Air Source Heat Pump Freezing

matt_drummer

My heat pump will heat to 60c at -10c outside if I wanted it to.

The trouble is that it would cost an absolute fortune to run, I mean a crippling amount of electricity.

My heat pump is currently heating our whole four bedroom detached house and conservatory to 23c at 2c outside with the mean flow temperature through the radiators at less than 30c. It is consuming 1kW of electricity doing this and producing just over 4kW of heat.

I am guessing but I think if I was heating the water to 60c it would be using five times the electricity.


Radiators are cheap in the main. many of mine are Stelrad from Wickes.

Our cloakroom had a 400mm x 600mm single panel convector, I replaced it with a 600mm x 600mm double panel convector. That is three times the size and it cost £45

In the bedrooms I replaced 600mm x 800mm K1s with 600mm x 1200mm K2s for £77 each, again that's three times the size and for all four bedrooms the cost was £308.

There is also the possibility that some radiators in the house can be repurposed, move radiators from bigger rooms to smaller ones and only replace those in the bigger rooms, that minimises the cost.

The radiators do not take up the whole wall as you can probably work out, there is barely any noticeable difference as the radiators in most houses are already bigger than they need to be to run at 70c

It doesn't take very long running at 30c to get the money back.

There are no barriers to heat pumps in terms of running costs, a properly sized heat pump with radiators that can run at 35c or less will achieve a SCOP of 4. On a decent electricity tariff such as Octopus Tracker that puts the running costs firmly on par with the cheapest gas available.

Lack of insulation is no issue, if the house isn't very well insulated then that is the case wherever the heat comes from.

The only problems at the moment with heat pumps are poor installers and a lack of understanding of how to get the best out of them.

It will get better in time, the installers will improve and more and more people will gain the experience and knowledge to allow them to help others get them working as they should. 

QrizB

matt_drummer said:

My heat pump is currently heating our whole four bedroom detached house and conservatory to 23c at 2c outside with the mean flow temperature through the radiators at less than 30c. It is consuming 1kW of electricity doing this and producing just over 4kW of heat.
I am guessing but I think if I was heating the water to 60c it would be using five times the electricity.

Putting 5kW in to get 4kW out would be a COP of 0.8, so worse than simply using direct electric heating

matt_drummer

QrizB said:

matt_drummer said:

My heat pump is currently heating our whole four bedroom detached house and conservatory to 23c at 2c outside with the mean flow temperature through the radiators at less than 30c. It is consuming 1kW of electricity doing this and producing just over 4kW of heat.
I am guessing but I think if I was heating the water to 60c it would be using five times the electricity.

Putting 5kW in to get 4kW out would be a COP of 0.8, so worse than simply using direct electric heating

If I heated my water to 60c I would get more than 4kW of heat, it wouldn't be of COP of 0.80

With my heat pump it would deliver it's maximum heat output but not for long and then shut down, maybe something like 10kW of heat for a few minutes.

Then it would have another go when it was ready.

The COP would be somewhere between 1 and 2 I would expect, probably closer to 1 than 2.

I was never suggesting it was a good idea or that I would do it.

BobT36

Moneysavingchap said:

matt_drummer said

The main problem will be the size of the radiators, it always is. Radiators running at 30c flow in a room at 20c need to be about 8 times the size of radiators that are just adequate at 70c flow in a 20c room.

Yeah, that's just not happening for people who have gas systems with flow temps between 60-80c (what many gas heating systems have been designed for). The radiators would need to be the size of the entire wall! 

What sort of innovation and development is happening with heat pumps? Is it likely that at some point in the future (5, 10, 15 years?) that heat pumps capable of having a flow temp of 60c or more in say -10c conditions? 

What's more concerning is that in many newer builds they're installing those "baby / compact" sized radiators in every room, including huge master bedrooms. Sometimes completely incorrectly, too. I've seen many buyers get the calculations from the builders and found that they've intentionally undersized them. (This is for GCH)

You'd think if these heat pumps are "the future" they'd be installing better radiators for future compatability. Unless it's just a given that completely new (and massive) radiators are meant to come along with every pump? 

@Matt_Drummer do you think that traditional GCH would have been better in your setup? (Disregarding any "green" focus or solar comparability etc.). Not trying to put words in your mouth, just curious how you feel after having used a heat pump, as I've never even seen one myself. It does sound like the USER is expected to become quite an expert on the requirements & configuration. 

matt_drummer

Hi Bob,

I have no regrets at all.

The solar and not burning stuff is a big part for me as most people here that are interested already know.

But leaving all that aside I would still do it.

I have a minor issue in that I have the wrong heat pump, it is not actually too big, but it's design means that it doesn't modulate down to anywhere near what I need it to. 

The last couple of weeks have been perfect as I just use the minimum output and it's enough to keep the house at 23c downstairs and 21c upstairs as designed. It is warmer than many people would like but that is my choice.

I never liked the way a gas boiler heats for a while and then stops, having the temperature in the house fluctuating and having a blast from hot radiators.

With the heat pump (of the correct size) I just get a constant low heat, the house is just warm but you don't really know where it is coming from as the radiators are luke warm. It is just that they are so big that the heat output is the same as a smaller hotter radiator.

It's just like a pleasant summer's day, just warm.

From a cost point of view, taking my daily consumption, it's no different from gas if I was on a standard variable tariff. I could buy gas cheaper on something like Octopus Tracker but then I could do the same with electricity.

As you can imagine, some days are worse than others but on average I get an efficiency of around 400% now I know what I am doing.

When my heat pump is changed soon to a more suitable unit I anticipate that my annual efficiency will be closer to 500%, maybe more if my calculations are correct. That makes it cheaper than gas. This includes DHW production.

Now my gas boiler has gone it has freed up space in the kitchen so we have made some improvement there.

The other bonus of the heat pump installation was that my hot water system was upgraded. I now have an unvented system with no booster pump that I had before. It is a massive improvement that I estimate would have cost two thirds of what I paid for the whole heat pump installation.

The heat pump isn't noisy. Generally people can be standing in its vacinity and not realise it is running. It is noisier at times of course but I wouldn't say it is excessive. It is subjective obviously.

As I explained earlier, radiators don't have to be overly expensive but they are a key part of making the heat pump work efficiently. Low flow temperatures make it affordable to run, if you have to heat to 40c plus then the running costs go up and the costly defrosts are more frequent meaning you need even higher flow temperatures to get the heat you need.

There is a learning curve, you need to be interested and it needs a certain amount of engagement from the owner.

I would say now though, that I could set another one up very easily, not necessarily the same as mine as each house is different but I know what I am looking for now.

I think it will become a case of those that know helping those who don't to make a success of heat pumps, there can be a lot to adjust. It sounds like a problem, and it is, but it is also the benefit of heat pumps, they can be tailored to each home to get the most out of every kWh of electricity.

I would be happy to help friends and neighbours if asked and I know many other people would too.

The only other thing that I would add is there is one piece of essential equipment that makes the process easier. That is a proper monitoring system. I have billing grade heat and electricity meters fitted so I know exactly what my heat pump is doing every second of the day if I want to know. It is invaluable and if it was taken away I would feel completely lost.

After a slightly traumatic three months of heating with my heat pump I am confident that I will set the replacement up really quickly and will be able to leave it alone to do its thing whilst I get on with something else.

Heat pumps are complicated but once set up it's very rewarding sitting comfortably knowing that you  are not burning anything.

Spoonie_Turtle

BobT36 said:

Moneysavingchap said:

matt_drummer said

The main problem will be the size of the radiators, it always is. Radiators running at 30c flow in a room at 20c need to be about 8 times the size of radiators that are just adequate at 70c flow in a 20c room.

Yeah, that's just not happening for people who have gas systems with flow temps between 60-80c (what many gas heating systems have been designed for). The radiators would need to be the size of the entire wall! 

What sort of innovation and development is happening with heat pumps? Is it likely that at some point in the future (5, 10, 15 years?) that heat pumps capable of having a flow temp of 60c or more in say -10c conditions?

@Matt_Drummer do you think that traditional GCH would have been better in your setup? (Disregarding any "green" focus or solar comparability etc.). Not trying to put words in your mouth, just curious how you feel after having used a heat pump, as I've never even seen one myself. It does sound like the USER is expected to become quite an expert on the requirements & configuration. 

If I may add my rather different experience,

We've had a heat pump since 2019, installed by a company chosen by the Housing Association, zero instructions or explanation or any helpful information - the 8-page 'manual' given to us actually says the installers will have set it to the best settings, don't touch them.  So absolutely no use whatsoever and I am not an expert by any stretch of the definition.  I find it really difficult to learn new things if I don't understand the underlying principles of a subject, and it seems this is an area beyond me because I truly don't understand how heat pumps work or heat loss calculations or anything like that.

With that in mind, in the past year and a half I have learned how to change the basic settings: DHW temperature, minimum DHW temp before it starts heating again, legionella cycle, thermostat, and the schedule for both heating and hot water.  I have absolutely no clue what the flow temperature is or how much heat is actually being given out, although we do have access via the controller to the kWh consumed and delivered (on a cumulative basis) which is how I work out the COP for each month and year.

I wish we could set DHW to every other day or just specific days of the week in summer, since we have an electric shower (not entirely by choice).  I also wish we had a setback temperature for overnight, but we have neither - or I simply haven't worked out how to do them, which I guess is equally possible. 

However with some simple tweaks - mainly setting a schedule to turn heating off overnight, and to confine DHW to certain hours rather than all day like it was before, we do seem to be consuming less and getting a more efficient output than before any tweaks were made:
2021 in 3585  out 9546  COP 2.66
DHW in 1121  out 2465  COP 2.20
Heat in 2464  out 7089  COP 2.88

2023 in 2785  out 8259  COP 2.97
DHW in 615    out 1774  COP 2.88
Heat in 2170  out 6484  COP 2.99

(Tweaks were made partway through 2022 so comparing data for that year isn't particularly helpful.  That's also when I first accessed the annual input/output total, so can't go any further back than 2021.)

Oh also, this is a vampire unit that uses 30-70kWh per month in the summer for literally 0 heating.  Drives me bonkers, such a waste!  So take that vampire usage in unheated months out and the COP rises to 3.28 for heating.  Still not sure what to do about that, but that's a consideration for later in the year.

So the point of the ramble is, you don't need to be an expert to make beneficial settings changes.  It might not be the best efficiency but it keeps us warm, which is something we've never had in this house before, and at a relatively affordable level of usage.

Also for additional context our house is a 1940s 3-bedroom semi, just under 90m² and EPC rating low C (just scraped up from a D since the previous EPC even though literally nothing has changed, except floor area is now down as 87m² from 89m² before … I am well aware how unreliable EPCs can be).  We keep the thermostat at 18℃ and heat water to 50℃.

matt_drummer

Your `vampire load' as you call it may well be a setting related to the circulation pump.

On my Daikin you can choose between the pump running continuously or sampling.

The heat pump needs to assess the water temperature to decide whether to heat or not and it can do this by running continuously or just every once in a while.

Obviously running continuously consumes electricity so everybody I know chooses sampling.

We can also set the pump speed used when sampling.

This may or may not be an option with your heat pump but it is worth investigating.

My Daikin uses 23w on standby which is more than a lot of others use.

Spoonie_Turtle

matt_drummer said:

Your `vampire load' as you call it may well be a setting related to the circulation pump.

On my Daikin you can choose between the pump running continuously or sampling.

The heat pump needs to assess the water temperature to decide whether to heat or not and it can do this by running continuously or just every once in a while.

Obviously running continuously consumes electricity so everybody I know chooses sampling.

We can also set the pump speed used when sampling.

This may or may not be an option with your heat pump but it is worth investigating.

My Daikin uses 23w on standby which is more than a lot of others use.

Thank you, is that an internal or external pump?  What I've assumed to be the circulation pump goes continuously overnight in winter, this is internal and also drives me a bit bonkers but I think it's to prevent freezing?  (If we had a setback temp we wouldn't have to turn it off overnight!) 

If that is the circulation pump then it definitely doesn't go continuously in summer.  However if there is a sampling of water temperature going on, of any frequency, would turning the heating off altogether stop it?  I meant to do that this year to see if it made a difference to consumption but June was cold and I forgot after that.

BellaBlondykeTheThird

@matt_drummer could I suggest you put a link to your heat pump mega thread to these chats otherwise they all appear to regurgitate the same info.

This also goes for the other heat pumpers here that have existing long threads about their heat pumps and setup.

Otherwise it all becomes.about their setup and what they are doing next and the same info repeated and it is not always relatable to the original issues. The threads go off topic.

Just my opinion bin the idea if you like.

matt_drummer

BellaBlondykeTheThird said:

@matt_drummer could I suggest you put a link to your heat pump mega thread to these chats otherwise they all appear to regurgitate the same info.

This also goes for the other heat pumpers here that have existing long threads about their heat pumps and setup.

Otherwise it all becomes.about their setup and what they are doing next and the same info repeated and it is not always relatable to the original issues. The threads go off topic.

Just my opinion bin the idea if you like.

I agree.

But I was asked specific questions and i thought it would be rude not to answer them.

Threads often develop and widen in scope.

Anyway, when somebody asks me directly if I would have been better off with GCH and do I regret getting a heat pump I think it deserves an answer, don't you?

Anything else I posted was relevant to heat pumps icing in freezing conditions as far as I can remember.

Anyway, you don't need to worry too much as I don't intend to be posting very often so you won't be skipping past my boring regurgitated information on a regular basis.