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This has led to significant involvement by NBI staff in the following: Continuing partnership with the Consortium for Energy Efficiency(CEE) Leadership with the startup team that created the Western HVACPerformance Alliance, a key stakeholder group with regulators,utilities, HVAC industry partnering–2009 Leadership in the successful Rooftop Unit Fault Detection andDiagnostics Mandatory Measure Project in the California 2013 Title24 building energy standard–2011 Leadership with the NW Energy Codes Group in proposing theRooftop Unit Fault Detection and Diagnostics Mandatory Measurein the 2015 International Energy Conservation Code. It is expectedthat the International Green Construction Code will adopt the samemeasure.Figure 1: Percent of NW InstalledRTUs by SizePercent of Installed Units in the Pacific NW35%RTUs in Commercial Buildings30%25%66% of all RTUs are 6 tons or less20%15%10%5%0%12345678.5 Unit Size in Tons of Cooling CapacityResearch demonstrates what any aerial view ofcommercial buildings will attest: RTUs are a very commonchoice for air conditioning and heating in small tomedium-size buildings (50,000 SF and below) and largerone-floor buildings like retail big box stores or warehousesin the U.S. The Energy Information Association in 2003found that approximately 46% of commercial buildingsuse RTUs, accounting for 60% of total floor space.Source: Northwest Energy Efficiency AllianceCommercial Building Stock Assessment.A frequent approach in smaller buildings is to use a “one-per-zone”design where each temperature zone gets a thermostat and an RTU toserve it. This design preference shows up in the frequency of RTU sizeby cooling capacity, expressed in ‘tons’ of cooling (a ton is equivalentto 12,000 Btu/hour of cooling capacity). Data collected from the PacificNorthwest reveals the frequency of RTU size byTable 1: RTUs an aging fleetcooling capacity tonnage. The majority of units are51% of the units have been on thesix tons or smaller, creating cost constraints thatroof for over a decade!impact feasible efficiency measures. Data from theAge categoryUnder 5 tons 5 to 10 tons Over 10 tonsPacific Northwest shown in Figure 1 supports this44%36%20%size distribution assessment.0 to 417%30,00024,00014,0005 to 1032%56,00046,00026,00010 to 1935%62,00050,00028,00020 years16%28,00023,00013,000Source: NWPPC 6th Regional Power PlanWe know from survey data that RTUs are an agingfleet. Data from the California Energy Commission(CEC) and the Northwest Power and ConservationCouncil’s 6th Power Plan show that more than halfof all RTUs are at least 10 years old.As RTUs age they begin to malfunction and degrade in performance.Unless there is an occupant complaint, many RTU-based HVAC systemsdo not receive any further maintenance than an occasional change of airfilters. These complaints are typically driven by temperature discomfort,RTU Savings Primer3

but many problems can occur which do not jeopardize comfort and sogo unidentified. These can cause the RTU to use far more energy than isneeded.RTU Performance DegradationAccording to the DOE, older inefficient commercial RTU air conditioningsystems are common and can waste from 1,000 to 3,700 per unitannually, depending on building size and type. So where are the failuresoccurring that cause unnecessarily high energy usage?Field work conducted by NBI and others reveals some of the mostcommon equipment failures. These studies allow for two broadconclusions:1. Most RTUs Operate Inefficiently and Have Equipment ProblemsOperating inefficiently means the RTU uses more energy thannecessary to provide conditioned air. This could include many specificproblems, but certain general areas are: Outside air/economizer dampers are malfunctioning or broken The refrigerant system is improperly calibrated The control system is incapable of optimizing operation Leaks and broken equipment allow too much outside air to enterthe building Over ventilation2. Many RTUs Operate UnnecessarilyUnnecessary operation means that even if operating efficiently duringregular hours, the unit may be running at times when no heating,cooling or fresh air is necessary. Causes could be:Figure 2: NW and California RTUProblem AreasEconomizerThermostatRefrigerant CircuitAir FlowSensors01020304050% of Problem FrequencySource: Four studies of 500 RTUs4607080 Thermostat settings are not correct ormonitored Sensors are out of calibration Controls are too simpleWhen examining data more specifically,using studies from NBI and others, anumber of findings were clear. Figure 2shows a distribution of detected problemsin a combination of studies. Approaches torepair, retrofit and replacement must addressthe most common problems and preventrecurrence.Utility Incentives and RebatesA market survey conducted by NBI of 143major utility and state programs for commercialRTU Savings Primer

efficiency shows many utilities are not accessing the savings opportunitiesin RTUs outside of providing modest incentives for a higher efficiencyreplacement RTU1.The market survey found 88%, or 126, of programs offer rebates formeasures directly targeting RTUs. Of these offerings, the majority ofprograms offer incentives for replacement RTUs based onAir-conditioning, Heating & Refrigeration Institute (AHRI) ratings.2 Ofthe 126 programs offering RTU incentives, 90% have incentives thatrange from 10 per ton to a maximum of 500– 600 for a 5-ton unitbased on specific ratings or calculations. Many programs reference theConsortium for Energy Efficiency Tiers of performance which provide asimple classification based on performance ratings. Because the cost ofa new ‘code-level’ 5-ton RTU can be around 5,000 and prices for highperformance units are higher, an incentive of 10% or less may not besufficient to impact the market.The program incentives and frequencies are summarized in Table 2. Thecategories are based on the descriptions of measures described later inthis primer. Of course, programs vary by region. Some climates are notsuitable for certain measures due to high humidity in the summer or becausethe summer is too short for the measure to be effective at energy reduction.Table 2: RTU Programs SurveyResultsAll SurveyedRTU Specific ProgramsRepairRTU MaintenanceThermostats and Sensors CheckRetrofitAdd EconomizerDuct SealingSupply Fan ECMsAdvanced RTU ControllersDemand Controlled VentiliationThermostat or EMS UpgradeOtherReplaceNew Equivalent High Efficiency RTUComplete RedesignEvaporative RTUNumber ofPrograms143126Percentof n/an/an/an/a88%***Programs for variable speed drives (VFDs) and electrically commutatedmotors (ECMs) typically exist at many utilities but are targeted at eitherlarge, built-up HVAC installation fans (as opposed to small unitary RTUs)or refrigeration equipment motors.The category “Advanced RTUTypical IncentiveControllers” in Table 2 refers tocontrollers suitable for unitaryFlat amount from 50 to 1250 per unitequipment that provide variableOften part of ‘RTU Maintenance’control of fan speeds (andpotentially compressor speeds) andFlat amount from 200 to 250outside air dampers while providingPer SF or per CFM amount*No specific programs**Demand Controlled VentilationStill an emerging technology with a huge potential.(DCV) and fault detection. TheseSee section below.programs are few in number andIncentive dollars per SF or per CFMFlat amount from 20 to 150are not the same as traditional VFDIncludes EMS, ERVs, and specific productsincentive programs.Incentive based on AHRI rating: Ranges from 10 to 125per tonFalls under New Construction incentivesNo data* square feet (SF) and cubic feet per minute (CFM)**Incentive programs for ECMs do exist but do not offer incentives specifically for RTU supply fans.***The percentages in the table don’t add up to 100% because some programs have multiple incentive categories.1.This does not include ‘custom’ programs which allow for any type of upgrade that is incentivized based on performance2.Energy performance is rated by the American Heating and Refrigeration Institute (AHRI) which provides ratings of EnergyEfficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER). Also used is the Integrated Energy Efficiency Ratio(IEER) is a measure of effectiveness at less than full load.RTU Savings PrimerThe landscape of RTU programsis driven by regulatory proceduresand ongoing research. Efficiencyprograms work hard to designincentives based on existing andcontinuing research and must takeinto account what can be justified toregulators. These processes requirea high level of capacity to maintainavailabilty of system analytics whichcan aid greatly in this effort.5

Potential Savings Still AvailableAs code baselines get stricter there is a perception that savings aredrying up for many measures, including those for RTU programs. Thisperception is exacerbated by the fact that many RTU programs useAHRI ratings to determine unit eligibility and incentive levels. Those sameAHRI ratings are typically used in energy codes to establish minimumperformance requirements.Whole Building Electrical Savings Percentage (%)Figure 3: RTU Capability per CertainStandardsDespite the tightening requirements, there are still significant savings onthe table for programs in the RTU space. This is because many measuresaddress areas of efficiency for the RTU that are not impacted by the levelof AHRI rating. The AHRI ratings address the efficiency of the refrigerationloop at specific conditions, butmany performance issues areunrelated to the refrigeration loop.These include power needed toprovide ventilation air, the ability touse free cooling, advanced controlstrategies and fault detection.Consider the analysis of a twostory office building using energymodeling and supplemented bydata from Pacific Northwest NationalLaboratory’s (PNNL) work withcontrol analysis. Figure 3 comparesbuilding energy use changes fordifferent baselines compared to aStandardsProgramsAdvanced Controlsbuilding with RTUs that adhere toImpact from Improvements to RTUsASHRAE 90.1 – 1999. As codesadvance in time a certain level of savings is achieved through improvementsin ratings. Then the existing ‘like-for-like’ RTU incentive programs areconsidered, resulting in additional but modest savings. Using PNNL’scalculator, certain retrofit control products are considered and savingsincrease dramatically. Couple this with more climate-specific design, andthe possibility for significant savings is realized.Accessing These SavingsThe measures attempt to address the well-known failure mechanismsand shortcomings of RTUs in the field. The incentives paid by utilities,states and other energy efficiency and green building programs for thesemeasures amount to a few hundred dollars and are often too small tobe of interest to a particular contractor or owner. Emerging research isshowing much greater opportunities in RTUs both in replacement unitsand by examining common areas of failure and new ways of improvingefficiency in ways that aren’t captured by standardized testing.Those interested in developing programs to access these savings should:1. Reevaluate current RTU programs and see what other approachesmight be considered for their region.6RTU Savings Primer

2. Access existing research and work with utility personnel in areas thathave programs or pilot projects underway or completed.3. Consider a pilot program to establish savings to your regulators usingthis guidance on measures and analysis.4. Join national initiative efforts such as Consortium for Energy Efficiencyand DOE’s Advanced RTU campaign.5. Identify partners to facilitate data analysis that will result in defensibleprojections of savings for regulators.Non-Energy BenefitsOwners and managers of commercial buildings with RTUs often havetenants that pay the electrical bill. This owner/tenant split incentive resultsin cases where owners and managers do not see the value of the work indollar savings.One method for counteracting this problem is to highlight non-energybenefits: i.e. features that provide value directly to the owner or managerby increased control over the site or increased ability to attract and retaintenants. Measures that provide increased control and monitoring to eitherthe owner or tenant can yield this value and result in greater programpenetration.Some measures discussed in this primer provide internet connectivity andremote control over settings that owners and managers can use to trackproperties. Other features provide advanced scheduling and controllabilityor fault detection to tenants that may improve tenant retention. Theseupgrades can also increase facility valuation and translate into financialbenefits for the owner or manager.Other measures can reduce runtime on the compressor or othercomponents, leading to increased RTU lifetime. This is also of realfinancial value for the owner. Although we cannot calculate an exactdollar value on each of these non-energy benefits, these features can behighlighted as part of a program to make it more compelling.Design Resources:Ducts, Zoning and Lockouts, and the Building EnvelopeNBI HVAC Design Guides:http://newbuildings.org/hvac-resourcesOf course, not all energy usage problems are related to the RTUequipment or its controls. System design, installation, commissioning andthe characteristics of the zone that it serves all influence the RTU’s abilityto operate efficiently. If the zone being served has a lot of infiltration or theducts are poorly designed, then the RTU will work much harder to meetthe set point temperature than a similar RTU with the same interior loadsbut with well-designed, well-sealed ducts and a good building envelope.ASHRAE Small Building Design echnology/advanced-energydesign-guidesNBI RTU Research:http://newbuildings.org/hvacAdvanced Buildingshttp://www.advancedbuildings.net/Outside of duct design and sealing, building and system design relatedissues can be addressed during new construction or major renovation.We discuss this in the ‘Replace’ section, but additional resources may beconsulted at the left.RTU Savings Primer7

The RTU Efficiency FrameworkUsing primary and secondary research, NBI has identified savingsopportunities for RTUs with examples from energy efficiency and greenbuilding programs and data from projects and modeling analysis. A simpleframework of measures is used to organize the approaches to addressRTU efficiency. These are the three “Rs”:RepairRetrofitReplaceIncentivizing maintenance personnel to visit a site and makestandardized maintenance upgrades to a particular RTU and/orcontrols.Adding a new component to an RTU, its components, or controls,to improve the thermodynamic operation, enable advanced orimproved functionality or connectivity, or add diagnostic capability.Completely remove existing RTU/controls and replace it with ahigher efficiency unit or completely change the HVAC designapproach.Measures that fall into these categories apply either to the RTU equipmentoutside the building (typically on the roof) or to mechanical componentsor controls and sensors inside the building. This Primer Guide discussesmeasures in terms of ‘Inside’ and ‘Outside’ solutions.InsideInside the building, the RTU thermostat, duct work and additionalsensors are designed to maintain comfort based on occupantwork schedule. Measures to improve performance includerepairing and recommissioning the controls, installing a remotelymonitored thermostat system, addressing duct leakage andinstalling lockout controls for doors and windows.OutsideThe heating, cooling and ventilation unit itself is typically onthe roof. This label refers to repairs and measures that improvethis RTU so that it delivers requested cooling (or heating) moreefficiently.In this way measures can be better understood in terms of how theyaddress the typical problems that occur in RTUs. Within each categorythere can be more than one measure.In the next section we provide some data and findings for differentmeasures that fall into these categories. The categories are inherentlylinked and interdependent with training and education of both theworkforce and the customer. Without aware end-users along with skilledHVAC contractors and technicians, required equipment maintenance istoo often neglected, retrofits are not installed properly and replacementequipment is likely to be oversized (matching the oversizing of the originalequipment) thereby repeating the downward efficiency cycle.8RTU Savings Primer

SUMMARY OFSTRATEGIESTable 3: Summary of Strategies forRooftop Units Efficiency—Repair,Retrofit and tsideSummary of Strategies: Measure SavingsExpectations and Cost EffectivenessThis guide presents strategies and measures to help direct the efficiencyefforts and programs of building owners, managers, operators, engineers,contractors and utilities. Table 3 summarizes the measures by group—Repair, Retrofit, and Replace—and divides measures into Inside andOutside categories within each group. The table also provides a simpleassessment of the cost, savings, and cost-effectiveness of each measureor strategy. This broad view can guide the selection of areas of interest,depending on existing programs and incentive levels.Short sections on each measure provided in this primer have descriptionsand the status of program activity if available. The next section addressesRTU measures and strategies in more detail.MeasureMore InfoCostSavingsCost EffectivenessRTU MaintenancePage 10LowMediumHighFault Detection and DiagnosticsPage 11LowMediumHighInsideThermostats, Sensors, and ControlsPage 12LowMixedHighRetrofitMeasureMore InfoCostSavingsCost EffectivenessAdvanced Variable Speed ControlsPage 14Medium-HighHighMediumECM for Supply Fan MotorPage 18MediumMediumMedium-LowOutsideInsideAir-Side EconomizerPage 18MediumMediumMediumEvaporative ‘Side Car’ UnitPage 19Very HighHighLow*Evaporative Condenser Pre-CoolingPage 20Very HighHighMedium-Low*Advanced Wireless Controls and/or EMSPage eMore InfoCostSavingsCost EffectivenessHigh Efficiency RTUPage 21HighHighMediumHVAC System RedesignPage 22N/AN/AMedium-LowHVAC System RedesignPage 22N/AN/AMedium-Low* Excludes humid climatesRTU Savings Primer9

REPAIROutside EquipmentRepairRetrofitReplacelOutside - Repair OutsideInsideRepair covers approaches considered ‘maintenance’ rather than‘service’ of the units and systems. The term ‘service’ is used to describethe minimum approach needed by owners and contractors to keepequipment operating for occupant comfort (such as filter changes andcomplaint responses). The term ‘maintenance’ is used to describe amore comprehensive approach aimed at optimizing and maintainingperformance of the equipment and the entire system.Cost EffectivenessHighCostLowSavingsMediumRTU MaintenanceOutside repair programs perform maintenance using a trade ally to visita customer and verify that the unit is operating to the manufacturer’sspecifications and make small necessary repairs. This may include amulti-year program of continuous service. Programs for RTU maintenanceare surprisingly infrequent: only 9% of major utility RTU rebate programssurveyed provide incentives for RTU maintenance. The scope of themeasure involves having a contractor provide specific services, such as: Coil cleaning Fan Maintenance Refrigerant charging and leak repair Economizer testing and repair RTU controller replacement Economizer control upgrade Replacement damper motor Thermostat replacement and schedule adjustment (see InsideRepair below)Source: CQM mea

utilities, HVAC industry partnering–2009 Leadership in the successful Rooftop Unit Fault Detection and Diagnostics Mandatory Measure Project in the California 2013 Title 24 building energy standard–2011 Leadership with the NW Energy Codes Group in proposing the Rooftop Unit