hello mattC and welcome

not going to go into the installer companies at this stage, although I would suggest a) let us know where you live. someone may have a local company they know b) look up "heat geek" and see if you can get one of their qualified people to take a look.   

first and most important questions are always to get the size of the thing right. Who from and what brand are 2nd priority, along with design and quality of install (which can have a strong correlation to who from)

- do you know what the heat usage of your house is? based on gas meter data perhaps. per day on a cold day (below zero) vs per day on a mild day (around 7) is golden information.

- please describe your house roughly (m2, level of insulation etc)

- what information have you been given by way of heat loss surveys from these companies. not what size heat pump. what actual heat loss have they calculated. there should be a big spreadsheet of room sizes, radiators and heat losses. Feel free to share those.

Heat loss figures from EPC will be almost impossible to use for heat pump sizing and usually wrong so don't worry about those too much.

@mattc

Hi Matt

With respect to the Mixergy cylinder, I think the overall opinion is that if you are going to heat it with a heat pump, there are probably better options. That said I have one and love it, but I heat it via an immersion using ultra cheap rate electricity at night (I have an EV).

What I find is that because of its technique of heating from the top, I dont need so much hot water. We have a 120 lt Mixergy and TBH I generally only heat it to 50% full, and thats enough for the two of us with the occasional bath. There is also the option just to boost it if you are a bit low. Generally I use about 3-4 kWh per day so the comparison in terms of energy would be if you would need to heat a larger heat pump cylinder with maybe 8-10 kWh at a COP of 2.5ish.

Because of the cheap 7.5p per kWh I am paying I would have to get a hot water COP of 3.5ish to match it financially with the heat pump. Full details are on my blog in the signature below.

Hi Ian

Thanks for your response.

We're near Peterborough, Cambs, and the last company on my list is local.  Any other suggestions are, of course, welcome.

The house is about 100m2, semi-detached.  Almost all of the external walls are part of a recent extension, so well-insulated up to current specs, and the rest have retro-fitted cavity wall insulation from around 20 years ago.  The loft is insulated to around 240mm, apart from one small area is boarded so just has 130mm under the boards.

In terms of gas usage, it ranges from about 110kWh per day when it's particularly cold (like it was a couple of weeks ago) down to about 50kWh per day when milder (like the last week).  This is with the main stat at 20C and a flow temp of 50C, for 16 hours per day.

As I mentioned, I haven't yet had a survey from any of these companies.  My plan is to choose two and ask for full surveys from these before making a final decision.  Hence my question about good/bad experiences with any on the list.

@bontwoody

Thanks.  The reason I was originally looking at a Mixergy is because, most of the time, there are just two of us in the house, but occoasionally, everyone else turns up and there can be up to 10, including small grandchildren.

From what I can gather, as soon as you connect the heat pump to the Mixergy, it switches to 'conventional' mode, so you end up heating the whole cylinder and lose out on some of the benefits.  Is this right?  Using the heat pump, I'll probably aim to heat the water at night when the electricity is cheaper.

Hi, Matt C I can only inform you of our experience with Greener Living.

We moved into brand new property with newly installed mitsubishi ecodan and we had no heating downstairs. Developer paid for greener living to come out to check system, turned out ufh  mannifold was switched off, I asked the guy to go thru settings with me has we had no handover, we were totally clueless, he told me to set it at 60⁰ on fixed flow, "set it and forget it" in his words. He left after 10 minutes 🙄.

They were maybe able to get away with this when electricity was 10p but not now.

No mention of Weather compensation just fixed flow, the consensus is the most efficient way to run ashp is on weather compensation.

We tried the following year to have them come out to service the system, after wks of leaving messages we finally gave up and had mitubishi service it. So zero after care.

Couple of other issues we had was 2 of the room thermostats were wired incorrectly, the hall which is quite a big area was crossed over with the closet quite small area, so hall never got to temp.

We got our electrician to fix this he said they took care with insulating the pipes but took no care tidying electric cables.

The other small issue we had was that the radiator pump was set to max 3 so the transfer of heat to the rads was not great its set to 2 now and rads/ rooms warmer.

Looks to like me they set everything  thoughtlessly on high regardless of efficiency.

Even though this all sounds negative I love the ecodan its kept on working kept the house lovely and warm we've just had to do loads of research to get it running optimally and efficiently, helped by the knowledgeable helpful people on this forum.

For us getting to grips with weather compensation has been the hardest thing to get right,  I would grill your potential suppliers about the most efficient way to run the system if they say fixed flow at 60⁰ that should ring alarm bells 😁 hope that helps.

@mattc Thats my understanding of how it works with the heat pump Matt. I originally heated it via a solar diverter but it made more financial sense to export instead and heat it at night. I think you need to do some estimates about how big a cylinder you need and the various costs of heating it different ways. My feeling is you wouldnt want a big cylinder for the two of you just for the times when others visit, if you can get cheap electricity than a smaller Mixergy might work well heated by an immersion as its reheat times are fast.

Posted by: @mattc

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In terms of gas usage, it ranges from about 110kWh per day when it's particularly cold (like it was a couple of weeks ago) down to about 50kWh per day when milder (like the last week).  This is with the main stat at 20C and a flow temp of 50C, for 16 hours per day.

ok so that's really good data to have and good that you are trying to run the boiler constantly. 110kwh of gas = 93.5kwh of heat (boiler at best 85% efficient).  Divide by 16 hrs = 5.8kwh per hour.  that says the heat input of your house on the very cold day over that 16hr period was just under 6kw. Taken over the whole 24hrs though, its just under 4kw.

You therefore can't possibly need a 12kw heat pump. even an 8 seems too big, but might be ok if from a brand that downrates well. thats the other issue - the min output when its mild. some can be as bad as only going down to 50%. (so if a 12kw unit, its minimum output might be 6kw).

based on your house size and description that would ring true as well.  you can glean a lot from comparing to other people's houses and system sizes - for comparison my house is 1973, 210m2,  detached, not that well insulated in the cavities. It needed 9kw in the cold blast 2 weeks ago.

it'll be interesting to see what the heat loss survey data comes up with.

the 2nd stage issue is then getting a quality install thats not inefficient and/or badly designed. To that end the other organisation you should definitely talk to at is "Heat Geek". find their installers list and see if you can someone to take a look. 

Thanks all for your insights.

@sand  Did GL do the original installation in your case or were they just called in afterwards to advise?  Also, how long ago was this?

Anyone had experience with any of the other companies?

@mattc they did the install for all the properties on a small development. This was commissioned by the developer. 

What was extremely frustrating was in the ecodan manual it says speak to your installer to change any settings but obviously they just weren't contactable The receptionist would say give me your details but we never got a call back over a number of weeks. 6 properties on the development, I imagine would be a doddle to service, and good annual income but they weren't interested. Probably happy with the money from the developer but no interest in customer service for the end user.

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Posted by: @mattc

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Between them, they have suggested Mitsubishi, Daikin and Midea units, ranging from 8 to 12 kW.  I get the impression that the choice of manufacturer is less important than some other factors, but thoughts about any of these would be helpful too.

I was originally planning to install a new Mixergy cylinder, but have read that the advantages of these over convental tanks are less clear when paired with ASHP.  We don't (yet) have solar installed.

I think I would go for the installer that doesn't want to

Fit a unit that is far too big (I agree 12kW is well oversized, based on the very limited info you have provided you are looking at 6-max 8.5 kW unless you are happy to suffer a penalty to have bags of leeway, which you may well be.)

Fit a buffer tank, llh, phe in the primary (a phe plus pump instead of a large coil dhw cylinder is ok, arguably the better solution).

Upgrade the dhw primaries to 28mm unless you have specified rapid recovery as a requirement.

If you have decent water pressure, upgrade the CW feed to the dhw tank from 15 to 22mm

Use a pre plumbed cylinder

Fit any external controls.

That may well narrow it down to one or possibly zero.

Seriously the first three are red flags.  The use of a pre plumbed cylinder is ok provided it makes sense given the layout of your house, otherwise it tells you they are shoe-horning it in because they employ rookie plumbers.

Surprised vaillant isn't on the short list.  Their nominally 7kW unit (actually nearer 8.5 in the South of England) might be a good fit, possibly even the next size down.

Like @iancalderbank I'd spend a bit of money or effort getting the system sizing right.

Posted by: @iancalderbank

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Posted by: @mattc

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In terms of gas usage, it ranges from about 110kWh per day when it's particularly cold (like it was a couple of weeks ago) down to about 50kWh per day when milder (like the last week).  This is with the main stat at 20C and a flow temp of 50C, for 16 hours per day.

ok so that's really good data to have and good that you are trying to run the boiler constantly. 110kwh of gas = 93.5kwh of heat (boiler at best 85% efficient).  Divide by 16 hrs = 5.8kwh per hour.  that says the heat input of your house on the very cold day over that 16hr period was just under 6kw. Taken over the whole 24hrs though, its just under 4kw.

You therefore can't possibly need a 12kw heat pump. even an 8 seems too big, but might be ok if from a brand that downrates well. thats the other issue - the min output when its mild. some can be as bad as only going down to 50%. (so if a 12kw unit, its minimum output might be 6kw).

based on your house size and description that would ring true as well.  you can glean a lot from comparing to other people's houses and system sizes - for comparison my house is 1973, 210m2,  detached, not that well insulated in the cavities. It needed 9kw in the cold blast 2 weeks ago.

it'll be interesting to see what the heat loss survey data comes up with.

the 2nd stage issue is then getting a quality install thats not inefficient and/or badly designed. To that end the other organisation you should definitely talk to at is "Heat Geek". find their installers list and see if you can someone to take a look. 

 

Ian,

I would suggest caution when encouraging people to go for smaller capacity heat pumps, since I feel most would be much happier having a heat pump that may be slightly oversized, but keeps their home warm, as against one that may turn out to be undersized and not keep their home warm.

I fully agree with your sentiment about getting the size correct, but don't forget DHW production and defrost cycles, as well as the fact that ambient temperatures below the design temperature do occur.