LOAD ESTIMATION - COOLING AND HEATING ESTIMATION

# LOAD ESTIMATION - COOLING AND HEATING ESTIMATION

## LOAD ESTIMATION - COOLING AND HEATING ESTIMATION

Principles of Heat transfer .

Methods of Heat Transfer

Methods of Heat transfer
• Conduction .
• Convection .

• Load type (Sensible Heat Qs - Latent Heat  QL)

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 .

### Sources of Heat gain ( loss) .

• Solar radiation on opaque boundaries .
• Heat transmission due to temperature difference
• Infiltration .
• Ventilation .

• Lights .
• People .
• Appliances .
• Miscellaneous sources . ( hot water pipe and tanks .Unexpected Loads ) .
• Electric motors .
• etc

• 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 .

• 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

• other equi (sensible only . example : computer,printer,.....)
In case of equipment inside the kitchen .

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.

• 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 = .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   m
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