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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.
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
If you divide your previous years gas kWh usage by 2900 you come to the power of the ashp you need to heat your home.
Obviously this is a one calc fits all and assuming no other work is done to insulation level or rad sizes.
I am helping my friend build to passive House standards . It's a steel frame and sip panel build . It's not a case of make it airtight , leak down check , and it's now a passive House. Otherwise I could build one with a marble floor , copper sheet roof , single pane windows and single skin brick wall. Make it airtight with crazy foam and silicon and conjure up air loss figure to passive house standard and it would be like living in a tent.
It's a underground up total build solution. The level of detail required is pretty high and alot of thought goes into how a steel portal frame can be insulated, the slab , ufh , ashp , window spec ,roof design , log burner with external air supply , kitchen extraction etc .
, log burner with external air supply ,
In a passivhaus? That seems like a stunningly bad idea.
No , it isn't. You need to buy a specific model that doesn't draw air from inside the structure.
Otherwise, yes a log burner inside a sealed room using the air from in that room for combustion is really rather dangerous.the mvhr create pressure that affects the burn and could draw CO back into the building.
By buying an external vented model the fire draws cold air in from outside, increased efficiency as you are not using already heated air from inside, then the flue exits normally
So it's a closed system, apart from a few seconds when the next log is chucked on.
In a passivhaus? That seems like a stunningly bad idea.
I think the point being a Passivhaus is unlikely to need that level of heat, and certainly not the 'uncontrolled' and intense heat of a log burner.
Still deciding what to do with our old (1890) 2 bed brick cottage.
Solid brick walls, loft well insulated, new double glazed windows and composite doors. Floors not insulated only about 6” of space under there (checked with remote camera)
Small solar and 5kw battery setup. No existing central heating (or oil or gas) currently running electric radiators using home automation to heat during the lowest Agile rates. TBH we like a cool but obviously not cold house. 5kw log burner in the living room for main comfort.
Do heat pumps stack up on old houses? after all there is only so much can be done to minimise heat loss. (External wall insulation is not an option due to the area and planning)
If the pipe work is done nice we have no issues with it all being exposed and visible as a feature (rather than rip up nice original oak flooring)
hmmmm….
I think the point being a Passivhaus is unlikely to need that level of heat, and certainly not the ‘uncontrolled’ and intense heat of a log burner.
Exactly.
Logburner....
I think the point being a Passivhaus is unlikely to need that level of heat, and certainly not the ‘uncontrolled’ and intense heat of a log burner.
That's definitely an issue. The in-laws built a highly insulated/airtight MVHR house with a pellet burner boiler(1) but insisted on an open fire much to their architect's annoyance. I don't know how the input ventilation was solved for it (it's open to the room). As you'd expect, the uncontrollable heat is a real issue - regularly end up sweating in a t-shirt in winter as David throws another log onto the fire. Given whats known about the pollution of even the 'greenest' wood burners I dont think anyone should be considering them now. A lifetime of open fires almost certainly a contributory fact in his lung cancer as well.
1) pellet burner looked a sensible tech at the time. There was a local supplier and UK manufacture and cost was reasonable. It's not not local, manufactured in Europe and relatively expensive. Also needs a bulky storage hopper and much more maintenance. Air or ground source heat pump is the only sensible choice now.
That's why there is an 8 X 4 roof lantern that can be opened electrically. If it gets too hot.
The building is in woodland with overhead power so the log burner is back up in case of long term power cuts
If you divide your previous years gas kWh usage by 2900 you come to the power of the ashp you need to heat your home.<br /><br />
Could you please explain that a bit more. Just applied it to mine and ended up with 5.5kw. Seems a bit low.
As an aside, ran the boiler at 35degC output for 6 hours on Saturday. Outside temp was around 10degC max. House struggled to hold temp with each room showing a slow decrease in temp over that time from a starting point comfortable 19 / 18degC. I thought our house was reasonably well insulated. In fact there’s not much more we can do other than external cladding (which we can’t as in a conservation area.) Bigger rads needed before we go down the ASHP route!
That’s why there is an 8 X 4 roof lantern that can be opened electrically. If it gets too hot.
So overheat the house then send it to the sky. Genius.