Integrating lighting and HVAC retrofits
The renovation of lighting and the HVAC system in an existing building can greatly reduce energy consumption and greenhouse gas emissions.
There is approximately 80 billion sq-ft of commercial floor space in the United States, and this number is expected to grow to more than 100 billion sq-ft by 2030, according to the Buildings Energy Data Book published by the Dept. of Energy. More than 80% of the commercial buildings in the United States were constructed prior to 1990. Unfortunately, there were no mandatory restrictions on energy consumption in commercial buildings until the Energy Policy Act of 1992 was passed, which made following ASHRAE 90.1-1989 mandatory. Consequently, many of these older buildings consume large amounts of electricity due to inefficient lighting and HVAC equipment.
By 2030, more than 75% of the commercial buildings will have been in existence since 2010 and more than 60% from 1990 or earlier. Renovation of these inefficient buildings can help significantly reduce national energy consumption and lower the amount of greenhouse gases emitted from electricity generating. So while future energy goals like the 2030 Challenge are very important in new construction, it is also crucial to recognize that there is a significant amount of energy savings to be realized in existing construction.
Lighting and HVAC equipment are major consumers of electricity in commercial buildings. While responsible design of new facilities is critical, renovation of existing facilities also can greatly reduce national consumption and greenhouse gas emissions.
According to the DOE’s Buildings Energy Data Book, more than $200 billion is annually reinvested in existing buildings for improvements and maintenance. It is critical for designers to maximize this reinvested money by applying energy-reduction techniques and selecting equipment that maximizes the investment for the future.
HVAC energy-reduction techniques
There are numerous innovative HVAC techniques that can help reduce a building’s overall energy consumption, but the ideal solutions for each building will vary depending on the building’s existing HVAC system. Among these solutions: the proper maintenance of the HVAC system (changing filters; replacing defective/missing insulation; cleaning heat exchangers and cooling and heating coils; and repairing leaks in equipment, ductwork, and piping); installing variable frequency drives (VFDs) where applicable; replacing old, inefficient equipment with higher energy-efficiency ratios (EERs); using either water- or air-side economizers; installing CO2 sensors to allow for reduction of outdoor air; replacing old motors with high-efficiency or premium motors; or using a BAS to ensure the system is operating properly.
One simple solution would be to implement VFD where possible in a particular HVAC system. Over the past few years, the prices (and sizes) of VFDs have drastically been reduced, allowing them to be used much more frequently with a much better payback. They have become so cost-effective that installing them on motors as small as 1 or 2 hp can payback in a relatively short amount of time. Proper engineering judgment should be used, as certain motors are not meant to operate by a VFD and certain HVAC systems are meant to be constant volume.
A second solution would be to install CO2 sensors in densely occupied spaces. These sensors can detect the concentration of CO2 in a space and relay this information to the BAS. The BAS can then send a signal to the damper controlling outdoor airflow to that space. The signal can modulate the damper to reduce the quantity of outdoor air supplied to that space below the code minimum requirement based on CO2 readings. As an example, assume a conference room requires 250 cfm of outdoor air when fully occupied. Most conference rooms are frequently either unoccupied or only partially occupied. By using a CO2 sensor to determine how many occupants are actually in the conference room, and reducing the amount of outside air supplied via the BAS, a significant amount of energy savings can be realized by not conditioning the code required amount of outdoor air during this unoccupied time.
Another way to reduce the amount of energy consumed by HVAC equipment is simply to replace it. As HVAC equipment ages, it becomes less efficient because internal parts can wear down, creating more friction; it can become dirty or corroded; and it may even be susceptible to small refrigerant leaks. Another benefit to replacing old equipment with new is that ASHRAE 90.1 has increased minimum required efficiency on most types of HVAC equipment as of Jan. 1, 2010. A heat pump installed 10 years ago was not designed to meet to stricter standards set forth by ASHRAE 90.1-2007.
Taking the previous solution a step further, even more energy savings can be realized by replacing an older HVAC design with a newer, more energy-efficient system. Provided the project budget will allow it, implementing a new HVAC system such as variable refrigerant flow, chilled beams, under-floor air distribution, or even geothermal heat pumps can significantly reduce the overall amount of energy consumed. When paired with a dedicated outdoor air unit (DOAU), these systems have typically proven to be much more energy-efficient than a traditional variable air volume (VAV) air handling unit system. This is due to the large amount of outdoor air needed in a VAV system versus the DOAU, and the large amount of energy required for reheat at terminal boxes. Implementing an entirely new HVAC system in an older building can prove to be very difficult, as complications with the existing structure, ceiling space, power requirements, and phasing require proper planning prior to designing a new system.
Lighting energy-reduction techniques
Energy reduction in existing facilities can easily be achieved by replacing existing inefficient lighting products. Most commercial buildings built prior to 1990 typically are illuminated with T12 fluorescent, incandescent, high-pressure sodium (HPS), or metal halide lamps. These luminaires typically operate on inefficient magnetic ballasts when required by the lamp type. T12 fluorescent lamps are the only one of the four lamps mentioned above that is no longer viable, as they have been replaced with more energy-efficient T8 and T5 lamps.
As Figure 2 indicates, both T8 and T5 lamps produce substantially more lumens per W (approximately 100) than the T12 (approximately 60). One other advantage to the T5 and T8 lamps is their physical size. A T12 is 12/8ths of an inch, a T8 is 8/8ths, and a T5 is 5/8ths. There are advantages of this smaller lamp envelope; luminaires can be specifically designed around the lamp, allowing them to more easily control light distribution from the smaller source. This allows the luminaires to be more efficient at delivering the light to where it is intended. Simply replacing T12 fluorescent lamps with T8 or T5 can reduce the lighting load of a building by up to 40%.
Incandescent lamp and halogen lamps are slowly being phased out by energy legislation, but they still have several applications and therefore cannot be considered an antiquated lamp source like the T12. (Editor’s note: Suitable incandescent applications are not discussed here as they are not typically applicable to the majority of commercial buildings.) One location where incandescent is not practical anymore is for general illumination of commercial buildings. Removing incandescent luminaires and replacing them with the energy efficiency of T8, T5, or compact fluorescent lights (CFLs) can reduce consumption and maintenance costs dramatically. A typical 60 W A-lamp screw-in incandescent will produce only about 15 lumens/W versus the 100 noted above for T8 and T5.
In some cases, the incandescent lamps will need to be replaced by CFLs, which are not quite as efficient as linear T8 and T5 lamps but still produce about 60 lumens per W or four times that of an incandescent lamp. Use of LED luminaires also has gained significant steam over the past few years due to millions of dollars of federally funded research and advancement in the technology. LEDs can typically take the place of just about any incandescent lighting application and do it more effectively—and much more efficiently. While the future for LEDs is bright, how they are applied in retrofit applications should be carefully evaluated.
Commercial buildings primarily have metal halide and HPS lamps for large spaces such as lobbies, atriums, warehouses, and parking garages. Currently, both are viable solutions in many settings and can compare favorably to fluorescent in certain applications. One important aspect to consider is that metal halide lamps as they were five years ago (probe-start) are no longer available. Pulse-start metal halide technology improved on the efficiency of metal halide sources dramatically, and legislation such as the Energy Independence and Security Act of 2007 (EISA 2007) has all but outlawed standard metal halide lamps as they cannot meet the more stringent requirements.
Replacing old probe-start metal halide sources with newer pulse-start lamps can reduce energy consumption by up to 25%. To push these savings even further, electronic metal halide ballasts can be used to greatly reduce or eliminate energy loses in the ballast itself. HPS still has applications, but rarely inside commercial buildings due to its very poor color rendering (22 CRI) and warm color temperature (2100 K).
Warehouses, garages, and high-bay areas still have HPS lights. HPS is an efficient light source similar to metal halide but often is not perceived that way due to its “orange” color. When measuring light levels, HPS will produce light levels (measured by a photometer) similar to those of fluorescent and/or metal halide; however, they will not seem as bright. This is due to how the human eye functions at different wavelengths. The light produced by a HPS source is a longer wavelength (approximately 640 nm), which typically will be perceived by the rods in the human eye, and not the cones (which allow us to see color). This is referred to as scotopic vision, or night vision. When cones are not fully functional, such as under HPS lamp sources, objects seem to have no color or appear orange. While photometric measurements will be similar, some suggest that HPS lamp sources should have a reduction factor of up to 25% of this light output due to the poor color rendering and orange color temperature. This issue should be considered when retrofitting HPS spaces.
Beyond lamp and ballast combinations, lighting controls can be used to dramatically reduce energy consumption by lighting systems. In general there are three basic control systems:
- Occupancy control
- Time of day control
- Daylight control.
All three methods are effective means of reducing overall energy consumption and operating costs by automating the lighting systems. Automated controls allow building owners to avoid leaving lights on or having them on when natural daylight renders them ineffective. ASHRAE requires automated controls in all buildings larger than 5,000 sq-ft, so when retrofitting a building with a new lighting system, it is imperative that one or more of these techniques are used to be in compliances with the code.
Occupancy sensors can produce the greatest energy savings of all control devices in many applications. It is often a misconception that occupancy sensors turn on lights automatically because this is what we see, but in reality their function is to turn lights off automatically. There are several different types of occupancy sensors, each with its own specific applications. Every space in a building should be evaluated for occupancy sensors, and they should be used when possible. In space where occupancy sensors may not function, time of day switching via relays would more than likely be the next control device to consider. It is estimated that occupancy sensors can reduce the lighting load in commercial building by 30% just by automatically turning off the lights when a space is vacated. In private offices, restrooms, and storage closets, occupancy sensors can have a dramatic effect in reducing this consumption.
Time of day control allows building owners to operate their facility on set schedules. Typically time of day control is executed by a time clock and automated switching relay or contactor. Relays allow for much more flexibility than typical contactors and are recommended due to their longer life (more operations) and ease of control. Often relay-based switching (or dimming) systems will have an integral astronomical time clock that keeps accurate time for the building, adjusts for daylight savings, knows holidays, and can keep schedules. In buildings that are constantly occupied for set hours, such as office buildings, schools, and recreation centers, a relay-based time of day system makes perfect sense. While it is hard to quantify the energy savings using this type of system due to widely varying functions of commercial buildings, one thing is for sure: The lights will not be left on all weekend or all night in an unoccupied building.
Daylight control or daylight harvesting is another control technique that can have a dramatic effect on the energy consumed in a commercial building. In spaces where significant amounts of natural light are available, a daylight system should be considered. Using the sun as a light source is the most efficient way to illuminate a space, as it requires no electricity. Sunlight is not always available, so it must be combined with a lighting system capable of balancing the two. Photocells often are used to measure light levels in a space; if the natural daylight in that space is significant enough, the photocell will communicate this to the daylighting system and either turn off or dim the luminaires in that space.
The two ways to control light output from luminaires in a daylighting system are either by switching them on and off, or by dimming them. This is often a financial decision as dimming adds a premium to each luminaire in the system. There are payback advantages to using dimming; it will produce greater savings in energy usage over the typical switched system. While savings can greatly vary, correctly designed daylight switching systems will typically save about 20% of the lighting consumption and daylight dimming systems will be closer to 40%.
Multidisciplinary energy reduction
While HVAC and lighting system retrofits can have a dramatic savings in energy consumption individually, they also can have a synergistic effect on energy reduction. HVAC systems are designed to a cool a space based on exterior and internal heat load. One of the major components of internal heat load is generated by space lighting. When the lighting load is reduced via the use of automated lighting controls, HVAC equipment (i.e., fans, pumps, compressors) can be throttled back. So by reducing the lighting load in a building by 40% using occupancy sensors, the total amount of energy consumed by the HVAC equipment serving these spaces could be reduced by 10%. It should also be noted that when the overall lighting load for a building is reduced, so can the total capacity of HVAC equipment (i.e., a lighting load reduction of 20% can net an initial HVAC equipment cost savings of 5% to 7%).
BAS that control both HVAC equipment and lighting equipment can provide building owners with information that is monitored, recorded, and analyzed to determine whole building energy consumption. Data can then be used to maximize HVAC equipment efficiency and allow for adjustments as necessary to keep the building operating at optimal conditions at all times. Such a level of control can have a significant impact on reducing energy consumption, particularly in large facilities such as hospitals or campuses.
One of the benefits of new construction is that an MEP engineer is essentially working with a blank canvas and can design freely. In an existing building, however, typically numerous obstacles must be overcome when attempting to retrofit existing lighting or HVAC equipment. Many older buildings do not have the floor-to-floor heights needed to accommodate recessed luminaires, larger ductwork, and HVAC equipment. Because of this, alternative HVAC systems, such as a variable refrigerant volume system requiring much less ductwork, may prove to be a better solution. The existing structure may also limit the size of equipment that can be located within or on top of a building; it can also alter the routing of piping and electrical conduit throughout the building. In a building with concrete waffle slab, it may prove to be difficult to route ductwork, piping, and conduit vertically.
Another obstacle to overcome is attempting to meet current building codes with existing HVAC systems that are not compliant. As building codes progress over time to promote building safety and occupant well-being, and to reduce energy consumption, older buildings fail to meet several areas of the current code. Frequently in older HVAC designs, corridors were used as return air paths, but this does not meet Section 601.2 of the International Mechanical Code. Also, when using the ceiling space as a return air plenum, all devices in that space including cabling must be plenum-rated. This could cause issues with existing systems that initially were not planned to be part of a HVAC renovation, such as fire alarms or telecommunications.
A third noncompliant issue often recognized is the failure to properly ventilate the building per ASHRAE 62.1 standards. This applies to both the outdoor air requirements for spaces and the amount of exhaust air required from certain spaces. Another code issue worth mentioning is maintaining the fire-rating of the building. This can include adding fire, smoke, or combination fire-smoke dampers with smoke detectors in the areas that are renovated that may not meet current code requirements.
Determining how to deal with these noncode compliance issues can present some challenging obstacles to the design engineer. Of course, many code requirements are “grandfathered” into existing buildings, but once a renovation of any type takes place, these issues should be addressed. Suppose an older building uses the ceiling space as a return air plenum, but plenum rated cable was originally not installed. Does it make sense to replace all the wiring with plenum-rated cable, or should the return air path now be ducted? The economical ramifications, building occupant safety, and one’s professional judgment should be used to determine the best way to comply with building code requirements. It is also important to have discussions with the local code inspector and with the building owner to ensure that all parties involved are aware of potential issues.
When renovating existing buildings, especially those built prior to 1990, one must remember to factor asbestos abatement into the construction budget. Asbestos is a fibrous-like mineral that was used in many building materials (fireproofing, ductwork and piping insulation, and flooring), but was banned in 1989 because it has been proven to cause mesothelioma (a malignant form of cancer in the lining of the chest or abdominal cavities). It can be costly to perform thorough asbestos tests on building materials, and even more costly and time-consuming to properly abate it, but keeping the contractor’s staff and building occupants safe, avoiding work stoppages, and avoiding potential lawsuits make abetment a necessity.
There are countless methods to reduce energy consumption when retrofitting an existing building with new HVAC and/or lighting systems. Some methods will demonstrate a dramatic reduction in energy consumption with a relatively quick payback, while others will provide the building occupants with a safer environment and higher levels of comfort and control. Retrofit options—for example, switching from incandescent lamps with a life of about 1000 hours to fluorescents with a life of about 20,000 hours—can also drastically reduce maintenance costs. Existing buildings vary drastically by user and building type, but by understanding the existing conditions and project goals up front and choosing the appropriate critical design path, engineers can ensure that the HVAC or lighting retrofit has a dramatic impact on not only the amount of energy consumed, but more importantly on an owner’s wallet and the environment.
- Biada is project manager/mechanical engineer with Advanced Engineering Consultants, and Gray is a project manager/electrical engineer/lighting designer with Advanced Engineering Consultants.