Air Handling Unit Test - Air Heating Problem

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Discussion Overview

The discussion centers around the testing of an Air Handling Unit (AHU) with a focus on raising the internal temperature by 30 degrees Celsius while adhering to an energy input limit of 500W. Participants explore calculations related to the heating effect of fans and the requirements for additional heating to achieve the desired temperature increase.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant inquires about calculating the temperature increase from the energy input of 384W from the fans, assuming all energy becomes heat in a closed system.
  • Another participant reiterates the assumption that all energy input from the fans converts to heat and provides a formula for calculating temperature rise based on air volume, specific heat, and power.
  • A participant expresses concern about potential misunderstandings regarding the energy conversion and emphasizes the need to avoid debate on this point.
  • One participant calculates the air volume in the unit and applies the specific heat to find a significant temperature rise, questioning the correctness of their formula.

Areas of Agreement / Disagreement

Participants generally agree on the principle that energy input from the fans becomes heat, but there is uncertainty regarding the calculations and the application of the formula for temperature rise. The discussion remains unresolved regarding the accuracy of the calculations and the necessary heater size.

Contextual Notes

Participants have not reached a consensus on the correctness of the formula used for temperature rise calculations, and there may be missing assumptions regarding the specific heat capacity and the conditions of the air within the unit.

JaredJames
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We are testing an Air Handling Unit, we need to raise the internal temperature by 30 degrees to pass the test, but cannot exceed an energy input of 500W.

It is a completely sealed unit.

We have four fans constantly running, consuming 384W. Firstly, how can I work out what temperature they will raise the unit to? The fan manufacturer says that all energy input becomes heat (due to it being a closed system, but please let's not debate this, just accept it for the purpose of this question and use the full 384W).

Secondly (if part 1 doesn't raise the temperature by 30 degrees), what size heater would we need to achieve the increase?

Box Dimensions: 1.2x1.2x3.0m
Fan Input: 384W
Must not exceed: 500W (but I would like some answers even if they do exceed it to show me what we would need to do to achieve the required temperature increase)


Also, is there a way to work out how many Watts are required to raise the temperature of air by 1 degree celsius in one hour?
 
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jarednjames said:
The fan manufacturer says that all energy input becomes heat (due to it being a closed system, but please let's not debate this, just accept it for the purpose of this question and use the full 384W).
Nothing to debate - it's true!
Also, is there a way to work out how many Watts are required to raise the temperature of air by 1 degree celsius in one hour?
Air volume times specific heat times power = temperature rise.
 
russ_watters said:
Nothing to debate - it's true!

I know it's true, but I put that because with someone in work who didn't understand it I had to spend an hour explaining the concept to him and didn't fancy having to go through the same thing again.

russ_watters said:
Air volume times specific heat times power = temperature rise.

Thank you for this.
 
Hi, that gives me 4.23cubic metres of air, specific heat of 1.005kg/kg K and a power of 384W. Which is over 1600 when multiplied together, which is one hell of a temperature rise.

Is the formula correct or am I making a mistake somewhere?
 

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