Any way to calculate the savings from airtightness/heat recovery

imitation

Is there any way for a layman to determine what somebody could saving by say boosting the air tightness rating of there build from 3 m2/m3/hr to say 1.5 m2/m3/hr ?

sinnerboy

1. Appoint a BER assessor or PH Consultant
2. Ask them to run different options through DEAP or PHPP

The savings will vary depending on ALL building data entered into the software

Lantus

yep.

the change in air presuure rate equates to an infiltration rate or how much air trickles through the dwelling. If you use a peak winter equation for heat loss you can compare the overall heat loss when compared with the higher value and when added with the the fabric elements heat loss (walls and windows etc.) deterine what the peak heat loss is. This would inform of an overall boiler size reduction.

Calculating over the year would require the creation of a thermal model in a suitable piece of software. a more accurate way of doing it but it's costs a load.

consult a specialist....

sinnerboy

Lantus wrote: »

but it's costs a load.

No it doesn't . A BER assessor may charge as little is €400-500 to answer this - and many other spec option queries .

Everybody , one day , will have to have a BER assessment carried out . This is the very smartest use - before the building even exists .

imitation

Thanks, I'll consult with my engineer.

Im currently looking at the airtightness of my future house, and how low I should be aiming. I have zero feel for how much airtightness is actually worth. The rest of the house should be hitting about an A2 rating, so im trying to figure out where the money would be best spent.

Lantus

sinnerboy wrote: »

No it doesn't . A BER assessor may charge as little is €400-500 to answer this - and many other spec option queries .

Everybody , one day , will have to have a BER assessment carried out . This is the very smartest use - before the building even exists .

I meant to buy a professional piece of thermal modelling software (not the stuff the BER chaps use.)

Lantus

imitation wrote: »

Thanks, I'll consult with my engineer.

Im currently looking at the airtightness of my future house, and how low I should be aiming. I have zero feel for how much airtightness is actually worth. The rest of the house should be hitting about an A2 rating, so im trying to figure out where the money would be best spent.

CIBSE TM_23 suggests that good practice for a dwelling is 15m3/hr/m2 of facade @50Pa, best practice 8.0.

A Passiv Haus aims for around 1 which is pretty damm airtight. I think if you can specify for no more than 10 your doing well unless you are aiming for a really energy efficient design. Even so you will need some good detailing to achieve this and of course a test to back it up which is easy enough.

sinnerboy

Lantus wrote: »

I think if you can specify for no more than 10 your doing well

No . You are aiming at just complying with the min requirements of TGD L 2008 . Draft TGD L 2010 requires 7 .

imitation

The house will be using HRV ( which I should have mentioned) , so as far as I have read I would want at least 3 m3/hr/m2 .

beyondpassive

For MHRV to work effectively you should have leakage below 2 air changes, ideally 1.5 m3 pr hour per m2. An airchange of 10 is akin to leaving the back door open. The equivalent leakage area for a 300sqm house at 10 airchanges with a storm pressure flow rate, is almost 2 sq.meters.

If you are building a new house, it would be usefull to use the passive house approach to evaluate, the effect of different construction techniques and try out various window and ventilation techniques. It takes the guesswork out of it.

It well worth getting construction details done for the major junctions, such as floor to wall, wall to roof, suspended floors etc. It easy to have everything down on a drawing, rather than make it up on site. These drawings will show how the continuous airtight vapour control layer is to be installed.

I've noticed in the last year, we've drawn a line under the old celtic tiger building practices of bad workmanship and site supervision. Clients now have more leverage to demand that things are done right.

Lantus

sinnerboy wrote: »

No . You are aiming at just complying with the min requirements of TGD L 2008 . Draft TGD L 2010 requires 7 .

cheers, good to know.

beyondpassive wrote: »

For MHRV to work effectively you should have leakage below 2 air changes, ideally 1.5 m3 pr hour per m2. An airchange of 10 is akin to leaving the back door open. The equivalent leakage area for a 300sqm house at 10 airchanges with a storm pressure flow rate, is almost 2 sq.meters.

If you are building a new house, it would be usefull to use the passive house approach to evaluate, the effect of different construction techniques and try out various window and ventilation techniques. It takes the guesswork out of it.

It well worth getting construction details done for the major junctions, such as floor to wall, wall to roof, suspended floors etc. It easy to have everything down on a drawing, rather than make it up on site. These drawings will show how the continuous airtight vapour control layer is to be installed.

I've noticed in the last year, we've drawn a line under the old celtic tiger building practices of bad workmanship and site supervision. Clients now have more leverage to demand that things are done right.

Just be careful. Air changes is a totally different kettle of fish to air leakage or air permeability. air changes are measure in ac/hr. i.e the number of times the volume of a space or room will entirely change over the course of an hour.

Air leakage is measured as m3/hr/m2 of facade and done at 50Pa.

While you can crudely convert air leakage to approximate air changes it needs to be taken with a pinch of salt because air changes depends on the weather, where your building is situated etc and will vary. An air change rate of 2 and an air leakage rate of 2 (stated without units) mean very different things.

galwaytt

..don't forget that method-of-build is also a factor, as the amount, and cost of work, to get from say your figure of 3.0 to 1.5 needs to be considered, and the payback needs to cover the capital cost of increasing the airtightness level, not just any nett savings in energy bills.

beyondpassive

Lantus wrote: »

While you can crudely convert air leakage to approximate air changes it needs to be taken with a pinch of salt because air changes depends on the weather, where your building is situated etc and will vary. An air change rate of 2 and an air leakage rate of 2 (stated without units) mean very different things.

no the conversion is based on absolute values.

According to Sinnerboy, 'Q50 in m3/hr/m2 is a function of the enclosing surface area and n50 is a function of volume in air changes per hour. In a particular case the enclosing surface area and the volume of the building can have similar numbers, i.e a building with an enclosed surface area to volume ratio of 1:1 n50= q50. For more compact or passive house it can be 2:3, for sprawling bungalows with lots of annexes and sticky on bits it can be 2:1.

Variables such as weather and pressure which can affect the weight of air going through the fan are eliminated in the air test for q50 and n50 outputs.

You are right though the the air leakage and permiability metrics are not directly interchangable, Passive house and engineers like leakage and the BER likes permiability, so for now we have to keep both. Lets just say that over 2 in either currency is simply crappe workmanship

galwaytt

beyondpassive wrote: »

.... Lets just say that over 2 in either currency is simply crappe workmanship

Actually, no, let's not. :mad:

As someone who builds houses in the .5 - 1.6 range myself, even I regard that statement as too simplistic.

You're also conveniently ignoring the fact that if you open a window or 2, then what ? Houses have to be built for people, not the other way round.......

beyondpassive

This has nothing to do with opening windows. We're talkin uncontrolled air leakage, so all windows are closed during the test and vents are blocked and it measured at storm pressure. The idea is to measure how mush air can be pushed through gaps, tears and services routes, (or those holes that the mice squeeze through.) These leakage paths allow moist warm air to pass uninhibited through the fabric where it can condense, causing structural damage or mould growth.

When you recognise that hole in the wall vents just don't work, you have to look at systems that uses balanced pressure or the bouyancy of air to get the required fresh air flow rates. Now tear holes in your fabric, particularly in the roof where the air is bouyant, and youre wasting heat. In summer, air from unvented cavities comes back into the room, resulting in bad air quality. Then there is acoustics, insects etc.

Houses built for people.

galwaytt

beyondpassive wrote: »

This has nothing to do with opening windows. We're talkin uncontrolled air leakage, so all windows are closed during the test and vents are blocked and it measured at storm pressure. The idea is to measure how mush air can be pushed through gaps, tears and services routes, (or those holes that the mice squeeze through.) These leakage paths allow moist warm air to pass uninhibited through the fabric where it can condense, causing structural damage or mould growth.

Houses built for people.

Sorry, but you're missing OP's point: he asked what return he'd get for the spend in going from a leakage rate of 3.0 to 1.5. What we don't know is the subjective measure he has in mind, bearing mind how he'd use the house. Therefore, we can give no objective answer - and the window comment was to illustrate that point. If he is of the type that likes plenty of fresh air, or habitually opens the windows - or has big open fires, then the return in the extra spend - if any - is nigh-on impossible to measure. Is there a question in the DEAP/PHPP along the lines of 'do you open the windows often/sometimes/never ? ' No there isn't, which is why there's a gulf sometimes between what those programmes deliver in terms of numbers, and the questions client's are actually asking......

beyondpassive wrote: »

When you recognise that hole in the wall vents just don't work, you have to look at systems that uses balanced pressure or the bouyancy of air to get the required fresh air flow rates. Now tear holes in your fabric, particularly in the roof where the air is bouyant, and youre wasting heat. In summer, air from unvented cavities comes back into the room, resulting in bad air quality. Then there is acoustics, insects etc.

I agree completely that 'holes in the wall' don't work - the West of Ireland is littered with newspaper-stuffed and sellotape'd over, Hit & Miss grille's......and I don't think window trickle vents work, either. Why is why I have MHRV, not because I want the H but I do want the V !

Of course you're roof scenario only applies to cold roof construction........and that's a subject of it's own.......;)

And yes, I've noticed acoustics in ours is remarkably much better than 'std' construction.......because of airtightness.

beyondpassive

Good points,

PHPP can consider opening windows for the summer period as a cooling mechanism to reduce overheating risk.

sinnerboy

galwaytt wrote: »

Is there a question in the DEAP/PHPP along the lines of 'do you open the windows often/sometimes/never ? '

Houses don't demand heat - people do . Or don't !

End user education and behavior are vital of course . Even the most fuel efficient family car will eat petrol if you use it to deliver concrete blocks

But don't lump PHPP and DEAP together . The PHI have demonstrated by monitoring built passiv houses that PH does deliver in practice .

http://www.passiv.de/07_eng/PEP/PEP-Info1_Kronsberg.pdf

Turn to page 84 for measured energy consumption levels in 1999-2000 of 32 Passive House in the same development . Each house consumed a different amount

Each a very very low amount of energy .

The report states

Savings measures through construction/technology efficiency improvements are in many ways more effective than attempts to change occupant behaviour:
- they lead to similar high relative savings, whether the occupant is frugal or wasteful.
- as the Hannover Passive House project has shown, they are cost-effective to implement and hold their effect over the useful life of the building.
- they do not patronise nor point with the raised finger.
- they allow each occupant to have the thermal comfort level he/she wishes.

imitation

Gimme some credit here guys , I do intend on keeping the windows shut during periods when the heating will be in use. During the summer.. is it an issue ? I personally don't intend on heating the house during this period, then again, I'm sure some people out there do. Either way, when your making these figures you have to assume people aren't going to act the maggot.

Apologies for the vagueness of my post so far, a brief summary of the build is as follows.

Roof 0.10 W/m2k Mineral wool
Walls 0.16 W/m2k Polyiso 300mm cavity + drylining
Floor 0.13 W/m2k Polysio
Windows 0.9 W/m2k Triple glazed
Openings and ceiling will be taped up with membrane
MHRV

sinnerboy

Again - the unique areas and other features of the elements of your build will affect the outcome of moving from 3 to 1.5 Q50 .

BER or PHPP consultant enters data , and
answer 1 based on 3 = XX kw/hrs per year x your chosen fuel cost = cost 1
answer 2 based on 1.5 = YY kw/hrs per year x your chosen fuel cost = cost 2

galwaytt

imitation wrote: »

Gimme some credit here guys , I do intend on keeping the windows shut during periods when the heating will be in use. During the summer.. is it an issue ? I personally don't intend on heating the house during this period, then again, I'm sure some people out there do. Either way, when your making these figures you have to assume people aren't going to act the maggot.

Apologies for the vagueness of my post so far, a brief summary of the build is as follows.

Roof 0.10 W/m2k Mineral wool
Walls 0.16 W/m2k Polyiso 300mm cavity + drylining
Floor 0.13 W/m2k Polysio
Windows 0.9 W/m2k Triple glazed
Openings and ceiling will be taped up with membrane
MHRV

With that level spec, MHRV - even a basic one - will be necessary. Mind you, I see no mention of airtightness targets....

The 300mm cavity - have you got someone to sign that off ?? Seems very wide to me.

imitation

Sorry, cavity should be 150mm. The target we set was 3.0 m2/m3/hr @50pa.

Thanks sinnerboy, I know its quite a complex calc as one has to consider almost every element of the house.