Mechanical Systems Group of TIAX

Cambridge, United States

Mechanical Systems Group of TIAX

Cambridge, United States
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Dieckmann J.,Mechanical Systems Group of TIAX | Cooperman A.,Mechanical Systems Group of TIAX | Brodrick J.,U.S. Department of Energy
ASHRAE Journal | Year: 2011

An overview of solid-state cooling vs. conventional vapor cycle and an update of the status of Peltier devices is presented. The key challenge to implementing solid-state cooling is to find materials and configurations that minimize their inherent losses. The Peltier effect causes heat to flow from the cold side to the hot side, in the same direction of current flow through the P-type pellets and in the opposite direction of current flow through the N-type pellets. Much research has focused on creating quantum wells or quantum dots that provide greater electron mobility for the electrons that are actually transporting heat, while decreasing the thermal conductivity at the same time. In conventional, commercially available devices, the electric resistance and thermal conduction losses are significant enough to limit ZT at room temperature to 1.0, with the maximum COP being well below the COP of vapor cycle systems.


Dieckmann J.,Mechanical Systems Group of TIAX | Cooperman A.,Mechanical Systems Group of TIAX | Brodrick J.,U.S. Department of Energy
ASHRAE Journal | Year: 2011

Permeable membrane-based liquid desiccant cooling systems are capable of dry cooling systems that do not offer the added benefit of dehumidification. The system uses a membrane contactor between the liquid desiccant and airstream. Desiccant solution circulates through the system, absorbing moisture from the process air in the dehumidification column, and rejecting moisture in the regeneration column. The air is dehumidified as liquid desiccant flows counter to it, with the membrane contactor preventing desiccant droplet formation and entrapment in the airstream, simplifying the downstream processing needs of the system. Energy savings are realized by using active desiccant dehumidification only when the outdoor air humidity is too high for indirect evaporative cooling to provide the necessary cooling. To date, permeable membrane based desiccant cooling systems are in the research and development phase.


Dieckmann J.,Mechanical Systems Group of TIAX | Cooperman A.,Mechanical Systems Group of TIAX | Brodrick J.,U.S. Department of Energy
ASHRAE Journal | Year: 2011

Several solid-state cooling devices are the subject of active research, but are not yet commercialized. Examples include electron tunneling, the electrocalorie effect, and the thermoelastic effect. This column covers the current state of research into these technologies and the prospects of bringing products based on these technologies to market.


Cooperman A.,Mechanical Systems Group of TIAX | Dieckmann J.,Mechanical Systems Group of TIAX | Brodrick J.,U.S. Department of Energy
ASHRAE Journal | Year: 2011

Significant energy savings could be obtained through the use of evaporative condenser cooling in residential and light commercial air-conditioning systems. Three basic ways to implement evaporative condenser cooling are, directly evaporatively precooling the cooling air, flooding water over the condenser coil, and use of a cooling tower to evaporatively cool cooling water. The condenser coils can be sprayed with water as outdoor air is drawn over them or immersed in cooled water. This increases heat transfer between the refrigerant and the heat sink due to increased evaporative heat transfer coefficients. A study of evaporative condenser technology in California by Pacific Gas and Electric found that EC units are more efficient than conventional air-conditioning units having seasonal energy efficiency ratios (SEER) of both 10 and 12 and demand less energy. It is also found that EC units demand less energy and maintain their design capacity at higher temperatures than vapor compression units.

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