Octopus Heat Pumps

koru

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.

Reed_Richards

Out of interest, how did they do the heat loss test?  I suspect that heat loss may be influenced by the wind speed and can be greatly offset by solar gain on a sunny day so you would probably have to monitor over several days to get a really accurate measurement.   

murmeltier

Octopus did our survey a few days ago. Took 3.5 hours, overall a pleasant experience. Surveyor seemed very diligent, but I'm not an expert.

I haven't seen the detailed calculations etc yet.

Heat loss came out at 10kWh, roughly where my gut feeling was given the size of the property (just under 200sqm), its age (1960s), its quirky extensions over the years and its insulation (average in most areas, very good in some). Radiators that need upsizing were the ones I was sort of expecting (mostly the rooms with the biggest heat loss), so no real surprises there. Apparently we came out very close to their limit where they wouldn't be able to proceed.

He said he was going to specify the 10.6kWh Daikin (EDLA11DA3V3).

Now - given the discussions in this thread and others around matt_drummer's experience with this type/size of heat pump (I've tried to read through them and I get the gist of it but I'm struggling with the exact details and implications) - if we decide to go with this proposal, are we going to set ourselves up for trouble?

The defrosting that's been mentioned - at what outside temperature does this kick in and is this something to potentially worry about?

Their estimate (haven't seen the final quote yet) is unbeatable by miles at the moment.

Thinking about getting Heat Geek in for another survey, but I suspect their heat loss calculation will be similar. 

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.

A tough one.

Based on my experience that my data backs up, you need massive radiators to make the Daikin perform really well.

I get close to the best performing heat pumps but struggle to match the Vaillant when it is warmer.

When it is cold I do much better, perhaps the best of all.

Daikin heat pumps are pretty good in the cold but so far I cannot get mine to perform as well as others when it is warmer.

In the course of a year I think my Daikin will be close to as good as anything, but I do have really big radiators. Those with less radiators don't do so well.

The Vaillant will be easier to live with.

koru

murmeltier said:

Thinking about getting Heat Geek in for another survey, but I suspect their heat loss calculation will be similar. 

Either way, it gives you peace of mind, as you either have confirmation Octopus are right or you know they aren't. They charge £350 for the survey. I decided it was worth it.

The Heat Geek guys are the only ones that have spotted that routing the pipes through our attic won't work, because it is flat roof above the boiler cupboard.

koru

Reed_Richards said:

Out of interest, how did they do the heat loss test?  I suspect that heat loss may be influenced by the wind speed and can be greatly offset by solar gain on a sunny day so you would probably have to monitor over several days to get a really accurate measurement.   

This video gives a good idea, though I think my guys did thermal imaging as well. https://www.youtube.com/watch?v=ruZvmAgvWoo
 Octopus were similar, but all manual measurements. I suspect a lot depends on assumptions made, such as how often air refreshes.

koru

matt_drummer said:

Based on my experience that my data backs up, you need massive radiators to make the Daikin perform really well.

I get close to the best performing heat pumps but struggle to match the Vaillant when it is warmer.

When it is cold I do much better, perhaps the best of all.

Daikin heat pumps are pretty good in the cold but so far I cannot get mine to perform as well as others when it is warmer.

In the course of a year I think my Daikin will be close to as good as anything, but I do have really big radiators. Those with less radiators don't do so well.

The Vaillant will be easier to live with.

I guess that even though there aren't many cold days, they are the ones when you would need most heat, so being efficient on cold days is more important than being efficient on cool days.

You've gone for triple radiators everywhere, right? It will be interesting to see what Heat Geek specify for me, as they try to design the system to run at low temps.

murmeltier

koru said:

murmeltier said:

Thinking about getting Heat Geek in for another survey, but I suspect their heat loss calculation will be similar. 

Either way, it gives you peace of mind, as you either have confirmation Octopus are right or you know they aren't. They charge £350 for the survey. I decided it was worth it.

The Heat Geek guys are the only ones that have spotted that routing the pipes through our attic won't work, because it is flat roof above the boiler cupboard.

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? 

matt_drummer

koru said:

matt_drummer said:

Based on my experience that my data backs up, you need massive radiators to make the Daikin perform really well.

I get close to the best performing heat pumps but struggle to match the Vaillant when it is warmer.

When it is cold I do much better, perhaps the best of all.

Daikin heat pumps are pretty good in the cold but so far I cannot get mine to perform as well as others when it is warmer.

In the course of a year I think my Daikin will be close to as good as anything, but I do have really big radiators. Those with less radiators don't do so well.

The Vaillant will be easier to live with.

I guess that even though there aren't many cold days, they are the ones when you would need most heat, so being efficient on cold days is more important than being efficient on cool days.

You've gone for triple radiators everywhere, right? It will be interesting to see what Heat Geek specify for me, as they try to design the system to run at low temps.

By cold days I mean 7c or less.

So quite a lot of days really.

At 5c and below my Daikin is really good but that is because I can run a really low flow temperature and still get the heat I need.

What I struggle to do is run lower flow temperatures as it gets warmer, the Vaillant is better at this.

I have the biggest K3 radiators I could fit everywhere with no trvs. I also have fan assistance on all of them.

Each radiator is matched to the heat loss and design temperature of the rooms. The last thing you want with heat pumps are zones and trvs, you need all the heating capacity you can get at low flow temperatures.

Of course, you can have trvs and zones but at the expense of efficiency.

Low flow temperatures come at a financial cost, one that Octopus won't design for, they design to run at 50c flow at -2.3c outside in my experience.

A Heat Geek installer will be different but you will have to pay for that.

matt_drummer

murmeltier said:

Octopus did our survey a few days ago. Took 3.5 hours, overall a pleasant experience. Surveyor seemed very diligent, but I'm not an expert.

I haven't seen the detailed calculations etc yet.

Heat loss came out at 10kWh, roughly where my gut feeling was given the size of the property (just under 200sqm), its age (1960s), its quirky extensions over the years and its insulation (average in most areas, very good in some). Radiators that need upsizing were the ones I was sort of expecting (mostly the rooms with the biggest heat loss), so no real surprises there. Apparently we came out very close to their limit where they wouldn't be able to proceed.

He said he was going to specify the 10.6kWh Daikin (EDLA11DA3V3).

Now - given the discussions in this thread and others around matt_drummer's experience with this type/size of heat pump (I've tried to read through them and I get the gist of it but I'm struggling with the exact details and implications) - if we decide to go with this proposal, are we going to set ourselves up for trouble?

The defrosting that's been mentioned - at what outside temperature does this kick in and is this something to potentially worry about?

Their estimate (haven't seen the final quote yet) is unbeatable by miles at the moment.

Thinking about getting Heat Geek in for another survey, but I suspect their heat loss calculation will be similar. 

If your heat loss is really 10kW then the 11kW Daikin will not be enough.

You may as well just have the 16kW as it is the same heat pump as the 9, 11 and 14, just not turned down at all at the top end. In fact you will need the 14kW as a minimum I would say. I know somebody with a heat loss similar to yours with the 11kW Daikin and it is not enough when defrosting is a problem. Their only saving grace is big radiators.

Defrosting is a big issue with that range of heat pumps below about 5c outside and at the worst it will be defrosting for 10 minutes in every 30 minutes, it will reduce your heat output to something like 70% of the rated 10.6kW.

It is worse the higher the flow temperature you need to run. If you don't have emitters that enable you to run at less than 35c flow temperature at 0c outside defrosting will be a big problem.