Thermodynamic and economic evaluation of trigeneration systems in energy-intensive buildings

Abstract

Within the building sector, supermarkets are responsible for 3-5% of the electricity consumed in developed countries. To mitigate the associated environmental impact of this consumption, a growing interest has been developed in local combined heat and power (CHP) systems, due to their higher total efficiencies. However, CHP efficiency is highly dependent on the thermal output utilisation. In food retail buildings, where refrigeration dominates the building energy use, a promising means for utilising the thermal output is by using this to operate absorption chillers. This paper reports on a technical feasibility and financial viability study of an ammonia-water absorption chiller, coupled to a CHP unit, that is also compared to a conventional electrically-driven vapour-compression equivalent. A typical distribution centre located in the UK is selected as a case-study. Three alternative systems are considered: i) a conventional grid connected system; ii) a CHP system; and iii) a trigeneration system. Typical daily cooling, heating and hot-water demand data are provided on an hourly basis, and the system’s ability to cover these loads is assessed. The results indicate that the trigeneration system can reduce the electricity demand by 16% compared to the baseline system, while offering a 48% annual energy cost saving. The system’s primary energy utilisation rate exceeds 60%, while the power-to-heat ratio of the building demand improves from 7.0 to 0.9, thereby more closely matching the CHP system generation profile. Furthermore, the trigeneration system achieves CHPQA rating of 106, and it is qualified for enhanced capital allowance for the CHP plant. The results highlight the great energy and cost savings potentials of integrating trigeneration systems in energy-intensive buildings.