LOAD ESTIMATION - COOLING AND HEATING ESTIMATION
Principles of Heat transfer .
Methods of Heat transfer
- Conduction .
- Convection .
- Radiation .
Load description :
- Load type (Sensible Heat Qs - Latent Heat QL)
- Sours of heat (External load and Internal load)
Sensible Heat : Is the load that results in change in temperature .
Latent Heat : Is the load that results in change from one phase to another .
Cooling Load Components
Air Conditioning Load Estimation .
Sources of Heat gain ( loss) .
- External Load .
- solar radiation through fenestration
- Solar radiation on opaque boundaries .
- Heat transmission due to temperature difference
- Infiltration .
- Ventilation .
Internal Load
- Lights .
- People .
- Appliances .
- Miscellaneous sources . ( hot water pipe and tanks .Unexpected Loads ) .
- Electric motors .
- etc
Building Survey And Load Estimation
- Orientation of building .
- Use of space(s).
- Physical dimensions of space(s).
- Ceiling height - floor to floor height, floor to ceiling .
- Construction materials .
- Windows - Size and location .
- People - Number .
- Lighting - Wattage at peak.
- motors- location, nameplate.
HINT
Out door design condition ( by knowing place and direction of building is determined
T dp : dry bulb temperature .
T wb : wet bulb temperature .
Ex cairo ( T db = 105 F , T wb = 78 F)
In door design
Depending on the application
Famous applications ( T = 24 C , RH=(40-50%) were RH is relative humidity
For other application we get from ASHRAE Code .
(A)-Internal Load .
- People Load (sensible load-latent load)
- The sensible and latent load per person is based on the person's activity . we get this value from the ASHRAE tables .
- We get the number of people from the architectural drawing. or as per application each square meter will be taken as person . we get it from the code .
Light Load ( Its a sensible load only. it can be obtained in tow ways ) .
- N of lambs : the number of lambs is obtained from the electrical engineer .
- Q Lamb : Heat load each lamb . is obtained from the electrical engineer.
- Light intensity : Is obtained to from ASHRAE code .
Appliances
- Kitchen equi (Sensible load-latent load)
- other equi (sensible only . example : computer,printer,.....)
In case of equipment inside the kitchen .
(B) External Load
Solar radiation : All walls are exposed to sun rays .but the temperature varies from one direction to another . so you must be know the direction of the wall.
Solar radiation : All walls are exposed to sun rays .but the temperature varies from one direction to another . so you must be know the direction of the wall.
The north direction of the building is less exposed to heat than the south direction.
Factors effect on solar Load
- Direction
- Materials
- Month (sun heat in month 8 is not the sun heat in 1 month)
- Hour (sun temperature of the hour 1 pm is not the hour 8 pm)
- Shade ( color and location )
External wall
U overall : from ASHRAE CODE
ROOF
Glass or sky light
- SHG : Solar Heat gain Factor ( depended on the direction and component of the glass)
- SC : Shading coefficient (depended on type of the glass)
SC= .83 Clear glass (without shade
SC= .6 shaded
SC = .2 reflected
QS TOTAL = QS External wall + QS Roof +QS glass
Heat transmission due to temperature difference .( Wall , roof, glass)
- Wall : heat transfer through the wall due to temperature difference
Wall ( External : is exposed to the sun , partition : is not exposed to the sun )
QT wall = U Overall * A Wall * ( TO - TR)
To : outside temperature ( external wall , partition)
U overall : we get from the code .
- ROOF
Heat transfer through the roof due to temperature difference.
QT Roof = U overall * A roof * ( TO - TR )
A roof : roof area m2
U overall : Overall heat transfer coeff W/m2 . k
U . variable value according to shape and condition of roof.
- Glass
QT window = U overall * A window * ( TO - TR)
QT total = QT roof + QT partition + QT external wall + QT glass
Ventilation
Q ventilation = m ( HO - HR)
HO : outside enthalpy KJ / kg
HR : inside enthalpy Kj / kg
calculated to from the psycrometric chart or the program
M : amount of fresh air . obtained to from
The second way to calculate cooling and heating load by ( HAP ) Program
HAP : Hourly Analysis Program
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