# Query on DesignBuilder and EnergyPlus: Impact of air velocity on thermal comfort

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Hi,

I am trying to model the impact of ceiling fans on thermal comfort in a warm-humid climate, for a naturally ventilated building. Intial simulation runs obviously show a lot of discomfort with PMV going upto 5.5 during peak summer. We want to model ceiling fans so that the impact of air velocity on thermal comfort is captured. Naturally this wont lead to achieving thermal comfort conditions in the space but we feel that it should at least result in PMV coming down to 4-4.5. I am not sure if doing this is possible in DesignBuilder but I think one can specify an object called AirVelocity schedule in EnergyPlus, where one can input air velocity in m/s in one of the fields (the current EPlus default being 0.137). I want to know that if we modify (increase) the value of air velocity to about 0.7 (for ceiling fans), would it be used for comfort calculations? I thought the Fanger comfort model algorithms use air velocity for calculations but I can't see that
happening anywhere in the Eplus Engineering reference, which could also have been a resultant of my limited understanding of the subject matter. I also noticed that the Pierce model takes air velocity into account. Does this mean that we should rather look at the Pierce model rather than the Fanger model in order to arrive at an adaptive model of thermal comfort? What we basically want to do is to make sure that the increased air velocity is used for calculation of PMV in EnergyPlus to model the impact of ceiling fans.

I would be really grateful for any help.

Regards,?
?
Sanyogita Manu

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Joined: 2011-10-02
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ASHARE 55 does give a bit of information about the thermal comfort in section 5.2.3.

However the section says that the elevated speed can be used to offset the temperature by not more than 30 C (5.40 F).

The air speed considered here is however in the range of 0.8 m/s to 1m/s. However the ceiling fans designed in here in India

gives an air speed of about 2m/s for which the temperature that could be offset can be more.

No specific relation as such is given as to determine the temperature that can be offset for higher air speeds.I have referred the

Thermal Comfort chapter of the ASHRAE Fundamentals handbook,however no particular specifics is given as to relation between the

Air speed felt on the skin and the temperature that can be offset due to it. Definitely the personal comfort level also varies with person to person.

If anyone knows about any other standard or reference manual giving information on this matter or can throw more light on this it

will be greatly appreciated.

Regards,

Sanjay Cholekar

Sanjay Cholekar

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Joined: 2011-08-09
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Hi Sanyogita,

Just to mention that in DesignBuilder, you can define the velocity to be used for the comfort calculations on the Simulation tab of the model options dialog, under the Advanced header. I tried changing from the default air velocity from 0.137 m/s to 2 m/s and obtained very different results for all comfort indices, including Fanger PMV.

Regards,

Andy

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Joined: 2011-10-02
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EnergyPlus does include room air velocity term in Fanger model. It looks like this detail did not make it into the E+'s Engineering Reference, but a value for forced convection surface heat transfer coefficient is calculated using:
Hc = 12.1 * SQRT(velocity)

However, the calculations take the larger of either a natural convection Hc or the forced convection Hc, so the air velocity might not be used in all situations.

Brent

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Hi Andy,

I could not find the input field for specifying?velocity anywhere. Is it something to do with the version; I am using 2.0.4.002. And one more question: when we use the Operative temperature control in DesignBuilder, it takes radiant fraction of 0.5 by default, and its not possible to change it, am I right?

Thanks a lot,
?
Sanyogita

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Joined: 2011-10-02
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Sanyogita

The below screen shot will show you where the comfort velocity is in the
model options tool (spanner icon) under simulation tab in the advanced
option

Operative temperature description can be found here:
http://www.designbuilder.co.uk/programhelp/calculation_options.htm

Eric

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Joined: 2011-10-02
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Sanyogita

Try upgrading to the latest V2.1 release

Eric

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Hi?Eric,
?
I dont know why but I still dont see it anywhere. Is there some some other?precondition?within the program or model options for it to appear??
(snapshot attached)
?

Sanyogita Manu

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Joined: 2011-10-02
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Happy new year.
Would nay one recommend a geothermal enginnering or contracting company who have experience in horisontal or Pond geothermal system. This is for a 48 unit residential project with an exisitng water pond that might be used in a geothermal heat pump system for HVAC and water heating in Goergia.
Thank you
H. Abaza

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