Help with Air Change Rates....

[bigDog]

Hi all, I am specifying an AHU for a cinema and need a bit of help with Air Change Rates...

Now I have calculated the heat loads in the auditorium to be 37Kw

15.45m wide x 11.83m long x 4m High
150 persons @ 100w Sensible
1 ACH Natural infiltration

now CIBSE states for auditoriums it has to have an ACH of 10, if i change my calculations it adds over 15KW to the total load if i change my ACH from 1 to 10

Now, should this not be taken into account as it is "added" by the AHU????

P.S I am using grills near the feet of the people sitting, and sending air in at around 4m/s

Any help is greatly appreciated reference the ACH please.

[bigDog]

And im in the UK

[bigDog]

Or would you just worry about cooling the room, not necessaraly ventilating it...

[frank]

The Air Change Rates mentioned in CIBSE refer to the amount of air to be circulated, which is different to the fresh air requirements of the occupants. You will find that the occupants need a minimum of 10l/s per person.

To achive 10ACH in the Auditorium you will need (15.45x11.83x4x10)/3600 = 2.03m3/s

The fresh air requirement for 150 persons will be (150 x 10)/1000 = 1.5m3/s

So, to achieve the minimum ACH rates and Fresh air requirement, you will need to circulate 2.03m3/s of which, 1.5m3/s will be fresh air and 0.53m3/s will be recirculated air. You will need to have an extract fan rated at 1.5m3/s to balance the system.

The air infiltration rate should be included in your heat load/heat loss calculations but excluded from your fan sizing calcs

[RSTC]

If you are using an AHU and worried about the energy: use a rotary heat exchanger - it can be turned off to give free cooling. Useful, as the busiest times are often at night.

I wouldn't suggest dropping below 10 l/s/p but alot non-heat exchanger installs have the fresh air throttled well below this (I suppose in a attempt to reduce heating costs) and don't seem to have too many complaints.

If cheap and purposeful is your thing then a gas fired rooftop pack is fine. But have an separate extract fan.

For the above calcs you can ignore the infiltration as you will be slightly over-pressurising the room - and a (good) cinema will be very well insulated for sound which will mean it will be tightly sealed.