PHPP Ventilation Design Air Flow Rate (maximum)

[Anonymous]

I have searched the forum and it appears this has not been asked before, but aopologies if I have missed it.

Basically, I have a terrace of 3 PH units that I am currently in the process of designing and I have a question about how PHPP comes up with the Design Air Flow Rate (maximum).

I understand this is usually the maximum of the supply or extract air demands based on occupancy and number of kitchens, bathrooms, etc, but in my case it would appear to be taking a higher value. When I click on cell G21, the formula reads =MAX(G15,G19,G8*0.3*1.3), which translates to the ventilated volume (G8), multiplied by 0.3 ACH, multiplied by 1.3. My question is what is the 1.3 value and where does it come from? My G15 and G19 cell values are 90m³/h and 120m³/h respectively, but the design air flow rate (max) is coming out at 168m³/h. The total ventilated volume for the terrace is 431m³.

Can anybody shed some light on this for me?

Thanks.

[Anonymous]

That's an interesting one, anyone any ideas? A bonus 30%! My only thought is that if it is choosing that option of the three then that is the absolute minimum ventilation you could get away with, and you are setting that as Max flow. The box below then allows you to design the different control options and the default setting is for only running 30% of the time. The factor makes sure you can't underspec the ventilation or improve the energy performance by saying there's no ventilation!

Is that with the option in O25 Verification set to design? Check it with verification too.

[Mark Siddall]

Leigh,
I suggest that you joint the Passivhaus Trust so that you can gain access to the iPHA forum – there was a very involved discussion on there a few months ago (I don't have time to summaries it right now.)

Mark

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