1. Heat gain and heat loss in buildings
1.00 Modes of heat transfer
Mainly involves conduction, convection, and radiation.
Evaporation is less important when there is no moisture involved.
2.00 Heat flow through solids
Conductivity: Designated by k. Represents BTUH that flows through 1 sqft of material, 1 in. thick, when temperature drop through this material is 1°F.

2. Heat gain and heat loss in buildings
Conductance: Designated by C. Represents BTUH that flows through 1 sqft of material of a given or specified thickness when temperature drop through this material is 1°F.
Resistivity: Hours needed for 1 BTU to flow through a solid, 1 in. thick, when temperature difference is 1°F. It is an index of the tendency of a material to resist heat flow per inch of its thickness. Reciprocal of k. Deisgnated by r.

3. Heat gain and heat loss in buildings
Resistance: Hours needed for 1 BTU to flow through a given thickness of a solid when temperature difference is 1°F. It is an index of the tendency of a material of given thickness to resist heat flow. Reciprocal of C. Deisgnated by R.
U-value: Overall coefficient of heat transmission of an assembly of materials. This is a single, composite heat transfer coefficient that is used to correlate the overall rate of heat transfer with surface area and temperature difference. Reciprocal of R. U = 1/R
C = 1/R = 1/rx = k/x, where x = thickness
R = 1/C = rx = x/k, where x = thickness

4. Heat gain and heat loss in buildings
3.00 Heat flow through air
Wind outdoors has to be taken into consideration.
Air films both inside and outside building envelope affect heat flow.
A combination of dead air spaces and reflective surfaces produce very efficient insulation materials.

5. Heat gain and heat loss in buildings
4.00 Heat flow through building envelope
4.01 Heat flow due to temperature difference
Rate of heat flow (U)
U-values for roof, wall, floor, etc. may be calculated by finding the resistance of component materials, air films, and internal air spaces.
For floors and walls in contact with the ground, use (1) a factor of 10°F or above, (2) a factor of below 10°F.
Use overall U-values for different types of windows (residential or commercial).

6. Heat gain and heat loss in buildings
Area of construction (A)
Calculate wall, roof, window, door, and floor areas from architectural drawings.
Temperature difference (TD)
Calculate the difference between inside and outside temperatures of the building envelope.
5.00 Formula for calculation of heat gain/loss through a building envelope
Q = U*A*TD
Where Q = quantity of heat flow in BTUH