Advice on space heating passive house

[Iceverge]

@TerryE has chapter and verse on them on his top blog. 

[Russdl]

@dnoble I’m no plumber, though I suspect I’m going to have to learn fast.
 

This is our set up, sadly still not up and running after many months so I can’t comment on its efficiency or otherwise. 

 

The Willis heaters are on the right of the picture with a grey buffer (or is it expansion?) tank above it. The UFH manifolds are hidden behind the non commissioned sunamp. 

 

 

[TerryE]

Yup, we have a stone-clad 3 storey MBC TF house with UFH in the groundfloor slab.  This UFH is heated by a single Willis heater.  Though typically Dec -> Feb or thereabouts I also have a small electric oil-filled heater in an office that also dumps some kWh into the first floor during E7.  The single Willis could do everything, but using the heater means that we do most of the heating on E7.  The house stays at ~22.3 °C with maybe a ½-1°C ripple over the day.

 

We've also got the ducting in place for an external ASHP, but after over 2 years living in the house, I haven't bothered to buy and to install one.  It might save maybe £4-500 p.a. on electricity charges, but then I've got the purchase and installation costs to amortise and this only makes economic sense if I do the work. If I get an installer to do it, then I won't even recover the costs over the expected lifetime of the ASHP, and I would also need to consider an annual maintenance contract.  Nope, I think that "keep it simple, stupid" is the best option for us.

 

BTW, no buffer tank.  No extra pump.  The slab is the buffer, all 27 tonnes of it.  The UFH manifold does include a TMV but this is because it was std in the Wunda kit.  It is always set to open so the single pump will always cycle the water through the UFH loops (which are configured as a single zone) and the Willis.  Each night at midnight my NodeRED control system calculates the heating estimate based on the forecast temp for the next 24 hours and the delta between the actual average house temp for the previous day and the set point (22.3).  This number is then used to plan the heating profile for the Willis the next day.  I don't really get involved in the day-to-day control; the system just does its thing.

 

Edited January 9, 2021 by TerryE

[SteamyTea]

8 hours ago, joe90 said:

Anyone

Was it @TerryE

[Russdl]

@SteamyTea check the post above yours ?

[SteamyTea]

8 minutes ago, Russdl said:

@SteamyTea check the post above yours ?

Seems events overtook me.

[dnoble]

2 hours ago, TerryE said:

Yup, we have a stone-clad 3 storey MBC TF house with UFH in the groundfloor slab.  This UFH is heated by a single Willis heater.  Though typically Dec -> Feb or thereabouts I also have a small electric oil-filled heater in an office that also dumps some kWh into the first floor during E7.  The single Willis could do everything, but using the heater means that we do most of the heating on E7.  The house stays at ~22.3 °C with maybe a ½-1°C ripple over the day.

 

We've also got the ducting in place for an external ASHP, but after over 2 years living in the house, I haven't bothered to buy and to install one.  It might save maybe £4-500 p.a. on electricity charges, but then I've got the purchase and installation costs to amortise and this only makes economic sense if I do the work. If I get an installer to do it, then I won't even recover the costs over the expected lifetime of the ASHP, and I would also need to consider an annual maintenance contract.  Nope, I think that "keep it simple, stupid" is the best option for us.

 

BTW, no buffer tank.  No extra pump.  The slab is the buffer, all 27 tonnes of it.  The UFH manifold does include a TMV but this is because it was std in the Wunda kit.  It is always set to open so the single pump will always cycle the water through the UFH loops (which are configured as a single zone) and the Willis.  Each night at midnight my NodeRED control system calculates the heating estimate based on the forecast temp for the next 24 hours and the delta between the actual average house temp for the previous day and the set point (22.3).  This number is then used to plan the heating profile for the Willis the next day.  I don't really get involved in the day-to-day control; the system just does its thing.

 

Thanks for this. I think I might go for this as a short term plan. I already have E7 leccy which tops up the Sunamp.

 

I have a mate who’s a qualified electrician  and plumber.

Currently there are just a dozen UFH pipes sticking out of the slab.

As well as the Willis pump and a suitable manifold, what else would I need to set it all up?

I think just a timer so it comes on for 6 hours overnight would be as much control/monitoring I’d need.

 

[willbish]

Hi Dan,

 

This thread has a few pointers and pictures of how not to do it

 

 

[TerryE]

2 hours ago, dnoble said:

I think just a timer so it comes on for 6 hours overnight would be as much control/monitoring I’d need

 

I personally think that just using a timer could be a bit problematic.  Read my blog posts on how I set my system up.  I use a Raspberry Pi based system with 4 solid state relays (SSRs) switching the 2 × SunAmps, the circulating pump and the Willis.  I take a lot of temperatures and a met-office feed to drive the calculation of how many minutes of heat I need each day.  This might seem complicated, but not for me: I have been programming for over 50 years and helped develop some real control systems in my time.  This approach for me is straightforwad and cheap. 

 

I don't say that a simple timer based system couldn't be made to work satisfactorily, but more that I simply haven't done this so I don't know.  However if you are going this route then IMO you will need to limit the out temperature of the water going into the slab to no more than, say, 35 or 40 °C  by trimming the thermal cut-out on the Willis heaters or having a separate on on the manifold out.

 

Just for interest here are the peak out, return and Willis temperatures as well as the average ground floor hall temp for the last couple of months.  The average outside temp can shift from 10°C to 2°C in a day or two and this has a big impact on the daily heat losses and therefore how much you need to add back in to keep the house temperature stable.

 

 

[dnoble]

Hi Will. Thanks for this, looks important.

Thanks too, Terry. Is this because there’s a risk of overheating or damaging the slab? 

I assumed this will be a slow, non-reactive system. The house is fairy constant temp between 15-20deg and I was hoping that just warming the slab for a few hours overnight would bring up the background temp by a few degrees. I don’t have any programming skills and want to keep everything  as simple/idiot proof as possible. 

 

I am also wondering if, using a Willis heater (obv element switched off) would there still be a way of cooling the slab in summer by circulation cold water as someone mentioned previously in this thread?

[SteamyTea]

3 minutes ago, dnoble said:

I am also wondering if, using a Willis heater (obv element switched off) would there still be a way of cooling the slab in summer by circulation cold water as someone mentioned previously in this thread?

Circulating may even out the temperature (closer to the mean slab temperature) which may cause a bit of cooling in areas that are overly warm, but will only cause a small temperature drop.

Much of this is to do with the specific heat capacity of air (needs little energy to raise its temperature, and concrete (or whatever the floor is made from).

 

[joe90]

@Jeremy Harris built his own programming a bit like @TerryE but stopped using it in favour of a simple room stat which he found worked better ( I know zilch about programming ?).

[TerryE]

4 hours ago, joe90 said:

@Jeremy Harris built his own programming a bit like @TerryE but stopped using it in favour of a simple room stat which he found worked better ( I know zilch about programming ?).

 

Actually our approaches were different. Jeremy used a buffer tank and attempted to micro-control the UFH circulation temperature.  My program just does some calcs every midnight to work out, say: tomorrow I'll need 20 kWh of heat going into the slab.  As much heat as possible is dumped in during the E7 window and the rest in short bursts each hour once the hall temp falls below 22 °C.  If in reality I needed 25 kWh then no big deal: the house temperature fails by maybe 0.1 °C, and because I have a delta temperature feed forward compensation, the system will adjust for this and put in a bit more the next day to compensate.

 

Using a fixed time each night will probably work so long as the flow temp into slab is max limited (and yes this is to avoid over stressing the system).  However you will need to do a similar compensation manually: what is the temperature forecast over then next few days; is the house slowly heating up or or cooling down and adjust the timer setting accordingly.  A small hassle every couple of days, that I don't have because my calculation is automated.

Edited January 9, 2021 by TerryE

[joe90]

15 minutes ago, TerryE said:

Actually our approaches were different.

Ah, didn’t know that. I am still thinking about using E7 (note to self “get on with it!”). My UFH is within a 70mm screed rather than slab. I think my supplier charges £100 to change the meter!

Edited January 9, 2021 by joe90

[SteamyTea]

5 hours ago, TerryE said:

Actually our approaches were different.

 

5 hours ago, TerryE said:

As much heat as possible is dumped in during the E7 window

 

5 hours ago, TerryE said:

the temperature forecast over then next few days

If you really wanted to get posh, and do some interesting programming, link in wind vectoring to it.  This could be especially useful for dumping PV generation in during the hours of daylight, for that 'fine tuning' and minimizing imports.

Trouble is, with a thermally stable house, not really worth the effort.

[TerryE]

On 09/01/2021 at 13:04, dnoble said:

I am also wondering if, using a Willis heater (obv element switched off) would there still be a way of cooling the slab in summer by circulation cold water as someone mentioned previously in this thread?

 

Sorry, I missed addressing this point.  IMO, the major functional advantage of an ASHP would be to provide slab chill-down in the peak summer months, as we don't currently have this.   

 

Another option -- if we had planned it during the build would have been to add something like a single 12,000 BTU wall-mounted (room) bi-block aircon.  These are relatively cheap at ~£450 and can pump ~3½ kW heat in or out of the house at a CoP of 3-3½ and hence an electricity use of ~ 1kW.  As Nick (@SteamyTea) mentioned, the whole house is pretty thermally stable: there is a lot of thermal capacity internal to the insulation layer and not much internal insulation so the interior of the house stays in broad balance. The insulation keeps the warmth in in winter and the heat out in the summer.  Putting such an aircon in our living room or kitchen / diner and running it for say 7 hrs during the E7 window could dump up to 20kWh heat in the summer or add the same in the winter for just over 50p per day.  Yes, they are a bit noisy, but we don't need to run it when the room is in use.  This would give us most of the advantages of an external monoblock ASHP,  with perhaps half the operating cost savings  at a fifth of the investment cost.

 

However in the meantime, we tend to operate in one of two modes: for 7 months a year, the house is air-tight using the MVHR to recover heat and the Willis topping up if necessary and the house temperature is stable at that 22-23 °C.   For 5 months a year we've got heat excess so the Willis never comes on, and we use MVHR bypass or simply opening the odd window to dump heat.  Our house has a SSE  principle face. We have a 3-storey hall way with a velux in the loft landing so we can open this and exploit the heat chimney; we open a back window (or two) in the morning when the back is cool and a front window in the evening when the front is in the shade.  The house will typically peak at perhaps 25°C during August peaks, but I don't mind that.  The hassle is having to open and close windows.  Yes, the temperatures vary a bit more during the summer months, but this also gives a summer feel to the house.

 

Thinking a bit more about this, I think I might discuss adding a room aircon with Jan. 

Edited January 11, 2021 by TerryE

[Dan F]

@TerryE Seems your system works very well, but wouldn't an ASHP also reduce your DHW costs where an air-con unit couldn't? 

 

[TerryE]

@Dan F, sorry for my late reply.  The trade-offs for efficient DHW are nuanced.  We have a KISS approach of having a couple of SunAmp PVs (the older and IMO better engineered model) heated by E7.  Quite honestly we just don't use enough DHW for any running cost savings to merit the extra complexity.  If I had a young family and lots of hot baths per day, then we might have a different sweet spot.  Getting an ASHP to heat up to 35°C can run at a CoP of approaching 4. Getting up to the high 40s can drop the CoP well below 3.    You could consider a hybrid where you use a buffer tank heated to, say, 35°C and use this via a PHE to preheat the water passing through a SunAmp PV so that the E7 energy boost the DHW from 35°C to 48 or whatever you have as your DMW mix-down temp.

 

The one big advantage of our system is that we don't have a services room.  All of our services fit into a cupboard off the ground-floor toilet measuring roughly 0.7m × 1.4m and this houses our SunAmps, UFH manifolds, water softener, Potable manifolds, riser etc. -- and is used as general storage as well.  There is very little that can go wrong. 

Edited January 16, 2021 by TerryE

[Dave Jones]

On 07/01/2021 at 13:07, dnoble said:

We're in our second winter in an MBC timber frame house. 

5 bed, 4 kids. 240m2 approx

It has UFH pipes installed but I experimentally haven't connected them up. 

I think it's OK (with thermal longjohns etc ), but some of the less robust members of my house feel we need "proper" heating. 

It was 15 degrees inside this am (-2 outside overnight).

We do have a plug-in panel heater which will warm a single room quickly. 

We have a 9kW Sunamp unit which supplies hot water. This is mainly charged by solar PV. 

 

Question; 

Should we connect UFH to the Sunamp? Obv this will greatly increase drain on it and it'll need more topping up from the grid.

Is it worth getting an ASHP? I have left penetrations through the wall for one. 

If so would this heat the Sunamp more efficiently than grid, or can it directly connect to the UFH?

Or would it be most expedient just to get a couple of extra panel heaters on smart timers?

I'm reluctant to spend many Ks and get my head round yet more technology for the sake of a few degrees or saving a few quid. Is another big mental and financial outlay worthwhile (sorry for a rather subjective question)

Dan

 

 

 

 

these people walk among us! Freeze the family as they too tight to put the heating on.

 

How your mrs hasn't kicked you into touch by now is amazing!

[Simon Brooke]

We are now in our second winter with a system very similar to yours although I suspect your mbc frame will have a better airtightness rating than ours. Sunamp themselves have accepted that their spec of a 9kw battery is insufficient and are exploring ways to help which  may involve a second battery and an ashp. This help does seem a long time in arriving though!

In the meantime we have been experimenting with the underfloor heating using the Sunamp and believe we are quite close to a solution that will work for us. We have closed the loops that feed the bedrooms so now only have underfloor heating running in the daytime living areas. We are on economy seven and start the heating at 1.30am which gives the battery 1.5 hours of top up. The heating then continues to 4am which gives a further 3 hours to recharge the battery for the day's hot water. In addition we have two electric towel rails which are on for a total of 4 hours . Temperature in the living room is 21 degrees this morning which is fine for us. We have consistently used 19 kw of cheap rate eletricity over the past 30 days which I estimate is split roughly 50/50 hot water and heating. I am hoping we will need heating for 100 days each year but time will tell. If we do conclude that we need additional then a Willis heater seems the simplest add on with no maintenance costs. Hooe this helps.

[Pete]

25 minutes ago, Simon Brooke said:

We are now in our second winter with a system very similar to yours although I suspect your mbc frame will have a better airtightness rating than ours. Sunamp themselves have accepted that their spec of a 9kw battery is insufficient and are exploring ways to help which  may involve a second battery and an ashp. This help does seem a long time in arriving though!

In the meantime we have been experimenting with the underfloor heating using the Sunamp and believe we are quite close to a solution that will work for us. We have closed the loops that feed the bedrooms so now only have underfloor heating running in the daytime living areas. We are on economy seven and start the heating at 1.30am which gives the battery 1.5 hours of top up. The heating then continues to 4am which gives a further 3 hours to recharge the battery for the day's hot water. In addition we have two electric towel rails which are on for a total of 4 hours . Temperature in the living room is 21 degrees this morning which is fine for us. We have consistently used 19 kw of cheap rate eletricity over the past 30 days which I estimate is split roughly 50/50 hot water and heating. I am hoping we will need heating for 100 days each year but time will tell. If we do conclude that we need additional then a Willis heater seems the simplest add on with no maintenance costs. Hooe this helps.

We moved into our passive house just before xmas and are still adjusting things to suit how we live. I notice you have shut the heat off to the bedrooms, how has impacted on your energy consumption and the comfort levels in the bedrooms?

[ProDave]

I think there is a misconception here that a "passive house" does not need heating.

 

I think in the UK climate most will need some form of heating, but just not very much of it.

 

 

[Simon Brooke]

Shutting off the bedroom heating has made a big difference. Last year when we ran the underfloor heating as recommended we found that the 9kw Sunamp ran out of puff very quickly leading to cold water rather to often. As noted on other Buildhub posts the mvhr is not that efficient in redistributing heat so we have an approx. 2 degree difference in the room temps. The cooler bedrooms suit us , the only downside is that the bathrooms which are part of the bedroom loops (bungalow) are a bit chilly and definitely need the towel rail boost. I recognise that our approach is a compromise and does make proper use of the underfloor heating but the costs of an ashp ,both capital and servicing , coupled with the disruption to the finished build are putting us off that route.

[TerryE]

@Simon Brooke, Do you have E7?  We don't have any CH on the top two floors, and like you during the coldest months the 1st floor is maybe 1½ - 2 °C cooler ran the ground floor. However I use a small oil-filled electric radiator in the doorway of my study which opens onto the hall landing.  This is on a timer and dumps maybe 10 kWh space heat onto the first floor (and second floor by convection), and this gets rid of this layering.   It's 10kWh into the general mix for house heating for under £1 per night.  Still, it keeps the first floor nice and means that I can wander around bollock naked during the night and still be very comfortable -- though my wife (and son who live on the top floor) might not be, but that is only visual ?.

[dnoble]

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