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Center for Housing Innovations

The Chinese University of Hong Kong

AirpakAirpak Tutorial: Office VentilationTutorial: Office Ventilation

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Center for Housing Innovations

The Chinese University of Hong Kong

How to model an office shared by two people working at computers

You will learn:

- model airflow, heat transfer and associated phenomenon in anenclosed space

- Include effects of relative humidity distribution in the simulation

- Model the effects of radiation

- Examine the comfort level in the room by calculating the predicted

mean vote (PMV) and predicted percentage dissatisfied (PPD)

IntroductionIntroduction

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The Chinese University of Hong Kong

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The Chinese University of Hong Kong

What is Thermal ComfortWhat is Thermal Comfort

That condition of mind which expresses satisfaction with the thermalenvironment. (ASHRAE Standard 55)

People will get Thermal Comfort when heat produced by metabolism equalsthe heat lost from body.

Comfort criteria developed by Fangerf (M, Icl, V, tr, ta, Ps) = 0

where, M = metabolic rate (met)Icl = cloth index (clo)V = air velocity (m/s)

tr = mean radiant temp. (oC)ta = air temp. (oC)Ps = water vapour pressure (kPa)

Source: Fanger, P.O., Thermal Comfort: Analysis and Applications in Environmental Engineering. 1970, New York:McGraw-Hill Book Company

Heat

Produ-ced

HeatLost

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Prediction of Thermal ComfortPrediction of Thermal Comfort

Fangers equation is too complex for architects, but it may be transformed to comfortdiagrams

Source: ASHRAE, Standard 55:Thermal Environmental Conditions for Human Occupancy. 2004, Atlanta, USA: GA.

It can also be used to yield other indices, such as:- predicted mean vote (PMV)- predicted percentage of dissatisfied (PPD)

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PMVPMV

A complex function of six major comfort parameters (M, Icl, V, tr, ta, Ps)

Predict mean value of the subjective ratings of a group of people in agiven environment

PMV= (0.352e0.042(M/Adu) +0.032)Load

M/Adu: internal heat production;Load: heat load= Heat got-heat lost

The PMV index is used to quantify the degree of comfort for thermalenvironment evaluation

- +3 Hot- +2 Warm- +1 Slightly warm- +0 Neutral

- - 1 Slightly cool- -2 Cool- -3 Cold

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Center for Housing Innovations

The Chinese University of Hong Kong

PPDPPD

Determined from PMV as a quantitative measure of thermal comfort

Dissatisfied means not voting -1, +1 or 0 in PMV

Predicts the percentage ratio of dissatisfied peoplePPD=100 - 95 * EXP(-0.03353 PMV4- 0.2179 PMV2)when PMV=0, 5% occupants will feel uncomfortable;when PMV=1,-1, 26% occupants will feel uncomfortable.