Can I Calculate the Maximum Air Flow for Maintaining Room Temperature Below 36C?

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Discussion Overview

The discussion revolves around calculating the maximum air flow required to maintain a room temperature below 36°C, given specific dimensions and heat dissipation from equipment. It includes considerations of air mixing, heat capacity, and the time to reach steady state temperature.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant presents a scenario involving a room with specific dimensions and heat dissipation, seeking to calculate the necessary air flow.
  • Another participant suggests ensuring the air is well mixed and provides a formula relating mass flow rate and heat dissipation.
  • Questions arise about the definition of "well mixed" air and the meaning of variables in the provided formula, specifically W (mass flow rate) and Cp (heat capacity).
  • Concerns are raised about the need for additional mixing and proper air exit pathways to avoid direct channeling of intake air to exhaust.
  • Participants inquire about the unit and value of heat capacity, and whether it can be obtained from a psychometric chart or if it is a constant.
  • There is a request for a formula to calculate the time to reach steady state temperature in the room.
  • One participant expresses skepticism about the intent of another, suggesting a focus on obtaining free consultation rather than genuine learning.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and interest in the calculations, with some focusing on technical details while others question the motivations behind the inquiries. No consensus is reached on the best approach to the problem or the specifics of the calculations.

Contextual Notes

Limitations include potential assumptions about air mixing and the dependence on specific definitions of heat capacity. The discussion does not resolve how to accurately model the system or the exact calculations needed.

yeswan
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Hi all,

I have a question here. If I have a room with size of 3m x 7m x 3.5m with equipment of heat dissipation of 4kW. A blower fan is installed in the room to draw in the ambient air into the room to reduce the room temperature. At extreme condition the ambient temperature is around 33C. What is the calculation of the maximum air flow is if we want to maintain the room temperature below 36C?

Thanks.
 
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Welcome to physics forums.

You need to make sure that the air in the room is well mixed. Then,

WC_p(T - T_{amb}) = 4 kilowatts
 
Hi! Thanks for your reply in advance!

By the way, how to consider the room is well mixed?

And for your formula, what is the W and Cp stand for?

Since this is related to a room volume, doesn't it the room volume have to be considered as well??
 
yeswan said:
Hi! Thanks for your reply in advance!

By the way, how to consider the room is well mixed?

And for your formula, what is the W and Cp stand for?

Since this is related to a room volume, doesn't it the room volume have to be considered as well??

Well, you have a fan blowing air in, so that does some mixing, but the room is pretty big. Maybe another fan would help. You also need to provide an opening where the air can exit the room, and, by supplying the mixing, you want to make sure that the intake air does not channel directly to the exhaust fan so that it avoids mixing with the other air in the room. You can check to see if more mixing is needed by moving a thermometer around the room.

In the formula, W is the mass rate of flow of air through the fan and exit port, and Cp is the heat capacity of air.

The room volume only has to be considered if you are trying to estimate how long it takes for the system to reach steady state. That amount of time will be on the order of the room volume divided by the volume rate of flow of air through the room.
 
Mmm... What is the unit for heat capacity? How do we know that the heat capacity is? Is it get from Psychometric chart or there actually is a constant?

If we also want to calculate the time to steady the room temperature, what is the formula like?

Thanks.
 
It is close enough to constant. You can google specific heat capacity of air...
 
yeswan said:
Mmm... What is the unit for heat capacity? How do we know that the heat capacity is? Is it get from Psychometric chart or there actually is a constant?

If we also want to calculate the time to steady the room temperature, what is the formula like?

Thanks.

I'm beginning to get the feeling that you are not so much interested in learning Physics as you are in getting some free consultation on a specific system you are dealing with. If you want some consultation, many of us can accommodate you, but not for free.
 

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