PHPP Controlled ventilation rate vs UK Building Regs.

[Mark Bennett]

PHPP states a target controlled air change of 0.3 ac/h. Assuming a ceiling height of 2.5m (default in PHPP) this is equivalent to 0.21l/s.m2 (of floor area) when converted into units for UK building regs - if my maths are right.

However, the building regs (Part F 2010) specify a minimum average controlled ventilation rate of 0.3l/s.m2 of floor area.

This means that the controlled ventilation being assumed for PHPP energy calculations is less than that required for the UK building regulations.

Is my maths right?

If so, then either I stick with the PHPP value, which means I am breaking the Building Regs or I go with Building Regs, which means my energy calculations in PHPP are optimistic and I need to factor in a larger MVHR system.

There is a get out in the building regs related to performance based ventilation but this seems complicated and difficult to prove.

What is the generally accepted approach?

I'm sure this is covered elsewhere, but I've done a search and not managed to find anything.

[Dave Howorth]

This means that the controlled ventilation being assumed for PHPP energy calculations is less than that required for the UK building regulations.

Is my maths right?

I think so, yes. I asked a similar question a while ago. I think it was on this forum but I can't find it now. MVHR systems do have speed controls. I remember speculating about making a system with buttons for 'PHPP certification' or 'Building Regs Compliance Test'. 

When I looked into air quality (IAQ) further, it seemed to me that current thinking indicates that even higher ventilation rates are better so the whole issue became moot in my mind.

If so, then either I stick with the PHPP value, which means I am breaking the Building Regs or I go with Building Regs, which means my energy calculations in PHPP are optimistic and I need to factor in a larger MVHR system.

There is a get out in the building regs related to performance based ventilation but this seems complicated and difficult to prove.

What is the generally accepted approach?

You'll need to find somebody else for an expert opinion!

Don't forget the measured floor areas are different as well. Plus you also need to consider what the actual occupancy will be versus the occupancy used for the various calcs when considering the required l/s.m2

[Mark Bennett]

This means that the controlled ventilation being assumed for PHPP energy calculations is less than that required for the UK building regulations.

Is my maths right?

I think so, yes. I asked a similar question a while ago. I think it was on this forum but I can't find it now. MVHR systems do have speed controls. I remember speculating about making a system with buttons for 'PHPP certification' or 'Building Regs Compliance Test'. 

When I looked into air quality (IAQ) further, it seemed to me that current thinking indicates that even higher ventilation rates are better so the whole issue became moot in my mind.

Ah. That would definitely mean I needed a bigger, more expensive and less efficient MVHR unit.

If so, then either I stick with the PHPP value, which means I am breaking the Building Regs or I go with Building Regs, which means my energy calculations in PHPP are optimistic and I need to factor in a larger MVHR system.

There is a get out in the building regs related to performance based ventilation but this seems complicated and difficult to prove.

What is the generally accepted approach?

You'll need to find somebody else for an expert opinion!

Don't forget the measured floor areas are different as well. Plus you also need to consider what the actual occupancy will be versus the occupancy used for the various calcs when considering the required l/s.m2

I'm aware that the area calculations are different but that just seems to exacerbate the situation since the PHPP treated area is smaller than the SAP area. The house is actually pretty large for the normal number of occupants, so I don't think we'll really have any air quality issues even at PHPP levels.

Perhaps switchable PasivHaus and Building Regs modes is the best option!

[Mark Siddall]

Mark,
In reality you are likely to fnd that B.Regs will result in overly dry air due to a low RH. PH levels of ventilation are better but it is emerging that you may find that you will need nearer to 5lt/s/person in reality (for a balance of RH and indoor CO2 - at low levels of ventilation care is needed to control VOCs i.e. attention to materials and finishes). Retaining some ability to control ventilation, a means of recomissionging during the first year or so of occupation would be worthwhile.

Mark

[Mark Bennett]

Mark,
In reality you are likely to fnd that B.Regs will result in overly dry air due to a low RH. PH levels of ventilation are better but it is emerging that you may find that you will need nearer to 5lt/s/person in reality (for a balance of RH and indoor CO2 - at low levels of ventilation care is needed to control VOCs i.e. attention to materials and finishes). Retaining some ability to control ventilation, a means of recomissionging during the first year or so of occupation would be worthwhile.

Mark

Thanks Mark.

We're way over 5l/s/person (18m3/h) based on either floor area in either PHPP or Building Regs so this shouldn't be a problem. I don't think air quality as such is an issue in this case.

My main concern is more of a "legal" issue about whether building control will accept a lower air change rate than Building Regs, and if not do I need to take into account the extra air flows when sizing my MVHR and calculating energy consumption in PHPP.

It sounds like I'm safe sticking with the PHPP values and trying to convince Building control that it is safe under the performance based exception. Our BCO is a pretty reasonable chap and is very willing to help us find good solutions rather than be dogmatic about the rules.

Does anyone have any links to useful published material about indoor air quality that I can use to build an argument?

[Dave Howorth]

Does anyone have any links to useful published material about indoor air quality that I can use to build an argument?

I have three links from my notes. Hopefully other people have more.

http://sspc622.ashraepcs.org/pdf/iaqgrimsrud.pdf

 "It is shocking that searching the building research literature from the past 25 years yields only seven studies that attempt to address the question of the health basis for residential ventilation standards."

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V23-4VXB8SC-1&_user=1861184&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000055073&_version=1&_urlVersion=0&_userid=1861184&md5=4e3685d13ec7b4e165fc472fb07c418e

"the degree of control, as perceived by occupants, seemed more important for the prevalence of adverse symptoms and building-related symptoms than the ventilation mode per se. This result indicates that even though the development and application of new indoor environment sensors and HVAC control systems may allow for fully automated IEQ control, such systems should not compromise occupants’ perception of having some degree of control of their indoor environment."

http://www.passivehouse.com/English/AirH.htm

[Nick Grant]

Mark

Our Building regs compliant house has crappy trickle vents and air quality is very variable. 15-20m3/h/person would be lovely. As Mark says over venting in cold weather can make building too dry.

Remember you will be running at 77% of MVHR capacity normally so have some boost in reserve.

Re Building Regs I'm sure they will let you open the window for extra vent rates for purge etc. We are taking that approach in schools and offices.

Normal UK ventilation is totally hit and miss.

Nick