根据美国能源部（DOE）测试程序（1-3），住宅储水式热水器的额定值为每台64.3加仑（244升），大多数热水器每天运行一到两个小时即可满足这一要求。在一天22到23小时的剩余时间里，热水器以待机模式运行。备用期间必须提供能量，以将储存的水保持在水箱温度。对于燃气热水器，待机期间消耗的能量通常约为提供每日热水所需能量的30%至70%。考虑到备用能耗，热水器的整体效率（DOE能量因数）约为DOE回收效率的60%至75%。 如果将空间加热负荷添加到水加热负荷中，则当仅用于加热生活用水时，组合电器的整体效率可以大大高于加热器的效率。新增负荷的能源消耗净增加量是额外恢复所消耗的能源减去替代的备用能源消耗。在增量基础上考虑时，可以证明为空间供暖提供额外热水的效率高于能源部的回收效率。本文对这些关系进行了量化，并提出了一种确定组合电器空间加热效率的方法，可用于与空间进行比较- 加热单功能设备的年度燃料利用效率（AFUE）。单位:双引文:研讨会，ASHRAE交易，1986年，第92卷，pt。2B，波特兰，或

Residential storage water heaters are rated in accordance with the Department of Energy (DOE) test procedures (1-3) on the basis of a hot water usage of 64.3 gallons (244 litres) per Most water heaters can provide this requirement in one to two hours of operation per day. For the remainder of the 22 to 23 hours in the day, the water heater operates in a standby mode. Energy must be supplied during standby to maintain the stored water at tank temperature. For a gas water heater, the energy consumed during standby is typically about 30% to 70% of the energy required to provide the daily hot water requirement. The overall efficiency (DOE Energy Factor) of the water heater, taking standby energy consumption into account, is about 60% to 75% of the DOE Recovery Efficiency. If a space-heating load is added to the waterheating load, the overall efficiency of the combination appliance can be increased substantially over the efficiency of the heater when used to heat domestic water only. The net increase in energy consumption for the added load is the energy expended for additional recovery less the displaced standby energy consumption. When considered on an incremental basis, the efficiency of providing the additional hot water for space heating can be demonstrated to be greater than the DOE Recovery Efficiency. In this paper relationships are quantified and a method is presented for determining a space-heating efficiency for the combination appliance that can be used to compare against a space-heating Annual Fuel Utilization Efficiency (AFUE) of a single function appliance.Units: Dual