I agree that the night time decrease in U-value is a big deal, especially if the base window is low performance and there is no HVAC.
But I concur in the general observation that something is wrong in the E+ model’s optics portion and have personally never trusted it with interior shading devices. As Joe said, a highly reflective interior device should make the whole window system reject more shortwave than the model seems to ever do. If you need to model interior blinds or shades, I would suggest trying out the newer ASHWAT equivalent layer model or even the new complex fenestration model, instead of the original window model. The original is good for no shading devices and with exterior shading devices.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Thursday, October 9, 2014 4:21 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] why blinds not reducing heat gain through window?
I'd run the simulation again - but opening the blinds at night... as suspect that the heat is trapped within the room...blocking heat loss to the night time sky is (dare I say it) the prime cause of the urban heat island effect.... it would be an interesting result if open the blinds after sunset reduced overheating risks!!
J
From: "'Dr Yi Zhang' yi@xxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Thursday, 9 October 2014, 22:54
Subject: RE: [EnergyPlus_Support] why blinds not reducing heat gain through window?
Good analysis, Joe! One possible explanation to the higher room temperature may be that shortwave radiation would have fell on the concrete floor without the blinds. So the internal blinds in effect quicken the thermal response of room�
Yi
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: 09 October 2014 19:17
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] why blinds not reducing heat gain through window?
What you say is true, but it's not the only effect of window blinds. Of the solar radiation that's intercepted by window blinds, most of it is reflected back out of the window depending on its reflectance, a small fraction (< 5%) is transmitted, and the remainder absorbed and reradiated as long-wave radiation. So, when I hear that window blinds actually increase the indoor air temperature, this would imply that the reradiated long-wave is significantly greater than the reflected short-wave, which would happen only if the blinds are heavy and dark. However, all the blinds I've seen, especially those used for solar control, are either white or very light in color.
It's pretty well-known that external blinds are more effective than internal blinds for reducing unwanted solar gain. However, this is the first I've heard that internal blinds are not just ineffective, but counter-productive. In rereading the original post, I noticed it said "Zone mean air temperature" and "Surface inside face temperature" have both gone up. I'm not particularly surprised at the latter, because blinds tend to have higher absorptivity than glazing (although I would caution not to ignore the transmitted short-wave through the window in comparing surface temperatures), but I am surprised at the former. I don't want to speculate further on this until I know more how the blinds are being modeled, how the zone is being controlled, and how the HVAC, if there is one, is being modeled.
The following link is for a paper done in 2004 studying the same issue in a similar building (80% glazing on the facades) and comparable climate (Canada). That study concluded that internal blinds reduced cooling loads on a continuum depending on their reflectance, with the best (90% reflectance) approaching but still significantly less effective than external blinds.
http://sbrn.solarbuildings.ca/c/sbn/file_db/Doc_File_e/Simulation%20design%20study%20for%20the%20facade%20renovation.pdf
Joe
Joe HuangWhite Box Technologies, Inc.346 Rheem Blvd., Suite 205AMoraga CA 94556yjhuang@xxxxxxxxxxxxxxxxxxxxxxxxhttp://weather.whiteboxtechnologies.com/ for simulation-ready weather data(o) (925)388-0265(c) (510)928-2683"building energy simulations at your fingertips"
On 10/8/2014 10:58 PM, Almofeez almofeez@xxxxxxxxx [EnergyPlus_Support] wrote:
It may be explained that, the blinds absorb short wave solar heat and radiate long wave heat. We know glass is opaque to short wave radiant heat. Therefore heat is trapped inside room.
من جهاز الـ iPhone الخاص بي
في ٠٩/١٠/٢٠١٤، الساعة ٨:٣١ ص، كتب "'jeannieboef@xxxxxxxxx' jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>:
I can't point to a study, but the guys at trnsys have told me that studies have shown that internal blinds bring little to no positive effect on room heat gain.
However, as we're on the topic of blinds, could someone please draw up a table showing which controls are effected by which input parameters, e.g. Control type glare - does it go the the "fixed slat" position on trigger or does it change possition between min/max slat angles to maintain a setpoint?
There are a lot of control options...a table would be a great addition to the documentaion.
Jean
On 09.10.2014, at 03:04, "Joe Huang YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Hmmm, interesting. Wouldn't the blinds reflect a fair amount of the solar back out through the window? Seems counter-intuitive that deploying blinds behind a window will increase rather than decrease the mean air temperature of the space. Have we been wrong all these decades? I'd still
like to know the thermal/optical characteristics of the window and the blinds. I suppose having a black
blind behind a window with very low IR transmissivity might create problems.
Joe
On 10/8/2014 4:45 PM, 'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support] wrote:
The low mass blinds will also absorb all the solar and transfer it to the interior air. Without blinds, the solar hits a more massive floor/walls with much less immediate transfer to the air. This could give you higher cooling peak demand.
Ned Lyon, P.E. (MA, WV)
Staff ConsultantSIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
http://www.sgh.com/
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Wednesday, October 08, 2014 7:07 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] why blinds not reducing heat gain through window?
I suspect there's something wrong in the modeling of the blinds. The effect of night sky radiation is not so pronounced on a window, because (1) half of what it sees is ground, (2) the other half is the sky at low angles where the sky temperatures are much less depressed as they are looking straight up the sky.
JoeJoe HuangWhite Box Technologies, Inc.346 Rheem Blvd., Suite 205AMoraga CA 94556yjhuang@xxxxxxxxxxxxxxxxxxxxxxxxhttp://weather.whiteboxtechnologies.com/ for simulation-ready weather data(o) (925)388-0265(c) (510)928-2683"building energy simulations at your fingertips"
On 10/7/2014 11:00 PM, 'jeannieboef@xxxxxxxxx' jeannieboef@xxxxxxxxx [EnergyPlus_Support] wrote:
If you have a building with lots of glass, don't forget the radiant exchange with the night sky at -60 C. The "radiant night cooling" is possibly being blocked by the blinds, if the blinds are there during the night.
Mit freundlichen Grüßen- Sent from my iPhone (excuse the brevity)
i. A.
Jean Marais
b.i.g. bechtold
Tel. +49 30 6706662-23
On 06.10.2014, at 21:53, "annavenediki@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Hello,
I've designed a south facing room with a floor- to-ceiling window and blinds covering the whole surface of the window. I run two simulations, one with no blinds on the window and one with blinds covering the window in order to compare the results. The building's location is in Eastern Europe. The run period is from July to August (sunny and hot period). Both output variables "Zone mean air temperature" and "Surface inside face temperature", have much higher values when the simulation is run with the blinds on the window. How can this be possible? Can it be explained in a way or is there something wrong with the data?
Thanks in advance,
Anna V.
__._,_.___
Posted by: "Brent Griffith" <Brent.Griffith@xxxxxxxxxxxxxxxxxx>
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
__,_._,___