Know efficiency standards for HVAC system design

Education and diligent analysis will help engineers navigate new U.S. Department of Energy pump-efficiency rules.

02/08/2017


Figure 1: Education on the proper design, installation, and maintenance of hydronic and steam systems is a continuing focus for engineers in 2017. All graphics courtesy: Xylem Inc.Learning objectives

  • 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 benchmarks

Table 1: The U.S. Department of Energy defines equipment lifetime as the age when a pump is retired from service. The average lifetime by equipment class is listed.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.


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