Good morning,
I cannot say much about the trench collector, only about the company Lüumel, since we ourselves have a heat pump with a surface collector from them. If I had known about the trench collector back then, I would probably have chosen it over the surface collector, since a lot of space is lost with the surface collector where nothing can be built or trees/bushes planted.
I'll start with the question about the heat meter.
We do not have a heat meter or a separate electricity meter. In hindsight, I regret this a bit, since I cannot check either the share of heating electricity or the efficiency of the heating system.
I have been reading the electricity meter almost every day since October 28, 2014. Until October 28, 2015, we used a total of 6300 kWh for household electricity and heating. In the summer (heating only for hot water), we consumed about 7 kWh daily. In winter, you certainly need a bit more, so I assume about 3000 kWh for household electricity and about 3300 kWh for heating electricity for 125 m² of living space. (This is only an estimate due to the lack of sub-meters.) However, this figure should be somewhat relativized.
1.) In the first year, we already heated more than necessary to remove the moisture.
2.) It was found that too little refrigerant was filled, so only the first part of the surface collectors was used. This then led to icing and lifting in the area of the surface collectors in winter.
In the last 35 days, I now have the first comparison with the previous year. During these days, we used 25% less electricity and thus an estimated 50% less heating electricity. However, it is currently quite warm for the season. The previous year was also mild during these 35 days but still somewhat cooler than this year.
I cannot say exactly what this lower consumption is due to (milder weather, optimized heating settings, more refrigerant). Probably a bit of everything.
As I wrote above, our lawn already lifted significantly in winter (about 25-30 cm) and lowered again in summer. We have a passage for garbage bins, etc., at the edge of the collectors behind the garage. This passage was completely torn apart by the lifting and lowering. We are in negotiations with the company Lüumel there. They claim that we were not allowed to build over this area and had to keep at least 1 meter distance (although this is not clearly stated in their brochure, since according to the brochure, one is allowed to build over water-permeable surfaces). I then wonder why the water-permeable lawn lifts by 30 cm and what would have happened to a water-permeable path?
However, in my opinion, they should also have filled the refrigerant correctly. Since they allegedly cannot do this correctly during non-heating periods, they have to come again in winter. Since I believe there is partial fault on both sides, we are trying to reach some compromise. We will redo the passage ourselves and get 2-3 free maintenance visits or something in return. Let's see what comes of it.
In our residential area, there is a second Lüumel system where the collectors were built over by a path, and there were no problems at all.
Regarding the heating system itself:
- relatively uncomplicated
- direct evaporator
- maintenance required due to the amount of refrigerant (maintenance cost about €170)
- stratified storage tank
The stratified storage tank certainly has advantages but also a significant disadvantage. On cold winter days, the hot water gets really hot (>70°C). You have to be very careful that no one burns their fingers.
I hope this helps. I am happy to answer further questions.