Calculate Room Temp with Radiator at 0 C Outside Temp

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Discussion Overview

The discussion revolves around calculating the room temperature when a radiator is used under specific conditions, particularly with an outside temperature of 0°C. Participants explore the implications of reduced water flow and temperature adjustments based on outside conditions, focusing on the theoretical and practical aspects of heat transfer and system performance.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions how to incorporate the adjustment of water temperature delivered to the radiator based on outside temperature into their calculations.
  • Another participant critiques the question as poorly framed and lacking sufficient data, specifically mentioning the need for a flow rate.
  • A different participant suggests using the heat flow equation Q(dot) = m(dot)Cp(T2-T1) and implies that an integral might be necessary to account for changing temperatures.
  • A participant provides a calculation using English units to estimate flow rate and temperature differences, concluding that the reduced flow rate would lead to a lower leaving water temperature and raises concerns about potential boiler damage.
  • There is speculation about whether the water system could be calibrated to maintain the same heat loss as the room, but doubts remain about the sufficiency of the provided data to determine the room temperature accurately.

Areas of Agreement / Disagreement

Participants generally express disagreement regarding the adequacy of the information provided to solve the problem, with multiple competing views on how to approach the calculations and the implications of the reduced flow rate.

Contextual Notes

Limitations include the lack of specific flow rate data, assumptions about the relationship between water temperature and room temperature, and the unclear impact of the water system's calibration on the calculations.

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A room has a need for 2000W for an outside temp of -20 C. A radiator with this capacity is installed and receives water at 90 C, which exits at 70 C. But because of some error only 40% of the intended water amount flows through the radiator. The water temp delivered to the radiator is adjustet according to the outside temp, and is 60,5 C when outside temp is 0 C. What will the temp in the room be at an outside temp of 0 C ?

What I don't get is how to incorporate the fact that the water delivered to the radiator is adjustet according to the outside temp. How do I put this into my calculations?
 
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This question is just bad. It doesn't provide anywhere near enough data and it's poorly framed.
 
Agreed. I think you will need at least a flow rate of the water, not just 40% of original flow rate. Given that you have a flow rate, you can find heat flow based on
Q(dot) = m(dot)Cp(T2-T1)
If the change in temperature is being changed constantly according to the outside temp, I assume some smart guy here could set up an integral or something...I'm not sure where to start based on the information given though.
 
I work in English units and I am not sure of the conversions, but here is a start:

Gpm = btuh/((EWT - LWT) * Specific Heat of Water * 60 * 8.33)

6800 btuh /((194-158) * 1 * 60 * 8.33) = .38 Gpm

40% of that would be about .15 Gpm

This flow rate will lower the leaving water temp to 103 deg F giving a 91 deg F Temp Difference (EWT-LWT).

The water temp entering when the outside air is 0 deg C is 141 Deg F - 91 deg F = 50 Deg F. Which is crap. Better get that flow restriction cleared or you'll crack your boiler.

Or are we to assume that the water system has been calibrated to give us the same loss due to reduced Delta T as the room will lose? Thus reducing the temperature difference. This would be common for an automatic outdoor reset system, but I don't think we have suffiecient data to determine the room temperature other than to say it should be the same as the design condition. The water temp changes not the room temp.
 

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