Understanding my air test results.

[ProDave]

I had my house blower door air tested this morning.  The tester seemed to think it was a "good" result but at the moment I don't think it is.  But the result is expresses in unit's I don't understand and so can't gauge how good it is.

 

The test result has come out as 1.44m³/m²/hr at 50 Pa.   I don't know how to convert that to ACH (which is what most on here use)  when I asked him he punched some numbers on a calculator and said "about 1"

 

A few points.  He measured the building himself (I had sent all the drawings) and came up with a volume of 385m³  If you are going to be pedantic, the actual volume from the design drawings is 434 m³ which includes the loft space that is within the air tight envelope but outside the area he measured.  I don't know if including that would make the figures better or worse.

 

So given that test figure and the building volume, how do you convert that to ACH?

[IanR]

The figure you've been given is correct for building regs. In England the max for a new build is 10 m³/m²/hr at 50 Pa. 

 

The ACH figure often quoted is what Passivhaus uses.

 

The m² in your figure is the surface area of the building envelope (internal layer of the thermal envelope), including walls, roof and floor. Small detail is ignored ie. window rebates etc. so just use the overall sizes.

Have you got the full report where the tester has stated the value used for this?

If so, then multiply the 1.44 by the envelope area used and you have the total volume of air loss. 

As AHC is also measured @ 50 PA, then you can divide the total volume of air loss by the total volume within the thermal envelope, and you have your ACH

Edited August 18, 2021 by IanR

[ProDave]

All the figures I have are in my first post. In his test report he states the "envelope area" as 385

 

I know from the design SAP report that the building volume is 434.52m³

 

I don't understand your conversion?  you say multiply the 1.44 by the envelope area used which was 385, so that gives 554.4 (not sure what units)

 

Then you say divide that by the total volume which would be my 434.52 so that would be 1.27, but all I seem to have done there is correct between his measured volume and my calculated volume?

[IanR]

6 minutes ago, ProDave said:

All the figures I have are in my first post. In his test report he states the "envelope area" as 385

You'd stated that as the volume in your first post.

If that's the surface area used then 1.44 * 385 / 434 = ACH @ 50 Pa

If he's used the incorrect Surface area, you need him to redo the calcs, it will make a difference, and it does need to include the entire thermal envelope.

Why does your SAP say 343.53m³ but in your first post you say its 434m³. Is the loft missed out of the SAP?

Edited August 18, 2021 by IanR

[ProDave]

Following on from this, the air test results enabled me to submit that and a whole host of other paperwork to get the design SAP updated to the as built SAP and the final as built EPC issued.

 

The result is an EPC of A94.  The usual recommendations that it could be improved to A96 by adding solar thermal (at a cost of £4K-6K) and could be further improved to A109 by adding a wind turbine at a cost of £15K to £25K  I won't be doing either of those.

 

The calculated space heating is 6295kWh per year which compares to a real life electricity consumption for heating of 1712kWh which either suggests my ASHP is averaging a COP of 3.67 or the real heat requirement is lower than calculated.

 

The calculated DHW is 2336kWh which compares to the ASHP consuming 997kWh for DHW so again suggests  the ASHP is achieving a COP of 2.34 for DHW.  Obviously those are only very approximate.

 

Just one thing that confuses me on the EPC.  On page 2 there is a "Summary of the Energy Performance Features of this home"  Here all building elements are given a star rating from 1 to 5 stars.

 

Everything here gets 5 stars, except the Main Heating, which is correctly listed as ASHP / UFH that only gets 3 stars for Energy Efficiency and 4 stars for Environmental.  Why is that?

 

[Mr Punter]

I have a feeling they still punish electric v. gas.

[saveasteading]

Congratulations, that is a very good figure.

If he had measured the loft then you would have had a greater surface area, with which to divide the same air loss, so it would have been even better. 

I would chat it through  with them before they issue a certificate, just in case I have it the wrong way round.

 

Speaking only for commercial properties I found this, which probably apply in the main:

The calculation is done in a black box which has the algorithm in it, riddled with inaccuracies, approximations and errors of understanding.

 

My company once got the programme so that we could play around with it (which the powers that be don't like) therefore we found anomalies to play with.

This was not being bad, as the programme didn't acknowledge lots of good things.

For example there were glitches in insulation thicknesses, so it was better to enter smaller amounts than the actual used, on one occasion.

 

On the full printout we always had an allowance for the electricity used for air-conditioning, even when there was none and could never be any.

 

That  may not apply to your situation, but you can be sure that the system is highly flawed.

 

For example, as you say, it is clearly stupid to have a small wind turbine but they still give points for having one. Years have passed since that craze was proven to be stupid, but they have not bothered to change the formula. Actually I think they don't understand. I have met these people who set up the system,  and then passed their exam which required knowing the expected answers, not the reality.

 

Isn't your result good enough though? I always thought 3 was good (on large commercial). 94 is an A pass.

[ProDave]

Yes the figures are good.  It's perhaps my expectation that was set too high.  This was never designed to be a passive house but I kind of hoped it would get close.  It is certainly way above the requirements for a building control pass.  I won't be arguing the finer details with anyone.

[joth]

1 hour ago, ProDave said:

Everything here gets 5 stars, except the Main Heating, which is correctly listed as ASHP / UFH that only gets 3 stars for Energy Efficiency and 4 stars for Environmental.  Why is that?

 

Maybe the scale has room for improvement when new not-yet-invented energy sources come onto the market? To avoid the A++++ situation we had with the old EU appliance energy labels

But yeah, more likely it still punishes electricity assuming a dirty grid.

 

1 hour ago, ProDave said:

The calculated space heating is 6295kWh per year which compares to a real life electricity consumption for heating of 1712kWh which either suggests my ASHP is averaging a COP of 3.67 or the real heat requirement is lower than calculated.

They assume a whole house temperature set point of what? If you have a lower set point or don't heat all rooms to that level all the time, consumption will be lower than their building model even if the model is perfect (which it almost certainly isn't!)

 

3 minutes ago, ProDave said:

It's perhaps my expectation that was set too high.  This was never designed to be a passive house but I kind of hoped it would get close

You are close!

What is the surface area of the finished floors?  How does 6295 kWh / floor_area look ?  It would need to be 15kWh/m2 for PH, 25 for PH retrofit, or 40 for AECB silver.

 

[saveasteading]

Quite right. A higher number would have been even more satisfactory.

[IanR]

2 hours ago, ProDave said:

Everything here gets 5 stars, except the Main Heating, which is correctly listed as ASHP / UFH that only gets 3 stars for Energy Efficiency and 4 stars for Environmental.  Why is that?

 

It's got to be more subtle than just that you're using electricity for space heating. On my EPC it lists the same ASHP and UFH (above insulation), but gives 5 stars.

 

On the as built SAP it records the "boiler" efficiency (SEDBUK), it's got mine as 384%. 

I thought it might be Design Flow Temp, but on my SAP that's recorded as "unknown", so that can't be effecting it. 

[ProDave]

49 minutes ago, joth said:

You are close!

What is the surface area of the finished floors?  How does 6295 kWh / floor_area look ?  It would need to be 15kWh/m2 for PH, 25 for PH retrofit, or 40 for AECB silver.

 

That opens a minefield of "statistics"

 

Floor area is 158 square metres.  I believe they have included in that the unheated "plant room" above the garage that is included in the air tight envelope of the house.

 

The calculated heating energy usage of 6295kWh calculates to 41.95 kW per m²

 

My measured heating energy use of 1712kWh calculates to 10.83kWh per m² but that is electricity in to the ASHP so at a COP of 3 would be 32kWh of heat per m²

 

So some way short of PH but still a "low energy" house.

[Oz07]

I had 1.19 and I thought it converted to around .6ach but I could be wrong. I think I googled some conversion?

 

Your blower door man should of known it was a good figure he would of had to close up all the holes in his door bar one. The guy I used was about creaming his pants but he was used to doing bog standard newbuilds

[Iceverge]

2 hours ago, ProDave said:

Yes the figures are good.  It's perhaps my expectation that was set too high.  This was never designed to be a passive house but I kind of hoped it would get close.  It is certainly way above the requirements for a building control pass.  I won't be arguing the finer details with anyone.

 

 Your measured energy usage is excellent. Even the most diligently put together computer programmes are full of assumptions so could be looked at as rough estimators. 

 

I remember you fitted a stove in your house which are unfortunately poor performers when it comes to airtightness. in this case 0.5ACH all by itself.

 

https://www.greenbuildingstore.co.uk/cumberworth-radical-retrofit-airtightness-test-wood-burning-stove/

 

Did you have any leaks here during the test? 

Also your gains from lighting it are hard to measure.

 

Once you reach an ACH of less than 2 the gains are small in any case. 

 

IMO is your SAP is good enough I'd just file and forget and enjoy your nice house. 

[Olf]

4 hours ago, ProDave said:

The calculated space heating is 6295kWh per year which compares to a real life electricity consumption for heating of 1712kWh which either suggests my ASHP is averaging a COP of 3.67 or the real heat requirement is lower than calculated.

Perhaps incidental heating contributes enough to skew the result. In a perfect 'passive house' it would contribute 100% and give COP of infinity

[ProDave]

2 hours ago, Oz07 said:

I had 1.19 and I thought it converted to around .6ach but I could be wrong. I think I googled some conversion?

 

Your blower door man should of known it was a good figure he would of had to close up all the holes in his door bar one. The guy I used was about creaming his pants but he was used to doing bog standard newbuilds

Yes we do have a stove. In theory it is room sealed, i.e. combustion air ducted from outside.  But when the blower was on, the roof penetration for the stove flue was one place where a small draught was just detectable.  That and one of the velux windows had a leak in the corner, not between the frame and the building, but between the frame and the window, i,e, it was not sealing perfectly.

 

[ProDave]

1 hour ago, Iceverge said:

Your measured energy usage is excellent. Even the most diligently put together computer programmes are full of assumptions so could be looked at as rough estimators. 

 

I remember you fitted a stove in your house which are unfortunately poor performers when it comes to airtightness. in this case 0.5ACH all by itself.

 

https://www.greenbuildingstore.co.uk/cumberworth-radical-retrofit-airtightness-test-wood-burning-stove/

 

Did you have any leaks here during the test? 

Also your gains from lighting it are hard to measure.

 

Once you reach an ACH of less than 2 the gains are small in any case. 

 

IMO is your SAP is good enough I'd just file and forget and enjoy your nice house. 

Yes we do have a stove. In theory it is room sealed, i.e. combustion air ducted from outside.  But when the blower was on, the roof penetration for the stove flue was one place where a small draught was just detectable.  That and one of the velux windows had a leak in the corner, not between the frame and the building, but between the frame and the window, i,e, it was not sealing perfectly.

 

Yes I am happy with the EPC and it and the air test will be submitted to BC for completion and then just filed.

[willbish]

Please could someone check my thinking on ACH and m3/m2/h?

ACH is easy right, 1.0ACH is just the volume of the airtight envelope house per hour. In my case 407.5m3, and 0.6 or possibly even 0.4 is just a fraction of the 400 figure.

m3/m2/h has no volume element so is the internal surface area of the airtight envelope; floor, walls, roof.
1m3/m2/h is equal to the surface area, in my case 377m2

If the above is correct then the following should be true

[IanR]

9 minutes ago, willbish said:

ACH is easy right, 1.0ACH is just the volume of the airtight envelope house per hour. In my case 407.5m3, and 0.6 or possibly even 0.4 is just a fraction of the 400 figure.

 

Yes, that's correct.

 

9 minutes ago, willbish said:

m3/m2/h has no volume element so is the internal surface area of the airtight envelope; floor, walls, roof.
1m3/m2/h is equal to the surface area, in my case 377m2

 

Yes, also correct, accept units are 1m³/m².h       (it is of course @50Pa, before someone corrects me)

Edited October 12, 2021 by IanR

[A_L]

12 minutes ago, willbish said:

m3/m2/h has no volume element

 

The m³ is a volume element, the volume 'leaking' per hour.

 

I am not sure what you are asking, perhaps an example will help.

 

With an infiltration of  407.5m³ / hr (1.0ACH) and an internal surface area of 377m² then 407.5/377 = 1.08m³/m²/hr

[SteamyTea]

17 minutes ago, IanR said:

it is of course @50Pa, before someone corrects me

Which is near enough 5.1 kg/m²

 

[willbish]

Thanks @IanR

 

20 minutes ago, A_L said:

The m³ is a volume element, the volume 'leaking' per hour.

Yes. When I said no volume element I suppose I meant the volume of the house has no bearing on the m3/m2.h score.

 

Preparations for the test are going well, Ive rigged up a 220W 14inch car radiator fan, no idea if this is powerful enough to simulate 50Pa. Found and treated quite a few minor leaks but no idea if Im likely to score 4ACH or 0.4ACH

 

Edited October 12, 2021 by willbish

[SteamyTea]

13 hours ago, willbish said:

Ive rigged up a 220W 14inch car radiator fan, no idea if this is powerful enough to simulate 50Pa

Have you used a manometer?

Then worked out the pressures.

 

[ProDave]

50Pa is only 5mm H2O on a manometer.  Hard to read with any accuracy but you will get an idea.  An inclined manometer may be more accurate.

[Marvin]

10 minutes ago, ProDave said:

manometer

Surely a personometer or a theyometer or an itometer?