It was a dry summer. The owners of a green roof were short of buckets to keep the greenery on their roof sufficiently wet. Here and there complete sprinkler installations have been installed. On the ground floor, the grass withered and plane trees shed their leaves.
It was not exceptionally warm. The poor bastards of Weeronline and Weerplaza managed to pick up some records (never before has it been this hot on July 19 and on August 14 and 25) but almost everyone understood that this was just another nonsense. Coincidentally, it had never been extremely hot on those days in the past 120 years, that just happens, but on many other August days it had sometimes been much hotter than on August 14 and 25. And that record of 19 July only applied to Maastricht, it was a local record.
Oh well, you give the weather bureaus their little trickery, the chimney must smoke anyway. But you can look up the records yourself just as easily, the historical extremes are clearly arranged on the site weatherstatistics.nl. Tip: September 17, 21 and 23 also have a vulnerable record.
It didn’t get extremely hot, but the National Heat Plan was set up again and the newspapers didn’t stop explaining how to cope with the heat. The elderly had to dress lightly, eat popsicles and sit with their feet in cold water, without resorting to paddling, because that is disastrous, just as the cold shower is a wrong grip. Hot tea is good, because hot tea makes you warm and then you sweat and then you get cold again. It’s dead simple: don’t sit in the sun when the sun is shining.
Bottle of frozen water
The advice is wonderfully persistent to put a bottle of frozen water in front of the fan. It doesn’t work, it’s easy to demonstrate, but the combination sounds so appealing that many consultants succumb to it. (The opposite applies to the advice to shave off the hair.)
What also regularly returns is the tip to hang wet cloths in the room during intense heat. It is fairly common to believe that moist air is colder than dry air, which is precisely why it is so ‘nice and cool’ in the forest in summer, wrote The watchword just recently. Perhaps the consulted specialist in sustainable urban development – he also wants to paint roofs white – was misquoted. Under the trees of the forest it is cool because the sun does not shine and the forest retains its forest air nicely.
Now, it was a small effort to hang a wet bath towel in the study. It had no influence on the temperature around the desk, but the cloth itself turned out to be strangely cool. On very hot days (room temperature 26 degrees) it was five or six degrees with the surrounding air. Under normal circumstances (22 degrees) only a few degrees. The temperature drop was reasonably reproducible on a case-by-case basis.
Let it pass
The drop became even more pronounced if the wet towel was hung in front of a fan or if it was swung around for a few minutes, but it was impossible to predict exactly how big the drop would be in a particular case. Air temperature, relative humidity and ventilation all affect it. In fact, the drop in temperature that occurs under conditioned ventilation is used to measure the relative humidity to decide.
It is not easy to understand why the wet towel has no effect on the room temperature. In the air of a room of 40 m3 content only needs to be 52 kilojoules of heat withdrawn to lower the temperature by one degree. The towel easily evaporates 25 grams of water per hour and 56 kJ is absorbed for this. So why is nothing happening?
It is due to the enormous amount of heat that was absorbed by floors and walls, which can provide their warmth for days. This is most apparent if you had let your house pass through at night in accordance with the – useful – advice. When equilibrium with the outside air is established at seven o’clock in the morning, the temperature inside immediately rises again by a few degrees as soon as windows and balcony doors are closed. That’s what the walls do.
per dm3 can a brick wall store up to 1,100 times as much heat as a liter of air. Wooden and steel tables and chairs also work well, but due to their shape and conductivity (steel), they always quickly dissipate the stored heat. The temperature buffering comes from the walls.
It was only this summer that the decision was made to check whether the heat storage in walls was also too much to measure is. It turned out to be a piece of cake: you drill a hole in the stones and insert a thermometer. After the second near-heat wave of August 21-25, the temperature of the drilled wall was found to be well above that of the room air for two more days. Remember that this also works the other way around and that it makes sense to cool walls considerably before it gets hot.