[Bldg-sim] air flow sensors

[Chris Jones]

Thanks Ken and everyone.  It sounds like a big challenge.  As it is a 
spare time research project, I am going to keep expenses as low as possible.

One issue I realize will be a big problem is spot measuring all open 
windows at once - in the time it takes to move from a ground floor 
window to the second floor, the conditions can change significantly.

The windows have insect screens which may eliminate some of the cross 
currents outside the window.

Once I obtain the measuring instruments, I will be back for more advise.



At 04:30 PM 03/07/2012, Ken Kolkebeck wrote:
>I'm not 100% sure I understand the application but I will assume it is for
>some type of test. What you are trying to measure (natural draft or
>induced draft) will be important because that will dictate the velocity
>you are dealing with. The higher the velocity the easier to measure. The
>lower the more difficult and the more subject to disturbances on either
>side of the aperture.
>
>The problem is somewhat similar to that of measuring the velocity across a
>fume hood where measureable velocities run in the 50 to 150 feet per
>minute range. These are of course induced drafts which while low in
>velocity are high enough to be measured. The fact that modern fume hoods
>have somewhat aerodynamic entry which reduces turbulence enhances the
>ability to get clean measurements. Even when using the most accurate
>device, traverse technique and cross currents are the biggest causes of
>errors which can run 25%.
>
>Two methods are commonly used here-
>Hot (or Warm) wire anemometers as suggested by another responder. TSI
>being a common brand. The issue here is that these do not sense direction
>and on the face of an open window are going to be impacted by cross
>currents caused by wind outside the building. The other thing is you
>really need a grid of them across such a wide area because the gradient is
>likely to be large.
>
>Shortridge "Velgrid" which is in essence a pitot type device however the
>key to the way it works is with a very sophisticated pressure sensor which
>has all kinds of error corrections built in. These are not your standard
>HVAC pressure transducers as they are designed to operate in the
>differential pressure ranges well below 0.01 inches water column. The
>transducer zeros itself before each reading to null out errors associated
>with hysteresis and thermal effects.
>
>The pitot is actually a one by one grid of high and low sensors and has a
>multiplier effect so the velocity is going to be about 2000 times the
>square root of the differential in inches of water. 100 fpm therefore gets
>you about 0.0025 inches; 50 fpm gets you a quarter of that. For fume hoods
>we always mounted the grid on a stand because it is difficult to hold
>steady and the movement induces errors. Unfortunately, this device too is
>subject to cross current errors.
>
>A flow hood, also made by Shortridge, should work provided there are not a
>lot of other windows open which will be the paths of least resistance and
>will impact the reading because the hood induces a back pressure.
>
>Good luck and have fun. Sounds like a tough one.
>
>Regards,
>Ken Kolkebeck
>Certified Automation Professional, ISA
>Certified Building Commissioning Professional, AEE
>NJ Office: 201-784-8700
>
>
>
>
>**We've moved**
>420 Bedford Street, Suite 350
>Lexington, MA  02420
>
>
>-----Original Message-----
>From: Chris Jones [mailto:cj at enersave.ca]
>Sent: Tuesday, July 03, 2012 9:25 AM
>To: bldg-sim at lists.onebuilding.org
>Subject: [Bldg-sim] air flow sensors
>
>I am wondering what kind of air flow sensor one would use to measure the
>flow through opened windows?  This is for a house monitoring projects.  I
>have the DB and WB loggers.  Would you do a transverse with a pitot tube?
>Would a flow hood work?
>
>
>  >>
>Christopher Jones, P.Eng.
>Suite 1801, 1 Yonge Street
>Toronto, ON M5E1W7
>Tel. 416-203-7465
>Fax. 416-946-1005
>email cj at enersave.ca

 >>
Christopher Jones, P.Eng.
Suite 1801, 1 Yonge Street
Toronto, ON M5E1W7
Tel. 416-203-7465
Fax. 416-946-1005
email cj at enersave.ca