Best way to wind-proof OA Press Ref

[dingman]

Gents-
I haven't had to deal with this for a few years but it does crop up every now and then.
I'd like to hear of a few diff techniques of buffering an outside air building pressure reference. I'm curious as to what are y'all's favorite solutions.

For physical accuracy, I prefer getting the end of the tube as high above the building as possible and since I'm in Iowa (-10° to 10° for the last two weeks) I have to watch for condensation freezing in the tubing. Thus, sleeving a 1\4" line within a 1\2" line works fairly well and pressurizing the space between the two tubes works really well.

For buffering, a 4" PVC tube 24" long placed between the DDC input and the reference works fairly well, tho I tend to use Siemens "time averaging" programming filter more than any physical filter\buffer.

For really messy sites (i.e., on top of a hill), I'll use all of the above...
1) get the outside tip of the tube as high above the building as they will allow
2) put a large PVC canister inline with the end of the tube and the DDC input.
3) Use any programming available to finish the "smoothing" of the value that's used to control the building pressurization system.

Obviously, the ultimate goal is to keep the building pressure under control but those are my best methods for accurately measuring OA pressure reference.

[habs]

How do you pressurize between the 1/4 and 1/2 tubes? I am having a major pressure problem in a building right now, when the wind blows the building goes into a negative. I have tried to put the pressure pick up in a spot where it won't be affected by outdoor air but am not having much luck.

[codewriter]

If the 1/4" line is landed on the controller, the 1/2" line will be left open to the building, then the other end will be open to the outdoor, so if the building is under a positive pressure, it should venture up and out the 1/2" tube.

I have always used the Red-Birds and a Snuber and so far they have always worked out.

[dingman]

That is correct Codedude on the part about leaving the 1\2" tube open to the interior of the building. One factor on the other end is to to keep the 1\2 tube trimmed at least a foot away from the end of the 1\4" to prevent adverse affects (mostly condensation in the winter).
I hate winter. We're up to a balmy 9° today.;)

[twisted pair]

I had a historic museum that was sandwiched between a few 30 story high rises. The engineer specd this device in my attachment. I know it looks ridiculous and they are stainless, so the cost is $$$, but they worked great.

[habs]

Could you explain further about the 1/4 and 1/2 inch tubing. The building I am working in has a bulding static pressure sensor in each rooftop with a positive which I connected a 1/4 tube to and put in the space and a negative terminal which I connected to a device to measure reference, when the wind is not blowing hard the building works good (after addind the reference device) but when the wind picks up the building draws a negative and the front doors are hard to open. There are four rooftops each with their own vfd exhauster and pressure sensor. The sensors are sentra and send a 0to 5 volt to the rooftop controller, 2.5 volts is the 0 pressure point.

Any suggestions would be greatly appreciated.

[dingman]

Basically, where the poly (or copper) penetrates the building, I've sleeved the 1\4" with a 1\2". On the outside, the 1\2" runs at least a couple of feet out from the building and on the inside, it should run to a pressurized space.

It's far from a perfect solution, but I've had instances of condensation developing around the penetration and then it's either frozen or it dripped down into the transducers.

The more common problem, of course, being what some of you mentioned and that's wind\pressure making your outside reference bounce all around. That device above looks to be a pretty good design. Then again, as I mentioned in my first post, if you have the option of getting the outside reference above the roof by 4' or so and put a good "cap" on it, it should be fine.

I have a newer building that's just been set up with a outside reference that is piped to all four sides of the building. I'll be interested to see how it does.

[twisted pair]

For rooftop units I like to use the Dwyer model A-306. The only problem I have had is sometimes after a few years the tubing may need to be replaced. In most cases we try and minimize the amount of tubing that exposed to the outside. The shield they provide works great.

I do not have a data sheet, but I have included a picture of one. You can get them form Kele, Trane parts centers or any other HVAC/Controls source.

[Balibe]

I know this topic hasnt been discussed in a bit, but was looking for something on kele.com, came across the device below and remembered this topic. I havent used one, but will keep it in mind and try it next time I have an issue. Thought others might be interested and its only $60 [list price] ....

http://www.kele.com/olcat/P4/SD-SER-V.PDF

http://www.kele.com/olcat/P4/10052.html

[dingman]

Thanks, I've saved the PDF and will consider it for a couple of my buildings.


I know this topic hasnt been discussed in a bit, but was looking for something on kele.com, came across the device below and remembered this topic. I havent used one, but will keep it in mind and try it next time I have an issue. Thought others might be interested and its only $60 [list price] ....

http://www.kele.com/olcat/P4/SD-SER-V.PDF

http://www.kele.com/olcat/P4/10052.html