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Grant1962  
#1 Posted : 12 August 2011 08:47:24(UTC)
Rank: Forum user
Grant1962

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
HSSnail  
#2 Posted : 12 August 2011 09:18:41(UTC)
Rank: Super forum user
HSSnail

Grant you need an Anemometers that shows volume of air movement as well as velocity. By using this at extraction point (s) you can see air leaving building and from volume of building calculate air changes. If you have extraction fans you should be able to find out the volume of air they move and again do the calculation. That is of course assuming they work. Very simple explanation and its a little more complicated but an Internet search should give you more details. Brian
Birchall31628  
#3 Posted : 12 August 2011 16:22:06(UTC)
Rank: Forum user
Birchall31628

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!
Birchall31628  
#4 Posted : 12 August 2011 16:28:35(UTC)
Rank: Forum user
Birchall31628

I would use basics for your width and height etc (eg in feet so 20ft x 19ft x 14 ft x 6 (air changes) divided by 60 (minutes) So, for example 5320 x 6 (air changes) divided by 60 is 532cfm. Extract that will cope in excess of 532cfm will suffice. I am really not a ventilation salesperson so not sure what's on the market.
chris42  
#5 Posted : 12 August 2011 19:13:41(UTC)
Rank: Super forum user
chris42

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
leadbelly  
#6 Posted : 12 August 2011 19:24:17(UTC)
Rank: Super forum user
leadbelly

Does anyone else remember MDHS73: Measurement of air change rates in factories and offices? It was printed in 1992 and has been long out of print. LB
descarte8  
#7 Posted : 15 August 2011 12:06:52(UTC)
Rank: Super forum user
descarte8

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
Barrie(Badger)Etter  
#8 Posted : 15 August 2011 12:45:32(UTC)
Rank: Super forum user
Barrie(Badger)Etter

In continuing the vein of ignorance and BH's comment on using an Anemometer by using it at the extraction point, my question would be if you do not knw where the extraction point is can the input point sat the blower on a air con unit be used to measure the 5 to 8 m/s air flow? As an aside ebay have some going for £15 min price, handy looking gadgets. Badger
Barrie(Badger)Etter  
#9 Posted : 15 August 2011 14:11:57(UTC)
Rank: Super forum user
Barrie(Badger)Etter

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
HSSnail  
#10 Posted : 16 August 2011 07:58:38(UTC)
Rank: Super forum user
HSSnail

Barrie I am not an engineer hence me saying that my answer was very simplistic. Not sure if the air con would work. These units work in a number of ways and the air coming out of them is not always being extracted from the room. Sometimes they work by a heat exchange between two different flows. If its so critical that you know the flow as others have said get an engineer in. I know you did not want that answer but sometimes its the only way. Brian
descarte8  
#11 Posted : 16 August 2011 08:50:59(UTC)
Rank: Super forum user
descarte8

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
HSSnail  
#12 Posted : 16 August 2011 09:16:19(UTC)
Rank: Super forum user
HSSnail

descarate8 not to disagree but some anemometers do a volume movement as well as air speed
descarte8  
#13 Posted : 16 August 2011 10:06:30(UTC)
Rank: Super forum user
descarte8

No worries Brian, I have one which has that feature, but I have to input the area in m² for it to work :-)
Barrie(Badger)Etter  
#14 Posted : 24 October 2011 15:45:32(UTC)
Rank: Super forum user
Barrie(Badger)Etter

I have an anemometer that reads m/s does anyone know of a formula to convert from m/s to l/s? Badger
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