Integration of lighting and HVAC systems: New technologies come of age
Driven by market demand to reduce operating costs, the combination of efficient lighting technology, versatile controls, and sophisticated modeling tools offers new opportunities to improve overall building performance.
The use of solid state lighting (SSL) products – specifically light-emitting diodes (LEDs) – in commercial lighting design represents one of the fastest technology adoption trends in recent history (IMAGE 01). With luminous efficacy reducing overall energy costs and projected life reducing maintenance costs, codes and standards now hold SSLs as the baseline efficiency for commercial lighting design in new construction and major renovation.
These electronic boards that provide light have introduced a host of new opportunities for advanced lighting control and integration with building systems. While previous designs consisted of luminaires separated from the lighting control systems that operated them, new technology is bringing those worlds closer together, making them one and the same.
In the same way that lighting specifications have changed, lighting control technology has changed as well. Distributed controllers and gateways now allow lighting and HVAC technologies to communicate without the cost, complexity, incompatibility, and physical limitations of previous designs, and allow the same sensor to actuate both systems. Furthermore, smarter devices allow smaller control zones, resulting in greater energy and cost savings.
Today’s building management systems (BMS), the necessary technology backbone for the simultaneous modulation of lighting and HVAC systems, have further developed to support deeper integration of building systems. Well-informed design, supported by the degree of verification made possible by today’s suite of modeling tools, can leverage these advances to realize the functional performance, occupant comfort, and operational efficiency represented by the best of lighting and HVAC technologies. In order to capitalize on these new technologies, we must first understand the fundamental changes that have occurred and the many new options available.
LEDs, fixtures, sensors, and control technologies.
LEDs differ from fluorescent lamps in how they operate: electrical energy is directly converted into light without the intermediate step of excitation in a gas discharge. As a result, they are able to turn on instantly and last longer, even with frequent switching. Their inherently dimmable operation makes them a “no-questions-asked” alternative to fluorescent. Where fluorescent dimming was previously significant additional cost, there is no additional fixture cost associated with the standard dimming of LEDs. These factors, along with their continuing drop in cost, make them prime candidates for use with advanced lighting control systems.
Sensors are getting smarter. Until recently, photocells had to be specified separately from occupancy sensors, and occupancy sensor technologies – such as passive Infrared (PIR), ultrasonic, and microphonic – had to be determined and specified depending on the obstructions in the space and use of adjacent spaces. In addition, auto-on/auto-off or manual-on/auto-off, and vacancy time-out/delay settings had to be programmed during installation via dipswitch or pushbutton. Because those adjustments often require a facilities person on a ladder and some disruption to occupants, sensor settings were rarely changed or fine-tuned once the space was in use. Smart sensors now incorporate a wide variety of sensing technologies, and in most network control systems have the capability to be addressed remotely via desktop or phone apps.
With the adoption of LEDs, many new lighting controls products have emerged in the market that utilize wired, wireless, or hybrid devices. The platform on which these various devices operate continues to be a struggle across the industry. Although 0-10V control has become an accepted standard, manufacturers have not widely accepted DALI (Digital Addressable Lighting Interface) as their standard platform for individually addressing luminaires. Most systems work with standard, non-proprietary 0-10V dimming drivers, so no customization of luminaires is required. While some companies offer control within the driver of the luminaire, others offer control devices that attach to each luminaire. In addition, many luminaires are now available with built-in occupancy sensors and photocells. To address the need to provide emergency lighting, UL listed emergency can be added to individual luminaires located in the path of egress or provided at the controller for zoned control. The relays force the luminaire to be turned on at full output during loss of power, but be controlled based on preferred settings during normal use. This range of devices, all integrated at the luminaire level, allows the luminaires to operate independently or in easily re-configured zones with more intricate control commands, resulting in greater energy savings.
When deciding on the sensor and controls approach, the design team must fully understand not only the energy goals of the building, but also the level of technology awareness of the people within it. By creating a list of detailed questions with which to engage the Owner, building users, and building operators, the energy goals for the building can be better understood. If this information is obtained at the beginning of the design process, the building energy model can to be tuned to better reflect the proposed energy usage of the building. For instance, what are the building’s hours of operation? Should all operation be fully automated, or will there be occupant overrides available? How long should lights stay on after no occupancy is detected? What minimum light levels are required during daylight harvesting hours? What are the size of control zones? Will areas be reconfigured after initial occupancy? Are shading devices also to be controlled?
With the adoption of networked control systems, facility-driven layered control strategies can be utilized. Advanced control strategies include lumen maintenance and task tuning. Lumen maintenance reduces LED output at the beginning of rated life and increases output over time to maintain a specified illuminance level as the source output depreciates. This strategy can save 30% in initial installation, averaging 15% savings over the course of the luminaire’s rated life. Task tuning (also referred to as high-end trim, or institutional tuning) reduces output and consequent energy use by tailoring the illuminance levels to the specific needs of the space.
However, while energy savings is a primary motive, there needs to be a balance between saving as much energy as possible and not creating annoyances that will affect occupant comfort and productivity - or create the desire to override the systems in place. For instance, the application of small lighting control zones with more intricate control commands in applications such as open plan offices can invite nuisance issues if range and cutoff angles of various sensors are ignored. Daylight harvesting has long been a way to save energy, but systems must be calibrated so that footcandle levels and time delays for shades and automated dimming are appropriate for the use of the space. A short time delay may save energy, but possibly at that expense of adversely affecting building occupants.
Whether a wired, wireless, or hybrid, system is selected, the BMS architecture is now able to directly tie zone sensors, switches, relays, and actuators straight to multi-purpose digital controllers, completely eliminating the need for individual system gateways for individual HVAC, lighting, and other building systems. Digital control systems are now able to interface directly with the BMS for simple on, off, airflow modulation, and light dimming commands. The rapid change and development of these separate, but co-dependent systems, has not only been fueled by the need to make our buildings increasingly more efficient to meet new code requirements, but by building owners wanting to streamline building operations. Previously, lighting control systems were often kept simple and separate to operate on their own since most building operators only knew how to operate the BMS system set before them. Now that lighting control can be simply integrated in to the BMS and controlled via a variety of different apps or from remote locations, the advantages to the overall building operation are significant and Owners are taking notice (IMAGE 02). As always, their successful implementation is dependent on a thoroughly considered, well documented design.
Modeling integrated lighting and HVAC controls.
With the desire to reduce carbon emissions and operating costs amplifying market demand and THE accelerating development of stringent codes and standards, prescriptive and performance-based design paths for building systems require new systems, controls strategies, and a higher level of system integration. To meet these needs, energy modeling provides design teams with a powerful tool for predicting how system design characteristics will affect energy use and cost, assisting in the creation of integrated building systems that can meet or exceed building performance targets associated with project program and budget goals. Particularly in an emerging opportunity such as integration of light and HVAC controls, energy modeling provides knowledge essential to making informed decisions.
Electric Lighting and Building Energy Models
Modeling integrated HVAC and lighting controls involves successfully representing three key components: electric power consumed by lighting luminaires when fully on; year-around utilization of these light sources, including their dimmed states and hours of operation; and, the heat gain from these sources at each time-step in the analysis.
Codes and standards concerning lighting energy use now prescribe solid state lighting as the base efficiency for lighting design. Consequently, both space-by-space and whole-building lighting power allowances are lower than they were in versions of design standards from the past decade. Energy analysts must ensure that the modeled lighting power density (LPD) inputs accurately reflect these more stringent standards.
Annual utilization schedules represent the predicted utilization for all the installed light fixtures. These include predicted hourly use based on space type and activity, and schedule modifications that may be necessary to model individual or integrated controls, such as time-of-day shutoff, the use of vacancy/occupancy sensors, and daylight-based dimming. A resulting use schedule that captures these energy conversation measures must be carefully developed to reflect anticipated real occupant/system interactions as much as possible.
With regard to heating/cooling loads, because there is no latent heat gain from luminaires, a fraction of the input electric power is assumed to result in instantaneous sensible heat gain only. Most energy modeling tools include the “Sensible Heat Gain Ratio” or comparable input (IMAGE 03) to model this. Typically, a luminaire placement input is also available, allowing analysts to specify how much of instantaneous sensible heat gain is absorbed by the room air, and what portion of it is carried away by room return/exhaust. Each of these inputs must be carefully selected to accurately model the radiative and convective heat gain in the space. It must be noted that although this heat gain results in increased cooling load, it has the opposite effect when designing and modeling heating energy consumption.
Reconsidering heat gain from lighting for LEDs
Heat gain from electric lighting fixtures is a crucial part of load calculations and building performance modeling. Most engineers and building analysts assume that all power supplied to luminaires is immediately converted to sensible heat gain in the space. Therefore, depending on the building type, heat gain from installed luminaires has traditionally accounted for as much as 30% of the peak cooling load and annual space cooling energy consumption. However, this assumption was based on the physics of heat transfer associated with incandescent lamps – with LEDs this must be carefully reconsidered.
In the case of incandescent lamps, approximately 4% of all input power gets converted to light energy in the visible light spectrum. The rest is lost to the space as instantaneous heat gain through convection to the room air (about 20% of total) and radiation emitted in the IR region. Therefore, although approximately 4% of visible light results in a delayed heat gain in the space, it is reasonable to assume that nearly 100% of the input electric power is instantaneous sensible heat gain. In the case of LEDs, however, about 50% of the input electric power is converted to radiation in the visible light spectrum (with a minimal IR component), and only the remaining input electric power is lost to the space in the form of instantaneous heat gain. Therefore, it is important to carefully consider the “Sensible Heat Gain Ratio” input available in most load calculation and energy modeling tools to avoid over-estimating the heat gain from LEDs -- as well as fluorescent lamps (IMAGE 04). Lighting and daylighting controls further reduce instantaneous cooling load from these luminaires and are seldom accounted for in cooling load calculations. More broadly-inclusive model inputs – combined with updated lighting heat transfer assumptions – become all the more important as passive design and net zero energy design concepts gain more momentum, most crucially in climate zones that allow a building to ride annual weather extremes with little, if any, support from active systems.
Challenges with Modeling Combined Controls
Integrated occupancy-based lighting and HVAC controls pose a modeling challenge because end use utilization schedules assume a greater significance. This is because lighting use schedules approximate the effectiveness of vacancy/occupancy sensors, but the operation of HVAC schedules is also governed by similar utilization based on similar controls. Adjustments made to lighting use that account for variation in room occupancy must therefore also apply to occupancy-based HVAC airflow schedules. A modified lighting schedule also impacts the projected savings from daylighting controls because the lights are switched on for fewer hours.
Driven by code and owner commitment to sustainability, most buildings today are required to implement complex combined control strategies involving: daylight-integrated lighting controls; occupancy-based lighting and HVAC controls; advanced fenestration systems with automated shades or electrochromic glazing; and, IoT applications, among others. Some of these strategies have been modeled individually for many years, but integrated controls sometimes require separate dedicated building models that seamlessly interface with one another to successfully capture system dependencies and synergistic impacts. For example, even advanced whole-building modeling tools are incapable of accurately modeling advanced dynamic controls for modern shading and/or glazing systems. To accurately model advanced facades, the analyst’s workflow must include dedicated daylighting tools that use raytracing techniques, include contemporary sky models, allow flexible geometry inputs, and model dynamic shading/glazing controls. These tools must also effectively pass illuminance and loads information to fairly complex building energy models capable of accurately simulating building loads and heat transfer phenomena, while providing sufficient flexibility to capture the effect of advanced HVAC systems controls.
Other modeling challenges include accurately representing real-world system interactions. Consider situations where vacancy sensors used in offices are left off by the occupant. Although the lights are turned off, the thermal zone must call for outside air because it is occupied. Therefore, integrated lighting and HVAC schedules must be developed cognizant of these differences.
Another potential issue involves the mismatch in lighting zone boundaries and HVAC zone boundaries. Four private offices may have individual vacancy sensors to control space lighting, but four such spaces are commonly designed to be served by a single VAV box modulating airflow to them as a single thermal zone. Detected occupancy in any one of the lighting zones will result in supply airflow to all four thermal zones. Staggered occupancy across all these zones at different times of the day could potentially result in diminished HVAC energy savings. Incorporating such nuanced details in an energy model, considering the capacities and limitations of distinct systems and their controls – as well as potential impacts of user variance – is increasingly possible for modeling practitioners using contemporary tools.
Installation and operations.
Certain caveats bear consideration for the design team to assure that the controls for an integrated lighting and HVAC system are implemented and operated as designed. While collaborating with the contractor early in the design process and stipulating that the installer be National Advanced Lighting Controls Training Program-certified, the specifications must clearly describe the intended operation of the system and include training of facilities personnel. To ensure that commissioning will be revisited after the opening of the building, specifications now also require a re-training session after 3-6 functional months of “learning the ropes” and observing practical implications of settings, with this training conducted by the manufacturer’s employee or representative who executed initial programming.
Just as analysis software has continued to evolve, so has the software that integrates and implements the lighting controls and BMS functions. A tile-based or floorplan-based graphic user interface (GUI), allows for more streamlined set up and commissioning than was previously possible and new apps allow for user interface while seated in the building, or at remote control from any distance away. These user friendly tools, will provide an outcome that will benefit both building occupants and facilities groups equally as a result of shared attention to setpoints that may need adjustment over time.
Previously, building occupants may have tried to override programmed controls and then compromised intended system performance. With operators now being able to easily reprogram locations where light levels are too low (daylighting calibration) or too high (too much light), or there is a frustrating occ sensor actuation (bad positioning), keeping the building tuned to the optimum performance at which it was intended to operate is much easier.
As stricter energy codes continue to be introduced and enforced the design and construction of high performance building is becoming standard practice in some parts of the country. A recently completed laboratory building in central California implemented a network control system utilizing a hybrid wired and wireless approach by combining lighting, daylighting, and HVAC zones to optimize controls.
Within a large open office area in the building, long suspended indirect/direct LED luminaires are controlled in 8’ increments with integrated sensors in each section. These sensors not only control the lighting but also the VAV boxes that are part of the mechanical system. As a result, the lighting and temperature within these larger spaces has become more granular, only controlling the specific areas that are detected as being occupied. While the daylit sections of the open office may ultimately require greater cooling in the summer, this becomes offset by the savings of reduced electric lighting. Smaller spaces are managed as single zone areas, particularly those that are infrequently occupied, such as break rooms and small conference rooms. Space types that fall between those extremes, such as private offices, can be tailored to a specific occupant’s preferred temperature and illuminance level.
No space size or type is excluded from this use of integrated network lighting and HVAC control technology. With appreciable benefits to occupants and continuing reduction in cost through further market adoption and competition, these strategies appear to be increasingly applicable across building types.