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Control of Floor Heating.
Many years ago in the beginning of the 70's, we had a simulation project for Wirsbo AB. They had started to manufacture plastic pipes for floor heating. Wirsbo is today a major player in this field, as well as all kinds of plastic pipes for high temperatures.
Wirsbo had installed a number of heated floors by introducing pipes in normal constructions. Even if the Arabs and Romans more than a thousand years ago used similar types of constructions, it was new techniques for the modern engineers. The experience was not very good, since it was large problems in using the modern control equipment, especially those based on outside sensors. The result was high energy consumption and less comfort than expected. Our task in the project was to simulate the floors in different building constructions, define the problem and suggest solutions that included the new type of control equipment.
We did a number of simulations of different constructions and presented our report which basically said,
- The problems experienced were a result of the slow reactions of the construction and a fast control system. It was a larger version of the "0 degree mystery". This resulted in the large energy consumption and negative effects on the comfort. The way to fix this was either to make a faster construction or use special control system. It was very important to make them work together instead against each other.
- If we would adapt the floor to the control system, the best way to do this would be to introduce a layer of insulation between the basic floor construction and the heated part. This to achieve a fast reacting floor and simulate a radiator, for which the control systems were designed. We suggested some samples of construction. This present a solution for most cases, but if the building was very well insulated and had a high accumulation, the problem would remain independent of which type of heating system that was used. This method also introduced higher construction costs.
- If we would adapt the control system to the heated floor, we had to do more simulations and research to design it. We suggested investigating two avenues. The first one would be a simple system based only on the room temperature and pulse feeding of energy to the floor. The other one would be a microprocessor based system that could adapt to the slowness of the construction. We recommended to do special control systems because this choice had lower costs and higher potential for energy savings.
The project leader at Wirsbo was a young and enthusiastic HVAC engineer who very much liked the idea to make a better control system for heated floors. He was unfortunately offered a better job outside Wirsbo and decided to take it. Since Wirsbo couldn't find a suitable replacement, they decided to work with the construction recommendations and suspend further research until they had a suitable project leader. The latter never happened.
The construction recommendations worked and today every supplier of pipes for heated floors in the world have copied them. This without having any knowledge of why the construction recommendations introduce the extra insulation. I had HVAC engineers explaining to me that this extra insulation is necessary for reduction of heat losses and other funny reasons, but no one has ever given me the original reason for the construction.
Later during 1985-1986 we had some opportunities to do limited calculations for other type of control systems. I had a house in Spain where I used heated floors without the additional insulation and controlled it with a programmable microprocessor system (natural with my computer background), this with large success and savings. The only problem was the unreliable supply of electricity with power breaks longer than the battery supply for the microprocessor. I had to reprogram the control system around 40 times in 10 years.
Engelbrekt Isfelt did a project with only pipes in the floor, where he used the simple system philosophy with success and the result is shown below. It also confirmed the historical usability, since the Arabs and Romans had limited access to modern control equipment.
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