Flow Rate and Temperature Relationship in Air Change Calculations

[Brendan Webb]

MODERATOR'S NOTE: NO TEMPLATE BECAUSE THREAD WAS SUBMITTED TO ONE OF THE REGULAR FORUMS

Summary: Calculate the air change rate required to keep a certain temperature

In question d above, you were asked to calculate how long the air flow in the system would be active in a day. Now factor in the following to address temperature readings and flow requirements. The occupant desires the temperature in the space to be a constant 22°C. When the air flow is at 30 litres per second, this is maintained. The outside air temperature today is 10°C and the air temperature through the system is 24°C. How often will the system need to change the air in the 2.43 metre wide by 3.04 metre long and 2.43 metre high cubicle to meet the desired temperature?

Cubic area of space to be cooled = 2.43 × 2.43 × 3.04
= 17.95 m³
30 L/s = 0.03 m³/s

To maintain 22°C, the space gets changed every:
= 17.95 m³ / 0.03 m³/s
= 598 s

** From here, I don't know what to do. I know there is a relationship between flow rate and temperature but I can't figure it out**
*The formulas they give us are just the basic flow rate equations with no variable being temperature, therefore I am assuming that this question can be figured out using proportions, but I have no idea how to proceed**

 

[Andrew Mason]

When the air flow is at 30 litres per second, this is maintained.

We are missing some information here. Obviously, the temperature depends not only on the flow rate of the air but also on the temperature of the flowing air. Can you provide us the wording of the whole question (ie. we need to see part d that is referred to in the question)? Thanks.