ᐅ Operate fresh water systems with partially very high and low buffer temperatures
Created on: 18 Apr 2020 14:29
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fraubauer
Hello.
I have noticed that with really warm weather now, the solar system is delivering good performance to the buffer tank.
The buffer temperature in the afternoon currently rises to about 80°C (176°F) at the top of the tank, where the supply to the domestic hot water is located.
In the evening, however, the buffer temperature at the top drops to about 60°C (140°F).
(The pellet boiler only starts when the sensor reaches 55°C (131°F), so currently it turns on in the mornings).
Question:
The domestic hot water is currently set to a target temperature of 58°C (136°F) for production.
The circulation is set to 53°C (127°F).
The supply line from the buffer to the domestic hot water is limited to 65°C (149°F) using a simple mixing valve.
Does it matter for the domestic hot water if in the evening it is only fed with about 60°C (140°F) from the buffer?
Producing 58°C (136°F) with a 60°C (140°F) supply is actually quite tight. It should really be around 65°C (149°F).
However, I wouldn’t mind if the domestic hot water is produced around 55°C (131°F) instead of 58°C (136°F) during this time.
When the boiler delivers again (with 65°C (149°F) at the top of the buffer), there will be enough supply temperature for the domestic hot water again.
Thank you very much.
I have noticed that with really warm weather now, the solar system is delivering good performance to the buffer tank.
The buffer temperature in the afternoon currently rises to about 80°C (176°F) at the top of the tank, where the supply to the domestic hot water is located.
In the evening, however, the buffer temperature at the top drops to about 60°C (140°F).
(The pellet boiler only starts when the sensor reaches 55°C (131°F), so currently it turns on in the mornings).
Question:
The domestic hot water is currently set to a target temperature of 58°C (136°F) for production.
The circulation is set to 53°C (127°F).
The supply line from the buffer to the domestic hot water is limited to 65°C (149°F) using a simple mixing valve.
Does it matter for the domestic hot water if in the evening it is only fed with about 60°C (140°F) from the buffer?
Producing 58°C (136°F) with a 60°C (140°F) supply is actually quite tight. It should really be around 65°C (149°F).
However, I wouldn’t mind if the domestic hot water is produced around 55°C (131°F) instead of 58°C (136°F) during this time.
When the boiler delivers again (with 65°C (149°F) at the top of the buffer), there will be enough supply temperature for the domestic hot water again.
Thank you very much.
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fraubauer19 Apr 2020 10:23Joedreck schrieb:
Yes, exactly like that. A fresh water unit is basically just a heat exchanger. The warm water from the buffer tank heats the cold water from the supply line in a flow-through process.
If the water from the buffer tank is no longer warm enough, the fresh water unit simply heats it as much as possible.
Completely harmless. Hello.
Regarding the "scaling of the heat exchanger in the fresh water unit," I have a question.
Limescale is released starting at around 60 degrees Celsius (140°F). The higher the hot water temperature above 60°C (140°F), the more limescale is released. So the heat exchanger scales faster and loses efficiency.
Question:
Since the flow temperature from the buffer tank in summer is very high (sometimes above 70 degrees Celsius (158°F)) and the bottom of the buffer tank is also very warm, the mixing valve has limited effect in lowering the flow from 70°C (158°F) to 65°C (149°F) or even 60°C (140°F).
That means the fresh water unit receives flow temperatures of up to 70°C (158°F) from the buffer tank, to produce water at 58°C (136°F).
Does this cause the heat exchanger to scale faster (due to the 70°C / 158°F flow temperature)? Or does scaling only begin inside the heat exchanger when the hot water is actually produced (currently reduced from 70°C (158°F) to 58°C (136°F), although the display shows a setpoint of 65°C (149°F) for the hot water)?
How can limescale formation in the heat exchanger be reduced during summer when the buffer tank flow temperature is high?
Thank you.
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fraubauer19 Apr 2020 11:19Joedreck schrieb:
With the right mix before the heat exchanger by adding cold water.Understood. In my case, the "cold water" is supplied from the very bottom of the storage tank. And that water is actually very warm during summer as well. I don’t have a separate cold water supply to the storage tank’s supply line for fresh water. Thank you
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fraubauer19 Apr 2020 11:22Joedreck schrieb:
Yes, it makes sense and is easily doable. Depending on the situation, you can turn off the heating including the domestic hot water yourself, as long as the temperature of the hot water in the morning is still sufficient for you. Hello again.
Is it normal for a domestic cold water system to have slight temperature fluctuations (meaning you have to occasionally adjust the set shower temperature during the shower)?
Several apartments share this single cold water supply.
There is plenty of buffer volume for the cold water (500 liters of 1000 liters (132 gallons of 264 gallons)).
However, I have read that pressure fluctuations cause these slight temperature changes, and that they are unavoidable in a domestic cold water system.
It is quite annoying during showering when you have to adjust the set temperature repeatedly.
Installing a separate shower thermostat valve is also not the solution.
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fraubauer19 Apr 2020 11:46Joedreck schrieb:
Actually, that would be the solution. With my fresh water system back then, there was no such problem. But if multiple draw-off points are needed now, 500 liters (130 gallons) is not much. Also, the question is what flow rate the fresh water system can deliver.50-100 liters (13-26 gallons) flow rate. So it is generously sized for the multi-family house. The 1000-liter (260 gallons) buffer tank was practically divided so that 500 liters (130 gallons) are reserved solely for the fresh water. The supply line for the underfloor heating is located exactly in the middle of the buffer tank.Similar topics