SHORT-TERM DATA LOGGING TO IDENTIFY LOW-COST/NO-COST OPPORTUNITIES FOR IMPROVING ENERGY EFFICIENCY

Tom White, P.E., CEM; Chief Engineer, Green Building Initiative

Ken Anderson, P.E.; Principal, The Energy Gleaners

Paul Williamson, EMC; Principal, Planwest Partners

Kevin Stover, P.E.; Commercial Programs Consultant, Green Building Initiative

ABSTRACT

The objective of energy auditing is to uncover opportunities for improving energy efficiency at a facility and to collect information useful for estimating potential savings from selected energy efficiency measures (EEMs). This paper describes an approach for using data loggers and hand-held instruments to record key operating parameters of energy using equipment.

The emphasis is on: (1) inventorying energy systems; (2) identifying key operating variables to be measured (what short-term data to collect); (3) specifying data collection points (for where and how to instrument or monitor a system); (4) analyzing the data and apportioning annual energy by end uses; and (5) estimating the energy savings that can be attributed to low-cost/no-cost EEMs, which subsequently can be implemented as a result of the auditing, data collection, and analysis. An example of calculating energy savings for a compressed air system, using this five-step approach, is reviewed.

OVERVIEW: ENERGY AUDITING TO IDENTIFY ENERGY EFFICIENCY OPPORTUNITIES

The Green Building Initiative (GBI) in Portland, Oregon is the licensed developer of the Green Globes ™ rating system in the United States. The Green Globes environmental criteria used for certifying sustainable commercial buildings are based on best-practices in seven key areas: integrated project management and design, site development, energy efficiency, water use, materials selection, indoor environmental quality, and reduced emissions. Although a building’s architecture and engineered systems are the basis for a sustainable design, the performance of a building is highly dependent on how the building is operated. This principle of managing operations to achieve high performance is especially true for energy systems.

Quoting a common business aphorism, “You can’t improve what you don’t measure,” gets right to the point of this paper. Without knowing how energy systems are actually performing, it’s not possible to determine the relative impact any remedial action might have for improving a system’s energy efficiency. This paper takes a practical, first-hand look at how to collect key

operating information and evaluate the performance of common energy systems in buildings.

With measured results in hand, energy analysts can determine reasonable estimates of energy savings that can be attributed to applied energy efficiency measures (EEMs). Once the challenge of data collection and analysis has been addressed, the implementation of recommended no-cost/low-cost measures to realize energy savings can be passed on to the building owners or managers to take corrective action.

Energy-efficient systems, left by themselves, cannot be expected to generate energy savings. These systems have to be managed – by adjusting set points, reversing operation overrides, re-commissioning equipment and sequences of operation, implementing preventive maintenance to avert performance drift or degradation, and committing to a host of other follow-through operations and management (O&M) activities that help ensure energy-efficient performance. Research from a number of studies [1] suggests that active O&M and occupant behavior practices can alter energy use significantly, resulting in savings in the range of 5% to 15%. What’s even better, such improvement strategies can most often be implemented for little or no cost.

A general approach for realizing energy savings can be summarized as a sequence of seven steps, outlined by asking the following key questions:

1. Where is energy being used in my facility? [taking an inventory]

2. What data do I collect to characterize how my systems are operating? [depends on the system]

3. How do I measure these data? [using short-term logging/data collection methods and tools]

4. How do I analyze the collected data to estimate annual energy end use? [system-specific examples are explained]

5. What kind of energy efficiency measures (EEMs) can be applied to these systems?

6. How do I calculate energy savings from the proposed EEMs?

7. What are the financial criteria for selecting no-cost/low-cost EEMs for improving energy efficiency?

Of course, answers to these questions depend on the energy systems in use at a given site. The overriding question comes down to this: What kind of short-term data can I collect, on which systems, and how would I analyze this data to estimate energy savings that are possible from low-cost/no-cost EEMs?

Levels of energy auditing – different emphasis, different outcomes

Energy auditing is the practice of assessing how energy is used at a site, for the purpose of identifying opportunities for eliminating waste and improving energy-efficient operation. ASHRAE describes three levels of energy audits [2], which are successive levels of energy use investigation summarized as follows:

Level I – A walk-thru of the building and its systems, gathering information that can be collected mainly by observation and spot measurements, such as ambient space temperatures, lighting levels, or inches of duct or pipe insulation. No detailed measurement or analyses are involved. Recommended EEMs are based on what is apparent and can be readily adjusted or fixed, such as: lighting levels too high, windows or doors not closing or left open, dampers rusted shut, valves stuck, inadequate pipe and duct insulation, space temperatures too high/too low, or systems operating when not needed.

Level II – A higher-level effort to collect data for characterizing system operations and for identifying potential EEMs and corresponding savings. For example: temperature, pressure, and flow data for assessing whether air or water systems are operating within design; voltage, amp, and power factor to characterize motor performance; exhaust gas analysis to determine boiler operating efficiency; lighting schedules and switching controls to evaluate whether lighting meets or exceeds occupant needs.

A key objective of a Level II audit might be to complete an estimate and apportioning of the building’s annual kWh and therm usage split out by end uses – heating, cooling, lighting, hot water, fans and pumps, ventilation, and plug loads. Level II results are often the basis for determining what systems might warrant a Level III audit.

Level III – Often referred to as an “investment grade audit,” this level of audit implies full characterization of major energy systems such as boilers or chillers, over a range of operating conditions. The purpose is to learn, with some accuracy and confidence, what the energy use differences would be if you were to spend a lot of money to swap out the current system or its major components with expensive new or refurbished equipment.

For example, an investment grade audit (Level III) might be carried out to derive a part load performance curve for an existing chiller, and corresponding kW/ton efficiency at each operating point. Using life-cycle costing and engineering analysis, the performance results and operating costs of this chiller would be compared to a replacement chiller, figuring out the kW/ton differences and the expected energy savings over the life of the system. From these results, you’d get a rate of return (ROI) for an investment.

One emphasis of a Level III audit might be to collect enough building operations and control data to inform a building energy model to the extent that the “tuned” model accurately represents that actual building performance. Once the building model has been calibrated with Level III data, the model can be run with any

“what if” scenario, allowing analysts to look are realistic energy use profiles of individual systems.

DATA COLLECTION – LOGGING, METERING, MONITORING

The terms data collection, logging, metering, and monitoring are often bandied about interchangeably.

Metering and monitoring are often used synonymously, with the difference being that metering uses instruments to measure data elements whereas monitoring implies a broader effort to collect, but also especially, measure key performance information. Metering implies measurement of a quantity such as gallons, kWh, Btus or CFM and the data is a snapshot at a given moment. Monitoring is a generic term for tracking any energy use on any scale, perhaps to compare results against an objective. For example, energy use monitoring could mean to gather and review kWh and therms from monthly utility bills and evaluate whether the totals are within range of an expected value.

Logging is a term that spans both quantitative measurements of operational data, but also accounts for key parameters such as how frequently a compressor engages or lights turn on and off. Logging also implies collection of data over time rather than a one-time measurement.

Data collection covers the gamut of all kinds of information gathered by multiple means – values from monthly utility meters for gas, water, electricity; number of times a compressor motor starts and stops in a given interval, the pressures at different points in a piping system; a histogram of the range of responses from building occupants on a thermal comfort survey. The variation in the types and frequency, and the degree of resolution and different methods of data collection, vary widely. The key question would be: What systems do you want to evaluate and what are the operating parameters that define the system’s performance?

For example, say you want to determine the energy use of a pump. In this case, you would measure the pressure difference across the pump (head), its RPM, the voltage and current to the motor (multiple legs if the motor is more than one phase), and the power factor. With this data, you can plot the operating conditions of the pump using the manufacturer’s pump curves and determine pump efficiency, gpm, and kW. With additional information about pump ON-OFF cycling times you can create and operational profile and then calculate cumulative energy use. If the pump cycles are intermittent or the pump operates at different RPMs, the calculation of aggregate energy use can be a little more complicated. But, typical use patterns, logged over short periods of time, give you a basis for aggregating total energy.

If adding a VFD to a pump motor is an energy-efficiency option, you can use affinity laws or more exacting power calculations to determine energy savings at different RPMs or gpm flows, head pressures, and kW levels.

Another example of short term system measurements might be in evaluating the heating and cooling heating capacities (in Btu/hr) of an air handler, at different air delivery rates, and at various cooling and heating coil temperatures and flows. Your purpose might be to characterize the system sufficiently to optimize cooling coil gpm for a given delta-T at varying rates of supply air CFM delivered. Your objective might be to measure fan and

pump energy with an eye toward modifying controls or adding VFDs to make fan and pump operations more efficient.

As with most any energy systems, performing a First Law energy balance would be the approach. A system diagram of the air handler, with its mass and energy inputs and outputs, suggests what operating variables to measure at what points of the system.

To evaluate air handler performance, you would need to collect data on at least the following parameters: temperature, humidity, and CFM of the return (RA) and outside air (OA) streams (inputs), and the same parameters for the supply (SA) and exhaust (EA) air streams (outputs); flow rates and temperatures in and out of the cooling and heating coils; the air temperatures before and after passing over the heating and cooling coils. And, of course, the electrical energy to fans and pumps would have to be accounted for through measurement.

Sources and types of data to be gathered for energy auditing

There are many kinds of useful information that can be collected in an audit, both qualitative and quantitative, which you can use to inform your assessment of how energy systems are performing and how to improve those systems.

Audits can cover a broad range of data and information, from surveys or interviews of occupants, to detailed, automated electronic reporting of key operating characteristics, system by system.

There are two general classes of information or data to be gathered – quantitative and qualitative – and two ways to go about gathering key information, by observation and by measurement.

Quantitative data have numeric values: 40°F, 125 psi, 12 minute cycles, 341 kWh – and lends themselves to calculations and analysis. Qualitative information is more about characterizing a status or condition: “Windows were left open over-night; the boiler is 25 years old and badly in need of repair.” Qualitative information can inform what kinds of quantitative data might need to be collected to resolve open questions about system performance – suggesting what systems an audit needs to focus on.

Although measurements are clearly quantitative, observations can be both quantitative and qualitative, depending on what is observed: “insulation levels were applied inconsistently along the piping,” or “only 3ft of the 21ft pipe length was insulated.”

Here is a list of key information sources and the kinds of results that can be gleaned from the details:

Surveys and interviews, O&M records – Useful for identifying occupancy concerns, O&M issues, repairs and change histories.

Building drawings and equipment schedules – Typically indicate how the building is zoned, conditioned, lighted, and the capacities and specifications and controls for major energy systems such as HVAC and lighting, envelope construction – although the older the building, the less likely the details are accurate.

Monthly utility bills – At least a year’s worth of monthly gas and electricity or other fuel bills reveal patterns of energy use. Seasonal variations and peak demands can be gleaned from the bills, and the kWh and therm profiles are essential for calibrating building energy models. For

example, if gas is only used for hot water and space heating, and there is no heating during the summer months, the gas usage profile during the summer represents only hot water heating, which might be taken as a relative constant load.

Utility interval data – With the advent of electricity smart meter technology, facilities have begun using 15-minute interval data, rather than relying only on a single monthly value, to detect anomalies and variations in operating schedules. Interval metering is a powerful tool for evaluating energy use impacts from such factors differences in occupancy profiles (weekday/weekend, occupied/unoccupied), utility-triggered demand response (turning off air-conditioners for short, rolling periods), after hours events, and human overrides of control settings such as lighting sweeps.

Building Automation System (BAS)/Energy Manage-ment System (EMS) – These centralized controls systems have dozens of inputs and outputs – including zone temperature set-points, ventilation rate scheduling, lighting controls. Polling the building BAS/EMS offers an opportunity to track variables and trend energy use correlated with other factors, such as outdoor weather, occupancy patterns, and control sequences of operation.

End-use profile monitoring – Emphasis on short-term metering and logging to develop operation profiles of energy systems, measuring such values as lighting levels, temperatures, pressures, flows, power, run time, humidity, CO2, and other key variables that influence energy system controls and performance.

FIELD AUDITING TOOLS AND DATA LOGGERS

Once the data collection points are identified, the next step in planning for an audit is to select appropriate instrumentation to measure the operating parameters, or variables, of the energy systems. There is virtually no limit to the variety and capabilities of different instrumentation and measuring devices.

Some examples of hand-held tools are shown in Figure 1, and many of these devices are relatively inexpensive. Here, you see some energy auditing tools used to make spot checks of lighting levels, power draw of electrical equipment, temperature, air flow, rotational speed, and other operating parameters.

Flow rate bag. A simple calibrated bag that is used to check the water flow rate from faucets and shower heads when there is no labeled aerator.

Amp/Voltmeter. A clamp-on device for checking power or current draw through one leg of an electrical device. A one-time check of current and voltage of each leg can be used to get an estimate of total energy use when only one leg is data logged.

Air flow meter. A wheel-type anemometer with around fan that spins as air flows through it. The display reads the air velocity. You can use this instrument, for example, to check various locations across a vent or duct, then average the velocity and multiply by the cross-sectional area to get an estimate of the CFM air flow.

Light meter. This device has an electric eye on the spiral cord placed horizontally on its face to measure the foot candle of illumination. You can spot check lighting levels

at various locations in a room, and determine whether, for example, a space is over-lit, which indicates possible de-lamping or replacing lighting fixtures to reduce lighting loads.

Tool kit. The kit shown had a screw driver type handle with various tips especial useful is 1/4“ and 3/8” cap screw for opening the covers on HVAC systems. Other tools that might come in handy include vice grips, pliers, sets of Allen head hex keys, flat head and Phillips head screwdrivers, and even files, a hack saw, and pipe wrenched. (Depending on the kind of equipment or systems you intend to audit, other simple tools could be included, such as soapy water bottle to detect air leaks).

Mag Ballast. When exposed to a fluorescent light this instrument determines whether the fixture has old magnetic or newer electronic ballasts.

Laser tape measure. Uses a laser to measure the distance to an object; very helpful for quickly measuring the dimensions of a room.

Mirror. This type of dental mirror is very useful for looking at otherwise inaccessible nameplate data on motors or other equipment.

Tape. Both duct tape and electrical tape are indispensable when a motor logger will not stay attached to the motor case or when some other object needs to be held in place.

120V Watts This device plugs in between a wall socket and an appliance. It records how many kilowatt hours of energy are consumed by the appliance from the time it is attached until it is removed.

RPM meter. Also called a tachometer this device measures the revolutions per minute (RPM) of a spinning device such as a fan blade or pump motor. RPM is essential variable for determining motor performance.

IR Temp. This point-and-shoot style gun measures the surface temperature of an object. However, this instrument does not work well on copper or bronze pipes and it does not register air temperature.

Thermometer. A basic thermometer measures air temperature. A high temperature metal probe thermometer can be used to determine the flue gas temperature of a boiler or furnace which will allow one to estimate the burner efficiency.

Tape measure, flashlight, stop watch. A few additional, inexpensive tools that have universal application for measuring short lengths (from inches to multiple feet), seeing into unlit areas or reading in the dark, and timing durations of data collection, measurements or cycles.

Figure 2 shows some of the most useful data loggers for energy audits.

FIGURE 1 - ENERGY AUDITING TOOLS

Temp/RH/light logger. This instrument has an internal temperature sensor and relative humidity sensor and a built-in light meter so it measures and logs these values over time. It also has one external input that can accept an external sensor such as a temperature or a current sensor.

4-External channel logger. This instrument has no internal sensors but has four external inputs to accept temperature, CO2, current, voltage and other sensors.

5-wrap coil. This home-made coil of wire can be inserted in-line on one leg of a motor or other electrical power line. The five wraps when run through a current transformer will amplify the reading so a 5 Amp current would read as 25 Amps, making it possible to use an oversized current transformer (CT) to measure current flow to a smaller device or motor.

Clamp-on CTs. Also called a split core Current Transformer, this instrument measures in Amps the current flowing through a wire inside its loop. One CT is rated for 20 to 200 Amps. The smaller CT of 100 Amps can measure a maximum current: if applied to a wire carrying more than 100 Amps, this unit will register up to its 100 Amp read-out and stop. For this reason, a low range CT is only accurate down to 10 Amps. If the subject current wire runs less than 10 Amps the 5-wrap coil can be used to register current as low as 2 Amps.

External Temperature Sensor. This device is a thermistor-type temperature sensor with a 25 foot cable. It is only good for temperatures in the range of 32°F to 212°F.

Motor ON/OFF Logger. This device detects the magnetic field of a motor when it is running and uses this information to record when the motor comes ON and when it goes OFF.

EXAMPLE OF HOW END-USE METERING INFORMS ENERGY AUDIT RESULTS

During 2013 – 2014, Ken Anderson and Paul Williams, two of the authors of this paper, performed a series of energy audits for several Portland-area buildings under the auspices of the Existing Buildings Program of the Oregon Energy Trust [4]. An example from their field work and energy analysis results is presented here. The purpose of the system characterizations was to establish a baseline of energy use, and to identify energy efficiency measures that could be applied to reduce utility bills for the building owner.

FIGURE 2 - Data Monitoring Tools Used in Energy Audits

FIGURE 4 – COMPRESSOR MOTOR LOGGER DATA FOR 29 DAYS

Compressed air system motor logger for energy use and leakage estimate

In this example, the authors placed a motor logger on an air compressor, used in the shop of an auto dealership. The logger tracked ON-OFF times. Figure 3 shows how easily the logger can be installed.

Logged data, collected every 2-minutes over a 29-day period, and

graphed in Figure 4, reveal that the compressor is running

virtually all the time (black spikes), even on weekends and over a

holiday when no compressed air is needed.

The data from the motor logger in Figure 5 represents a short period of little more than a day. From 1:00 AM to about noon, and from 6:00 PM to 6:00 AM, the compressor goes on and off on a very regular basis, a periodic pattern that indicates running only to compensate for leakage since the shop is unoccupied and the compressor air is not used. So, the motor run time for the unoccupied period allowed the field team to estimate the compressed air system leakage.

Figure 6 recounts a calculation of 631 annual hours of total compressor motor energy use just to compensate for leakage. During the 29-day period the logger tracked compressor ON time, the compressor was used only 30 times but only for a few minutes cumulative; the rest of the time, the compressor turned ON just counter pressure loss.

In a ~29-day period, the total run-time to counter leaks is calculated at 1.73 hours/day, which is 7.21% (3,006 minutes of the ~41,760 minutes of logger run). When multiplied by the motor horsepower and converted to kWh, the total energy loss is about 2,352 kWh/yr.

Having the compressor motor on a time clock would prevent a lot of overnight and weekend leakage. An even better solution is to have shut off valve on a time clock to confine the air in the tank. Note too, that the 5 HP rating is nominal. More accurate voltage

FIGURE 3 - MOTOR LOGGER MAGNETICALLY

= ~29 days * 24 hr/day * 60 min/hr

= 41760 min / (60 min/hr)

= [(696 hr duration/29 days) *

= 365 days * 1.73 hr/dayfrom compressor nameplateconversion factor

= 631 hr * 5 hp * 0.746 kW/HP

and current measurements would refine this energy estimate further.

FIGURE 5 - DETAILED MOTOR RUN TIME

SUMMARY AND RECOMMENDATIONS

When entering a site to conduct an energy audit, a few important guidelines are worth keeping mind.

Safety first and always! Many kinds of measurements – especially those involving electricity or high temperatures – present serious hazards. No one should attempt auditing and data collection without proper training and without wearing appropriate protective clothing.

What to meter and measure. With limited time and resources, it’s important to focus auditing efforts on systems that are likely to result in the largest savings.

Accuracy. With instruments, both the measurement range and accuracy are key factors in collecting useful data. Instruments must be properly calibrated and the range of data read-out be selected according to the expected values to be measured.

Spot checking. You can use spot checks to calibrate metering sensors for example, measure a known value and compare it an instrument reading.

Sensor response time. An instrument must have a short enough response time lag that it can measure a variable value that is changing rapidly.

Enough data? For any measured parameter, it is important think through how long to meter and what time interval to use if sufficient data and resolution is to be gained.

General rule. The longer you measure, the more useful or sufficient the results. But, too much data is a waste.

Adjusting for seasonal variation. Weather and other external variables can significantly affect the performance of energy systems. It’s important to take into account seasonal variations when characterizing the performance of such systems.

Interval duration. Intervals need to be short enough to capture changes in state that might occur between measurements.

Data logging multiple variables. When setting up data logging periods, it’s important to match intervals so that the data profiles from multiple parameters can be combined on one graph.

REFERENCES

[1] No-Cost/Low-Cost EEMs – A Guide to Energy Auditshttp://www.pnnl.gov/main/publications/external/technical_reports/pnnl-20956.pdf http://www.ecova.com/media/173057/no-cost_low-cost_conservation_strategies.pdf

[2] ASHRAE levels of audit http://www.microgrid-solar.com/2010/11/the-difference-between-ashrae-level-1-2-3-energy-audits/

[3] CBECS Commercial Buildings Energy Consumption Surveyhttp://www.eia.gov/consumption/commercial/

[4] Energy Trust of Oregon, Existing Buildings Program

http://energytrust.org/commercial/equipment-upgrades-remodels/

[5] PNNL re-tuning websitehttp://buildingretuning.pnnl.gov/index.stm

[6] IPMVP protocols website http://www.evo-world.org/

[7] UC Berkeley M+V website http://mnv.lbl.gov/home

AUTHOR BIOS

Tom White is the chief engineer at the Green Building Initiative (GBI), based in Portland, Oregon. Tom’s primary responsibilities include investigating and resolving technical issues, ensuring that Green Globes and Guiding Principles rating systems and criteria are well-founded in both concept and application, and offering guidance and direction to customers on initiatives that affect their green building projects. Tom is a registered professional engineer, with CEM and LEED AP credentials, and holds both bachelors and master's degrees in mechanical engineering. tom@thegbi.org

Kevin Stover is a registered professional engineer and the commercial programs consultant with the Green Building Initiative. Kevin’s technical guidance supports the development and application of the Green Globes rating systems for certifying the design, construction and operation of commercial green buildings. Kevin is responsible for tracking registered projects, collaborating with staff members and customers, alike; addressing technical issues; and reaching out to prospective users, organizations and public organizations. kevin@thegbi.org

Ken Anderson is registered mechanical engineer, principal of the Energy Gleaners, a Portland-area company providing high end engineering and energy services to building owners in Oregon as well as other parts of the country. Ken has more than 30 years of experience in field work evaluation and analysis of energy systems. kenja777@comcast.net

Paul Williamson, principal of Planwest Partners, has spent most of his career in the management and delivery of energy efficiency programs, products, and services. As the Energy Smart Design program manager for Clark Public Utilities in Washington, Paul delivered energy efficiency design and commissioning services to several hundred utility customers who also received incentives for their building improvements. He worked closely with building design teams and their contractors as well as vendors of energy-efficient products.

At Ecos Consulting, Paul was a program coordinator for the regional ENERGY STAR Lighting and ENERGY STAR Homes NW programs, establishing successful networks with trade allies, supporting training programs and maintaining utility relationships. His direct industry experience includes managing Energy Star light fixture manufacturing and distribution for both national and regional companies. While working for Seattle and Globe Lighting, he secured the highest honors available in this industry from the National ENERGY STAR Lighting Program including the Lighting Retailer of the Year Award in 2008. In the last several years, Paul has designed a suite of portable high efficiency task/ambient light fixtures, built prototypes and demonstrated them for leaders in the efficient lighting industry.

Paul holds a B.S. degree from the University of Oregon School of Architecture and Allied Arts and an Energy Management

Certificate through the Northwest Water and Energy Education Institute. pwilliamson5158@gmail.com