Committee on the Environment

How do we communicate the benefits of daylight harvesting to a client?

Daylight harvesting, done right, will require controls that normally the client is hesitant to invest in, but this is one area where the pay back, often is less than 3 years.

So, communicating the potential for daylight harvesting is key to convincing the entire team to buy in on this. I find simulating the various lighting scenarios essential to the success of this technique.

Here's a simple 5 step simulation approach I use to communicate the potential savings.

http://visualizegreen.posterous.com/visualizing-daylight-harvesting

What are your thoughts? Have you used other methods to communicate daylight harvesting?

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Premnath Sundharam AIA
Senior Associate
DLR Group, Inc.
Phoenix AZ
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These diagrams are very helpful, however, do you also run a scenario to try to predict $ savings?

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Gail Ann J. Goldstead AIA
Wheaton IL
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Hello Gail,

Predicting energy savings through daylight harvesting can be done in one of the following two ways. Both has its advantages and disadvantages.

1. Simple fixture count and amount of fixtures potentially turned-off due to daylight. Using the difference to predict electrical lighting energy savings
2. Using an energy modeling program to predict electrical energy savings due to turned-off fixtures as well as heating and cooling energy impacts

I lean towards method 1 during early schematic design stages.

Let us say, the simulation is for a school, I will perform these tests for classrooms with different orientation. Then based on how many fixtures I can turn-off in each classroom, I just do a simple math and calculate the total watts saved per day and eventually per year.

Assuming a flat utility cost per kwh, I can then estimate a simple electrical energy savings due to daylight harvesting. This is typically, a good start for early schematic analysis.

The disadvantage of method 1 is:
1. Obviously, it is not taking into account the impact on heating and cooling energy
2. You are assuming the savings based on an average day (equinox), so the actual savings could be different

Advantages of method 1:
1. It is fairly quick and that is what you need during early design stages
2. It helps decision making, since you can figure out rough pay back and convince your owner. Caution: I tend to underestimate the potential for savings using this method to give me a factor of safety.
3. Skill level required is basic to intermediate

Second method, using energy modeling program is rather complicated and needs advanced skill level, but it will bring our prediction closer to reality. The program I would use among others is IES VE, since it can automatically turn off the light fixtures as daylight levels are achieved and it will also incorporate heating and cooling impacts, peak demand charges from the utility rates into the equation - so you get a much truer picture.

Often times, I have found that if you start your design with good basic principles of orientation and appropriate glazing types for your climate, your method 1 prediction will be close to your method 2 prediction.

Hope this is what you were looking for.

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Premnath Sundharam AIA
Senior Associate
DLR Group, Inc.
Phoenix AZ
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Original Message:
Sent: 09-27-2011 08:06
From: Gail Ann Goldstead
Subject: Visualizing Daylight Harvesting

These diagrams are very helpful, however, do you also run a scenario to try to predict $ savings?

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Gail Ann J. Goldstead AIA
Wheaton IL
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I also use AGI32 for nearly all of my lighting design work.  Not only is it an incredible tool for designing lighting layouts that do not overlight spaces and thus waste lots of energy, its the easiest and fastest way to predict and demonstrate daylighting contribution to a space.  (as demonstrated)

It is very useful to obtain NOAA (National Oceanic and Atmospheric Admin) percentage of possible solar data for calculating savings from daylighting.   I try to use monthly data, so that potential monthly savings can be calculated.  The data clearly shows that some winter months have a lower % solar potential, but that many months are quite good, even here in Vermont.  It's a good idea to simulate not only the maximum solar contribution for Sept/Mar, but also for Dec and June when solar angles are significantly different.  NOAA's web site is www.ncdc.noaa.gov.

Collecting weather data ..... just one more critical function of government that many people don't think about. 

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Donna Leban AIA
Light/Space/Design
South Burlington VT
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Original Message:
Sent: 09-27-2011 08:06
From: Gail Ann Goldstead
Subject: Visualizing Daylight Harvesting

These diagrams are very helpful, however, do you also run a scenario to try to predict $ savings?

-------------------------------------------
Gail Ann J. Goldstead AIA
Wheaton IL
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