Magic Heat Pumps
(Page 2 of 8)
April/May 2005
By Greg Pahl
Admittedly, heat pumps use technology that could be avoided with passive solar design. Passive solar heating, however, does not work well on cold, cloudy, winter days in northern climates. Heat pumps, on the other hand, do not suffer from these shortcomings. They are an intriguing marriage between technology and renewable resources.
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Air-source Heat Pumps
Air-source heat pumps deliver on the promise that you can heat and cool your home out of thin air. They are the most popular type of residential heat pump — about 1.8 million units were sold in 2004.
While operating costs for ground-source heat pumps are usually less, air-source heat pumps are the least expensive heat pump to install. They work extremely well in moderate climates, but because they rely on outside air as their heat source, they don’t work as well in areas that have extended periods of subfreezing temperatures.
Air-source heat pumps are well suited to new construction because you can plan in advance for the system’s components. Replacement or add-on systems are also possible in most situations. Air-source heat pumps generally have two main components: an indoor unit and an outdoor unit. The most common type of air-source heat pump is the air-to-air system. In this design, heat is extracted from the air and then moved inside or outside your house. This type of system also can remove a significant amount of dust, pollen and other allergens from indoor air.
Virtually all air-source heat pumps require 200-amp electrical service. While most new homes have 200-amp electrical service or higher, many older homes do not. Upgrading the service can be an expensive project, requiring a professional electrician. And because they need electricity to operate, an air-source heat pump should have some form of backup, especially if it is the primary heat source. Having an electrical generator for backup power is a good strategy to consider.
Correctly sizing an air-source heat pump to match the heating requirements of your home is extremely important. Critical factors include the dimensions of your home, the number of windows and doors, type of insulation and local climate. Installing an oversized unit will result in excess energy consumption, inferior humidity control and shorter equipment life.
Conversely, an undersized heat pump will force your supplemental heat system (if you have one) to operate more, increasing your utility bills. If you want to use your heat pump for cooling, you’ll need cooling load calculations to determine the right capacity. Your contractor should be familiar with methods for determining heating and cooling loads based on data from the American Society of Heating, Refrigerating and Air-conditioning Engineers.
You can easily judge an air-source heat pump’s performance by checking its efficiency ratings. The heating- season performance factor (HSPF) indicates the heating efficiency. The seasonal energy-efficiency ratio (SEER) indicates the cooling efficiency. The best approach is to look for an Energy Star label, which is awarded to units with an HSPF of seven or greater and a SEER of 12 or greater. Any manufacturer that produces Energy Star-rated units is worthy of your consideration.
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