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?
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Factor
Age
Sex
Activity
Clothing
Diet
Warm
Older
Female
Sitting
Light
Low Calorie
Temperature
Cold
Cooler
Male
Working
Heavy
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.