Know efficiency standards for HVAC system design
Education and diligent analysis will help engineers navigate new U.S. Department of Energy pump-efficiency rules.
- Analyze the ways in which the U.S. Department of Energy (DOE) pump-efficiency rules will affect HVAC design.
- Understand the new pump efficiency guidelines that will go into effect in 2020.
Though the calendar has turned to 2017, it’s 2020 that’s looming large with the U.S. Department of Energy (DOE) pump-efficiency rules set to take effect at that time. Since the Energy Conservation Standards for Pumps was issued in late 2015, the industry has been buzzing about what the ruling’s impact will be on pump manufacturers, building owners, engineers, and others whose work involves centrifugal pumps.
The path toward compliance with the DOE ruling isn’t the only topic that will affect engineers in 2017. There are new American National Standards Institute/Hydraulic Institute standards, known as ANSI/HI standards; increased pressure to enhance sustainability in all aspects of HVAC system and building design; continued integration of technology; new terms and formulas; more and better data; a pressing need for education; and new ways to deliver what the customer has always demanded-reliable, quality equipment and systems.
The DOE effect
The goals of the new regulations are energy conservation and minimizing carbon emissions and greenhouse gasses. With about 20% or more of the electricity in the United States consumed by commercial and industrial pumps, creating an energy-efficient product that is less costly to operate will help achieve those goals.
Of the clean-water pumps on the market today, an estimated 25% do not meet efficiency standards. These products must be improved if the manufacturer wishes to sell them beyond 2020 or they must be retired; pumps currently in use are not affected by the new regulations. The DOE expects to realize substantial energy savings by 2025 through a combination of attrition and incentives to replace inefficient pumps.
The standards target five classes of rotodynamic pumps designated for use in pumping clean water in commercial, industrial, agricultural, and municipal applications:
- ESCC: end-suction close-coupled pumps
- ESFM: end-suction frame-mounted pumps
- IL: in-line pumps
- RSV: radially split, multistage, vertical, in-line casing diffuser pumps
- VTS: vertical-turbine submersible pumps (submersible turbines).
The standards apply only to pumps with an input power at a best efficiency point (BEP) between 1 and 200 hp; a BEP rate of flow of 25 gpm or greater; a BEP head of 459 feet or less; a temperature between 14° and 248°F; and/or nominal speeds of 1,800 and 3,600 rpm. Pumps, like double-suction pumps, that are not within these parameters are not included in the standard.
The DOE has established a new metric called the pump energy index (PEI) to rate the energy performance of pumps. All pumps must have a PEI of less than or equal to 1.00. The PEI is a ratio of the representative performance of the pump being rated over the representative performance of a pump that would minimally comply with any prospective DOE energy-conservation standard for that pump type.
Minimally compliant pump efficiency is determined by a calculation that includes specific speed, the BEP flow in gallons per minute, and a specified C-value. A C-value is the translational component of a 3-D polynomial equation that describes the attainable hydraulic efficiency of pumps as a function of flow at BEP, specific speed, and C-value. When a C-value is used to define an efficiency level, that efficiency level can be considered equally attainable across the full scope of flow and specific speed constant (C) that varies by pump type. This determines the pump energy rating (PER), the weighted average of input power to the motor at defined duty points, and is the standard basis for all PEI ratings.
Testing for compliance with the new regulations is a big part of the process. The Hydraulic Institute (HI) created a pump efficiency test standard, Standard for Methods for Rotodynamic Pump Efficiency Testing (HI 40.6), to meet the needs of the DOE. HI 40.6 was adopted by the DOE and written into the pump rule in 2016. It has been revised to match all the test requirements within the DOE rule.
The HI established a Pump Test Lab Approval Program (HI 40.7) in 2015 to help manufacturers and other pump test facilities improve current procedures and create testing protocols that are accurate, uniform, and repeatable in accordance with the new rules. According to HI, performing tests in a lab that not only apply the pump efficiency test standard (HI 40.6), but also stand up to an independent third-party audit, will build confidence in the market that the stated efficiencies will be achieved.
The ruling requires testing methods for both PEI constant-load (PEICL) and PEI variable-load (PEIVL) equipment classes. A metric of PEICL applies to pumps sold without variable-speed controls; PEIVL applies to pumps sold with variable-speed controls. Both PEICL and PEIVL describe the weighted average performance of the rated pump at specific load points, normalized with respect to the performance of a minimally compliant pump without controls. Several manufacturers have received HI test-lab approval and, in fact, already have products in the marketplace that achieve and exceed efficiency targets, having begun the process of retooling pump lines several years ago in anticipation of the efficiency standards. Not all manufacturers are fully engaged with the pending changes. There is a lot of support from industry organizations like the HI to help them get there.
It is incumbent on engineers to have a strong working knowledge of the efficiency ratings of the pumps they are specifying, along with the testing methods used to rate them, to optimize system design. It’s still the responsibility of system designers to select the right components and analyze the data. Something as simple as comparing the average equipment lifetime can yield immense savings; lifecycles for the same type of pump from different manufacturers might vary by 30% or more. DOE defines equipment lifetime as the age when a pump is retired from service and has established typical pump lifetimes by class of equipment.
An in-depth review of the DOE regulations reveals a few loopholes that must be eliminated by 2020, some of which, if not addressed, would allow manufacturers to skirt the intent of the new rules. For example, some have discovered that by putting a variable frequency drive (VFD) on a noncompliant bare (constant-load) pump, the pump can meet PEIVL standards. This clearly is not what the DOE intended and almost certainly will be addressed by the DOE in the near future by requiring manufacturers to specify both PEICL and PEIVL in all applications.
DOE regulations aside, industry organizations have long been proponents of improving efficiency. Much of these efforts are being driven by ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings and the ASHRAE roadmap for the HVAC industry on how to achieve net zero energy buildings in its report ASHRAE Vision 2020.
These and other efforts have created a greater awareness of energy efficiency and a shift toward a systems-focused approach to meet design requirements and efficiency benchmarks in the engineering community. For example, engineers are rethinking the common practice of oversizing pumps in favor of matching high-efficiency pumps and variable-speed controls to reduce overall energy consumption.
To that end, new tools for properly sizing and selecting HVAC equipment have entered the marketplace. Part-load efficiency value (PLEV) is a new pump-selection criterion. PLEV is a calculation that represents the efficiency of the pump at partial flow rates and can be used to gauge true pump performance within a hydronic system.
General industry practice has been to make pump selections based on a system’s design load, or the maximum capacity of the system, even though centrifugal pumps installed in HVAC systems operate a majority of the time at part-load conditions. Flow requirements fluctuate constantly throughout the year based on the heating or cooling load of a building at any given time.
However, with the traditional pump-selection approach, pumps were selected at 100% load conditions, even though the system generally only operates at that level 1% of its yearly operation. Actual efficiency depends on the configuration of pump versus load and flow conditions.
The PLEV calculation accounts for the entire variation profile and flow requirements based on the actual heating or cooling load in a commercial-building HVAC system, not just the BEP. It is derived from the successfully integrated part-load value (IPLV) performance calculation developed by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) in AHRI 550/590-1998: Standard for Performance Rating of Water-Chilling Packages Using The Vapor Compression Cycle. The proven formula describes the equipment efficiency while operating at various capacities of a chiller system and is crucial in supporting energy use and operating costs throughout the lifetime of the system. Due to its wide acceptance by chiller manufacturers as a baseline comparison between manufacturers, similar correlations can be adopted for centrifugal pumps used in both heating and cooling systems.
A B C D A, B, C, and D are the pump efficiency values at 100%, 75%, 50%, and 25%, respectively, of flow rate and at the corresponding head value on the control curve. Based on the equation, during any given year the pump will operate at 100% flow (duty point) only 1% of the year, at 75% flow 42% of the year, 50% flow 45% of the year, and 25% flow 12% of the year.
The subscript "v" denotes variable-speed operation with the control, or fixed head, calculated within a system’s critical circuit. Selection software that includes the PLEV calculation defaults to 30% of pump total design head (TDH) to represent the minimum control head within a system.
ASHRAE Standard 90.1-2013 requires that the total head loss in a system be calculated, making it natural to calculate the critical zone’s fixed head, too. This is the number that should be used because it represents a more accurate calculation, which will be reflected in the cost analysis.
Most heating and cooling systems are closed-loop and require a constant head differential at all times. The constant head differential is necessary for system control and to ensure that the required differential head across any controlled subcircuit is maintained during operation. PLEV can be used to accurately compare pumps from different manufacturers to identify overall operational efficiency. The 30% of TDH (or calculated minimum control head) within the equipment schedule, along with specifications, will ensure a fair "apples-to-apples" comparison among manufacturers.
PLEV provides system designers more latitude in selecting pumps slightly to the right of BEP, as long as a detailed system head loss is calculated. Pump selections to the right of BEP may have a higher PLEV than other selections because the PLEV load profile is heavily weighted at part-load conditions, mainly at 75% and 50% operation. These load-profile points alone account for 87% of operating hours. It is important to note that designers need to be aware that even though a majority of the building’s operation is at 87% part load, pumps still need to operate at the 100% full-load condition.
It’s also important to note that the PLEV selection criterion itself does not provide energy savings in an HVAC system. Rather, it is a tool to help designers select pumps that operate at the highest efficiencies across a building’s operating conditions. When combining highly efficient pumps with the PLEV selection criterion, system designers can maximize operational performance while realizing energy and cost savings as well as environmental benefits.
Pumping up data
The evolution to more integrated electronics in pumps will continue in 2017, providing pump operators and engineers alike with more precise and detailed data.
The integration of motors and controls on self-contained systems means the pumps themselves provide a wealth of information about power consumption and other indicators. The users of the equipment can monitor the pump for trends, which might indicate the pump is wearing out or that a bearing is going bad. Pump operators can then schedule planned outages for maintenance rather than being surprised by a pump’s failure.
Engineers can achieve optimum pump system performance by considering the motor, pump, and drive as one unit instead of individual components and how they react to system requirements. They also can take into account the payback in energy savings with these newer control systems when designing an HVAC system.
With VSDs becoming more prevalent, there is more interest in retrofitting existing systems to improve efficiency and lower operating costs. Awareness of the benefits of a variable pumping system means there is more pressure from end users on system designers to incorporate energy-saving components. This underscores the necessity for specifying engineers to become educated not only on new products and technologies, but also on how to maximize efficiency through total system design.
Other tools that focus on achieving the owner’s project sustainability goals, such as basis of design (BOD) documents, are becoming more widely used as projects become evermore technical in nature. A BOD promotes integration of the various disciplines throughout the whole building design process. It is a valuable tool to ensure the owner’s design intent is clearly represented throughout the many twists and turns of a construction project.
For HVAC design, a BOD includes specific details on the codes and standards that must be considered as well as how the components of the system will meet those requirements. Engineers must also increasingly consider the impact of building envelope construction and strategies, such as daylighting and shading, when designing HVAC systems.
In 2011, ANSI/HI issued its global standard for pumps, Rotodynamic Pumps for Hydraulic Performance Acceptance Tests (HI 14.6), which replaces ANSI/HI 1.6: Centrifugal Pump Tests and ANSI/HI 2.6: Vertical Pump Tests. ANSI/HI 14.6 contains a number of changes in test acceptance requirements for pump test facilities or laboratories. HI 14.6 was updated in 2016.
New to ANSI/HI 14.6 are three grades of accuracy for pump-acceptance criteria, which align it with existing ISO Standards and ANSI/HI 11.6: Rotodynamic Submersible Pumps: for Hydraulic Performance, Hydrostatic Pressure, Mechanical and Electrical Acceptance Tests and specify test criteria for submersible pumps. Previous ANSI/HI standards used only two grades of accuracy.
It’s important for specifying engineers to note under which grade a pump has been tested to be sure they are making accurate comparisons among manufacturers. They also must look closely at default settings in online pump-selection software.
In 2017, engineers can expect revisions from ANSI/HI regarding vibration standards for vertical-turbine pumps, responding to requests from users and operators. In addition, expected revisions to intake standards will help prevent improper flow patterns in small and large pumps to improve operational efficiency and maintain longer life.
A new order
Under President Barack Obama, government policies designed to reduce greenhouse gases and carbon emissions have resulted in rising electricity costs and a shift from coal to other forms of energy, such as solar power and natural gas, creating a greater need to realize energy savings through decreases in energy demand. It remains to be seen how newly elected President Donald Trump’s priorities will affect existing energy directives, though he, too, has said he is committed to reducing emissions.
Current policies have presented both an opportunity and a necessity for engineers to manage their energy savings through efficient HVAC system design. With ultra-efficient pumps, advanced controls, and integrated design, engineers can make environmentally conscious choices today and be on the road to energy efficiency well in advance of the 2020 mandates.
-Mark Handzel is vice president of product regulatory affairs and director of HVAC commercial buildings with Bell & Gossett, a Xylem brand. He is a member of the Appliance Standards and Rulemaking Federal Advisory Committee’s Commercial and Industrial Pumps Working Group.
-Paul Ruzicka is global COE of residential, commercial wastewater and chief engineer at Xylem Inc. He is a member of the Hydraulic Institute and was named HI member of the year in 2015 in part for his work as HI technical representative with the DOE and for his role in mentoring young engineers.