Heat pump thread

Just reading this thread – again with an eye that when our gas boiler dies it’s new central heating system and heat pump.

Those being told it will work with microbore and existing systems – is it a case of it will work, but maybe not as efficiently?

Those being told it will work with microbore and existing systems – is it a case of it will work, but maybe not as efficiently?

Possibly. Depends on the size of the pipe, and the size of the radiators. Look at it this way, the pipes have to pass the energy through them. If they are big, more energy can pass through, small, then they are limited a bit.

It is explained on this page: https://www.heatgeek.com/does-my-pipework-need-upgrading-for-a-heat-pump-with-cheat-sheet/

Note the table halfway down. The typical speed of water in the pipes is 0.9mps. 15mm pipe can handle 2.75kW of power. 10mm can only handle 1.15kW. There are ways to get it working, speeding up the water flow, raising the incoming temperature, increasing the spread between the flow and return temperatures (DT), and others, but they all reduce efficiency, so will cost more to heat the house.

If you have 10mm pipe from your boiler to the radiators, then I’d take a guess that you will need to increase the pipe size. If you have 15/22 pipe running round, then 10mm feeding the rads on short stubs from the 15/22mm then you may not need to increase the size. It needs an heat loss survey, then working out what piping you have to see if it can be reused.

An easy way to find out if a HP will work in your house is to turn your flow temperature on your boiler down as low as possible, 35 deg C is good, though some wont go that low. If the gas boiler copes at a 35 deg flow temperature, and your house stays warm, then a HP will be an almost direct swap.

As I suspected – and our house is almost entirely 8mm microbore from one manifold per floor…

I’m kicking myself that I’ve only managed to replace a few pipes with larger over the years – I should have done more, but budgets and all that… I have managed to upsize radiators as they needed changing. This means the boiler is rarely above halfway on the heat output.

@molegrips @flicker

Those Cop figures are the efficiency that the HP is at when it’s flow temp is at ‘x’

The HP will be connected to a weather compensation sensor, so if it is cold outside, the flow increases and mild it decreases. This trys to match the heat being lost from the building with a proportional heat input. You therefore cannot ask what the outside temp equates to which CoP.

A reasonable exercise for a gas boiler household is to run the flow at 35-40°c through the winter and see if the house can achieve your desired room stat temp. This exercise will off course raise the next problem with UK heating design…..

Thanks @buttonmoon but unless I’ve misunderstood something it’s not possible for the cop to remain the same regardless of external temperature. The lower the external temperature the lower the cop.

Lifted from Viessman website

With an outdoor temperature of 8.3 °C, your heat pump could achieve around 3.8 CoP. However, if the temperature drops to around -8.3 °C, your heat pump’s efficiency could drop to around 2.3 CoP. If the outdoor temperature drops too low for your heat pump to produce any heat, a backup may be required. This is unlikely to occur in the UK, however, heat pumps in countries such as Canada may need to rely on a backup. This can become expensive,so if you live in an extremely cold climate, a heat pump may not be the most efficient way to heat your home.

If the outdoor temperature drops too low for your heat pump to produce any heat, a backup may be required

What kind of negative temps are needed to cause an issue?

We’re in a frost hollow and shaded by the hill and trees behind. It’s not unusual to see -5 to -10 for a week at a time…

A reasonable exercise for a gas boiler household is to run the flow at 35-40°c through the winter and see if the house can achieve your desired room stat temp. This exercise will off course raise the next problem with UK heating design…..

This, but remember to run you timer circuit on always on, otherwise it won’t be representative.

@flicker. There are 2 variables going on. The outside temp reduces which via the weather compensation increases the flow temp as the property will compensate for the property which will be losing more heat.

Those figures should be taken with a pinch of salt though as the main variable is the system design, which if wrong will blow those manufacture quoted figures out of the water due to short cycling of the HP.

What i’d say is that as electric is 3x the price of gas, you are breaking even if you average a CoP of 3. You need to be on a elect tariff that reduces your elect cost to make a saving.

If the outdoor temperature drops too low for your heat pump to produce any heat, a backup may be required

What kind of negative temps are needed to cause an issue?

We’re in a frost hollow and shaded by the hill and trees behind. It’s not unusual to see -5 to -10 for a week at a time…

It all goes to the heat loss of the house. If the house has been assessed properly, each room will have its heat loss, and the house will have a total heat loss figure. Heat Loss surveys just dont happen in the majority of houses with gas boilers, as the same boilers are put in to each dwelling, anything from 20-35kW gas boilers are fitted, when the actual heat loss of the building is, or should be, less than 10kW.

The heat loss design should be explained to the householder, as a number of assumptions are made. The big one is the range of temperatures. Typically, a figure of -4 to 21 degrees will be used for Perthshire, but, if you are in a particularly cold Glen, then you may want to specify -7 to 21, or -7 to 19 deg. C.

If the house is designed for -3 to 21 deg. C, then once the outdoor temperature gets below -3, the heat source will not be able to get to 21 degrees. It’s worked out as the range, and the range is -3 to 21, so 24 degrees range, the heat source will only ever get the house to 13 degrees if the outside temp is -11,  (this doesnt really happen in real life, but in theory, it’s what should happen).

If you specified -7 to 21, then you have a 28 degree range, so at -11, the house should get to 17deg. Note, for most houses, there will always be a time when the heat source cannot heat the house enough to reach the required temperature, as we all have the occasional -5 or -8 night. However, heat loss calcs nearly always over-estimate the heating requirement. Add in the warmth from mammals in the house (a typical human gives off 100 watts of heat), cooking, hot water, sun/solar gain, and you can see the heating source does not have to work so hard when the house is occupied, and the requirement for an extra heat source is very rare.

Gas boilers have always been over-sized, so never have this problem of not being able to reach the required room temperature on the coldest day.

Going back to temperatures too cold for HPs, I know Daikin units the best, they say their units will work up to -25 deg. C. It will be nowhere near as efficient at that temperature, but, it will still outperfom an electric element heater. Of course, the upside is the efficiency is brilliant once summer comes around,and you will see 5:1 or better. In the typical 10 degree UK climate, it will, or should, get a steady 3:1+ efficiency.

Interesting. With the flow at 40, the rads only get to 35. The boiler is cyxlinf6 between 45 and 35 so the water is approaching average temp (and then cooling a bit on the way to the rads).

Ours works down to -20C with a COP of 1.6 at that point.

The outdoor temperature control of flow temperature works really well once you settle on the right calibration curve. It senses the increased demand as soon as it happens, rather than waiting for the internal temperature to drop (which lags due to the thermal mass). So it doesn’t matter that heat pumps can’t react to big demands for heat, because if specced and used properly they don’t need to.

We are 15mm on all the radiator drops, and mix of 15 and 22 on the runs. The only 28mm is flow and return between HP and under stairs cupboard where cylinder, buffer, expansion vessels, pump, filter and controller etc are all crammed in. Pipe cross sectional area goes up with the square of radius, so a small size increase allows a lot more flow.

It is not just temperature outside but also the humidity. Heat pumps work well in minus conditions in the scandanavian countries but there air is much drier.

I’m soon moving into a new build. It’s abnormally well insulated – not far off passivhaus. It has underfloor heating. It doesn’t yet have a heat source. It would be perfect for a heat pump but for… reasons… I don’t qualify for the grant so I’m getting a gas boiler. I’ve been trying to future proof for a heat pump but it’s a total minefield of information out there and the accredited installers want nothing to do with me without a grant. The irony is I think I could install a gas system to get an EPC signed off and then immediately rip it all out to get a grant funded pump straight away. The raise in the grant makes it hurt even more!

Can anyone tell me exactly what ends up inside you house and how much space it takes up?

I think there are two grants. Everyone is eligible for the £7k no?

No the BUS grant has criteria that must be met. We have someone who spends hours dealing with the applications. It is a real pain.
not sure why a company will only deal with clients who get the grant, I think I would avoid them. Seems they want the grant money as it is guaranteed to some extent. We do lots of installs where there is no BUS.

Well what I mean is they’re not interested in telling me how to future proof to make their life easier once I can use the grant, which is fair

I should change that – I think the £7k is for everyone who has suitable loft insulation and a gas boiler right now? But the full install grant is for people on low incomes who haven’t had any central heating before…?

“I’m soon moving into a new build. It’s abnormally well insulated – not far off passivhaus”

That’s not abnormal, at all, if it’s been built to current Part L (came into force June ’22) then most new houses are close to passivhaus standard. 

Passivhaus standard is just an excel spreadsheet, by the way. It’ll be forgotten here in the next few years as English (and soon after Welsh) Building Regulations will be at or above that level, as standard. 

In my experience (20 years in Building/Building Control), air source heat pumps are only efficient and cost effective in highly insulated, air tight (and then you need a proper ventilation system) houses with underfloor heating. Everyone else reports huge running costs, even before electricity prices shot up. 

But, it all depends on the competence of your installer, good ones will keep coming back (or monitor your system remotely) to balance it, monitor your usage/behaviour and help you program the system to be as efficient as possible. Don’t expect any rapid rises in temperature, it all needs to be done very gradually. To get the most out of ASHP you need weather compensation too. 

One last word – if you’ve an open plan ground floor, don’t bother installing underfloor heating at first floor (well I wouldn’t regardless of ground floor), it’s so much hassle and additional cost for something most people never use. Warm air rises…

is there a technical reason it wouldn’t be possible to engineer a solution that “doubles up” a heatpump – that is to say, get loads and loads of warmish water out of a normal heatpump (which isn’t going to work for microbore), then use another heatpump (obviously not a standard one) to generate less really hot water from the warm water that can be sent around an existing central heating system? Might be too expensive to be feasible (no idea)?

But, it all depends on the competence of your installer, good ones will keep coming back 

This is key, from my very limited knowledge.

Three neighbours have had pumps fitted in the past couple of years, and I’m considering one myself as the house is well suited.

A knowledgeable/ enthusiastic installer coming back several times over the first few months is key to getting it working well.  It’s not fit and forget.  Tweaking setup seems to be essential.

is there a technical reason it wouldn’t be possible to engineer a solution that “doubles up” a heatpump – that is to say, get loads and loads of warmish water out of a normal heatpump (which isn’t going to work for microbore), then use another heatpump (obviously not a standard one) to generate less really hot water from the warm water that can be sent around an existing central heating system? Might be too expensive to be feasible (no idea)?

I’m not sure there would be any difference between that and simply using a heat pump that can supply water at the desired temperature anyway. Except for the extra general efficiency losses like more fans, electronics etc. You can get hot water out of a heat pump; you just can’t necessarily get as hot water as from a gas boiler for less money at UK prices.

Our house is well insulated generally – I guess I could have a stab at working out the heat loss – but it has no fancy features, just bog standard 2007 level stuff with our own tweaks. But now I’m thinking wet UFH downstairs would be a major benefit. I’d consider installing this myself but the main issue is with the extra height of the floor in the kitchen. I guess I could refit my kitchen – I could keep the granite worktops and just move them up a bit, and refit cupboards.

A passive house is not just a well insulated house with an mvhr unit and the new building regs are no where near Passive House standard (assuming new builds actually have the quality control to not have a large performance gap from design to as built). There seems to be a total lack of understanding of what the Passive House standard is by both developers and some in building control and the ‘almost a passive house’ phrase is used far too often where it really dosnt apply.

in terms of fitting heat pumps. Proper heat loss calcs and a system design by someone that knows what they are doing is essential. There is a lot of false information out there.

As a slight aside amongst all this (very interesting) tech speak but does anyone have a recommendation for an installer in the north west (Wirral) and/or can recommend an online portal to start building quotes?

With microbore (in a well insulated house) there will be work to be done but we have to replace our old boiler soon..

Cheers

If you do t get a personal recommendation try finding someone who has done the heat geek training. There is a list on their website. Local is very useful as they are far more likely to fix your broken pump on Christmas Eve than some random company from miles away.

We signed up over the summer for a Daikin heatpump from Octopus. 

Incredibly good deal. 8kW Daikin, 180l cylinder and most of the radiators replaced with upgrades for £1900 (the £7500 new grant picks up the rest). Install is planned for mid february. 

Incredibly good deal. 8kW Daikin, 180l cylinder and most of the radiators replaced with upgrades for £1900 (the £7500 new grant picks up the rest)

I’ll take one of those too please thanks.

Octopus wouldn’t entertain my query though, guessing they have no-one in my area.

“I’m soon moving into a new build. It’s abnormally well insulated – not far off passivhaus”

That’s not abnormal, at all, if it’s been built to current Part L (came into force June ’22) then most new houses are close to passivhaus standard.

That’s complete nonsense for the mass house builders.  UK building reg insulation requirements, which is all any of the mass house builders build to (and all most other builders and even architects will do unless you insist on more) are still way less than PH.  Sister has just moved to a brand new Redrow home and

– double glazing

– extractor fans in each bathroom (and cupboard to washing machine) plus trickle vents on windows make very *VERY* dubious about the claimed airtightness.  Theres little point in airtighting the walls and then punching some holes through for fans – they don’t even have flaps that close when they’re not in use.

My house has draughts that come in through brick vents into the cavities and then into the poorly sealed interior and then the space between the dry lining and the inner walls. This is because as above, every time they put a hole in the wall e.g. for windows, pipes, extractor fans they didn’t seal it. I was able to seal some of the French windows which helped a lot. I don’t know if I need to check under the rest of the window sills as well.

If there’s any installer recommendations in the Scottish Borders, I’m all ears please

My house has draughts that come in through brick vents into the cavities and then into the poorly sealed interior and then the space between the dry lining and the inner walls. This is because as above, every time they put a hole in the wall e.g. for windows, pipes, extractor fans they didn’t seal it. I was able to seal some of the French windows which helped a lot. I don’t know if I need to check under the rest of the window sills as well.

If your reveals were anything like mine, then yes do it if you can. They may not cause huge draughts, but they all add up and sorting them out will certainly reduce the cold “feel” when you get little draughts here and there.

Hello, total plumbing doofus here. Is there an easy way to tell what kind of pipes I have in my house? Is it as easy as getting a caliper on the radiator pipes or do I need to start finding the actual plumbing?

FWIW, I recently had a long chat with a pal who is a building physicsist specialising in heat. His rule-of-thumb advice was:

 – the biggest impact you can have on CO2 emissions is go from gas boiler -> heat pump, almost regardless of the state of your house.

 – The biggest impact you’ll have on comfort is better insulation and airtightness.

He sensibly wouldn’t comment on the economics of it because the costs of all of that ^^^ depends on a whole bunch of stuff.

If there’s any installer recommendations in the Scottish Borders, I’m all ears please

I’m in Ecclefechan. I generally don’t do new installs, so have never bothered with the MCS accreditation, and the majority of people only want one when they can get the Grant, for which the Installer has to be MCS accredited [1]. I do a lot of follow ups after the original Installer has made a mess of their grant funded install. I’ve been to 2 this week installed by Greener Energy Scotland, both were a farce, and no way did they meet the MCS criteria, and, of course, they never answer phone calls, never mind organising a visit to correct their faults.

If you want a chat about it,PM me and I’ll give you my phone number.

[1] I can get the grant through Heat Geek, with their umbrella scheme, however, they charge me around £2000 for each HP installed, as well as supplying all of the kit at a not very discount price. I disagree with that, and, could, in many cases, beat their price by buying independently, but, the grant went up to £7.5k from £5k, and now there is no way I can do it competitively, so, the customer almost always goes for the grant funded install by a larger company, rather than a small one or two man business.

Passiv House is way more than a spreadsheet, clearly never seen one put together, or if you have it wasn’t done properly

With an outdoor temperature of 8.3 °C, your heat pump could achieve around 3.8 CoP

Are those sorts of figures with a ground source heat pump?  I followed our water temp during winter last year and it rarely got up to 40 and our pipework is 20mm so I suspect we are in not bad shape but we run our house cold really – a bit warmer would be nicer.  Trying to work out if we really need to take the hit on going ground source but we could do it if we really need to

the biggest impact you can have on CO2 emissions is go from gas boiler -> heat pump, almost regardless of the state of your house.

Yes, but that may come at a high cost.  If you consume the same amount of energy to heat via a heat pump, you will emit about half or a third the CO2 than if you use a gas boiler. But you will pay four times as much.  Now, you won’t use the same amount, you might use a third the energy, which means you’ll emit way less CO2 – but you would still end up paying more.

If your reveals were anything like mine, then yes do it if you can. 

The window frames get cold in the winter – I assumed it was the frame itself.  How can you insulate inside the cavity walls without removing the windows?  Drill into the walls?

How can you insulate inside the cavity walls without removing the windows?

Builder not fit cavity closers where they should have ?

I don’t know. I’m going to have to pull it apart and have a look!

To do it properly, we moved the windows right to the edge of the outer brick. Plasterboard and window board then removed. Poorly fitted cavity closers removed as they were pointless with big gaps or in some cases weren’t there anyway. This allowed air from the cavity to get straight behind the rest of the plasterboard. I topped up the cavity insulation right the reveal edge (less a bit so the new closers weren’t crushing the new insulation but still touching). Then we used ct1 or sticks like **** and expanding foam on the new closers. Clout nails also used into the block to hold the closers as well. I then taped the nail heads with airtight tape. New triple glazed windows or existing were then put back in the right place so they came inward over the closers by as far as we could whilst the outer brick still taking most of the weight of the windows.

@molgrips

The window frames get cold in the winter – I assumed it was the frame itself.

What are your windows made of and what sort of glazing? I’ve got fibreglass framed 3G windows (Passive house certified. It’s not that cold out today so the inner pane of the window is only about 0.5C less than the internal walls in the room, but the frame around the glass is still a degree cooler.

Frames (and the junction with the building) are the weak point