From the “especially if the EV’s are on fire” department…
The heat given off by car engines warms up underground car parks in such a way that the heat passes through the ground into the groundwater. In Berlin alone, enough energy is transferred to the groundwater to supply 14,660 households with heat. This finding was made by a team from Martin Luther University Halle-Wittenberg (MLU), the Karlsruhe Institute of Technology, and the University of Basel. According to the researchers, this warming could have long-term effects on groundwater quality. In their study, published in the journal Science of The Total Environment, they also propose a solution. Using geothermal energy and heat pumps, the heat could be extracted from the ground and utilized.
The researchers examined temperatures in 31 underground car parks in various cities throughout Germany, Austria and Switzerland. In six of them, they were also able to measure the temperature of the groundwater in the immediate vicinity. This allowed a heat profile to be created for all locations. Their investigations showed that underground car parks heat up the groundwater throughout the year. The volume of traffic in the underground car parks, their proximity to the groundwater and ambient groundwater temperatures were the biggest influencing factors. “Public underground car parks heat up the groundwater more than private facilities as they are often deeper and the cars park there for shorter periods of time,” explains Maximilian Noethen, a geoscientist from MLU.
According to the team, geothermal energy and heat pumps could help utilise the excess heat in the ground. “This would have the advantage of extracting energy from the groundwater and thus cooling it down,” says Noethen. Based on modelling for 5,040 underground car parks in Berlin, the team calculated groundwater warming from the underground car parks for the city. Since many underground car parks in the central districts of the capital are located in or near groundwater, a particularly large amount of heat is transferred to the groundwater there. According to their calculations, around 0.65 petajoules of energy are emitted annually in Berlin. This could theoretically supply around 14,660 households with heat. “Of course, heat from groundwater alone is not enough to cover the heating needs of a city like Berlin or even a country like Germany. Nor are the temperature levels of the groundwater near the surface high enough to provide heat without a heat pump. However, we do know from previous studies that the potential for geothermal energy goes well beyond this and that it could make a significant contribution to supplying sustainable heat,” says Professor Peter Bayer from the Institute of Geosciences and Geography at MLU.
Groundwater temperatures have been rising for decades as a result of global warming. In cities, this is exacerbated by dense urban development, soil sealing, lack of vegetation and heat radiating directly from tunnels and underground car parks. Since the organisms in the groundwater are adapted to constant temperatures, species composition could also change. “This could affect the quality of the groundwater from which we draw large parts of our drinking water. This development needs to be controlled through a variety of measures,” concludes Bayer.
The study was funded by the Deutsche Bundesstiftung Umwelt (DBU) and the Margarete von Wrangell Program of the Ministry of Science, Research and the Arts of the State of Baden-Württemberg.
Study: Noethen M. et al. Thermal impact of underground car parks on urban groundwater. Science of The Total Environment (2023). doi: 10.1016/j.scitotenv.2023.166572
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How much thermal energy is there in a couple of hundred kilogrammes of Bavarian V8 at 60C? It must be easier to extract that energy from the air near the car park ceiling rather than waiting for it to be absorbed by the concrete floor.
OMG, this is a testament to the axiom “A little knowledge is a dangerous thing”. Are these people completely ignorant of realities? Have they ever spent time walking through underground car parks? (they are NEVER warm, and almost always cooler than ambient air temps at the surface)
Concrete has very substantial heat capacity and high density, and as such would not transmit heat to the underlying ground until it has absorbed significant quantities of heat.
Car parks must have substantial fresh air flow, to prevent plain asphyxiation or poisoning of persons walking through them from the car exhausts, and because engines would not start if O2 levels were too low.
This airflow is the primary removal element of the heat of IC cars parked. Radiative cooling is practically non existent, as the engine is located beneath numerous layers of metal, plastic and often even felt like insulation for sound. And in fact all German made cars have actual felt layers underneath their cars as shields against sound, and road debris. Hence there can be virtually no radiative cooling downward from the engine bay. All the heat released from a parked car goes into the air, which is whisked away by high turnover rates to keep pedestrians from dying.
Let’s do a reality check with some actual numbers:
average car engine is mostly aluminum, with some steel, and the composite heat capacity is 800 J/kg-C. It weighs average of 150 kg. It operates at 80C, and takes an hour to cool down to 20C.
So 150kg x 800J/kg-c x 60C delta = 7.2MJ of heat released. Virtually all of this goes into the air.
Let’s construct a 100 car underground park, which requires 708 m² of floor space, and standard depth of the floor concrete makes the floor roughly 1.7 million kg of concrete (concrete is 2400 kg/m³). Concrete has a heat capacity of 880 J/kg-C which yields 1,565 MJ per degree C for this floor mass.
Now suppose this theoretical car park has a turnover of 50 cars per hour, each releasing 7.2 MJ over an hour, for 360MJ released. If only 20% of the heat carried by the airflow through the carpark is transmitted to the floor concrete, this would heat the floor by 72/1565 = 0.046 degrees C.
50 cars per hour turnover is unreasonably high, more like 20 for a 100 space parking structure, so the concrete temperature rise from the car engines cooling to ambient is only 0.009 degrees C.
I call bull schist on this study from a practical, realistic perspective! (and because any underground car park I have ever been in is colder than above ground ambient air providing sensible confirmation that engine heat is not substantially heating the car park)
The hunt for topics for grad student theses is huge and most of what they can work on is bullshit..
The “publish or perish” mindset in academia is universal, so what they publish will have a high bullshit factor.
The belief of young academics is that their work needs to be useful to humanity, probably laudable, but causes them to willingly polish turds to get a paycheck.
Making something that is bullshit sound important and journal publishable is a full time topic in the grad lounges at universities. Second best is getting a media article to hype your “research” on the internet, with a vid on OohTube being top glory.
The belief of old academics is that they need to keep on “keepin’ on” until their pension kicks in.
You won’t get the truth out of them till they retire, and usually they will say their research is now outdated but they enjoyed shaping young minds.
So a self generating bullshit factory with not even a 1% “good stuff” component.
All these could combine to a massive couldn’t. Ignore all the heat that is lost to the ventilation and the access or upwards into the building structure; then ignore how diffuse this heating would be and almost impossible to collect efficiently. Ignore that the timings might not correspond to when the heat might be demanded. Just add up all the numbers and write an article.
It is like the sort of analysis of how a few minutes of total solar illumination is equivalent to decades of power for application x.
I am beginning to think Pol Pot had the right idea driving all the academics into the countryside to work the land.
At least they actually did some measurements and observations.
I am an engineer. While living and working in Alaska in the mid 1870s, I took a course in Arctic Engineering. The course included an analytical method for calculating heat loss from ground structures using flow nets. Ergo, I am highly skeptical if the proposition presented here. I’m originally from Missouri, so show me the analysis.