Thermal Comfort Building Physics, Lo-Lo CDT Thursday 6 th October 2011

Thermal Comfort

What is Thermal Comfort?

Definition of Thermal Comfort “That condition of mind which expresses satisfaction with the thermal environment” (ISO 7730)

Thermal Comfort Variables Thermal Comfort TS may also be the mean vote for a group of individuals

Necessary Conditions for Thermal Comfort 1.Heat balance of the human body 2.Comfortable psychological conditions

Heat Balance of the Human Body Metabolic heat production

Components of the Environmental Heat Loss and the Human Heat Balance T a, rh rh

Factors Affecting Human Heat Balance Environmental parameters –Air temperature (Ta) –Mean radiant temperature of surfaces (Tr) –Air velocity (va) –Air relative humidity (rh) Personal factors –Physical activity (M) –Clothing insulation (Icl)

Personal Factors: Clothing Clo: a unit used to express the thermal insulation provided by garments and clothing ensembles: 1 clo = m2 °C/W

Personal Factors: Clothing

Personal Factors: Metabolic Rate Met: a unit used to describe the energy generated inside the body due to metabolic activity. It is defined as 58.2W/m 2 which is the energy produced per unit surface area of an average person, seated at rest: 1 met = 58.2 W/m 2

Metabolic Rates for Typical Tasks Activity Metabolic rate (Met) Reclining0.8 Seated, quietly1.0 Sedentary activity (office, dwelling, lab, school)1.2 Standing, relaxed1.2 Light activity, standing (shopping, lab, light industry)1.6 Medium activity, standing (shop assistant, domestic work, machine work) 2.0 High activity (heavy machine work, garage work)3.0 © ASHRAE

Effect of Activity Level

Physiological Conditions for Thermal Comfort Esk = [ (M-W)-Pa] [(M-W) ] Sweat rate

Predicted Mean Vote The mean vote of a group of individuals can be predicted. The Fanger model of human thermal comfort enables this. The model is really only applicable for a body in thermal equilibrium with it’s surroundings. PMV is calculated on a 7-point scale from -3 to +3 – so it is directly comparable with TS.

Comfort Equation (Fanger) Metabolic heat generation [W/m 2 ] External work [W/m 2 ] Skin evaporation [W/m 2 ]: - Moisture diffusion - Evaporation of sweating Respiration [W/m 2 ]: - Latent heat loss: Lr - Convective heat loss: Cr Lr+Cr= M(5876-Pa) M(34-Ta) Ts = Body’s mean surface temperature Tr = Mean (radiant) temperature of surrounding surfaces

Resultant Temperature - T res h = hc + hr Dry heat loss = Surface convection + Thermal radiation hc Ta + hr Tr hc + hr T res = In indoor spaces: hc ~ hr :

Calculating PMV

The complete equation set

Comfort Zone / Envelope Comfort ‘zone’ or ‘envelope’

Comfort Envelope (ASHRAE Std 55R) o o

CIBSE: Recommended Design values for T res (now T op is used) T res has been replaced in UK thermal comfort work by the operative temperature (T op ).

ASHRAE (USA): acceptance of adaptation Applicable to buildings that are: naturally ventilated buildings, not mechanically cooled, have operative windows.

BS EN15251: UK and Europe Applicable to free-floating buildings PPD=20% Operative temperature Weighted running mean ambient temperature Cat III Cat II Cat I

BS EN15251: UK and Europe

Thermal comfort: an important factor in satisfaction and productivity assessment. ISO measurement questionnaire

POE: Comfort and productivity Thermal comfort ranked most important for productivity in all building types. Perceived productivity increases with better thermal comfort in all building types. Source: Leaman and Bordass (2007) Are users more tolerant of green buildings, BR&I, Vol. 35, no. 6, pp

Summary Thermal comfort is important for well-being and productivity Comfort depends on environmental factors (Ta, Tr, Va, Rh) Comfort depends on personal factors (Met, Clo) Guidelines for indoor comfort are now based on T op (which replaces T res ) or comfort envelopes