Residential Micro-CHP system with integrated phase change material thermal energy storage

Abstract

This paper presents an analysis and experimental investigation of the effect of integrating Phase Change Material (PCM) within a heat exchanger within a Micro Combined Heat and Power (Micro-CHP) system intended for residential applications. A commonly used Micro-CHP layout is replicated in a test rig to characterise the performance of two alternative heat exchanger arrangements. The first is a conventional arrangement where the exhaust gas produced by the prime mover is directed to an air-to-water heat exchanger to heat water and store it in a tank. In the second arrangement, PCM material is encapsulated within specially designed compartments in a heat exchanger to store part of the exhaust thermal energy from the prime mover while heating the water in the storage tank. The time needed to heat the water and discharge heat is compared for both cases, as well as the amount of thermal energy stored during the same operating period. The study also explored the potential to improve the designed unit by using different PCM materials. The test results show that adding 4.7 L capacity paraffin compartments within the heat exchanger extended the discharge time of the hot water by over 400 %, which reflects a marked improvement in the heat storage capacity of the system. This would result in a significant increase in the viable operating period of a CHP system. The one-dimensional analysis revealed that replacing the paraffin with ClimSel C58 PCM can reduce the charging time of the water tank by around 54 % improve the heat storage capacity by factor of 2.35 comparing to Paraffin. The proposed heat exchanger with encapsulated PCM has a potential in other applications such as storage of excess renewable energy or integration with heat pumps to improve matching of supply and demand and thus flexibility of an energy system with integrated intermittent renewables.