SI conversion

[mcjo tech]

Hello,

I am the creator of the ExactCharge Calculator.
We are currently working on a conversion from USA scale to SI scale to expand our product to make it more useful for worldwide distribution. We understand the conversion from PSIG to Kpa and Fahrenheit to Celsius. My question is about Duct Sizing. We use Cubic Feet per Minute and Velocity to readout duct size in inches. For your scale would we use Cubic Meters per Minute and Velocity for a duct size readout in centimeters? Because of my lack of knowledge about SI units this conversion has been more difficult then we originally anticipated. Any help woud be greatly appreciated.

Thanks,

Joe
ExactCharge Industries,Inc. USA

[Argus]

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Velocity is normally expressed in metres per second (m/s);

Volume can be either cubic meters per minute (m3/min) or litres per second (l/s), depending on the quantity of air in question.

Generally, small scale air movement is shown as l/s, larger air volumes in m3/min. Either can be used to result in a usable figure, so long as the nomenclature is clear and consistent. It's an easy matter to move the decimal point.

Either way, it’s important to note that ‘metre’ or ‘litre’ is spelled differently over here and in mainland Europe.

Hope it helps

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[The Viking]

And duct work's cross sections are normally measured in mm, length in meters.

[Brian_UK]

..... length in meters.

DOH

See post from Argus above

[mcjo tech]

Thanks for your help. I very much appreciate it.

Joe

[The Viking]

DOH

See post from Argus above

Careful now
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Or I start to post in Swedish!

[mcjo tech]

Thanks guys for the information. I have been doing some studying on conversion from USA scale to SI scale. I just have a couple more questions that I am hopeful you can help me with. For residential Duct Sizing calculations do you input litres per second and correspond with a duct diameter in millimeters? Also do you have a SI duct sizing slide rule that is commonly used?

Thanks again for any help you can provide.

Joe
ExactCharge Industries,Inc.

[penair]

Hi Joe
For duct sizing I use a metric ductsizer which is like a round slide rule. It is a Holyoake product which calculates and cross references the following. check out holyoake on google
-Friction per metre of duct - Pa / air volume - m3/sec
-Round duct diameter - mm
Rectangular duct dimensions - mm
Velocity - m/sec / air volume - m3/sec

[Argus]

I agree with Penair.

But for consistency I would urge establishing and using the same units throughout.

I can’t speak for the rest of the world, but in Europe I see small air volumes expressed as l/s more often than m3/sec. In fact 0.5 m3/s is the same as 500 l/s.
That’s the beauty of SI….. we just move the decimal point.

However, l/s becomes an inconveniently large figure for large volumes and converting to m3/min requires a simple calculation. So we sometimes find the two existing side by side.

For example, a large air handling unit serving many small terminal units on several floors of a building would be measured in m3/min. The individual terminals themselves would be measured in l/sec.

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[mcjo tech]

Thanks to all of you for your help. We have completed conversion to SI Scale. Please let me ask just another question, I would very much appreciate any help you would be willing to offer. I am now involved in testing this new version and am still having problems with the Duct Sizing aspect. Because I am completely unfamiliar with SI I don't understand what would be a valid input. We are inputting in litres per second with velocity in metres per second and a readout in millimetres. I believe this to be correct but do not have a cross reference to test by. I was hopeful that you could help in providing me with some valid inputs with corresponding outputs so I can test the process and any other insights that you would be willing to provide.

Thank you,

Joe
ExactCharge Industries,Inc USA

[Josip]

Hi, mcjo tech

I would like to say the best way is to use base units and then derived (which are obtained by using the standard mathematical operator signs for multiplication, division, and exponents) regarding given situation but leave that to user.

Of course it is good to have additional feature to convert i.e. cubic meter/per hour, minute or second to cubic centimeter or millimeter or liter/per hour,minute or second.

The best is always the simple one.

Please read this http://en.wikipedia.org/wiki/SI#Units

Best regards, Josip