Energy storage in a central heating system: Spa School field trial

Abstract

Building Sew. Eng. Res. Techno]. 8 (1987) 79-84 Printed in Great Britain Summary C d e l d Institute of Technology and British Gas plc have undertaken a collaborative programme of tests of a system which interposes a heat store between a boiler and a distributive central heating network. This has culminated in a field trial at Spa School in London. It was predicted to lead to significant energy savings, to a lower installed boiler capacity requirement, and to reductions in installation costs for new and for some retro-fitted systems. Specifically, a thermally insulated 3235 1 hot water store was installed in the circuit between the existing modular boiler set and the hydronic 'radiator' network. The pipework was arranged so that the heating system could be operated either as configured originally or in the storage mode, in which case two of the five modular boilers were valved off. The two configurations were operated alternately (for four week periods), and their performances were carefully monitored over the 1985/86 heating season. The storage system performed successfully with a 40% lower installed boiler capacity. Boiler cycling was reduced by a factor of 15 and the mean boiler load factor rose from 37 to 70%. Analyses of results show that a 6% saving in annual fuel consumption was achieved by the storage system as compared with that of the highly efficient conventional system employing direct external compensation of the boilers. However, all this saving is attributable to the faster building preheat achieved with the store as, surprisingly, the annual efficiencies of the two systems were the same (in contradiction to the findings of other trials). The reasons for this are examined. Where direct compensation is not possible, the reduction in boiler cycling demonstrated will lead to a further substantial efficiency advantage of at least 10%.The Spa School heat storage field trial represented a key phase in the collaborative programme of research and development into the use of heat storage in central heating systems by Cranfield Institute of Technology (CIT) and British Gas (BG) plc. It followed from a detailed assessment study based on computer modelling(') and a preliminary field trial at the British Gas offices in Reigate('). Concurrently, integrated storage systems in the domestic sector have developed rapidly(3); these have now been c~mmercialised(~).The three purposes of the field trial were to gain a comprehensive understanding of how a large hot water storage system operates in all likely conditions, to quantify theenergy saving potential and to determine theacceptability (with respect to cost, reliability and ease of maintenance) of such systems for building owners and occupiers.The main potential benefits of incorporating thermal storage within central heating systems have been described elsewhere(') and may be summarised as:-fuel savings resulting from an increase in boiler efficiency through reduced boiler cycling and an increased boiler load factor -additional fuel savings in intermittently heate...

The use of the pre-heat margin in heating system design: a review based upon published literature

“…The authors do not indicate how the 33% was evaluated. Work by Cohen et al 16 carried out field trails on a thermal storage system added into an existing system, it was found that the fuel savings gained by the use of thermal storage were all due to the faster pre-heat times that were made possible by the stored hot water. This work indicated that the installed boiler capacity in the building examined could be reduced by 40% with the use of a thermal storage vessel.…”

Comparison of methods for verification of energy efficiency improvements

“…On-Off. The on-period (retrofits activated) energy consumption is compared to the offperiod (retrofits deactivated) consumption (Woller 1989;Cohen et al 1987).…”