State-of-the-Art Heat Pumps
Most U.S. homes are heated with either a furnace or a boiler, and a small fraction of homes employ heat pumps which use energy (typically electricity) to move ambient heat from the outside environment to the interior of the home. High efficiency furnace and boiler systems remain expensive and require low heating temperatures to maintain maximum efficiency; under high heat load conditions, the efficiency will often drop. Electric heat pumps have been available for many years, however, they have not received widespread acceptance due to poor performance in cold climates. Efficiency decreases at low temperatures, when heat is needed most, which requires supplemental fuel or electric heating that can increase costs.
Air conditioners (A/C) are heat pumps that transfer heat from colder to hotter environments. The vast majority of A/C systems are vapor-compression cycle, with a small installation of absorption systems, and represent the largest portion of electricity consumed in a home (22%). A/C systems are primarily electrically driven and run during the summer months, thus requiring electricity when it is least available and most expensive. Vapor-compression systems also utilize refrigerants that present a variety of environmental concerns, including ozone depletion and greenhouse effects.
Vuilleumier Heat Pumps
The ThermoLift technology is based on the Vuilleumier Heat Pump (VHP), which can be considered a heat engine directly coupled to a heat pump. The VHP moves a working gas, such as helium, between three chambers within a closed system. Two displacers reciprocate within a cylinder to move the working gas between separate hot, warm, and cold chambers. The thermodynamic cycle utilizes differences in pressure, temperature, and volume (ideal gas law) to create a pressure wave, resulting in pockets of both very hot and very cold temperatures. This heat difference can be exploited to extract heat from one environment and move it to another environment, while also doing so at very low ambient temperatures. The VHP is an extremely efficient way of capturing heat energy, as opposed to traditional heat pumps that use energy-intensive electricity to create heat and mechanical force. The VHP uses heat only and avoids the energy losses associated with the conversion and phase changes of conventional compressor based heap pump systems.
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The first efforts at creating a VHP were completed by NASA and the US Air Force in the 1960’s. Since then, the most comprehensive investigation into the VHP as a heating system was completed by Bosch-Viessman Energie (BVE) in 1991. During this work, BVE built and tested three VHP machines, each tested for over 6,500 hours and yielded efficiencies that exceed current DOE performance targets for natural gas driven HVAC technologies. BVE data demonstrated a coefficient-of-performance (COP) of 1.65 at an ambient temperature of 47 °F and 1.3 at -13°F.