As adoption of dimmable lighting grows, task tuning, a lighting control strategy, is becoming increasingly viable as a way to save energy while increasing occupant comfort.
Also called “institutional tuning” and “high-end trim,” task tuning involves reducing lighting in a space based on IES-recommended maintained task light level requirements or user preference for individual spaces rather than the originally designed maintained light levels, which may be higher than needed.
Dimmable lighting can still be controlled as usual to implement other strategies such as manual control and daylight harvesting. However, with task tuning, the high-end level is capped, resulting in permanent savings through dimming.
As lower light levels are the tradeoff of energy savings with task tuning, it is ideally suited to overlighted spaces, and works best for occupied spaces when tuning is adjusted based on occupant feedback.
From an economic point of view, it is also ideally suited to dimmable lighting already installed or intended to be installed, as the cost of implementing task tuning becomes marginal depending on the control system being utilized. This includes spaces with dimming ballasts, such as daylight harvesting control zones, and a majority of LED luminaires, which are dimmable as a standard product offering. If the LED lighting is operated by an intelligent control system, task tuning can be implemented with more flexible zoning down to individual tasks.
According to a meta-analysis published by Lawrence Berkeley National Laboratory in 2011, in which 88 papers and case studies were analyzed, institutional task tuning produces an average 36 percent energy savings. LBNL included task tuning controls plus ballasts with a more flexible range of ballast factors, group controls, and lumen maintenance controls.
What’s more, it is understood that dimming reduces internal operating temperatures of LED devices, which can preserve lumen maintenance and therefore contribute to longer service life.
The Minnesota Department of Commerce went farther to evaluate the energy-savings potential of task tuning in commercial buildings. The state engaged consulting firm Seventhwave, which selected 17 office, public assembly and education spaces in Minnesota and Wisconsin for a study.
The firm measured energy consumption and task light levels and isolated seven spaces that were overlighted. In these spaces, Seventhwave measured energy consumption for the existing and lighting and control systems, implemented task tuning based on recorded and IES-recommended light levels, and then measured again to produce energy savings estimates.
% each space was overlighted relative to IES recommendations. Image courtesy of Seventhwave.
The researchers determined that task tuning generated an average 613 kWh of energy savings for every kW of lighting found to be dimmable, or about 22 percent. Energy savings by space, however, varied widely from 5-36 percent depending on the space characteristics.
Distribution of measured energy savings resulting from task tuning. Image courtesy of Seventhwave.
Energy savings tended to correspond favorably with overlighted spaces, large dimmable lighting loads with long hours of operation, lighting and control systems that were not commissioned by the owner, and systems that were designed by a contractor and not a lighting designer or engineer. (Task tuning implemented with dimmable lighting designed for A/V presentation spaces, however, did not produce satisfactory savings.)
The energy savings, while significant, are not enough to justify the cost of a dimming control system. In applications where a dimming control system will be or has been installed for other purposes, however, task tuning can be very cost-effective as the cost may be limited solely to the time associated with task tuning. Seventhwave estimated the cost of task tuning in the studied spaces to be $0.03 to $0.06 per sq.ft., resulting in a simple payback of 0.5 to 1.1 years. For this reason, task tuning is ideally suited to new construction projects where a dimming control system is being planned as well as existing projects in which a dimming system is already installed.
As task tuning poses a tradeoff between light levels and energy consumption, time must be taken to ensure occupant satisfaction. The researchers recommended incorporating occupant feedback into the tuning process, though this may require a little more time.
Task tuning is a viable, cost-effective lighting control strategy that can be implemented in tandem with other control strategies for dimmable lighting. As dimmable lighting, particularly intelligent LED lighting, becomes increasingly adopted, task tuning may continue to gain adoption as a means of producing energy savings in overlighted spaces.
For more information about the Minnesota task tuning study, visit the Seventhwave website here.
Leave a Reply