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Tham khảo tài liệu '1999 hvac applications part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 49 SNOW MELTING Heating Requirement Hydronic and Electric . 49.1 Pavement Design Hydronic and Electric . 49.9 Control Hydronic and Electric . 49.9 Hydronic System Design . 49.10 Electric System Design. 49.12 The practicality of melting snow by supplying heat to the snow-covered surface has been demonstrated in a large number of installations including sidewalks roadways ramps and runways. Melting eliminates the need for snow removal provides greater safety for pedestrians and vehicles and reduces the labor of slush removal. This chapter covers three types of snow-melting systems 1. Hot fluid circulated in embedded pipes hydronic 2. Embedded electric heater cables or wire electric 3. Overhead high-intensity infrared radiant heating infrared Components of the system design include 1 heating requirement 2 pavement design 3 control and 4 hydronic or electric system design. HEATING REQUIREMENT HYDRONIC AND ELECTRIC The heat required for snow melting depends on five atmospheric factors 1 rate of snowfall 2 air dry-bulb temperature 3 humidity 4 wind speed and 5 apparent sky temperature. The dimensions of the snow-melting slab affect the heat and mass transfer rates at the surface. Other factors such as back and edge heat losses must be considered in the complete design. The processes that establish the heating requirement at the snowmelting surface can be described by inspecting the terms in the following equation which is the steady-state energy balance for the required total heat flux power per unit surface area qo at the upper surface of a snow-melting slab during snowfall. The general discussion of the heat balance will be followed by a detailed description of how each of the terms is evaluated. qo q qm Ar qh qe 1 where qo total required heat flux W m2 qs sensible heat flux W m2 Ar snow-free area ratio dimensionless qm latent heat flux W m2 qh convective and radiative heat flux from snow-free surface W m2 qe heat flux needed for evaporation W m2 Heat Balance .