Abstract
This paper reports on an evaluation of several energy conversion systems utilizing the Total Equivalent Resource Exergy (TERE) method (Zhang and Reistad, 1998). The systems are residential gas furnace and heat pump systems. The TERE method uses exergy as an overall evaluation parameter for energy conversion systems which combines energy and environmental resource (global warming) consumption. The method evaluates the exergy of the fuel, the exergy for the material in the system and the exergy required to recover the total global warming impact caused by CO2 equivalent emissions. This is done for both the energy conversion and production systems. The results illustrate comparisons of the systems for their consumption and their total lifetime impact including global warming.
Results of these comparisons, with the assumptions made, indicate that the high efficiency natural gas furnaces have less lifetime impact (greater efficiency) in satisfying a specified heating load as compared to low efficiency natural gas fueled furnaces. Some very high-efficiency furnaces with large blowers may, however, have greater lifetime impact than units that have moderately high efficiencies and smaller blowers. Relative to the three heat pump systems considered, the high efficiency gas furnaces were evaluated to have less lifetime impact than the air-source and direct-expansion, ground-source heat pumps, but more lifetime impact than the vertical ground-source heat pump. The annualized TERE values of the high efficiency gas furnaces are about 94 GJ compared to the greater than 100 GJ of the first two types of heat pumps. The vertical ground-source heat pump has the lowest annualized TERE value of 88 GJ.
These comparisons should be viewed in light of the following:
• The CO2 recovery exergy assumed here is not a precise value. This recovery exergy does have a major influence on TERE.
• The energy requirement and heat pump performance taken in this evaluation is based on one certain location in the U.S., a Northwest region, and the results do not necessarily apply to other locations and climate patterns.
• The accurate evaluation of scarce information such as weight and material of each component in the energy conversion systems is difficult; the information used in this evaluation is based on estimations.
Damage event analysis of vertical ground source heat pump systems in Germany
