Reccommended Air Changes Energy Use - Can Someone Check my Maths Please?

[martinwinlow]

I gather 'the old system' (pre-part L) recommended 4 air changes per hour generally in domestic premises but that was for an average air-tight building. Given the one in question is a bit more airtight, let's go with three. What follows is a calculation to determine what three changes of air per hour will cost in terms of energy:
House is 130m2 floor area x 2.5m (ceiling height) = 325m3
Density of air is 1.2 kg/m3
Weight of air lost each hour is therefore: 3 air changes x 325m3 x 1.2kg/m3 = 1170kg (sounds insane!)
Specific heat capacity of air = 1000J/kg/degC.
1J = 0.000000277777778kWh
If we use an ambient outdoor temperature of 0degC and raise it to 20degC (Δθ = 20), the amount of energy (ΔQ) needed per hour to do this is:
ΔQ = mcΔθ
ΔQ = 1170kg x 1000J/kg/degC x 20degC = 23,400,000J x 0.000000277777778kWh = 6.5kWh ... and that's every hour.
Is it just me or isn't this patently ridiculous as the cost would be astronomical... (or my maths could be adrift!)
MW

 

[robinbanks]

Passivhaus implementations indicate 0.6ACH are fine, and heat recovery contributes to staying within the heat demand needs per unit area

UK regs have always been crap for air tightness (thankfully improving), but while no one mandates installing systems for proper ventilation and bashing holes in the structure to permit uncontrolled ventilation is par for course you do rather need the gale blowing through to counter the moisture generation from human activity, and then pour a boatload of money into heating the world too

Not all of your energy loss through warm air leakage has to be replaced by the heating system, by the way - all energy use in the house contributes, as does insolation - and those ACH are limits, not measurements