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WindandStackOpenArea question

asked 2016-11-23 10:35:03 -0500

poppo92 gravatar image

updated 2016-11-28 21:19:11 -0500

OpenStudio. I want to show you 1) the left pic is the energy simulation of all south-west thermal zones of my building without anything (no hvac, no ventilation, no infilitration) just the building with loads, people, schedules ect. And then the right pic. 2) the building using the "WindandStackOpenArea" measure, setting the minimum indoor T = 22 C, and the maximum indoor T = 26 C. I would have expected that this measure works only during the summer, but in my case temperatures go higher than 26C (the limit I set). Anyway it seems that it works (I don't know why) also during the winter, why? Have a look at the image: in the left case WindandStackOpenArea is not set, and the temperatures in January-February are in the range 20-25 C, but in the right case temperatures in Jan-Feb are LOWER than 22C. Why? I set the minimun indoor T should be 22C, not the maximum. I don't see why WindandStackOpenArea seems that has worked also in these cold months. Then, during the summer it seems that WindandStackOpenArea has no more effect because of the high temperatures, and I can understand it. image description

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answered 2016-11-23 17:25:21 -0500

StefanG gravatar image

The minimum and maximum indoor temperatures describe when the windows are allowed to open, so when the interior temperatures drop below 22C, the windows close. When temperature go above 26C, the windows also close.

In your model, i'm guessing in the summer your indoor temperatures will at some point go above 26C, since naturally ventilated buildings typically will float this high in most climates. The windows all close at this point, but since you still have internal gains and envelope gains which contribute heat to the building, causing the temperature to continue to rise.

Since the windows are closed and there is no HVAC system, there is no way for the building to lose heat, so heat perpetually increases in the space until the climate has cooled enough to allow the building to cool below 26C and your windows are able to open again.

In the winter, your windows stay open until the building drops below 22C, in which case the windows close. The building still loses heat through the envelope however, so the air temperatures inside fall below the 22C threshold.

I would suggest looking into adding controls for the outdoor temperature as well as in the indoor temperature. Maybe switch your 26C limit to the outdoor temperature limit so that the windows are able to be opened in the summer.

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thank you, very exhaustive. Just one more question: is there a max air velocity that commonly is used for office buildings? something like a limit I can find maybe in ASHRAE? thank you anyway

poppo92 gravatar image poppo92  ( 2016-11-24 04:46:20 -0500 )edit

If you're referring to the indoor velocity for use in thermal comfort calculations, ASHRAE standard 55 lays out the criteria in section 5.3.3. Essentially it's as follows:

  • if using natural ventilation, max allowable airspeed is 0.8 m/s
  • if occupants have user-controllable fans, the maximum airspeed is 1.2 m/s

Anecdotally I've heard that that above 0.6 m/s there are issues with papers getting thrown around.

StefanG gravatar image StefanG  ( 2016-11-28 12:30:10 -0500 )edit

@StefanG no I'm talking about the data to fullfill in the Windstackopenarea measure, that asks the "Max Wind Speed (m/s)", so the outdoor wind. Should I set it as an average wind speed of all the summer season? or should I use the maximum wind speed of the summer season?

poppo92 gravatar image poppo92  ( 2016-11-29 05:08:25 -0500 )edit

@poppo92

I'm not sure, but I think the max wind speed is only for closing the windows during high wind events for safety issues. I don't have a good number on hand but I would set as a sufficiently high number to allow natural ventilation to occur most of the times you want it and rely on temperatures to control when the windows open and close.

StefanG gravatar image StefanG  ( 2016-11-29 11:19:10 -0500 )edit

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Asked: 2016-11-23 10:35:03 -0500

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Last updated: Nov 23 '16