Daylighting controls can be a very effective addition to automated building systems. Daylight harvesting — bringing in the maximum amount of daylight into an office space to reduce the amount of artificial light used in a facility — can be one of the most effective ways to save on electricity costs.

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I recently sat down (at least “virtually” — via email) with David Wilson, president of Lighting Control & Design, to get his perspective on this technology. This is a short excerpt of that conversation.

Sinclair: How do you see the current state of daylight harvesting?

Wilson: Just a few years ago, daylight harvesting was something people only talked about. But in the last five or six years, it has really moved into the mainstream. As with many new building technologies, the first systems lacked the proper feature set to accommodate the multitude of user requirements and varying building designs we encountered. Luckily, digital systems allow us to add and upgrade features swiftly.

Once the new feature sets were in place, we ran into the second major hurdle: collaborative design among disparate disciplines was missing. Typical issues included: unidentified ducting, which obstructed photocells, window treatments or awnings not reported to the electrical engineer (responsible for the lighting and daylight harvesting plan), mechanical shade or skylight louver integration requirements not communicated across divisions. Working with other manufacturers and specifiers has ironed much of this out.

Coordination is required across divisions for roofing, fenestration, electrical, placement of lighting, space planning (particularly room geometries), and even building orientation. Design issues had to be identified and ironed-out well before plans were ready for bid.

Sinclair: Were there other challenges?

Wilson: Once this was done (and it remains a constant struggle for all) the next goal became to quell a small tide of user concerns regarding local control. Daylight harvesting is by definition an automatic response of electric lighting to daylight. But to be truly successful, we found the needs of the room occupant for local control also had to be considered.

To solve this, we have developed what we call a “semi-self-regulating” user experience; in other words, we empower the room occupant to locally adjust lighting levels, within pre-defined boundaries. To meet the needs of multiple building types and customer requirements, those “boundaries” need to be extremely flexible.
The ideal daylight harvesting systems reflects a balance between the energy manager’s requirements for return on investment, and the HR manager’s concerns for occupant satisfaction (keeping in mind that daylight harvesting might save money in energy costs but a drop in morale can be expensive too!).

Most recently we see an increasing trend to tie-in distributed control strategies such as daylight harvesting, with centralized requirements such as building automation, power use trending, and even utility-side load-shedding. In other words, it’s important to have a holistic energy management strategy.

Sinclair: So how does this tie into demand response situations?

[an error occurred while processing this directive] Wilson: The times of the highest demand are of course when it is hottest and the sun is shining brightly. This works right into the daylight harvesting scenario, which reduces lighting power during these peak times. An obvious candidate for daylight harvesting is warehouses. These cover acres of space and are frequently lit with HID or fluorescent lights. Though many of them have skylights not all do, and not all have a control system. With as little as three per cent of the roof surface covered with skylights we have seen projects where all lights are turned off during daylight hours with totally adequate illumination within the warehouse. These customers, who usually do not air condition the warehouse, do not need some sophisticated demand response warning system since they are already turned down to the minimum.

A utility can initiate a load-shedding command as needed with a participating commercial power user. If that power-user also has a daylight harvesting strategy in place, a demand call for load shedding will be less noticeable as loads have already been reduced (depending on available daylight).

Sinclair: New buildings seem to be getting better in adopting this technology, but how about existing buildings?

Wilson: Here again we have a goal that can only be achieved by the interaction of companies encompassing different disciplines. We have been working with sky lighting companies that provide both Prismatic and Tubular skylights. They find application in different types of projects with some overlap. These companies run into the standard problem that they can provide the sunlight properly filtered to keep out the heat but until the lights are turned off there are no energy savings. We provide a distributed control system that places the points of control near the loads. This is frequently much easier to retrofit than using a centralized panel. Of course there are situations where a centralized panel works just fine. Such applications would be a factory or warehouse for instance which is installing new skylights. The distributed system is linked by data cable that usually does not need to be run in conduit. This simplifies installation while bringing each point under control. Networked photocells can measure the level of light at the work surface and adjust the lighting and sometimes the louvers that control the amount of light appropriately.

In conclusion I would say that we have only just started to realize the energy savings that can be accomplished. As controls become more of a commodity item and the populace become better educated in what they can do we will see more and more businesses become “net zero” loads on the grid.

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