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The Cool City Lab is an experiment to investigate the impact of surfaces on temperatures. On this page, you can follow the experiment and download the measured data.

It is simlpe and inexpensive to build the Cool City Lab. Building instructions are provided in the PULCHRA Handbook of Educational Materials.

Here you find direct links to the videos, data, and information:

The latest Photo of the Cool City Lab




Today the fan, which causes the permanent air flow in the radiation shield of the weather station, was replaced. From now on the measured data of air temperature and humidity are again of the same quality as before 13.03.2022. During the maintenance work the weather station was also completely cleaned. Due to the work, there was a data outage between 12:45 and 14:45.


The temperature data from the boxes had to be corrected. The reason was that the decimal places of the temperatures are understood as a separate integer value when importing into the spreadsheet. This value must be added to the integer part of the temperature. Example: The number 12.734 appears as 12 and 734. The temperature is composed as 12 + 734 / 1000. If the non-integer part has a zero at the end, e.g. 12.730, this was cut off before. So it was calculated 12 + 73 / 1000 = 12.073.
This error has now been corrected. In the new file of the temperatures in the boxes, the time series is now also without gaps. If there is no value at a point of time, the column of the temperatures shows #NV.


At the bottom of the weather station, in a white radiation shield, is the temperature and humidity sensor. The fan ensures that there is permanent air movement here and that the sensors really measure the temperature of the outside air. This fan has been making increasing noises for some time. These became so loud now that the fan had to be shut down by taping off the solar cells. A replacement part has been ordered. Until the replacement part is installed, the temperature data of the weather station are of poorer quality.


When reading the temperature data today, it was found that one of the temperature sensors does not work anymore. It is the one with the ID 15 from the red box (sand). It was replaced with a new one. Data since the last reading is lost.


New data on temperatures and water are online. Unfortunately, there are gaps without data in both datasets. Furthermore, the automated irrigation has been removed from the experiment, because autumn temperatures are rather cool and it is raining frequently.


The outlets of the automated irrogation have been changed. Now, about 85 ml are drained per irrigation event. The reduction compared to the set 100 ml is probably due to impurities in the hose or in the area of the pump.


Today, automated irrigation starts again. Apparently, limescale has accumulated in the water outlets. The amount of water per irrigation is only about 50 ml (instead of 100 ml). There is no data on seepage water until 2021-10-18.


Today is the restart of the experiment. At about 04:20 pm, the surfaces were placed on the boxes again. When analyzing the data, note that the boxes are now in a different order on the shelf (see video). The assignment of the temperature sensors to the boxes and surfaces remained unchanged.
The measurement data from the phase in which the temperature sensors were in the same box are online, too, so that they can be compared.


As announced in the video, all temperature sensors have been transferred to the red box today (at about 9:20 am).

The new lawn has been sown.


There is a new video on the current state and on the upcoming restart of the experiment.


Surfaces removed; temperature sensors remain in boxes without surfaces; automated irrigation deactivated; order of boxes on the shelve changes. Everything is explained in the vide from 2021-08-09.


Automated irrigation reactivated, lawn has dried up.

about 2021-07-18

Automated irrigation failed, lawn starts to dry up.


Extremely severe storm in Cologne.


The lawn is placed on the experiment again. The resawn seeds started to germinate.


Since the automated irrigation does not work, the lawn will be taken off the green box until 2021-06-06. It would dry up otherwise.


First data of the temperature sensors are online.


The surfaces have been placed on the boxes. Assignment:

Surface Color Temperature sensor ID
Tar black 19
Sand red 15
Lawn green 16
Gravel white 18


Videos from the Cool City Lab

[This content is not available in "Englisch" yet]

The videos explain the parts of the Cool City Lab, give an insight into the work steps for setting it up, convey the technical principles of the measurement processes, show some steps for ensuring data quality, accompany the evaluation of the measurement data and answer questions that arise among the students. Not all videos have scientific content. For example, the videos on setting up the experiment are there to get close to the Cool City Lab project and to get an insight into the things that have to happen around such a project.

The videos are kept as short as possible. They only go into depth where this is required to understand the processes. For the most part, the videos are so-called first takes, which means that they were used as recorded. Deficits in the quality of image and sound are accepted. This is due to time constraints, because the original work plan of the PULCHRA project did not include the Cool City Lab as an online project. As a result, I sometimes get muddled and there are repetitions in the text, statements sometimes are inaccurate or some information is missing. To compensate for this, text windows are inserted, similar to what Harald Lesch does in his Terra-X videos, which show short correcting or supplementing statements.

The videos are imperfect because there was no previous experience with shooting, creating and dubbing video material. Due to the urgency to provide material, which otherwise would have been produced on site, to schools in times of the pandemic, no training was possible.

We hope that the videos will nevertheless be a useful addition to the data provided. Feedback on this is welcome and can be directed to Tim Reichenau.


This video contains a brief introduction to the Cool City Lab and to what will happen on this website in the future.

Introduction to the weather station

This video introduces the weather station that measures meteorological parameters as part of the experiment.

Setting up the weather station

Here I show how I build up the weather station. This is not scientific content, but it is interesting to follow the progress of the project. Also, you get to know a few important criteria when building such a station.

Setting up the experiment

Here I show how the experiment has been set up. There is little scientific information, but it shows a few things to watch out for. This is interesting for all who want to be more closely involved with the experiment.

The parts of the experiment

In this video I show what parts the Cool City Lab experiment consists of and I explain what the parts are for. This is good to know to understand later what happens on top of and inside the boxes while the experiment is running.

Our temperature sensors

The temperature is measured inside the boxes of the Cool City Lab. Here I show the temperature sensors we use to do this and explain how to use them.

Testing the seepage water collection

At the Cool City Lab, the idea is to collect the water that seeps through the surfaces. In this video, I check whether the same amount of water is found in all bottles after a rainfall event when the surfaces are not placed on top of the boxes. In addition, I check the accuracy of the kitchen scale used.

Preparing the surfaces

This time, the various surfaces are finally being prepared to be tested in the Cool City Lab for their temperature effect. Another question is how permeable the surfaces are to water.

Different amounts of seepage water - cause and solution?

In an earlier video, I showed that different amounts of water are found in the seepage water collection bottles after a rainfall event. Here I show what this is probably due to and try to do something about it.

The experiment begins

Finally, the actual experiment is started. In this video I show how the final preparations are made and you can see how the surfaces are placed on the boxes.

Interim status at the beginning of August and preparation for the restart.

In the last weeks, the Cool City Lab was not intensively cared for. In the process, the meadow has dried up due to the failure of the automatic irrigation system. In this video, I show what the experiment looks like right now. The data from the past persiod of time have to be interpreted differently. Hints are given in the first part of the video.

Now the experiment is to be restarted. In the second part, I show what will be changed. In the next days the experiment will run again but initially without different surfaces.

Data from the Cool City Lab

Here you find the weather data, measurement data from inside the boxes, and data on the amounts of water.


Weather data from the Cool City Lab

Here you can download the weather data time-series measured by the weather station at the Cool City Lab. Please note that the time shown is UTC (Coordinated Universal Time), which differs by one or two hours from Central European Time. The legend for the data table can be found here. The current weather data can be viewed either at the top of the page or, if the window is too small, at the bottom under "More information". The current weather data can be viewed either at the very top of the page or, if the window is too narrow, at the bottom under "More information".

Data from the temperature sensors

The measurement data of the temperature sensors in the four boxes of the Cool City Lab can be downloaded here. The data are in the unit degrees Celsius (°C). The assignment of the data to the boxes can be taken from the corresponding video or from the table in the news on top of this page. In the data table there is also data from the time before the experiment started, when the temperature sensors were at first all in one box and then in individual boxes, but still without the surfaces. These data are color-coded.

The data is available here: Temperatures in the boxes

Amounts of water

Here is the data on the water in the Cool City Lab. This includes the water that collects in the seepage water collection bottles, but also the amounts of water used to irrigate the lawn. Also, some surfaces have been weighed to find out about the amounts of water there.

The data are here: Water data from the Cool City Lab

Photos from the Cool City Lab

The Cool City Lab was supposed to include a webcam that automatically takes a picture twice a day. Unfortunately, the supplied device did not work, and now there is no time to install another model. Therefore, there are only manually taken photos. The latest photo can always be found at the top of the page.


This project has received funding from the European Union's Horizon 2020 research and innovation programme under the grant agreement No. 824466.