12/5/2023 0 Comments Radiant heating and coolingIn buildings, thermal radiation occurs mostly in the infrared (longwave) region because the temperature of the bodies in a building environment is low. This sensation is caused by the decrease in the amount of heat received from solar radiation, although there is little, if any, change in the ambient air temperature. If a cloud passes in front of the sun, there is an instant sensation of cold. This generates secondary rays that are a combination of the wavelength produced by the temperature of the objects and the wavelength of the reflected rays. Other rays are absorbed by or reflected from surrounding objects. Some of the rays come directly from the sun and include the entire electromagnetic spectrum. One example of heating by thermal radiation is the feeling of warmth when standing in the sun’s rays on a cool, sunny day. View factor between the emitting and receiver surfaces (viewing angle of the occupant to the thermal radiation source) Reflectance, absorptance, and transmittance of the receiver Temperature of the emitting surface and receiver Chapter 16 of this volume covers high-temperature panels over 300☏, which may be energized by gas or electricity. For snow-melting and freeze-protection applications, see Chapter 52 of the 2019 ASHRAE Handbook-HVAC Applications. This chapter covers temperature-controlled surfaces that are the primary source of sensible heating and cooling in the conditioned space. In hybrid (or load-sharing) systems, the air system may provide significant additional capacity (e.g., where cooling loads exceed the capabilities of a radiant slab system). In decoupled systems, the air system provides ventilation air and meets dehumidification needs. Panel systems may be combined either with a central forced-air system of one-zone, constant-temperature, constant-volume design, or with dual-duct, reheat, multizone or variable-volume systems, decentralized convective systems, or in-space fan-coil units. Panel systems are characterized by controlled surface temperatures below 300☏. A temperature-controlled surface is called a radiant panel if 50% or more of the design heat transfer on the temperature-controlled surface takes place by thermal radiation. PANEL heating and cooling systems use temperature-controlled indoor surfaces on the floor, walls, or ceiling temperature is maintained by circulating water, air, or electric current through a circuit embedded in or attached to the panel.
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