Module 4: Heat Load Calculations - Heat Transfer in Buildings

Flashcards covering the fundamental modes of heat transfer, material properties, and various heat load calculation methods for building air conditioning and ventilation systems.

Conduction

The movement of heat through a substance or between two substances in contact with each other as heat moves from one molecule to another.

Convection

Heat transfer between a surface and a moving fluid (a gas or a liquid) or the movement of molecules from one region in a fluid to another due to the motion of the heated fluid.

Radiation

Heat transfer involving the movement of energy by electromagnetic waves, which travel at the speed of light ($186,000\,\text{miles per second}$ or $300,000,000\,\text{meters per second}$).

Building Envelope

The outer shell of a building through which heat moves by radiation, conduction, and convection, primarily by conduction and radiation for solid, opaque elements.

Transmission Heat Loads

Heat losses or gains resulting from heat passing through a building material (such as glass) or through an assembly of materials (such as walls, ceilings, and floors).

Heat Transfer Coefficient ($U$)

A coefficient that denotes the three modes of heat transfer into one value, calculated as the inverse of resistance ($U = 1/R$).

External Wall

Any wall that faces a direct ray of sunlight, often requiring the calculation of heat load using the adjusted cooling load temperature difference ($CLTD_{adj}$).

$$CLTD_{adj}$$

The adjusted value of cooling load temperature difference, calculated using the formula $(CLTD_{sel} + LM)K + (25 - t_i) + (t_{avg} - 29)$.

Solar Heat Gain ($H_{SG}$)

The component of heat load for glass or roofs that are exposed to direct rays of sunlight, calculated using the maximum solar heat gain factor ($SHGF$) and shading coefficient ($SC$).

Thermal Heat Gain ($H_{TH}$)

The component of glass load caused by the temperature difference between the conditioned space and the outdoor surrounding, calculated as $H_{TH} = U \cdot A \cdot \Delta T$.

Partition Loads

Heat loads created by partitions (walls, glass, floor, or ceiling) that are not hit directly by sunlight but experience a temperature difference between sides.

Infiltration Heat Loads

Heat losses or gains relating to air leakage through the building envelope, commonly around doors and windows, and the energy required to heat the unconditioned air.

Sensible Heat Load ($H_S$)

A load experienced due to temperature difference, calculated using the formula $H_S = 1.23 \cdot Q \cdot (t_o - t_i)$ in Watts, where $Q$ is in $L/s$.

Latent Heat Load ($H_L$)

A load experienced due to the difference in humidity ratio of air, calculated as $H_L = 3000 \cdot Q \cdot (w_o - w_i)$ in Watts.

Design Basis for Wind Speed

The average wind velocity in the Philippines used for infiltration calculations, ranging from $6.5\,\text{m/s}$ to $7\,\text{m/s}$.

Utilization Factor ($F_u$)

A factor used in lighting and equipment heat load calculations, defined as the ratio of actual usage time to total operation hours per day.

Ballast Factor ($F_b$)

A multiplier used in cooling load calculations for lighting, typically valued at $1.2$ for fluorescent lamps.

Occupant Load

The internal heat generated by people based on their activity level and the number of occupants, divided into sensible and latent heat components.