First year Heating Energy Use in Passive(I hope) House

[SteamyTea]

1 hour ago, AliG said:

 

I am less sure about the energy needed to evaporate water

243,000 J/g at 30°C.

So 67.5 kWh per litre.

[JohnMo]

I've been monitoring our gas consumption and it remarkable how the gas consumption has decreased since moving in last September.  When we first put the heating on we used loads of gas almost double for the same weather conditions, compared with a couple of weeks ago. Some of the decrease is refining the way the heating system is controlled, I suspected part drying out and part getting the building up to temperature, but also part think what I have done wrong.

 

Our average from October to now for an exposed (NE Scotland) site is 6.8 W/m2 for heating excluding DHW.

[MikeGrahamT21]

Could be drying out still… last time I did a rough WUFI calc for adding EWI to my 60 year old bungalow, it took around 4-5 years for the humidity in the masonry to absolutely settle out and that’s a long time after construction.

[AliG]

4 hours ago, SteamyTea said:

243,000 J/g at 30°C.

So 67.5 kWh per litre.

I think that it is around 2300KJ per gram, so 0.67kWh per litre. Decimal points got moved somewhere there.

 

 

[SteamyTea]

https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

Says 2257 J/g.

 

So yes, think I did get it wrong.

So ten times less as you said.

[TerryE]

@Iceverge,  I would get too upset about the delta.  As you say, there are a lot of reasons for the variation as we've also found, e.g. you find that you prefer a warmer environment than your PHPP set points; laxness about sealing the house on ingress/exit, ...

 

Like us, you now have a baseline, and you really need to base any potential changes in terms of RoI and any assessment of increased benefit vs hassle and stress of change, and we've found that this sets a high barrier to change.  However, a couple of thoughts:

• What sort of time constant does your house have?  E.g. ours loses about 1°C per day in deep winter if unheated.  With this sort of house response you can shift heating times without noticeable effect: you need to put X kHr into the house per day, and it really doesn't matter when  and where you do it.  I don't know if you use a dual tariff, but when we did the calcs this saved use about 40% on our cost of electricity: heating, DHW heating, dishwasher and washing machine are all on cheap rate.  We have a larger (~260m² IIRC) house, and use a 3kW Willis + UFH for our primary heating, but I also have a 2kW oil-filled rad on our 1st floor landing in the winter that I run for a few hours overnight to top up the heat in the upper floors.  You could just run your heater overnight (or add another if necessary).
   
• To keep your house near setpoint, you just need to top up the heat daily. It does really matter where or when.  You could consider adding a split aircon unit in a hallway or living room (something like this sort of unit). There are lots of choices at around 12K BTU / 3kW for around 600€.  This can easily dump a few kW into the house at a CoP of around 4.  Don't put in a bedroom, because they still generate around 30 dbA at a medium setting which is audible and you will probably want to run it at night for cheap rate pricing.  Jeremy Harris fitted one and did a topic on doing this (here).  He used a pre-charged one that can be fitted without any specialist certifications.   So long as you do and seal the through-wall duct and run the external SWG feed (the internal unit is powered from the external), and mount the units physically, then paying someone to wire it in should only be in the 100€s. 
   
• If you are looking at Home Automation, then HomeAssistant can be used to schedule your rad timing and control most WiFi enabled aircon units.

Edited April 18, 2022 by TerryE

[Iceverge]

4 hours ago, TerryE said:

What sort of time constant does your house have?  E.g. ours loses about 1°C per day in deep winter if unheated.

 

I don't know. It's slow for sure. When we had power cuts in February it was still 20 deg after a day without heating but it wouldn't have been much below 10deg outside. 

 

 

4 hours ago, TerryE said:

With this sort of house response you can shift heating times without noticeable effect: you need to put X kHr into the house per day, and it really doesn't matter when  and where you do it

 

 This was my original intention. However as the convective radiator has to heat the air first of all, and then the air heats the structure to buffer the energy for later. It doesn't seem to work as well as directly heating an insulated slab. If we pumped in more heat the air temp would get too high and there'd be complaints! As it is we run the rad slightly colder during the night and turn it on again at about 6pm on a low setting to keep everything toasty. 

 

5 hours ago, TerryE said:

I don't know if you use a dual tariff, but when we did the calcs this saved use about 40% on our cost of electricity: heating, DHW heating, dishwasher and washing machine are all on cheap rate

 

I know. The fight is real!  For us night rate is 1/2 day rate. I'll keep petitioning. 

 

 

5 hours ago, TerryE said:

To keep your house near setpoint, you just need to top up the heat daily. It doesn't really matter where or when. 

 

Consistency is key here to make any kind of inference. As I speak some small hands are dragging the cheap radiator across the kitchen like a doggy and little fingers are happily adjusting the dog's "numerical face" . As usual the real problem with living in an experiment is that not everyone treats it with quite the scientific rigour as the main professor.  

 

 

5 hours ago, TerryE said:

  You could consider adding a split aircon unit in a hallway or living room (something like this sort of unit). There are lots of choices at around 12K BTU / 3kW for around 600€.  This can easily dump a few kW into the house at a CoP of around 4.  Don't put in a bedroom, because they still generate around 30 dbA at a medium setting which is audible and you will probably want to run it at night for cheap rate pricing.  Jeremy Harris fitted one and did a topic on doing this (here).  He used a pre-charged one that can be fitted without any specialist certifications.   So long as you do and seal the through-wall duct and run the external SWG feed (the internal unit is powered from the external), and mount the units physically, then paying someone to wire it in should only be in the 100€s. 

 

I'm familiar with that thread, it sounds quite doable. I have a spot nominated for it with a fused spur too.

 

However, like you say , the value in doing anything is really financially questionable when dealing with small numbers. I'm procrastinating on that for the moment whilst waiting for more data to come in. There's probably easier ways to save €200-300 per year from a family budget. 

5 hours ago, TerryE said:

If you are looking at Home Automation, then HomeAssistant can be used to schedule your rad timing and control most WiFi enabled aircon units.

 

To give you an idea of my mindset on the topic I'm thinking about doubling the current automation levels by investing in a second one of these!  

[SteamyTea]

53 minutes ago, Iceverge said:

 

Or go digital, for 11 quid.

https://www.ebay.co.uk/itm/184762902220

 

54 minutes ago, Iceverge said:

There's probably easier ways to save €200-300 per year from a family budget.

Drive up hills at a constant speed, accelerating against gravity cost way too much.

[Iceverge]

4.6l/100km on a round trip to the seaside today, pleasantly surprised myself. 

 

Of course the real the true Passiv aficionado would have taken a canoe to the local stream to go there and hand glider home on the prevalent South Westerlies. 

 

 

 

 

Or better yet, wouldn't have gone, just hopped into a cold bath with some seagull noises 

[TerryE]

  

6 hours ago, Iceverge said:

12 hours ago, TerryE said:

With this sort of house response you can shift heating times without noticeable effect: you need to put X kHr into the house per day, and it really doesn't matter when  and where you do it

 

 This was my original intention. However as the convective radiator has to heat the air first of all, and then the air heats the structure to buffer the energy for later. It doesn't seem to work as well as directly heating an insulated slab. If we pumped in more heat the air temp would get too high and there'd be complaints! As it is we run the rad slightly colder during the night and turn it on again at about 6pm on a low setting to keep everything toasty. 

 

I agree that heating a lump of concrete in the 10s of tonnes does act as a good smoothing buffer, but I did play around with a simple thermal model to investigate the characteristics of the house dynamic.  Do you have a digital spot thermometer? You can get them for under £20 now; borrowing one is even cheaper.  Probably not wonderful in terms of absolute accuracy but good within ½°C or so relative.

 

What is your total daily electricity use in winter?  Let's just use 35 kWh as a strawman.  You can really just about ignore the split between DHW, rad, other use because thanks to entropy every kWh you use (excepting perhaps HW that goes down the plughole) ends up as heat in the environment.  And that heat is slowly lost externally through MVHR losses, radiation through fenestration, and radiation through other external facing surfaces.  Let plug in some rough numbers, but you can do the exact ones.  If 50% of the heat is lost through surfaces and you've say 400 m² external surface, that's about 3½W per m², so your external walls will be roughly ½°C cooler than the average air temperature.  In other words 2 shades of bugger all. 

 

Try checking external and internal surfaces with a spot thermometer.  I did.  The worst I found in our house was along the edge of the reveals where the plasterwork meets the window frames which was maybe 3°C colder than room temp.  Basically everything else was within a degree or so of the same temp.  The lag transferring heat from airspace to surfaces isn't that great.  Though local overheating can arise if you put the rad in a room and shut the door. 

 

That is why I suggest that you invest in a second rad, and as Nick suggests more child-safe digital timers.  (Masking tape over controls to denote "do not touch" and whatever your favourite admonishment techniques should be effective with tinies.)  A good location for the rad is a hallway, and leave some adjacent doors open.  The MVHR can help circulate the heat throughout the house as well.  

 

Edited April 19, 2022 by TerryE

[SteamyTea]

7 hours ago, Iceverge said:

4.6l/100km

Around 61 MPH gallon then.

Sea is only a couple of miles from me.

7 hours ago, Iceverge said:

Or better yet, wouldn't have gone, just hopped into a cold bath with some seagull noises 

Tell that to the emmets in St. Ives.

[Iceverge]

21 hours ago, TerryE said:

Do you have a digital spot thermometer?

 

No, but I'm hoping Santa will rise to a thermal camera at some stage. 

 

21 hours ago, TerryE said:

 

What is your total daily electricity use in winter?  Let's just use 35 kWh as a strawman.

 

Very close, about 38kWh! 

 

21 hours ago, TerryE said:

excepting perhaps HW that goes down the plughole

 

This and the somewhat greedy biocycle wastewater treatment unit. 

 

21 hours ago, TerryE said:

That is why I suggest that you invest in a second rad, and as Nick suggests more child-safe digital timers.  (Masking tape over controls to denote "do not touch" and whatever your favourite admonishment techniques should be effective with tinies.)  A good location for the rad is a hallway, and leave some adjacent doors open.  The MVHR can help circulate the heat throughout the house as well.  

 

 

I suspect it'll be next winters task at this stage.  I'll probably screw it to the wall of the utility out of harms way, maybe with a digital electricity meter in the fuse box too. A part of the experiment was to see where the best spot was for a single heat source. As you say it doesn't make much of a difference so long as you don't choose too small a room and close the door. 

[TerryE]

I use a Sonoff Power-usage plug that I can control with my Home Automation system, but you can also get Android timer apps and they are also programmable with Google Home if you are happy letting Uncle Google control your devices. 

[Iceverge]

Living quite too much of my life in hotels with unusably complex automation systems I was determined to have as little as possible in the house. A light switch by the door of every room and a couple of mechanism timers.  ( I lie, we have a robot vacuum too)

 

 

In good news I went to the dump today and found this fine article someone had disposed of. Not too often you find a fully working entire "central heating" system for free!!!

 

 

Gotta love low energy demand houses😁

[Iceverge]

So we just left the house unoccupied for a few days. 

 

Nothing remained running except the MVHR at normal occupied levels, the fridge freezer, the waste treatment plant blower and the borehole pump. 

 

Total background load was about 87w. ( only rough calcs, 6kWh over 69hrs). This is about €120 per year on our current tariff.  €0.22 per kWh from 09:00-00:00 and €0.11 from 00:00 to 09:00.  

 

I suspect the waste water treatment plant is the chief suspect. I will revisit the next time we take a few days out of town. 

 

[Iceverge]

On 27/03/2022 at 18:50, Iceverge said:

PHPP predicted 14kWh/m2/year *175m2 = Total of 2450kWh total annual energy for heating. 

Our daily electricity usage was 18.1 kWh/day in the summer months. Of this 10kWh for DHW.  ( 2 adults + 2 preschool kids) 

Our total annual usage was 9876 kWh. Isolating DHW at 3650kWh and everything else at 2956 kWh left 3270kWh for space heating. 

 

 

An update and comparison for years 2021/2022 and 2022/2023

 

I've adjusted the dates to the end of April to ensure I encompass a complete heating season. 

 

April 21 to April 22 9639 kWh

April 22 to April 23 9125 kWh 

 

Total 49kWh/m2/annum energy usage. 

 

For weather comparison heating degree days at 15.5deg from a local station were

 

April 2021 to April 2022  HDD 1916.7

April 2022 to April 2023 HDD 1919.5

 

So for an almost identical heating demand we had a reduction of about 5% usage. I don't think the house was running colder. It has dried out a bit however. 

 

 

This equated to about 3100 kWh of heating supplied to the house or 16.75kWh/m2/annum. Disappointingly still outside the PHPP predicted amount.  Peak heating load has never exceeded about 1500w (supplied by 2 resistance heaters)  which betters the PHPP prediction so far.

 

Annual cost this was broken down to 1350kWh @ €0.47/day-unit and 1650kWh @ €0.14/-night-unit so €533+€231 per night unit so our years heating costs were €764. 

 

 

DHW is still about 10kWh/day @ €0.14 so about €511 per year. 

 

 

I've bought a Daikin FTMX25R A2A heat pump to be installed this summer so that should take the heating bill to less than €200. Solar PV is the eventual plan for the DHW hopefully taking that to less than €200/year too. 

 

 

I've been searching my head for the reasons the house isn't matching  PHPP. We're about 600kWh short. 

 

My leading theories in no particular order. 

 

      1. I have a very old copy of PHPP and it overestimates internal gains for modern appliances. 

      2. Our MVHR is closer to 75% efficient rather than the stated 86% (I only DIY balanced it) 

      3. My wretched family have been letting windows and doors open!

      4. The EPS beads k value of 0.033 is optimistic. 

      5. Thermal bridging at the wall floor junction is greater than accounted for. 

      6. The thermal bridging around the windows is greater than I accounted for. 

 

Some thermal pics of the windows from the inside taken with my Flir One.  The colours are representative not absolute. If there is a spread of 2 deg or 20 degrees over an image the display will still use the whole yellow to blue colour spectrum available. 

 

 

And the outside.

 

 

Note the dot to the left of the window below.  That's the extractor fan exhaust. It has 2 x anti backdraft airtight magnetic shutters but still you can see the hot area.  External areas are hard to quantitify as the emissivity of a surface seems to make a big difference. A shiny surface will appear different than a dull one despite both being the same temperature. You can see my thermal reflection in the window too.  

 

 

 

Things that I have ruled out. 

 

1. Full fill of the EPS beads. I checked all areas with the Thermal camera and found no gaps. I climbed into the attic and checked the areas of the eaves where the EPS beads were pushed up under the DPM cavity closer and found no settlement. 

2. Air leaks. We had a small gap at the corner of a T&T window that was whistling slightly in very strong winds. Once adjusted it became silenced. No other leaks have been noticed, even in gales. 

3. High thermal bridging through SS wall ties. The thermal imaging could find no evidence of this internally or externally. 

 

 

I did consider externally insulating the Window frames with pre rendered EPS sections to reduce heat loss but doing the sums on it suggested that we would still need some heating and the investment would be about the same as an A2A for far less energy savings. 

 

 

The house is comfortable, never chilly with young kids. Despite having no UFH the floors aren't cold.  There's no smells with the MVHR. It's very quite too. It takes days to get a meaningful change of temperature. Last year in 30deg plus for a few days the bedrooms never got above 23 deg. It may have been less had we kept all the external doors and windows closed, but as it turns out we're not beyond enjoying the fine weather. The bedrooms have only about 2.4m2 of glazing each over 2 windows on opposite walls which helps both control the solar gain and cross ventilate. 

 

Similarly even after 24hrs of a power cut in the Snow in Feb 2022 the house was 19-20 deg.  

 

 

Questions and comments are welcome. 

 

 

 

 

 

 

 

 

 

 

 

Edited May 10, 2023 by Iceverge

[SteamyTea]

35 minutes ago, Iceverge said:

 

For weather comparison heating degree days at 15.5deg from a local station were

Have you check it at the temperature you actually turn your heating on.

My minor improvements dropped the temperature by about 1°C.  I used to turn the heating on after the first full week when the OAT was 10°C, now do it at 9°C.

HDD use a standard distribution (near enough) for OAT temperature, dropping a degree may seem small, but may be a lot of hours in reality.

[Iceverge]

Will check.

 

[Iceverge]

26 minutes ago, Iceverge said:

Will check.

 

 

About 8 to 9 degrees I think. I'm not to familiar with HDD. I don't think it accounts for sunlight so that can vary the energy balance quite a bit. Clear skies and cold temperatures require less heating than cool overcast days. 

 

 

[SteamyTea]

1 minute ago, Iceverge said:

I'm not to familiar with HDD

It is a crude tool, though useful for year on year comparisons.

From my weather and energy usage analysis, OAT is the biggest driver by far, but much of that is to do with my house being a mid terrace.