ᐅ How do temperature fluctuations occur in a domestic hot water system?
Created on: 2 Jan 2020 12:23
F
fonsi99
Hello,
I hope this is the right forum.
Can someone explain to me how temperature fluctuations can occur in domestic hot water?
The domestic hot water is set to 60°C (140°F). The circulation is at 55°C (131°F).
It receives water from the buffer tank at 65°C (149°F) (limited by a mixing valve), which operates at around 70°C (158°F).
At the apartment outlet, the domestic hot water is delivered at a consistent 60°C (140°F).
However, sometimes the hot water temperature seems to fluctuate slightly while showering.
It’s not constant as it was set at the single-lever mixer.
How can this phenomenon be explained or fixed?
Could it be because when many users demand hot water at the same time, the domestic hot water does not reach 60°C (140°F)?
Or could it be that the demand at that time is actually too low?
Thank you.
I hope this is the right forum.
Can someone explain to me how temperature fluctuations can occur in domestic hot water?
The domestic hot water is set to 60°C (140°F). The circulation is at 55°C (131°F).
It receives water from the buffer tank at 65°C (149°F) (limited by a mixing valve), which operates at around 70°C (158°F).
At the apartment outlet, the domestic hot water is delivered at a consistent 60°C (140°F).
However, sometimes the hot water temperature seems to fluctuate slightly while showering.
It’s not constant as it was set at the single-lever mixer.
How can this phenomenon be explained or fixed?
Could it be because when many users demand hot water at the same time, the domestic hot water does not reach 60°C (140°F)?
Or could it be that the demand at that time is actually too low?
Thank you.
@fonsi99
Lowering the buffer temperature might help with the overshoot. However, this can only be determined through experimentation in the end, especially if you don’t know the root cause yet...
The buffer circuit has a mixing valve before the domestic hot water system. I would now suspect the mixing valve or the charging pump.
The domestic hot water doesn’t normally pass through a mixing valve. At most, it’s the return line from the circulation loop, which hopefully feeds back into the cold water line before the plate heat exchanger via a check valve. That could be an idea to check—maybe the check valve isn’t tight, and you’re getting cold water from the circulation loop into the hot water line.
By the way, what kind of domestic hot water unit is it (manufacturer, model)?
Lowering the buffer temperature might help with the overshoot. However, this can only be determined through experimentation in the end, especially if you don’t know the root cause yet...
The buffer circuit has a mixing valve before the domestic hot water system. I would now suspect the mixing valve or the charging pump.
The domestic hot water doesn’t normally pass through a mixing valve. At most, it’s the return line from the circulation loop, which hopefully feeds back into the cold water line before the plate heat exchanger via a check valve. That could be an idea to check—maybe the check valve isn’t tight, and you’re getting cold water from the circulation loop into the hot water line.
By the way, what kind of domestic hot water unit is it (manufacturer, model)?
Domski schrieb:
@fonsi99
Lowering the buffer temperature might help with overshooting. However, this can only really be determined through experimentation since you don’t know the cause yet...
The buffer circuit has a mixer before the domestic hot water. I would suspect that one or the loading pumps.
The domestic hot water flow actually doesn’t go through a mixer. At most, the return flow from the circulation, which hopefully feeds back into the cold water line before the plate heat exchanger via a check valve. That might also be something to check—perhaps the check valve isn’t tight, and cold water is getting into the hot water line through the circulation.
By the way, what kind of domestic hot water system is it (manufacturer, model)?Hello.
We have a good one from Sailer, the Friwast50plus. I’ll take a closer look at the exact temperatures of all thermometers while the domestic hot water is running. Thanks so far.
PS: What happens if, during summer, the solar system heats the buffer completely up to 70°C (158°F), but then I set the domestic hot water setpoint to 50°C (122°F)? The domestic hot water mixer couldn’t possibly mix down to 55°C (131°F) since the storage tank is at a full 70°C (158°F) when the sun is strong! That means the buffer would supply the domestic hot water at 70°C (158°F), even though the domestic hot water should only need to be heated to 50°C (122°F).... Just thinking out loud in case I want to set the domestic hot water to a 50°C (122°F) target someday...
Domski schrieb:
Of course, it can then generate 50 degrees on the fresh water side.But doesn't that promote limescale buildup? And won't that cause greater temperature fluctuations? Or does it not matter what supply temperature the fresh water is operated at?What matters is the temperature the fresh water reaches in the heat exchanger. At 50°C (122°F), limescale buildup would not occur.