Advanced Rooftop Unit Controls (ARC) Retrofit
Rooftop Unit Controls: Advanced with Remote Access and Monitoring vs. Conventional On-site
Controllers to retrofit existing rooftop units to optimize performance by providing remote energy monitoring and control as well as variable speed drives, demand-controlled ventilation, and other features.
Item ID: 338
HVAC--Rooftop Units & Air Handling Units
Technical Advisory Group: 2011 Energy Management TAG (#4)
Average TAG Rating: 3.5 out of 5
TAG Ranking Date: 09/29/2011
TAG Rating Commentary:
- This technology can provide significant savings, although the savings depend on the functions that the controller supports.
- These are interesting and promising but probably belong to the HVAC TAG/experts?
- Technology sounds good, but belongs in HVAC TAG, not EM TAG
- A controls system without verification of screen data is not always reliable or accurate. Any new controls on RTU-s should include video assistance to validate screen data.
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.7 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- Works well for lots of packaged single zone equipment. Adds complexity and cost. Vulnerable to programming errors.
- At least for Industry leaders and for those who have good results from third party evaluations. It is constantly changing and evolving.
- BPA already has a measure for this technology, but it hasn't had much uptake. A recent call with 5 PNW utilities, indicated different requirements and limited non-energy benefits.
- I think it is well established through work in California as well as by PECI, etc. The big question is how to do retrofits cost-effectively with the available technician pool.
- I strongly support the RTU systems that have adjustable speed drives and demand ventilation controls with CO2 sensors. The SPEED program tested the Catalyst System and there are many other field demos showing 40-50% electrical savings and 10-30% HVAC savings. All RTUs need continual monitoring and commissioning to have long term savings.
- This technology meets all 5 of the criteria admirably.
- BPA first needs to develop a framework for quantifying the energy savings. Products continue to be offered by the marketplace, but currently a path does not exist to credibly quantify energy savings - a robust evaluation framework is needed.
This measure highlights rooftop unit (RTU) retrofit controls with supervisory capability for small commercial buildings and big box stores.To produce electrical energy savings, minimum requirements are supply fan control with a variable-frequency drive (VFD) or fan cycling control, upgraded economizer controls, and remote web control and monitoring. Additional desirable features include web-enabled scheduling and setpoint adjustment, energy and performance monitoring, demand-controlled ventilation (DCV), other control optimization, and basic measurement and verification data collection. Products from several manufactures can be utilized to achieve this (see Products section below).
RTUs are estimated to be used in 46% of all commercial buildings and serve about 69% of the cooled floor space in U.S. commercial buildings. A 2013 study by Pacific Northwest National Laboratory involved installing advanced controllers on 66 RTUs on eight different buildings involving retail, office space, food sales, and healthcare. Of the 66 RTUs, 17 were packaged heat pumps with the rest packaged air conditioners with gas heat.The advanced controllers reduced normalized annual RTU energy consumption between 22% and 90%, with the average being 57% for all RTUs.
This measure is very similar to ET #246 Advanced Design Rooftop Unit, which is an entirely new RTU because the advanced controls provide the great majority of the energy savings. For facilities with fairly new but code-minimum RTUs, this retrofit may be the best choice. Facilities with older RTUs may benefit more from a wholesale replacement of the RTUs.
BPA has tested field retrofits of Advanced Rooftop Control (ARC) (Wang, 2013), and in 2015 will begin field testing ARC-Lite. ARC-Lite limits the controls package to those that are the most cost-effective: adding variable speed and the ability to reduce fan speed to pre-set levels (BPAARC-Lite, http://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-Reports-Archives/Field-Tests/Documents/FY15_ET_Field_Test_Pilot_Announcement_Final.pdf).
Baseline Description: Adjustments to HVAC Made During Scheduled Maintenance
Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 Commercial Building Stock Assessment gives the actual electrical building Energy Use Index (EUI) for various types of heating and cooling systems (CBSA Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding values are 19.9 and 9.4 kWh/sf/year, respectively.)Because this technology can be applied to many types of non-office buildings, a baseline energy use of 10.5 kWh/sf/year is assumed (NEEA, 2009).
Manufacturer's Energy Savings Claims:
"Typical" Savings: 35%
Savings Range: From 30% to 60%
Energy savings will depend greatly on what features are implemented and the condition of the existing equipment to be retrofitted. Transformative Wave estimates energy savings of 25% to 50% (Transformative Wave, 2013). Bes-Tech estimates energy savings at 40% to 60%, and estimates peak demand reduction at 30% to 60% (Bes-Tech,2013).
Best Estimate of Energy Savings:
"Typical" Savings: 45%
Low and High Energy Savings: 24% to 90%
Energy Savings Reliability: 6 - Approved Measure
BPA, in conjunction with Peninsula Power and Light, conducted an emerging technology field test on two 15-ton RTUs serving a small retailer. The measurement and verification (M&V) indicated a 45% reduction in total HVAC electrical energy use
(http://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-Reports-Archives/Documents/ARC_casestudy.pdf). Energy savings of 60% are noted in a report by the Oregon Energy Office and the Northwest Energy Efficiency Alliance (NEEA), (Stipe, 2003).
A 2013 study by Pacific Northwest National Laboratory involved installing advanced controllers on 66 RTUs on eight different buildings involving retail, office space, food sales, and healthcare. Of the 66 RTUs, 17 were packaged heat pumps and the rest were packaged air conditioners with gas heat. The advanced controllers provided a reduction in normalized annual RTU energy consumption between 22% and 90%, with the average being 57% for all RTUs (Wang, 2013). A demonstration project involving 35 RTUs with a combined 202.5 tons of cooling at the Lawrence Middle School and the Los Angeles Center for Enriched Studies (part of the Los Angeles Unified School District) showed energy savings of 45% HVAC with Transformative Wave's Catalyst.
RTUs with DCV and economizer control features alone are found to save about 30% of energy use for most occupancies and locations.
A California State Partnership for Energy Efficient Demonstration project found HVAC energy savings of 51% at a California State University Long Beach dance complex and 29% at a San Diego State University aquaplex (Grupp, 2013).
Omaha Public Power District tested Digi-RTU with 30 RTUs and found 52% kWh savings and better humidity control (Sunde, et. al., 2011).
Snohomish County PUD tested CATALYST at one facility and found 48% kWh savings.
HPAC Engineering Journal (Aug 1, 2011) published a case study about an Enerfit installation with electrical savings of 53%. Some of these savings came from air leakage repairs performed when the Enerfit was installed.
The DOE Office of Energy Efficiency and Renewable Energy (EERE) will soon post a "Retail Energy Alliance" guide for retrofitting to VAV. An energy savings calculator for big box and grocery stores in 16 climate zones will show 50% to 75% fan energy savings.
Energy Use of Emerging Technology:
5.8 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
RTUs are estimated to be used in 46% of all commercial buildings and serve about 69% of the cooled floor space in U.S. commercial building (Grupp, 2013). The cooled floor space in the commercial sector in the Northwest accounts for about 2,289.7 million square feet, according to table C-GB4 from a report from the Northwest Energy Efficiency Alliance (NEEA, 2009). Taking 69% of this total yields a potential of 1,579.9 million sf. This technology is most cost-effective for that portion (28.7%) of the regional conditioned floor area that uses electricity as the primary HVAC fuel. This brings the total square footage down to about 453,431,000 sf. Additional savings can be gained from the 66.3% of conditioned space that uses natural gas for space heat and electrical energy for cooling, although it will not be as cost-effective from the electric savings perspective. Therefore, the technical potential estimate here is understated or conservative.
It is not known what percentage of this floor space is already served by advanced rooftop controls, so we are estimating that none of it is, given that it is still an emerging technology.
Regional Technical Potential:
2.14 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $1.13
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.01
Installed cost for the advanced control units are approximately $450/ton for a 5- to 10-ton RTU (Wang, 2013). Assuming 1 ton of capacity for 400 sf, then the initial cost is $1.13/sf.
Note: This is a deemed measure under the October 1, 2014 BPA "Energy Efficiency Implementation Manual." The deemed amount for an advanced rooftop unit control retrofit is $150 to $225.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): 2.7
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
This is more cost effective on larger RTUs, 8 to 10 tons or greater.
TES Engineering tested Enerfit in 11 buildings and found a payback of 2 to 3.5 years in nine buildings but it was not cost-effective in two buildings.
This technology provides a combination of optimized RTU controls and monitoring via a web interface. Minimum requirements to provide electric savings are supply fan control with either a variable-frequency drive (VFD) or fan cycling control, upgraded economizer controls, and remote web control and monitoring. Minimum and desired features are detailed below. As you can see, when studies report incremental cost and energy savings from advanced RTU controls, exactly what that means can vary. However, the estimates provided reflect the most commonly adopted set of features.
Minimum Control Requirements:
-Supply fan control (variable speed drive [VSD] or cycling)
-Demand controlled ventilation
-Digital integrated economizer control
-Differential economizer high limit
Minimum Monitoring Requirements:
-Web-based setpoints and scheduling
-Time series point monitoring (trending)
-Monitored point threshold alerts
Desirable Control Options:
-Occupancy vent and temperature standby
-Night flush cooling
-Demand management or response
-Split DX coil flow control
-Compressor variable control
-Condenser fan variable control
-Optimum start with OAT input
Desirable Monitoring Options:
-Fault detection and diagnostics
-Time-series energy monitoring
-RTU energy benchmarking (single unit)
-RTU energy benchmarking (multiple units)
-Demand response measurement and verification (M&V)
For the addition of a VSD, in most cases the motor does not need to be replaced. A VSD addition works best for three-phase motors. Small RTUs less than 7 tons tend to have single-phase motors, and cycling is more likely to be successful for these fans. In all cases where the fan speed is managed or cycled, provisions to vary ventilation with fan speed are required. Demand controlled ventilation provides the most successful approach.
• CATALYST efficiency enhancing controller (EEC), by Transformative Wave Technologies, the technology development division of Performance Mechanical Group. CATALYST includes demand controlled ventilation (DCV) and economizer controls.
• Enerfit, by ECI (Electronic Controls Inc.).
Enerfit also includes demand controlled ventilation (DCV) and economizer controls, fault detection and diagnosis (FDD) and a well-sealed damper. Enerfit is most cost-effective for single-zone multi-compressor systems that are 8 tons or larger.
• Digi-RTU Roof Top Unit Controller, by DTL Controls.
Digi-RTU has the option of adding VFD to the condenser fan.
• Optimum Energy Products is developing a comparable product
For DCV with fan cycling or VSD, the premium ventilation sequence can be implemented with Alerton VLD, Innotech innTOUCH/MicroMAX and KMC FlexStat. For these products, the VSD is an external unit controlled by the premium ventilation sequence that includes night flush, ruggedized optimum start and occupancy sensor standby.
BPA has tested field retrofits of Advanced Rooftop Control (ARC) (Wang, 2013), and in 2015 will begin field testing ARC-Lite. ARC-Lite limits the controls package to those that are the most cost-effective: adding variable speed and the ability to reduce fan speed to pre-set levels.
(BPA ARC-Lite, http://www.bpa.gov/EE/Technology/EE-emerging-technologies/Projects-Reports-Archives/Field-Tests/Documents/FY15_ET_Field_Test_Pilot_Announcement_Final.pdf)
In the Northwest, 60% to 80% of economizers in existing RTUs do not work properly.
Even though 95%+ operation is at partial load, most RTUs have single-speed fans. At partial loads, these perform poorly.
While variable air volume (VAV) operation is well known, until now it has mainly been applied to centralized HVAC systems rather than packaged RTUs.
Early market introduction, some availability in the Northwest. See equipment under Detailed Description and Products sections above. See Advocates below for case studies.
Variable-speed operation is generally quieter than constant-speed equipment and improves equipment life. Earlier detection of equipment anomalies can lead to maintenance adjustments rather than more expensive equipment failures.
End User Drawbacks:
- A primary barrier is first cost, which can be addressed with financial incentives.
- Care should be taken to assure the existing blower motor can be equipped with a VSD without overheating.
- For the small commercial building sector, an excellent promotional program is essential. Financial incentives alone are unlikely to get traction without excellent promotion.
- Manufacturer's warranties may be violated, so it is best to check with equipment vendors.
- To meet energy code requirements for fresh air despite slower fan speeds, this may require DCV or adjusting the damper along with the fan speed.
Operations and Maintenance Costs:
Baseline Cost: $100.00
per: square foot per year
Emerging Technology Cost: $100.00
per: square foot per year
There should be no difference in maintenance costs.
Anticipated Lifespan of Emerging Technology: 25 years
The controller should last as long as the RTU it is attached to. The RTU might last longer if the new controller provides 'soft starts' on the compressors and blowers.
Some energy management systems, such as the Kite & Lightning Unity, improve economizer function without adding VAV capability (see ET #347 Low-Cost Energy Management and Control System for Small to Medium Commercial Buildings). This issue can be addressed with an integrated control and monitoring solution. Alternately, a control solution can be coupled with an independent monitoring solution.
Reference and Citations:
Katipamula, et al.,
Advanced RTU Campaign Webinar
U.S. Department of Energy, Better Buildings Alliance
A Better Buildings Alliance webinar presentation
Premium Ventilation Package Proof of Concept and Field Test
Bonneville Power Administration E3T
Hancock, et. al.,
Advanced Rooftop HVAC Unit Controls Pilot
Minnesota Center for Energy and Environment
Hart, et. al.,
Unitary HVAC Premium Ventilation Upgrade
2011 ASHRAE Winter Conference Technical Program
Sunde, et. al.,
Digi RTU Optimizer Case Study: New Technology to Maximum Energy Efficiency
ACEEE Summer Study on Energy Efficiency in Industry
Demand-Controlled Ventilation: A Design Guide
Oregon Office of Energy for the Northwest Energy Efficiency Alliance
Standards, Innovation Lead Rooftop Efficiency
Air Conditioning, Heating & Refrigeration News
Katipamula, et. al.,
Demonstration of Smart Building Controls to Manage Building Peak Loads: Innovative Non-Wires Technologies
Pacific Northwest National Laboratory
Heschong Mahone Group,
Advanced Controls Retrofits For Packaged HVAC Systems in Small and Medium Commercial Buildings
Pacific Gas and Electric Company
NBI Puts High Performance HVAC Units to the Test
New Buildings Institute
2010 Puget Sound BetterBricks Awards - Service Contractor (YouTube video)
Pump Down the Volume and Chill: Converting to Single-Zone VAV
24th Annual E Source Forum
Retrofit System, Variable-Frequency Drive Cut Energy Costs and Increase Comfort
Catalyst: The Proven RTU Retrofit Solution
Transformative Wave Technologies
Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance
Wang, et. al.,
Advanced Rooftop Control (ARC) Retrofit: Field-Test Results
Pacific Northwest National Laboratory
Grupp, et. al.,
RTU Efficiency Optimizers
CA State Partnership for Energy Efficient Demonstrations