Advice on space heating passive house

[EmB]

apologies to jump in

i can't believe i am talking to all you knowledgeable guys as someone who does not know very much about this but I do have an old oil fired boiler which seems quire efficient but do not in actuality know how much energy / oil it is using @ 20degrees all day every day which is what we used in other place and found to astonishment that the bills were way cheaper - was just a flat and i do not yet know if that will be different

But am a little confused in the tale - to be clear :  you have  “bought a flow meter and installed that so I had a measure of the water flow rate that I was achieving, and that came back with a figure of 14 litres per minute.” but “  LG technical to be told the flow switch is "Set to 10 litres per minute plus or minus 3"” and now you have “boosted my flow rate to 20 litres per minute  “  “

 

is there not an issue right there? ... the flow rate 10+3 = 13 or 10-3 = 7?? but then you have boosted it even further out of kilt to 20 litre per minute or was that a mistake in the original post??

 

 

 

Edited February 3, 2021 by EmB

[ProDave]

13 minutes ago, EmB said:

But am a little confused in the tale - to be clear :  you have  “bought a flow meter and installed that so I had a measure of the water flow rate that I was achieving, and that came back with a figure of 14 litres per minute.” but “  LG technical to be told the flow switch is "Set to 10 litres per minute plus or minus 3"” and now you have “boosted my flow rate to 20 litres per minute  “  “

 

is there not an issue right there? ... the flow rate 10+3 = 13 or 10-3 = 7?? but then you have boosted it even further out of kilt to 20 litre per minute or was that a mistake in the original post??

 

 

 

Was it me that originally posted that?  I think so but not in this thread?

 

Just to clarify, my measured flow rate was not satisfying the flow switch so my flow switch in my heat pump must be well on the pessimistic side, or my own flow meter is reading a bit high, or a combination of both.

[TerryE]

10 hours ago, dnoble said:

I’ve got it up and running with a Willis heater ...  and a cheap mechanical timer.   The manifold + pump was the main outlay around £400.

It took about 3 days continuous running the get the slab up from 18 to 25deg. Now I’m running it only from 12.30 at night till 7.30am when I get cheapo electric.

... All the gubbins is under the counter in the utility room next to the Sunamp

 

@dnoble,  Some comments:

1. The Willis units aren't repairable if the heating element goes, so the only practical maintenance option is to replace.  Given that they are so cheap, my recommendation is to buy yourself a spare Willis now with the same form-factor as the current one and that way you won't have all the hassle of doing this on failure and have the system off for days.
2. I am a little surprised that you are doing the Willis loop in 15mm pipe.  I suspect that the water could be circulating at over 1 m/s and so this will be quite noisy.  You can estimate the flow rate from the temperature delta across the Willis, simple physics, but the output of the Willis is roughly 2.88 kW so the formula for 15mm pipe works out at roughly v = 4/Δt where v is in m/s and Δt is in °C.
3. If it is, then one little project for the summer would be to put the two Willis, as per (1), in parallel with ins and outs combined with a 15/22/15 T and the combined in and out to the manifold plumbed in 22mm.  This would drop the overall flow rate through this piping by roughly 2× with the water running 50:50 through the 2 heaters in parallel, one heating and one unpowered.  You only need to wire up one of the heater to the timer, so for example the powered Willis might raise the temp by 6°C say, so the delta across the manifolds would be half this at 3°C.  Now if a Willis fails then the swap is a 5mins wiring job at the wall and no need to drain anything against the clock.
4. The fill should not really be directly attached to the potable water system.  This is bad practice (and against regs)  as you can risk back-flow; better to add a double check valve on potable side of the 1st valve, IMO.   The Building inspector might pick this up on inspection, so just detach the fill flexi-hose before the inspection so the two systems are physically separate.
5. Where is your pressure meter on the UFH circuit?  The potable system will typically be at ~3 bar, but there is no point in having the UFH circuits at anything like that.  1 bar is more than adequate.
6. Double check your cheap rate window.  (It should be on your bill.) It can vary not only by supplier and DNO, but also by type of meter (smart or not).
7. Make sure that the leads from the flexible tail into the timer have crimped ends.  You will be pulling 3kW through these for extended periods and these get quite warm (mine are at about 35°C when operating).  Uncrimped, the multicore flex leads will rapidly tarnish which increases the resistance, increasing the temperature and leading to a runaway failure.  I had all three of my Willis and 2 × SumAmp fail this way and ended up having to strip back 4cm of cable to get untarnished copper and add crimped terminations.  An easy job, but I learnt this at the cost of CH / DHW downtime, plus needing to replace 3 × SSRs at ~£40 e.a.
8. Why have the timer so inaccessible?  You will need to tweak this every 2°C or so in average outside temp, so why crawl under the bench to do so?  (Especially as in my case where this ends up as storage for salt for the water softener, bog rolls, etc.)  Better to remote this to somewhere easily accessible.  Another alternative, if you feel uncomfortable putting in an Raspberry Pi or the like, is to fit a smartphone settable WiFi operated timer switch (possibly with a manual parallel and series switches next to the remote switch to bypass / override).  There are a lot to choose from.  Just read the reviews and make sure that the one you choose has been used for 12A long duration switching.  That way you are your partner can tweak the time on the spur of the moment using your smart phone from your living room.
9. Remember that you really need a water softener on your house supply.
10. Also consider the previously mentioned option of supplementing with a 2kW oil-filled radiator on a timer.  Useful in the Dec-Feb period if you want to just use E7 rate, and also when you want to step the temp up a bit quicker.

Hope this was useful.  ?

 

PS. remember to bleed the system at the upper manifold after a couple of months operation, just in case any air has come out of solution. 

Edited February 4, 2021 by TerryE
Add PS

[Iceverge]

10 hours ago, dnoble said:

Thanks for input everyone.

I’ve got it up and running with a Willis heater off amazon (labelled “Tesla” rather unexpectedly) and a cheap mechanical timer. 

The manifold + pump was the main outlay around £400.

It took about 3 days continuous running the get the slab up from 18 to 25deg.

Now I’m running it only from 12.30 at night till 7.30am when I get cheapo electric.

The floor doesn’t feel “warm” but it no longer sucks the heat from your body when you walk on it and everyone’s stopped moaning.

The house feels remarkable warmer! Temp is hanging around 20deg. 

Here’s a pic. All the gubbins is under the counter in the utility room next to the Sunamp

 

 

Well done. I’m beginning to think this is an excellent method of heating a passive house. It is relatively cheap to install, zero maintenance and super simple so shouldn’t break down.  The main one is though the ability to use all that slab concrete as a giant storage heater.

 

If i suggest to our builder at this stage we dig up the slab to install pipes I suspect the only way he’ll agree is if he can bury me under it!

 

Out of interest have you any idea how much electricity you’re using compared to what phpp predicted?

 

 

[TerryE]

3 minutes ago, Iceverge said:

Well done. I’m beginning to think this is an excellent method of heating a passive house. It is relatively cheap to install, zero maintenance and super simple so shouldn’t break down.  The main one is though the ability to use all that slab concrete as a giant storage heater.

 

Read my blog, and the other posters who have adopted this approach.  We added the UFH to our slab pour with was only a £2K increment.  The other costs were small and pretty much the same as @Iceverge says.

 

4 minutes ago, Iceverge said:

If i suggest to our builder at this stage we dig up the slab to install pipes I suspect the only way he’ll agree is if he can bury me under it!

 

It depends where you are in your build.  I am quite surprised that you didn't go for UFH as this is the norm for passive house supplementation.  You don't need to dig up anything.  If you have a passive-class house then the slab should be heavily insulated / isolated from the external environment or your phpp rating will absolutely suck. The slab is effective part of the heated thermal mass of the house anyway so acts as a storage heater, directly heated or not.  Adding UFH after the slab has been poured only raises the FFL by ~5 cm, and this includes the levelling pour.  The approach still works.

 

4 minutes ago, Iceverge said:

Out of interest have you any idea how much electricity you’re using compared to what phpp predicted?

 

This is nothing to do with the heating approach; the as-built vs as-designed performance is all down to attention to detail during the build.  If your house leaks, or has bad cold bridges or missing insulation then your actual performance can be terrible.  We've come across many horror stories from posters on this site when this attention hasn't been paid.  My advice is to not leave this to your builder but you personally (or a project manager that is truly trustworthy) needs to keep attention to all the details.

 

In our case everything (with one exception) performed as designed.  That one exception was that we have an external stone skin which required a separate outer ring beam to carry it that the foundations SE used rebar coupling between the two ring beams which was a huge thermal bridge. We largely mitigated this as discussed in my blog, but I reckon my actual heating costs are maybe 10-20% higher than planned as a result.  But in the scheme of things ...

 

Whether this works for you depends on the predicted / actual thermal performance of your build.  We have a reasonably efficient 3 storey build and our average daily heating demand Dec-Fed is maybe 35-40 kWh and over the total heating days we do maybe 90% of our heating using E7 @ 9½ p per kWh or under £4 per day.  No conventional CH system installation costs. No radiators anywhere. No boiler maintenance.

 

We've plumbed in the external pipes to allow installation of an ASHP.  (We would have to install one if we ever decided to sell this house as no prospective buyer would believe that something the size of a thermos flask could keep the house so warm.)  Using one might save ~£300-500 p.a. depending on how much of the ASHP running time is in the E7 window.  But then we'd have the installation and maintenance costs, and so I would struggle to get a sensible payback time unless I did this work myself.

 

[dnoble]

I opted to have the UFH pipes installed pre slab pour as an insurance though I had hoped after speaking with Jeremy that I might not need it. It was only 1700 quid extra but very much more expensive to retrofit so I'm glad I didn't scrimp then!

 

have you any idea how much electricity you’re using compared to what phpp predicted?

I didn't do a PHPP prediction and the house isn't certified. 

It should cost about £2.10 per night for the winter months with economy electric if that's any help (7 hours of 10p/kwh with a 3kwh heater)

 

This seems like a parsimonious solution and cost well under a grand. Compared to the 10-15K quotes I was getting install an ASHP (I know cheaper if self installed which I may do one day when they're cheaper and I have more time) it would take a very long time to payback the outlay. Glad I sought the wisdom of this forum!

 

Thanks for all these useful points TerryE.

I'm not entirely sure of the point of lowering the flow rate?It isn't really noisy when running. 

Getting a spare Willis pump really good idea in anticipation.

Any recommendations on water softeners? 

 

Dan

Edited February 4, 2021 by dnoble

[Bitpipe]

11 minutes ago, dnoble said:

 

Any recommendations on water softeners? 

 

Dan

 

We have a bog standard Harvey Dual Flow unit supplied and installed by the plumber, takes the pellet salt which is widely available and inexpensive (I get a bulk delivery of 20 x 25kg bags every 18 months or so). It's wholly automated, does not need any power supply.

 

It's a bit messier to refill than the block salt alternatives and it's run out a few times without me noticing so I now tend to top up weekly on bin night just to make it a regular habit.

 

I recall that block salt was in short supply last year so maybe that's a consideration.

[Iceverge]

13 hours ago, TerryE said:

 

Read my blog

@Iceverge

 

 

 I have and enjoyed it too!

 

13 hours ago, TerryE said:

 

It depends where you are in your build.  I am quite surprised that you didn't go for UFH as this is the norm for passive house supplementation.  You don't need to dig up anything.  If you have a passive-class house then the slab should be heavily insulated / isolated from the external environment or your phpp rating will absolutely suck. The slab is effective part of the heated thermal mass of the house anyway so acts as a storage heater, directly heated or not.  Adding UFH after the slab has been poured only raises the FFL by ~5 cm, and this includes the levelling pour.  The approach still works.

 

We're about to move in so I don't think it's a runner as we'd have to take up all the floors bathware, stairs etc. We have 200mm EPS under the floor and strip foundations not unlike the denby dale version. There is a thermal bridge there but I've modelled it and accounted for it in PHPP and increased the insulation elsewhere.

 

For our build it was about €5000 cheaper to take this approach although that might have changed in the last 2 years as I've noticed a developer near us using the KORE insulated raft on a development.

 

13 hours ago, TerryE said:

This is nothing to do with the heating approach; the as-built vs as-designed performance is all down to attention to detail during the build.  If your house leaks, or has bad cold bridges or missing insulation then your actual performance can be terrible.  We've come across many horror stories from posters on this site when this attention hasn't been paid.  My advice is to not leave this to your builder but you personally (or a project manager that is truly trustworthy) needs to keep attention to all the details.

 

 

+1 on the rigorous oversight needed but I was more hoping @dnoble could provide verification of both the software process and the build integrity with his electricity readings for the heating component. 

 

13 hours ago, TerryE said:

Whether this works for you depends on the predicted / actual thermal performance of your build.  We have a reasonably efficient 3 storey build and our average daily heating demand Dec-Fed is maybe 35-40 kWh and over the total heating days we do maybe 90% of our heating using E7 @ 9½ p per kWh or under £4 per day.  No conventional CH system installation costs. No radiators anywhere. No boiler maintenance.

 

We've plumbed in the external pipes to allow installation of an ASHP.  (We would have to install one if we ever decided to sell this house as no prospective buyer would believe that something the size of a thermos flask could keep the house so warm.)  Using one might save ~£300-500 p.a. depending on how much of the ASHP running time is in the E7 window.  But then we'd have the installation and maintenance costs, and so I would struggle to get a sensible payback time unless I did this work myself.

 

 

I aimed to keep the house as "dry" as possible for long term reliability (100 years +)and with that in mind we have no conventional heating either. Just an UVC for hot water.  I was unconvinced by the Sunamp's benefits given the price uplift. We may well switch in the future. The unoccupied house is currently sitting at 17.8 deg with an overnight topup from a 2kw fan heater ( €1.28/day) and capital cost was €0 as a friend was throwing it out! (BTW I returned my Lidl model mentioned in another thread)  We have left provision to install an Air to Air split unit if out heating demand requires it. About €1500 with a COP of 6. With this in mind I couldn't make the sums work for an ASHP either. Payback was in excess of 25 years. 

 

Much like @dnoble I hope to wait and see what the first full heating season works out as (winter 2021/22) and redo my sums then. BTW a neighbour of ours has a passive house built in 2010 and has never needed to install any heating. SW Ireland gets less temperature extreme than England.  

 

2 hours ago, dnoble said:

I didn't do a PHPP prediction and the house isn't certified. 

It should cost about £2.10 per night for the winter months with economy electric if that's any help (7 hours of 10p/kwh with a 3kwh heater)

 

 

@dnoble

 

Thats a great result.

 

Working backwards for 125 days @ 21kwh/day for heating = 2625kwh/annum  for 240m2 is  10.93kwh/m2/annum. Better than passivhaus. 

[TerryE]

@Iceverge, I think that you would need some form of heat supplementation in the winter months even in S Eire. If you lose X kWh in a day and input the X kWh somehow into the house then the overall temperature will remain in balance.  The internal R values are so much lower than the external that if it is typically of the order of 20 kWh or so then the inter-room variations should be acceptable.

   

The trade off is whether you use straight resistive heating a CoP of 1 at an investment of 10s-100s € or some form of heat-pumped heating at a CoP of say 4 and an investment of 1000s € plus on-going maintenance costs / hassle.  As I have said here and on other posts, I find it difficult to make the case for latter in our house.  A simple bi-block A2A  unit at 9000 BTU / 3kW costs around 500€ and is pretty simple to install and gives you that CoP of 4.  The only problem is that they are bloody noisy so I wouldn't want one running in a room that I was occupying.  

 

UFH is only one valid approach and was feasible in our case because it was a low cost option to include it in our slab pour.   The main advantage for us of doing this over direct air heating is the large thermal inertia of going via the slab means that if we heat during 0-7am, say, then the air temperature doesn't actually peak until around 11 am and the ripple over the day is only around 1°C.

 

As to the control of this, I use an RPi which controls some SSRs.  In essence the approach is simple and you really only need 2 inputs: the predicted average external temperature , E, over the next 24hrs and the average internal temperature over the last, T.  I compute the total heating demand of the form aE + b + k(T - T_target) once a day, and that determines how long I am going to need the supplementation.  I do the bulk overnight in the E7 and top up a slice hourly thereafter, but only if the current temperature is below T_target.  I use NodeRED for this, but any scriptable implementation will do.  I did a bit of perfboard building to mount connectors for my SSR output and input thermometers, but you don't need to do this, as you can get WiFi or USB attached power switches and thermometers off-the-shelf these days.

Edited February 4, 2021 by TerryE

[Gone West]

17 hours ago, Iceverge said:

I aimed to keep the house as "dry" as possible for long term reliability (100 years +)and with that in mind we have no conventional heating either. Just an UVC for hot water.

That was exactly our thought and we keep our house warm with electric towel rails.

 

17 hours ago, Iceverge said:

We have left provision to install an Air to Air split unit if out heating demand requires it.

IIRC Owlman on the GBF heats his house with A2A HPs.

[Iceverge]

I know it rules out the possibility of using an ASHP but has anyone embedded resistive wire heating in the slab (not on top of)?

 

You could have the same delayed energy release of a water heated slab with no moving parts and no water. 

[SteamyTea]

5 minutes ago, Iceverge said:

I know it rules out the possibility of using an ASHP but has anyone embedded resistive wire heating in the slab (not on top of)

Was popular in the 1960s to do this in flats, was because energy was going to be too cheap to meter.

 

The problem may be that an element will be running at a higher temperature than a liquid system, this may cause hot spots.  Easier it heat a liquid first and then pump that around.

[Iceverge]

3 minutes ago, SteamyTea said:

Was popular in the 1960s to do this in flats, was because energy was going to be too cheap to meter.

 

The problem may be that an element will be running at a higher temperature than a liquid system, this may cause hot spots.  Easier it heat a liquid first and then pump that around.

Ah, I didn't consider the hotspots. 

 

I suspect electricity will never get cheaper or more expensive than the majority can afford to pay. 

[ProDave]

37 minutes ago, Iceverge said:

I know it rules out the possibility of using an ASHP but has anyone embedded resistive wire heating in the slab (not on top of)?

 

You could have the same delayed energy release of a water heated slab with no moving parts and no water. 

You have just re invented the electric storage heater, with all the same problems making sure the overnight heat input is correct for the daytime heat actually needed. 

 

Not far different to what others have done but you want some decent controls to predict the amount of heat needed.

[Iceverge]

1 minute ago, ProDave said:

You have just re invented the electric storage heater, with all the same problems making sure the overnight heat input is correct for the daytime heat actually needed. 

 

Not far different to what others have done but you want some decent controls to predict the amount of heat needed.

Yup, all be it 100 times larger!

 

@TerryE has cracked it I think, although the approach of Jeremy Harris with a simple thermostat is probably good enough. 

[joe90]

2 hours ago, Iceverge said:

the approach of Jeremy Harris with a simple thermostat is probably good enough. 

It was my approach (cus there’s no way I could build or programme something complicated ?‍♂️) and it works very well, the only problem I have is the hysterisis is too great (3’) so I need to replace it with one that’s 1’.

 

actually I have an electric storage radiator, lecky drives the ASHP which heats the slab which slowly releases it to the house ?.

[Russdl]

I really think this is the best way to heat a passive house (kudos to TerryE,  I think he was the inventor?). 

 

My Willis heater UFH was recently commissioned and within a few days the trades were asking for the heat to be turned down. We have no controls for it so it was turned off. A week later, in freezing conditions it was still pleasantly warm inside. 

 

We do have a problem though as the left hand of the two Willis heaters doesn't work, and evidently from my energy usage it never has, so I guess it was never tested. Who would have thought.

 

 

There is a peak in consumption as they were turned on on the 27th Jan but not enough of a peak to suggest that both heaters were working, probably just the RH Willis heater and the kettle. The following day it's just one Willis heater and the odd bit of kettle action. It's not the reset button on the bottom, so it needs to be replaced.

 

 

 

I think I've found the exact model and as @TerryE pointed out, they are so cheap I may as well get a couple of spares. I guess it's going to be easy to replace.

 

 

 

 

How do I go about replacing it without filling the whole system with air again - or is that inevitable?

 

I also need to get some inhibitor in the system, should I do it when I replace the defective Willis heater or should I run the system for a few days to make sure all the air is out before I put the inhibitor in?

 

 

 

[PeterW]

Change the thermostat first. They are prone for issues as they are quite short and it could be a duff one that has tripped out and not reset. 

[Russdl]

1 minute ago, PeterW said:

Change the thermostat first

 

Can you give me more clues? How would I do that?

[joe90]

Can only find this fir an immersion but should be the same.  https://www.diydoctor.org.uk/projects/immersionheater.htm

[Russdl]

@joe90 That looks like it may be the thing, they look very similar but I wonder if it's worth the faff?

 

Any idea how I check to see if that really is the bit that is screwed? Well outside of my skill set which is why I got a 'pro' in to do all that stuff in the first place...

[PeterW]

It’s inside the head. Left looks to be off anyway ..? 
 

Small but on the bottom of the unit, steel lid comes off. The thermostat will be wired into the live and then there will be a wire off it to the element. Unscrew the contacts and it will drop out. Will be a 7” thermostat. 

[joe90]

13 minutes ago, Russdl said:

@joe90 That looks like it may be the thing, they look very similar but I wonder if it's worth the faff?

 

Any idea how I check to see if that really is the bit that is screwed? Well outside of my skill set which is why I got a 'pro' in to do all that stuff in the first place...

They are pretty cheap, good to have as a spare anyway, saves draining down etc, just make sure the electrics are isolated if you remove it.  To check it in situ, (with the electrics on) use a multimeter or tester screwdriver (neon in the handle) and see if you have voltage both sides of the two terminals on it, it’s basically a switch that’s controlled by heat, if it’s cold it’s switched on, if it’s hot, it’s will switch off.

 

 

Edited February 14, 2021 by joe90

[Russdl]

2 minutes ago, PeterW said:

Left looks to be off anyway ..?

 

Good spot, it had been on for 3 days before I worked out it wasn't working. When it became obvious the LH one wasn't working, I left it off.

 

5 minutes ago, PeterW said:

Small but on the bottom of the unit, steel lid comes off. The thermostat will be wired into the live and then there will be a wire off it to the element. Unscrew the contacts and it will drop out. Will be a 7” thermostat. 

 

That sounds even simple enough for me to do, thanks.

 

6 minutes ago, joe90 said:

To check it in situ, (with the electrics on) use a multimeter or tester screwdriver (neon in the handle) and see if you have voltage both sides of the two terminals on it, it’s basically a switch that’s controlled by heat, if it’s cold it’s switched on, if it’s hot, it’s will switch off.

 

As it happens we had an electrician in the house for a totally unrelated reason whilst I was away last week. The good lady asked him to take a look at the suspected defective Willis heater and he declared it dead, no mention of the thermostat specifically being dead just "it's dead". The electrician as it happens is well versed in Willis heater UFH having worked with the installer of our system in the past.

 

 

[joe90]

7 minutes ago, Russdl said:

just "it's dead".

not wishing to question your electrician, but still might be worth testing to find out what’s wrong, Do you have a multimeter Russ? Or a testing screwdriver with a mean in the handle?

 

Edited February 14, 2021 by joe90