Air Conditioning Systems(Cooling Loads)
- Cooling Loads
- Computed for worst case scenario:
- Summer at max. outdoor design dry bulb temp.
- ( o.4 % ASHARE or Egyptian environmental agency)
- Include:
- n Solar radiation
- n Heat gain from people, lights, and equipment
- n Ventilation ( Fresh air)
- Factors that influence the cooling load
- SENSIBLE
- n Glass windows or doors
- n Sunlight from windows, skylights, or glass doors
- n Exterior walls, Partitions, Ceilings, Roofs & Floors
- n Air infiltration through cracks in doors, and windows
- n People, Equipment and appliances and Lights
- n Other sensible heat gains such as: Ductwork located in an unconditioned space & Ventilation air introduced into the building
- LATENT
- Moisture is introduced into a structure through:
- n People
- n Equipment and appliances
- n Air infiltration through cracks in the building, doors, and windows
- Room Load –VS- System load
- n Room Load:
- From People, Walls and roof Heat transfer, Solar, Lights & Equipment
- n System Load:
- = Room Load + Ventilation Load
- Load Through Building
- • Space heat gain: How much heat is entering the space?
- • Space cooling load: How much energy must be removed from the space?
- • Cooling coil load: How much energy is removed by the C.C
- Load depends on:
- • ∆T between outside temp.& desired room temp.
- • Construction type & amount of insulation (U-value)
- • Building orientation & direction of sun rise and fall
- • Surface area of the walls.
- • Infiltration from door gaps, cracked windows
- • Number of people.
- • Activities & equipment
- • Room lighting.
- • Appliances generate heat
- •
- Sensible & Latent Loads
- Sensible:
- • H.T. thru floors, ceilings, walls
- • People body heat
- • Appliance & Light heat
- • Solar Heat gain thru glass
- • Infiltration of outside air
- • Air introduced by Ventilation
- Latent:
- • Outside air form Infiltration & Ventilation
- • Occupant Respiration & Activities
- • Moisture from Equipment & Appliances
- •
- •
- Outdoor Design Conditions (ASHRAE Fundamentals)
- • Dry bulb(DB) temp: corresponding to 0.4%, 1.0% and 2.0% annual cumulative frequency of occurrence and the mean coincident wet-bulb temp. (MWB) .
- • Wet-bulb temp: corresponding to 0.4%, 1.0% and 2.0% annual cumulative frequency of occurrence and the mean coincident dry-bulb temp.
- • Mean daily range (DR) of the dry bulb temp.
- Required outdoor air : 10-15 L/s per Person
- Outdoor air for ventilation & pressurization
- •
- Cooling load calculation methods
- n Transfer Function
- n Total Equivalent
- Temp. Difference (TETD)
- n Cooling Load Temp. Difference / Cooling Load Factor (CLTD/CLF)
- n Heat Balance Method (HBM)
- n Radiant Time-Series Method (RTSM)
- Using spreadsheets and/or computer programs
- CLTD
- n CLTD is a theoretical temperature difference for combined effects of inside and outside air temperature difference, daily temperature range, solar radiation and heat storage. It is affected by orientation, month, day, hour, latitude, etc.
- n CLTD factors are used for adjustment to conductive heat gains from walls, roof, floor and glass.
- n SCL factors are used for adjustment of heat gains from glass.
- n CLF - radiant energy that enters the conditioned space at a particular time does not become a part of the cooling load instantly, calculated as functions of solar time and orientation and are available in the form of tables in ASHRAE Handbooks.
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