Household Appliances (White Goods) / HVACR / Heating & Cooling / Cooling Technologies / Fluid Handling & Water Processing / Motors, Fans & Blowers

Cooling Technologies: Changing Speeds

September 1, 2011
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Variable speed compressor technology keeps indoor temperature consistent while outdoor temps fall.



The lifetime cost to power an air conditioner is almost three times the cost to buy one. As homeowners feel the pinch of rising energy costs, they increasingly prioritize energy savings as they evaluate and purchase home HVAC systems.

In a survey conducted last year by Emerson Climate Technologies, 57 percent of homeowners indicated energy savings was the most important factor they would consider when buying a new system. Not surprisingly, consumer interest in energy efficient systems has driven growth in high-efficiency heat pumps and air conditioners, where compressor technology is key to achieving greater energy savings for the homeowner. More specifically, recent breakthroughs in variable speed scroll compressor technology are enabling significant improvements in heat pump efficiency and year-round comfort.

Optimized for heat pump applications, this variable speed compressor can control the speed of its heat pump to regulate its energy usage. Image: Emerson Climate Technologies

Heat Pump Trends Drive Adoption

The growth in sales of heat pumps in North America is closely tied to the overall trend for energy-efficient heating and cooling solutions. Over the past five years, heat pumps have grown from 28 percent of the market to 37 percent last year. According to the Air-Conditioning, Heating, and Refrigeration Institute (AHRI), shipments of air-source heat pumps in the United States in December 2010 increased 22 percent, to 134,444 units, up from 109,949 units shipped in December 2009.

The industry expects heat pumps to continue growing to approximately 45 percent of the residential unitary market by 2015. Other growth drivers include rising costs of electricity and natural gas, pending regional energy standards, and tax credits.

Variable speed technology enables systems to better meet contractor and homeowner demands for comfort and energy savings. As a result, these high-efficiency systems, especially heat pumps, are expected to significantly grow as OEMs develop them and contractors learn of their benefits. Image: Emerson Climate Technologies

Addressing Unmet Needs

Scroll compressor technology has been, since its introduction in the late 1980s, an important component of heat pump applications. Manufacturers learned to make scroll compressors efficient, reliable and durable enough to survive the harsh, year round usage required for reversible heat pump applications. However recent rising energy costs have created a greater emphasis today on efficiency.

From contractor market research conducted by Emerson Climate Technologies, “cold supply air” is the number one need for an improved heat pump.

As outdoor ambient temperatures fall, traditional heat pumps lose capacity, reducing the supply air temperature. As a result, the air feels cold to the homeowner, which leads to some dissatisfaction with comfort related to heat pumps.

Homeowners are requiring HVAC systems to deliver both temperature consistency and improved comfort while reducing use of fossil fuels and lowering electric heating costs. Variable speed scroll compressor technology delivers on homeowners’ needs for both comfort and energy savings. New heat pumps with variable speed compressors can also offer consistent, higher supply air temperatures, even with low outdoor winter temperatures. As shown in the variable speed hot air supply graph, traditional fixed speed heat pumps lose capacity at low ambient temperatures, producing a cool draft, while systems with variable speed scroll compressors can maintain capacity at low ambient temperatures; provide consistent hotter supply air; and satisfy the number one need for improved heat pumps.

By better matching load in heating and cooling, heat pumps with variable speed scroll compressors can reach a high heating seasonal performance factor (HSPF) for increased heating efficiency and high seasonal energy efficiency ratio (SEER) for increased cooling efficiency. Heat pumps equipped with variable speed scroll compressors can deliver 29-69 percent greater HSPF than the same manufacturer’s modern heat pumps, with 20 SEER cooling efficiency. This can drive significant annual energy savings for homeowners.

Most of the energy savings is in heating. With variable speed, HSPF can increase from 7.7 (industry minimum) to 13 HSPF. Meanwhile SEER can increase from 13 (industry minimum) to 20 SEER. Even with this breakthrough improvement in heating and cooling, 75 percent of the energy savings is in heating. As contractors recognize the value of heating efficiency, heat pumps with variable speed scroll compressor technology are expected to grow significantly.

Systems with variable speed deliver many other important benefits. Summer humidity control is important to improving comfort, especially in the Midwest and Southeast regions. By reducing capacity to match load, systems with variable speed scroll compressors increase run time to remove moisture and reduce relative humidity. Other benefits of variable speed that appeal to contractors are quieter operation ease of installation, and on-board diagnostics for better troubleshooting and protection.

Variable Speed Scroll Compressor Technology

The key to variable speed technology are changes made to the scroll compressor. Built upon this platform, several key features enable the superior system performance.

In high-efficiency applications, most variable speed compressors use brushless permanent magnet (BPM) motor technology. Some of the most advanced BPM motors use concentrated wound, segmented stators, enabling even greater efficiency. With the broad frequency range and DC input required, variable speed applications utilize motor control drive inverters to power the BPM motor and control the operating frequency. The motor control drive contains algorithms that enable the drive to operate efficiently and protect the compressor. Some of the most advanced drives are also approved by safety agencies and include diagnostics to help contractors service the equipment.

Other features of variable speed compressors include temperature sensing and optimized scrolls for greater efficiency.

Most variable speed compressors and drives are applied as part of an OEM’s communicating system. Thermostats designed for variable speed applications provide a “percent speed” command based upon the proportional demand required to satisfy the load. This data is then communicated to the system control, which commands compressor speed, fan speeds, and EXV position for optimal system performance.

For more information, visit: www.emersonclimate.com

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