0:00 - How to make a solar heater from aluminum cans
0:51 - Solar space heating that house. Нis experiments
2:38 - How do those solar heaters work?
4:10 - How effective are the mirrors?
5:54 - Nuances
These solar heaters are heating houses in different countries, and they are made from used aluminum cans that are assembled into pipes. These pipes must be connected in this way so that some fan will direct the air along this path.
Now you will see a little experiment with this fan which directs cold ambient air through those black pipes, where solar radiation heats the air to 45 ⁰C, which is measured by this sensor. Let's look at how several of these solar heaters will heat this house in the city of Zaporizhzhya. This city with a population of almost a million is located 30 kilometers from the front line, and the enemy army has already gathered almost 200,000 soldiers to destroy and occupy Zaporizhzhya.
This is the south wall of that house, and here we see 3 solar heaters with a total area of 10 sq.m, and this is another 7 sq,m of solar heaters.
We see that the ambient temperature is 16 ⁰C below zero, and now we will see that the cold ambient air being heated by one of those solar heaters to 69 ⁰C. This is the outlet of that hot air from one of the solar heaters, and the homeowner says that those 17 sq.m of solar heaters reduced his home heating costs by almost half, but I think that this is an exaggeration.
Nevertheless, he does interesting experiments, and now I will show one of them, when hot air from 2 solar heaters goes through this heat exchanger, where the air heats water to approximately 45 ⁰C. This hot water circulates through similar pipes inside 80 sq.m of concrete floors, and it is obvious that the water heats the concrete which will heat the house in the evening and at night.
This is another his experiment, where these mirrors give additional solar radiation to these 2 solar heaters. Now he will show how those mirrors help heat the air to temperatures above 100 ⁰C, and these are the air temperatures from those 2 solar heaters with the mirrors. Here we see the air temperature of 109 ⁰C, and this is several tens of degrees higher than what was in these measurements of the air temperature from solar heaters without mirrors.
Let's analyze how practical it is to place mirrors in front of solar heaters, and you will be surprised that adding such mirrors increases the production of solar heat several times.
Let's imagine that our solar heater has an area of 1 sq.m, and this is a flow of solar radiation with a power of 800 W onto its glass. Not all of these power will be absorbed by the black walls of these pipes, because 20 % will be reflected by this glass, or absorbed by the glass, or scattered by the black paint of the pipes. Therefore, we lose these 160 W, but the remaining 640 W heat these front walls of the pipes to about 41 ⁰C. Some of that thermal energy will go to these back walls of the pipes due to the good thermal conductivity of the aluminum walls of the cans.
These hot walls of the pipes will heat this air, which moves through the pipes and has an average temperature of 35 ⁰C. Unfortunately, the hot pipes lead to these heat leaks through this thermal insulation, as well as these heat radiation and heat leaks through the glass. These three types of losses increase if the difference between the average temperature of this air and this ambient temperature increases, and this case of a 30-degree difference leads to these general losses.
So, only these 300 W will transfer from the hot walls into this air which moves through the pipes, and it is this thermal energy that will heat a house. It is obvious that an increase in this air temperature leads to an increase in this temperature of the pipes, which leads to a change in these numbers.