To improve my education:
Can anyone tell me how we measure the air changes in an office environment. I understand that we need six changes per hour but not sure how it is measured.

Please do not answer get a consultant in!

I just want to know the methods of testing

Yes, it's a ventilation engineer you need as he can advise on the extract required.

He will measure room volume I think so L X W X H multiplied by 6 (air changes required) divided by 60 (minutes in the hour). This will give the cubic feet per minute. With that figure he can recommend the extract for that specific work area.

I think!

Six changes per hour seems a lot for an office, ( once every 10 minutes – hope you have a heat exchanger or some very good radiators). You may want to have a look at this for new buildings, section 6.

www.planningportal.gov.u...s/br/BR_PDF_ADF_2010.pdf

It depends what you have in the office, but gives a volume per person. I’m not an expert, but I would calculate the volume of air flow out at each opening using the anemometer mentioned above. Do the calcs based on the size of each individual opening , then add together. Don’t forget for air to go out, some also has to find its way in, so check which way it is flowing.
Have fun

The other angle to look at this from rather than doing volume and air flow measurements would be to check the levels of CO2 in the room.
~/+1000ppm and I would investogate further

Additional resources you can use include:

Building Regulations F:
http://www.planningporta...tf/bcapproveddocuments4/
Ventilation Rates 2.10
States the 10l/s per person

HSE Workplace Health and Safety Regulations
http://www.hse.gov.uk/pubns/indg244.pdf
Windows or other openings may provide sufficient ventilation but, where necessary, mechanical ventilation systems should be provided and regularly maintained.

Approved Code of Practice: Workplace health, safety and welfare. Workplace (Health, Safety and Welfare) Regulations 1992
http://www.hse.gov.uk/pubns/priced/l24.pdf
Regulation 6 - Ventilation
Enclosed workplaces should be sufficiently well ventilated so that stale air, and air which is hot or humid because of the processes or equipment in the workplace, is replaced at a reasonable rate
In many cases, windows or other openings will provide sufficient ventilation in some or all parts of the workplace. Where necessary, mechanical ventilation systems should be provided for parts or all of the workplace, as appropriate.
The fresh air supply rate should not normally fall below 5 to 8 litres per second, per occupant. Factors to be considered include the floor area per person, the processes and equipment involved, and whether the work is strenuous.

HSE General ventilation in the workplace: Guidance for employers HSG202 - May now be outdated as no longer available from the HSE website, however can be found here:
http://www.ucu.org.uk/me...HSG202_-_Ventilation.pdf
Provides general guidance on the above HS&Welfare regs

HSE Measurement of air change rates in factories and offices MDHS 73 - This has now been taken out of circulation as well
HSE guidance note EH22 - I cannot find available any more

CIBSE also give recommended guidance on ventilation rates for various workplaces, though you would have to pay for this some details can be found for free here:
http://www.arca53.dsl.pi...om/index_files/vent2.htm

I should start charging for some of this info :-)

Des

Dyslexic keyboard fingers, I'll try that again ...

My question would be if you do not know where the extraction point is can the output point at the blower on a air con unit be used to measure the 5 to 8 m/s air flow?

Badger

If the air con unit is bringing in fresh air from the outside and not just recirculating it could be classed a source of "fresh air supply". BUT i feel we may be getting a bit mixed up, m/s being speed and litres per second l/s being volume, the requirement being 5-8l/s not 5-8m/s.

If you do use an anemometer you would need the cross sectional area of the duct / window etc. and multiple measurements of air flow across the face at various locations (usually plotted on a grid) then you can use the area and the average speed to give you the volumetric flow rate.

Des

No worries Brian, I have one which has that feature, but I have to input the area in m² for it to work :-)