Trigeneration refers a technology that generates simultaneously electricity, useful heating and cooling power from the same energy sources. It is an emerging technology with a potential to provide energy efficiency and environmental benefits by reducing primary energy consumption and associated greenhouse gas emissions. Research on trigeneration in the past has been mainly focused on very large scale systems and much less attention has been paid to micro-trigeneration or residential trigeneration.
Researchers with University of Leeds and Institute of Process Engineering (IPE) proposed a novel energy storage system for domestic households as well as small scale office buildings. This is a trigeneration system which store excessive energy in the form of compressed air and thermal heat.
Figure 1 shows a schematic diagram of the system, where electricity and thermal heat are taken as the primary movers for generality. For better control of energy release process, thermal fluid for heat storage is used.
In their work, air compression and storage unit, thermal energy storage unit and energy extraction unit of the micro-trigeneration system were analyzed assuming the kinetic and potential energy of the fluids were negligible.
Results indicated that the system was different from the conventional compressed air energy storage (CAES) technology in that it allowed trigeneration of electrical, heating and cooling power in energy releasing process. Uniquely, the cooling power was generated by direct expansion of compressed air instead of the use of absorption chilling technology.
In their experiments, a new parameter, the comprehensive efficiency, was proposed to evaluate the performance of the trigeneration system. Energy requirements of a small office building located in Chicago was used for the evaluation. With a careful selection of the system scale, the average comprehensive efficiency can be around 50% and 35% in winter and summer, respectively, which were much higher than the conventional trigeneration system.
The system is therefore very promising for practical applications particularly for the use of renewable energy due to good flexibility and simple configuration. This work represents a first step towards developing such a system for the applications in domestic households and small scale office buildings.
The paper was published in Applied Energy.
Fig. 1. Schematic of the proposed micro-trigeneration system. (1) air compressor, (2) cooler, (3) drainer, (4) dryer/moisture trap, (5), (7) and (14) cut-off valve, (6) high pressure vessel, (8) regulating valve, (9) heat exchanger, (10) expander, (11) generator, (12) heat storage tank, (13) pump and (15) control system.
