Fresh air requirement question

[nh3simman]

would 8 litres per second per person be near ?

8 l/s/p is a bit high.

If there is no smoking, you can go down to 2.5 l/s/p for a typical office. Fresh air is a big load so you should keep it to a minimum.

You are right to base the quantity on the number of people. I have seen estimates based on a fraction of the supply air but this is when you don't have any better figures.

[stevo]

Thanks for your replies ! anyone else with ideas ?

[frank]

CIBSE guide recommends 8 l/s/person as a minimum fresh air requirement (20 l/s/person for airconditioned spaces) or 6 air changes per hour for an office environment.

So, for 10 persons you would require 80 l/s or 0.08m3/s or for 6ACH you would require 0.67m3/s.

The additional cooling load, UK conditions would be 1.51kw or 1.26kw respectively

0.08m3/s would require a duct @ 150mm dia to give a reasonable velocity and pressure drop.

[stevo]

Many thanks Frank, Just the info i can use !

[nh3simman]

CIBSE guide recommends 8 l/s/person as a minimum fresh air requirement (20 l/s/person for airconditioned spaces) or 6 air changes per hour for an office environment.

Good advice, always check your local requirements.

In SA with +35degC ambient and poorly sealed buildings, we try to keep the fresh air to a minimum.

ASHRAE does not actually give a fresh air recommendation but rather a guideline.

[frank]

ASHRAE does not actually give a fresh air recommendation but rather a guideline.

The English CIBSE Guide is also a "Guide" but it is adopted by most design engineers to be incorporated into new build projects, as it sets a baseline for the performance of the services.

[stevo]

Good advice, always check your local requirements.

In SA with +35degC ambient and poorly sealed buildings, we try to keep the fresh air to a minimum.

ASHRAE does not actually give a fresh air recommendation but rather a guideline.

Pheww thank god for that ay !!!

[Abby Normal]

8 l/s/p is a bit high.

If there is no smoking, you can go down to 2.5 l/s/p for a typical office. Fresh air is a big load so you should keep it to a minimum.

You are right to base the quantity on the number of people. I have seen estimates based on a fraction of the supply air but this is when you don't have any better figures.

2.5 l/s is bare bones minimum in many places. Think the first number ever used was 4 CFM per in the Houses of Parliament. Heard an urban legend they used to give coal miners 5 cfm per to keep productivity up.

[nh3simman]

2.5 l/s is bare bones minimum in many places. Think the first number ever used was 4 CFM per in the Houses of Parliament. Heard an urban legend they used to give coal miners 5 cfm per to keep productivity up.

I wouldn't say 2.5l/s/p is a bare bones minumum.
We add outside air for 2 reasons

1. Supply of O2
2. removal of CO2

People need 0.2l/s of O2. This is a fresh air rate of 1 l/s/p.