A PCM/heat pipe cooling system for reducing air conditioning in buildings: review of options and report on field tests

Air conditioning is now seen as a new and major contributor to CO2 emissions in the UK. This is partly due to global warming and partly to the increased use of IT systems. A novel system for reducing or eliminating the need for air conditioning was developed to the proof-of-concept stage under an earlier project at the University of Nottingham. The system makes use of heat pipes to transfer heat into and out of a phase change material which is 'frozen' during the night and 'melted' during the day. This paper describes a number of concepts for 'free cooling', and the background to the current concept, before detailing field tests on the system that have recently been completed and which demonstrate its effectiveness under real operating conditions. Systems were installed in two offices and detailed monitoring of their performance was carried out during the summer months. On the basis of the results obtained it is concluded that the system functions very well and is practically and technically the most attractive of the available alternatives to air conditioning. The fact that it is suited to retrofitting in existing buildings means that both the potential market and the CO2 reductions are large. Practical application: The paper describes a novel system that is intended to provide passive cooling in naturally ventilated buildings. The novelty lies in the use of heat pipes and a fan to enhance the heat transfer to and from the phase change material (PCM) and the air. That this has been successful is shown by the ability of the system to exercise a degree of control over the room air temperature that is comparable to that of a conventional airconclitioning system. The review provided in the paper may also be of use to other workers on PCMs and night cooling of naturally ventilated buildings.