HEAT LOAD CALCULATION

by | Sep 30, 2022 | Air Conditioning

Modes of heat transfer

Definition:
  • Heat is a form of energy associated with the motion of atoms or molecules.
  • Transferred from the objects at a higher temperature to objects at lower temperature
Classification:
  • Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole. It occurs through direct contact.
  • Convection is heat transfer by mass motion of a molecules/fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it.
  • Radiation is energy transferred in the form of rays or waves.

Terminology

  • DRY BULB TEMPERATURE (DBT)
  • WET BULB TEPERATURE (WBT)
  • RELATIVE HUMIDITY (RH)
  • HEAT TRANSFER CO-EFFICIENT (U)
  • SENSIBLE HEAT
  • LATENT HEAT

Data to be collected

  • Latitude, altitude and north orientation of the project.
  • Application of the area.
  • From architectural drawings: Dimensions of the area, wall, roof, floor, ceiling, windows, doors and thermal conductivity (U-value).
  • Outdoor condition
  • Indoor design condition
  • Internal heat load from: Occupants, equipment’s, lighting.

Classification of heat

Sensible heat:

  • Solar heat gain though glass
  • Solar and transmission gain though walls and roof
  • Transmission gain except walls and roof
  • Internal heat (Occupants, equipment’s, lighting load etc.)

Latent heat:

  • Outside air heat
  • Infiltration heat
  • Heat from occupants
  • Appliances involved with steam applications

List of terms to be calculated

Solar heat gain through wall: Heat gain (Btu/hr) = U x A x Delta T Where, U – Overall heat transfer coefficient (Btu/Hr-sq. Ft.-deg. F) A – Area in sq.ft Delta T – Temperature difference between outdoor and indoor

Valpico – Clubhouse (Fitness room)

DATA:

  • Outdoor design condition: Cooling DBT = 38.4 deg. C = 101 deg. F WBT = 21.1deg. C = 70 deg. F
  • Indoor design condition: Cooling = 75 deg. F, heating = 70 deg. F, RH = 50%
  • Application: Health club/weight room
  • Area = 1115 square feet, Slab height = 12 feet
  • Number of occupant = 10 x 1115 / 1000 = 11.15 = 12 people
  • Number of walls exposed to exterior = 3 (South, west and east), no partition
  • U factor: Walls = 0.077, window = 0.5, roof = 0.039
  • Lighting load = 7.8 watt per square meter = 0.7 watt per square feet
  • Ventilation rate: Ventilation per person = 20, ventilation per square feet = 0.06
  • Sensible and latent heat from occupant = 295 Btu/h and 455 Btu/h