MC-GAIH84
在温和的气候条件下，可以通过中央空气处理系统中的盘管或热泵提供热量。热泵的优点是可以根据需要在加热和冷却模式之间切换。屋顶单元提供成套供暖和制冷。屋顶单元的加热通常由燃气或燃油炉或电热盘管进行。蒸汽和热水盘管也可用。在较冷的气候条件下，尤其是在大型窗户下，通常需要外围加热。热泵使用标准制冷组件和换向阀在同一单元内提供加热和冷却。在加热模式下，通过盘管的制冷剂流反向流动，将热量从热源输送到空调空间。当使用热泵将建筑内部的热量交换到周边时，不需要额外的热源。热回收系统通常用于使用大量室外空气的建筑物。有几种类型的热回收系统可用，包括热泵、试车系统、旋转热交换器和热管。在狭条排印系统中，盘管安装在室外送风管道和排气管道中。泵使介质（水或乙二醇）在盘管之间循环，以便由排气加热的介质预热进入系统的室外空气。旋转式热交换器是一种填充有金属网的大轮子。车轮的一半位于室外进气口中，另一半位于排气管中。当车轮旋转时，金属网吸收排气中的热量并在进气中散热。

In mild climates, heat can be provided by a coil in the central air handling system or by a heat pump. Heat pumps have the advantage of switching between heating and cooling modes as required. Rooftop units provide packaged heating and cooling. Heating in a rooftop unit is usually by a gas- or oilfired furnace or an electric heat coil. Steam and hot water coils are available as well. Perimeter heat is often required in colder climates, particularly under large windows. A heat pump uses standard refrigeration components and a reversing valve to provide both heating and cooling within the same unit. In the heating mode, the flow of refrigerant through the coils is reversed to deliver heat from a heat source to the conditioned space. When a heat pump is used to exchange heat from the interior of a building to the perimeter, no additional heat source is needed. A heat-recovery system is often used in buildings where a significant quantity of outdoor air is used. Several types of heat-recovery systems are available including heat pumps, runaround systems, rotary heat exchangers, and heat pipes. In a runaround system, coils are installed in the outdoor air supply duct and the exhaust air duct. A pump circulates the medium (water or glycol) between the coils so that medium heated by the exhaust air preheats the outdoor air entering the system. A rotary heat exchanger is a large wheel filled with metal mesh. One half of the wheel is in the outdoor air intake and the other half, in the exhaust air duct. As the wheel rotates, the metal mesh absorbs heat from the exhaust air and dissipates it in the intake air.