ASHRAE Journal -November 2012 - B22

20 Relative Visual Performance (%) 18 16 Percentage of Dissatisfied 14 12 10 8 6 4 2 0 64 66 68 70 72 74 76 78 80

100 90 80 70 60 50 40 30 20 10 0 20 30 40 Illuminance (fc) 50 60 10 Point Font – High Contrast 10 Point Font – Low Contrast

Room Temperature (°F) This graph shows how dissatisfaction with the thermal environment changes as the room and room surface temperatures change. This plot is based on typical air movement, business attire, and a typical office work activity level. Dissatisfaction estimated from the predicted mean vote (PMV). (Source: Fanger, P 1973. .O. Thermal Comfort. New York: McGraw Hill Book Company).

The relative visual performance is a percentage expected performance while reading 10 point font under 100 fc. Ten point font is the lower limit for most printed office material. High contrast is similar to black print on white paper. Low contrast is similar to a newspaper article. Most offices and classrooms are designed to provide 50 fc at the desk level. As you can see, the illuminance can be dramatically decreased before a considerable decrease in visual acuity is expected. Adapted from: Rea MS. 2000. The IESNA Handbook. Ninth Edition. Illuminating Engineering Society of North America. New York.

Figure 1: HVAC demand response requires recovery time, which may affect occupant comfort and decrease productivity. In particular, making small adjustments to the lighting levels can result in optimal performance and system efficacy. For example, assume that a DR event relying strictly on HVAC curtailment does not go far enough to achieving energy goals or to realizing the facility’s requirement to generate an additional 100 kW in power reductions. The lighting system can deliver a 10% to 20% reduction over the course of 60 seconds to immediately deliver the required savings in a manner that is less intrusive and virtually undetectable to employees and other occupants in the space. This can be particularly important for buildings that attempt to generate 100% of their energy needs through renewable on-site generation, which is known to have inconsistent energy output. In another scenario, HVAC demand response may be so aggressive that the building environment becomes too uncomfortable, and the system is required to react equally aggressively to recover from the demand event, which elevates the potential for peak charges. An integrated strategy would enable the responsive nature of the lighting system to quickly offset the HVAC, and help to avoid peak charges. Using a single BMS with the ability to manage both lighting and HVAC allows the HVAC to provide the main adjustment and lighting to accomplish the fine-tuning.

Figure 2: Lighting demand response requires no recovery time and results in little change in comfort or productivity. ment to integrate lighting into the mix. The biggest hurdle to integration may lie in different electrical expertise. Traditionally, the specifiers, contractors, and installers who work with HVAC and BMS are mechanical in nature; those who work with lighting systems are electrical in nature, and neither has been comfortable in the other discipline. Today, this divide is less prominent, driven mostly by the changes in the specifications. Since 2004, the CSI Master Format has added “Division 25 – Integration” as the umbrella specification for all system integration requirements. Some lighting control manufacturers are embracing BMS protocols like BACnet instead of using limited third-party gateways. These manufacturers are embedding or making “native” BACnet in controls, and certifying devices to assure proper communication with independent agencies like BACnet Testing Labs (BTL).

New Opportunities in Lighting DR
Traditionally, lighting control has been about electric lighting, but there is largely untapped potential for DR strategies that control daylight in conjunction with HVAC. Integrating active fenestration systems, such as controllable window shades, controllable louvers, and dynamic glazing into the BMS management umbrella can significantly reduce or eliminate the heat contribution from solar radiation, which can be up to 93 W/ ft2 (1000 W/m2), while controllable window shades can also provide an air barrier for additional R-value. The interaction between these systems can greatly reduce the load on the HVAC system with minimal change to the thermal environment, but can potentially increase demand for electric light by reducing available daylight in the space. Ideally, a DR strategy will enable the user to simultaneously analyze, manage and adjust
November 2012

Specifying Lighting and HVAC to Work Together
Together, HVAC and lighting systems that are managed by a single BMS, seem to offer a DR strategy that most effectively achieves curtailment goals. Why, then, isn’t this combined strategy implemented much more broadly? In large part, it is a function of habit. Building management systems traditionally have been used as a front end to the HVAC system, and only recently, with the introduction of lighting control systems made with proper BMS integration features, has there been a moveB22

B A C n e t ® To d a y a n d t h e S m a r t G r i d | A S u p p l e m e n t t o A S H R A E J o u r n a l

ASHRAE Journal -November 2012

Table of Contents for the Digital Edition of ASHRAE Journal -November 2012