Energetic and exergetic study of a potential interconnection of a natural gas engine, heat pumps with a thermal and a mechanical compressor

Abstract

• The COP R is given with a new factor and the operating temperatures. • Creating the primary exergy ratio of complex systems using the analogy of the PER. • Simplified PER and PXR equations with the consumption shares for a GECAHP system. • Energetical and exergetical comparison of a trigeneration GECAHP system's operating modes. HVAC systems in buildings are significant energy consumers. It is proposed to utilize energy production systems that allow the generation of several types of energy from the same primary energy source. A solution of a CCHP, which consists of two types of heat pumps and a gas engine, was analysed in this article. The analysed solution can work in three operating modes, which allows the operators to avoid running both heat pumps, e.g., in the case of reduced demand or maintenance problems. These three operating modes are compared from energetical and exergetical. For a qualitative comparison of the operating modes, PXR is defined, and COP of heat pumps with a mechanical compressor is specified in an alternative way. Simplified equations are developed to determine PER and PXR to facilitate comparison. These equations can also be used to calculate the cases where the energy produced by the gas engine is not necessarily fully utilized by the heat pumps. The comparisons are also made via a case study. It is concluded that operating both heat pumps is the best option from energetical, but from exergetical, it is the worst. From the exergetical, if the required chilled water temperature is higher than 15.67 °C, or if the external air temperature is lower than 32.22 °C, then it is advisable to operate only the absorption heat pump from the gas engine. From the energetical, this can only be the second-best option if the generator temperature is above 85.02 °C.