True Analytics™ - Energy Savings, Comfort, and Operational Efficiency
For some time now global warming or "climate change" has been the driver for various green-building initiatives. More recently attention has been brought to limitations in our energy sources. One result of these restrictions has been increased energy prices, and despite the increasing pressure for "fuelless" sources such as wind and solar, prices will remain high for some time to come.
Commercial buildings are an obvious place to reduce energy consumption because they represent approximately 18% of all energy consumption in the U.S. One goal is to produce buildings that are "zero net energy" – which means a building produces as much energy as it consumes over a period of time – a capability that obviously requires energy-generating capability in the building, but also requires substantially less energy consumption.
Achieving Energy Efficiency
We have been here before, starting with the OPEC oil embargo of the early 1970s. One response was the development and ratification of ASHRAE Standard 90-1975, whose goal was to reduce the energy consumption of buildings by 40%. The successors to that standard, up through 90.1-2007, have become steadily more stringent.
And yet, thanks to the relatively cheap energy we have enjoyed since, a significant amount of U.S. floor space today is not covered by even the simplest energy-saving strategies. And even where energy efficiency was intended, it's often not achieved due to system faults and system misconfiguration.
This will change. The Federal Energy Independence and Security Act of 2007, for example, calls for policies for new commercial buildings to be zero net energy by 2030. ASHRAE is developing a building labeling system similar to the one established by the European Union’s Energy Performance of Buildings Directive, seen below in Figure 1.
Figure 1. European Union’s
Building Rating System
Fortunately, there is significant research into, development of and experimentation with energy-efficient building, the results of which are codified in standards for energy-efficient buildings. And these standards enumerate the roles of the BAS in meeting mandates for energy-efficient buildings.
The Faces of Energy Efficient Standards
Several organizations have produced standards for energy-efficient buildings, but the best-known are ASHRAE and the U.S. Green Building Council (USGBC). ASHRAE’s Standard 90.1 is the baseline for the other standards, including ASHRAE's developing Standard 189.1P, “Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings.”
ASHRAE is also producing a series of Advanced Energy Design Guides for 30% more efficiency than Standard 90.1-1999. Already published design guides include K-12 schools, retail buildings, small office buildings and small warehouses. Design guides for 50% and 70% greater efficiency are in development.
USGBC and LEED
Meanwhile, the USGBC has published a series of Leadership in Energy and Environmental Design (LEED) standards, which also build on ASHRAE 90.1 and which, in terms of the role of the BAS in reducing energy consumption, are a superset of the other standards and design guides. The 2009 versions that have been through public review include Commercial Interiors, Core and Shell, Existing Buildings Operations and Maintenance, New Construction, New Construction: Retail, and Schools. Others in development include Healthcare, Homes and Laboratories.
In the LEED rating systems, points are awarded for a number of aspects of a building including the choice of site, reduced potable water use—meaning reducing the energy used to treat and move water—reduced energy use, recycling materials, reducing construction waste, improved occupant environment and so on. Most of the LEED 2009 rating systems identify a total of 110 points that can be earned: 40 points earn LEED certification, 50 points earn LEED Silver certification, 60 points earn LEED Gold certification, and 80 to 110 points merit LEED Platinum certification.
The methods by which LEED points can be earned are a superset of the recommendations in the ASHRAE 30% Advanced Energy Design Guides and the requirements of ASHRAE Standards 90.1-2007 and 189.1P (second public review version). This makes it useful to look at the LEED standards as guides to the various ways in which the BAS can be used to reduce a building’s energy consumption, though there is little novelty in each of the recommendations.
The collection of methods, the number of points and the specific requirements for similar points vary across the LEED standards, but they can generally be summed up into five categories: Potable water use reduction, lighting controls, occupancy and CO2 sensors, measurement and monitoring, and BAS.
Potable water reduction
Some purposes for which potable (drinking) water is used carry hidden energy wastage. A significant portion of U.S. energy usage goes into processing available water to potable quality and transporting it – only to have significant amounts of it used in applications for which water with a much lower energy investment could be used. For this reason potable water use reduction (PWR) appears in the LEED standards.
PWR seems an odd application for a BAS. However, building owners can take advantage of the BAS to provide the monitoring, control and recording capabilities needed to implement a PWR system. To earn these points, the building must be designed to collect rainwater, stormwater, air-conditioning condensates and/or greywater, and then use this water for applications such as flushing and irrigation instead of highly-processed potable water.
A PWR system obviously begins with a storage tank. But the water level needs to be monitored with a capability to switch over to municipal water when the tank level is too low. Pumps need to run when needed, and the runtimes of filtration units need to be accumulated for replacement at the appropriate times. In addition, a building can earn extra LEED points by metering and recording potable and non-potable water usage, and even “micro-irrigation” using moisture sensors.
All of this can be done independently of the BAS, but the engineering effort can be simplified using the BAS with a water level sensor for the tank, detection of water need by whatever mechanism is required by the system's design, and pump on/off controls. In addition, runtime accumulation is a common feature of a BAS, it becomes possible to use the BAS' alarm system report faults or maintenance requirements of the PWR system. A final advantage, if the PWR system elements are distributed, is to utilize the BAS networks instead of additional wiring.
By having a potable water use reduction, a building can earn 7 to 14 points toward LEED certification, depending upon the choice of LEED system.
It is necessary to check state or local laws before implementing such a system. For example, an old Washington State law asserts state ownership over all rain falling within its borders and collecting too much may be illegal. How much is not clear, but this law did not prevent the city of Seattle from using such a system in its new LEED Gold City Hall building.
Lighting controls appear in ASHRAE’s Advanced Energy Design Guides and Standard 189.1P as well as in the LEED systems. This is understandable because about 11% of U.S. electricity consumption is used for commercial building lighting. Specific identified measures include daylighting controls, individual controls for 50%, sometimes 90%, of a building’s occupants, non-emergency lighting dimmed or turned off during night-time or non-business hours—although the primary objective of the latter is not to save energy but to reduce the amount of light pollution cast by the building at night. Elements of these measures include the use of occupancy sensors for automatic turnoff, scheduled off times, and timed overrides.
Occupancy and CO2
Occupancy and CO2 sensors also appear in the Advanced Energy Design Guides and Standard 189.1P as well as the LEED systems. Occupancy sensors are used to determine whether zones are occupied or not so that the HVAC system can respond accordingly; it should be noted that, in some applications, simple (infrared) PIR sensors may suffice and in others, combined PIR/ultrasonic sensors may be required. Building owners can also earn LEED points by turning off non-emergency interior lighting when an area is unoccupied. CO2 sensors may be used for demand-controlled ventilation in densely-occupied areas, which are variously defined as accommodating either 25 or 100 people per thousand square feet.
Measuring and monitoring
The measuring and monitoring category is the most varied across the LEED standards, not even appearing in one standard but offering a potential for 24 points in another. Much of this category involves measuring or metering and trend-logging various items including tenant energy usage; end uses including lighting, variable frequency drives (VFDs) and water—both potable and non-potable—for various uses including cooling towers. It also includes monitoring ventilation system performance, which includes HVAC system self-diagnostics, such as those created by NIST, and issuing alarms when the system’s performance strays too far from its design values.
Finally, the BAS category appears in ASHRAE’s Advanced Energy Design Guides and Standard 189.1P as well as the LEED standards, and is specified as a system controlling at least HVAC and lighting, with scheduled HVAC setbacks.
In terms of qualifying for LEED certification, an HVAC control system earns very few points by itself—on average only three points—and a lighting control system does no better. But with the addition of the necessary sensors and building controls, the number of achievable points grows almost tenfold—on average to 25 points—and in some cases, a building could almost achieve LEED certification based on the fully integrated system alone. With integrated systems, the building can earn multiple LEED points with cost savings by taking such measures as having a zone’s occupancy sensor control both the lighting and HVAC.
A BACnet BAS is Best
Any sufficiently capable BAS, regardless of whether its protocol is standard or proprietary, can achieve LEED points along with the corresponding energy reductions. But for other reasons the BAS should be BACnet. Now plenty of reasons have been given for specifying BACnet that all remain true—standard protocol, not locked into a single manufacturer, no fees, etc.—but in the context of energy efficient buildings, BACnet has a unique advantage: It enables the future.
Some synergies arising from combined systems have been noted above, but there will be new dynamics that will arise as BACnet’s capabilities expand to support more of the building’s systems, including more complex lighting controls, physical access control, and increased sensing capabilities through wireless communications. These are just three areas currently under development in BACnet.
But in a time of increasing energy costs, increasing energy demand and an overstretched electrical grid, the work of a fourth area becomes increasingly important. The BACnet Committee’s Utility Integration Working Group is currently working with representatives from the Lawrence Berkeley National Labs, the California Energy Commission and others to develop communications between buildings and energy utilities to support automatic demand reductions when needed, real-time pricing information and bidding on energy by buildings. This will help reduce the big fluctuations that sometimes overstretch the energy utilities’ ability to supply energy at cost effective rates and will also lower the cost of operating commercial buildings.
The road to zero net energy buildings and new energy sources will be a long one and it is hard to predict just where it will lead. But with BACnet in the building, new capabilities—even from companies that do not exist today or technologies we find difficult to even imagine—can later be integrated into the existing BACnet BAS at little cost. This flexibility will be critical for taking advantage of new technologies for future reductions in the already-lowered costs of operating a “green” building.
About the Author
Bill Swan works with building
automation related standards, primarily BACnet and LEED. He was chair of the
BACnet committee from 2004 to 2008, is secretary of ISO/TC 205/WG 3 which
maintains BACnet as an ISO standard, and a member of the BACnet Testing Lab
working group developing testing for BACnet devices.
Bill is a LEED AP, has a Master's degree in Electronics Engineer and Computer Science, and has implemented communications-protocol stacks for BACnet and other protocols, and designed firmware and electronics for the building automation, test and measurement, and RF communications industries.
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