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Heat gain in buildings: Other factors

Heat gain in buildings: Other factors. Solar radiation Classification of solar radiation Direct radiation: Radiation that reaches earth's surface direct from the sun. Diffuse radiation: Radiation that has been scattered or re-emitted.

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Heat gain in buildings: Other factors

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  1. Heat gain in buildings: Other factors • Solar radiation • Classification of solar radiation • Direct radiation: Radiation that reaches earth's surface direct from the sun. • Diffuse radiation: Radiation that has been scattered or re-emitted. • Total solar heat quantity falling on a surface consists of (1) unshaded direct radiation, (2) unobstructed diffuse radiation from sky, and (3) reflected solar radiation from adjacent surfaces. • Solar heat gain through windows depends on its location on the earth's surface (latitude), time of the day, day of the year, and the direction it faces.

  2. Heat gain in buildings: Other factors • Formula for calculation of solar heat gain: Q =SF*A*SC, where SF = solar heat gain factor that specifies solar radiation in BTUH/sqft., A = glass area in sqft., and SC = shading coefficient that specifies the percentage of solar heat passing through the glass.

  3. Heat gain in buildings: Other factors • Equivalent temperature difference (ETD) • ETD is an increased temperature difference that allows for heat gain through opaque surfaces caused by both air temperature difference and direct solar radiation. • Apart from direct solar radiation, ETD is also affected by • Surface color and weight (density) of the materials. • ETD takes into account the density of construction, degree of exposure, time of the day, location, and orientation and design conditions. • Formula for calculation of heat gain through opaque surfaces such as roofs and walls, taking direct solar radiation into consideration: Q = U*A*ETD

  4. Heat gain in buildings: Other factors • Internal loads • People: • Sensible heat • Latent heat • Both sensible and latent heat components should be calculated using the formula: Q = # of persons*heat generated per person • Lighting • Heat gain due to this factor may be calculated using the formula: Q = 3.4 *watts/sqft*floor area

  5. Heat gain in buildings: Other factors • The total amount of heat gain due to this factor depends on number of people, duration of occupancy, and activity level. • Electric light fixtures convert electrical power into heat and light. Even light is eventually eventually converted into its equivalent heat energy in the space; so, in effect, all electrical power entering a light fixture ends up as heat in a space.

  6. Heat gain in buildings: Other factors • Equipment: There is almost an infinite variety of equipment that contribute to heat gain to the conditioned space. The designer has to be thorough in identifying all the heat-producing equipment in a given space. In order to calculate heat gain due to the effect of equipment, the formula for lighting may be used as an approximation. • Kitchen appliances: The total residential equipment loads can be approximated by the major appliances in the kitchen. A value of 1200 BTUH may be used as heat gain from residential kitchen appliances.

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