underfloor heating under floorboards - any ideas on the numbers?

[Stinsy]

I don’t want to sound like a broken record but: don’t discount A2A! Cheap to buy/install, efficient, reliable…
For me the perfect system for most houses is: 2x A2A, 2x SH, 1x WBS.

Don't worry... I want to google a bit for myself but I'm more than half way convinced to do air source - air to water anyway, to help spread the hear around the place

what's SH ?

I'm keen on a WBS but not sure yet, don't want to be humping wood around when I'm old and knackered.

SH is storage heater.

There are a few things that you need in order to have a satisfactory A2W HP installation:

- Correct Sizing - The HP needs to run constantly if it is to be efficient. If it cycles on and off it will be very inefficient and suffer unreliability/shortened lifespan. A typical HP can throttle down to 25% of its rated power. The problem here is that a HP sized for the worst possible conditions will cycle on and off frequently in more-moderate conditions. This is where an additional heat source is critical. So if you design your HP to maintain an 18℃ indoor temperature when it is -2℃ outside, then you can use the WBS to give you 21℃ when it is -2℃ outside or on the rare occasions when it is lower than -2℃ outside. This smaller HP will cycle much less in more-moderate conditions, and when you only need a little heating (eg a cool spring/autumn evening) you can light a small fire in the WBS and keep the HP off.

- Large emitters - The larger the emitter the lower flow temperature you'll need to give off the same amount of heat. The lower the flow temperature the more efficiently the HP will run. Low flow temperatures also allow your emitters to self-regulate. For example if the room temp is 15℃ and your flow temp is 35℃ you have a Δt of 20℃ whereas when the room temperature 25℃ and the flow temperature is 35℃ your Δt will be 10℃. The heat output by the same emitter and flow temp will vary by a factor of 2 in the temperature range you can reasonably expect in your house. This is a mong way of explaining that the emitters will give off more heat when you need them to and less heat when you don't, all passively and naturally, no fancy electro-mechanical system required.

- Large Pipework - In order to shift the same amount of energy at a lower flow-temp you need to shift a lot more water. It is also beneficial to keep the velocity slow to keep wear and noise down. Therefore you need big pipes. You can do the calls simply enough but basically this means 22mm flow and return with 15mm to each rad (just like we used to...).

[Fintray]

I don’t want to sound like a broken record but: don’t discount A2A! Cheap to buy/install, efficient, reliable…
For me the perfect system for most houses is: 2x A2A, 2x SH, 1x WBS.

Don't worry... I want to google a bit for myself but I'm more than half way convinced to do air source - air to water anyway, to help spread the hear around the place

what's SH ?

I'm keen on a WBS but not sure yet, don't want to be humping wood around when I'm old and knackered.

I know what you mean, my WBS hasn't been on since I got the heat pump installed, I've even sold my petrol chainsaw!

[AGT]

Can I ask if you were insulating a suspended floor from below cause it was sanded/nice finish and you insulated with say friction fit rock wool between the joists would a membrane stapled to the underside of the joists be beneficial for wind washing? If so what kind of membrane would you consider?

[knighty]

Can I ask if you were insulating a suspended floor from below cause it was sanded/nice finish and you insulated with say friction fit rock wool between the joists would a membrane stapled to the underside of the joists be beneficial for wind washing? If so what kind of membrane would you consider?

if you want to fit it like that you need something which can breath - something like normal plastic membrane will lock moisture in and can lead to damp - warm air/moisture getting down through the insulation, hitting the cold membrane and condensing to water

[AGT]

Appreciate the info, so something like roofshield breather membrane as used under slates/tiles would be a good option?

[knighty]

I don’t want to sound like a broken record but: don’t discount A2A! Cheap to buy/install, efficient, reliable…
For me the perfect system for most houses is: 2x A2A, 2x SH, 1x WBS.

Don't worry... I want to google a bit for myself but I'm more than half way convinced to do air source - air to water anyway, to help spread the hear around the place

what's SH ?

I'm keen on a WBS but not sure yet, don't want to be humping wood around when I'm old and knackered.

SH is storage heater.

There are a few things that you need in order to have a satisfactory A2W HP installation:

- Correct Sizing - The HP needs to run constantly if it is to be efficient. If it cycles on and off it will be very inefficient and suffer unreliability/shortened lifespan. A typical HP can throttle down to 25% of its rated power. The problem here is that a HP sized for the worst possible conditions will cycle on and off frequently in more-moderate conditions. This is where an additional heat source is critical. So if you design your HP to maintain an 18℃ indoor temperature when it is -2℃ outside, then you can use the WBS to give you 21℃ when it is -2℃ outside or on the rare occasions when it is lower than -2℃ outside. This smaller HP will cycle much less in more-moderate conditions, and when you only need a little heating (eg a cool spring/autumn evening) you can light a small fire in the WBS and keep the HP off.

- Large emitters - The larger the emitter the lower flow temperature you'll need to give off the same amount of heat. The lower the flow temperature the more efficiently the HP will run. Low flow temperatures also allow your emitters to self-regulate. For example if the room temp is 15℃ and your flow temp is 35℃ you have a Δt of 20℃ whereas when the room temperature 25℃ and the flow temperature is 35℃ your Δt will be 10℃. The heat output by the same emitter and flow temp will vary by a factor of 2 in the temperature range you can reasonably expect in your house. This is a mong way of explaining that the emitters will give off more heat when you need them to and less heat when you don't, all passively and naturally, no fancy electro-mechanical system required.

- Large Pipework - In order to shift the same amount of energy at a lower flow-temp you need to shift a lot more water. It is also beneficial to keep the velocity slow to keep wear and noise down. Therefore you need big pipes. You can do the calls simply enough but basically this means 22mm flow and return with 15mm to each rad (just like we used to...).

A bunch of the old big pipework is in the way to stop me exploring properly but the whole heating system needs re-plumbing anyway, I'll sort that in the summer, I was thinking 28mm feed and return with 15 to each radiator.

I'll add what underfloor heating I can... even if it's not great there's a lot of area there I can cover - need to insulate under there anyway so I can do it all at once

I have my f-gass qualification so I'm good to go with heat pumps (just never have before, always refrigeration)

I was thinking smart thermostatic valve son the radiators to help monitor and control the heating - advantage is I can use those same smart valves to monitor room temperatures and control the under floor heating zones

there's only 1 phase connected but I'm pretty sure there's 3 phase at the meter head, the battery in my meter died when I went to check, but if there is it opens up a lot of heat pumps and overnight battery charging to me

I was thinking about a large thermal store to heat overnight when needed - could run the heat pumps full belt in the cheap electric hours

[knighty]

UFH with a suspended floor basically comes down to one run up and down the room between each joist which should give a decent output provided you can fix and draughtproof the insulation to a good standard between the joists. Tackling that from underneath is almost impossible IMO, how would you cross over the joists for example? It's not something I would be willing to try. Taking up the floor sounds like a big job but it will be a much more accessible task without all the detritus falling in your eyes and up your nose. Done well it will improve the comfort no end. Personally never seen any of the humidity levels Stinsy mentioned, mostly 90 year old wood is as dry as it will ever get.

Desp

I saw ufh a friend installed from underneath - it was for the 2nd floor, he took the ceiling down in the room under it and installed it like that

drilled holes through the joists at one end of the room for the feed/return and then looped one length of pipe through the lot

thinking now... I guess I'll have to make some kind of insulated duct to run all the feeds/returns for each zone in so I'm not drilling a million holes in the joists but apart from that should be ok (I'm not great at explaining things, I have a picture in my head of how to do it)

[knighty]

What do you have planned for the land ?

Just thinking that the first thing I would do would be a 16kWp ground mount near to the house, then I would ffind some big thick internal walls and make them in to feature walls that can be charged with heat from the solar array via electric elements embedded in the walls or infrared panels etc you could even plaster electric underfloor mats to the walls to charge the masonary.

That would get you enough heat to warm up the place while you refine your plans.

City plumbing have bidirectional 500 Wp panels for 67 quid so 2144 pounds buys you 16kWp add in the mounts and inverters and it’s still a really cheap route to getting the place heated and comfy for not a lot of effort / cash later as you develop the heating and refine the varied methods the excess power can be used elsewhere or some of it exported but at current panel costs even if you let the panels “stagnate” in summer it wouldn’t be a disaster and it’s usually easy to find new uses for excess power eg car charging etc.

Instead of under floor also consider ceiling mounted far infrared as that might also be a possible solution.

I wish you well in your endeavours it sounds like it’s going to be a fabulous adventure.

Moxi

There's a LOT of trees causing shade in the garden :-(

We'd like to keep the trees - and there's a tree protection order anyway (tree protection order might have been a result of the previous owners trying to get permission to build houses in the garden)

I'd like to knock down the garage/out houses and rebuild it bigger and better, with a roof ready for as much solar as possible

there's decent roof space, but it's not great for solar, there's essentially 4 roofs, on the left there's 2 running north south on the right there's 2 running east west... so they'll shade each other a lot :-(

plan right now is solar on the roof, garage, and then maybe ground mount some

[Stinsy]

A bunch of the old big pipework is in the way to stop me exploring properly but the whole heating system needs re-plumbing anyway, I'll sort that in the summer, I was thinking 28mm feed and return with 15 to each radiator.

I'll add what underfloor heating I can... even if it's not great there's a lot of area there I can cover - need to insulate under there anyway so I can do it all at once

I have my f-gass qualification so I'm good to go with heat pumps (just never have before, always refrigeration)

I was thinking smart thermostatic valve son the radiators to help monitor and control the heating - advantage is I can use those same smart valves to monitor room temperatures and control the under floor heating zones

there's only 1 phase connected but I'm pretty sure there's 3 phase at the meter head, the battery in my meter died when I went to check, but if there is it opens up a lot of heat pumps and overnight battery charging to me

I was thinking about a large thermal store to heat overnight when needed - could run the heat pumps full belt in the cheap electric hours

There are a bunch of calculations you can do for pipe sizing, it depends on length, number of fittings, flow temp, water velocity, heating power, etc.. You can find the relevant calculators online. However 28mm Flow/return and 15mm to individual rads is almost definitely correct.

If you're f-gas then you really should consider A2A!

Have a look at what "Heat Geek" has to say about TRVs!

3-phase really opens up the opportunity to have a very large solar array, several EV charging points, electric showers, and other unusually large consumers of electricity.

However in reality, from what you have described, you should be fine on single-phase.
- A 7kW HP will only pull 8ish Amps at full chat and even an 11kW HP is fine on single-phase if the house is particularly mahoosive.
- Most people with several EVs find a single charging point copes just fine (not many people have several cars all doing 200-miles a day!).
- Electric showers are easily avoided.
- A big 10kWp solar array marries nicely with a 5kW inverter and 30kWh battery pack.

All of the above will fit nicely on a single-phase supply. Sure, if you want/need to go bigger than the above then by all means go for 3-phase.