2 What is Thermal Comfort? - That condition of mindwhich expresses satisfactionwith the thermal environment.ISO 7730Definition
3 When we talk of human comfort, various aspects are important: Thermal ComfortAcousticLightingPsychologicalErgonomics.
4 “Thermal Comfort” of a human being is influenced by: Individual factorsActivityClothingEnvironmental factorsAir TemperatureRelative HumidityAir SpeedMean Radiant temperature
5 Mean Radiant Temperature Actual roomImaginary roomRR’t4trt1Heat exchange by radiation:R=R’t2t3The Mean Radiant Temperature is that uniform temperature of an imaginary black enclosure resulting in same heat loss by radiation from the person, as the actual enclosure.Measuring all surface temperatures and calculation of angle factors is time consuming. Therefore use of Mean Radiant Temperature is avoided when possible.
6 Activity Affects the Level of Comfort restinglight industrialoffice workhigh activity
7 Metabolic Rate0.8 Met1 Met8 Met4 MetEnergy released by metabolism depends on muscular activity.Metabolism is measured in Met (1 Met=58.15 W/m2 body surface).Body surface for normal adult is 1.7 m2.A sitting person in thermal comfort will have a heat loss of 100 W.Average activity level for the last hour should be used when evaluating metabolic rate, due to body’s heat capacity.
10 Met Value ExamplesWalking 3.5 km/h2.5 METJogging8 METAfter 10 MET
11 Influencing Factors Other factors affecting comfort: age adaptation sensation of old people and younger peopleadaptationpeople in warm climates may adapt to hot environmentsexwomen: lower skin temp., evap loss and lower met. rateclothing and perferrence of temp.
12 Complying with ASHRAE 55 or ISO 7730 would mean: Maintain operative temperature between:20.0 to 23.5o C in winter22.5 to 26.0o C in summerMaintaining Rh between 30 to 60%AIR Speed between 0.1 to 0.35 m/s
13 Body Temperature Regulation and Control Four ways the body regulates heat:conductionconvectionthermal radiationevaporationSpace conditions to control:surface temperatureair temperaturerelative humidityair motionSurfaceTemperatureAir MotionConvection
14 Body Temperature Normal body core temperature: 37 oC. HotCold37 oC34 oCNormal body core temperature: 37 oC.We have separate Heat- and Cold- sensors.Heat sensor is located in hypothalamus. Signals when temperature is higher than 37 oC.Cold sensors are located in the skin. Send signals when skin temperature is below 34 oC.Heating mechanism:Reduced blood flow.Shivering.Cooling mechanism:Increased blood flow.Sweating (Evaporation).
15 The Energy Balance Heat Heat Produ- Lost ced Thermal Comfort can only be maintained when heat produced by metabolism equals the heat lost from body.
17 Why thermal comfort is important? Occupant Satisfaction and Productivity75% of all occupant complaints within buildings are thermal comfort relatedThe thermal environment has been shown to have up to a 10% effect on worker productivityEnergy consumptionOver $80 billion per year is spent to heat and cool buildings