4.5 Infiltration (aeraulic data)
Indalo® utilises whole building air permeability not a per room infiltration value. Indalo® also utilises the Frensch air permeability indicator Q4Pa-surf, which is the airflow rate at 4Pa per unit of envelope surface area EXCLUDING the lowest floor (m3/h.m2) as per RT 2012 & ISO-9972:2015. See https://maisonrt2012.wordpress.com/tag/q4pa-surf/.
Typical values for Q4Pa-surf:
· Typical mean Q4Pa-surf values for French housing 0.4 - 1.62 m3/h.m2 .
· Typical mean Q4Pa-surf values for French non-residential 0.82 - 4.73 m3/h.m2 .
· RT 2012 residential single Q4Pa-surf 0.6 m3/h.m2 (BEPOS 2017 0.4).
· RT 2012 residential multi Q4Pa-surf 1.0 m3/h.m2 (BEPOS 2017 0.8).
· French regulations 2012 default non-residential Q4Pa-surf 1.7 m3/h.m2 .
UK CIBSE / BRE / UK Part L Air permeability, on which CIBSE A tables A4.13 to 4.21 are based (4.7.2.2) is defined at 50 Pa and the envelope surface area INCLUDING the lowest floor (4.8.1). Typical values:
· Leaky 20 m3/h.m2 .
· 2002 Regs 10 m3/h.m2 .
· Moderately tight 7 m3/h.m2 .
· Tight 5 m3/h.m2 .
· Very tight 3 m3/h.m2 .
· AECB 1.5 m3/h.m2 .
· EnerPHit 1 m3/h.m2 .
· Passivhaus target 0.6 m3/h.m2 .
· Passivhaus good 0.3 m3/h.m2 .
· Passivhaus ‘zero’ 0.05 m3/h.m2 .
Passivhaus uses n50; this is the leakage rate (air change/h) at 50Pa; this is based on volume not exposed envelope area and as such is not ideal and not considered further.
The VE export to Indalo® converts the VE infiltration APS output to a Q4Pa-surf air permeability value. The method used is:
1. Use APS simulation data to derive an annual mean air change value for all rooms (total average flow / total volume).
2. Convert the annual mean air change value to a UK Air permeability at 50 Pa (using CIBSE A fig A4.10 using a best fit relationship) .
3. Multiply UK Air permeability at 50 Pa by envelope area including lowest floor to get Q50 (m3/h).
4. Divide Q50 by envelope area excluding lowest floor to get Q50surf (m3/h.m2).
5. Scale Q50surf from 50 Pa to 4 Pa utilising the power law equation:
Q4surf = Q50surf * (4/50) ^ 0.67 (m3/h.m2).
Because of the nature of air permeability data & metrics conversion will introduce some errors, see 3.1 in the following reference:
Air permeability is defined with internal envelope areas; the script assumes external areas as we are using the areas as a ratio so the error is small compared to the coarseness of infiltration figures, for example: two 8x8x3m rooms with 0.3m walls & ceiling depths rooms adjoined along one wall, using: external areas 272/400 = 0.68, internal areas 243/361 = 0.67.
