Laboratory Tests of Chemical Reactions and Prototype Sorption Storage Units : Report B4 of Subtask B

• Five laboratory prototypes of thermochemical and sorption storage are described in this report as well as the material characterisation of a promising thermochemical reaction with MgSO4.7H2O. Measured results and projected heat storage densities for units of 70 and 1000 kWh storage for single family houses are reported. Four of the five prototypes are closed sorption units and act as thermally driven heat pumps. Two work with absorption: three phase absorption process, Thermo Chemical Accumulator (TCA) with Lithium Cloride/water, and two phase absorption with Sodium Hydroxide/water. Two work with adsorption, one with zeolite and the other with silica gel. The fifth prototype that is reported, Monosorp, uses an open adsorption process integrated into a standard ventilation system with heat recovery. The different technologies are at very different stages of development. The TCA technology is in the process of commercialisation by the Swedish company ClimateWell AB, and over 35 storage systems have been delivered, mostly in Spain. The other technologies are in the prototype stage with no companies intending to develop and market them. The Modestore store (silica gel /water) was developed in a European project, and the main company within the project (Sortech) is commercialising the technology as a heat pump with essentially no heat storage. The storage density for cold (based on total system volume), when compared to water, is more favourable than for heat. For the ClimateWell 10 commercial heat pump/store, the storage density for cold is 4.7 that of water whereas for heat it is only 1.2 times greater. This is due to the fact that the temperature range available for water storage for cold is much smaller (~10°C) than for heat (~60°C). For short term heat storage, none of the technologies have a significant advantage compared to water in terms of storage density. The energy density can only be slightly greater than that for water, mainly due to the space required for heat exchangers and other components. The best technology in this aspect is Monosorp, which has a density twice that of water. In addition all of the storage systems have irreversibilities in the processes themselves during charge and discharge. Most of this is due to the different temperature levels of charge/discharge and the related sensible energy between these. For longer term storage (1000 kWh) the energy density for the TCA technology and NaOH storage systems is nearly three times that of water, for Monosorp twice and for MgSO4.7H2O nearly. In addition, once the sensible heat from the solution has been lost (or at best recovered), the energy can be stored indefinitely, a significant advantage compared to water. In terms of material cost, all materials are expensive compared to water. However, NaOH, zeolite 4A and MgSO4.7H2O are significantly less expensive than the other materials reported, LiCl, silica gel and zeolite 13X. The cost for the whole storage system has not been estimated here. For the ClimateWell 10, the projected cost is ~8000€ for a heat pump system consisting of two units in parallel, with a total heat storage capacity of 70 kWh.

Publication and Content Type

vet (subject category)

rap (subject category)