Measures of efficiency
Building systems data can be used to manage equipment operations and determine how to run the building more efficiently.
Rob Knight, Environmental Systems Design, Chicago
Imagine driving a car without a speedometer, gas gauge, or tachometer. You could get from point A to point B, but would have no feedback on compliance with speed limits or the efficiency of your driving. No one would think of buying a car today without instruments to measure the most basic operational parameters. So, why should you settle for a building without such basics?
Meters and metering systems are a building’s gauges, measuring and communicating the building’s electrical, mechanical, water, and gas usage back to the building users and operators. Once obtained, these data can be used to manage equipment operations and determine how to run the building as a whole more efficiently.
While you wouldn’t drive a car without gauges, buildings are often built without meters. Still perceived as a high-priced luxury, metering systems are often the first thing value-engineered out of a project’s budget. But, if an owner is going to spend the capital to specify an efficient piece of mechanical, electrical, or plumbing equipment, he should demand a measure of its efficiency on the job as well. Instead of viewing metering as an extra, when included in the design plan from day one, it can be more economical than you think.
No two buildings are the same. With different combinations of HVAC systems, chillers, roof, and envelope designs, there’s no one-size-fits-all to running a building.
Today, many buildings run automatically. HVAC systems are operated by the BAS, programmed to automatically run equipment with the goal of satisfying the current thermal load and maintaining comfort conditions. But, what happens when the thermal load changes, or the comfort setpoints are modified? A commercial building will change function multiple times in the course of its life. For example, consider a typical office facility. The day it opens, it may be at 25% occupancy, while two years later it may reach 90% occupancy or even be fully leased. Occupancy patterns may shift between 9 a.m. and 5 p.m. or in two or three shifts. A portion of the space may become a data center, full of blade servers. Or maybe corporate initiatives cause many employees to begin telecommuting from home. Each of these scenarios demands different engineered systems output to satisfy the load.
Day after day, year after year, operators and building users make choices about how to operate a building’s equipment. The automatic choices are made based on software programming, which may be based on a design engineer’s sequence of operations. Operators often make manual choices, such as whether to start the chiller at 4 or 6 a.m., not start it at all, or determine what the ideal chilled water temperature setpoint should be. Each choice involves trade-offs. Save energy or satisfy thermal comfort (thereby reducing hot calls)? Spend energy at the chiller to save pump horsepower, or not? Metering energy use will provide the information operators need to make informed decisions. Metering energy use also provides essential information to the commissioning agent when recommissioning or retro-commissioning a building.
Additionally, each building system, while often integrated, will have its own strengths and weaknesses. How a chiller performs on day one is not how it will perform five years later, as mechanical parts may degrade over time. Programming and setpoints may be adjusted incorrectly by well-intentioned operators. Monitoring equipment and total systems performance is possible through metering. This permits analysis of systems performance over time against a baseline, in order to detect and correct for the slow slide from efficient to inefficient operation. The system could be a chiller plant (kW/ton), a data center (power usage effectiveness, or PUE), or lighting in an office building (W/sq ft).
Owners of a multitenant building may install meters in each leased space to determine how much energy is being consumed per tenant. With this knowledge, owners can pass the utility costs directly onto their tenants, use the information to create a different rent structure, or encourage their tenants to lower consumption by sharing this information through a public portal.
Green rating systems, such as the U.S. Green Building Council’s LEED program, recognize the essential role of meters as a feedback mechanism for the operation and maintenance of a building, and they award points for carrying out a proper measurement and verification (MV) plan, which may include real-time energy metering. Future revisions to LEED and other rating systems are likely to place an even greater emphasis on metering than ever before, by stressing the importance of real-time data from advanced metering systems and related initiatives such as monitoring-based commissioning and automated demand response.
By monitoring the real-time use of electricity, potable water, natural gas, steam, and hydronic energy (chilled water and hot water used to heat and cool the building), metering can provide invaluable data to facilities personnel and building owners alike. This feedback is required to optimize the lifecycle costs of any building.
Three ways to meter in real time
In the late 1980s, the first significant rise in utility costs, set against a backdrop of growing concern for environmental conservation, led to the popularization of metering. Although the practice had been around for some time, it advanced significantly in the past few decades in both its abilities and its applications. From simple to complex, meters can document the use and performance of just about any building system, with a wide range of tasks and desired analysis.
On the simple end of the spectrum, there are some low- or no-cost methods of obtaining basic meter data (see sidebar, “Getting started with metering”). The focus of this article, however, is real-time metering. Also known as advanced energy metering systems, real-time metering systems are defined in the U.S. Dept. of Energy’s 2006 “Guidance for Electric Metering in Federal Buildings” as follows:
Advanced meters have the capability to measure and record interval data and communicate the data to a remote location in a format that can be easily integrated into an advanced metering system.
An advanced metering system collects time-differentiated energy usage data from advanced meters via a network system on either an on-request or defined schedule basis. The system is capable of providing usage information on at least a daily basis and can support desired features and functionality related to energy use management, procurement and operations.
The following examples illustrate the range of ways real-time metering systems can be applied to building systems:
Option 1: Install a stand-alone system package that consists of meters and specialty software. At a minimum, the system should read and record 15-min interval data from each meter and provide a basic set of software visualization and reporting tools. Packaged meter solutions are a great fit for many users, as they generally provide the most attractive beginning price point. However, these solutions can be difficult to interface to other systems and often lack flexibility as needs change. While presumably more cost effective, this approach forgoes some of the most compelling ancillary advantages of metering, as in Options 2 and 3.
Option 2: Install communicating meters and hook them into the BAS so that the BAS becomes the interface for dashboards, reports, and analysis tools on the data received. The benefit here lies in the opportunity to use energy use data to better inform daily operations. For example, when an operator sees the impact of the time of day he starts his chiller on power usage, as well as on the ability to reach proper temperatures, he can make better operational decisions.
Taking this a step further, energy data can be used as an input to advanced automatic control strategies such as demand response, or peak shaping, shaving, and shifting. These strategies all essentially attempt to reduce the portion of the electric bill attributed to the peak demand. Depending on the utility rate structure in effect, the peak demand surcharge can be a significant component of the bill. Demand response or peak shaving attempts to reduce demand as it approaches its peak, by raising setpoint temperatures or dimming lighting, for example. These strategies rely on a slight and imperceptible change in space conditions to save total energy at its peak.
Peak shifting and shaping attempts to modify the time of use, such as starting a chiller earlier to precool a thermal mass instead of running it during the peak period. But while such measures may reduce the peak, the total energy expenditure may remain unchanged. When analyzing data from the meter, the BAS is also aware of which equipment was running and why. Powerful new BAS are beginning to include fault diagnostic algorithms, which can predict future equipment failure or degraded performance, and these algorithms may rely on energy performance for predictions.
An advantage of this approach over Option 1 is its ability to select from a wide range of available meter hardware for each application, picking the right combination of form-factor, accuracy, and cost for each location. The downside to this approach, however, is that many BAS aren’t well suited for serious analytics, complex energy reporting, or slick energy dashboard tasks. As specialty needs arise, including showing compliance with regulations, providing evidence for use in cap-and-trade, carbon trading systems, or creating an “energy portal” on a corporate website or kiosk, the typical BAS might not provide the tools needed. Before selecting this option, determine if the existing BAS is able to perform basic analytic chores such as normalization against outside air temperature or square footage.
Option 3: The high-power option for metering is to build upon Option 2 above, with communicating meter hardware integrated into the BAS. Once meters are integrated into the BAS, Option 3 would be to add specialty energy software tools “on top” of the BAS to perform tasks like energy analytics, reporting, and dashboards. Exporting data gained from metering to specialized software will further the useful life of the metered data to target potential operational gains and further sustainability. Gaining popularity, this option has grown as the corporate spending climate has evolved to promote energy-efficient measures in an effort to cut operational spending. There is now a diverse world of software available to suit nearly any specialty need.
The primary advantage to Option 3 is the ability to decouple the various purchase decisions. The best-in-class product can be selected for each application, including: metering hardware, BAS (where the actionable strategies for optimization remain), dashboard/visualization software for public consumption (such as LEED kiosks and corporate Web portals), professional dashboard tools for operators/energy managers/corporate finance users, tenant billing applications, advanced fault diagnostics, energy analytics, and reporting applications. The obvious disadvantage to this wide range of à la carte choices is a higher price tag.
Metering and the MV plan
More MV plans are surfacing in today’s building projects. An ideal MV plan will describe the ways in which building energy performance can be measured and validated periodically. The most common standard used for MV is the International Performance Measurement and Verification Protocol (IPMVP), available from the Efficiency Valuation Organization.
It is worth noting that IPMVP does not require installed real-time energy metering as part of an MV plan. In some cases, the proper combination of appropriate assumptions and stipulations with occasional spot measurements may be satisfactory for the MV goals. However, most new construction high-performance projects will apply IPMVP Volume III, Option D. This option requires creating a whole-building energy model, making adjustments for weather, and calibrating the model to match actual measured energy consumption, adjusting model parameters until it predicts actual consumption within an acceptable margin of error. Installed real-time energy submetering at the system level is invaluable to calibrating the model.
Regardless of the chosen method, a proper MV plan can be used to ensure building owners that their investment in state-of-the-art energy-efficient systems will deliver as-designed performance year after year. Along with a periodic recommissioning of building systems, or even automated continuous commissioning software, the MV plan and its execution help a building to continue operating at peak performance year after year.
As the MV plan becomes a more central piece of high-performance building projects, especially when encouraged by building rating systems such as LEED, it’s likely to come full circle and influence the design and adoption of metering systems. This will lead to better meters at a lower cost and to a greater accountability of the design and operation of building systems for today’s progressive building owner.
While the axiom “You can’t manage what you can’t measure” is cliché to discussions surrounding energy metering, it bears repeating for its simple message. Like driving a car without gauges, managing a facility without proper efficiency measures is counterintuitive. When owners spend significant capital on efficient systems, they must come to demand the proper accountability.
Knight is senior associate, controls engineer at ESD, where he uses his specialized experience with open protocol systems integration to deliver integrated control and monitoring solutions for ESD’s clients.
Getting started with metering
Before breaking the budget to install an expensive metering solution, there are a few low- or no-cost ways to start gathering meter data without specialty hardware or software:
- Start small by plugging into the utility company’s existing meter. For a small fee (or even for free), the local utility will come in and equip a meter to provide a pulse output. The pulse output might connect to a spare point on a BAS system controller. The meter will click the pulse output (like flipping a light switch) for every unit of energy consumed. Pulses can be totaled to determine the total consumption (energy or volume) used, and the rate of clicks can be used to derive the rate of consumption (power or flow).
- A number of building systems may already have the capacity to report their own electrical consumption without a dedicated external meter, including chillers, variable frequency drives (VFD), and uninterruptable power supply (UPS) systems. Check existing mechanical and electrical systems for available communications interfaces. In many cases, these devices (and the points within) may already be integrated into the BAS.
- Other aspects of an existing BAS may already provide points that can be used to approximate energy consumption. For example, the position of a pressure independent control valve can be used to estimate flow with reasonable accuracy. If supply and return water temperature sensors are added, thermal energy can be computed with fair accuracy. While this solution cannot match the accuracy of a new precision thermal energy meter, it can be a useful, low-cost “foot in the door” to thermal energy metering.
- Most public utilities now allow building owners or operators to download historical data from their website at no extra cost, even without a dedicated meter at the building.
Metering for tenant billing
A popular way to reduce energy expenditure in a multitenant building is to institute tenant submetering. The metered energy could be directly billed back to each tenant or could merely be communicated on a lobby kiosk or building website. When the goal is tenant billing, a few additional tips apply:
- Lease agreements with each tenant, local government, and utility company regulations will all determine whether tenant billing for utilities is possible. It is often illegal to resell a utility for profit. Get proper legal advice.
- If you are able to bill tenants for their consumption, make sure all the energy used by each tenant is being captured. Outlets, lighting, and HVAC systems may be powered by different electrical distribution systems or operate at different voltages. Multiple meters may be required.
- Make sure to consider the various forms of energy used by each tenant. Steam heat and chilled water cooling are often overlooked, but making those utilities (i.e., running a boiler or chiller) probably represents a significant component of the building’s energy expense.
- Apply equipment, processes, and analysis to meet recognized standards. IPMVP and ASHRAE Guideline 14 provide good guidance, and the utility should be able to provide reference standards for suitable hardware.
- Know what kind of meter accuracy is required and ensure that the meters deliver that accuracy, as installed. If tenants are being billed from the meter, it must meet requirements of the local authority having jurisdiction and the utility, and it must be defensible if a billing dispute arises.
- Make sure to include software with special tools or report formats for automatically generating tenant invoices. If not, invoicing tenants could be a time-consuming monthly process.
- Consider possibly tying the energy software into the owner’s back-office accounting system to include the metering as another line item on the tenant’s monthly bill.
- LEED 2009 for Commercial Interiors encourages tenant submetering. For a project less than 75% of total building area, two points are available for tenant submetering, and three points are available for negotiating a lease where utility costs are directly paid by the tenant rather than included in the rent.
- Submetering is too often handled as a last-minute addition, late in the design of new construction or large renovation projects. This can result in expensive and complex solutions, which puts meters first in line for value engineering. Instead, if building distribution systems are designed with metering requirements in mind, the cost of the metering system can be drastically reduced, whereas reworking the distribution systems or adding more meters may be cost-prohibitive.
- Define what to measure and to what level of detail at the start of a project.
- Consider measurement requirements of applicable codes, requirements, and credit opportunities of voluntary green rating systems and requirements of any financial incentive or rebate programs (such as tax credits or utility incentives).
- Determine whether measurement is required to support any contractual obligations, or is needed as the basis for revenue (such as an energy performance contract).
- There are often multiple project stakeholders, including end-user groups, who will have interest in the metering strategy. Unfortunately, many of these stakeholders typically aren’t consulted until it is too late to incorporate their needs cost effectively. Whenever possible, bring together all these stakeholders during initial planning to ensure that the strategy satisfies all end users.
- Defining metering on day one of design will also provide proper metering integration with mechanical, electrical, plumbing, and fire protection systems. Knowing that the power of each air handler will be measured will cause the building team to make different decisions about how fan powered boxes are circuited, and so forth.
- Define the software requirements for metering. Without parameters, engineers are often guessing what type of data building owners and operators will want to collect.
Energy consumption feedback on consumer behavior
There has been much recent discussion about the importance of real-time energy consumption feedback in influencing consumer behavior. The discussion entered the spotlight when Google, The Climate Group, and a coalition of businesses and nongovernment organizations sent a letter to President Obama in April 2010, urging him to “adopt the goal of giving every household and business access to timely, useful and actionable information on their energy use.”
Additional studies and research are ongoing, but the idea that feedback can change behavior to achieve energy savings is further explored in the June 2011 report from the Obama Administration’s Cabinet-Level National Science and Technology Council, “A Policy Framework for the 21st Century Grid: Enabling Our Secure Energy Future.” Various cited studies claim 5% to 15% energy savings simply by providing real-time feedback to energy consumers. Various Smart Grid initiatives and businesses are sure to provide additional data on this topic in the coming months.