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“Semi-open” residential water heater concept promises high efficiency, lower cost

August 17, 2016 - A team of scientists from the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) and the University of Florida (UF) has developed a method that could yield lower-cost, higher-efficiency systems for water heating in residential buildings.

August 18, 2016  By  Anthony Capkun

A new class of gas-fired heat pump water heater systems

“When applied, the new concept could result in better than 100% energy efficiency because the system draws energy from the surrounding air as well as from the natural gas,” said ORNL’s Kyle Gluesenkamp, lead author of “Efficiency analysis of semi-open sorption heat pump systems”.

The theory behind the newly termed “semi-open” natural gas-fired design reduces the cost and complexity of traditional closed gas-fired systems by streamlining—even eliminating—certain components.

The design combines water heating and dehumidification functions; in the semi-open scenario, the absorber device acts in place of the traditional evaporator component, pulling water vapour directly from the air through a membrane into a liquid solution. As the vapour is absorbed, much of the heat is transferred to domestic hot water (Photo 1, courtesy ORNL).

The simpler semi-open system would operate at the surrounding atmospheric pressure, using an “inexpensive, non-sealed solution pump”. This approach eliminates the need for vacuum pumps found in closed systems that purge gas build up, explains ORNL. It also allows manufacturers to consider lower-cost, lightweight polymers instead of costly, bulkier metals to build equipment, making it less susceptible to corrosion.

“The semi-open architecture introduces a new class of ultra-efficient heat pump water heaters that could become commercially available in a few years to homeowners seeking to replace their existing gas water heater,” Gluesenkamp said.


UF researchers are leading the development of a semi-open gas-fired heat pump prototype, and are using both ORNL’s Building Technologies Research and Integration Center and UF facilities to evaluate the potential of commercial applications (Photo 2, courtesy University of Florida).

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