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

Abstract

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 CO2reductions 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 airconditioning system. The review provided in the paper may also be of use to other workers on PCMs and night cooling of naturally ventilated buildings.

Novel cooling unit using PCM for residential application

“…The free cooling technique by using phase change materials in buildings can provide better indoor thermal comfort, and help reduce the need of air-conditioning use and sizes of air-conditioning systems (Turnpenny et al, 2000(Turnpenny et al, , 2001Zhu et al, 201;Etheridge et al, 2006). However, this concept is only feasible in climate conditions with relatively large temperature differences between day and night in Summer (Takeda et al, 2004;Medved and Arkar, 2008).…”

Experimental studies on improvement of coefficient of performance of window air conditioning unit

“…They concluded that with the incorporation of HPHX the cooling capacity of the system is increased by 20% to 32.7% and the RH level maintained below 70%. Etheridge et al [2] have conducted a research on phase change material heat pipe cooling system for reducing AC in buildings. They report that the objective of their research is to retrofit the existing (AC) units in the buildings with previous cooling system on commercial scale and to reduce the carbon emission to save the environment.…”

Experimental and numerical investigations of a lauric acid-multichannel flat tube latent thermal storage unit

“…Air has been used as HTF in specific occasions, such as in solar air heating systems, air preheaters, flue gas waste thermal recovery, and building heat . If water is used as HTF, then an air‐water heat exchanger should be added to transmit heat from water to air.…”