An ice cellar under a house... for heating

By Ivars Bušmanis (Latvijas Mediji

127 apartments with a shared car and a reservoir for heating have been sold this year in Stuttgart

This is not the type of ice cellar that can be found in fishing villages, where during the winter, ice blocks were brought in to keep the fish fresh. This is also not the type of ice cellar you would find in Lodina beer cellars, where ice blocks are cut and brought in from Memele. This one is built under the Rozenstein residential quarters in Stuttgart to provide heating in winter and cooling during the summer.

Producing their own electricity and heat

“Our energy concept is based on the idea that each facility management service provider should be able to produce their own electricity and heat” says the executive director of “Immotherm GmbH” Ulf Kuhn. “All of the communal utilities – electricity, heating, ventilation, elevators, electric car charging points – are powered by electricity that we produce. However, apartment owners and tenants can choose from whom and at what price to purchase electricity for their own private use.”

The initial project had rooftop solar panels and collectors that would have been used to produce heat and electricity. However, when the sun is shining, people use their electric cars and there is no need to heat apartments, so both heat and electricity had to be stored. While working on the project, we came to the conclusion that we needed to store electricity in batteries and heat in water,” says architect Christoph Welsch.

“Beneath this house we have an oval concrete reservoir. It is 6 m deep, 9 m wide, 17 m long and it holds 880 m3 of water,” Ulf Kuhn points to the ground. Water pipes running through the bottom and on the sides of the reservoir are used to transfer heat. They run through a heat exchanger and end up in underfloor heating radiators. During summer and autumn, the heat gathered by solar thermal collectors is used to heat the underground reservoir. But in winter, heat energy is transferred away from it, and eventually the water becomes a frozen block of ice,” Ulf Kuhn explains. He points to a computer monitor that shows a live feed from the ice cellar.

When it becomes too hot during the summer, the floor acts as a cooling system. “Then we run the system at 22-23 °C. You would not want your feet to get cold during the summer,” explains the energy manager. “In summer, solar energy melts the ice and warms the water. The water reservoir is used as a heat accumulator. However, if during winter the temperature drops particularly low, and we need extra heat, we turn on the natural gas boiler,” he says.

But what are the economics behind all this? The cost of this complex power supply system is €1.7 million, but the asking price of an apartment – €3,800 to €5,000 per m2 – even falls a bit below the average price in Stuttgart, which is over €5,000 and sometimes reach up to €8,000 or even €10,000 per m2. We are only selling the apartment walls, and we’ll get the return on our power supply investment by selling heat. All year round owners pay a constant monthly fee for the heat – 74 cents per m2. We can use the sun for free,” smiles Kuhn. “We should get a full return in 7 years,” he explains. 

We’ll see in a couple of years whether our calculations are correct. Residents have moved in, and this winter will be our first test. Siedlungswerk, the building developer ,is preparing to build even larger quarters nearby. These would house 500 apartments and would also require their own heating grid, this time even bigger.

“Selling an apartment with a car"

The noisy location near a station where a chemical plant once stood did leave the project developers wondering how to attract people to this, until now, unattractive location. Residents of the Rozenstein quarters are offered one more energy efficiency perk.
“We understood that the latest generation can do without a car, but they definitely cannot do without a smartphone. So, we decided to reduce noise and pollution levels just outside the windows and purchased three electric cars for the residents. These are shared-use cars, and people can book them when necessary. Price – €25 per day. To get people used to this idea, we gave away vouchers worth €200, and now about 15 families are testing the programme,” reveals the architect, Christoph Welsch.

Who cleans, charges or repairs the car – these are among the first questions that arise concerning joint ownership. “We are building developers, not a repair workshop. Therefore, we have a contract with the “Stadtmobil” car-sharing system, which is a member of the Federal car-sharing association.” But will there be enough cars to go around? Three cars for 125 apartments doesn’t seem like very much. “We’ll buy more,” promises Ulf Kuhn.

Actually, each family already has a car. In Germany it is required by law that a parking spot be provided for each new apartment that is built. In this case, they are all located underground below the apartment buildings. This programme could be used as a substitute for buying a second family car or  could be a nice option where residents have invested their funds into buying an apartment and do not have enough left for a car ownership.

Original article in Latvian