Solar Energy 75 (2003) 27–34 Heat retaining integrated collector / storage solar water heaters a, a b * M. Smyth , P.C. Eames , B. Norton a Centre for Sustainable Technologies, School of the Built Environment, University of Ulster, Newtownabbey BT37 0QB, Northern Ireland, UK b Dublin Institute of Technology, 30 Upper Pembroke Street, Dublin, Ireland Received 22 August 2002; received in revised form 15 May 2003; accepted 28 May 2003 Abstract An integrated collector / storage solar water heater (ICSSWH) that can signiﬁcantly reduce heat loss to ambient during non-collection periods has been developed. Two thirds of the ICS vessel is mounted within a concentrating cusp, McIntire ‘W’ modiﬁed concentrator and incorporates an inner heat retaining vessel. The remaining upper 1 / 3 of the vessel is situated outside the reﬂector cavity and is heavily insulated. Over 60% of the thermal energy stored within the total vessel, and up to 67% of that in the upper immediate draw-off region can be retained over a 16-h non-collection period. Results of an experimental analysis of this design and a comparison with a standard ICS design are presented.  2003 Elsevier Ltd. All rights reserved. 1. Introduction effects of vessel wall conduction. The inner store, due to the low thermal conductivity of the inner sleeve material From their inception, integrated collector / storage solar reduces thermal loss and retains a higher core temperature water heaters (ICSSWH) have employed a transparent during night-time and low insolation periods. The present aperture cover to reduce heat losses to ambient (Kemp, study reports on the performance under solar simulated 1891). Though an aperture cover reduced convective heat conditions of two heat retaining ICSSWH designs incor- losses, radiative heat losses remained large, especially on porating the heat retaining sleeve reported by Smyth et al. cloudless nights. Consequently, irrespective of solar energy (1999). collection efﬁciency, unless the hot water was withdrawn fully at the end of the collection period, heat losses to ambient led to only lukewarm water being available early 2. Design and construction of the prototype ICSSWH the next day. This reduced the overall solar fraction rendering the ICSSWH less viable economically. Two full-size prototype ICSSWH types, illustrated in A heat retaining ICS vessel has been developed (Smyth Fig. 1, were designed and fabricated. Type A utilised a et al., 1999) consisting of an outer absorbing section and 1.0-m-long ICS vessel, which was enclosed fully within a an internal perforated inner sleeve manufactured from a reﬂector cavity. Type B utilised a 1.5-m-long ICS vessel, material with a low thermal mass. During energy collec- which was enclosed partially within the reﬂector cavity. tion periods, thermal buoyancy leads to natural circulation The upper 1/3 of the 1.5-m-long vessel was located within the vessel(s). Water adjacent to the exterior surface outside a reﬂector cavity and was thermally insulated with is heated, rises, and passes through the perforated inner a 50-mm-thick polystyrene foam casing, as were the sleeve into the inner store, leading to a high degree of exposed end plates of each vessel. The store volumes were thermal stratiﬁcation within the inner store. The stratiﬁca- 57 and 85 l for types A and B, respectively. Each vessel tion is improved as it is disrupted less by the convective was fabricated from 1-mm-thick aluminium sheet and motion. Due to the pressure of the sleeve, the stratiﬁed seam welded together with a welded base at one end and water is segregated from convective motion and from the an open ﬂange arrangement at the other. The inner sleeves were made from unplastised-polyvinylchloride (uPVC) pipe with a wall thickness of 8 mm. The size and conﬁgu- *Corresponding author. Tel.: 144-28-9036-8119. E-mail address: m.smyth1@ulst.ac.uk (M. Smyth). ration of the perforations on the sleeve were based on an 0038-092X / 03 / $ – see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016 / S0038-092X(03)00229-9