Freshwater station causes temperature fluctuations

Good day. I came across this forum to get advice about my domestic hot water system. I hope I am in the correct category (Heating or Sanitary?). Problem: My domestic water system (domestic water) causes temperature fluctuations (especially when showering). The temperature sometimes fluctuates by about 5 degrees from the setting (single-lever mixer). So there is a slight drop in temperature, which requires readjustment (frequently). Of course, that is annoying. No consistent temperature. PS: Thermostatic cartridges are not installed! I need to find out the cause of the fluctuations (even if thermostats would solve this). Multi-family house with 5 units, 4 years old. Problem has existed since construction. Sometimes more, sometimes less pronounced. Flow rate 50 l/min supplied by a 1000L buffer tank (50% reserved for domestic water. So a large amount!) Buffer is charged from above at 70 degrees. Buffer temperatures thus about 70 degrees at the top to about 60 degrees in the middle of the tank. Temperature limiter 65 degrees for domestic water. Domestic water draws supply from the buffer connection at the top! So the hottest spot. Therefore, manual temperature limiter set to 65 degrees. Domestic water target temperature 57 degrees, supply 65-68 degrees (partially more than 65 degrees passes through the limiter) Circulation 52 degrees Temperature production from domestic water initially about 60-62 degrees dropping to about 55 degrees (at full load). Temperature at consumer points in apartments about 55 to 57 degrees. Supplier: 5 units (not all showering or bathing at the same time! Well distributed) Please do not write "run your domestic water at 50 degrees etc." 57-60 degrees production is desired and should be maintained. Even if this increases lime deposits (water hardness approx. 10 °dH). The question is, why does the domestic water with the above data produce fluctuating temperatures, which is annoying when showering. In summer - with solar support - this problem is not as pronounced. Maybe someone knows this problem with a domestic water station. Many thanks for the help!

Has the water pressure of the fresh water in the house been slightly varied before to see if this change might possibly bring an improvement? Could it possibly be that unwanted turbulence in the buffer tank leads to imperfect stratification?

Temperature fluctuations at fresh water stations unfortunately seem to occur here and there in some systems.

I also suspect turbulence, which then temporarily causes problems with the flow. The fresh water flow rate should actually be fine.

I also suspect turbulence, which then temporarily causes problems in the flow. The flow rate of the fresh water should actually be fine

Hello. Yes, the flow should be completely sufficient. Powerful fresh water.

Regarding stratification. According to the thermometer or boiler sensor, the layers should actually be okay. Buffer top about 65-70 degrees (the flow to the fresh water passes here. In between is a simple temperature limiter set to 65 degrees). Middle layer of the storage about 63 degrees (so 500 liters between 70 and 63 degrees) Here the underfloor heating takes water, which runs at about 35-38 degrees flow. Buffer bottom layer about 53 degrees. Return fresh water about 52 degrees (almost at the very bottom).

The buffer charges when the buffer temperature at the bottom has reached about 57 degrees, and then charges up to 57 degrees buffer middle. Special feature!!! Since the upper buffer sensor (buffer "off") is located in the middle of the buffer storage (instead of at the top!) (therefore larger buffer volume for the fresh water), these are also set to "off" at 57 degrees at the top (so buffer middle). That corresponds to a temperature from top to buffer middle in the buffer of about 70-63 degrees. A modification of the upper sensor would be possible, but it would greatly reduce the buffer volume. I have already noticed that the sensors were not mounted "normally." The reason is simply the larger buffer volume for the fresh water.

But whether this is the problem with the fluctuating hot water temperature, I still have to find out...

Yes, when the water is still, the layering is correct. The question is, what happens when it is tapped? Does the water in the entire buffer get mixed up by the return flow of fresh water and thus cause the fluctuations?

Yes, when the water is still, the layering is fine. The question is, what happens when water is drawn? Does the water in the entire buffer tank get stirred up by the fresh water return flow, causing the fluctuations?

Yes, that could be true. But then that would be the case with all such systems. Fresh water return always enters at the bottom. And fresh water is drawn from the top of the storage tank, where the boiler supply is also located. The underfloor heating is also fed back in at the bottom and drawn from the middle for the underfloor heating. But the temperature differences between the layers are not that high. The fresh water return is about 52 degrees. And these temperatures are normal at the bottom of the tank. If that is the case, then the principle of buffer tank and fresh water is not conclusive. Therefore, I suspect another problem.