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]

7 minutes ago, saveasteading said:

Oops that was for 1m/s

 

So 28.26 x 0.8

= 22.6.

 

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

Then forget.

[Adrian Walker]

4 hours ago, 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?

 

 

 

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

[SteamyTea]

7 minutes ago, Adrian Walker said:

 

 

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

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

[Adrian Walker]

3 minutes ago, SteamyTea said:

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

 

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]

Just now, Adrian Walker said:

I do hate it when people use centimetres rather than millimetres

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]

1 minute ago, Coanda said:

Thank you one and all.

 

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

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

[JohnMo]

2 hours ago, Adrian Walker said:

 

 

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

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]

14 minutes ago, 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.

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]

27 minutes ago, 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.

 

 

 

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

[SteamyTea]

38 minutes ago, Coanda said:

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

Is Aircon.

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