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Figure 6-8 Figure 6-9 size panels so they can deliver design space heating output using a supply water temperature no higher than 120oF. An example of a panel radiator with integral thermostatic radiator valve is shown in Figure 6-8. Panel radiator manufacturer’s provide “reference” output ratings for their panels assuming that they operate at a specific average water temperature and in rooms with a specific air temperature. Correction factors are then given that allow the heat output rate to be adjusted for other average water temperatures and room air temperatures. As an approximation, a panel radiator similar to the one shown in Figure 6-8, operating with an average water temperature of 110oF, and in a room with 70oF air temperature, provides approximately 27% of the heat output it would have at a reference average water temperature of 180oF and room air temperature of 70oF. Larger panels (e.g., longer, taller and deeper) are available to increase surface area to compensate for lower average water temperatures. The panel radiator shown in Figure 6-8 will release about 3,400 Btu/hr into a room at 70oF, when operated at an average water temperature of 110oF. FAN-ASSISTED PANEL RADIATORS One of the newest low-temperature heat emitters is a fan- assisted panel radiator. These units use an array of small, low-power fans installed between the front and back surfaces of the panel. The fans automatically change speed based on room temperature relative to setpoint. They significantly increase convective heat output at low supply water temperatures. Each fan only requires about 1.5 watts of electrical power at full speed, and thus, electrical energy consumption is negligible, especially when compared to the electrical energy savings associated with operating the heat pump at lower water temperatures and higher COPs. Fan-assisted panel radiators can operate at water temperatures as low as 95oF. They have integral controls that can be set for a “boost” mode (e.g., full-speed fan operation) when the system is recovering from a setback temperature. FAN-COILS One of the benefits offered by air-to-water heat pumps is the ability to create chilled water for warm weather cooling. Successful implementation of hydronic cooling must address sensible cooling (e.g., lowering the temperature of interior air), as well as latent cooling (e.g., lowering the moisture content of interior air). The latter process implies that some of the water vapor in the air must be condensed into a liquid. Condensation will occur on any surface that is below the dewpoint temperature of the surrounding air. The lower the surface temperature relative to the dewpoint temperature, the faster the rate of condensation. On humid days, the dewpoint of untreated interior air can reach well into the low to mid-70s oF range. This is much higher than the chilled water temperatures that air-to-water heat pumps can produce, which are often in the range of 45 to 60oF Panel radiators, fin-tube baseboard and radiant panels are not intended to operate under condensing conditions. Courtesy of Rettig Group Courtesy of Andrew Jones 50PDF Image | Heat Pump Systems 2020
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