Temperatures in a central heating system

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Discussion Overview

The discussion revolves around the operational temperatures of a central heating system, specifically comparing the effects of running at 80/60 degrees Celsius versus 60/40 degrees Celsius. Participants explore the implications of these temperature changes on water flow rates and heat transfer efficiency within the system.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that to maintain the same heating effect with a lower temperature range (60/40), more water will likely need to flow through the pipes, but seeks clarification on how to calculate this.
  • Another participant argues that the energy transfer is similar due to the consistent temperature drop (20 degrees) in both systems, suggesting that the specific heat of water at these temperatures is negligible.
  • A different viewpoint emphasizes that the heat supplied to the room will be less effective at the lower radiator temperature (60 degrees) compared to the higher temperature (80 degrees), indicating that more water circulation is necessary to achieve the same heating effect.
  • One participant points out that the delta-T (temperature difference) remains the same at 20 degrees for both systems, questioning the implications of this on heat transfer rates.
  • Another participant discusses the concept of approach temperature, suggesting that while lower temperatures may reduce heat transfer, the specifics of how heat is dissipated are not clear, leaving room for various interpretations.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the temperature changes on heat transfer and water flow rates. There is no consensus on the best approach to maintain heating effectiveness with the lower temperature range, and multiple competing perspectives remain unresolved.

Contextual Notes

Participants have not fully explored the assumptions regarding the type of heating units used (e.g., fan coil units) or the specific conditions under which the heat transfer occurs, which may affect the overall analysis.

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A central heating system has been thought to run with temperatures 80/60, and so the flow of water through the system has been calculated accordingly. Now it turnes out that it will run with 60/40 instead. In order to have the system deliver the same effect, I assume more water will need to flow through the pipes. But how do I find out how much?
 
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Minor difference. Since there is a 20 deg Temperature drop in both systems, and the ranges are not that different, the energy transfer is similar, with the only difference being a slight drop in the specific heat of water, usually considered negligible (a value of 1) at those temperatures.

However I would be careful returning water to the boiler at 40 deg C, there is a risk of thermal shock. You should use some sort of secondary loop at that low return temperature.
 
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I would have thought the major difference was the heat to be supplied into the room. With the radiators at 60deg the dT to the room will be 2/3 what it would be at 80deg and so to give the same heating effect you are going to have to push more water around.
 
The dT between the radiators and the room temperature (say 20deg) is either 60 or 40.
The rate of heat transfer from the radiator to the room is proprtional to dT.
 
That's called approach temperature and though it is true that with a lower approach temperature you will get less heat transfer, he didn't say how the heat would be dissipated or why the temp would be lower, only that the delta-T is still 20. Ie, maybe they are fan coil units and in addition to lowering the boiler temp, they raised the airflow. We just don't know.
 
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