Development of a control system to cover the demand for heat in a building with algae production in a bioenergy façade

Abstract

In the present study a control system was developed and tested which allowed to maintain an optimum of both heat and microalgae production in a bioenergy façade and use of the heat to supply a residential building with hot water and heating. The control was developed for and implemented in the residential building BIQ Das Algenhaus, Hamburg, Germany. It automatically operates all system components of the 170 m² bioenergy façade as well as the management utilities which supply the building with heat. During a one-year monitoring in 2017/18, it was shown that the temperature in the culture medium of the bioenergy façade could be kept at the optimal cultivation temperature range between 20 and 35 °C. In addition to the biomass production, the façade produced heat as a result of the solar radiation. This heat has been extracted from the façade and utilized as a heat source for the building's supply system. The ratio between the solar radiation on the façade's surface and the heat produced – called energy conversion coefficient – was 0,38 across the year. The system supplied 59% of the building's annual total heat consumption of 63 MWh/a for hot water and heating. In the months May to August, the bioenergy façade served as the sole primary heat source for the building and the 50% surplus heat were stored in the soil below the building. The heat stored in the soil resulted in a regeneration of the soil temperature and allowed to cover the heat demand during winter.80% of the heat extracted from the façade were used instantaneously and without intermediate storage. This indicates that the control optimally regulates the heat flows for direct use and thus minimizes storage losses.The results show that bioenergy façades can be perfectly integrated into cities to help transfer them from being places of abundant resource consumption to places of production of resources by producing heat and biomass concomitantly.