Designing for Daylighting
For more LEED-specific information on daylighting, please see LEEDuser's IEQc8.1 guidance for : NC-v2.2 | NC-2009 | CS | Schools | CI | EBOM IEQc2.4
In addition to making your space more pleasant visually, daylighting reduces the need for electric lighting. As long you avoid excessive solar heat gain, reduced electric lighting also reduces cooling loads. Studies suggest that occupant health, student test scores, office productivity, and retail sales all benefit from daylighting.
Designing for daylighting calls for an integrated approach beginning in early planning phases and factoring in issues including building geometry and orientation, passive solar gain and loss, glazing specifications, reflectivity of interior finishes, lighting power, and lighting controls. Daylight modeling or daylight measuring are excellent tools for optimizing daylighting in a...
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Modeling energy savings from daylighting & control system
I am working on a project with daylighting and a lighting control system. I'm trying to find guidance related to properly take credit for reducing lighting power via daylighting under the Energy Performance - whole building energy simulation method.
ASHRAE 90.1 2007 Appendix G, Table G3.1, Section 6, Lighting states: "Credit may be taken for the use of automatic controls for daylight utilization but only if their operation is either modeled directly in the building simulation or modeled in the building simulation through schedule adjustments determined by a separate daylighting analysis approved by the rating authority."
90.1 seems vague on what level of schedule adjustments are required. For instance we could run a single daylight analysis at noon in the middle of summer but that would not address the change in daylight available to reduce lighting power throughout the entire day and year.
I need to verify how detailed the schedule input into the energy model from a separate daylight analysis needs to be (ie every hour; daily; monthly etc) to ensure compliance and maximize lighting energy savings.
An excellent question. Let us know if you come up with an answer. The text also does not address what target light level to use.
I would use my own experience with lighting design in combination with the IES Handbook to come up with target light levels. I would then do calculations on a 2-hour basis for the summer and winter solstices and the equinox and then break up the year into seasons. Since they give no other guidance, I don't know how they could complain about it. Good luck!
In discussion with the energy modeler's in the office you would be best off finding a energy sim program that models this. Otherwise you need to perform and exceptional calculation. To answer the daylight simulation part, would need to provide at least hourly results if you were to use your described method. Not sure what simulation program you would be using, but to provide hourly results, year round, to justify the savings, you;ll need to go with Daylight Autonomy and extract the daily and hourly information.
Good to know, Todd. Do you mind offering where it is you found the hourly requirement? And, do you know if reviewers require a specific 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. requirement or do they allow the designer some leeway?
What software do you use, Keith? Some of the energy modeler softwares are capable to do daylighting impact with its certan limitation.
Eddy, I believe even if your energy modeling software can measure daylighting impact, you still need to set the time increment and target light levels. Or am I misunderstanding?
Jill,
In discussion with the energy modeler's, they are saying that an hourly requirement is based upon the requirement in Appendix G that an energy simulation needs to be 8,760 hrs long. It really is not a requirement but makes the most sense to use. Basically, in trying to use the a methodology as first asked, it is really based on logic and using a very conservative method. It is better to use a program such as E-quest to document this rather than perform a separate exceptional calculation. They highly recommended that if this method is used, that it is well documented.
Jill, yes, you can to set the ballast type, schedule (lighting schedule and the occupancy) and target light in the energy model. Even, you can analyze potential glare as well based on the illuminance level. I haven't used Equest for a while, but if you have more detail questions, I could try to check again. OpenStudio with EnergyPlus engine is also good one if you want to check the relationship of the daylight and energy.
My point was that even if your modeling software has the capabilities, which many of them do, I was suggesting that Keith's question was more about what the rules are from the USGBC for what to set these variable to in order to ensure a level playing field for everyone using this method. As far as I know, there is no LEED text specifiying this (for example 1 hour increments at 25 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.), as he points out. We are all just making recommendations on what we would do.
Design of the artificial lighting
Hi,
My question is linked to daylighting and also not. It has been put to my attention that in LEED it is not obvious to find out what are the base requirements for artificial lighting? Indeed, we take into account daylighting levels and design, LPDLighting power density (LPD) is the amount of electric lighting, usually measured in watts per square foot, being used to illuminate a given space. requirements from the energy credits, and what else? I mean we currently work on a double certification that aims at both LEED and the French label HQE. The latter defines clearly base requirements for artificial lighting design (following standard NF EN 12464-1 including requirements such as color rendering index and so on). I can't find any reference to such requirements in LEED. Is it normal? Is there another reference to a standard that I did not see that would likely to be a prerequisite?
Thanks,
No, you are right. There are no other prerequisites or standards than the energy codes for lighting.
There are credits for lighting controls.
There is only a pilot credit in lighting quality that you check.
IEQ Credit 8.1
I am currently working on calcs for the daylighting 8.1 credit. Looking at the side-lighting daylight zones: 'zone floor area' - Is this 'zone floor area' basically just the width of my window multiplied by the daylight zone (or 2X the Height of the window)?
This question might be better addressed if it is posted under the "LEED Credits" heading, under the version you are working on then under the specific credit.
Make sure that this calculation option applies to your space since it actually applies to very few realistic spaces. For example, if your space is non-rectilinear or your space accesses daylight through another space you can't use this method.
In May 9 2011 an addenda came out removing reference to all of this business about "daylight zone" and 2X the head height since it has nothing to do with the calculations. The best way to do it is to use the room walls. If there aren't any or you have to break up your room due to differing window sill or head heights, pick a point directly in between. Then, if your number comes out below 0.150, divide the number by 0.150 and multiply by the floor area. This gives the percentage of that area that complies. You never have to report the width or length of your area. If it is above 0.180, according to LEED, you are over-lighting your space and none of the area complies. If you are between 0.150 and 0.180, all of the area complies. You may want to and are perfectly allowed to play around with these boundaries to your advantage.
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