Heat Load Calculation: Basics, Types & Key Factors

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