ARI Guideline V – Characterizing the Efficiency of Energy
Recovery Ventilation and Informing the Design of HVAC Systems
Energy recovery ventilation is currently available technology that conserves energy and reduces
electricity demand associated with the heating, cooling, humidification and dehumidification of
buildings. While it promises significant benefits and is currently available in a wide variety of
HVAC products, energy recovery ventilation will only achieve its potential when a large
percentage of installations include the technology. The industry, as represented by the Air
Conditioning and Refrigeration Institute (ARI) and the American Society of Heating
Refrigerating and Air-Conditioning Engineers (ASHRAE), is committed to providing sound
guidance that will assist in transforming the HVAC market, reducing building energy use in a
cost effective and responsible manner. The newly published ARI Guideline V-2003, “Calculating
The Efficiency of Energy Recovery Ventilation and Its Effect on Efficiency and Sizing of
Building HVAC Systems”, is the latest product of this effort.
ANSI/ASHRAE Standard 84-1991, ANSI/ARI Standard 1060-2001 and ARI Performance
Certification provide for characterization of the performance of energy recovery ventilation
components. With the publication of ARI Guideline V-2003, the industry has made available a
standard methodology for calculating the efficiency of air-to-air energy recovery ventilation
equipment. More importantly, for the first time, it is possible to calculate the contribution of this
equipment to the efficiency of heating and cooling systems using an industry approved consensus
document. According to recent DOE research, energy recovery ventilation represents one of the
single largest sources of energy efficiency improvement available to the HVAC industry. The
availability of the Guideline means that it is now possible to take credit for these system
efficiency gains, effectively removing another barrier to their implementation.
Guideline V presents a rigorous methodology for determining the efficiency of energy recovery
ventilation systems. This is based on the standard calculation of useful energy delivered by a
process divided by the energy consumed in that process. To distinguish it from similar
calculations of energy efficiency ratio or EER for unitary equipment, a new term, recovery
efficiency ratio (RER) is introduced. In the case of energy recovery ventilation this is a measure
of useful space conditioning energy recovered over the extra fan energy required to move the two
airstreams through the energy recovery device (an air-to-air heat exchanger). Certified data for
effectiveness at a given airflow from ARI Standard 1060 allows the accurate determination of
energy recovered. Certified data for pressure loss, combined with available information on the
efficiency of the air moving device(s), and any additional power input to the energy recovery
device provides the denominator in our equation. Because the recovered energy can be very
substantial while the energy used is relatively small, typical RER’s for energy recovery range as
high as 120.
More easily understood in the context of accepted ratings of efficiency is the new term
“combined efficiency” (CEF). Straightforward in concept, the CEF combines that portion of the
cooling or heating work done by the unitary equipment at its efficiency (EER or COP) and that
portion of work done by the energy recovery system at its efficiency (RER) into a single number.
CEF is expressed in the same terms as the familiar EER or COP for unitary equipment. For the
purposes of characterizing the performance of systems with and without energy recovery or
systems with various types of energy recovery, the CEF is directly comparable to the traditional
EER at any given set of conditions. This makes the CEF descriptor particularly useful for
characterizing efficiency at design conditions. The addition of energy recovery ventilation to
typical systems results in a 10% to 40% improvement in efficiency at design. Utility rebate
structures that provide incentives for reduced demand can use this information directly in an
apples-to-apples comparison with other methods of improving efficiency.
Another critical element addressed by Guideline V is the proper sizing of unitary air conditioners
when used with energy recovery. As recognized by major manufacturers and discussed in the
ASHRAE Handbook, Systems and Equipment, Chapter 44, energy recovery effectively reduces
the load of outside air at design, in turn allowing the heating and cooling equipment to be reduced
in size. In order to calculate the CEF, the guideline determines that portion of the design load
provided by the energy recovery. The capacity required of the unitary air conditioner is
effectively reduced. This “downsizing” of the air conditioning system is critical to the economics
of energy recovery and to optimum control of indoor humidity (by avoiding oversizing and
attendant short cycling).
It is the goal and intent of this effort that Guideline V will assist in market transformation,
reducing peak electric energy demand, contributing to Federal and industry goals for reduction of
building energy use over the next 10 to 30 years, and capturing the 0.55 quads of annual energy
savings (as determined by a U.S. D.O.E. study) available through the widespread use of energy
recovery ventilation. This represents approximately 18% of current building HVAC&R energy
use.
In summary, ARI Guideline V is a first step in describing the efficiency of systems that utilize
more than one heating or cooling technology to meet the building load. Specific to combinations
of energy recovery ventilation and packaged unitary HVAC equipment, the Guideline provides
accurate information on equipment sizing and system efficiency that is essential for proper
design, product selection and system optimization. The Guideline also highlights the need to
consider component application in selecting the appropriate certified or application ratings for use
in efficiency calculations. Whether the energy recovery component is integrated in the air
conditioner design, added as an accessory in the field, or provided in a separate stand alone
package in conjunction with unitary equipment, Guideline V allows the system efficiency to be
accurately characterized, providing a level playing field for technology in the context of
engineering tradeoffs, utility demand management incentives and government marketing
programs.
ARI Guideline V-2003 is available for free download at the standards section of the ARI CoolNet
website, www.ari.org. The Air-Conditioning and Refrigeration Institute (ARI) is the national
trade association representing manufacturers of more than 90 percent of North American
produced central air-conditioning and commercial refrigeration equipment.