Good day.
I came across this forum seeking advice about my domestic hot water system.
I hope this is the right category (heating or plumbing?).
Problem:
My domestic fresh water system is causing temperature fluctuations, especially while showering.
The temperature varies by up to 5 degrees from the set level on the single-lever mixer valve. You can notice a slight drop in temperature, requiring frequent readjustment. This is obviously annoying. The temperature is not stable.
PS: There are no thermostatic mixing valves installed! I need to identify the cause of these fluctuations, even if thermostatic valves might solve the issue.
It is a multi-family house with 5 units, 4 years old. The problem has existed since construction, sometimes more pronounced, sometimes less.
Fresh water flow rate approx. 50 liters per minute (13 gallons per minute).
Supplied by a 1000-liter (264 gallons) buffer tank, with 50% reserved for domestic fresh water. So, a large volume!
The buffer is charged at 70°C (158°F) at the top. Buffer temperatures range approximately from 70°C (158°F) at the top to about 60°C (140°F) in the middle of the tank.
Temperature limiter set at 65°C (149°F) for the domestic fresh water. Fresh water draws feed water from the top buffer connection—the hottest spot. Hence the manual temperature limiter set to 65°C (149°F).
Target hot water temperature is 57°C (135°F). Buffer supply temperature is 65–68°C (149–154°F), sometimes pushing above 65°C despite the limiter.
Circulation line temperature is 52°C (126°F).
The domestic hot water generated initially starts at around 60–62°C (140–144°F) but drops to about 55°C (131°F) under full load.
At the consumption points in the apartments, temperature is approximately 55 to 57°C (131–135°F).
Supply: 5 residential units (not all showering or bathing simultaneously—usage is well distributed).
Please do not suggest lowering the fresh water temperature to 50°C (122°F) or similar. Producing water at 57–60°C (135–140°F) is desired and should remain. Even if this leads to increased scaling (water hardness about 10 °dH).
The question is: Why does the domestic hot water system produce fluctuating temperatures with the conditions described above, which is annoying when showering?
During summer, with solar assistance, this problem is less noticeable.
Perhaps someone has experienced a similar issue with a domestic hot water station.
Thank you very much for your help!
I came across this forum seeking advice about my domestic hot water system.
I hope this is the right category (heating or plumbing?).
Problem:
My domestic fresh water system is causing temperature fluctuations, especially while showering.
The temperature varies by up to 5 degrees from the set level on the single-lever mixer valve. You can notice a slight drop in temperature, requiring frequent readjustment. This is obviously annoying. The temperature is not stable.
PS: There are no thermostatic mixing valves installed! I need to identify the cause of these fluctuations, even if thermostatic valves might solve the issue.
It is a multi-family house with 5 units, 4 years old. The problem has existed since construction, sometimes more pronounced, sometimes less.
Fresh water flow rate approx. 50 liters per minute (13 gallons per minute).
Supplied by a 1000-liter (264 gallons) buffer tank, with 50% reserved for domestic fresh water. So, a large volume!
The buffer is charged at 70°C (158°F) at the top. Buffer temperatures range approximately from 70°C (158°F) at the top to about 60°C (140°F) in the middle of the tank.
Temperature limiter set at 65°C (149°F) for the domestic fresh water. Fresh water draws feed water from the top buffer connection—the hottest spot. Hence the manual temperature limiter set to 65°C (149°F).
Target hot water temperature is 57°C (135°F). Buffer supply temperature is 65–68°C (149–154°F), sometimes pushing above 65°C despite the limiter.
Circulation line temperature is 52°C (126°F).
The domestic hot water generated initially starts at around 60–62°C (140–144°F) but drops to about 55°C (131°F) under full load.
At the consumption points in the apartments, temperature is approximately 55 to 57°C (131–135°F).
Supply: 5 residential units (not all showering or bathing simultaneously—usage is well distributed).
Please do not suggest lowering the fresh water temperature to 50°C (122°F) or similar. Producing water at 57–60°C (135–140°F) is desired and should remain. Even if this leads to increased scaling (water hardness about 10 °dH).
The question is: Why does the domestic hot water system produce fluctuating temperatures with the conditions described above, which is annoying when showering?
During summer, with solar assistance, this problem is less noticeable.
Perhaps someone has experienced a similar issue with a domestic hot water station.
Thank you very much for your help!
HabneFrage schrieb:
Yes, that could be correct.
But that would apply to all such systems.
Fresh water return always enters at the bottom. And fresh water is drawn from the top of the tank, where the boiler supply is also located.
Underfloor heating is also fed back at the bottom and drawn off around the middle for the underfloor heating.
However, the temperature differences between the layers are not that high.
Fresh water return is around 52 degrees Celsius (126°F).
And these temperatures at the bottom of the tank are quite normal.
If that were the case, the concept of the buffer tank and fresh water system would not be logical.
That’s why I suspect a different problem. I might be wrong, it’s been a while since I worked with a heating system including a fresh water module.
But in my opinion, there are buffer tanks that use baffle plates in the return line to reduce turbulence.
Of course, it could also be something completely different. Perhaps the hot water pressure briefly drops because someone else taps water at the same time. Heating engineers for multi-family buildings are probably my second-best skill.
Joedreck schrieb:
But in my opinion, there are buffer tanks that reduce turbulence in the return flow using baffle plates.Yes, there are buffer tanks of the "simple cylinder" type, as well as those that use sophisticated internal designs with perforated plates or other structures to achieve better temperature stratification. Whether this really helps in practice is difficult for private users to measure, but it certainly seems plausible.Since the flow rate is quite high at 50L (13 gallons), a more detailed analysis regarding turbulence would definitely be interesting. With less strong backflow of fresh water into the buffer, there is less turbulence. Therefore, an interesting test would be to limit the fresh water flow rate by reducing the fresh water pump capacity and see if temperature consistency improves. If so, this would indicate a turbulence issue.
H
HabneFrage25 Nov 2020 21:08BobRoss schrieb:
Yes, there are buffer tanks of the "simple cylinder" type, as well as those that use sophisticated internal designs with perforated plates or other structures to achieve better temperature layering. Whether this really helps in practice is difficult for private users to quantify, but it does seem plausible to me.
Since the flow rate is quite high at 50 liters (13 gallons), a closer analysis regarding turbulence would certainly be interesting. With less strong backflow of fresh water into the buffer tank, there are fewer turbulences. Therefore, an interesting test would be to limit the fresh water flow rate by reducing the fresh water pump power and see if the temperature consistency improves. This would indicate a turbulence issue. Good evening.
Thank you for your message.
I know the type of buffer tank installed.
It’s a Clima PSRR with a capacity of 1000 liters (260 gallons).
It does not have any baffle plates or similar.
Best regards
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