Measured Performance of Heat Pump Clothes Dryers

Within a 53 home monitored sample, long-term energy use of electric resistance clothes dryers was sub-metered. Average measured dryer energy use was 3% of total household energy or 814 kWh/year. Hourly dryer electrical demand profile showed large coincidence with utility summer afternoon peak and significant increases over weekends versus weekdays. After collection of baseline data, electric resistance clothes dryers were replaced with a new condensing and unvented Heat Pump Clothes Dryer (HPCD) and matched ENERGY STAR® clothes washers in eight homes. Six homes had interior utility rooms; at two sites the sets were located outside the conditioned zone. Savings were achieved at all homes, with a median annual energy savings of 34% (312 kWh/year). The dryer was paired with a high-efficiency washing machine designed to remove more moisture than typical models. While the impact of the washing machine on the HPCD was not measured, a benchmark calculation suggests 35% of the HPCD savings may be attributable to the new washers improved moisture removal ability. Although the unvented HPCD uses less electricity than a standard resistance dryer, it was found to release a significantly more heat than a conventional dryer during operation. The unvented units located inside the homes led to very high utility room temperatures and an increase in space cooling energy that may compromise identified savings. However, with a current retail cost of $948 there is only a small premium on the HPCD dryers, making them costeffective when chosen at time of replacement.