Air Source Heat Pump Freezing

Strummer22

matt_drummer said:

Strummer22 said:

@matt_drummer sorry to hijack the thread somewhat, but I take it your system doesn't have a buffer tank? Do you have room for one?

I ask because, to my mind at least, it would solve your problem, not that it needs it now you've resized the radiators. The heat pump could operate at or near minimum load to heat your buffer tank and radiators, then when buffer tank reaches temperature the heat pump would turn off and the heated water circulate in the central heating until the temp in the buffer tank decreases by some preset delta T (6°C, say), which given how efficient your house is might be several hours, then repeat. No short cycling, and no loss of COP due to nowhere for the heat to go, given that it would be going to the buffer tank. Just curious if you considered this option or you have it already and it didn't work for some reason.

The heat pump I have now has to go, it is just way too much for the house, the reality is that it is -4c here today and I I only need 4.5kW of heat to keep the house at 23c, the same amount of heat I get when it is +14c outside.

I wish my house was that efficient. I need 10kW of heat (sometimes more) to keep mine at 18­°C! 

NB I have a GSHP so don't have nearly as much hit to efficiency in cold weather as an ASHP. COP still about 4 in the recent subzero weather.

matt_drummer

Strummer22 said:

matt_drummer said:

Strummer22 said:

@matt_drummer sorry to hijack the thread somewhat, but I take it your system doesn't have a buffer tank? Do you have room for one?

I ask because, to my mind at least, it would solve your problem, not that it needs it now you've resized the radiators. The heat pump could operate at or near minimum load to heat your buffer tank and radiators, then when buffer tank reaches temperature the heat pump would turn off and the heated water circulate in the central heating until the temp in the buffer tank decreases by some preset delta T (6°C, say), which given how efficient your house is might be several hours, then repeat. No short cycling, and no loss of COP due to nowhere for the heat to go, given that it would be going to the buffer tank. Just curious if you considered this option or you have it already and it didn't work for some reason.

The heat pump I have now has to go, it is just way too much for the house, the reality is that it is -4c here today and I I only need 4.5kW of heat to keep the house at 23c, the same amount of heat I get when it is +14c outside.

I wish my house was that efficient. I need 10kW of heat (sometimes more) to keep mine at 18­°C! 

NB I have a GSHP so don't have nearly as much hit to efficiency in cold weather as an ASHP. COP still about 4 in the recent subzero weather.

I remember you have a GSHP, part of the reason the COP is better is that you don't suffer defrosts.

Mine is actually at a COP of 4 for the last 30 minutes at 0c outside, it's pretty good, especially without frequent defrosts, they are a lot of the hit to the efficiency as heat from the house is used to defrost the heat pump.

My house is very well insulated but it's also not huge, 100m2 plus a 15m2 conservatory.

The house only actually loses around 3kW, the conservatory loses the other 1.5kW at -4c

AuntyPolly

Maybe our installers miscalculated what a property of our nature would require.  We live in an old stone 1 1/2 storey property that was extended to 4 beds, it is insulated, but not fully double glazed (we have yet to get the old sash windows secondary glazed units added) so we appreciate that some heat loss there. We also have a stream running along side the property and lots of trees, we basically live in a glen.

Our unit is a Grant HPID13R32 so 13kw, I believe Grant only do one other domestic heat pump that is larger the 17kw one.

Unfortunately for us, today the unit has developed a fault and is no longer working. We are waiting to speak with technicians at Grant themselves as our installers are getting them to call. 

It appears there is a communication error between boards on PCB, this is possibly a loose wire. Our theory is it may be caused due to the extra vibration due to the amount of time it has been spending in defrost mode.  The alternative is that one of the two boards has failed an needs replacing, which would not be a good given the pump was only installed in 27 October 2023 so is only two and half months old.

Even if we get the unit working again, I am now concerned given all the comments on here that it may not be the correct pump for our property and unfortunately we don't have any more funds to be trying alternative setups. 

We put our faith in the advice being given and not sure how we can go about getting things right moving forward.

MultiFuelBurner

AuntyPolly said:

Maybe our installers miscalculated what a property of our nature would require.  We live in an old stone 1 1/2 storey property that was extended to 4 beds, it is insulated, but not fully double glazed (we have yet to get the old sash windows secondary glazed units added) so we appreciate that some heat loss there. We also have a stream running along side the property and lots of trees, we basically live in a glen.

Our unit is a Grant HPID13R32 so 13kw, I believe Grant only do one other domestic heat pump that is larger the 17kw one.

Unfortunately for us, today the unit has developed a fault and is no longer working. We are waiting to speak with technicians at Grant themselves as our installers are getting them to call. 

It appears there is a communication error between boards on PCB, this is possibly a loose wire. Our theory is it may be caused due to the extra vibration due to the amount of time it has been spending in defrost mode.  The alternative is that one of the two boards has failed an needs replacing, which would not be a good given the pump was only installed in 27 October 2023 so is only two and half months old.

Even if we get the unit working again, I am now concerned given all the comments on here that it may not be the correct pump for our property and unfortunately we don't have any more funds to be trying alternative setups. 

We put our faith in the advice being given and not sure how we can go about getting things right moving forward.

The comments here, at least ones I make are not to you. You are not the OP (Original Poster) and any under sized heat pump comments are made towards the information they have provided 4 bedrooms a kitchen and a lounge and a heat pump that can max delivery 5-6kWh of heat.

We don't know enough about your property such as EPC, the heat loss surgery/installation survey you had which would have been used to calculate your heat pump size or how you are using it. Who installed your heat pump etc etc.

Maybe start your own thread with as much detail as possible and the problems you are facing.

matt_drummer

MultiFuelBurner said:

The comments here, at least ones I make are not to you. You are not the OP (Original Poster) and any under sized heat pump comments are made towards the information they have provided 4 bedrooms a kitchen and a lounge and a heat pump that can max delivery 5-6kWh of heat.

My house is four bedrooms, a lounge, kitchen, dining room and two bathrooms. My heat loss is 3kW at 21c inside and -3c outside.

Our conservatory loses another 1.5kW making a total of 4.5kW but I don't have to heat the conservatory.

The OP's heat pump would heat our house with ease so it may well be capable of heating theirs too.

But it will never do it if it needs to get to 50c flow temperatures in freezing conditions.

But we don't know the OP's heat loss so I can't be sure, but it is entirely possible that the heat pump is big enough. It is certainly big enough to supply a proportion of the heat required that could be supplemented where needed.

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.

Maybe the OPs defrosting issued are caused by a lack of system volume, maybe the radiators are too small and there just isn't enough water to fully defrost the heat pump?

The other one, a 13kW Grant heat pump really should be enough for an average four bedroom house, I could only ever imagine that it would be too big.

I agree with @MultiFuelBurner that they should start their own thread and give full details of their house and what is installed.

Strummer22

AuntyPolly said:

Maybe our installers miscalculated what a property of our nature would require.  We live in an old stone 1 1/2 storey property that was extended to 4 beds, it is insulated, but not fully double glazed (we have yet to get the old sash windows secondary glazed units added) so we appreciate that some heat loss there. We also have a stream running along side the property and lots of trees, we basically live in a glen.

Our unit is a Grant HPID13R32 so 13kw, I believe Grant only do one other domestic heat pump that is larger the 17kw one.

Unfortunately for us, today the unit has developed a fault and is no longer working. We are waiting to speak with technicians at Grant themselves as our installers are getting them to call. 

It appears there is a communication error between boards on PCB, this is possibly a loose wire. Our theory is it may be caused due to the extra vibration due to the amount of time it has been spending in defrost mode.  The alternative is that one of the two boards has failed an needs replacing, which would not be a good given the pump was only installed in 27 October 2023 so is only two and half months old.

Even if we get the unit working again, I am now concerned given all the comments on here that it may not be the correct pump for our property and unfortunately we don't have any more funds to be trying alternative setups. 

We put our faith in the advice being given and not sure how we can go about getting things right moving forward.

PCB failed on our unit within 6 months of installation. Replaced under warranty and going strong over a year later. Don’t know why it would fail but maybe it’s a vulnerable component.

AuntyPolly

Ok thanks, will look at posting a new thread. Didn't want to double up as it at first seemed to be same issue. Freezing ASHP. 

I think I'll dig out calculations too. Obviously the current error and not working is a different issue to the low room temp due to freezing conditions which was our original connection to the OP. 

And this is something we will probably need further advice on as likely to still be present after, unless by some chance the board fault contributed to the lower room temps someway. 

Moneysavingchap

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

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? 

The radiators need to be the same size whatever heating system you have or are replacing if you want to run at 35c flow temperatures or lower.

They do not need to be the size of the entire wall of a room, just big enough and probably double or triple panel convectors.

Heating water to 60c+ will always be more expensive than heating it to 30c, it is much better to run at lower temperatures.

The radiators cost money but they more than pay for themselves over their lifetime by allowing lower flow temperatures.

It is happening for some people who had gas, I am one of them.

The innovation and development is to make them more efficient, you don't do that by heating the water to higher temperatures.

QrizB

Moneysavingchap said:

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? 

They already exist. However, as matt says:

matt_drummer said:

Heating water to 60c+ will always be more expensive than heating it to 30c, it is much better to run at lower temperatures.

You effectively have a choice of a cheap installation (using your current rads) or cheap running costs (using low flow temperatures to achieve a high COP).