It has been a windy week out here in Phoenix, AZ this past week.

I have a few tricks that I have used that works only sometimes. I use an empty plastic water bottle and put my reference to outside hose inside and try to shield it as much as possible. This has not worked so well the past few days where we have had gusty winds over 20+ mph.

I am open for some input on this, as my calendar is now chaos from all of the rescheduling.

Tags: Basline, Blower, Door, Testing, Wind

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I don't have any magic to cancel out the wind, however, to help your schedule you can consider going ahead with the audit and return on a calm day to do the BD testing.  Distance and other factors will determine when this is an option, but you are now seeing the chaos that repeated rescheduling can cause. 

I'm in cold country and there are many cases where I need the cold or cold with no sun to give me the infrared images I want.  When mother nature is not co-operating I tell the home owner that I may have to come by at 4 AM to do some testing.  Often the wind calms down after dark as well.  There are many services that are necessarily inconvenient and we should not hesitate to tell them, an energy audit can be one of them.

Glad to hear you are busy.

Bud

Thanks Bud. 

When you see your baseline jump around like a grasshopper on a hotplate it might not be a good idea to test.

I listened to an online seminar once where it was suggested during windy conditions to multipoint test in both directions with no time averaging and results will be close.

I am not sure the risk outweighs the reward or visa versa. That would be a judgment call you need to make.

I like that grasshopper analogy, thanks for the feedback.

Multipoint testing will improve precision, mostly because (after you get experience with doing dozens of them) you can throw out data that doesn't fit the curve. It is probably not worth all the grief if you are testing a SF house, and a number that's +/- 5% is good enough. But I do it regularly when doing multifamily tests on large apartment buildings. It is true -- if you need more accuracy, testing both ways will help.

If you are running a single fan, a longer time average will help improve precision. It is sort of a low-tech way of doing a multipoint test. I have just set my DG-700 to "long" and let it run for several minutes to get a number that I trusted a little more.

The fastest way to get better precision and better accuracy might be to set yourself up where you can see a flag, or leaves, or something that will act like a wind sock. Then grab your data when it shows you that the wind is momentarily calm. That's because wind always makes a house seem a little tighter than it really is. More of the shell is subject to negative external pressure than to positive pressure, when a wind is blowing around a generally unshielded house. This is why testing both ways (de-pressurize AND pressurize) gets more accurate results -- it averages out the Bernoulli effects across the house shell induced by a wind.

That was extremely helpful, thank you. I would do this method if time would allow, however I am usually performing three to four audits a day on average a 2000 sq ft home, I have rescheduled as needed but not without a valiant effort. I have tried the opposite side of home (opposite from wind direction) and had better results. I have also been doing all of the other tasks other than blower door testing and it has helped out a lot. Thanks again Don.

Colin at Retrotec has told me that you can't get any more accurate than a 120 second baseline and a 120 second time average blower door test, multi-point included.

However, bear in mind that the ASTM standard states 20 MPH as the upper limit, and RESNET has rules about using standard deviation tables to determine accuracy.   So it depends on who you are reporting to - remember that we still use a 1989 version 62.2 that has not been supported for over 20 years.

Thanks Ed

I use a T on my outside hose and run hoses from each side of the T around either side of the house. 

I did a bunch of row houses recently where I couldn't use this trick and found that just extending my outside hose well away from the house worked pretty well too.

The first method averages out the pressures on two sides of the house.  Really to take this method to its full extent, I should be averaging all four sides but I find two sides works pretty well except on the windiest days.

The idea of the second method is to try to get away from the eddy effects of the house -i.e. high pressure on the windward side and low pressure on the leeward side.

I have found that trying to shield the end of the hose in a pop bottle or mailbox doesn't work either.  I suspect that beer or whiskey bottles will not work either, but I haven't tried.

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