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.