Commissioning:
A Neglected Opportunity
Commissioning:
A Neglected Opportunity
The map is not the territory. Actual and predicted lighting energy savings can differ significantly. One solution is commissioning-to check that the systems are installed and operated as intended.
The successful implementation of any energy-saving measure is a multi-staged process. It begins with identifying and analyzing possible savings opportunities. Promising candidates make it to the engineering and design stage and are finally installed in a new or existing building. But the process does not end with the flick of a switch.
When people have the courage to measure energy savings, they often find that the actual performance does not match the design calculations. This can occur if systems are not installed or operated as assumed by the designer or engineer who made the pre-construction energy use estimates. This "performance gap" can be dramatic.
Energy-efficient lighting improvements are particularly vulnerable to this problem. While some efficient devices need only be "plugged in", lighting measures typically consist of a complicated network of technologies: lamps, ballasts, luminaires, sensors, and controls, as well as special user interfaces.
To address the need for better continuity from the design through implementation phases, a new discipline in energy-efficiency has emerged. It's called "commissioning". Commissioning is a comprehensive process of reviewing design documentation, verifying installation, testing equipment and system performance, training building operators, and analyzing the operation of the new system. Entire conferences are now devoted to the topic, and some interesting examples have been documented in the case of lighting.
LIGHTING COMMISSIONING
Many things can run awry in lighting installations. For example, specifiers who fail to actually visit and inspect the building in question may instead work from out-of-date floor plans and (unknowingly) place photocells or occupancy sensors in inappropriate locations. A photocell placed too near or far from a window will not send the right signal to a dimmable ballast. An occupancy sensor placed behind a barrier may fail to "see" an occupant.
Another typical problem is that when occupancy sensors are installed, work crews are tempted to set them on the shortest possible cycling time (in order to test them quickly) and may neglect to reset them to a more functional level. Occupants will find that the sensors turn the lights off too often, and they may complain about the sensors or even take more drastic steps. In the US Energy Edge Project occupants of one office tied a string to a small fan and left it running to keep the occupancy sensor from turning off!
Special needs for commissioning arise when computerized energy management and control systems (EMCS) are linked to lighting systems. An EMCS can be set to periodically "sweep" through a building and turn off lighting. Common problems include sweeps not being fully enabled at the outset, local overrides that do not function properly, and sub-optimized zoning of sweep areas and their override switches.
In an illuminating case study, occupancy sensors in a 1000 square-meter building failed to save much energy during periods before and after the normal working day. The reason for this was that a guard came on duty each night at 24:00 and continuously tripped the occupancy sensors as he did his rounds. When the problem was discovered, new switches were installed that automatically turned lights off but required a manual "on" switch to override the sensors. When this problem was discovered, the new sensors finally began to save energy.
Lighting commissioning can make a real difference in energy use. On September 27, when the occupant sensors were installed, lighting consumed 68 kWh/day. After the occupancy sensor switching adjustment, consumption was reduced by nearly 10% to 62 kWh/day.
Keeping a close eye on energy data helped reveal another situation in which energy savings were being eroded in the building. New dimmable ballasts were limited to less than full light output. The intention was to increase the current as lamp lumen depreciation set in. But an electrician visiting the building unwittingly turned the centralized dimmer up to full, thereby increasing the lighting load from 6 kW to 7.5 kW (73 kWh/day). This problem was later detected by looking at the diagrams At the same time, nighttime energy use increased again. Upon investigation, it appears that this may be because the electricians installed incandescent lamps in a number of previously unlamped sockets in the building lobby (an area uncontrolled by the occupancy sensors).
DON'T FORGET RE-COMMISSIONING
Commissioning isn't only for new buildings. Various events can trigger the need for re-commissioning. For example, when offices are renovated lighting systems are often removed and updated. If office furniture is added or rearranged, the old lighting system may no longer be optimal. Activities in a building can also change. For example, if a food store is converted into a bank, the lighting needs will change. Even more subtle changes, such as when a drafting office changes from primarily paper-based drafting to computer-based drafting, can require substantially different lighting design. Even changing the windows or the color of the walls will affect the performance of a lighting system.
Evan Mills