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8kW Mitsubishi ASHP – looking to make the system more efficient

 
Air Source Heat Pumps (ASHPs)
Last Post by Derek M 3 years ago
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 dinkydo
(@dinkydo)
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Topic starter 18/12/2021 10:14 am  

Hi. I bought a 2 bed end terrace house in Nov 2016 in a small village near Grimsby with no mains gas supply. The heating system was not working (coal fired back boiler) and when I was quoted £13k to have the system replaced I decided to look into having an Air Source Heatpump fitted.

Before moving into the house I had a new roof installed and a 3.6Kw solar system fitted. I then had an 8Kw Mitsubishi Air Source Heatpump installed along with an ecodan FTC5 Hydrobox.

My latest addition is a 10KW battery system.

I have no point of reference to compare electricity usage as I never lived in the house prior to having these improvements done (apart from the batteries).

All I can say is my electricity consumption is about 4200Kw per year and as that covers everything from heating, hot water and cooking I don't think it is too bad.

The batteries were only installed in Sep 2021 so it is too soon to say what difference they will make to overall electricity consumption. All I do know is they are already saving me money. As soon as I ordered the batteries, I changed electricity supplier to one that did time of use tariff. I managed to get an 18 month fixed rate of 7.14p low rate, 17.53p normal rate and 31p high rate. As they work on normal usage of 50% normal, 43% low and 7% high rate my bill for 4200Kw in a year should come to £588 approx.

With the current increased charges new customers are being quoted 19.2p low, 27.37p normal and 53.44 high. 4200Kw at these rates would be £1078 approx. As you can see, my batteries are already saving me £490 per year as without them I would not have changed supplier and would more than likely be paying much more per Kw for my electricity than last year.

As I now charge my batteries at the low overnight rate and use that electricity during the day and can at most times avoid the higher rate totally, plus I have started using the washing machine and tumble dryer on the lower rate overnight my bills should be even lower. Also, as I am predicting using almost zero electricity during sunny months as the batteries will be charged by solar my total Kw consumption should be much lower and I wiil save money that way.

I realise I am in a much better position than most but it just shows that with the right systems in place it is possible to avoid being held captive by high energy prices. I have spent a lot of money, but look on it as paying my electricity in advance and possibly saving some money in the future.

 

 


   
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 Kev M
(@kev-m)
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18/12/2021 11:36 am  

@dinkydo,

I like the sound of your set up and well done on getting a good fixed rate. 

I assume from the fact your house had a coal back boiler it is quite old.  If so, yours would be quite a good case study about how ASHPs can work in such properties.  Even if it includes your PV, 4200kW is good.

Kev


   
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 dinkydo
(@dinkydo)
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Topic starter 18/12/2021 12:49 pm  

My house was built around 1960. It has cavity wall insulation, triple glazed windows on the front north facing and double glazing on the rear south facing so as to take advantage of solar gain which would not happen with triple glazing I believe. The loft is well insulated.

My 8kw Mitsubishi air source heat pump is returning a COP of just under 2.5. Not perfect, but acceptable.

I keep my heating at 21C and have recently started keeping in on 24 hrs per day. I did not believe this would be the most economical, but it seems true at the moment. Instead of increasing the size of my radiators I went the other way and reduced the size by installing Smiths ecorads in all rooms apart from the bathroom. These run at a lower temperature, contain less water which heats up much quicker and have small electrical fans to circulate the heat around the room. 
All in all I am more than happy with my decision to fit an air source heat pump.

This post was modified 3 years ago by dinkydo

   
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 Derek M
(@derek-m)
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18/12/2021 1:29 pm  

@dinkydo 

You could be getting a COP of 3 or more with a little optimisation.


   
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 dinkydo
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Topic starter 18/12/2021 2:03 pm  

@derek-m Any ideas on how to optimise would be appreciated.


   
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 Derek M
(@derek-m)
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18/12/2021 2:22 pm  

@dinkydo 

How are you controlling your system at the moment?

Running the sanitisation cycle during the cheaper rate will save money if not energy.

There are quite a number of ways to improve efficiency dependent upon how your system is configured.


   
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 Derek M
(@derek-m)
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19/12/2021 2:44 pm  
Posted by: @dinkydo

@derek-m Any ideas on how to optimise would be appreciated.

Hi Dinkydo,

ASHP's operate at their most efficient when the water flow temperature they are producing is at the lowest possible that meets the heat demand.

The easiest way to improve efficiency would probably be to operate your heat pump in weather compensation mode, with auto adaptation if possible.

A second way could be to reduce the required indoor temperature, either throughout the whole day or during overnight periods.

The next easiest could be to improve the level of insulation and/or draft proofing, with improving the output capacity of the heat emitters as a fourth way of improving the overall efficiency of the system by lowering the water flow temperature.


   
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