中央空调冷却塔英文文献翻译 第8页
Vertical Packaged Units
Vertical packaged units are typically designed for indoor or through-the-wall installation. These units are applied in hotels and apartments. Some designs have a water-cooled condenser, which can be fed from a cooling tower and/or city water. Many others use standard air-cooled condensers. Both style units have all other components mounted inside the package. Ductwork, if needed, can be connected to the unit to distribute the air.
FIGURE 4.2.20 Split system diagram (courtesy of the Trane Co.).
Split-System Packaged Units
Split-system packaged units can have the condenser mounted on an outdoor housekeeping pad or on a rooftop. Refrigerant piping connects the compressor section to an indoor air handling unit and evaporator coil. Unless they are heat pump type units, they cannot provide heat to the space. Heating coils can be installed in the air handling section, particularly if there is a central source of heat such as hot water or steam from a boiler. Alternatively, the indoor unit can be coupled to a gas-fired furnace section to provide heating.
Air Source Heat Pumps
Air source heat pump (ASHP) systems are typically rooftop units, either packaged complete or as split systems. Split-package heat pumps are designed with an air handling unit located inside the conditioned space, while the condenser and compressor are packaged in units for outdoor installation on a housekeeping pad or on the roof. During cooling mode, the heat pump operates an air conditioner. During heating mode, the system is reversed and extracts energy from the outside air and provides it to the space. Each of these cycles is shown schematically in Figures 4.2.21 and 4.2.22, respectively. The size of unitary heat pump systems ranges from approximately 5 to 70 kW (11/2 to 20 tons). In some cases, existing packaged cooling units with electric resistance heat can be upgraded to heat pumps for improved energy efficiency.
Heat pump applications are best suited to mild climates, such as the southeastern portion of the U.S., and to areas where natural gas for heating is less available. Space heating needs may exceed the capacity of the heat pump during extremely cold weather. This is because the units are most often sized to satisfy the cooling load requirements. As the outdoor temperature drops, the coefficient of performance (COP) of the heat pump decreases. A 26 kW (71/2 ton) rooftop heat pump unit that has a high temperature (8.3°C) COP of 3.0 can have a low temperature (–8.3°C) COP of 2.0 or less. Because the capacity also drops with outdoor temperature, heat pumps require supplemental electric resistance heat to maintain temperature in the building. Figure 4.2.23 shows typical trends in capacity and COP for an air source heat pump. Chapter 4.2 discusses the characteristics of heat pumps.
FIGURE 4.2.21 Air or water source heat pump in cooling mode (courtesy of the Trane Co.).
FIGURE 4.2.22 Heat pump schematic showing heating cycle (courtesy of the Trane Co.).
FIGURE 4.2.23 System heating capacity as a function of outdoor air temperature.
上一页 [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] ... 下一页 >>
中央空调冷却塔英文文献翻译 第8页下载如图片无法显示或论文不完整，请联系qq752018766
