Draft
STANDARD SAVINGS ESTIMATION PROTOCOL FOR
REFRIGERATION CONDENSER FAN VFD
Submitted to
REGIONAL TECHNICAL FORUM
Submitted by
SBW CONSULTING, INC.
2820 Northup Way, Suite 230
Bellevue, WA 98004
January 28, 2011
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD
TABLE OF CONTENTS
1. PURPOSE............................................................................................................ 1
2. DEFINITION
OF KEY TERMS ..................................................................................... 1
3. ELIGIBLE PROJECTS ............................................................................................... 1
4. REQUIRED KNOWLEDGE AND SKILLS OF PRACTITIONER ................................................... 2
5. REQUIRED COMMISSIONING .................................................................................... 2
6. DATA COLLECTION REQUIREMENTS ........................................................................... 3
6.1. Condenser Fan Motor Specifications ................................................................................. 3
6.2. Condenser Operations ....................................................................................................... 3
6.3. Post-Period Electrical Measurements................................................................................ 3
6.4. Facility Control System Post-Period Trend Logs ................................................................ 4
6.5. Typical Meterological Year (TMY) Weather Data .............................................................. 4
6.6. Inputs for Cost-Effectiveness Analysis ............................................................................... 4
7. PROVISIONAL DATA REQUIREMENTS ......................................................................... 5
8. SAVINGS ESTIMATION STEPS ................................................................................... 5
8.1. Compute Savings for Trend Log Intervals .......................................................................... 5
8.2. Annualized Savings: Determined by OAT and Schedule .................................................... 6
8.3. Annualized Savings: Determined by OAT, Production and Schedule ................................ 6
8.4. Life Cycle Costs and Benefits ............................................................................................. 7
9. SAMPLING PROCEDURE .......................................................................................... 7
10. RELATIONSHIP TO OTHER PROTOCOLS AND GUIDELINES ............................................... 7
11. TYPICAL COST OF APPLYING THIS PROTOCOL ............................................................. 8
12. USER’S GUIDE TO THE SAVINGS CALCULATOR ............................................................ 9
SBW Consulting, Inc.
i
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD
1. PURPOSE
This protocol establishes a method by which annual electrical energy savings (kWh) can be estimated for
a refrigeration condenser fan that has been upgraded by the addition of a Variable Frequency Drive
(VFD). VFDs reduce electric use by adjusting the fan motor’s speed to match the required load. It is
more efficient to operate the condenser fans continuously at a reduced speed than to cycle them on and
off to meet the heat rejection load.
This protocol specifies minimum acceptable data collection requirements and the method by which
these data are to be used in computing savings for refrigeration condenser fan VFD upgrades. For some
data elements, alternative sources of data, considered to be of superior quality, are also defined and are
allowed. Savings are computed using the Excel workbook (to be developed) that accompanies this
document to ensure standardized application of the savings estimation methods.
2. DEFINITION OF KEY TERMS
Project. A project consists of one VFD installed to control all the fans associated with a single
condenser. All condenser fan data described in this protocol must be obtained for each of the
condenser fans controlled by the VFD.
Baseline. This modifier; as in baseline control strategy has one of two meanings. For condenser fan
units upgraded in existing facilities, it refers to the period prior to the upgrade. For units in new
construction, there is no such period. For them, the term baseline refers to the design specification for
the unit without the efficiency upgrade.
Post. This modifier; as in post current trend log, refers to the period after the VFD upgrade is installed
and fully commissioned.
Commissioning. This is the process of testing and adjustment required to ensure that the VFD is
operating according to its design intent.
3. ELIGIBLE PROJECTS
Following criteria define eligible projects.

The VFD can control only one condenser and the baseline control strategy must be fan cycling; the
fan cycles on and off to meet the heat rejection requirement.

Excluded control strategies include two speed motors, two speed operation using pony motors or
capacity control by use of inlet damper.

Both evaporative and air cooled condensers are eligible.
SBW Consulting, Inc.
1
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD

The condenser control changes must be limited to only the VFD upgrade and thus must not include
significant reduction in condensing temperatures or changing controls from staging two condensers
on one at a time to operating both at reduced fan speed.

Energy savings from concurrently installed refrigeration system measures should not exceed 20
percent of the total refrigeration system energy use.

Excluded applications also include those where the condenser is replaced with a more efficient
condenser with reduced fan horsepower.

The cost of implementing this protocol must not make the project economically unattractive.
4. REQUIRED KNOWLEDGE AND SKILLS OF PRACTITIONER
The practitioner who has lead responsibility for applying this protocol must have a full understanding of
the following:

Appropriate safety procedures for work involving refrigeration condensing units and the
measurement equipment required by this protocol.

This protocol and the accompanying savings calculator.
The practitioner must also be able to successfully perform the following tasks:

Identify, by inspection or interview, the condenser type and control strategy.

Identify the significant determinants of refrigeration load, which drives condenser fan operation: (1)
outside air temperature, (2) production level, or (3) facility operations schedule.

Supervise a licensed electrician in taking a series of spot measurements of true power and other
required parameters for the condenser fan.

Install and operate a current logger and outdoor air temperature logger.

Obtain trend logs (as alternate data source) from facility control systems.
5. REQUIRED COMMISSIONING
This protocol may only be used for projects that pass the following commissioning tests:

Practitioner reviews installation documentation to confirm that the VFD is responding to the control
sensor signal and is maintaining the condensing pressure/temperature at the set point.

Practitioner confirms by examining a plot of current versus time that the VFD was responding to the
control signal at least 90% of the trend log period (see Sections 6.3 and 6.4).
2
SBW Consulting, Inc.
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD
6. DATA COLLECTION REQUIREMENTS
The following data must be collected and entered into the savings calculator. The minimum acceptable
procedure for obtaining the data is specified. In some cases, alternative procedures are allowed which
would provide data of higher quality.
6.1. Condenser Fan Motor Specifications

Motor HP. For each condenser fan motor controlled by the VFD obtain the motor name plate HP
from the nameplate, if accessible, or from operator supplied documentation. Full load fan kW
(computed by the savings calculator) should not exceed 115% of fan motor HP times 0.746.
6.2. Condenser Operations


Determinants of Refrigeration Load. Fan operation will be significantly determined by the
refrigeration load, which is passed through the compressors to the condenser. Refrigeration load
will be determined by OAT. In addition, it may be determined by one or both of following: (1)
facility operations schedule or (2) production level.

Facility Operations Schedule. Obtain shut down schedules from the facility operator. It is
common in agricultural product storage facilities that the facility is empty with the refrigeration
system off a portion of the year. Alternately, a dedicated refrigeration system may serve process
equipment such as a blast freezer that may only operate a portion of each day or week.
Determine the system operating hours by time of day, day of week and season.

Production Schedule. Obtain the production schedules from the facility operator if the
refrigeration load typically varies with production level. This may be expressed as percent of the
total number of storage rooms in use for an agricultural product storage facility. It also may be
related to the operating schedule of a production line that operates for a portion of the day or
week, but is only a portion of the total load on a refrigeration system that serves other uses
such as product storage rooms. Determine the production schedule as percent of full production
level by time of day, day of week and season.
Weather Station. Identify the TMY (Typical Meteorological Year) weather station which is has the
most similar weather conditions. Consult the facility operator if appropriate.
6.3. Post-Period Electrical Measurements

One-Time Electrical Measurements. Taken by a licensed electrician under the on-site supervision of
the practitioner. Power meter is attached as needed to record true RMS poly-phase power and
current on one leg of the circuit supplying power to the VFD. These measurements are recorded
while the VFD is set to a series of at least 3 levels of %speed, including one at 100% speed.
SBW Consulting, Inc.
3
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD

Trend Log of VFD Current. A data logger is installed to measure 15-minute interval true RMS current
on the same leg of the circuit as was used in the one-time measurements. If the condensing unit fan
speed is primarily determined by OAT, the measurement period must be at least two months and
must start between August 15th and October 15th or between March 15th and May 15th in order to
capture measurements for a sufficient range of OAT values. If the refrigeration load is primarily
determined by facility production, current logging must occur for at least two weeks during each
different production level. If production varies from high to low across the year, such as for an
agricultural storage facility that is filled quickly during the summer or fall and then slowly emptied
over several months, then logging must occur for at least two weeks each during full , half full and
near empty periods.

Alternative Measurements.

True Power. In lieu of the one-time electrical measurements and current trend log this protocol
allows for a trend log of true poly-phase RMS power for the circuit powering the VFD. The same
measurement interval, period and timing requirements apply as described for the current
measurement above.
6.4. Facility Control System Post-Period Trend Logs

Trend Log of Facility OAT. This data may be obtained from the facility’s control system if it can be
programmed to record OAT at 15-minute intervals. This data must be collected for the same period
as the VFD current trend log. This data is required only if OAT is one of the determinants of
refrigeration load. If OAT is not available from the facility’s control system or appears unreliable, an
OAT data recorder should be installed to create this trend log.
6.5. Typical Meterological Year (TMY) Weather Data

TMY OAT. Typical hourly OAT data for Pacific Northwest weather stations are contained in the
savings calculator to be used in estimating annual savings. Data from the station selected in 6.2 will
be used.
6.6. Inputs for Cost-Effectiveness Analysis
The following data need to be gathered to support the cost/benefit analysis feature of the calculator.

Project completion date.

Measure cost. The initial cost of installing the new equipment, including all materials and labor
costs. This is the full cost of the VFD installation. This value must be supported by invoices or other
documentation.

Sector. Possible values are Agricultural, Industrial, and Commercial.
4
SBW Consulting, Inc.
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD
The following values are used in the cost-effectiveness calculation, but are pre-set in the calculator.

Electric shape. The calculator assigns an appropriate electric shape based condenser fan operation
data describe in section 6.2 and the profile of savings computed from the trend log data.

Periodic costs or savings. Any non-annual periodic costs associated with the measure, and the
associated time period. These are incremental costs of the efficient option over the costs of the
baseline. For a VFD upgrade, the calculator restricts this value to be zero.

O&M costs or savings. Annual O&M costs or savings associated with the measure. These are costs
or savings which occur with the efficient option that would not occur with the baseline option, i.e.
the costs associated with VFD maintenance. The calculator restricts this value to be zero.

Non-energy benefits. Annual non-energy related costs or savings associated with the measure. The
calculator restricts this value to be zero.

Measure life. Number of years the measure is expected to be in effect. For a refrigeration
condenser fan VFD, the calculator restricts this value to be 10 years.
7. PROVISIONAL DATA REQUIREMENTS
During the period that the RTF classifies this protocol as Provisional, the following data requirements
will be in force:

Post-Period Electrical Measurements. Trend log true poly-phase RMS power for the circuit
powering the VFD. The same measurement interval, period and timing requirements apply as
described under Trend Log of VFD Current in section 6.3.

Baseline Performance. Trend log true poly-phase RMS power during the baseline period for each of
the condenser fan motors, which will be controlled by the VFD. The measurement interval, period
and timing requirements apply as described under Trend Log of VFD Current in section 6.3.
8. SAVINGS ESTIMATION STEPS
Savings are estimated using the savings calculator that accompanies this protocol (To be developed).
Savings are estimated as follows.
8.1. Compute Savings for Trend Log Intervals

Data Synchronization. Start times for all trend log intervals are synchronized by moving each to the
closest standard interval start times of 0, 15, 30 and 45 minutes after the start of each hour.

Power and Current Curve Fit. Spot measurements of true power and current (taken at least for 3
levels of speed, including 100%) are fit to a linear equation.

Post kW. Calculate kW from fitted equation for each current value.
SBW Consulting, Inc.
5
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD

Power and Percent Speed curve fit. Spot measurements of true power and percent speed (decimal
fraction) are fit to an exponential curve.

Post Speed. Calculate the fraction of full speed from the fitted equation for each calculated power
value.

Fraction of Full Flow. Equals the fraction of full speed.

Baseline Fan Motor Full Load kW. Equals the one-time measurement of kW at 100% speed
multiplied by the VFD drive efficiency (default value of 97%).

Baseline kW. Calculate baseline kW as the product of the fraction of full flow and the baseline fan
motor full load kW.

Savings for Trend Log Period. Calculate the savings as the difference between baseline and post kW
values.
8.2. Annualized Savings: Determined by OAT and Schedule

Average Savings by Trend Log Temperature Bin. Average kW savings by two degree temperature
bins for all trend log intervals during operating hours, as defined by facility operations schedules
(Section 6.2).

Operating Hours by TMY Bin. Divide the 8,760 TMY OAT data into two degree bins and compute
frequency of annual operating hours for each bin, as defined by facility operations schedules
(Section 6.2).

Average Savings by TMY Bin. TMY bin average bin savings equal trend log average bin savings for
each matching bin. Extrapolate average savings for TMY bins that do not have trend log data by
using a best fit equation through the average temperature bin data values. No bin value is allowed
to exceed the total rated fan motor kW.

Saving by Bin. For each TMY bin, multiply the average bin savings by the number of operating hours
in each bin, to get kWh savings in each bin.

Annual Savings. Sum the kWh values across TMY bins.
8.3. Annualized Savings: Determined by OAT, Production and
Schedule

6
Average Savings by Production Level and OAT. For each defined production level, average kW
savings for all trend log intervals at two degree OAT bins, as defined by facility operations schedules
(Section 6.2).
SBW Consulting, Inc.
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD

Operating Hours by Production Level and OAT. Divide the 8,760 TMY OAT data into two degree bins
and compute frequency of annual operating hours for each temperature bin that occurs at each
production level, as defined by facility operations schedules (Section 6.2).

Average Savings by Production and OAT Bin. At each production level, TMY bin average bin savings
equal trend log average bin savings for each matching bin. For each production level, extrapolate
average savings for TMY bins that do not have trend log data by using a best fit equation through
the average temperature bin data values. For each production bin average bin savings equal trend
log average bin savings for each matching bin across all TMY temperature bins. For production level
that do not have values from trended data, linearly interpolate average savings for each TMY
temperature bin. No bin value is allowed to exceed the total rated fan motor kW.

Saving by Production Bin. For each production bin, multiply the average TMY temperature bin
savings by the number of operating hours in each bin, to get kWh savings in each production bin.

Annual Savings. Sum the kWh values across production bins.
8.4. Life Cycle Costs and Benefits
The calculator contains a model called ProCost which computes life cycle costs and benefits. Inputs to
the model include the estimates of first-year savings described in sections 8.2, 8.3 and 8.4 and the costeffectiveness input data described in section 6. ProCost computes life cycle costs and benefits from the
economic perspectives of the end user, utility, and region. The calculator can be used to review these
results.
9. SAMPLING PROCEDURE
No sampling is allowed for this protocol. Data collection and savings estimation is required for each VFD
upgrade regardless of the number of VFDs that may be upgraded at a facility.
10. 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 A - Retrofit Isolation: Key Parameter
Measurement described in the IPMVP, as a number of key parameters are measured (VFD current
and OAT). The use of default fan performance curves is consistent with this option.

M&V Guidelines: Measurement and Verification for Federal Energy Projects Version 3.0, U.S.
Department of Energy Federal Energy Management Program. The relevant part of this guideline
is Section 11.4 Variable Speed Motors. This guideline requires both baseline and post
measurements, which is not consistent with this protocol.
SBW Consulting, Inc.
7
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD

Regression Reference Guide, BPA. This protocol uses regression techniques to fit a linear equation
to the measurements of true power and current for the VFD and to extrapolate savings to
temperatures beyond those observed in the trend logging period (for condenser fans whose speed
is primarily determined by OAT). The application of these regression techniques is consistent with
the BPA guide.
11. TYPICAL COST OF APPLYING THIS PROTOCOL
Shown below is an estimate of typical M&V cost for a single condenser fan unit. Lower cost per unit is
likely for facilities that upgrade more than one condenser with VFDs. For sites that involve significant
variations in production levels across the year, additional expenses will occur for multiple site trips to
obtain trend data at different production levels, or for the cost of leaving current trend logger in place
for an extended period. Expense for alternative measurements allowed by this protocol, are not
included in this estimate of typical cost.
Item
Quantity $ / Hour Rental Total Cost
Equipment
Power Meter
1
100
100
Current Logger
1
200
200
Labor
Practitioner
Travel
3
110
330
Scheduling
1
110
110
Facility Operator Interview
2
110
220
VFD Inspection
0.5
110
55
Electrical Measurements
0.5
110
55
Install/Remove Current Logger
2
110
220
Savings Estimate
4
110
440
Travel
2
90
180
Electrical Measurements
1
90
90
2
150
300
Electrician
Controls Specialist
Setup and Export Trend Logs
Total
8
$2,300
SBW Consulting, Inc.
Standard Savings Estimation Protocol - Refrigeration Condenser Fan VFD
12. USER’S GUIDE TO THE SAVINGS CALCULATOR
[To be developed once this protocol is finalized and savings calculator is developed. This Guide and the
Calculator are outside the scope of SBW’s current contract.]
SBW Consulting, Inc.
9