metres per sec to m3 per hour.

[Coanda]

Could someone help?

 

If I know there is air flowing through a 100mm duct at .80m per second, how do I compute that to m3 per hour?

 

Edited October 29, 2023 by Coanda

[saveasteading]

7,800mm2 x 1,000mm   per second

= 7,800,000 mm3 / s

X 60  x60

/ 1,000 /1,000/1,000

 

  28.26 m3 / h.

 

Somebody check this please.

[SteamyTea]

π x r² = area of pipe

 

3.1416 [π] x 0.05² [m] = 0.007854 [m²]

 

Flow rate x area = volume per unit time.

 

0.8 [m/s] X 0.007854 [m²] = 0.0062832 [m³/s]

 

3600 seconds in an hour.

 

0.0062832 [m³/s] x 3600 = 22.61952 m³/h

 

For bonus marks

 

Approximate density of air 1.25 kg/m³

 

22.61952 [m³/h] x 1.25 [kg/m³] = 28.2744 kg/h.

 

Specific heat capacity of dry air approximately 1 kJ/kg.K

So to heat (or cool) 28.3 kg by 1K will take.

28.3 [kg] x 1 [kJ/kg.K] x 1 [K] = 28.3 kJ

 

To convert to kWh, multiply by 0.00027778 (1 / 3600 [s])

 

28.3 [kg] x 0.00027778 = 0.007861111111 kWh.

 

As this relates to the flow rate per hour, dividing by 1 hour will give the power, in kW, multiply by 1000 will convert it to watts.

 

0.007861111111 [kWh] x 1000 = 7.9 W.

 

I think, please check.

 

Edited October 29, 2023 by SteamyTea

[saveasteading]

Oops that was for 1m/s

 

So 28.26 x 0.8

= 22.6.

 

[SteamyTea]

  On 29/10/2023 at 17:35, saveasteading said:

Oops that was for 1m/s

 

So 28.26 x 0.8

= 22.6.

 

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Easy error to make, I usual reduce to a reciprocal and then multiply at the end.

Then forget.

[Adrian Walker]

  On 29/10/2023 at 13:18, Coanda said:

Could someone help?

 

If I know there is air flowing through a 100mm duct at .80m per second, how do I compute that to m3 per hour?

 

Expand  

 

 

BTW it is normal to have the answer in litres/second for MVHR calculations. 

[SteamyTea]

  On 29/10/2023 at 17:52, Adrian Walker said:

 

 

BTW it is normal to have the answer in litres/second for MVHR calculations. 

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I have never understood why, we have SI units to make life simple.

[Adrian Walker]

  On 29/10/2023 at 18:01, SteamyTea said:

I have never understood why, we have SI units to make life simple.

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Because it's easier for most people to imagine 9 litres per second rather than 32.4 cubic metres per hour, that said SI units do make life simpler. I do hate it when people use centimetres rather than millimetres.

[SteamyTea]

  On 29/10/2023 at 18:09, Adrian Walker said:

I do hate it when people use centimetres rather than millimetres

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Or metres even.

[Coanda]

Thank you one and all.

 

I was very good at math in school but alas, that was a long time ago.

[SteamyTea]

  On 29/10/2023 at 18:13, Coanda said:

Thank you one and all.

 

I was very good at math in school but alas, that was a long time ago.

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You have to use it to very day. Even then it is easy to make errors.

[JohnMo]

  On 29/10/2023 at 17:52, Adrian Walker said:

 

 

BTW it is normal to have the answer in litres/second for MVHR calculations. 

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The house is measured in metres so its volume in m3 is an easy calculation, air changes an hours (ACH) is m3/h - an easy outcome, so the maths in the same units is super simple. Changing the litres/second don't see the point.

 

House 200m2, 2.5m tall, is 500m3, 0.5ACH, is 250m3/hr.  All maths done in the head, my flow meter works in the same units, you just need to work out the room flow rates from there. Why bother the litres/sec

[SteamyTea]

  On 29/10/2023 at 20:58, JohnMo said:

The house is measured in metres so its volume in m3 is an easy calculation, air changes an hours (ACH) is m3/h - an easy outcome, so the maths in the same units is super simple. Changing the litres/second don't see the point.

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In the US of A, they measure houses in feet, but oddly don't use fluid oz for volume, they stick to cubic feet per minute.

 

As an aside, when I listen to energy traders/experts on the radio talking about 'the energy crisis', they keep talking about the price of a therm pf gas.

And the government uses barrel of oil equivalent in reports.

And how often do we hear someone say they use a lot of energy, then say it is "£300 a month".

 

SI and the derived units are so easy to understand.

 

[Coanda]

  On 29/10/2023 at 21:18, SteamyTea said:

In the US of A, they measure houses in feet, but oddly don't use fluid oz for volume, they stick to cubic feet per minute.

 

 

 

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A utube video I saw from the USA talked about ton units for MVHR or was it aircon.

[SteamyTea]

  On 29/10/2023 at 21:47, Coanda said:

A utube video I saw from the USA talked about ton units for MVHR or was it aircon.

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Is Aircon.

Think it is the amount of energy to cool a ton of water 1⁰f.