That depends on air temperature and turbulence rate. 1,5 m/s seems a rather high value. ISO standard 7730 (2005) is recommended as a guideline.

I agree with Evert De Ruiter.

Hello Evert/Boris

Thank you both so very much,

Table A.5 of ISO 7730 outlines a maximum mean air velocity of 0.12 and 0.1 m/s in summer and winter respectively for offices. Also Appendix G states there is no ‘minimum air velocity’ that is required for thermal comfort however increased air velocity can be used to offset increased temperatures. I suppose that is as authoritative as I can hope for.

Many thanks once more

Mohammad

See article below:

Article Towards a Brazilian standard for naturally ventilated buildi...

Thanks John

I was particularly interested in what was regarded as excessive air velocities but can see from the publication you suggested that minimum values were also worked out for warmer climates.

Thanks

Dear Mohammad. It is obvious that the answer to your question is strongly related to the presence of HVAC systems. In this case, ISO EN 7730 reports, depending upon the class of environmental quality, a figure (A.2) were the limit values of velocity are depicted as a function of the operative temperature and Turbulence intensity. These values are designed to minimize the effect of local discomfort due to draughts. These suggested values fall in the range 0.1-0.3 m/s (summer and winter). On this perspective I strongly agree with Evert De Ruiter

Moreover, about figure G1, please observe that:

1) Values in figure G.1 are referred to overall comfort (PMV), not to local discomfort (draft risk, radiant asymmetry and so on).

2) In the note of the figure G1 you can read: "Figure G.1 applies to an increase of temperature above 26 °C with both tr and ta increasing equally. When the mean radiant temperature is low and the air temperature is high, elevated air velocity is less effective at increasing heat loss. Conversely, elevated air velocity is more effective at increasing heat loss when the mean radiant temperature is high and the air temperature is low. Thus, the curve in Figure G.1 that corresponds to the relative difference between air temperature and mean radiant temperature must be used. Large individual differences exist between people with regard to the preferred air velocity. Therefore, the elevated air velocity must be under the direct control of the affected occupants and adjustable in steps no greater than 0,15 m/s."

You can find some other details in a recent review of our Group (Energy and Buildings 81 (2014) 326–336). If you want a copy, please send me a private message.

Best regards

The theme of "productivity" is a main issue in such cases. Limitation of air velocity depends on productivity of office occupants.

I would like to draw your attention to the following points for guidance on acceptable draft inside air conditioned spaces -

As per CIBSE standards, 0.1 m/s or stand still air velocity is assumed for analytical calculations. for more information refer to CIBSE Guide.

The best person to ask is probably Richard De Dear at University of Sydney. He has a whole indoor air quality lab that studies such things in great detail... and he (along with Gail Braeger at Berkeley) were the ones that discovered the limits of thermal comfort that you cite. 

Thank you all for your contributions. I think I have a fair idea now on how to proceed,

Thanks once more

In addition to following the above guidelines you should also consider the context before stating that X is fine and Y is not fine. For instance whilst an air speed of 0.15 m/s is generally considered the lowest that can be detected as air movement or a draught it also depends on where that air is in relation to the occupied zone and also what temperature the room and supply air are at. For example it is known that higher velocity air can be tolerated when it is being used to cool a space that is uncomfortably warm. Also, it is not uncommon in Passivhaus buildings to use high velocity diffusers to 'jet' air deep into an occupied space using the Coanda effect, where air will be moving at circa 1 m/s, but this is done adjacent to the ceiling typically and not in the so called occupied zone (

I work regularly and happily in the tropics with a desk fan air velocity at more than 1 meter per second and temperature of 29C. I believe that the claimed low limits on air velocity (< 1 m/sec) are for office environments with a high culture of complaint (#1 UK, #2 USA), an antiquarian attachment to paper shuffling,  and a commercially induced,  presumptive need for air conditioning.

Book Tropical Cool: A Buddhist Manual of Air Conditioning

I entirely agree with you Richard,

Admittedly higher air velocities are far more tolerable at high temperatures. The generation of hermetically sealed office buildings in Northern European/American climates with little environmental controls available to the occupant is what has provided the guiding star for the standards pointing to very low air velocities as 'acceptable'.

And here in my beloved adaptive country- England- office workers love to complain about their thermal environment!

There are two types for guidelines for indoor air velocity (because this a relative term with respect to occupants skin) for air conditioned and naturally ventilated buildings. There are also local factors that adds to it. It is generally found that occupants in NV buildings are more tolerant to high air movement (depending on the season i.e. winter or summer and persistent relative humidity). So my advise will be not to generalize it rather consider the functionality, occupants activity and mode of ventilation specific to the building you are talking about. You also must have knowledge about the clothing pattern of occupants and local discomforts due to radiant asymmetry.

Lot of literature is available on this. Refer ASHRAE 55-2014: it also talks about adaptive thermal comfort

In addition to issues related to thermal comfort and the impact of wind speed as a parameter; Wind speed more than 1 meter per second exceeds the performance of paper on the desk. So we can say that performance is more important component of the wind speed in the office environment.

Speaking again from personal experience in the tropics, a close 12 inch desk fan set at low velocity can be directed at the upper body and face. With velocities >1 m/sec Thai workers and I too feel comfortable at even 32 deg and papers are not disturbed with this setup as they might be with ceiling fans. This cuts electric costs in half compared with aircon.

Book Tropical Cool: A Buddhist Manual of Air Conditioning

Dear mohammad. You can find your answer in chapter 9 of ASHRAE fundamentals and also, ASHRAE-55

GOOD LUCK

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