ALDI 2010 – New Energy Concept for a Supermarket

© ALDI SÜD Rastatt GmbH
The new ALDI SÜD supermarket in Rastatt.
© Startdesign GmbH
Interior view of the supermarket. The skylights with their microscopic gratings and the display refrigeration units, which are cooled with a CO2-based system, are visible.

About 7 million CO2-equivalent tonnes are emitted annually in Germany from the refrigeration units of food retailers. This emission consists of both direct emission due to refrigerant leaks and indirect emission caused by energy consumption. If the effects of refrigeration, lighting and other types of electricity consumption are totalled, more than 1 % of German greenhouse gas emission is due to the food retail sector. The combination of various types of technology for building services, daylighting and the application of natural refrigerants such as CO2 with a low greenhouse potential can significantly improve the environmental footprint of supermarkets.

In collaboration with the building owner and the planning team, Fraunhofer ISE prepared a novel energy concept for the new ALDI SÜD supermarket in Rastatt. The aim of the energy concept was to reduce the primary energy demand of this supermarket by 50 % compared to the standard version by an integrated combination of numerous individual measures concerning the generation of cooling power, refrigerated units, the building envelope and technical building services. Energy efficiency in supermarkets is achieved primarily by efficient commercial refrigeration and by utilizing the potential for heat recovery and use of waste heat. Both the refrigeration methods and the refrigeration equipment for the new supermarket were selected and further developed according to energy-relevant criteria. In addition, skylights with a highly reflective microscopic grating in the space between the panes of the low-e coated triple glazing were installed. These ensure good visual contact and solar control simultaneously. For the artificial lighting, not only have highly efficient luminaires been installed but daylight-dependent control has been implemented.

The core of the concept is a geothermally assisted, CO2-based refrigeration network, which meets all energy demands for heating and cooling by consistent utilisation of waste heat from the refrigeration plant and free cooling from the borehole heat exchanger. As a result, there was no need for the other equipment which is usually installed, such as a gas-fuelled boiler for heating or an air-conditioning unit to cool the supermarket. One weakness of CO2 cooling systems is that the coefficient of performance drops markedly during periods of high outdoor temperatures if the gas cooler is cooled by outdoor air. In this project, this effect is reduced by combination with a borehole system to cool down the refrigerant.

The two-year monitoring phase started soon after the supermarket was opened in October 2010. The data to determine energy balances and to optimise operation were acquired and analysed continuously. Optimisation potential for controlling the CO2 refrigeration unit, which had been newly developed by the Hafner-Muschler company, was identified and implemented. The daylight-dependent control of the artificial
lighting was also continually improved with regard to energy efficiency and optimal visual comfort.