Heat Pump Pricing versus current costs

matt_drummer

DougMLancs said:

My installer did. Octopus also keep in touch with all their customers post install. I run mine 24/7 too but for those who are treating it like a gas boiler still, at least it helps. Best option for any heat pump is having a small battery that can use those cheap rates for charging.

I have met quite a lot of Octopus installers, they are very good at installing heat pumps but I haven't yet met one that really knows how to operate what they have installed. Actually, even the Daikin engineers know less about it than me and others do.

It takes a long time and detailed data to get the best out of their heat pumps.

michaels

matt_drummer said:

Reed_Richards said:

matt_drummer said:

I haven't seen any evidence that shows that R290 heat pumps are significantly more efficient than R32 heat pumps. I know that my R32 heat pump is as or more efficient than most if not all R290 heat pumps I have seen data for.

I read elsewhere a comment from somebody who tried to make a like-for-like comparison that an R290 heat pump is less efficient than the equivalent R32.

Quite possibly.

I think that what is beyond doubt is heating water to 65c will not be as cheap or as efficient as heating water to 30c with our current technology.

But the key question is, how much less efficient - would a 55-25 curve use 5%, 10%, 50% more energy than a 35-25 curve?

30-35% of our heat energy use is for hot water rather than space heating, for this portion we would presumably have to run at a higher temp to get the required hot water temp?

DougMLancs

Reed_Richards said:

DougMLancs said:

Reed_Richards said:

DougMLancs said:

I was listening to their Head of HP sales the other day and they find it’s not uncommon to design to 50 C and then they end up dropping the flow temp to 42-45 C. 

That's exactly what happened to me, temperature-wise, but there was no "they".  Installers don't come back to inspect your heat pump in the middle of winter and spend a few days in your house to find out what water temperature you really need.  If your Weather Compensation settings have been set too high then it is left entirely up to you to make adjustments.  It's a slow process of trial and error until such time as heat pumps are made "intelligent" enough that they can do a major self-adjust (in which case the second "they" in the sentence would be the heat pumps themselves).

DougMLancs said:

Their Cosy Tariff now has 8 hours at 11.2p/kWh with this in mind. 

Conventional wisdom is that you need to run a heat pump 24/7 so it's the cost of the other 16 hours that you need to factor in.  

My installer did. Octopus also keep in touch with all their customers post install. I run mine 24/7 too but for those who are treating it like a gas boiler still, at least it helps. Best option for any heat pump is having a small battery that can use those cheap rates for charging.

Did what, exactly?  I was suggesting that it would take days of observation to make a major adjustment to the leaving water temperature settings and know that it was correct.  But you could probably accomplish this via a succession of quick visits.  Is your installer is based close to where you live?  

Exactly that- it was installed in July so no chance of properly setting the weather comp curve. They also didn’t ask for the final payment £600 until they were happy with it. He’s only 45 mins away though. 

matt_drummer

michaels said:

But the key question is, how much less efficient - would a 55-25 curve use 5%, 10%, 50% more energy than a 35-25 curve?

30-35% of our heat energy use is for hot water rather than space heating, for this portion we would presumably have to run at a higher temp to get the required hot water temp?

You can find all this information quite easily from heatpumpmonitor.org

I just looked at one day of mine as an example.

To heat my dhw to 50c I need a flow temperature of 56c

At 8c outside my COP at 56c was 2.0, my heating at 30c had a COP of 5.20

It used 2.6 times more electricity heating water to 26c as it did to 30c at 8c outside.

The difference between 55c and 30c when it is -3c outside will be massive as my heat pump doesn't need to defrost at 30c very often whereas at 55c it will be defrosting like crazy.

My prediction would be 2 to 3 times more electricity consumption running at 55c rather than 30c

My experience with a grossly oversized heat pump and undersized radiators requiring me to run at 42c was that when I replaced all my radiators and then the heat pump my electricity consumption is 30 to 40% of what it was at the start.

The right heat pump and low flow temperatures make a huge difference to operating costs.

Heating large volumes of water with electricity will never be cheap and I suspect gas or oil will always be cheaper given the amount of hot water you desire.

smallblueplanet

matt_drummer said ...

The difference between 55c and 30c when it is -3c outside will be massive as my heat pump doesn't need to defrost at 30c very often whereas at 55c it will be defrosting like crazy.

I don't quite understand the defrosting thing, how does it work and why is it 'worse' at higher flow temp?

michaels

matt_drummer said:

michaels said:

But the key question is, how much less efficient - would a 55-25 curve use 5%, 10%, 50% more energy than a 35-25 curve?

30-35% of our heat energy use is for hot water rather than space heating, for this portion we would presumably have to run at a higher temp to get the required hot water temp?

You can find all this information quite easily from heatpumpmonitor.org

I just looked at one day of mine as an example.

To heat my dhw to 50c I need a flow temperature of 56c

At 8c outside my COP at 56c was 2.0, my heating at 30c had a COP of 5.20

It used 2.6 times more electricity heating water to 26c as it did to 30c at 8c outside.

The difference between 55c and 30c when it is -3c outside will be massive as my heat pump doesn't need to defrost at 30c very often whereas at 55c it will be defrosting like crazy.

My prediction would be 2 to 3 times more electricity consumption running at 55c rather than 30c

My experience with a grossly oversized heat pump and undersized radiators requiring me to run at 42c was than when I replaced all my radiators and then the heat pump my electricity consumption is 30 to 40% of what it was at the start.

The right heat pump and low flow temperatures make a huge difference to operating costs.

Heating large volumes of water with electricity will never be cheap and I suspect gas or oil will always be cheaper given the amount of hot water you desire.

Thanks, really helpful

matt_drummer

At certain outdoor temperatures and humidity ice will form on the evaporator.

At some point the heat pump won't be able to draw in air to extract energy from it as the ice blocks the fins on the evaporator.

The ice has to be removed.

The heat pump does this by reversing the flow of water to the house instead to from the house to enable the refrigerant to warm up and remove the ice as it flows around the evaporator.

That heat is taken from the house, heat that has been paid for.

Also, whilst this process is in operation the house isn't being heated.

At higher flow temperatures more energy is required to be extracted from the air and that means the fan spins faster.

The air therefore moves faster as a larger volume of air is being moved.

More air means more water to freeze and as it is going faster it is colder.

The ice builds up more quickly.

I have only had ice on my new heat pump once and that was only because i was experimenting in the early days.

My old heat pump defrosted for 20 minutes in every hour at its worst, that is 20 minutes of heat and 10 minutes of defrosting.

Not only was the heat pump taking energy from the house that I had already paid for, it then started a new heating cycle once every 30 minutes. The first 30 minutes was the most inefficient and consumed loads of electricity, it was always running in the most inefficient phase of the heating cycle.

As I run on batteries it meant I often exceeded the power my inverter could supply and would draw from the grid.

It was bad all round.


 

matt_drummer

I should add something about how heat pumps work.

The heat energy delivered to the house is produced by cooling air down which in turn heats up the refrigerant.

If you need to extract more energy to heat the refrigerant to a higher temperature the the there needs to be more air and it needs to get colder.

I'm not an expert or a scientist but this is the general idea, more energy extracted over a given surface area will make that area colder and ice will form more quickly.

Reed_Richards

matt_drummer said:

To heat my dhw to 50c I need a flow temperature of 56c

At 8c outside my COP at 56c was 2.0, my heating at 30c had a COP of 5.20

I find this a little surprising.  I was promised an SCOP of 2.95 for hot water at 50 C (with a flow temperature of 55 C).  Unlike @matt_drummer I have no means of measuring what COP I actually achieve but if I sometimes got a COP of 2 I would need a fair few days of a COP higher than 3 to compensate.  Fortunately, now I am on an EV tariff I can do all my hot water heating at 6.9p per kWh. 

matt_drummer

Reed_Richards said:

matt_drummer said:

To heat my dhw to 50c I need a flow temperature of 56c

At 8c outside my COP at 56c was 2.0, my heating at 30c had a COP of 5.20

I find this a little surprising.  I was promised an SCOP of 2.95 for hot water at 50 C (with a flow temperature of 55 C).  Unlike @matt_drummer I have no means of measuring what COP I actually achieve but if I sometimes got a COP of 2 I would need a fair few days of a COP higher than 3 to compensate.  Fortunately, now I am on an EV tariff I can do all my hot water heating at 6.9p per kWh. 

You are correct about your SCOP. Your COP for the dhw cycle at 8c outside will be better than 2 but there will be days when it won't be

I wasn't quoting the COP for the whole dhw cycle.

I quoted instant COP of 2.0 at 56c flow.

At the start of the dhw cycle it is closer to 5 and overall something like 3 on average.

But as I don't run my heating at much more than 30c I needed to find the COP at close to 55c flow temperature