked out at an average of about 50 degrees. I also left it on 24/7 with a thermostat temperature of 19 degrees.  I was able to achieve two things then.

a) know if the lower temperatures would work in the rooms with the current radiators.  Some were a few degrees short.  I have added a replaced a few radiators.

b) how much oil was used.  The manual for the boiler will tell you the oil usage per hour depending on the nozzle you have fitted.   Then download the wave form and the on/off periods are very clear.  Just use some audio software to measure the on/off timings and you will get oil usage per hour.     I tried to see the difference between windy and non windy days. I also had a raspberry pi and arduino recording the outside temperature and room temperatures every 15 minutes so I could correlate between oil usage and what was happening outside.  There was a little lag in the house due to the granite heat sink.  Could you record the weight of the wood being used to do something similar.  Approximate the calories per kg and the efficiency of the boiler stove?

In the end I went with a GSHP ( borehole) as the ASHP didn't make sense in Scotland with the colder weather.  The COP at colder temperatures drops off rapidly.  As long as you can stump up the money the RHI will pay for the install over 7 years.  So far its working out well though I am waiting for the first winter to finish.  One thing I didn't take into account is how quickly the house temperature drops when heating the water.  I had wanted a larger DHW tank with the intention of heating water at night to see us through the day.  However we had an integrated tank in the Nibe F2155.  It isn't large enough to see us through the day and ends up constantly topping up the tank temperature after use.  You can adjust the ratio of home vs water heating but we definitely feel a temperature drop.  It isn't entirely a fair setup yet as we have got all our radiators in whilst I finish building the kitchen and living room so it might not be so pronounced an issue later.

As others mention. Insulate.  I did the attics and removed all the downlighters which where effectively 20 x 4 inch holes in to the attic space.   The attic insulation is very cheap and a no brainer.  I also found a lot of mould in the attic.  We had a huge open chimney that was very effective at removing any heat we managed to make.  An extractor fan in the bathroom and a few vents in the tiles has fixed that.  Just be careful about leaving ventilation behind the walls as these old places need to breath.  The walls already had some insulation from the 80s and any time I do some work I am updating the wall insulation.  Before doing all the work even the oil boiler struggled to keep the temperature steady.


Title: Re: Nervous about ASHP
Post by: Westie on September 27, 2018, 04:42:31 PM
Just seen this thread.
I would stick with the LPG and go for a Robur K18 Gas absorbtion heat pump. I dont have one as my condensing boiler is working well. But its replacement, wherever I end up living ( if on mains gas or LPG) would be one of these or something similar that enters the market.

Although dearer than electric ASHP, It is a lot more powerful. I also can produce decent hot water output with little decrement to COP, Also electrical load is the air fan and circ pump, not the high powerred compressor. So more realistic chance of powerring it during a possible power cut, using smaller backup power source.

Philip R

It's a very interesting device. In particular the water temp delivery at up to 65C means the low flow rates of my microbore based CH system should be okay. I wonder what the reliability will be like, IIRC absorption fridges are very reliable as there is obviously no compressor.  Copy of a quote below.. it excludes installation....



Title: Re: Nervous about ASHP
Post by: djs63 on September 27, 2018, 06:05:54 PM
The accessories total seems to wrongly added up. Is that correct?


Title: Re: Nervous about ASHP
Post by: Philip R on September 27, 2018, 10:20:02 PM
Bear in mind that operating the output at 65 deg C will reduce its Cop. Size the heat emitters to run at say 50 / 55 deg C and the cop will be better than at 60 deg.

Absorbtion fridges are reliable.  seen some running older than me. So long at gas heated high pressure parts do not spall or rust, the device should be reliable.

This type of device is available in larger outputs from some of the commercial heating boiler companies.
The K18 is the first small device that can be called domestic. Whence some other companies enter the fold, the price should drop and then it will become the appliance if choice for gas heating, replacing the condensing boiler.

Philip R


Title: Re: Nervous about ASHP
Post by: Westie on October 13, 2018, 03:26:41 PM
I don't see why this heat pump from Robur doesn't qualify for RHI, I realise it burns gas (or even cleaner LPG in my case) but electrically powered ASHP use electricity from our grid that's still largely generated by gas!  
The vendor says it's because the government (DECC as was) decided they didn’t need to offer a payback incentive because gas is that much cheaper than electricity – and because their advisors are the Heat Pump Association (HPA) which is comprised of electric heat pump manufacturers. I checked the HPA membership and that does appear to be true so their advice to DECC is almost definately biased!


Title: Re: Nervous about ASHP
Post by: Philip R on October 13, 2018, 09:03:38 PM
Interested that these do not qualify for RHI.in the eyes of decc and hpa, gas driven heatpumps are less renewable than electrically driven ones. How bizarre. Shows the high level of thickness present in these governmental and trade associations. They are backward.

 Look on the upside. It does not need to be installed and signed of at great expense by rhi approved agent / contractor. Have you looked at the economics with and without the grant? Gas and electric. My take on things is that agreements can be broken. I believe fits and rhi agreements may be torn up before they officially expire.
I will check out what Gassafe have to say about which gas ticket is required for its legal connection to the gas supply.

Why do you think that LPG is any cleaner than natural gas?

Philip R


Title: Re: Nervous about ASHP
Post by: Westie on October 13, 2018, 10:10:40 PM
Re Propane vs NG I see your point, it's arguable.  Propane produces slightly more co2 than NG when burnt but requires only half the volume of gas to produce the same heat. Before it's burnt NG is methane - a powerful greenhouse gas so leaks have a  significant effect , propane isn't a greenhouse gas so leaks don't affect the ozone layer, although because it's  heavier than air it explodes well  sh*tfan:


Title: Re: Nervous about ASHP
Post by: Philip R on October 13, 2018, 10:43:01 PM
Methane is a greenhouse gas because it is lighter than air so floats up to the stratosphere. Propane is heavier than air so cannot rise to stratosphere. Instead it sinks into drains, basements and  dips in the ground. I am careful when i undertake gas work but a more so when doing LPG gas work. Because of its wider explosive range and higher energy density. Recall the Spanish campsite gas explosion of the 1970s.

Your safety justification is like saying you could get run over by walking on the pavement, so decided to walk in the road instead!

Philip R

Propane offers  a higher efficiency compared to natural gas because of higher allowable CO2 concentration in exhaust raises condensation temperature threshold, so boiler condenses water better.