As the global climate emergency becomes increasingly evident around the world, many businesses, organizations, and even countries have set a goal of reaching “net-zero” in their greenhouse gas emissions by improving efficiency and using renewable energy.

In the supermarket arena, German retail giant Metro AG In 2017 opened a 12,700m² (136,702ft2“net-zero” store in St. Pölten, Austria. This store’s goal is to use only renewable energy created on site with a 6,000m² (64,583ft²) photovoltaic system on the roof. It was also designed to realize a 60% reduction in energy demand as compared to the Metro worldwide average.

In November 2018, Canadian retailer Longo Brothers Fruit Markets opened a 40,000ft² (3,716m²) store in in Stouffville, Ontario, Canada, that it described as “near net-zero.” The store is equipped to use 35% less energy than other supermarkets and produce 65% of its own energy through renewable technologies, according to Natural Resources Canada, the country’s environmental agency.

One of the latest supermarket chains to try its hand at net-zero is German retailer Lidl, at a 2,057m² [22,141ft²] store/warehouse opened in September 2019 in Woerden, the Netherlands, on the site of an old demolished shop.

An important requirement from Lidl in the planning process for this store was to create an energy-neutral building, meaning that the power consumption of the whole building had to be fully self-sufficient and that no energy bills should be paid at any time during the year. All energy that is used in the store, such as for lighting, heating and cooling, the cashier tills and more, is therefore produced in the store itself from green energy sources, including 1,766 rooftop solar panels as well as thermal energy via a ground-source heat pump.

The Woerden store, like most of Lidl’s new stores, cuts its energy demand with LED lighting and efficient HVAC&R systems, and includes other environmentally friendly features like rainwater filtration. The Woerden store is particularly innovative with HVAC&R technology, using two transcritical CO2 systems – a refrigeration system, and the ground-source heat pump, which is also used as a chiller for air conditioning.

Lidl opened its first store in the Netherlands in 1997, and since 2014 all new stores in the country have been awarded the A++++ energy rating, the highest possible.

Leveraging pre-cast concrete piles

One of the key energy-saving technologies at the Woerden net-zero store is the (50kW/14.2TR) transcritical R744 ground-source heat pump provided by Dutch installer Frimex.

The heat pump is connected to special pre-cast concrete piles in the ground underneath the store and the parking lot, which serve as a thermal reservoir. Glycol is circulated via hollow tubes inside these thermal precast piles to transport heat to and from the thermal reservoir, taking advantage of the natural ground temperature during the year to complement the cooling and heating cycle in the building.

The heat pump can be used to create a comfortable climate inside the store when the refrigeration system doesn’t produce enough excess heat to heat the shop through heat recovery during the winter months. Conversely, the heat pump can also serve as an air-conditioning system during the summer by reversing its operation, using the cooler ground temperatures. Hot and chilled water tanks are used for climate control of the store.

A benefit of the system is that, as a result of pumping excess heat back into the thermal reservoir (via glycol), the refrigeration system’s CO2 refrigerant is cooled, increasing the efficiency of the system for the store/warehouse, and reducing the energy needs of the whole building.

Marcel Ganzeboom, Senior Manager in the Construction Department of Lidl Netherlands, and the initiator is of the net-zero project, confirmed the retailer’s satisfaction with the technical solutions. “It is a very closed chain of electricity generation and waste streams from cold and heat, which are used immediately or stored immediately,” he said. “Very genius to see how it works.”

The cooling power behind net-zero

The refrigerated cabinets in the new Woerden store are cooled by German manufacturer Teko’s ROXSTAsmart CO2 rack. The unit offers a medium-temperature capacity of 112kW (32TR) at -8°C (17.6°F) and a low-temperature capacity of 4kW (1.2TR) at -33°C (-27.4°F). This is needed to cool a total of 85m (279ft) of medium-temperature cabinets in the sales area, plus two cold rooms and one freezer room.

The ROXSTAsmart system was installed in a separate plant room above the warehouse, taking up minimal space. It only measures 2.6m by 1.9m by 0.98m (8.6ft by 6.2ft by 3.2ft), including a sound enclosure, three medium-temperature compressors, and one low-temperature compressor.

In addition to aiming for net-zero emissions, Lidl required that no synthetic refrigerants be used, and Frimex opted for CO2. “By using CO2, even though it is a greenhouse gas as well, we designed a system with minimal impact on the environment,” said Hendrine Kalkman, Head Engineer at Frimex.

While Lidl confirms that the investment costs for the net-zero store were higher than an average supermarket, the expected payback time will be around five to 10 years.

However, Lidl emphasizes that supermarket customers should not pay a premium for the sake of shopping in a sustainable store like this. “We do not charge sustainability to the customer; it is the other way around – it makes the shopping cheaper,” said Ganzeboom.

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