Heat pump quote

michaels

70sbudgie said:

I have been having further conversations with the company that provided me with the quote above. Based on my Heat Punk research and my subsequent questions to the installer, the quote now replaces more radiators and the design flow temperature has come down (albeit by only 2° to 45°C).

As part of the discussion, I was told verbally that the heat loss of my house has been calculated as 8.4kW. I asked if that meant I could install the smaller Ecodan unit. (8.5kW). The response in writing was "I would still be recommending the 11.2 kW system, I’m of the opinion that this is the best and most effective for your property." 

How hard should I push for the smaller unit? I am conscious of the discussions about oversizing, but at the same time, I don't want to install a HP that is too small.

If the price is the same if you replace more rads I would be tempted to replace as many as you can to chase a lower flow temp as even 45 is slightly on the high side for a really good SCOP.

As well as the size of the pipe on the rad tails you also need to worry about the size of the pipe in the 'loop' as again there is a maximum heat transfer rate given a sensible circuit flow rate. (We have 15mm loop around all our upstairs s rads which is pushing it for the heat output we need upstairs and would probably have to split our loop and feed the upstairs separately to actually get sufficient output upstairs.

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

Against that most ranges have a 'small form factor up to about 9kw and a 'large' form factor above that.  The small form factor is not only less intrusive but is normally quieter too (often because it has one fan rather than 2).

Final thought, Octopus have apparently ended their 'loss leader' pricing and the days of £500 after the grant are over, now they offer efficient (low flow temp) or standard (higher flow temp) starting at about 6k and 4k respectively after the grant is deducted.

barker77

michaels said:

70sbudgie said:

I have been having further conversations with the company that provided me with the quote above. Based on my Heat Punk research and my subsequent questions to the installer, the quote now replaces more radiators and the design flow temperature has come down (albeit by only 2° to 45°C).

As part of the discussion, I was told verbally that the heat loss of my house has been calculated as 8.4kW. I asked if that meant I could install the smaller Ecodan unit. (8.5kW). The response in writing was "I would still be recommending the 11.2 kW system, I’m of the opinion that this is the best and most effective for your property." 

How hard should I push for the smaller unit? I am conscious of the discussions about oversizing, but at the same time, I don't want to install a HP that is too small.

If the price is the same if you replace more rads I would be tempted to replace as many as you can to chase a lower flow temp as even 45 is slightly on the high side for a really good SCOP.

As well as the size of the pipe on the rad tails you also need to worry about the size of the pipe in the 'loop' as again there is a maximum heat transfer rate given a sensible circuit flow rate. (We have 15mm loop around all our upstairs s rads which is pushing it for the heat output we need upstairs and would probably have to split our loop and feed the upstairs separately to actually get sufficient output upstairs.

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

Against that most ranges have a 'small form factor up to about 9kw and a 'large' form factor above that.  The small form factor is not only less intrusive but is normally quieter too (often because it has one fan rather than 2).

Final thought, Octopus have apparently ended their 'loss leader' pricing and the days of £500 after the grant are over, now they offer efficient (low flow temp) or standard (higher flow temp) starting at about 6k and 4k respectively after the grant is deducted.

I’ve just had an octopus heat pump quote and was specd at 50c. Most bedrooms we actually used as office space so they are now rated for 21c vs 18 so I could choose to reduce temp in them to get higher efficiency, my question is tho should I go back and ask now they specifically do more efficient options ? 

Reed_Richards

70sbudgie said:

I have been having further conversations with the company that provided me with the quote above. Based on my Heat Punk research and my subsequent questions to the installer, the quote now replaces more radiators and the design flow temperature has come down (albeit by only 2° to 45°C).

As part of the discussion, I was told verbally that the heat loss of my house has been calculated as 8.4kW. I asked if that meant I could install the smaller Ecodan unit. (8.5kW). The response in writing was "I would still be recommending the 11.2 kW system, I’m of the opinion that this is the best and most effective for your property." 

How hard should I push for the smaller unit? I am conscious of the discussions about oversizing, but at the same time, I don't want to install a HP that is too small.

You need headroom.  Your heat pump will spend a portion of the day heating your hot water and, in certain weather conditions, a proportion of its time defrosting.  So let's estimate that could be as much as 10% of the total time.  If so your heat pump has to deliver an average of 8.4 kW in 21.6 hours each day so it needs an output of 9.3 kW to achieve that.

Also, although a smaller output unit would probably be a bit cheaper, the minimum output it can deliver is important because that determines its propensity to cycle in milder weather.  Is there actually a difference between the 8.5 kW unit and the 11.2 kW one?  If there isn't a difference then the only reason not to get the 11.2 kW heat pump would be that (perhaps) it costs more than the 8.5 kW one.  

70sbudgie

michaels said:

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

But I thought you weren't supposed to oversize a HP for best efficiency? 

The lowest temp we've had recently was -8°C. That did feel a bit cooler than comfortable, but not enough for me to go around and change all the heating settings. And I am currently running the gas boiler at ~50°C flow temp. 

10 Jan this year, Octopus Watch says the temp was -4.9°C. Octopus app usage data says the boiler peaked at 6.6kWh/half hour, but mostly ran at what appears to be the minimum of 3kWh/half hour. At 92% efficiency that suggests to me a peak of ~12kW and a minimum of 5.5kW. But at -4.9°C, that is rather cooler than my design temp. 

A couple days earlier, it was -2.2°C with a peak of 9.5kW and the same minimum. 

Are these peaks the numbers that suggest the 11.2kW unit?

Reed_Richards

A heat pump installed to MCS standards is sized to keep you warm enough 99.6% percent of the time at minimum.  This means on average there will be 36 hours per year, at maximum, when your heat pump does not keep your house warm enough.

michaels

70sbudgie said:

michaels said:

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

But I thought you weren't supposed to oversize a HP for best efficiency? 

The lowest temp we've had recently was -8°C. That did feel a bit cooler than comfortable, but not enough for me to go around and change all the heating settings. And I am currently running the gas boiler at ~50°C flow temp. 

10 Jan this year, Octopus Watch says the temp was -4.9°C. Octopus app usage data says the boiler peaked at 6.6kWh/half hour, but mostly ran at what appears to be the minimum of 3kWh/half hour. At 92% efficiency that suggests to me a peak of ~12kW and a minimum of 5.5kW. But at -4.9°C, that is rather cooler than my design temp. 

A couple days earlier, it was -2.2°C with a peak of 9.5kW and the same minimum. 

Are these peaks the numbers that suggest the 11.2kW unit?

So this was probably my peak day, Jan 18 2024. Chart although half hourly has hourly rate axis. Boiler was weather comp controls and probably running somewhere between 55 and 60 flow temp.

Suggests maintaining house temp took about 7.5kw of gas. Have to guess on efficiency.

AS above, you need some head room for defrost cycles, hot water heating and recovery if the temp falls for any reason.  Against that, most heat pump manufacturers have only 2 sizes of heat pump with software controls changing peak output, a 'small' up to about 8kw and a large 10kw+ with the small model offering lower minimum modulation and quieter operation.

FreeBear

michaels said: Final thought, Octopus have apparently ended their 'loss leader' pricing and the days of £500 after the grant are over, now they offer efficient (low flow temp) or standard (higher flow temp) starting at about 6k and 4k respectively after the grant is deducted.

Octopus quoted me £2700 this time last year, which would have included new, larger radiators all round and a DHW tank (a gas boiler was ~£2500 plus rads). Online quote a couple of weeks back returned a quote of £3700. Still undercuts local installers for both heat pumps and gas boilers.

NedS

70sbudgie said:

michaels said:

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

But I thought you weren't supposed to oversize a HP for best efficiency? 

The lowest temp we've had recently was -8°C. That did feel a bit cooler than comfortable, but not enough for me to go around and change all the heating settings. And I am currently running the gas boiler at ~50°C flow temp. 

10 Jan this year, Octopus Watch says the temp was -4.9°C. Octopus app usage data says the boiler peaked at 6.6kWh/half hour, but mostly ran at what appears to be the minimum of 3kWh/half hour. At 92% efficiency that suggests to me a peak of ~12kW and a minimum of 5.5kW. But at -4.9°C, that is rather cooler than my design temp. 

A couple days earlier, it was -2.2°C with a peak of 9.5kW and the same minimum. 

Are these peaks the numbers that suggest the 11.2kW unit?

It's difficult, and see @Reed_Richards reply above.

Rather than considering individual half hour usage, try looking at the total heat output/usage for the whole day (24h period), adjust it for your 92% efficient boiler, and divide by 24 to give you your kWh heat loss for that day. If you do this for the coldest day of the year, that is a good indication of the size of heat pump you will need.

As @Reed_Richards said in their reply above, the heat pump will need to be capable of actually delivering this much heat, in addition to any DHW cycles required for hot water and allowing for defrost cycles. Convention dictates that most heat pumps are rated for their heat output at 7C with a flow temperature of 35C, which implies that the 11.2kW unit is capable of delivering a maximum of 11.2kW output at 7C ambient temperatures for a flow temperature of 35C. It may only be able to deliver 10kW of heat at a flow temperature of 50C when it's -5C outside. Likewise, the smaller 8.5kW unit may only be able to deliver 7kW under the most challenging of conditions, so installers (and you) really need to check the manufacturers data sheets very carefully to be sure that 8.4kW unit is actually capable of meeting your 8kW heat loss under real world conditions.

Finding the right sized heat pump is somewhat of a goldilocks task. Too big and it will not be as efficient as it could be in the milder months, but too small and you'll be thrashing it in the depths of winter, and in worst case scenario it may not be able to keep the house warm. This is massively complicated by the way MCS heat loss calculations are performed, which often results in vastly inflated figures, and this is where using your own gas usage data will give you a decent sanity check.

But that said, I'd rather have an oversized unit than one that is undersized. Our own unit is massively over-sized for our property, but that has not made it inefficient. In the depths of winter, it's great as it can tick over at 32C and keep the house nice and warm, without ever breaking a sweat. Because it's barely ticking over, it does not frost up as much (because it's not working very hard), and we recover very quickly from defrost cycles due to the spare capacity. We can also operate overnight set backs (and peak rate setbacks), and recover easily the next day, again because we have plenty of spare capacity. In Autumn and spring we lose out a little because we are not able to run the heating constantly as the unit is putting out way too much heat for the house, even running on absolute minimum, so we run it for short periods of time, and then switch off for an hour or two. This does lose a little on efficiency, but nowhere near as much as people make out, and our energy usage at this time of year is minimal compared to colder months such as January, so I'd be more concerned with ensuring efficient operation when you are using most energy.

All of this goldilocks event of finding the perfectly sized heat pump is exasperated by the fact that your supplier probably only uses one or two makes of heat pump. In my case, my supplier used Samsung, which come in 5kW, 8kW or 16kW, with a 12kW unit which is actually just a software limited version of the 16kW model. My calculated heat loss was 7.4kW, which the 8kW unit was not capable of meeting on the coldest of days, so we had to have the 12kW unit (turns out this winter our largest usage was 4.2kW so the 8kW unit would have been fine and we may even have got away with the 5kW unit!). If they had offered another range, maybe there would have been the option of a 9kW unit rather than the nobbled 16kW unit we have.

IMHO if you can at least get your heat loss calculation in the right ballpark, using your own real energy usage data to support it, then having a heat pump a little oversized from that is not a bad place to be. Mine is potentially 3-4 times over-sized and it is still proving efficient to run. What will make far more difference is having sufficiently large enough emitters to ensure you can run flow temperatures as low as possible. For us that meant replacing all 12 radiators with the maximum size that would fit in each room which has allowed flow temps of 30-32C all winter resulting in a very efficient system. At 30C, it's difficult to tell the radiators are even on yet the house is warm.

70sbudgie

@Reed_Richards I am going to apologise here as well for missing your comment. I think I took too long to do my calculations and refreshed out of synch.

NedS said:

70sbudgie said:

michaels said:

The 11.2 probably makes sense.  If you have a modulating boiler currently and a smart meter you should be able to see your energy usage on a historic cold day check weather underground for a local station if you don't have your own 'weather station'.  From this I was able to see that on a sub-zero day our gas boiler was running full time modulated down to 8kw, assuming an efficiency of about 90% this gave a constant heat demand of about 7.2kw.  I am a bit surprised yours is more than that given the A EPC and a similar floor area to us.  With the Heat Pump you want to go a bit larger because (1) the heat pump also needs to do meet the hot water demand (2) the heat pump will run defrost cycles when the weather conditions lead to icing which reduces the proportion of time it is heating and (3) you may well want a night set back and recovery to full temp in the morning that can take a very long time if your max heat output is only really enough to maintain temp rather than increase.

But I thought you weren't supposed to oversize a HP for best efficiency? 

The lowest temp we've had recently was -8°C. That did feel a bit cooler than comfortable, but not enough for me to go around and change all the heating settings. And I am currently running the gas boiler at ~50°C flow temp. 

10 Jan this year, Octopus Watch says the temp was -4.9°C. Octopus app usage data says the boiler peaked at 6.6kWh/half hour, but mostly ran at what appears to be the minimum of 3kWh/half hour. At 92% efficiency that suggests to me a peak of ~12kW and a minimum of 5.5kW. But at -4.9°C, that is rather cooler than my design temp. 

A couple days earlier, it was -2.2°C with a peak of 9.5kW and the same minimum. 

Are these peaks the numbers that suggest the 11.2kW unit?

It's difficult, and see @Reed_Richards reply above.

Rather than considering individual half hour usage, try looking at the total heat output/usage for the whole day (24h period), adjust it for your 92% efficient boiler, and divide by 24 to give you your kWh heat loss for that day. If you do this for the coldest day of the year, that is a good indication of the size of heat pump you will need.

Using this method, I get 6kW! Surely that can't be right?

And whether that is -4.9°C or -8°C (the former temp coming from Octopus Watch, the latter being what I understood was the reported temp at the time), wouldn't this be within the 36hrs /year of insufficient heating? 

Taking on board the extra capacity for defrosting, DHW etc, if the 6kW is correct, is 2.5kW enough headroom?

I am sorry if it seems like I am going round in circles, there is a lot of information. I appreciate that I might be getting distracted by red herrings. (The installer sales initially mentioned an 8.5kW unit, but the designer hasn't actually put my house heat loss in writing, just the individual rooms. Getting written information out of them is extremely hard work. The quote I've had is for an Ecodan, which seems better than the Daikin that Octopus included for in their quick quote, which is much cheaper, but I will need to pay for another heat loss survey to get their actual design)

Also, other half doesn't really want a HP as he thinks there's plenty more life left in the gas boiler, so I'm trying to work out running costs that aren't a complete fabrication. I am aware that the MCS calculation is pretty rigid and I don't think it reflects our atypical house. Which we also run cooler (18-19°C in living areas, 16°C at night).

I also suspect (but haven't yet managed to verify) that the Ecodan 8.5kW and 11.2kW are different models, not just throttled versions of the same model.

Reed_Richards

70sbudgie said:

Taking on board the extra capacity for defrosting, DHW etc, if the 6kW is correct, is 2.5kW enough headroom?

The extra capacity you need is based around the percentage of the time that the heat pump is, or might be, doing things other than heating your house.  I believe this needs to be around 10%. so if your heat loss is 6 kW you need at least 0.6 kW headroom, if it's 8.5 kW you need at least 0.85 kW of headroom, so a heat pump capable of at least 9.4 kW of output at around 0 C.

Although you personally like a cool house, there are MCS standard temperatures for the various rooms in your house that are used in the calculation.  That's fair because you might sell your house to someone who likes things a bit warmer than you do.  If you, personally, like cooler indoor temperatures then your heat pump will be cheaper to run.