New technologies

based on the use of CO2

as a natural refrigerant

have been making progress

toward addressing

many aspects of energy

savings and environmental

protection, particularly

outside the United

States —until now.

B y M e r l e G . r o c k e

w w w . r s e s j o u r n a l . c o m

Although widely used throughout europe and Asia, co2-compressor technology has yet to take off in North America; but as focus continues on environmental repair, widespread use of this type of technology is on the horizon.

N e w T r e N d s i N

Heat pumps favorably impact energy consumption and environmental protection—two pressing issues expe-rienced around the world—because they deliver much

more heat for energy consumed than furnaces and heaters burning fossil fuel or using electricity. Heat pumps though have been restricted in application due to the limitations of available components and fluids designed for refrigeration. However, technology is evolving to enable a high-pressure transcritical cycle using non-regulated CO2 that extends the temperature range in which heat pumps perform effectively. The equipment carries a premium price, but in water-heating applications, an investment in a CO2 heat pump can deliver payback in 2–6 years because of the low energy consumption.

High energy consumption strains our energy supply and produces ever increasing volumes of green house gases. One clear approach to reducing consumption is to use energy more efficiently and to use energy that would otherwise be wasted. Heat pumps do just that.

Rather than using fuel or electricity to generate heat from a furnace or heater, a heat pump lowers the temperature of a source by pulling heat from it, and raises the temperature at the destination by de-livering heat to it using the thermodynamic properties of the intermediate fluid—refrigerant. Conventional heat pumps use the hot stream to increase temperatures at the delivery point and reject the cold to cool outside air. Likewise, convention-al air-conditioners and refrigeration units use the cold stream to lower temperatures at the heat source and waste the hot to heat outside air.

Heat pumps deliver several units of heat for each unit of energy consumed in the compressor during the compression part of the thermodynamic cycle, typically delivering a COP above 3, and sometimes more than 4. Since furnaces cannot provide more heat output than the energy contained in the fossil fuel or electricity consumed, they never have a COP greater than 1.

26 rses Journal OCTOBER 2010

sustainable HVAC Technology

All images courtesy of EcoThermics Corp.

w w w . r s e s j o u r n a l . c o m

Heat-pump technology continues to evolve to enable a high-pressure transcritical cycle using non-regulated carbon dioxide that extends the temperature range in which heat pumps perform more effectively.

However, conventional heat-pump market penetration is significantly limited for two reasons: lack of performance at extreme temperatures, such as cold climates or high-temper-ature water-heating; and the cost and risk associated with handling regulated HFC refrigerants—long-duration green-house gases.

Market trendsAccording to a June 2009 report from Priority Group and a 2006 report from U.S. Industrial Reports, the global heat-pump market is a $20-billion industry, and it has some of the fastest growing segments (17.5%) in the $65-billion global HVACR industry. Following are a few cases expanding upon this.

Heat pumps as a substitute for conventional HVACR products—Introduced in commercial markets dur-ing the 1960s for a variety of heating and cooling applica-tions, the heat pump soon expanded into residential markets as a substitute for less-efficient electric and fossil-fueled fur-naces and air-conditioners. While this market expansion con-tinues around the world, heat pumps have recently entered a new market segment—domestic and commercial water-heating. General Electric introduced an HFC heat pump in 2009, the GeoSpring hybrid water-heater, promising a reduc-tion in annual energy costs of 62% compared to a conven-tional natural-gas water-heater. Rheem introduced a similar product, the HP-50, promising a 50% reduction compared to a conventional electric water-heater. And the 2001 introduc-tion of the Eco-Cute—a play on the Japanese word for “sup-ply hot water,” which is “kyuto”—water-heater using CO2 as

a refrigerant has gained significant market share in Japan and Europe by demonstrating even greater energy-cost reductions of 80% and 36% compared to electric and HFC water heat-ers, respectively (Source: en-EX srl Italy, producing hot water at 65̊ C, 2009).

Natural refrigerants as a replacement for synthetic refrigerants—While synthetic refrigerants have dominated the market since their invention in the 1920s, natural refrig-erants—including CO2, propane, butane and ammonia—are growing in market share. Driven by regulation and econom-ics, this trend has been established most notably in refrigera-tors and coolers that use the Greenfreeze refrigerant, which is a mixture of purified butane and propane co-developed by Greenpeace in 1992. With 100 million units produced annu-ally—by all the major European, Chinese, Japanese and In-dian manufacturers—these products have a 40% share of the world market, and a 90% marketshare in Japan and Europe according to a Greenpeace report, titled HFCs, A Growing Threat to the Climate (2009 Updated Edition). This technolo-gy was first introduced to North America in 2009 with Bosch and General Electric refrigerators.

Naturally occurring carbon dioxide has great promise to meet long-term market and regulatory demands for safe, en-vironmentally friendly and sustainable refrigerant in a large range of heat-pump applications. The thermodynamic prop-erties of CO2 make it an effective refrigerant in transcritical cycles—crossing through the critical temperature and pressure below which the refrigerant is in a liquid and vapor mixture—extending the effective application range beyond subcritical cycles for which HFC refrigerants are optimized. This trans-lates into a compact package that can efficiently provide high-temperature heating and even pull heat from subzero sources.

Heat-pump systems using CO2 technology can benefit end-users with very low operating costs; and service technicians benefit because carbon dioxide is not toxic, flammable or reg-ulated, making component replacement in the field less com-plex and costly.

OCTOBER 2010 rses Journal 27

sustainable HVAC Technology

– –

w w w . r s e s j o u r n a l . c o m

Testing and field trials con-tinue on co2 com-ponents, such as this one being performed on a semi-hermetic co2 compressor.

Opportunities, problems, solutionsNatural-refrigerant products are creating market awareness and demand by demonstrating the efficiency advantages of CO2. According to Priority Metrics Group and U.S. Industri-al Reports, the global markets for heat pumps and compres-sors are $20 and $2 billion, respectively, and several compa-nies are developing CO2 compressors to embrace this new opportunity. Development has advanced furthest for <2-ton systems, such as hot water-heaters, vending machines, mobile transport and >7-ton large, cascade systems for food refrig-eration (per discussions with the U.S. Army Power Division, Environmental Systems Branch, OEMs, and U.S./European HVACR manufacturers).

CO2 compressors less than 7 tons successfully introduced in the market to date include a 2-ton, two-stage rotary com-pressor made by Sanyo used in a water-heater with the gener-ic name of Eco-Cute, and a smaller scroll unit used in vend-ing machines. Other CO2 compressors in the 3–7-ton-size segment now include recently introduced models from Dorin (Italy) and Bock (Germany) targeted for commercial and in-dustrial applications. Commercial-size, CO2 heat-pump water-heaters were introduced in 2009.

This being said, CO2 presents a set of difficult technologi-cal challenges beyond conventional HFC heat-pump expe-rience. A fundamental problem in transcritical compressor

development is attempting to adapt low-pressure (~400 psi) technology—such as HFC-compressor designs—to high-pres-sure (~1,600 psi) applications. There has been initial success in small applications. Due to the stringent engineering and manufacturing requirements with high pressures, the chal-lenge to adapt low-pressure technologies is even more difficult with larger-size compressors.

An axial piston compressor (developed by EcoThermics Corp. located in Peoria, IL) departs from conventional ro-tary, scroll, screw and reciprocating compressors adapted for use with CO2. The compressor was designed to tolerate the high-pressure and particular requirements of CO2. It is driven through an external input shaft, which allows system packag-ers the flexibility to have their choice of drive motors.

The Axial Transcritical 54cc (AT54) model has demon-strated durability and high efficiency in tests performed at both the company’s research facility and by Herrick Labs at Purdue University. Pilot production will begin in the second quarter of 2011 for the purpose of OEM system development and lab/field demonstration.

EcoThermics also is developing additional CO2 compressor technology that extends efficient heat-pump application to cold climates and high-temperature applications.

A 10–30 kW (3–7 ton) CO2 compressor, an enabling com-ponent for a wide range of CO2 heat-pump products also is

28 rses Journal OCTOBER 2010

w w w . r s e s j o u r n a l . c o m OCTOBER 2010 rses Journal 29

Circle Reader Service No. 57

being developed. The compressor is differentiated from other CO2 compressors in several respects. The multi-piston axial compressor design departs from conventional rotary, scroll, screw, reciprocating (piston/crankshaft) compressors original-ly designed for synthetic refrigerants manufacturers.

Also unique is an energy-recovery module designed to reclaim compres-sion energy for an improvement in ef-ficiency of up to 35%. Other benefits include high power density (manufac-turability, durability) and application flexibility (portability, optional diverse modular power inputs such as ac/dc electric, and hydraulic power for off-the-grid operation, and variable-output capacity to maintain peak efficiency for continuously changing system de-mands). A flexible modular design al-lows for custom builds to meet a broad range of OEM specifications.

Competitive advantages for OEM manufactured CO2 heat-pump prod-ucts include the following end-user benefits:g Reduced energy consumption;g Lower total cost of ownership; g Precise zone temperature;g Wider range of ambient

conditional;g Higher heating temperatures;g Greater durability;g Environmental sustainability;g Smaller size and less weight; and g Easy to install and service.

An advanced, sixth generation compressor prototype (the AT54, a single-stage 18-kW (4–5-tons) con-figuration is available today in limited quantities for pilot testing by prospec-tive OEM customers. The AT54 has demonstrated durability, high efficiency (>60% overall isentropic efficiency) and high power density. Pilot production

w w w . r s e s j o u r n a l . c o m30 rses Journal OCTOBER 2010

in the low hundreds will begin in Q2 2011 for the purpose of OEM evaluation and lab/field testing. These units have a tar-geted cost of $1,900.

Looking to the futureThe initial target customers for these compressors are OEM heat-pump system providers for water heaters in applications such as dishwashing, laundry, kitchens and numerous in-dustrial processes. The common requirement is hot water in excess of 80°C (180°F); and as was stated above, HFC heat pumps do not perform at these temperatures. Hot water at this temperature has conventionally been heated by electric, natural gas or propane equipment.

CO2 heat pumps consume as little as one-fourth the energy and present short payback periods since the initial installed cost is at a premium. With ease of installation in new and ret-rofit scenarios, energy-efficient CO2 heat-pump water-heaters will compete well. An important byproduct is water-chilling and space-cooling for little additional cost.

During the next several years, EcoThermics (among other CO2 compressor manufacturers) will be working closely with OEM heat-pump system providers that share compatible goals for CO2 heat pumps. The company will be identifying specif-ic opportunities that leverage the AT54 compressor, adjusting requirements for additional customer’s needs and completing UL certification of the production design. Full-scale produc-tion is targeted in 2013. Future development will focus on re-generating energy that is typically wasted in the heat-pump expansion cycle to improve system efficiency by as much as 30%; and supporting OEM-system providers to develop sys-tems that recuperate heat-pump waste streams typically re-jected to outside air.

Heat-pump systems using this new technology will not only benefit end users who will realize significantly reduced

equipment owning and operating costs—but HVACR service technicians as well. In the meantime, the world is watching and waiting to share in these advantages as natural-refriger-ant technologies spread across the globe.

[Editor’s Note: Check out this feature online for a direct link to a performance study, titled “Experimental Performance of a Prototype Carbon Dioxide Compressor,” that was done at Purdue University’s Ray W. Herrick Laboratories, School of Mechanical Engineering.]

Merle G. Rocke is the Chairman and CEO of EcoThermics Corp. He has an international background in manufacturing, technology, marketing, supply-chain integration and business consulting. For more information, e-mail Rocke at mrocke@eco thermics.com or visit www.ecothermics.com.

lab test results (available at www.rsesjournal.com) on co2 compressors will be an imperative resource to convince the marketplace that carbon-dioxide-based technology is worth the money, effort and time.

Heat-pump systems using this new technology will not only benefit end users who will realize

significantly reduced equipment owning and operating costs—but HVACr service technicians as well.

“