Air temperature and altitude corrections for ventilation systems

Altitude and air temperature make a substantial difference in the performance of any ventilation system. The calcuations I have provided here: http://mikeaurelius.wordpress.com/2007/12/25/ventilation-basics-part-two/ are based on sea level and 70 degrees F.

In the calculations, the only variable that needs modifying is VP, Velocity Pressure. The standard calculation is (V/4005) squared.

When applying temperature and altitude corrections, use the following equation: VP = ((V/1096.7) squared) times ‘density of the air in pounds per cubic foot’.

Ventilation question

From the ISGB forum:

Hi , right now I’ve been using the system Vince described in the Drew Fritts book. I had been using a minor and everything worked well.
Recently purchased an Lucio torch from Carlisle. I noticed I needed to upgrade my ventilation system. So I like to start from scratch, build a new hood etc. My room is 8 x 24.
I have also read an interesting article, and would like to get your thought on it please. Here is a link.
http://andreaguarino.com/ventilation/

I took a look at Andrea Guarino’s website and the link on her ventilation system. If you are a regular reader of my blog, you know my feelings on open duct ventilation (I don’t believe they work and don’t recommend them).

Same old, same old…

More fallacy from Dennis Brady on LE:

I mean 2 – 45 deg elbows connected together to produce the 90 deg bend. The wider arc causes less air flow resistance. Even better would be a wide arc curve (these are available for metal ducting but are pretty pricey).

For at least 40 years, the plumbing code for drains and vents stated specifically that in any run of drain or vent, one only 90 was permitted but an unlimited number of 45’s was allowed. If the experts insist that makes a critical difference for venting plumbing drains, it’s reasonable to assume it’ll make a significant difference for venting torching fumes.

I guess Dennis has never looked under his sink. A standard plumbing P trap consists of at least 3, count them, 3 90 degree bends to form the drain trap. 90 degree bends are in every single plumbing run made.

A rose by any other name

The ever delightful Dennis Brady never fails to entertain. His latest on using a window AC unit as a source of fresh air from LE:

Air is air. A specially dedicated incoming air supply is a lovely thing but is NOT essential. Whether or not air coming in through a heater or AC is sufficient replacement depends on the volume and consistency of that incoming air. If there’s enough volume to replace air being exhausted, and it comes in fairly steadily, it will work perfectly.

More on makeup air issues

As I’ve mentioned in the past, the folks who hang out at Wet Canvas seem to be living in their own little world, isolated from the rest of the glass world, at least as far as safety issues are concerned.

http://www.wetcanvas.com/forums/showthread.php?p=6984591#post6984591

The thread starts with a very good question, especially at this time of year:

Every year I have the same problem in the heat of summer. Obviously I want my exhaust to work well, but the window unit in my studio can not cool the replacement air fast enough. I thought I remembered a thread about this years ago, but I can’t find it? Opposite problem in the dead of winter with heating. Any ideas/solutions?

And immediately goes south:

Scratching my head…

Seems Dennis Brady wishes to re-invent the wheel:

http://www.lampworketc.com/forums/showthread.php?p=1984187#post1984187 (top of page two)

I’m hoping we can find some “formula” that equally, and with reasonable accuracy, considers hood size, distance from torch, and fan capacity. Any of those three factors is meaningless without considering how it’s affected by the other two.

Actually, Dennis, if you would take the time to do some very basic research (such as reading up on ventilation basics — you don’t even have to read what I’ve written, read Dale’s writings, read those of OSHA, NIOSH, or even the ACGIH) you will see that the formula already exists.