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Title: New configurations of a heat recovery absorption heat pump integrated with a natural gas boiler for boiler efficiency improvement

Conventional natural gas-fired boilers exhaust flue gas direct to the atmosphere at 150 200 C, which, at such temperatures, contains large amount of energy and results in relatively low thermal efficiency ranging from 70% to 80%. Although condensing boilers for recovering the heat in the flue gas have been developed over the past 40 years, their present market share is still less than 25%. The major reason for this relatively slow acceptance is the limited improvement in the thermal efficiency of condensing boilers. In the condensing boiler, the temperature of the hot water return at the range of 50 60 C, which is used to cool the flue gas, is very close to the dew point of the water vapor in the flue gas. Therefore, the latent heat, the majority of the waste heat in the flue gas, which is contained in the water vapor, cannot be recovered. This paper presents a new approach to improve boiler thermal efficiency by integrating absorption heat pumps with natural gas boilers for waste heat recovery (HRAHP). Three configurations of HRAHPs are introduced and discussed. The three configurations are modeled in detail to illustrate the significant thermal efficiency improvement they attain. Further, for conceptualmore » proof and validation, an existing hot water-driven absorption chiller is operated as a heat pump at operating conditions similar to one of the devised configurations. An overall system performance and economic analysis are provided for decision-making and as evidence of the potential benefits. These three configurations of HRAHP provide a pathway to achieving realistic high-efficiency natural gas boilers for applications with process fluid return temperatures higher than or close to the dew point of the water vapor in the flue gas.« less
 [1] ;  [2] ;  [3]
  1. Purdue University, West Lafayette, IN
  2. ORNL
  3. Southeast University, Nanjing, China
Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Energy Conversion and Management; Journal Volume: 87
Research Org:
Oak Ridge National Laboratory (ORNL); Building Technologies Research and Integration Center (BTRIC)
Sponsoring Org:
EE USDOE - Office of Energy Efficiency and Renewable Energy (EE)
Country of Publication:
United States
HEAT RECOVERY; DEW POINT; FLUE GAS Natural gas boiler; Absorption heat pump; Heat recovery; Dew point; Flue Gas; System Configuration