CI 2009 IEQc8.1: Daylight and Views—Daylight

You use the area in your daylight zone which is either determined by 2x the window height for the depth, or if there is an obstruction, i believe it is then a 63 degree angle. This is the area that is used in the calculations.

Cecillia,

See this guide by LEEDuser. http://www.leeduser.com/credit/NC-2009/IEQc8.1#doc-tab

And page 400 of this "Addendum Details". https://www.usgbc.org/ShowFile.aspx?DocumentID=9377

You use the floor area that makes the result come out between 0.150 and 0.180. If your initial result using the 140 sf comes out above 0.180, none of the area complies. If it comes out below 0.150, adjust the depth of your floor area down until the result is above 0.150. This is the area of the room that complies that you enter into the spreadsheet. You can break up the space how you like as long as each one is connected to a perimeter zone with a window.

Thank you Todd and Jill!! I will give this a shot. Cecilia.

Jill Dalglish wrote: "You use the floor area that makes the result come out between 0.150 and 0.180. If your initial result using the 140 sf comes out above 0.180, none of the area complies. If it comes out below 0.150, adjust the depth of your floor area down until the result is above 0.150."

Jill, just to clarify, are you saying that we are allowed to adjust 'bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. depth to core' as much as we want until we get a value between 0.15 and 0.18? Can you please clarify a bit if you don't mind, as this has not been my interpretation in the past - rather it has been that the depth is 2 x the wall height, or less based on a 63 deg angle if there is a dropped ceiling or other obstruction. This has always produced wildly different values for each zone, often out of the 0.15-0.18 range. As a result we have basically given up on the prescriptive path as it is far too rigid. If we have no control over the bay area or window area, we would basically need a different TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. for each zone, which is unrealistic. We have instead tried to learn Ecotect / Radiance to show compliance (which I think is more accurate / fun, but much more time consuming, and a big disappointment if you put in several hours of work just to see that you don't meet). In fact I have considered the rigidness of the prescriptive path is the US/CAGBCs way of saying "sure you can do it this way..but don't waste your time, it wont work unless you have a square box). If you are saying otherwise this may change a lot of our approach!

FYI, I am in Canada and using the LEED Canada Reference Guide, which is even more vague than the US version on this credit, proving to be very frustrating. As far as I can tell, our Ref Guide gives no indication to being able to adjust the bay area.

yes

I would not say that the prescriptive method is a means to calculate daylight. It is a method that is used to determined whether a space meets a certain set of criteria that would provide adequate levels of light. Its like the older glazing factorThe ratio of interior illuminance at a given point on a given plane (usually the work plane) to the exterior illuminance under known overcast sky conditions. LEED uses a simplified approach for its credit compliance calculations. The variables used to determine the daylight factor include the floor area, window area, window geometry, visible transmittance (Tvis) and window height. calculation where the area and property of the the space is used in a set formula to determine a number, nothing is based on any type of illuminance levels.

So if you are truly wanting to know the daylight levels of the space, simulations or actual measurements are the methods to use.

I would not use the prescriptive method if I designed a space which has exterior shading, light shelves, sloped ceilings, or any other implemented daylighting strategies. It, like you said, is just general.

If you have an open office space with just sidelighting, and or toplighting, and you just want to meet the credit requirement, then the precriptive method would be applicable.

I can email you a copy if you'd like.

That would be great if you could Todd. I would really apprecate that. My work email is ciaranmccabe@ethoseng.ie

Hi Todd,

If you don't mind, can you send me a copy as well.

dennisng@red-studio.ca

I believe the prescriptive path would be what you want to follow to help you determine compliance if you don;t want to go with simulation.You would be using the daylight zone, which would be the depth from the window wall, twice the window height, or at a 63 degree angle.

From what you are saying, I'm assuming perimeter offices about 10 feet in depth, then a corridor with more interior offices. The prescriptive path will not work in shared daylighting scenarios, so only the offices along the perimeter can be looked at. If thats the case, you would probably need a bilateral daylighting scenario, which would be toplighting and sidelighting. Areas under skylights can be analyzed using the prescriptive path.

There are simulation programs which do not have such a large learning curve as those you have mentioned. SPOT is one which can do simply geometries. Not sure what other programs you are using or have. If you have AutoCadd, there is 3D Studio Max or Ecotect. The learning curve is not as large (my opinon) as others.

Since this project is in the earliest stage of design, i would use this opportunity to look at the daylight, not to earn a LEED credit, but to provide the best daylighting scenarios to the occupants and for energy savings. This requires more work in the design phase, and to be done correctly you really need to use simulation.

Hi Todd,

Thanks for the reply. In actuality we have 25' of open offices around the perimeter, 5' corridor, then 12' deep offices (glazed towards the open office to allow for "borrowed" light to come through) With this layout, between the perimeter glass to the back wall of the offices is 45' or so. the core itself contains a meeting room and there are a lot of offices which do not have daylight from perimeter windows because they are located in the core. I think your opinion is dead on, having skylighting would definitely benefit in terms of health and well being standpoint.

I'll take a look at SPOT for quick analysis. We've been getting a lot of assessment related issues early on in the process to decide on what space is viable for LEED and daylighting. I guess this will be worth the investment in time to learn something quick.

If there are any other suggestions I'd be pleased to hear it.

Cheers,
D

Just an update. I tried sketchup and Daysim and it seems to be working out except intuitively I should be getting light into the offices (fully glazed wall oriented towards where the daylight is coming through) and the readings in the offices are 0. has anyone got a method to deal with this? i made a wall in sketchup and added a default single pane glass on it but no reading of light coming through, it's acting as though it's a solid wall.

any ideas would be greatly appreciated.

Thanks,
D.

Not knowing the location or climate of the project, clerestories are something you may also consider. Depending on the ceiling height and the size of the skylight, it may cause glare issues (over daylit) in individual offices because of the skylights orientation to the sky dome and climate. Clerestories can help reduce this issue because of the geometry. Roof monitors can also be implemented and orientation needs to be considered to reduce the effects of direct solar penetration. Another option may be solar tubes. they are smaller than skylights and can provide a effective level of illuminance in individual offices or small conference rooms. But simulation or measurements would be needed to demonstrate LEED requirements.

Are you using the Daysim materials file for sketchup?

Yes, i'm using the Daysim materials provided by the Daysim skethcup plugin. i tried a basic model, it was okay, now im implementing rooms and with full height glass and it's not working.

Denise, i cannot accurately say what is wrong with your model without looking at it. I don;t typically use Sketchup to Daysim and have only really just used Daysim that way a few times. I usually go from Ecotect to Daysim. Here is the link to the Daysim forum that may help answer your specific question.

http://groups.google.com/group/daysim

Thanks Todd. I'll look into it. I should probably try Ecotect since we have it in the office. :)

Cheers.
D.

One piece of advice with using Ecotect and Daysim, keep your file names short and your paths to those files as short as possible to reduce any errors. I highly recommend reading the Daysim Tutorial on how to export from Ecotect to Daysim.

Hi Denise,
A good rule of thumb for daylighting and the LEED daylighting credit is that usable daylighting reaches back into a space about 1.5 - 2 times the head height of the window. In your case about 1.5 x 12' or 18' around the glazed perimeter. As you can see with your very wide floorplate, reaching the LEED credit is not really attainable with just the windows. (120' + 120' + (120'-(18'x2))) x 18' = 5832 sf or 41% of your total space of 14,400. Even subtracting out the non-regularly occupied space isn't likely to get you to the 75% required.

To address what you asked about the depth in the LEED 2009 CI reference guide on pages 58 and 59 they allude to a recommended depth as Todd and I are saying of 2 x the window head height. I agree, it does not address the issue very well.

One method is to use the downloadable Supplemental Daylight and Views Calculations spreadsheet. The other option is to just create your own, which i prefer because the downloadable one sometimes has issues.

Just include the space name and number, total regularly occupied space, compliant space at 9am, compliant space at 3pm, total compliant space. I also include the file name of the results that are uploaded for that space. Final calculations at the bottom.

Look in the Reference guide for LEEDv 2009 in EQc 8.1 and there is an example calculation result.

Jos,

Recently the Supplemental Daylight and Views Calculations spreadsheet has been updated and is much more robust now. I find it works well. It is available under credit information -- credit resources in LEED-Online. The latest version of this spreadsheet is only available if you are using the latest version of the form as well (generally v03 or higher) and it can be used for IEQc8.2 too, which means fewer uploads and more consistency.

hi Emily, thank you for this update :).

The area of and close surrounding area of the reception desk must be included. The rest of the lobby can be excluded. All circulation areas, such as corridors and hallways can be excluded.

Can either of you help me out with understanding the 10% area exclusion option mentioned?

Jill did some digging on the templates and PIF forms and could not find a 10% exclusion option.

Robin,
What time of day did you take the measurements? I'm assuming they were done recently, in Oct or Nov? What is the transmission of your glazing? Do you have any shades or other glare protection and are they in place when you are doing the measurements? You need to have your glare mechanisms in place when you do your measurements. Are they automated? If you're shades are automated, you are excluded from having to be under the maximum. Are you taking the measurements in direct sun?

Your measurements are not outside of the normal range of direct sunlight. The swing is normal too.

For my own interest, do you feel there is too much daylighting and/or do you feel there is glare? I say "feel" because these things can be somewhat subjective. Your eyes might give you a different feeling from your light meter and your neighbor.

This is a good example of why the credit requires daylight to have glare control and be within a range of footcandles (min AND max.) Glare and over-lighting are the two main enemies of good daylighting. As you are over the max. fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. limit, it is unlikely you'll be able to swing the review team. What type of activities occur in the building? The only thing I can see that might convince them is if the activities require the amount of light you're getting per the IESNA Handbook. Which, in my recollection, is detailed surgery or hand drafting!

Close the blinds and retake the measurements early or late in the day (since this version of LEED doesn't prescribe a date or time to take measurements).

Let us know how it goes!

Hi Jill,

Thanks so much for your reply. The reference guide doesn't say that the glare control needs to be down when the measurements are taken so I had originally taken them will all of the blinds (manual and mechanized) up. I took the readings on September 7th from 11:30 - 1:30. There are blinds on every window, manual in open office areas for occupant control and mechanized on windows above head height and at the clerestories. Not sure what the TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. is for the existing glazing- it's definitely not clear. I will take the readings again with blinds down - ugh!!

The users are computer programmers and they keep the blinds down all the time. Amazingly, the space doesn't feel overlit even with the shades up. It feels really great. It was bewildering taking the readings and having them be so high because it feels nice in the space - not like your standing on the surface of the sun! :)

We have had zero complaints from what is a very sensitive user group with regard to light levels and glare. This tenant is very attuned to their employees comfort and have already sent out surveys soliciting this kind of feedback from them. Everyone LOVES the daylighting. No complaints about glare or light levels.

Our lighting power reduction, including the task lights is 46% below ASHRAE. I know they are saving more than that becasue the lights are only on for an hour in the morning and a couple of hours at the end of the day (especially this time of year). Great success story for daylighting - hopefully the second round of measurements will reflect this!

Any thoughts on an acceptable fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. range I should look for with the blinds down?

Thanks again for your help!!!
Robin

You're right, it doesn't say if the blinds should be down or up. This to me means it is your choice. Glad to hear this level is acceptable and there are no glare problems. The only other thing I would double check is that your meter is on fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. and not luxMeasurement of lumens per square meter.. I can't say what to expect for the blinds down because I don't know the transmittance of the blinds - hopefully below the 500 fc. Great job on the lighting power density. Good luck!

People will be more acceptable to higher daylight levels then electric lighting levels. So 50fc of electric lighting on a surface may seem glary or even too much, but daylight levels of 50 or even 100 are perceived differently and are more accepted. We are animals, therefore natural occurrences are accepted by us.

Two stories worth of glazing along with a bilateral lighting condition is the reason for such high illuminance levels. Typically one would not have that much glazing for computer use. I would look at levels with the blinds half down to be similar to single story glazing.

The reality with LEED is that not every project can earn every credit nor can every credit be tailored to meet every type of project or condition.

Hi Michael,

This credit focuses on "regularly occupied spacesRegularly occupied spaces are areas where one or more individuals normally spend time (more than one hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building.." So, you would not include the area of the walls... unless they are movable and some of the time may be occupied area?

Your not missing anything, what you are getting is the frustration with the prescriptive method. It is a formula, that does not consider climate, site orientation, interior reflectances, etc. It is meant to be used by projects, and you are correct, to reduce over or under daylighting space. Projects that ignore all apsects of daylight and create glass boxes will have a hard time meeting the prescriptive path. We have projects that meet LEED requirements through simulation, and actual measurements that would not have earned the credit using the prescriptive path. If we would have designed the space to meet the prescriptive path requirements, it would actualy be under daylit. North facing spaces in cloudy climates require more glazing and higher VLTs. If you truly want to daylight a space, then simulations or models is the best option.

Have you tried multiple zones in a space

What do you mean by there will be a problem with the sensor file? You can either create a sensor file using a text editor manually based on what you want your sensor coordinates to be or the SketchUp plugin su2ds will automatically create one for you based on the plane and spacing you define. See http://code.google.com/p/su2ds/

I want to say Daysim is your best bet but Sept 21 9am and 3pm may or may not be clear sky conditions (as the credit vaguely requires) depending on the weather conditions in the weather file. Directly in Radiance you can define the sky condition you want. IES-VE might be a good candidate.

Thanks Ramana. I now have the Sketchup plugin that will allow me to automatically create the text file.

I'll look into Radiance and IES-VE.

You're welcome Susan. AGI 32 is another tool that comes to mind.

Exporting to Daysim will give you Daylight Autonomy, which is based upon a year's worth of sky data for a location. The requirement is for a specific time and time condition, which Daysim does not create.

I would export your model into Ecotec, and then export to Radiance. Ecotec automatically creates the sensor file which is then used in Radiance and Daysim. You will be able to specify date, time, and sky condition in Radiance. However, your units will be in luxMeasurement of lumens per square meter., so you will need to revise the input lux data, which you write a simple formula in the calculation grid import table. This will convert your lux to footcandles. You could also leave it in lux and explain the levels to the reviewer.

Susan, as you can see, daylight modeling is nearly as complicated as energy modeling. Do you hire out for energy modeling? I would recommend the same for daylight modeling. Once you figure out all that is listed here, you still need experience to help you understand the results. Why spend your time and money on training and software when it is a small, specialized portion of your project? Plus, you will develop relationships with these experts who are also experts in glazing and lighting.

At first glance, it sounds like your meeting rooms, private offices, and open office areas would be regularly occupied spacesRegularly occupied spaces are areas where one or more individuals normally spend time (more than one hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building.. If the kitchenettes, lounges, and printing rooms are not places where people stand or sit to do work, they are typically excluded. Print/ copy rooms where people go to pick up prints and office supplies would not usually be considered "regularly occupied" whereas a high-volume printing room where people operate the machines as part of their job probably would be considered occupied.

For the open office areas, I think it's most common to include the circulation areas in and among the workstations, but exclude the main circulation area closest to the core.

You may get different results with a daylight simulation or by taking measurements with a light meter - the prescriptive method is a pretty rough approximation of actual performance and the least accurate.

A LEED interprestion on a different, but related topic on 6/26/01 states that the area between work stations in an open office should be included in the regularly occupied space, but the corridors or transitions spaces that go around this area are not. It would be difficult to calculate using the prescriptive approach and exclude the area between cubicles.

I agree with David on this and on the assessment of the other spaces. The prescriptive method is meant to be quick to use but isn't as accurate, telling or "giving" as the other methods.

Hello Tobie,
Yes, you can use the simulation method for one area and the prescriptive method for another. Document both methods as you would if you were doing them individually. It might be helpful to note on the plans "See prescriptive method for this area." Then, just submit some sort of summary table that lists the area that complies (an all or none for your prescriptive method spaces and the actual portion for your simulated areas). Take this divided by the total ROS and if that % is over 75, you have achieved one point, over 90 is two points.

Is that what you were asking?

Yes, that's exactly what I needed to know. Thanks!

The prescriptive path cannot be used to calculate borrowed light conditions such as yours. You will need to use a combination of methods.

Borrowed light came up for me as well. Is there a free software that can support modeling borrowed light?

Radiance is free and will calculate borrowed light in accordance with LEED requirements. However, there is a large learning curve.

Radiance will need to be used in conjunction with another program. Daysim is also a free program, it has a large learning curve unless used in conjunction with other programs. You can use Google Sketchup which has a plug in for Daysim. Both are free, sketchup is easy to use and the plug in can be a little hard to get it to work right. SPOT ( Sensor Placement Optimization Tool) is also free but i believe it cannot do borrowed light scenarios.

Radiance can be used on its own with a Unix machine.

Jill,
I stand corrected, you are right about that it can be used as a stand alone program.

There is also Desktop Radiance for Windows machines, but all versions do have something of a learning curve.

The 2.2 Reference Guide lays out the guidelines for actual measurements. The protocol for taking measurements is outlined in the LEED-NC v2.2 Reference Guide which states that measurements must be taken on a 10-foot floor grid for all occupied spacesOccupied Spaces are defined as enclosed spaces that can accommodate human activities. Occupied spaces are further classified as regularly occupied or non-regularly occupied spaces based on the duration of the occupancy, individual or multi-occupant based on the quantity of occupants, and densely or non-densely occupied spaces based upon the concentration of occupants in the space. and must be recorded on building floor plans. Per the daylight modeling protocol, measurements should be taken 30” off the floor, under clear sky conditions at noon. Please document the time of year the measurements were taken. Calculations should be taken at solar noon. This is the time of day that divides the daylight hours in half (between sunrise and sunset). Using this definition, daylight savings does not need to be taken into account. Since all measurements can't possibly be made all at once right at noon, take them within a reasonable timeframe before and after noon (i.e. between one hour before noon and one hour after noon) and do not take measurements in direct sunlight. Records of indoor light measurement must demonstrate a minimum daylight illumination level of 25 footcandles.

Hi Susan,
The more detail the model, the better the result. In addition, it also increases the modeling time.
Typically, the furniture should be included if the furniture has a significant impact to illuminance level. Typical chair and regular high desk may not affect significantly overall illuminance level. However, You may consult with your daylight consultant for further discussion.

I was under the impression that circulation areas in open offices would be considered part of the regularly occupied space. Given the additonal glare control provided by the shades, including the circulation area in this case may be consistent with the credit intent. Often there's a temptation to gerrymander the regularly occupied area because there's not enough daylight, which doesn't appear to be the case here. I'm interested to hear how others would interpret this!

In my knowledge, the prescriptive method has many inaccuracies. Therefore it will be difficult to discuss. You may see my discussion with Christina Agudelo in same credit in LEED NC 2009.
Regarding your question, I will see the only method is by doing daylight simulation.

The prescriptive path does not allow for the consideration of exterior or interior shading devices. If you truly want daylight to be a part of the project and you are not just chasing LEED points, it is highly suggested that simulation methods be used to provide occupants the best quantity and quality of daylight. There are alot of free daylight simulation programs available.

Todd, could you tell me where I can find these free daylight simulation programs? My project is in Revit 2010, would that be a problem for the daylight programs?

Leslie -

I am also having trouble with WFRWindow-to-floor ratio (WFR) is the total area of the window (measured vertically from 30 inches above the finished floor to the top of the glass, multiplied by the width of the glass) divided by the floor area. (window to floor ratio). I have a tenant fit-out and each of my offices have two standard size windows in them (approx. 3' X 6') and my offices are average size offices. However they do not fall within the .15 and .18 requirement. I seem to not have enough floor area for my windows. It seems very contradictory for the intent of the daylighting credit. I have both fixed exterior shading devices and interior roller shades. We meet all the energy requirements so I'm having a hard time figuring this out as well. What did you end up doing?

Don't get me wrong, I understand why they have the WFR requirement but in situations like these, I don't understand why the square footages of the offices can't count at all. Please any input would help. Thanks.