d. ​ Why does the sun feel warm when it is so far away?

This is infrared radiation (IR), which travels through the universe at the speed of light. When this infrared radiation hits the Earth's surface, it heats up. This means that the Earth's surface acts like a large radiator, which then also heats up the surrounding air.

e. ​Why is it colder in the mountains than in the valleys, even though you are closer to the sun?

This is because air pressure decreases at higher altitudes. And as air pressure decreases, the air temperature drops. This is caused by the air expanding as the air pressure decreases. As a result, the internal energy of the air decreases, which then leads to cooling.   

g. ​ ​How warm is it in the universe?

The universe is very cold, with a temperature of -273°C. It also has no atmosphere (air) as we know it on Earth. As far as we know today, interstellar and intergalactic space is largely empty. It consists of very little hydrogen and helium ions. In addition, there are some dust particles and electromagnetic radiation. And, unfortunately, in recent years, there has also been so-called space debris.

h. ​ Why does warm air "rise"?

Warm air does not rise. There is a simple reason for this: it weighs approximately 1.3 kg and is subject to gravity, just like any other matter. However, cold air is heavier than warm air because it contracts. The cooler air therefore displaces the warm air. And if the warm air cannot escape to the side because it is in a closed space, it is pushed upwards by the cold air.

i. ​ ​Warum kommt die Deckenheizung mit weniger Energie aus, als die Fußbodenheizung?

Das hat vor allem zwei Gründe:

• ​The drop in air temperature
  Colder air sinks and displaces the warmer air in a closed room upwards. This causes air movement throughout the room, which is perceived by our skin as a cooling effect. To compensate for this perceived cooling effect caused by the draught, the underfloor heating must heat the air temperature to approx. 4°C higher than the ceiling heating. This is because this air circulation does not occur with ceiling heating, but only when it is active over the entire surface. For every degree Celsius increase in temperature, 6% more energy is required. To achieve the same feeling of warmth, this already means 24% more energy consumption, even though comfort suffers under the air flow of underfloor or radiator heating.
  
  
• The lower flow temperature
  Ceiling heating systems can often be operated at a significantly lower flow temperature. A reduction in the required flow temperature by one degree Celsius reduces energy consumption by approximately 2%. In practice, ceiling heating often reduces the amount of energy required by 40 to 50%. But!!! This only works if the ceiling heating is operated over the entire surface, as otherwise unwanted air movement similar to underfloor heating is generated and a higher room air temperature is required.
  
  
• The fully active climate ceiling ensures that the air temperature in the room is lower than the temperature of the walls. This removes moisture from the walls. According to J. S. Cammerer (1928), however, a change in moisture in brickwork of +/- 4 per cent by volume leads to a change in the insulation value of +/- 50 per cent. As the insulation value of the wall is greatly improved by the fully active ceiling heating, energy efficiency increases significantly compared to ceiling heating or radiators.​