State-of-the-art in Residential and Small Commercial Air Handler Performance

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Although furnaces, air conditioners and heat pumps have become significantly more efficient over the last couple of decades, residential air handlers have not experienced similar improvement. The most common air handlers have efficiencies of only 10% to 15% (Phillips 1998, Gusdorf et al. 2002). These low efficiencies indicate that there is significant room for improvement of both electric motor and aerodynamic performance of air handler fans. The need to address this poor performance has been known for many years. For example, Ariewitz et al. (1983) developed a high efficiency blower for heat pump applications to address this issue.An important consideration in analyzing air handlers is the fact that essentially all of the wasted electricity is manifested as heat. This extra heat reduces air conditioning cooling and dehumidification performance and effectively acts as fuel switching for fossil fuelled furnaces. For electric furnaces, this heat substitutes directly for the electric resistance heating elements. For heat pumps, this heat substitutes for compressor-based high COP heating and effectively reduces the COP of the heat pump.Using a combination of field observations and engineering judgment we can assemble a list of the factors that lead to low air handler efficiency and potential solutions, as shown in Table 1. None of the problems require exotic or complex solutions and there are no technological barriers to adopting them. Some of the solutions are simple equipment swaps (using better electric motors), others require changes to the way the components are built (tighter tolerances) and others relate to HVAC equipment design (not putting large fans in small cabinets).

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Lawrence Berkeley National Laboratory