The association for the preservation of the bavarian tavern culture wants it. And the hotel and restaurant association (DEHOGA) anyway. But the fact that even parts of the green party and the federal environment agency consider it acceptable is new.
We’re talking about the mushroom heater – long pontificated as an "energy guzzler" and "climate saver", but now the hope of many restaurateurs in the corona winter. With a heater it is possible to stay in front of the pub or restaurant even in cold weather. In times of pandemic, it opens up an alternative to indoor spaces where the risk of infection is considered high. In addition, heated outdoor areas create additional space for innkeepers. On saturday, the "handelsblatt" reported that the heating mushrooms are even to be demanded by the federal government. But what about the energy and greenhouse gas balance of the emitters?? And what does it mean when more and more municipalities overturn their ban on mushroom heaters??
First, there are the numbers: a typical commercial propane gas heater with a heating capacity of eight kilowatts blows around 2.2 kilograms of CO2 equivalents into the air per hour, according to calculations made by the karlsruhe institute of technology (KIT) for dpa. This also includes emission values for the production of propane gas and the transport of the gas cylinders to the gastronomes.
What does this mean for a city?? At the beginning of 2019, there were around 20.000 gastronomic operations. According to the DEHOGA, it is not possible to determine how many of them were actually used for heating. But if we assume, for example, that one in ten of them sets up two gas-powered heaters for 20 weeks in winter and runs them for 20 hours a week, the KIT figures would give an output of around 3520 metric tons of CO2 equivalents – which also includes other greenhouse gases such as methane and nitrous oxide – for one winter.
Several thousand tons of greenhouse gases sound like a lot. Compared to the energy balance of a large city like berlin, however, the value again appears low. Road traffic alone blows several thousand tons of CO2 into the air every day. In the capital, there is already discussion about whether the use of heating mushrooms could simply be compensated for by a car-free sunday.
A similar picture emerges in terms of energy consumption: to reach ten percent of the city’s final energy consumption, several hundred thousand mushroom heaters had to run for around 20 hours a week all year round, as the KIT figures show.
Is the debate about mushrooms one thing above all: hot air?? "No matter whether the calculation comes up with 1000, 2000 or 5000 tons – in comparison, that sounds pretty low," says jens schuberth, who co-authored the federal environment agency’s mushroom study.
But if the goal of zero CO2 emissions by 2050 is taken seriously, mushroom heaters will create additional work elsewhere, schuberth continues. Even if so-called "heat islands" are not expected to develop, especially in winter, and the radiators directly heat up the air in the cities, "heating the pavements is still an obvious waste of energy."
So striking that several municipalities banned the mushrooms from their streets about ten years ago. But now corona – and the mushroom heater – is suddenly seen as a beacon of hope for restaurateurs, who could use it to serve their customers even in the cold season. Cities such as hamburg and stuttgart have already suspended their ban on heating mushrooms for the winter. Green politicians such as anton hofreiter and UBA head dirk messner also consider the use of mushrooms to be acceptable for the time being.
In such discussions, people often refer to the supposedly more efficient alternative to the gas heater: the electric heater, which heats less of the surrounding air and generates more direct infrared radiant energy instead. At first glance, electric radiators are also better in terms of CO2 equivalent emissions: 1.4 kilograms per hour are emitted by an exemplary 3000-watt unit with the german electricity mix in 2019, according to KIT calculations.
However, KIT expert jens buchgeister points out that a direct comparison between gas and electric heaters is difficult: on the one hand, it has to be taken into account that the radiation of infrared heaters only reaches people who are not covered by others. And secondly, the lifespan of the electric appliances under consideration is shorter than that of gas heaters, so that the cost of producing an additional electric appliance had to be added to the comparison.
UBA expert schuberth had already compared the heatable surfaces of electric and gas radiators in the 2009 heizpilz study. The result: "as far as emissions are concerned, there is no great difference between heating the rooms with electricity or gas."The CO2 emissions per square meter of heated area are about the same for both technologies. However, he also says, "compared to 2009, the electricity mix today is slightly better. That is, the electric radiators slip down a bit. But still not in such a way that they were significantly reduced."
And even if the radiators were only powered by eco-electricity, they were difficult to justify in terms of climate policy: "you have to ask yourself whether you can’t do something more sensible with the eco-electricity, which is also only available to a limited extent."Despite all the reservations, schuberth says: "i can understand if restaurateurs want to buy radiant heaters for this winter. It is important that the mushroom heaters are no longer used after the corona crisis."