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					                                                                                                          3/27/2009




                                                       Thermal Comfort
Thermal Comfort                                         How would you describe the thermal climate in
                                                        this room?

                                                          Hot,
                                                          Warm,
                                                          Slightly Warm,
                                                          Neutral,
                                  KARUNAPALA E.A.T.D      Slightly Cool,
                                  E/04/142                Cool,
                                                          Cold




                                                       Why is thermal comfort important?
What is Thermal Comfort
                                                        Thermal comfort is psychological, it may affect
                                                        our overall morale.
  According to ASHRAE and ISO 7730 standards
  thermal comfort is defined as “that condition of            p y        p         y        ,p          y
                                                          Employee complaints may increase, productivity may y
  mind that expresses satisfaction with the               fall and in some cases people may refuse to work in a
                                                          particular environment.
  thermal environment”.




Body Temperature Regulation                            Body Temperature Regulation
  The heat sensor is the
  hypothalamus (inside the                              If the body becomes too cold two mechanisms
  body)                                                 regulate the temperature:
  Main goal is to keep body
  core temperature at                                     Vasoconstriction – Reduction of blood flow
  37 °CC.
                                                          close to the skin.
  If the body becomes too hot
  two mechanisms
  regulate the temperature                                Increase in internal heat generation by
     Vasodilatation – Increase                            stimulating muscles which in turn cause
     of blood flow close to the
     skin                                                 shivering.

     Sweating
                                                        These cold sensors are situated near the skin




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Body Temperature Regulation               Conditions for Thermal Comfort
  The temperature
  regulation is governed by
  warm and cold impulses                    First, a combination of body core, and skin
  The number of impulses
                                            temperature must provide a sensation of
  sent to the brain is                      thermal neutrality.
  dependent on how
  quickly the temperature
  change.                                   Second, the heat produced by metabolism
                                            must be equal to the heat given off by the
  When totally relaxed and
  in thermal comfort, no
                                            body.
  impulses are sent to the
  brain.




On what does thermal comfort depend?      Air temperature

  Air tempereture

  Radiant temperature                       This is the temperature of the air
                                            surrounding the body. It is usually given
  Air velocity                                                 ( C)
                                            in degrees Celsius (°C) or degrees
                                            Farenheit (°F).
  Humidity

  Clothing Insulation

  Metabolic heat




Radiant temperature                       Air velocity

  Thermal radiation is the heat that
  radiates from a warm object. Radiant      This describes the speed of air moving
  heat may be present if there are heat     across the worker and may help cool the
  sources in an environment.                worker if it is cooler than the
                                            environment.




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Humidity
                                            Clothing insulation

 The amount of water vapour in the air        Thermal comfort is very much
 will provide humidity.                       dependent on the insulating effect of
                                                              wearer.
                                              clothing on the wearer




Metabolism                                  Metabolism
 The work or metabolic rate, is essential    Age, years                   Basal metabolic rate, W/m2
 for a thermal risk assessment. It                                         Woman              Man
 describes the heat that we produce               Newborn                    35                35
 inside our bodies as we carry out                      1                    60                64
 physical activity.                                     2                    61                66
                                                        5                    61                64
                                                        12                   55                50
                                                        20                   49                42
                                                        40                   44                41
                                                        70                   41                37




Metabolism                                  The Comfort Equation
                                              A heat balance for the body give:

                                              M = Qsk +Qres + S+W



                                                 Qsk         =Heat loss from skin
                                                 M           =Metabolism
                                                 Qres        =Heat loss by respiration
                                                 W           =Work
                                                 S           =Stored heat




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On what does the losses depend?                            Local Thermal Comfort
                                                            Draught
  Convective heat losses: Skin and ambient temperature,
  Heat transfer coefficient, Exposed area, Clothing
                                                            Thermal Radiation
  Radiative heat losses: Skin and ambient temperature,
    p
  Exposed area

  Evaporative heat losses: Skin and ambient temperature,
                                                            Vertical Air Temperature Difference
  Heat transfer coefficient, Exposed area, Clothing,
  Ambient humidity
                                                            Floor Temperature




Draught                                                    Thermal Radiation effect
  Unwanted local cooling                                    Warm ceilings and cold windows are the most
  of the body
                                                            uncomfortable.
  Dependent on the                                          Warm walls and cold ceilings seemed to be less
  velocity, the fluctuations                                uncomfortable.
     velocity,
  in velocity the air
  temperature

  Frequencies around 0.5
  Hz are the most
  uncomfortable.
  Frequencies above 2 Hz
  cannot be sensed.




Vertical Air Temperature Difference                        Floor Temperature
  Generally unpleasant to be                                Depends on the thermal
  warm around the head while                                conductivity and specific
                                                            heat of the floor material.
  being cold at the feet.
                                                                       footwear.
                                                            Depends on footwear
                                                            Temperature
                                                            of floor




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Temperatures to Assess TC     Mean Radiant Temperature
                               Uniform temperature of an imaginary black
 Mean Radiant Temperature      enclosure that causes the same radiant heat
                               exchange as the actual enclosure.
 Operative Temperature

 Equivalent Temperature

 Effective Temperature




Operative Temperature         Equivalent Temperature
 Move a person from            Move a person from the
 the real room to an           real room to an
 imaginary room and            imaginary room and
 adjust the temperature        adjust the temperature
 so the heat losses are
                               so the heat losses are
      same
 the same. The
 temperature in the            the same. The
 imaginary room is the         temperature in the
 operative temperature,        imaginary room is the
 if the humidity and the       equivalent temperature,
 air velocity is the same      if the humidity is the
 as in the real room.          same as in the real
                               room.




Effective Temperature         Differences
 Move a person from the
 real room to an
 imaginary room and            The difference between Equivalent temperature
 adjust the temperature        and the Effective temperature are dependent
 so the heat losses are        on the level of activity of the persons and their
      same.
 the same The                   l thi
                               clothing while th O
                                          hil the Operative t
                                                         ti           t   is
                                                              temperature i
 temperature in the
 imaginary room is the         independent of these factors
 effective temperature, if
 the relative humidity is
 50% and the air velocity
 is the same as in the real
 room




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Controlling thermal comfort
                                                   Administrative controls

  Administrative controls                            Administrative controls include planning and
                                                     rescheduling work times and practices and
                                                     rest schedules
  Engineering controls




Engineering controls
  These should be the first choice to improve or
  eliminate the thermal comfoart.

  Any practical solution to control the thermal
  comfort is likely to require a combination of
  different options alongside consultation
  between employers, employees and their
  representatives.




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