Octopus Heat Pumps

matt_drummer

koru said:

Thanks, Matt and Reed. Frustratingly, although I got two other quotes, they both specified the Daikin Altherma. It is puzzling that all three are specifying a model that is apparently so poor. Matt, can you point me to some of the key discussions on this? 

Interestingly, the other two quotes specified the 11kW model, so Octopus is suggesting lower power. To be fair, the other two quotes were desktop quotes, so perhaps they would have reduced if they had done a survey.

Are there models that modulate significantly lower?

The 11kW is the same as the 9kW and the 14kW and the 16kW. It makes little difference which one you have.

They all have the same compressor and massive circulation pump.

The two larger outputs have a marginally larger evaporator but the increase in output comes almost entirely from fan speed, the fan runs twice as fast at maximum output on the 16kW as it does on the 9kW

They all have the same minimum output of around 4kw.

So 4kW of heat on a warm day is good in a house that needs 16kW on a cold day, but not so great in a house that only needs 9kW on a cold day.

The 9kw has a very narrow range of outputs compared to many other heat pumps.

If you can make that work then it is ok but you will need massive radiators to do it at a low flow temperature with those heat pumps.

You can run at low flow temperatures and get a lower heat output but the efficiency will be poor as the minimum electrical input is around 900w.

So if you want 2kW of heat from a 9kW Daikin you will get a COP of a little over 2.0.

You can of course run at 4kW of heat output but with the size of radiator output I suspect you will have the heat pump will need to run at over 40c flow temperature and so you will use more than 900w of electricity.

You will find it difficult to run a heat pump like this without some form of detailed monitoring.

You will find more information here

https://heatpumpmonitor.org/

https://community.openenergymonitor.org/c/hardware/heatpump/47

koru

Thanks, Matt. I'll talk to Octopus about whether they are sure I need 9kW. I see that Daikin has an 8kW model, which seems to be a variant of a range that includes 4, 6 and 8kW models. So, perhaps the 8kW model would modulate to a much lower level? 

Which heat pump have you chosen as the replacement?

My heat loss is 8.5kW, according to Octopus.

matt_drummer

My 9kW was replaced with an 8kW, both Daikin from Octopus.

https://heatpumpmonitor.org/

There are lots of Octopus and Daikin heat pumps to look at here.

Mine is in Ipswich.

Select the last seven days and you will find my heat pump quite easily

It was swapped just over a week ago so the last seven days are a good indication of how it performs compared to the 9kW.

matt_drummer

koru said:

Thanks, Matt. I'll talk to Octopus about whether they are sure I need 9kW. I see that Daikin has an 8kW model, which seems to be a variant of a range that includes 4, 6 and 8kW models. So, perhaps the 8kW model would modulate to a much lower level? 

Which heat pump have you chosen as the replacement?

My heat loss is 8.5kW, according to Octopus.

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.

The defrosting will be worse the higher flow temperature you need to run.

With that range of heat pumps I would expect 70% of the rated output when it needs to defrost for 10 minutes once every 20 minutes or so.

The 11kW model is actually 10.6kW so if you need to run over about 32c at around 0c outside then the real output is only about 7.5kW.

If you are going with a Daikin, based on your heat loss I would say you need the 14kW model or massive radiators so you can run very low flow temperatures.

rjmachin

I had our heat pump survey by Octopus today.

They arrived at 9:15am this morning and left at 2pm, so were very thorough.  Just also to say they were very polite, nice, professional and loved our dog.

They pointed out a couple of issues, but also solutions.

1. The conservatory currently has a small radiator in it.  They said that this means it has to be classified as a room and needs to be taken into account.  The solution is to take out the radiator and cap off the pipes, and if needed, get a oil filled or electric radiator.
   As the small radiator doesn't do much and it probably just escapes through the glass, I am happy to remove it.
   
   
2. One of the bathrooms has a tall single panel radiator, not big enough for the room.  However, they think it will be okay because it is a mirror radiator, so may not need to do anything with that.

They found a suitable place for the heatpump outside and said our loft was suitable to place the water tank and other equipment.

Just need to wait for our full quote to come through now

Reed_Richards

If I were you I would classify your conservatory as a room but say that its desired temperature is 10 C, or whatever low temperature you would want to use.  It's silly not to make use of the pre-existing pipework and the superior efficiency of a heat pump.  I imagine all your radiators will have TRVs fitted as standard so just set the one on the conservatory radiator to a low setting.

Why does a radiator being a mirror radiator (whatever that is) make its low output okay?  The last thing you want is a cold bathroom.  I skimped a bit on a small bathroom , leaving an existing but undersized radiator in place.  What I should have done was fitted a second radiator/towel rail  

Water tanks lose heat.  If your tank is in the loft the heat it loses will be wasted, which wouldn't be the case if you could have it within the insulated fabric of the building.    

rjmachin

Reed_Richards said:

If I were you I would classify your conservatory as a room but say that its desired temperature is 10 C, or whatever low temperature you would want to use.  It's silly not to make use of the pre-existing pipework and the superior efficiency of a heat pump.  I imagine all your radiators will have TRVs fitted as standard so just set the one on the conservatory radiator to a low setting.

Why does a radiator being a mirror radiator (whatever that is) make its low output okay?  The last thing you want is a cold bathroom.  I skimped a bit on a small bathroom , leaving an existing but undersized radiator in place.  What I should have done was fitted a second radiator/towel rail  

Water tanks lose heat.  If your tank is in the loft the heat it loses will be wasted, which wouldn't be the case if you could have it within the insulated fabric of the building.    

The current radiator in the conservatory is probably 500x500 and the wall it is on is not wide enough to expand that way, so could only go up higher, but then the light switch will have to be moved to put a taller radiator in.

There is a glass conservatory sliding door between the house and the conservatory, which is closed the majority of the time, especially when its cold, so the house heating would not always be used to heat the conservatory.  I had a tiled roof conversion done on the conservatory to help with cooler summers and warmer winters, plus carpet in there as well.

The radiator in the wetroom is similar to this one, so is tall from floor to ceiling:
https://www.diy.com/departments/ximax-vulkan-square-silver-effect-vertical-designer-radiator-w-585mm-x-h-1800mm/725767_BQ.prd

There is no where else in my bungalow that I could place the water tank, currently I have a combi boiler.

Reed_Richards

Your comment implies that you will only heat your conservatory "if needed" in which case it is pointless and silly to get rid of the existing radiator.  You can use it to keep the chill off the room in winter and supplement this with an electric heater if you want to spend time in there.  You don't want Octopus to treat it as a room that has to be heated to 21 C,  so specify a much lower temperature.  If their software cannot cope with that then it's not very good software.

Your bathroom radiator has an output of 1861 W at delta T = 50 C, if I read the spec sheet correctly.  There is a complicated and barely-legible formula given for how the output varies with delta T but AFAIK all radiators follow the same rules.  In our big bathroom we put in a low-height radiator to supplement the existing towel rail, which worked very well.  

koru

matt_drummer said:
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.

So, when it is cold it will be inefficient and when it is warm it will be inefficient as it won't modulate down enough? They have specified a 50C flow temperature. Do Octopus do anything other than Daikin (until the Cozy is ready)? Other quotes are £7-8k more and they don't include radiator upgrades. And they were also specifying Daikin.

I'm going to do my own heat loss calcs, to get an idea whether Octopus might have over or underestimated. Comparing the heat loss per room, I'm wondering if they've made some mistakes. For instance, their heat loss for our ensuite bathroom with one external wall is as high as our bedroom which is at least double the size and has two external walls.

On the other hand, their theoretical calculation is that we require 12,000 kWh to heat the property, but we actually used 15,000 over the last 12 m, which perhaps suggests they have underestimated. I suppose it depends on how warm the winter is, but this winter hasn't been that bad.

matt_drummer

Efficiency is all relative.

Octopus installations are all really good, the work is done to a high standard at a really cheap price. They don't compromise on anything and I don't think you will get a significantly better installation whatever you paid.

What they aren't so good at is system design.

They only supply Daikin heat pumps as far as I am aware.

They always seem to design to run at 50c flow at -2.3c outside.

Their software to calculate heat loss is based on MCS requirements for room temperatures, air changes etc etc.

I always heated my house to 20c or so all day and all night so I could come to a very good approximation of my heat loss based on my gas usage on the coldest days.

Whether you can do the same, I don't know.

What you won't get from Octopus is a heating system designed to run at low flow temperatures where you will see the best efficiency.

My system was designed to run at 50c at -2.3c outside and I wasn't happy with it when I needed to start heating in October last year.

In the end I increased my radiator sizes by nearly 300% and at that I could run the 9kW Daikin at 33c flow at -4c outside. The house was 23c inside running like this.

Ironically I turned the flow temperature up to 34c and even 36c as it got warmer, it gave greater efficiency because of the inability of that heat pump to consume any less than 900w of electricity.

My 8kW Daikin is running at 28c flow today at about 4c outside. It will never need to run at more than 30/31c flow temperature.

This makes it really efficient.

But it all costs money, you generally can't have cheap and efficient, the heat pump itself is only part of the story, it is what you connect it to that counts.

These are long reads but they will explain in some detail the problems and solutions.

Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring - Hardware / Heatpump - OpenEnergyMonitor Community

My heat pump is too big, what should I do? - Hardware / Heatpump - OpenEnergyMonitor Community