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WP5 - Storage (Deliverable 5.3)

The full report is confidential and will not be distributed to the public. However, a brief summary of the contents are given here.

Within phase 3 of the MacSheep project four heat storage concepts are under development by the four different groups. These concepts include several that have been identified and analyzed within phase 1 and phase 2 of the project and which are documented in the deliverables 5.1 and 5.2. Taking into account the current status of the work in phase 3 (as summarized below), it is expected that the time plan and the objectives according to the DOW of MacSheep will be met in work package 5.

IWT, SPF and ESSA are developing a very compact concept with as many components as possible included under a VIP insulation shell. This will include heat traps with all pipes taken down to the bottom of the insulation, external DHW and solar heat exchangers as well as very short pipe runs. In the current design these pipe runs are a factor 3 shorter than those of state of the art systems. CFD simulation results show that the direct heat pump inlets lead to considerable mixing in the store even at relatively low charging flow rates and that diffusers will need to be designed and implemented into the store. The whole concept also includes the possibility of an ice store.

Ratiotherm and SERC have developed and built a prototype of a two stage heat pump with intermediate storage. The two stages can operate in cascade mode (both running simultaneously) when required, or can run independently with heat from the lower (colder) stage being stored in the intermediate store. This store is also used for low grade heat from the collector. The developed prototype is currently undergoing testing at the Ratiotherm factory. Initial simulation results suggest however, that a separate intermediate store is not cost effective and other studies are needed to determine whether it can be economically integrated in the existing combistore. The full concept includes a stratified combistore with external DHW and solar heat exchangers that is already on the market, and that is thus not part of the developments of WP5.

CTU and Regulus are developing a stratified store with VIP insulation, heat traps and decoupling of heat pump and heating system as well as separator plate between DHW and space heating zones in the store. CTU has used CFD simulations to analyze both sloping pipes and within-pipe heat traps. Further simulations will be carried out before the final choice is made. The external solar heat exchanger has two possible inlets allowing the charging of either upper or lower parts of the store depending on ambient conditions. A prototype store has been made and DHW discharge as well as heat loss tests have been carried out. Based on these a model was calibrated and then simulated in the complete system. Just replacing the store of the reference system with the new store results in a 12 % decrease in electricity use for the SFH45 house in Zurich climate.

INES and Viessmann are developing a stratified store with external DHW heat exchanger and integrated heat pump condenser as well as heat traps and reduced pipe runs. The condenser has been designed and manufactured and is undergoing pressure cycling tests to estimate its life time. The complete prototype store has been designed in detail and will be ready for testing in January 2014. Viessmann has also developed a multi-sensor device to measure stratification and will use this to determine the stratification in the store. The simulated performance of the store with integrated condenser is worse than the reference system, but the costs will be considerably lower and thus the changes are cost-effective.

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