Economic recovery has been more U shaped than V shaped, but the HVAC industry is slowly turning upward, as evidenced in a recent rise in some equipment sales numbers reported by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). March’s overall year-to-date factory shipments of central air conditioners and air-source heat pumps reached just over 1 million units, a 7 percent increase as compared to March of 2009. Measuring heat pumps themselves, these shipments have also increased 7 percent over March 2009 totaling 385,717.

Heat pump usage, especially in regions and climates ideal for the technology, are growing. This growth, coupled with energy efficiency and economic concerns, is generating innovative technology and fresh approaches to residential and commercial heat pump applications.

ABSORPTION HEAT PUMPS

Absorption heat pumps are essentially air-source heat pumps driven not by electricity, but by a heat source such as natural gas, propane, solar-heated water, or geothermal-heated water. Because natural gas is the most common heat source for absorption heat pumps, they are also referred to as gas-fired heat pumps. There are also absorption coolers available that work on the same principle, but are not reversible and cannot serve as a heat source. These are also called gas-fired coolers.

Residential absorption heat pumps use an ammonia-water absorption cycle to provide heating and cooling. As in a standard heat pump, the refrigerant (in this case, ammonia) is condensed in one coil to release its heat; its pressure is then reduced and the refrigerant is evaporated to absorb heat. If the system absorbs heat from the interior of a home, it provides cooling. If it releases heat to the interior of a home, it provides heating.

The difference in absorption heat pumps is that the evaporated ammonia is not pumped up in pressure in a compressor, but is instead absorbed into water. A relatively low-power pump can then pump the solution up to a higher pressure. The problem then is removing the ammonia from the water, and that’s where the heat source comes into play. The heat essentially boils the ammonia out of the water, starting the cycle again.

A key component in the units now on the market is generator absorber heat exchanger technology (GAX), which boosts the efficiency of the unit by recovering the heat that is released when the ammonia is absorbed into the water. Other innovations include high-efficiency vapor separation, variable ammonia flow rates and low-emissions, and variable-capacity combustion of the natural gas.

Although mainly used in industrial or commercial settings, absorption coolers are now commercially available for large residential homes, and absorption heat pumps exist and continue to be under development.

Robur has been making advances in its residential heat pump offerings. The new line - PRO GAHP line - are high efficiency gas-fired absorption heat pumps available for heating, heating or cooling, geothermal heating, and simultaneous production of hot and cold water, depending on the unit chosen.

ADVANCED HEAT PUMP FEATURES

A number of innovations are improving the performance of heat pumps. Two-speed compressors allow heat pumps to operate close to the heating or cooling capacity that is needed at any particular moment. This helps save large amounts of electrical energy and reduces compressor wear. Two-speed heat pumps also work well with zone control systems. Zone control systems, often found in larger homes, use automatic dampers to allow the heat pump to keep different rooms at different temperatures.

Some models of heat pumps are equipped with variable-speed or dual-speed motors on their indoor fans (blowers), outdoor fans, or both. The variable-speed controls for these fans attempt to keep the air moving at a comfortable velocity, minimizing cool drafts and maximizing electrical savings. It also minimizes the noise from the blower running at full speed.

Many high-efficiency heat pumps are equipped with a desuperheater, which recovers waste heat from the heat pump’s cooling mode and uses it to heat water. A desuperheater-equipped heat pump can heat water two to three times more efficiently than an ordinary electric water heater.

Another advance in heat pump technology is the scroll compressor, which consists of two spiral-shaped scrolls. One remains stationary, while the other orbits around it, compressing the refrigerant by forcing it into increasingly smaller areas.

Although most heat pumps use electric resistance heaters as a backup for cold weather, heat pumps can also be equipped with burners to supplement the heat pump. Back-up burners help solve the problem of the heat pump delivering relatively cool air during cold weather and reduces its use of electricity.

Since there are few heat pump manufacturers that incorporate both types of heat supply in one box, these configurations are often two smaller, side-by-side, standard systems sharing the same ductwork. The combustion fuel half of the system could be propane, natural gas, oil, or coal and wood. In comparison with a combustion fuel-fired furnace or standard heat pump alone, this type of system is also economical. Actual energy savings depend on the relative costs of the combustion fuel relative to electricity.

INDUSTRIAL AMMONIA HEAT PUMPS

Heat pump advances and innovations are being made on the commercial side of the HVACR market as well. With a focus on sustainability, a heightened interest in reducing the carbon footprint, and a desire to use natural refrigerants, industrial food and beverage processors are increasingly looking to ammonia heat pumps to bridge the energy gap between the refrigeration and heating needs for their processes.

Optimizing energy resources is critical to these industrial processors, given the considerable energy they consume, both electrical energy for the mechanical refrigeration to process and preserve products and fossil fuels for heating the water to cook and clean. Until recently, there’s been no way to use the significant energy absorbed by ammonia compressors in industrial refrigeration. The operating and differential pressure limitations of twin screw compressors prevented pumping the rejected heat up to pressures and temperatures viable to the extreme (135° to 200°F) hot water needs of these customers, and thus the energy was simply discarded into the atmosphere as heat rejection.

However, the high pressure capabilities of newer screw compressor technology - single screws with their balanced axial and radial internal forces - allows for operation at substantially higher pressures, providing condensing temperatures of up to 205°F. This new capability enables industrial food processors to not only renew waste heat as useable heat, decreasing overall energy consumption, but to also replace chemical refrigerants and their inherent global warming threat with ammonia, a natural refrigerant, reducing overall dependence on fossil fuels.

Vilter Manufacturing LLC, a business of Emerson Climate Technologies, has recently applied industrial heat pumps such as those discussed above, to help a molded chocolate candy producer in England loosen molds from chocolate and for cleanup.

Beyond industrial food and beverage processing, Vilter has been working with Star Refrigeration, the United Kingdom’s largest independent industrial refrigeration company, on a number of projects, including the design and manufacture of the world’s largest ammonia heat pump - with over 14MW - to satisfy the heating needs of Drammen, Norway, a town of 60,000 residents.

“Whether motivated by ecological, political, economic, or other reasons, our customers are asking us to help them move away from systems that burn fossil fuel,” said Dave Pearson, director of innovation for Star Refrigeration.

“Vilter has provided us with the key component in our heat pump solutions, backed by engineering support second to none, helping Star deliver all our customers’ drivers in the same package: an approximate 15 percent reduction in energy consumption, a 40 percent saving in life cost, and immunity from any projected or pending legislation.”

For additional articles on heat pumps, visit The NEWS’ HVACR In-Depth page.

Publication date: 05/24/2010