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.
Domski schrieb:
No, because that is not the purpose of the forum. You are welcome to post it here.Okay. But can we say that the buffer temperatures are appropriate? 65°C (149°F) flow temperature to produce 58°C (136°F) with 53°C (127°F) circulation. Or is that too high? Or too low?For a good supply of fresh water, it is absolutely sufficient. Whether it is too much, we cannot know, as we do not know the maximum simultaneous demand of your residents. Only you know this (or can determine it).
You can only approximate the minimum setting through empirical methods. A thermometer or possibly the system’s control unit, if it allows you to read real-time temperatures, can help with this.
You can only approximate the minimum setting through empirical methods. A thermometer or possibly the system’s control unit, if it allows you to read real-time temperatures, can help with this.
Domski schrieb:
For good fresh water quality, it is absolutely sufficient. Whether it is too much, we cannot know because we do not know the maximum simultaneous demand of your residents. Only you know that (or can determine it).
You can only approximate the minimum setting through empirical methods. A thermometer or possibly the system’s control, if it shows real-time temperatures, can help with this. Hello.
Could you please give me some advice again?
Is it possible that when too little hot water is used (for example, while showering), temperature fluctuations occur (an occasional cold burst in between)?
The buffer tank is fully charged (at about 70°C (160°F)), the fresh water runs at nearly 60°C (140°F), but only a small amount of hot water is used during the shower.
I have noticed this as well. When showering at a higher temperature, these fluctuations do not occur. They only happen when the single-lever mixer is set to a slightly warm temperature.
It can’t be a power issue. It’s more likely that the supply line temperature is too high.
I can give it a try @fonsi99, but my crystal ball doesn’t offer much insight.
Overall, this sounds either like insufficient heat in the buffer supply line or a control issue with the domestic hot water loading pump.
Insufficient heat: If your recorded temperatures from the sensors are correct, there should be a thermal short circuit causing too cool water to enter the domestic hot water system. We can investigate this if we have an accurate hydraulic diagram including the internal design of the buffer tank. How is the buffer charged—exclusively through the wood gasifier? What kind of return flow temperature offset is installed?
Control issue with the loading pump: I find this explanation more plausible. When only a small amount of hot water is drawn, the pump starts to load the domestic hot water. Due to the quite high buffer temperature, the domestic hot water overheats (exceeding the maximum temperature), and the loading pump switches off instead of continuing to load with a low flow rate to maintain a constant temperature at the domestic hot water outlet. In essence, this is an overshoot in the control system. Causes can be varied: too high minimum flow rate on the draw-off side, faulty sensors, defective loading pump, etc.
You can figure this out by monitoring all temperatures and the pump speed or pump flow rate during a shower. Is that possible for you?
Overall, this sounds either like insufficient heat in the buffer supply line or a control issue with the domestic hot water loading pump.
Insufficient heat: If your recorded temperatures from the sensors are correct, there should be a thermal short circuit causing too cool water to enter the domestic hot water system. We can investigate this if we have an accurate hydraulic diagram including the internal design of the buffer tank. How is the buffer charged—exclusively through the wood gasifier? What kind of return flow temperature offset is installed?
Control issue with the loading pump: I find this explanation more plausible. When only a small amount of hot water is drawn, the pump starts to load the domestic hot water. Due to the quite high buffer temperature, the domestic hot water overheats (exceeding the maximum temperature), and the loading pump switches off instead of continuing to load with a low flow rate to maintain a constant temperature at the domestic hot water outlet. In essence, this is an overshoot in the control system. Causes can be varied: too high minimum flow rate on the draw-off side, faulty sensors, defective loading pump, etc.
You can figure this out by monitoring all temperatures and the pump speed or pump flow rate during a shower. Is that possible for you?
Domski schrieb:
I can try, @fonsi99, but my crystal ball isn’t showing much.
Overall, this sounds either like insufficient heat in the buffer tank supply line or a control issue with the domestic hot water loading pump.
Insufficient heat: If your recorded temperatures from the temperature sensors are correct, there might be a thermal short circuit causing cooler water to flow into the domestic hot water. We can investigate this if we have an exact hydraulic diagram including the internal construction of the buffer tank. How is the buffer charged—exclusively by the wood gasifier? What kind of return flow temperature lift is installed?
Control issue with the loading pump: I would consider this more likely. When only a small amount of hot water is drawn, the pump starts loading the domestic hot water. Due to the relatively high buffer temperature, the domestic hot water heats up significantly (above the maximum temperature), and the loading pump switches off instead of continuing to load at a low flow rate to maintain a constant temperature at the domestic hot water outlet. In other words, the control system is overshooting. The causes can be varied: too high minimum flow rate on the tapping side, faulty sensors, defective loading pump, etc.
You can figure this out if you monitor all temperatures and the pump speed or flow rate during a shower. Do you have the possibility to observe that?Hello.
Thank you for your information.
I will check the values during a shower.
But: Could it possibly also be caused by this?
Buffer temperature is high at around 70°C (158°F).
The supply to the domestic hot water is mixed to 65°C (149°F) by a domestic water mixer.
65°C (149°F) supply produces 58°C (136°F) domestic hot water.
If only a very small amount of lukewarm water is drawn briefly, could it be that the domestic water mixer (which is a thermostatic mixer) is too slow to respond, and therefore the colder buffer water temporarily affects the supply temperature to the domestic hot water?
If the lukewarm shower water runs for a longer period without frequent interruptions, the temperature should be maintained steadily lukewarm.
I need to test this.
Or could it be that at low hot water demand these temporary cold phases occur?
Thank you.
fonsi99 schrieb:
Hello.
Thanks for your information.
I will check the values during a shower.
But: Could it possibly also be related to this?
Buffer temperature high at 70°C (158°F).
Flow to the domestic hot water mixed down to 65°C (149°F) by a mixing valve for domestic hot water.
65°C (149°F) for domestic hot water to produce 58°C (136°F).
If only a small amount of lukewarm water is drawn for a short time, it could be because the mixing valve (which is a thermostatic mixing valve) is too slow to react, and therefore the colder buffer water briefly affects the flow temperature to the domestic hot water.
However, if you run the lukewarm shower water continuously (without interruptions), the temperature should stay stable and lukewarm.
I need to test that.
Or could the problem be that short cold phases happen when just a small amount of hot water is used briefly?
Thanks PS: If I possibly reduce the buffer temperature from 70°C (158°F) to 66°C (151°F), that should provide enough flow temperature for 58°C (136°F) domestic hot water. Then almost no mixing would be needed at the valve, even with low water usage, right?
Similar topics