How Do?

[SlivenClod]

I'm Roger and we have just secured an option to purchase a plot in East Lancs. 

We foresee some issues with planning as it is outside the urban boundary, so fingers crossed.

This is our second self-build: we are leaving the first after 35 years to down size but only moving 150m.

Joined the site to get up to speed with latest materials and methods.

[Ferdinand]

Welcome Roger - ask away.

[jack]

Welcome Roger.

 

As I'm sure you'll have seen, we have all types of building methods in use. Brick and block, timber frame, insulated concrete formwork, with all sorts of insulation types. The general mantra is more insulation than building regs require (high decrement delay preferred) and much better airtightness. 

 

Do you plan to do much of the work yourself?

[TerryE]

As Jack says you can comfortably exceed BRs for little net impact on cost.  U-values for walls 0.15, floor and ceiling 0.12, fenestration 0.8 airtightness 1.0 ACH, or better for all. 

 

The planners wouldn't allow us to install PV but our total energy bill (electric only) this year has been about £1,400.  Our rates are 2× this.   Next year after we've installed the ASHP, this will fall to around £800.  No gas; no gas boiler service costs; no radiators anywhere, just UFH on the ground floor and house stays between 22-23°C 24×7 year round.   So it can be done.  We are in our 60s, so everything is design with little or no lifetime maintenance required.

 

Trawl the site; ask Qs; get yourself invited to look around the houses of other members who have gone through this journey, as you will find these face-to-face 1-1s extremely informative.

[epsilonGreedy]

10 hours ago, TerryE said:

The planners wouldn't allow us to install PV but our total energy bill (electric only) this year has been about £1,400.  Our rates are 2× this.   Next year after we've installed the ASHP, this will fall to around £800.  No gas; no gas boiler service costs; no radiators anywhere, just UFH on the ground floor and house stays between 22-23°C 24×7 year round.

 

 

I was reading older blog entries of yours elsewhere and noted you planned to charge your UFH slab with a 3kw inline heater during an overnight 3 hour charge slot. From this I concluded the daily heat input for your house is 9kwh, have you found that your space heating requirements are more or does hot water account for most of the expected £400 saving?

 

As background, looking at the projected heating loss for the Passiv version of 160 m2 model house in the Self Builder Bible, the book quotes a 3kwh heat loss rate across a 20 degree differential or say 70 kwh daily during a cold snap. However something call incidental gains reduces the heating uplift to just 12 degrees or 42khw daily. This leaves quite a gap, is it because your house exceeds the minimum spec for a Passiv house?

[TerryE]

@epsilonGreedy I do use a 3kW inline heater, and my current heating algo computes a predicted amount at midnight for the coming 24 hrs based on (1) the forecast average temperate for the following day, and (2) an adjustment based on the average temperature for the last 24 hrs.  It will then run the inline heater over night for up to 7 hrs overnight or the calculated amount (which ever is the lesser) to take advantage of E7 tariff.   The excess, if any, is only used if the hall temperature falls under a preset (currently 22.3°C).   At the moment with the outside temperature bubbling along at around 8-9°C we need about 15kW top up overnight.   Looking at my historic logs, this peaked at 40kWh on a few very cold days in Jan but the Jan actuals average was still only 23 kWh and March was 16 kWh / day. 

 

We also used a small electric oil-filled radiator in my upstairs office which ran 7 hours @ ~1 kW for a total of maybe 60 days during peak winter.   This added heat using E7 cheap rate upstairs rather than adding extra heat to the slab during peak hours. (The 40 kW peaks were before I started doing this).  The main difference that the ASHP will make is its CoP of ~3½ when heating water to <35 °C and this will factor down the heating energy  accordingly. and it will be cheaper to heat the slab during the day than use the oil-filled radiator overnight.

 

And yes, like Jeremy's,  our house does exceed the Passiv spec by a margin.  Also remember that pretty much all energy use (excluding bathwater going down the plug hole) ends up as waste heat inside the house, as well as any solar gain, of course.  Another advantage of our house is the very long decrement delays of the external fabric, so we only need to be concerned with overall average temperatures, and the predicted bills are largely driven by monthly averaged temperatures.

 

Exceeding this minimum cost was largely by design and by attention to detail during construction; it didn't materially add to the build costs, our heating system is cheap and almost zero maintenance cost.  The UFH added less than £2K to the cost of the slab; the UFH manifolds, relays, inline heater, RPi, sensors, etc. less than another £2K.  No rads or other heating in the rest of the house; no gas supply or gas appliances ... 

 

Edited April 8, 2019 by TerryE

[jack]

On 08/04/2019 at 18:15, TerryE said:

Also remember that pretty much all energy use (excluding bathwater going down the plug hole) ends up as waste heat inside the house, as well as any solar gain, of course.  

 

On the odd occasion we use a bath during the heating season, the water is left to go cold before draining.

[joe90]

21 minutes ago, jack said:

On the odd occasion we use a bath during the heating season, the water is left to go cold before draining.

 

Exactly what I do.

[TerryE]

Sad isn't it?  Though I tend to compromise and let it cool to around the high 20s since this is moderately quick and losing that last 7°C or so takes quite a long time.  What a bunch of sad old farts.

 

I must admit that you can get a bit too anal about this.  Bare with this seeming non-sequitur: Jan and I have a massage every two weeks turn and turn about (and before Clive starts chipping in with his dirty innuendos, this is a straight Swedish-style massage and no funny stuff).  Even before we add our ASHP, our monthly energy bill is almost exactly the same as our massage bill, and under half our council tax. 

Edited April 15, 2019 by TerryE

[joe90]

24 minutes ago, TerryE said:

What a bunch of sad old farts.

 

But if we weren’t then we could not afford things like massages, we would be spending it on heating bills instead, like most people do.

[jack]

27 minutes ago, TerryE said:

Sad isn't it?  Though I tend to compromise and let it cool to around the high 20s since this is moderately quick and losing that last 7°C or so takes quite a long time.  What a bunch of sad old farts.

 

I just leave it overnight and drain it in the morning. No idea what temp it reaches but I'm sure most of the temperature difference is captured this way. Life's too short to think any harder about it than that!

[TerryE]

4 hours ago, jack said:

I just leave it overnight and drain it in the morning.

 

Gives the tide mark too long to settle The boss likes a spotless bath.

[jack]

12 hours ago, TerryE said:

Gives the tide mark too long to settle The boss likes a spotless bath.

 

More than she likes the planet, it would seem.