Air Conditioning ppt - J&W Faculty

							    Air
Conditioning
 Definition:
 Any treatment of the environment air within a building is
  air conditioning.
 Air cooling is any process that reduces air temperature.
 Refrigerated air is produced by a mechanical
  refrigeration cycle.
 Examples:
 Air conditioning: fan that circulates air, filtering air,
  heating, cooling, humidifying, dehumidifying
 Air cooling: fan blowing, coolers, swamp coolers, open
  windows
 Refrigerated air: vapor compression, absorption cycles
Basic Refrigeration Cycle


                 Condenser
                              Compressor

     Expansion
       Valve


                 Evaporator
Terminology
 Dry Bulb Temperature
   measure of the rate of movement of air molecules
   measures the sensible heat of air
   conventional thermometer is used
   as air molecules move faster
       more energy
       more sensible heat
   no common comfortable dry-bulb temperature 65-72 degrees F?
 Wet Bulb Temperature
   measure of the total content of the air (sensible plus latent heat).
   measured with a conventional mercury-in-glass thermometer is
    covered with a piece of cloth that is saturated with water and the
    thermometer is exposed to air.
How Hot or Cold?
        Factor                   Temperature
                   Warm                Cold
        Age        Older               Cooler
        Sex        Female              Male
        Activity   Sitting             Working
        Clothing   Light               Heavy
        Diet       Low Calorie         High Calorie
Heat Load Factors

introducing new heat sources to the
 building without making appropriate
 reductions in the buildings heat load will
 strain the capacity of the system.
reducing the heat load reduces energy
 operating costs and equipment operating
 time, which reduces system maintenance
 and repair and increases equipment life.
Transmission and Residual Heat
Loads
 Depends on
    interior and exterior temperatures
    heat transmission coefficient
    surface areas exposed to the different temperatures
 Heat transmission coefficient
    based on the insulation of the walls and roof (U-value)
 Insulation thickness
    If cooling season is longer than the heating season, and
    summer temperature differences are greater than or equal to
     winter heating temperature differences,
    optimal is based on summer conditions.
 If an air-cooling system is constantly on, the residual
  load has little effect on the cooling requirements.
Solar Heat Load

produced by direct and indirect solar
 heating of the building
desirable during the heating season
undesirable during the cooling season
glass surfaces provide instantaneous heat
 gains
non-glass surfaces can either reflect or
 absorb solar energy (E-value)
Occupant Heat Load


Managers must take into consideration:
  Number of customers
  Number of employees
  Activity level
  Clothing
Infiltration Heat Load

movement of air
  through window and door frames
  from the outside to the inside of the building
   through open doors and windows
Appliance Heat Load

heat generated by operating appliances
can be reduced by:
  limiting appliance operating hours
  smarter appliance choices
  using more efficient lighting systems
  reducing light intensity
Ventilation Heat Load

Heat removed from air as it is cooled
Ventilation air can be:
  fresh air
  re-circulated air
  or a mixture of the two
Cool air is allowed to circulate throughout
 the building by a ventilation system
Air cooling systems
 evaporative cooler
  very common system used in hospitality operations
  very economical
      requires only two energy sources:
        • electricity to operate a fan
        • water
  total cooling energy required generally much less
  also filters air
  only work in dry climates
  be careful of harmful humidity
  works in kitchens
Refrigerated-Air Cooling Systems
 Ensures:
     Cool
     Dehumidified air will be available throughout the cooling season
 Air moisture:
     condenses from air when it strikes a cold surface
     releases its latent heat of evaporation.
 Moist air has a high dew point.
     The cold condensing surface (evaporator) must be below the dew-point
      temperature
     dehumidifies the air
 Depending on:
     Energy and initial cost preferences
         the manager generally has two choices:
             • Vapor compression
             • Absorption cooling
Types and Terms


Direct expansion
  cools ventilation air directly at the evaporator
  can be used for most cooling requirements
Chilled water
  common for medium or larger sized buildings
  uses basic water vapor system
  used to produce chilled water.
Absorption Cooling Systems

• Historically
  • Used lithium bromide absorption refrigeration
  • primarily used in large buildings
  • now being used in smaller buildings i.e. hotels
    with less than 100 guestrooms.