IES-VE User Forum

Hello All,

I've been advised to input a 5m3/hm2 air infiltration rate. Considering that the pressure in IES is set @50 P, what's the best way to convert this to ach? CIBSE TM23 recommends to multiply times the surface-volume ratio, but result seems to high.

Could anybody give me an advise on this?

THANKS!

Hi

I realise this was posted a while ago, but thought I'd add to it as I'd be interested to see what method everyone uses.

I usually use the tables given in CIBSE Guide A Section 4.6 which are based on empirical values for air infiltration rate. These give a relatively good idea of the infiltration rate for different types of building with various height/area combinations.

For converting from air pressure test values at 50 Pa to ACH, Figure 4.15 (CIBSE Guide A Section 4.6) gives a conversion factor relative to volume of enclosed space.

VEng

I'm assuming that this is for the purposes of carrying out a heating load calculation?

I'll tell you what I tell the mechanical engineers where I work. It's not the modellers job to decide on what infiltration rate should be. The person responsible for the mechanical design should be making that call.

Pointing at a pressure test target and telling you to use that frankly shows a lack of understanding.

Think about it this way, you could have two identical buildings, one in a city centre completely sheltered from the wind and the other near a cliff edge by the sea, totally exposed to the elements. If they both achieve 5 m3/m2.h @ 50pa in test conditions, does that mean they are going to have the same heating requirement?

Just food for thought.

All

The BSRIA guide for calculating heating loads refers to the use of the TM 23 value. It is usually a small value when expressed as ach, less than 0.1.

You can actually find this value calculated for you as ach in the Building Details tab of the Set Building & System Data in the SBEM/DSM module, because this is the default option for Part L compliance.

The reality is that new buildings are pretty air tight, even at the seaside, and mechanical fresh air loads are far more significant than infiltration losses

W