Transcript Air cooling
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 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.