SRS Blog

Building energy efficiency insights from the innovators behind EPIC
September 3, 2020

Devil is in the Details: Establishing Baseline Energy Efficiency Metrics

To estimate the percent energy consumption savings using energy efficiency metrics, knowledge of the energy performance of both the existing equipment and any proposed higher efficiency replacement equipment is crucial. The expected energy performance of replacement equipment is typically known or may be obtained from the manufacturer. Unfortunately, establishing the energy performance of existing equipment that may often be more than a decade old can present a challenge.

The percent energy consumption savings equations for some common equipment that may be replaced are presented below. It is evident that the calculations rely on energy efficiency metrics of both the existing equipment (baseline) and the proposed high efficiency replacement equipment.

Air Conditioning Units

Electricity savings, %  =  1 – [(1/IEERHighEfficiency)/(1/IEERBaseline)] x 100%

Heat Pumps

Electricity savings, %  =  1 – [(1/IEERHighEfficiency )/(1/IEERBaseline)] x 100%

Heating energy savings, % =  1 – [(1/COPHighEfficiency)/(1/COPBaseline)] x 100%


% cooling savings = [1-(IPLVHigh Efficiency)/(IPLVBaseline)] x 100%           


% heating energy savings = [(AFUEHigh Efficiency/AFUEBaseline) – 1] x 100%

Domestic Hot Water (DHW) Heating

% DHW heating energy savings = [1 – (EFBaseline/EFHighEff)] x 100%


IEER = Integrated Energy Efficiency Ratio, (Btu/hr unit capacity)/watts input (IEER replaced IPLV in January 2010 for part-load performance)
COP = Coefficient of Performance, dimensionless, e.g., kW output/kW input
IPLV = Integrated Part Load Value, kW/ton (The Non-standard Part Load Value or NPLV is a newer rating for chillers that provides a weighted average efficiency for a full year considering two main parameters: the % of operating hours at different loads and the different ambient conditions that can affect the entering water temperature.)
AFUE = Annual Fuel Utilization Efficiency, %
EF = Energy Factor-indicates a water heater’s overall energy efficiency based on the amount of hot water produced (energy out) per unit of fuel consumed (energy in) over a typical day (To enable greater consistency in equipment energy efficiency comparisons, EF ratings were replaced in June 2017 with the UEF or Uniform Energy Factor.)

An excellent source for the algorithms needed to estimate energy consumption savings is presented in Appendix X9 of ASTM Standard E3224-19, Building Energy Performance & Improvement Evaluation (BEPIE).

In these equations, the energy efficiency metrics for high efficiency replacement equipment is generally known (or should be readily available from the manufacturer). However, the challenge involves estimating the energy performance of existing equipment, particularly existing equipment that has remained operational beyond its expected useful life. Such equipment may, for example, no longer have an observable and readable identification tag (or nameplate), or the building owner/manager may not have access to the operating manual, original purchase order or proposal, or any other supporting documentation that might provide insight into the equipment’s energy efficiency rating when installed. An identification tag on the equipment would likely identify the manufacturer and model number which can then be further researched. However, finding specifications for equipment that may be more than a decade old can be challenging. Moreover, even if the research can successfully identify the unit’s original energy efficiency metrics, e.g., the original EER and/or IEER of a packaged rooftop air conditioning unit, the unit’s current efficiency would unlikely be at the same performance level as when it was newly installed, as its performance would be expected to degrade with time.

The question then becomes: what approach can be used to estimate the energy performance of existing equipment, i.e., the baseline energy efficiency metrics needed to estimate the percent energy consumption savings?

One approach might involve the following:

  1. If the existing equipment was installed by the contractor replacing it, information on the existing equipment may be available in the contractor’s files. Whether or not equipment energy efficiency metrics can be found is another question. Useful information may also be found on the equipment’s identification tag (or nameplate), assuming it still exists and is readable. At a minimum, the manufacturer, make and model number hopefully will be available because internet research might then provide the needed information. If it does not, the manufacturer, assuming the manufacturer is known, can be contacted to see if the needed information might be available.
  2. If (1) does not yield the needed information, based upon the approximate age of the equipment the building energy code (IECC/ASHRAE 90.1) in effect when the equipment was installed may provide insight into its energy efficiency metrics. If the local building energy code in effect at that time is not known, it can conservatively be assumed that the equipment’s energy efficiency metrics likely complied with the IECC or ASHRAE 90.1 standards in effect at that time (notwithstanding any lag time between the IECC or ASHRAE 90.1 standard in effect at that time and local building energy code updates). This assumption is reasonable considering most manufacturers design their equipment to comply with the latest ASHRAE 90.1 standard.
  3. Assuming the energy efficiency metrics of the existing equipment when initially installed can be established, a factor to represent performance degradation from the time the equipment was installed to the present should next be considered. Any performance degradation factor will most likely be dependent upon how the equipment was maintained and usually relies on the contractor’s experience.
  4. Once the baseline energy efficiency metrics can be established for the existing equipment and the energy efficiency metrics are obtained for the replacement equipment, an estimated percent energy consumption savings can be determined. This percent energy consumption savings would then be multiplied by the estimated weather-normalized energy consumption of the impacted end-use, e.g., space cooling, space heating, etc., to calculate an estimate of the annual energy consumption savings. The estimated energy cost savings can then be calculated by applying local utility energy unit costs.

The estimated energy cost savings calculation is critical as it provides the information needed to support the building owner’s return on investment (ROI) analysis. This is especially important when a contractor is proposing higher efficiency equipment at a premium price versus proposing only code-compliant equipment. Moreover, such cost savings and financial impact analysis can help answer the “tough” building owner questions, such as:

  • “Can you quantify the estimated ROI difference between high efficiency versus code-compliant equipment?”
  • “Does the enhanced performance associated with high efficiency equipment justify its price premium?”
  • “Which equipment replacement scenario optimizes lifetime cost savings?”

Fortunately, a new generation of software, data and predictive analytic solutions are emerging specifically designed to empower project developers and energy efficiency contractors to estimate energy efficiency metrics of existing equipment. This is crucial to calculating energy consumption and cost savings and making the business case to the building owner to invest in energy efficiency.

To learn more about how energy efficiency professionals are successfully meeting this energy savings challenge and driving sales of higher ticket, higher margin projects with SRS’s latest innovation: The Energy Performance Improvement Calculator (EPICTM), visit

About the Author

Anthony J. Buonicore is Director of Engineering at Sustainable Real Estate Solutions. Mr. Buonicore is a licensed professional engineer with almost 50 years' experience in the commercial real estate energy and environmental industry. He may be contacted through our Contact page.