Planned ASHP 1930s semi retrofit - experiences please?

[Greenbot]

Hello,

I have committed to an ASHP to be retrofitted but I am concerned about it's performance, and whether I'm making a mistake.  We renovated our 1930s, 130m2 3-bed semi back to bare brick and joists over the last 5 years, and despite my efforts at the time I couldn't get advice on low-carbon heating (and couldn't afford it at the time either).  What I am not working with is all new 22/15mm copper pipes in a 2 zone (up/downstairs) system on a very efficient gas combi.  The radiators are only just large enough for running at 55 degrees - I should have gone larger but they are expensive designer items that we will not be replacing, so we are comfortable with them at 55 degrees but I will be adding a couple of radiators in larger rooms to lower the running temperature.

 

The house has topped up loft insulation (300mm), all LED lights, cavity wall insulation (government grant 5 years ago), all double glazing, new composite doors, and I've installed floor insulation for the suspended timber (100mm mineral wool and air-tight membrane sealed around the perimeter of each room).  I've done a decent bit of draft proofing but need to look at the spot lights and consider a MHVR system for the bathroom next.  We see cold spots in the bathrooms where water vapour condenses on the dot and dab plasterboard performing thermal bridging.  The house has a mini-extension joining the garage to the house which has been converted from single-brick walls to a stud liner wall with 100mm extruded polystyrene insulation; pipes from the heat pump will pass under the floor into the main house (6m).  We already have a wood stove for additional heating if required.

 

Heat loss calculations say we're at 6.9-7kW at -3degrees, from 2 installer surveys.  We're provisionally going with a 7kW heat pump, a buffer connection it to the 22mm pipework coming into the house and a 200l DHW tank.

 

What I really need is to hear that somebody has a similar house and system, how well it works and their real-world running costs.  The GHG is very delayed, and due to other factors I'm considering pulling the plug.  My motivation is doing the right thing for climate change, so I don't expect total financial sense, but I also can't spend the coming years ripping it out and starting again / changing things if I get it wrong.

 

Thank you in advance, and please ask if I've missed anything.

[ProDave]

I am interested to know what you have dome to a 1930's house to get the heat input requirements down so low?  Loft insulation and new windows won't get it so low, I used to live in a 1930's house and remember it's appetite for heat.

 

Before committing to a heat pump I would want to be SURE that heat requirement calculation is correct.  It would be safer to base that on known gas usage over a cold winter.  The biggest cause of criticism with heat pumps is when they are sized too small and in cold weather and cannot keep the house warm.

 

And what is your motive?  It certainly will not lower your fuel bill.  It;s very honourable to want to reduce CO2 emissions, but it will cost you more.

[epsilonGreedy]

10 hours ago, Greenbot said:

Heat loss calculations say we're at 6.9-7kW at -3degrees, from 2 installer surveys.  We're provisionally going with a 7kW heat pump, a buffer connection it to the 22mm pipework coming into the house and a 200l DHW tank.

 

 

Have you read the other ashp thread where the householder was complaining about his ashp getting iced up? An iced up ashp then wastes energy defrosting itself. One explanation offered is that the ashp was over worked and so had little time to idle and shed frost build up. The worst conditions for frosting apparently are damp days when the ambient outside temp is a few degrees above zero, just like your typical British winter day. 

 

@SteamyTeawill be along shortly to restate all that in a far more scientifically robust way.

[Temp]

I would suggest getting a heat loss calculation from someone not trying to sell you ASHP.

 

What boiler do you currently  have?

Edited February 18, 2021 by Temp

[Greenbot]

Thank you for your replies.

 

16 hours ago, ProDave said:

I am interested to know what you have dome to a 1930's house to get the heat input requirements down so low?  Loft insulation and new windows won't get it so low, I used to live in a 1930's house and remember it's appetite for heat.

 

Before committing to a heat pump I would want to be SURE that heat requirement calculation is correct.  It would be safer to base that on known gas usage over a cold winter.  The biggest cause of criticism with heat pumps is when they are sized too small and in cold weather and cannot keep the house warm.

 

And what is your motive?  It certainly will not lower your fuel bill.  It;s very honourable to want to reduce CO2 emissions, but it will cost you more.

 

I've not done anything special - I tried to do everything I could when renovating on a budget, but I didn't know as much as I do now.  I've listed everything I've done already.  Good point on the gas comparisons - I used 2 years running on gas (with draughty old front door and a large, rotten single glazed bay window which are now replaced) and our usage (with 2 bedrooms rarely heated) was almost exactly 15,000kWh.  I calculated that as 14kW based on the boiler efficiency, and using an SCOP of 2.5 calculated the electricity demand for the heat pump to be 5500kWh.  That's included working at home in lockdown 1 and 2 up to December 2020.  I don't know if I can work out how to convert that to the power required for the heat pump, however I wanted to option to extend into the loft down the line so I've decided to upsize to the Daikin Altherma 3 H HT, which has far greater output (but the upgrade was a painful price).

 

My motive is indeed to reduce C02 - it's the right thing to do, and I want to tell the younger generations that I did my best.  In my opinion, if you are lucky enough to be ABLE to afford it, you should - and I am poor at spending my money.  We're not rich - we work in the public sector and neither of use earn near a GP salary.  I'm prepared for the slightly higher bills, and thank you for your comment.

 

15 hours ago, epsilonGreedy said:

 

Have you read the other ashp thread where the householder was complaining about his ashp getting iced up? An iced up ashp then wastes energy defrosting itself. One explanation offered is that the ashp was over worked and so had little time to idle and shed frost build up. The worst conditions for frosting apparently are damp days when the ambient outside temp is a few degrees above zero, just like your typical British winter day. 

 

@SteamyTeawill be along shortly to restate all that in a far more scientifically robust way.

 

Yes; the concern about that is a factor in deciding to upgrade to the Daikin and you've just made me feel better about that decision!

 

 

12 hours ago, Temp said:

I would suggest getting a heat loss calculation from someone not trying to sell you ASHP.

 

What boiler do you currently  have?

 

Baxi 38kW, very oversized - my partner's dad is a plumber and helped with the refurb!  Can you advise how to better check the heat loss?  One company spent 90 min here measuring up and provided a detailed breakdown, and did our EPC.

 

Another question - does anybody use a thermal store to take advantage of Octopus energy flexible tariff, so you could have 4p/kWh electricity pre-4pm and then heat the house in the evening?  I've not calculated how much heat would be useable from that but it would help and be future compatible with either type of solar panels that I would love to fit down the line.

 

It's all very interesting but the mind boggles at the number of factors you have to consider!!

[ProDave]

54 minutes ago, Greenbot said:

I used 2 years running on gas (with draughty old front door and a large, rotten single glazed bay window which are now replaced) and our usage (with 2 bedrooms rarely heated) was almost exactly 15,000kWh.  I calculated that as 14kW based on the boiler efficiency, and using an SCOP of 2.5 calculated the electricity demand for the heat pump to be 5500kWh.  That's included working at home in lockdown 1 and 2 up to December 2020.  I don't know if I can work out how to convert that to the power required for the heat pump,

So 15000kWh in a year, some VERY rough sums assuming you use heating for half the year is 82kWh per day for the heating season and a very rough guess that the coldest day will use twice that so 164kWh per day.

 

Assuming the heating is on 18 hours per day, that's an average of 9.11kWh for those 18 hours.  You are probably about right sizing a 14kW ASHP for that to give a bit of extra.

 

Assuming you can get a COP of 3, then your 15000kWh of heat would consume about 5000kWh of electricity.  You can have endless fun playing with different electricity tariffs to see how your bill might compare with your present gas bill.

 

If you want to do most of your heating in the cheap afternoon and store it for the post 4pm expensive period, you would need to be storing something in the order of 80kWh of heat in something.  and condensing your heating requirement into a shorter time period might push you to a larger heat pump.

 

Plenty for those with an analytical mind to chew over.

[SteamyTea]

14 minutes ago, ProDave said:

80kWh of heat in something.

Be about 3 tonnes of water.

Storage heaters would take up less room.

[TonyT]

Maybe a combination of a storage heater or 2 in hallway for shoulder season heating to take advantage of the agile tariff, coupled with immersion heaters heating water.

 

some PV would be handy , maybe the other half’s dad knows a sparky to fit some PV?

[Greenbot]

1 hour ago, ProDave said:

So 15000kWh in a year, some VERY rough sums assuming you use heating for half the year is 82kWh per day for the heating season and a very rough guess that the coldest day will use twice that so 164kWh per day.

 

Assuming the heating is on 18 hours per day, that's an average of 9.11kWh for those 18 hours.  You are probably about right sizing a 14kW ASHP for that to give a bit of extra.

 

Assuming you can get a COP of 3, then your 15000kWh of heat would consume about 5000kWh of electricity.  You can have endless fun playing with different electricity tariffs to see how your bill might compare with your present gas bill.

 

If you want to do most of your heating in the cheap afternoon and store it for the post 4pm expensive period, you would need to be storing something in the order of 80kWh of heat in something.  and condensing your heating requirement into a shorter time period might push you to a larger heat pump.

 

Plenty for those with an analytical mind to chew over.

 

Thank you very much for that, it's good to have another person check the calculations!  The 7kW pump certainly would have struggled.  My boiled would have used 15,000kWh at about 93% efficiency, and that was including DHW.  My gut is that with the insulation (new door and bay windows) and draft proofing I've now completed should hopefully mean we'd use closer to 13,000 kWh [ (15000 x 0.92 = 13,800), assuming 95% is space heating = 13,110kWh).

 

1 hour ago, SteamyTea said:

Be about 3 tonnes of water.

Storage heaters would take up less room.

 

Wow - thanks.  My DHW cylinder is going in the garage but I don't think it should be ALL water storage!  I assume the lower water temperatures of an ASHP requires a larger volume.

 

The current plan is for a water cylinder that has an immersion heater, so solar PV in future would be compatible.  I am wondering if I should attempt to keep options open for solar thermal in future via a thermal store, or whether it's viable to go for a large enough thermal store to use cheap electricity to contribute toward space heating?

 

I'm still hoping to hear from anybody who has retrofitted any similar ASHP to an older house.

[Greenbot]

47 minutes ago, TonyT said:

Maybe a combination of a storage heater or 2 in hallway for shoulder season heating to take advantage of the agile tariff, coupled with immersion heaters heating water.

 

some PV would be handy , maybe the other half’s dad knows a sparky to fit some PV?

 

I would love to add PV in future, but the budget won't stretch with a wedding and our garden and driveway to complete - hopefully in a couple of years!  The storage heater is a great ideal though, I will look into those thank you.

 

What we need is for the government to reduce the gap between gas and electricity prices to reflect their environmental impact - especially as we have more renewables coming into the grid.  16p for electricity vs 4p for gas is not right...

[Ultima357]

On the PV front, in winter it obviously generates less and as the ASHP will be running, you are unlikely to get much input to the immersion. Summertime yes and plenty of it if you have a decent PV array facing south. You haven't said what your EPC score is and that should come with an estimated heat load if you got a full one. Size of the property is a factor too but I think that ASHP will be an expensive option for heating. I'm running one in a new build passively insulated home (3 to 400mm insulation and triple glazed, mvhr etc), 253m2 and it's rated at 12kw. It copes even in the recent freezing conditions but they all ice up and COP is circa 2 at freezing fog temperatures. My EPC score is A98. Good luck. 

 

PS See the Cost of Electricity thread elsewhere on ASHP running costs in a renovated property. 

Edited February 19, 2021 by Ultima357

[Greenbot]

Thanks, that's what I understood for PV.  My EPC is high D, BUT that was not including the report's suggested under floor insulation with air barrier and double glazing / door upgrades which were recently completed.  My neighbour (practically identical house with far less insulation measures) is listed as C.

I've took a look at that whole thread; they seem to be chasing down power usage and using a lot of power.  It's going to be very interesting to see my actual use when i go through with it.

41 minutes ago, Ultima357 said:

I'm running one in a new build passively insulated home (3 to 400mm insulation and triple glazed, mvhr etc), 253m2 and it's rated at 12kw. It copes even in the recent freezing conditions but they all ice up and COP is circa 2 at freezing fog temperatures. My EPC score is A98. Good luck.

 

Thank you, I feel like I'll need it... Out of interest, your house sounds great and such a home is my long term goal (maybe a bit smaller!) but I though Passivhaus / passively insulated would require a barely and heat.  It's clearly a beautiful large home and therefore 12kW must still be very efficient, so what does passively insulated actually mean?

[JamesP]

I have recently built a new house which by chance meets the below Passive House specification , I did not set out to meet the specification but due to the amount of insulation, MVHR, PV, 3G windows and an ASHP it could be referred to as a Passive House spec without the certification.

https://passiv.de/en/02_informations/02_passive-house-requirements/02_passive-house-requirements.htm

Passive House requirements

For a building to be considered a Passive House, it must meet the following criteria ( for detailed criteria, please see the building certification section):

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand. 

In climates where active cooling is needed, the  Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with an additional allowance for dehumidification.

2. The Renewable Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic. . 

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).

4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C. For a complete overview of general quality requirements (soft criteria) see Passipedia. 

 

 

 

[ProDave]

52 minutes ago, JamesP said:

I have recently built a new house which by chance meets the below Passive House specification , I did not set out to meet the specification but due to the amount of insulation, MVHR, PV, 3G windows and an ASHP it could be referred to as a Passive House spec without the certification.

https://passiv.de/en/02_informations/02_passive-house-requirements/02_passive-house-requirements.htm

Passive House requirements

For a building to be considered a Passive House, it must meet the following criteria ( for detailed criteria, please see the building certification section):

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand. 

In climates where active cooling is needed, the  Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with an additional allowance for dehumidification.

2. The Renewable Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic. . 

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).

4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C. For a complete overview of general quality requirements (soft criteria) see Passipedia. 

 

 

 

Thanks, I had not seen that documented so succinctly before.  My house meets those energy requirements and I hope it will meet that air tightness level (will be getting it tested later this year)

 

Like many I strived to get somewhere close to passive house levels but without paying to have it certified s such.

 

You know when you have got it right, that your heating bills are a minor part of your total energy bills. In my case about 1/3 of total energy used. 

 

[Ultima357]

What does passive actually mean? There's a technical standard defined by the Passive haus institute detailed above which you can go for but that's just a vanity £5k spend on a certificate. It basically entails the level of insulation/heat loss and airtightness of the structure. In mine, its 300mm insulation in the walls plus 35mm dead air gap, 400mm in the attic, 300mm XPS under the floor tapered to a minimum 100mm at the dpc edge (so totally enclosed foundations) and triple glazing. All airtight to a measured 0.17ach @50pa. In heat loss terms of U values, walls are 0.1u, roof 0.1u and floor 0.12u. All windows/frames better than 0.8u. A 1930s cavity wall? Well the cavity is likely to be small, so I'd guess the u value would be around 0.5u. My running costs in the past freeze, 15th of Jan to 15th of Feb for heating and hot water around £65. £2 a day. Whole house at 22 to 23 deg plus warm attic circa 85m2 too. 14 zone UFH cast directly into the slab, 155ton heat store. Around 1.5km of pipes! 400l hwt

[Greenbot]

2 hours ago, JamesP said:

I have recently built a new house which by chance meets the below Passive House specification , I did not set out to meet the specification but due to the amount of insulation, MVHR, PV, 3G windows and an ASHP it could be referred to as a Passive House spec without the certification.

https://passiv.de/en/02_informations/02_passive-house-requirements/02_passive-house-requirements.htm

Passive House requirements

That's an excellent description, thanks.  I wasn't aware that £5k was needed for a certificate either.  I believe UK building regs will change in future toward better standards, it's a shame all new builds aren't currently somewhere near this.  If I achieve my own self- build I couldn't not aim for that performance, but many people don't seem to be interested.

[SteamyTea]

42 minutes ago, Greenbot said:

but many people don't seem to be interested

Why should they when gas is <3p/kWh

[Greenbot]

14 hours ago, SteamyTea said:

Why should they when gas is <3p/kWh

 

Indeed... I'm sure that's a rhetorical statement the forum we're on is for renewables, but obviously the answer is for the sake of sustainability and air pollution ?

 

I'm considering learning how to blog to document our install before and after, in hope that it may inspire others and answer the questions I've spent hours researching.  I've only found one such example but his heat demand for a terraced house doesn't compare to our semi unfortunately.  And my installation is a lot more.

https://tomkiss.net/life/one_year_with_an_air-source_heat-pump

 

Still a very useful starting point for research and one that informed my decision.

[ProDave]

46 minutes ago, Greenbot said:

 

Indeed... I'm sure that's a rhetorical statement the forum we're on is for renewables, but obviously the answer is for the sake of sustainability and air pollution ?

 

Not really, this is primarily a self build forum where we discuss all aspects of buildings and renovations.  Nobody is going to demonise you for using a gas boiler because that is what works best.

 

i have a particular concern that there are companies out there "selling" ASHP systems on the back of grants, and then sometimes installing something that is not up to the job, may not heat the house properly, or simply costs too much to run.

 

All very well being "green" and accepting that doing so may cost you more money.

[joth]

 

1 hour ago, ProDave said:

2 hours ago, Greenbot said:

Indeed... I'm sure that's a rhetorical statement the forum we're on is for renewables, but obviously the answer is for the sake of sustainability and air pollution ?

 

Not really, this is primarily a self build forum where we discuss all aspects of buildings and renovations.  Nobody is going to demonise you for using a gas boiler because that is what works best.

 

 

I think it was a reference to the sub-forum this is posted in, i.e: "Environmental, Alternative & Green Building Methods >>  Renewable Home Energy Generation  >> Air Source Heat Pumps (ASHP)"

 

(Yes, each of the categories are called "Forums" . all inside "the" forum, confusing)

 

 

[Greenbot]

19 hours ago, SteamyTea said:

Why should they when gas is <3p/kWh

 

Indeed... I'm sure that's a rhetorical statement the forum we're on is for renewables, but obviously the answer is for the sake of sustainability and air pollution ?

 

I'm considering learning how to blog to document our install before and after, in hope that it may inspire others and answer the questions I've spent hours researching.  I've only found one such example but his heat demand for a terraced house doesn't compare to our semi unfortunately.  And my installation is a lot more.

https://tomkiss.net/life/one_year_with_an_air-source_heat-pump

 

Still a very useful starting point for research and one that informed my decision.

[Greenbot]

Yes I was referring to the forum we're on and I appreciate that buildhub is a self-build forum.  I share the concern that some companies are biased and the risk of unsuitable systems is real, but I've vetted installers as much as possible, spoken to previous customers and read into their over 10-year long histories.

 

4 hours ago, ProDave said:

Not really, this is primarily a self build forum where we discuss all aspects of buildings and renovations.  Nobody is going to demonise you for using a gas boiler because that is what works best.

 

i have a particular concern that there are companies out there "selling" ASHP systems on the back of grants, and then sometimes installing something that is not up to the job, may not heat the house properly, or simply costs too much to run.

 

All very well being "green" and accepting that doing so may cost you more money.

 

Yes, although costing money is not the only cost I think we should consider.  When I weigh up the reduction CO2 emissions (I can expect around 67% decrease according to this: https://www.london.gov.uk/sites/default/files/heat-pump-retrofit-in-london-v2.pdf), I could argue that heat pumps are cheaper all things considered.  We need to consider all of the materials we use in building too; there's some excellent progress in Europe with increased timber for example.

 

I appreciate your replies to my thread ProDave, I hope the above isn't read as confrontational - just my answer to the 'why should they because gas is so cheap' question.  It's a like the ICE vs. electric car debate, I'd love to drive a 6-cylinder NA monster around but it just seems wrong to me and I hope that the subsidies for fossil fuel will reduce in future.  Thanks ?

[TonyT]

I’m on mains gas and will stay on it, as I upgrade my 1860 house, thermal improvements year on year as rooms are redecorated.

 

hopefully 10-15 years when boiler needs replacing will be able to run off ASHP.

 

Doing some work in the garden this summer and plan for some underground ducts to be installed to make the install easier when it happens...

 

ps thanks for the link above, some good reading!

 

 

Edited February 20, 2021 by TonyT

[Ferdinand]

40 minutes ago, Greenbot said:

 

Indeed... I'm sure that's a rhetorical statement the forum we're on is for renewables, but obviously the answer is for the sake of sustainability and air pollution ?

 

I'm considering learning how to blog to document our install before and after, in hope that it may inspire others and answer the questions I've spent hours researching.  I've only found one such example but his heat demand for a terraced house doesn't compare to our semi unfortunately.  And my installation is a lot more.

https://tomkiss.net/life/one_year_with_an_air-source_heat-pump

 

Still a very useful starting point for research and one that informed my decision.

 

Absolutely. We are not at all confrontational.

 

I'm sharpening my pitchfork as we speak ?.

 

If you drop a note to the mods, a blog can be created for you. 

 

Renovation blogs will be good alongside the new build blogs.

 

Remember that it is important to PROVE what you have done to the EPC surveyor, otherswise they have to make all sorts of pessimistic assumptions.

 

F

[Iceverge]

Is it an option to install an air to air heat pump in a central area and an immersion in the tank. 

 

You could use these to avail of low carbon electricity when available.  While leaving your boiler to top up when needed? 

 

Gas boilers are a still a very efficient method of using fossil fuels. In terms of your global carbon usage have you compared the benefit of house modifications Vs changing to an electric car for instance?