HEAT LOAD CALCULATIONS FOR HVAC SYSTEM

2. Dry-bulb Temperature
The temperature of air as registered by on
ordinary temperature.
Wet-bulb Temperature
The temperature registered by a thermometer
whose bulb is covered by a wetted wick and
exposed to a current of rapidly moving air.
Dry – Bulb Temperature Wet – Bulb Temperature
Dew – Point Temperature Relative Humidity
Humidity Ratio

3. Dew point Temperature
The threshold temperature below which the
moisture starts condensing into liquid is called
Dew point Temperature.
Relative Humidity
Ratio of the actual water vapor pressure of the air to
the saturated water vapor pressure of the air at the
same temperature.
Specific Humidity or Moisture Content
The weight of water vapor in grains or pounds of
moisture per pound of dry air.

4. Saturation Temperature:-
Saturation temperature means boiling point.
The saturation temperature is the temperature for a
corresponding saturation pressure at which a liquid
boils into its vapor phase
Tons Of Refrigeration:-
1 ton of refrigeration is the amount of heat required to melt
a 1000 kg of ice (One ton of ice) in 24 hours.
British Thermal Unit:-
It is the amount of work needed to raise the temperature
of one pound of water by one degree Fahrenheit.
1°F

5. Process of Heat Transfer
Sensible Heat results in a change of
dry-bulb temperature.
Latent heat is associated with the
addition or removal of moisture, or
phase change, for example water
converted to steam.

6. Convection
Conduction
Radiation

7. Convection is the transfer of heat by the actual movement of the warmed matter.
Conduction is the transfer of energy through matter from particle to particle.
Radiation Electromagnetic waves that directly transport ENERGY through space.

9. External Sources which are
affecting the building structure
SUN:
•Wall
•Glass
•Roof
•Floor, Ceiling, Partition
AIR:
•Ventilation
•Infiltration
Internal Sources which are affecting
the building structure
PEOPLE:
•Sensible Heat
•Latent Heat
LIGHT:
•Incandescent Lights
•Florescent Lights
APPLIANCE:
•Electronic
•Kitchen

10. The critical inputs and their associated risks discussed in this guide are:
 Design Conditions
o Location
o Latitude
o Elevation
o Outdoor temperature and relative humidity
 Orientation
 Internal conditions
o Indoor temperature and relative humidity
 Building Enclosure
o Insulation levels of walls, ceilings, and floors
o Window specification
o Thermal conductivity
o Solar Heat Gain Coefficient (SHGC)
o Infiltration and ventilation levels
o Interior and exterior shading
 Internal loads
o Number of occupants
o Electronics, lighting and appliances.

11. RESULT:
TR- TONS OF REFRIGERATION
CFM- CUBIC FOOT PER MINUTE (or)
L/S – LITRE PER SECOND
The Basic Formula to Calculate Heat Transfer thru SUN is
Q = U *A * T
Where,
Q - Rate of heat transfer in BTU/Hr,
U - Coefficient of heat transfer,
A - Area through heat transfer in SqFt,
T - Temperature difference in F.

12. Heat Load Calculation
The Heat Load Calculation for other Sources of Heat depends on
 Fresh Air Requirement
(As per No. of People & Building Application)
Residential = 20 CFM/Person; Office = 25 CFM/Person
Air Change per hour:
Residential = 1.5 Times; Hotel = 2; Office = 2
 Infiltration Air
(Thru Doors & Window Cracks)
 Number of Occupants - (As per Client Requirements)
Bedroom = 2 No.s; Offices = As per Workspaces)
 Lighting - (As per Electrical Design)
 Equipment
(As per Electrical Design)

13. Btu - British Thermal Unit
Btu/h - Btu per hour
Cfm - Cubic Feet per Minute
L/s - Liters Per Second
TR - Tons of Refrigeration
Gpm - Gallons Per Minute
Fpm - Foot Per Minute
ESP - External Static Pressure
HP - Horse Power
KW - Kilo watt
Ach - Air Change Per Hour
Sft - Square Foot
Gr/lb - Grains Per Pound
°F - Degree Fahrenheit
°C - Degree Celsius
°C x 9/5 + 32 = °F
(°F - 32) x 5/9 = °C
AHU - Air Handling Unit
FCU - Fan Coil Unit
FAHU - Fresh AHU

14. ASHRAE - American Society for Heating Refrigeration and Air Conditioning Engineers
ISHRAE - Indian Society for Heating Refrigeration and Air Conditioning Engineers
NFPA – National Fire Protection Association
IAQ – Indoor Air Quality
ASME – American Society of Mechanical Engineers
ASTM – American Society for Testing Materials
UBC – Uniform Building Code
SMACNA – Sheet Metal Air conditioning Contractors National Association
DW144 – Duct Work 144
UL – Underwriters Laboratories
IGBC – Indian Green Building Council