Heat loss sanity check

[Furnace]

12 hours ago, Iceverge said:

" Do your best and if there's any holes let me know and I'll sort them out". 

I like that approach in principle.

 

13 hours ago, Kelvin said:

air tightness hero t-shirts printed up if you’re expecting the trades that visit your site to wear them unless it’s just for you.

For me, since I'll be on site most days. I'm hoping it will remind all trades on site to be as diligent as possible.

[TerryE]

In our case the air-tightness barrier was done by the MBC crew.  The main barrier was an inner "green" OSB3 sheeting (that is with a green gas-tight plasticised surface). These sheets were but-jointed and taped on the TF verticals, with the service cavity spacer battens nailed to these verticals.  Having the service cavity in front of the barrier allows all cabling and pipe runs to be run in the cavity and pretty much eliminates the need to breach it for 1st fit.  A second MBC crew did the cellulosic fill and completed all taping up around fenestration, etc., then coordinated with the independent tester who did the air-tightness test.  So:

• The whole frame was airtight by design, with design detailing aimed at avoiding unnecessary breaches.
• Specialist crews who understood air-tightness requirements were used at key stages in the build.
• The rest of the trades (eg. electrics, plaster boarding out) had a simple set of rules to work to, and these didn't inconvenience their work, so were easy to follow.

 

 

[Furnace]

 

2 hours ago, TerryE said:

Having the service cavity in front of the barrier allows all cabling and pipe runs to be run in the cavity and pretty much eliminates the need to breach it for 1st fit

Having a service cavity seems pretty much essential to avoid the potential for numerous breaches.
Were the specialist crews supplied by MBC employees, or approved subbies?
Did you order windows from the plans prior to the frame being on site and assumed the frame apertures would be accurate? Getting the shell watertight ASAP iss a priority for me, and boarding up or plastic sheeting the apertures for a couple of months until the windows rock up doesn't fill me with joy.

Cheers

[Furnace]

Having built my own spreadsheet I feel pretty comfortable with the heat loss numbers based on local temperature data, and they largely agree with the PHPP consultant. The area of most difference is the air heat loss from infiltration and MVHR. I've not spoken to him about it yet, but it may be that he's input a different flow rate for the MVHR and a different adjusting factor for the ACH50 losses.

In the meantime, does this pass the general sanity test? Remember, it's just losses and no account is made for solar gain or internal equipment or human based gains


Next I need to get comfortable with the solar gains. Anyone done any work on this outside of the PHPP bird's nest?

Cheers

Mark

[SteamyTea]

4 hours ago, Furnace said:

I feel pretty comfortable with the heat loss numbers based on local temperature data, and they largely agree with the PHPP consultant.

Check against the HDD databases, the charts should be similar shape.

https://www.degreedays.net/

 

Solar gain is quite tricky.  When I plot my house data against weather data, there is not a very strong correlation.  I think there is a better correlation to windspeed, but when the wind is strongest, the temperatures are highest.  Not as if I get many clear skies caused by NE winds, in the summer.  Not as if I get many clear skies and warm SW winds in the summer either.

 

It rains most days here, and when it is not, it is dark.

[Furnace]

1 hour ago, SteamyTea said:

It rains most days here, and when it is not, it is dark

Do you moonlight for the tourist board?

 

1 hour ago, SteamyTea said:

I think there is a better correlation to windspeed,

Is your ACH50 high? Maybe strong winds are boosting infiltration losses?

1 hour ago, SteamyTea said:

Check against the HDD databases

I'll check the shape, although I suspect they'll be the same. I'm more interested if others have a sense if the real world experience supports these ballpark actual numbers.

 

Cheers 

Mark 

 

 

 

 

 

[TerryE]

22 hours ago, Furnace said:

Were the specialist crews supplied by MBC employees, or approved subbies?

MBC used a small number of "regular" subcontract teams who understood the quality issues.  I was always amazed by how hard they worked and to a standard that is pretty much unknown in the general UK building industry. 

 

22 hours ago, Furnace said:

Did you order windows from the plans prior to the frame being on site and assumed the frame apertures would be accurate? Getting the shell watertight ASAP iss a priority for me, and boarding up or plastic sheeting the apertures for a couple of months until the windows rock up doesn't fill me with joy.

 

We fitted the Internorm windows and doors on the day after the frame was finished.  (There was supposed to be a 7 day slack contingency but this all got used up by slippages in the erection team's previous build + 1 day on ours, so the contingency got eaten up.)  We had a 3 month lead time on the windows so we ordered the windows according the detailed frame drawings.  The window supplier was only willing to do this in the case of TFs using factory assembled cassettes.  Their normal practice for conventional block and brick builds was to measure actual openings in the erected skin.  Hence our TF was weather tight and lockable less than 2 weeks after there was just a bare slab; whereas convention builds can be exposed to the elements for months.

 

I double-checked all opening dimensions during frame erection and a couple were off by ~1cm.  However we had our windows in lined boxes (see this blog entry for a detailed explanation), so in these cases i got the framing crew to pack out between the  frame and the liner box.  The internorm fitting crew had no issues at all, and as a result they finished fitting a day early because they used none of their contingency.

[Furnace]

Internorm seem to have a good reputation. My architect typically specifies Norrsken windows and doors,although when I saw them at the NSBRC I was not overly impressed with the single compression seal range, nor with the tolerances>
 

9 hours ago, TerryE said:

I double-checked all opening dimensions during frame erection and a couple were off by ~1cm

10 ish mm sounds like quite the outer limit of what one would want given the accuracy available in a factory setting?

[TerryE]

20 hours ago, Furnace said:

10 ish mm sounds like quite the outer limit of what one would want given the accuracy available in a factory setting?

Yup, I talked to the MD of MBC about this. The timber lengths were all PNC cut so were pretty much spot on to the drawings. The prob seemed to be a few of the internal framing uprights were not machine place, so some laterals we being hand trimmed to fit by the assembly crews. They've since fixed this process.

Edited December 24, 2022 by TerryE

[Furnace]

On 24/12/2022 at 18:15, TerryE said:

They've since fixed this process.

Thanks Terry. That's encouraging

[Furnace]

On 22/12/2022 at 22:15, SteamyTea said:

Check against the HDD databases, the charts should be similar shape.

Pretty similar as expected. What I'm more interested is the order of magnitude of the losses. Any thoughts from similar size gaffs. My design is currently 236m² TFA with heat form factor of 3.06

 

 

Edited December 28, 2022 by Furnace