RTF REVIEW DRAFT - Feb. 7, 2012
STANDARD PROTOCOL FOR MEASUREMENT OF FAN
AND COOLING SAVINGS FROM COMMERCIALSECTOR PACKAGED ROOFTOP HVAC UNITS
Submitted to
REGIONAL TECHNICAL FORUM
Submitted by
NEW BUILDINGS INSTITUTE
1601 Broadway Street
Vancouver, Washington 98663
Table of Contents
1. PURPOSE............................................................................................................ 1
2. DEFINITION OF KEY TERMS ..................................................................................... 1
3. REQUIRED KNOWLEDGE AND SKILLS OF PRACTITIONER ................................................... 2
4. REQUIRED DATA LOGGER COMMISSIONING ................................................................ 2
4.1. One Time Site Measurements and Descriptions ............................................................... 3
4.2. Data Logger Measurements............................................................................................... 4
4.3. Typical Meteorological Year 3 (TMY3) Weather Data ....................................................... 5
5. SAVINGS ESTIMATION STEPS ................................................................................... 5
5.1. Compute Normalized Annual Consumption (NAC) for Pre-and Post-Data Logging
Intervals .................................................................................................................................... 5
6. ESTIMATE OF TYPICAL MEASUREMENT COST ............................................................... 6
7. RELATIONSHIP TO OTHER PROTOCOLS AND GUIDELINES ................................................. 8
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1. Purpose
This protocol establishes a method by which annual electrical cooling and fan energy use and savings
(kWh) can be estimated for a commercial packaged rooftop unit (RTU) that has been optimized for
energy efficient performance by physical improvements such as the addition of an economizer, or by
controls changes such as a change in the fan schedule. The protocol specifies minimum acceptable data
collection requirements and the method by which these data are to be used in computing savings. For
some data elements, alternative sources of data are also defined. Normalized Annual Consumption
(NAC) is computed using an Excel workbook that accompanies this document to provide standardized
application of the savings estimation methods.
2. Definition of Key Terms
Baseline. This modifier, as in baseline control strategy refers to the control strategy for the period prior
to the RTU upgrade. Baseline also refers to the conditions of the RTU prior to program intervention.
Pre. This modifier, as in pre measurement period, refers to the period prior to the RTU maintenance
repair.
Post. This modifier, as in post weekday hourly load factors, refers to the weekday hourly load factors for
the period after the RTU upgrade is installed and fully commissioned.
Commissioning. This is the process of testing and adjusting to ensure that 1) the data logging
equipment is operating as required, and that 2) the adjustments or repairs made to the RTU are
operating according to design intent.
RTU Upgrades. The following criteria define the eligible RTU upgrades that are known to be adequately
modeled by this protocol. The physical upgrades to the RTU include: thermostat
replacement/adjustment (schedule and set points), economizer addition or repair, airflow adjustment,
refrigeration cycle adjustment, drive belt shiv adjustment, and temperature sensor replacement.
Typically, these upgrades are in the context of utility energy efficiency programs that may also include
eligibility criteria, such as age or size of the RTU. The eligibility criteria described here apply only to the
conditions necessary to achieve an accurate estimate of energy savings.
 The RTU loads and schedules during the monitoring period should be representative of the RTU
loads and schedules based on regular year around occupancy.
 The RTU must be a packaged air conditioning (AC) unit including a supply fan. Since the protocol
estimates annual fan and cooling savings, the source of heat is not an eligibility criterion.
 The protocol is in review to determine its application for heat pump RTU cooling and fan savings.
The protocol will be amended to incorporate the results. The protocol has not yet been applied to
split HVAC systems or to variable capacity systems.
As additional retrofit measures become part of RTU energy efficiency programs, more analysis will have
to be conducted to determine the protocol’s applicability to the additional measures and determine
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what revisions to the protocol are appropriate. Other measures can include: 1) variable speed drive
(VSD) on fans and compressors, the Premium Ventilation Package for night flush, morning warm up,
strip heat lockout, 2) other HVAC products such as or variable refrigerant flow/variable capacity units, 3)
split systems, 4) heating savings.
3. Required Knowledge and Skills of Practitioner
The practitioner, who has lead responsibility for applying this protocol to an RTU, has to understand the
basic requirements in order to assure the accuracy and reliability of the data acquisition and analysis.
The practitioner must have a full understanding of the following:
 Appropriate electrical and related safety procedures for work involving an RTU and the
measurement equipment used in this protocol. This includes an understanding of three-phase
electric power measurements.
 The protocol and the accompanying Microsoft™ Excel-based spreadsheet Savings Calculator.
This
includes background for the theoretical and statistical basis for the measurement as provided in the
protocol.
The practitioner must also be able to successfully perform the following tasks:
 Identify by inspection: the control system or thermostat controlling the RTU, the number of cooling
stages, control settings including all schedules and temperature set points.
 Select appropriate data logging equipment from any one of multiple suppliers on the market with
appropriate data storage capacity determined by the data acquisition period for pre-post
maintenance intervals actually planned for the evaluation.
 As required by state electrical code, supervise a licensed electrician in taking a series of spot
measurements of true power at the electrical panel and properly installing the data logging
equipment.
 Monitoring and verifying the data logger data output.
 Ability to interpret the results.
4. Required Data Logger Commissioning
This protocol, applied to the pre- and post-retrofit RTU data, should portray the savings impacts of the
RTU upgrade. The data logging system must be carefully installed and tested. The following are the key
capabilities that must be verified before the data-logging unit can be considered operational:
 The data logger, its communications and memory storage must be commissioned.
 True power measurement and recording interval should be not longer than every three minutes.
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 True power is the product of instantaneous current and voltage using typical true power transducer
devices. Spot power measurements are made to verify and confirm true power measurement
accuracy.
 Spot power measurement should be taken only when the unit is brought to a steady power level.
 Temperature is measured to provide average hourly temperature intervals.
Temperature
measurement must be verified by spot temperature measurement using a second temperature
measurement device.
 If a supply air temperature measurement is made, the temperature sensor must be kept from
touching the walls of the supply air plenum.
 The full data set should be tested during the first few hours of metering operation to verify that the
integrity and accuracy of the power and temperature data, and the data storage system.
 Onboard data storage capacity for up to 70 days with a 3-minute recording interval.
 Offsite storage capacity should meet or exceed onboard data storage capacity.
4.1. ONE TIME SITE MEASUREMENTS AND DESCRIPTIONS
Data Collection Requirements The following data must be collected and entered into the Savings
Calculator workbook as instructed. All workbook formulas can be examined and key variables are
defined.
For the calculator, the following data are needed:
 True power spot measurements:
o Take spot measurements, averaged over 10 minutes, during each operating mode including
auxiliary (off) mode, fan only mode, and fan plus compressor stages.
o Starting with the unit off, check and calibrate the data logger by measuring auxiliary power
draw, then measure power draw of the fan only and then fan plus compressor in each stage.
It is important to get a fan-only power measurement because it is an input in the Savings
Calculator.
 Additional site information, if collected, can provide key market data for repair/retrofit/replace
program design as well as evaluation, and can help calibrate energy models, but is not required for
Savings Calculator input. Data may be stored on board the logger for manual downloading or data
can be automatically transmitted to offsite storage and retrieval locations. Onboard data storage
capacity is recommended for up 70 days with 3 minute recording intervals
o Building basic description: Location, occupancy type, number of stories between RTU and
served space and any unusual features that may affect RTU energy use.
o Baseline control strategy: RTU thermostat set points, number of stages and schedule.
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o RTU description: Make, model, serial number, nominal tons, number of compressor stages,
nominal age, voltage and number of phases.
o Fan motor horsepower: Obtained from the motor nameplate or product invoice.
o Floor Area Served: Estimate of the floor area served by the unit.
4.2. DATA LOGGER MEASUREMENTS
 RTU true power. Log pre- and post- RTU true power including the supply fan and all auxiliaries. In
some jurisdictions, a licensed electrician may be required to install true power measurement
equipment. In this event, the practitioner will supervise the installation. A three-minute interval is
the longest interval for the true power measurement.
 Outdoor air temperature. Obtain hourly outside air dry bulb temperature from a nearby,
representative weather station, especially a National Oceanic and Atmospheric AdministrationNOAA station. Monitoring costs can be reduced by using local weather station data. If, in the
judgment of the practitioner, the nearby weather station is not representative due to distance,
altitude, or unusual local geographic condition, hourly outside air temperature must be collected at
the RTU site. For on-site measurement, the temperature sensor should be mounted on the roof
near the RTU, in a location that is shaded most of the day, and at least 18 inches above the roof
deck. The outside air sensor must be installed inside a passively vented radiation shield.
 Supply Air Temperature. This temperature is optional because it is not necessary to calculate RTU
energy use and savings. The Savings Calculator will work without supply air temperature data
inputs.
However the supply air temperature can be used to classify operating modes, to verify economizer
operation and to estimate the minimum outside air fraction. The supply air temperature data should
be collected at three minute intervals. The Savings Calculator will accept and process the minute-byminute supply air temperature if it is available.
 Choice of Pre and Post Retrofit Measurement Periods.
Accurate estimates of cooling energy use
requires as wide a range of summer temperatures as possible. This requires careful staging of the
measurement periods and the retrofit activity within the cooling season. Pre and post measurement
periods must consist of four weeks with more than 20 hours of outside air temperatures between
60° and 80°F. The four-week pre retrofit measurement period should start no later than the third
week of May and the four-week post retrofit measurement should start no earlier than the first
week of August. The post measurement period could push farther into August as global/local
climate conditions continue toward warming.
 Choice of Retrofit Time.
The retrofit window consists of about four weeks, between the first week
in July and the first week of August. Even though this is the most active customer repair period for
most HVAC contractors, this four-week period is intended to provide flexibility for scheduling the
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repair work. If the repair staging is outside these seasonal parameters, the results may become
unreliable for analysis.
 Hot Climate Considerations. On the east side of the Cascade Mountains in the PNW, the July data
will probably need to be excluded because very little economizer operation is anticipated.
Experience has shown that long term metered data without economizer operation will result in
higher than expected annual energy use.
4.3. TYPICAL METEOROLOGICAL YEAR 3 (TMY3) WEATHER DATA
TMY3 data refers to the 1991-2005 National Solar Radiation Data Base (NSRDB) update. TMY, TMY1 and
TMY2 data are not compatible with TMY3 data and will not work in the Savings Calculator.
 TMY3 Outside Air Temperature (OAT). The annual energy estimate for the Savings Calculator
requires the input of long-term TMY3 OAT data from the most representative site in proximity to the
measurement site.
5. Savings Estimation Steps
Annual energy savings are estimated using the Savings Calculator that accompanies this protocol.
5.1. COMPUTE NORMALIZED ANNUAL CONSUMPTION (NAC) FOR PRE-AND POST-DATA
LOGGING INTERVALS
 Data Preparation. The data interval for a single NAC measurement will consist of at least 28 days of
logged power and temperature, with a three-minute data logging interval. Data of this sort may
have gaps and out of bounds values that need to be removed or resolved before the data is used in
the Savings Calculator. The details of this data management are common to any data logging effort
and are beyond the scope of this protocol to specify. In the Savings Calculator, the data must start
at 00:00 hour of the first day. Any days with significant missing data should be eliminated so that
only full days are used. Gaps in the time sequence caused by missing whole days are not a
significant problem. If only a few minutes of data are missing or corrupt, then replace with good
data from the prior minutes. The Savings Calculator has features to help the user eliminate
incomplete daily data and the Savings Calculator instructions provide information on the deselecting days, and what to do on each worksheet.
 Energy Savings Calculation Sequence.
To estimate savings, the Savings Calculator will be used
twice, separately characterizing the pre and post annual energy use. The measurement of the pre
retrofit annual energy use, NAC 1, is derived from the data collected for the pre-retrofit period, and
the post retrofit normal annual energy use, NAC 2, is derived from the data collected in the post
retrofit monitoring period. The annual energy savings for the monitored site is then NAC 1 minus
NAC 2.
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 Electric Load Shape Calculation Sequence.
This sequence distributes the daily energy use into
hours of use such that the total energy use predicted for each hour of the day will reconcile with the
metered data. This process predicts the average energy use for the hour by daytype and season
very accurately, though it will not predict the energy use for a particular hour exactly. A summary of
the process is as follows:
o Energy-weighted average hourly load factors are calculated from hourly and sub-hourly
minute data over the baseline and post measurement periods, and for fan-only and
compressor operations and for weekday and weekend operations. This occurs in the Savings
Calculator in the hourly load tab, and the annual hourly is developed on the annual tab.
o The normalized load factors are then used to parse the temperature-correlated energy data
to 8760 hour bins based on the TMY data and the annualization functions of the Savings
Calculator.
o This is done separately for the fan and compressor components for weekday and weekend
periods for both pre- and post-retrofit periods.
 Demand Savings Calculation Sequence. The Savings Calculator produces an estimate of maximum
demand versus temperature as well as the NAC. Currently this demand function is not used because
the primary measurement is focused on energy consumption. It can however, be used to report
demand impacts and examine performance, including determining if the unit is oversized, and if
there has been a change in maximum power due to measure implementation.
6. Estimate of Typical Measurement Cost
Cost profiles for two approaches of metering are presented. Both cost scenarios assume a mature
state of metering experience fully incorporating lessons learned from previous metering activities.
The calculator is designed to use the information from either of these approaches to develop an
annual savings estimate. The costs of both approaches are dominated by the labor costs. No training
costs are included in this estimate. However, the second approach requires a more qualified
practitioner.
The first approach is designed to minimize costs by using site circumstances to lower costs. It
assumes local NOAA hourly weather station data is available instead of site temperature monitoring. A
small self-contained power logger in used in the breaker panel. This approach can be used to meter
two three-phase units or three single-phase units at a time. This approach, referred to here as the
“expedited approach,” requires minimal practitioner training, but can only be applied where the
circumstances are suitable.
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Table 1: Cost for the Expedited Measurement Approach
For two delta wired RTUs in the same breaker panel
Item
Hours
$ / Hour
Rental
Total Cost
470
470
Equipment
Current Logger
Includes Current Transducers/Voltage Taps
Labor
M&V Practitioner
2
50
100
1.5
100
150
1
100
100
Checkout
0.5
100
50
Install/Remove Current Logger
0.5
100
50
Savings Analysis
1.5
100
150
2
100
200
Travel
Schedule/access
Install
Electrician/Certified HVAC Tech
Travel/Measurement
Total
$1,270
Cost/RTU for 2 RTUs
$635
Equipment if purchased:
Logger
$1000
Current Transducers (4) $300
Voltage taps (4)
$100
Note in Table 1, the total cost of the logger and equipment is not used; instead the equipment cost in
this table is considered a “rental” cost that is one third of the total cost on the assumption that the
equipment suite will be reused at least twice more.
The second approach is more comprehensive and collects rooftop site air temperatures and supply air
temperatures. This approach, referred to as the “comprehensive approach,” must be used when there is
no local NOAA weather data, where all the metered units are three phase Y-wired, and where the supply
air temperature is desired for deeper diagnostic information. This approach is significantly more
complicated (and flexible) than the expedited approach and requires more training because it involves
setting up a full data logging installation including communications and logger powering.
Table 2: Costs for the Comprehensive Measurement Approach
For three RTUs within 50 feet of each other on a single rooftop.
(Note that Table 2, as in Table 1, a rental cost for logging equipment equal to one third of the total
equipment cost is assigned.)
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Item
Hours
$ / Hour
Rental
Total Cost
800
800
Equipment
Power Meter
Current Logger
Labor
M&V Practitioner
Travel
2
50
100
Schedule/access
2.5
100
250
Install
5
100
500
Checkout
1
100
100
Install/Remove Current Logger
1.5
100
150
Savings Analysis
1.5
100
150
4
100
400
Electrician/Certfied HVAC Tech
Travel/Measurement
$2,450
$817
Total
Cost/RTU for 3 RTUs
Equipment if purchased:
Logger
$1100
Current Transducers (4)
$300
Temps sensor (4) with shields $350
WattNodes (3)
$750
7. Relationship to Other Protocols and Guidelines
The relationship between this protocol, and other relevant protocols and guidelines is as follows:

International Performance Measurement and Verification Protocol – 2007 (IPMVP) Efficiency
Valuation Organization. This protocol is consistent with Option D - Calibrated Engineering Model.
The use of this option has been refined by fieldwork that has showed that the staging of the
monitoring and the retrofit has a strong effect on the accuracy of the results.
 M&V Guidelines: Measurement and Verification for Federal Energy Projects Version 3.0, U.S.
Department of Energy Federal Energy Management Program. This guideline requires both
baseline and post measurements that are required by this protocol.
 Sampling Reference Guide, Bonneville Power Administration.
Relevant to program level impact
evaluation
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 Regression Reference Guide, Bonneville Power Administration.
The RTU protocol uses regression
techniques to fit a linear equation to the measurements of average daily true power and average
daily temperature.
 Additional RTU-related background information is found at the RTF/Rooftop Unit Working Group
website.
SAMPLING PROCEDURE FOR PROGRAM EVALUATION
One result of the research that produced this protocol was analysis of savings from field measurements
taken in 2008-2010 through Bonneville Power Administration RTU Pilot Servicing Programs. Testing of
the protocol on that data set revealed the general level of errors in the estimates of savings from the
measures installed in those programs at the participating sites. These typical errors have been worked
into Table 3, showing the sample size necessary to achieve an 80% confidence/20% precision
measurement for evaluating energy savings from similar programs on similar sites. The selection or
stratification of the sample will depend on the measurement objective at the discretion of the
monitoring party. The reader is also referred to the RTF GUIDELINES FOR THE DEVELOPMENT AND
MAINTENANCE OF RTF SAVINGS ESTIMATION METHODS.
The following is a program evaluation sampling procedure that can be applied for evaluation of an RTU
program measure package, but not to individual RTU component measures. Testing of the protocol
revealed the general level of errors typical in the estimates of single RTU savings. These typical errors
have been worked into Table 3, showing the sample size necessary to achieve an 80% confidence/20%
precision measurement for evaluating average program energy savings. The selection or stratification of
the sample will depend on the measurement objective at the discretion of the monitoring party. These
sample sizes are not directly related to the per unit savings protocol and Savings Calculator.
Table 3: Program Evaluation Metering Sampling Requirements
Program Size - # Units
Sample Size - Metered Units
100
55
500
60
1,000
60
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