Technical note: Thermal insulations for hot water cylinders: a review and a conceptual evaluation

Abstract

This paper presents a review and evaluation of thermal insulation materials for application in hot water storage cylinders. A range of thermal insulation materials including organic foams, inorganic insulations, composite insulations and vacuum insulation panels have been evaluated. The evaluation addressed parameters such as effects of insulation thickness on the energy saving and system cost. Vacuum insulation panels offered the best results in terms of energy saving and annualised system cost, given that the vacuum could be maintained at a desirable level throughout system lifetime. The overall evaluation indicates that polyisocyanurate (PIR) foam is the best overall single insulation material that could be applied for hot water storage cylinders when all the parameters including cost, thermophysical properties and environmental impact are taken into account. Microporous silica aerogel is more expensive than any other single insulation material that could be applied for hot water storage cylinders, but offers excellent performance in terms of reduced thickness and weight. When used in conjunction with PIR in a composite form, the combination offers a competitive performance in comparison with some of the conventional insulation materials, e.g. EPS, PU and glass fibre. Practical applications: The paper provides a comprehensive and compact summary and information on a range of thermal insulation materials for application in hot water storage cylinders. Although, the discussion is confined to hot water storage, the information is useful for a wide range of industries including construction industry, domestic appliance industry, technicians working in the above two industries and more importantly to R&D institutions. R&D institutions could directly benefit from the information provided in this paper, where the basic information and data are required to short list materials that should be given attention for further investigation for a given research area. Trade names normally dominate the industry with regards to material use; the paper provides basic scientific background on the origin of the thermal insulation materials, which are commonly known only by trade names within the industry, manufacturing processes, relative cost, their properties and related environmental impact. The paper provides awareness of other alternative insulation materials; that could be considered for a given application.