Integration of a Magnetocaloric Heat Pump in Energy Flexible Buildings

Description

To prevent future energy crisis and tackle the problems of climate change, modern society must promote a radical evolution in our energy systems. The building sector, and in particular its heating needs, have clearly been identified as one of the main targets for the reduction of the global energy usage. In addition, buildings are a key actor for the development of renewable energy sources.
The main objective of this research study is to investigate and demonstrate the possibility of integrating a magnetocaloric heat pump in a single-family house under Danish weather conditions. Moreover, the study includes a numerical analysis to increase the understanding of the heating energy flexibility potential of residential buildings using thermal storage in the indoor environment.
The magnetocaloric heat pump is an innovative technology employing the magnetocaloric effect of certain materials in active magnetic regenerator thermodynamic cycles generating a heat transfer from a heat source to a heat sink. Numerical investigations performed in this study demonstrated that this device can be implemented in a low-energy residential building in Denmark and provide for its indoor space heating needs. When coupled to a ground source heat exchanger and a radiant under-floor heating system in a single hydronic loop, the magnetocaloric heat pump can operate at maximum capacity with an appreciable coefficient of performance of 3.93. A control strategy taking advantage of the building heating energy flexibility potential has been developed for optimum operation of the magnetocaloric heating system in a multi-zone dwelling. The thermal energy is stored in the indoor environment, which allows a shift and a concentration of the heating loads in time and thus a maximization of the heat pump full-load operation time. Consequently, the maximum average coefficient of performance of the magnetocaloric heating system ranges from 2.90 to 3.51, which is comparable with conventional vapour-compression heat pumps.
More generally, energy flexibility strategies can be employed to adapt the energy usage of buildings to the grid requirements. They can therefore help to control Smart Energy Grids dominated by intermittent renewable energy sources. Among these strategies, the thermal energy storage in the built environment by means of indoor temperature set point modulation was found to be a cost-effective solution. This research study focussed on heating energy flexibility potential of residential buildings in Denmark. This energy flexibility is defined here as the ability of a dwelling to shift its heating use in time by accumulating and retrieving thermal energy. The numerical analysis showed that even though effective thermal inertia determines the maximum heat storage capacity of the building, the insulation level of the envelope sets the storage efficiency and is the most important building parameter with respect to heating energy flexibility potential. Well-insulated dwellings can thereby shift heating loads over long periods of time and poorly insulated buildings can only shift heating use over short periods of time. However, the latter can move a total amount of energy four times larger than high-insulation houses and thus have a larger impact on the energy grids.
This research project has also looked into the influence of additional thermal mass from indoor content items and furniture elements on the building thermodynamics and heating energy flexibility potential. Passive latent heat thermal storage solutions such as phase change materials integrated in wallboards or in furniture elements were found to significantly increase the total effective heat storage capacity of light-weight structure buildings. Moreover, it was demonstrated that assuming the indoor space to be an empty volume is not appropriate for dynamic energy simulations of houses with low structural thermal inertia. Transient thermal behaviour, building time constant, total heat storage capacity and therefore heating energy flexibility can be significantly influenced by the presence of indoor content and furniture in the built environment. To address that matter, this study reviewed the different methods for modelling items and furnishing elements present in the building indoor space. In addition, suggestions were made for choosing material characteristics of these indoor content elements.

Period	29 May 2018
Event type	Other
Location	Aalborg, DenmarkShow on map
Degree of Recognition	International