Octopus Heat Pumps

matt_drummer

koru said:

matt_drummer said:

If your heat loss is 8.5kW then you need more than the 8kW heat pump.

Even the 9kW Daikin won't be enough, and the 11kW will be marginal as that range of heat pumps has a propensity to ice up requiring frequent defrosts which will limit the heat output.

For the benefit of anyone else who is looking at Octopus and comes across this thread, here's the outcome for me:

I tried to raise the question of the heat loss with Octopus, but they were adamant that their survey could not be wrong. I decided that I needed to have some certainty about my heat loss, so I got the local Heat Geek Genius in to do a heat loss test. Their much more accurate analysis says my heat loss is 6.6kW. So, mine is another property in which Octopus has heavily overestimated the heat loss and specified a heat pump that is going to be unnecessarily inefficient. If I stay with Octopus, hopefully this will convince them to switch to the 8kW Daikin.

But I was really impressed with the Heat Geek guys. They would specify a 7kW Vaillant. I'm convinced that their system will be far better than the Octopus, but they are also going to cost a huge amount more than Octopus, so it's going to be a hard decision. In terms of money, I'll probably have lower power bills with Heat Geek, but it will take decades for the savings to repay the extra installation cost. So, financially, Octopus is the way to go, but I think I would be like you, Matt, I'd always be frustrated by the poor performance.

At a heat loss of 6.6kW I would say that neither the 8kW or 9kW Daikin will be enough unless you fit really big radiators, in fact the 9kW still probably won't be quite enough whatever you did, the 8kW may just do it with big enough radiators.

Defrosting in freezing conditions really cuts back the heat output a lot, you can expect about 70% of the rated output in the worst icing conditions, just when you will need your 6.6kW of heat.

Reed_Richards

I think it would be fair to say that @matt_drummer wanted his ASHP to achieve really top notch efficiency and therefore best running costs.  This requires that you use really low water temperatures which in turn requires that you use really large-area radiators.  Octopus quotes tend to be for more modest systems with higher target water temperatures and radiators that are not so large in surface area.  This might be easier to achieve in a retrofit installation and the cost of the radiators will be a bit less.  But the running cost will be higher.  If you think this will be frustrating you might consider reducing your running cost by improving your insulation, as an alternative to paying another installer a lot more than Octopus would charge.  Or consider another type of heat pump that should achieve better efficiency, like an Air-to-Air heat pump.    

    

matt_drummer

Reed_Richards said:

I think it would be fair to say that @matt_drummer wanted his ASHP to achieve really top notch efficiency and therefore best running costs.  This requires that you use really low water temperatures which in turn requires that you use really large-area radiators.  Octopus quotes tend to be for more modest systems with higher target water temperatures and radiators that are not so large in surface area.  This might be easier to achieve in a retrofit installation and the cost of the radiators will be a bit less.  But the running cost will be higher.  If you think this will be frustrating you might consider reducing your running cost by improving your insulation, as an alternative to paying another installer a lot more than Octopus would charge.  Or consider another type of heat pump that should achieve better efficiency, like an Air-to-Air heat pump.    

    

No, not entirely true, nor fair, running costs are of minor concern to me and I only want modest efficiency. The thing is, a SCOP of 3 is terrible, only the poorest of installations achieve a SCOP of 3 or less, it is truly rubbish.

My problem started with a heat pump that put out my heat loss at design temperature as a minimum output.

The heat loss of my house at -3c is about 4kW, exactly what my 9kW Daikin heat pump produced as a minimum.

It's a nightmare, the house gets really hot at any other outside temperatures and the automated controls don't work properly.

Insulating my house more would have made it worse, the house would have just got even hotter.


If I actually needed 9kW of heat I would never get it, that 9kW Daikin will put out 6.3kW when it has to defrost for 10 minutes out of every 30 minutes.


I know all this because I had one.


Try and operate one and see how you get on, if you think you can run it for 15 minutes an hour and it will all be good then you would be in for a big shock when you discover how inefficient that is.


I don't know anybody with a 9kW Daikin Altherma 3 that is happy with it.


But it did heat my house very well, just not that efficiently, not always comfortably and it used twice as much electricity as my now correctly sized heat pump.


The fact that it is also very efficient is secondary.


The planning of the heating system is the most important part, SCOPs of 3 these days are really poor, somewhere between 4 and 5 is easily achievable as any Heat Geek trained installer will tell you.

murmeltier

I believe the MCS calculations require you to assume we heat up living rooms etc up to 21C - which we have never done and will never do (we heat up living areas to 18C, bed rooms to 16C). I'm assuming this will reduce the heat loss, but is this linear?

I've booked Heat Geek now. I may prefer Vaillant over Daikin because of lower noise levels (we passed the noise assessment but we have awkward neighbours). I'm not that bothered about initial cost as long as it's reasonable. And yes, I would prefer a flow temperature lower than 50C if that can be achieved.

koru

murmeltier said:

You're right. I just needed a nudge ... I'm going to get them in for a second opinion. 

Do you know how long the wait is for a survey date? Presumably not as bad as with Octopus? 

Two days, in my case. But that will depend on your local Heat Geek affiliates. It seems to run as a sort of franchise. At least in my case, it was a local plumber/heating engineer who has done the Heat Geek training, has access to their software, and presumably lets them take a cut of jobs that originate via the Heat Geek website.

koru

murmeltier said:

 I may prefer Vaillant over Daikin because of lower noise levels (we passed the noise assessment but we have awkward neighbours). I'm not that bothered about initial cost as long as it's reasonable. And yes, I would prefer a flow temperature lower than 50C if that can be achieved.

I have the same issue. The Vaillant is significantly quieter, which could be key as we do need planning permission and I don't want to upset the neighbours. And it uses a refrigerant that is way, way, way less of a global warming gas and can operate at higher temperatures when needed. It is also much narrower. 110cm vs 140.

MultiFuelBurner

koru said:

murmeltier said:

You're right. I just needed a nudge ... I'm going to get them in for a second opinion. 

Do you know how long the wait is for a survey date? Presumably not as bad as with Octopus? 

Two days, in my case. But that will depend on your local Heat Geek affiliates. It seems to run as a sort of franchise. At least in my case, it was a local plumber/heating engineer who has done the Heat Geek training, has access to their software, and presumably lets them take a cut of jobs that originate via the Heat Geek website.

If that is your local heat geek can you ask them for local installs they have done and if those people will talk to you about their install.

Something you can't do with Octopus but may well swat you to pay the extra?

MultiFuelBurner

I do think quietness is a handful for some. When stated as significant what's the dB difference between Daikin and Valiant for matching output ASHP.

Also check what the normal dB level.is outside and lastly is the ASHP going where a fossil fuel flu once was and what was the reading of that when in full chat.

koru

MultiFuelBurner said:

I do think quietness is a handful for some. When stated as significant what's the dB difference between Daikin and Valiant for matching output ASHP.

Also check what the normal dB level.is outside and lastly is the ASHP going where a fossil fuel flu once was and what was the reading of that when in full chat.

Daikin is 62. Vailant is 55 or 53, but I can't work out which would apply to me. As it is a logarithmic scale, this means the Daikin is at least 50% louder and perhaps nearly 100% louder.

Outside it is pretty quiet, unless the wind brings motorway noise this direction.

There are 3 possible locations and two of them are close to the gas flue. I might use my phone to do a reading for that.

Reed_Richards

matt_drummer said:

................
The planning of the heating system is the most important part, SCOPs of 3 these days are really poor, somewhere between 4 and 5 is easily achievable as any Heat Geek trained installer will tell you.

I must admit I'm a little surprised by this.  Can you tell me what operating conditions are needed to achieve SCOPs of 4 to 5, or point me to a heat pump spec. sheet that does?  My promised SCOP was 3.2 for heating and 2.95 for hot water; I don't have monitoring equipment but that must be roughly what I do get.  And that was a retrofit installation at the end of 2020, not that long ago.  I could certainly do better by increasing the surface area of my radiators so as to use a lower water temperature but that would be very awkward in some rooms; indeed there are two rooms where the radiators are already undersized because there was no obvious space for a bigger one.

Also, with an ASHP you have to heat your rooms with water that is hotter than the room temperature you require whilst with an air-to-air heat pump you only heat the air to the temperature you want the room to be so that has to give you a greater efficiency and a higher SCOP, or be potentially capable of so doing.  I do regret not giving more consideration to this option before I installed an ASHP.