Worth changing from LPG? Help with comparison please!

Scottish_Dorset

We live in new, well insulated 3 bedroom semi, rural area.  We currently have an underground LPG tank and fill it up once a year, 2000 litres @ 62ppl and and annual standing charge of £100.  We have 4KW worth in total of solar panels.  Our electric bill is approximately £720 per year.  We earn a poor £60 per year on FIT.  We are with E-ON.  There are two of us that live in the house and we both work full time.  Hot water comes on for 1.5 hour during the day.  We have underfloor heating downstairs and radiators upstairs.  The underfloor is not very effective for our lifestyle but we can live with it.

I have been quoted by Octopus £1k to fit an air source heat pump, after the grant. Looking to see if this might be a better way forward for us, financially in particular for running costs.  Also we have the LPG tank underground right in the middle of our garden, we have had water problems with it.  The developer did not do a good job installing it. 

Any suggestions, advice, experiences would be very much appreciated. 

Thank you!

smallblueplanet

You probably won't get a better price than with Octopus as of course although you pay £1000 the 'cost' to you is actually £8500. You can use your solar to run the ashp and probably get better electric tariffs for other times?

Reed_Richards

Ideally if you have radiators and UFH, you would have these on different zones and an ASHP that would automatically reduce its output water flow temperature when there is no demand from the radiator zone.  Not all heat pumps can do this; mine cannot and I don't know about the ones Octopus can provide.

Without this feature then the leaving water temperature always has to be hot enough for the radiators and you don't get any running cost savings from your UFH.  With this feature you would be able to run your UFH all the time but very economically whilst turning your radiators off (or down) for most of the time you are at work.   

FreeBear

Crunching a few numbers for you. At 62p/l, that works out as 8.757p per kWh.

With electricity currently at 24p per kWh, you only need a SCOP of 2.75 to break even on running costs. Get a SCOP of 3.5 or even 4, and a heat pump will be much cheaper to run. For an installation cost of just £1000, I wouldn't hesitate to sell my first born to pay for it.

Getting rid of the LPG tank to avoid the annual standing charge may be problematic - You'd probably incur a hefty charge to dig it out unless you can get the developer to cover the cost (claim as a faulty installation ?).

koru

FreeBear said:

Crunching a few numbers for you. At 62p/l, that works out as 8.757p per kWh.

With electricity currently at 24p per kWh, you only need a SCOP of 2.75 to break even on running costs. 

And if you use the Octopus Agile tariff you can probably reduce your electric cost to less than 15p per kWh, on average. If the heat pump produces 3.5 times as much heat as the electric it uses (which I should think is achievable for a new home with UFH), you should be looking at a cost of less than 5p per kWh of heat. So, even bigger savings on the LPG.

Reed_Richards

koru said:

...If the heat pump produces 3.5 times as much heat as the electric it uses (which I should think is achievable for a new home with UFH), ...

This might well be achievable with UFH throughout, but is more difficult to achieve with a mix of UFH and radiators, as I tried to explain above.

koru

Reed_Richards said: 
This might well be achievable with UFH throughout, but is more difficult to achieve with a mix of UFH and radiators, as I tried to explain above.

I was thinking that UFH throughout might achieve a SCOP of 4 or more, so 3.5 might still be achievable, but I'm entirely guessing.

Reed_Richards

koru said:

Reed_Richards said: 
This might well be achievable with UFH throughout, but is more difficult to achieve with a mix of UFH and radiators, as I tried to explain above.

I was thinking that UFH throughout might achieve a SCOP of 4 or more, so 3.5 might still be achievable, but I'm entirely guessing.

The problem is that a mixture of UFH and radiators will not achieve a better SCOP then radiators alone unless your ASHP has some suitably sophisticated control features.  The COP at any time depends on the difference between the Leaving Water Temperature and the outside temperature.  If the radiators are sized to need hotter water than the UFH and you can only set the one Weather Compensation curve then you never get any benefit from the fact that your UFH could run with a lower LWT.