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 .
  • 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 . 
the calculated sensible load and latent load.




(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. 
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   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


THANK YOU

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