ASHRAE Journal - January 2013 - 65

emerging technologies

erV technology revisited S
By mildred hastbacka; John Dieckmann, Member ASHRAE; Antonio Bouza, Associate Member ASHRAE

ignificant developments have been made in energy recovery

ventilation (ERV) as the technology continues to emerge into the

commercial mainstream. Therefore, we are revisiting ERV, which we last covered in the “Emerging Technologies” column in August 2003.

As illustrated in Figure 1, energy recovery ventilation uses an air-to-air energy recovery heat exchanger to transfer sensible and sometimes latent heat between the building exhaust airstream and the outdoor ventilation makeup airstream, preconditioning the outdoor air before it is introduced into the building. In the warm weather months, heat and humidity are transferred from the incoming makeup air to the exhaust air, precooling the makeup air. In the cold weather months, heat and humidity are transferred from the exhaust air to the makeup air, preheating the makeup air. Air-to-air recovery exchangers may transfer sensible heat only or both sensible and latent heat. The former are commonly called heat recovery exchangers and the latter are called enthalpy or total energy exchangers. The effectiveness of the exchanger is a metric indicating how much of the enthalpy that could potentially be transferred (the supply airflow rate times the enthalpy difference between T1, H1 and T3, H3 in Figure 1) actually is transferred. A variety of air-to-air enthalpy recovery and sensible heat recovery exchanger configurations are commercially manufactured. They range from designs of rotary enthalpy recovery wheels and sensible heat recovery wheels to both sensible only and total enthalpy plate type heat exchangers. The latter of these uses moisture-permeable materials in the plates to transfer humidity. Sensible-only heat recovery can also be accomplished
January 2013

with runaround loops. Many manufacturers offer products with recovery effectiveness ranging up to 80%. There are three significant developments in the standards relevant to ERV that are facilitating increased acceptance of ERV technology: In 2011 AHRI updated Standard 1060 (first published in 2001), “Performance Rating of Air-to-Air Heat Exchangers for Energy Recovery Ventilation Equipment.” This standard is the basis for certified performance ratings of this type of equipment. With a certified performance rating, equipment can be purchased with full confidence that it will perform as rated. In 2003, AHRI published Guideline V (updated in 2011), which provides a method to calculate a combined efficiency rating for an HVAC product with integrated energy recovery, based on certified performance ratings of the individual cooling and energy recovery subsystems of the integrated system.

ASHRAE/IES Standard 90.1-2010 includes, for the first time, mandated use of energy recovery in most climate regions. Table 1, a reproduction of Table 6.5.6.1 from this standard, details the range of design parameters where energy recovery is required. The broadest requirements are for cold climates (Zones 7 and 8: northern Minnesota, North Dakota, and more northerly locations) and humid climates in the eastern half of the U.S. (Zones 1A, 2A, 3A, 4A, 5A, 6A; all of the continental U.S. that includes and is east of the Dakotas, Nebraska, Kansas, Oklahoma, and the Eastern half of Texas).

energy savings
Buildings that are good candidates for ERV are those that are (a) located in climates with moderate to extreme cooling or heating requirements; (b) require large amounts of outdoor air ventilation; and (c) new construction, to take advantage of the potential for HVAC system first cost reduction.1 Energy recovery systems have been demonstrated to reduce HVAC costs substantially while still enabling compliance with code requirements for outside air exchange. Turtle River

Energy Recovery Heat Exchanger T4, H4 Exhaust Return Air T3, H3

T1, H1

Outdoor Air

Supply Air

T2, H2

Duct Wall (typ)

Figure 1: Generic air-to-air enthalpy exchanger for energy recovery.
ASHRAE Journal 65

ASHRAE Journal - January 2013

Table of Contents for the Digital Edition of ASHRAE Journal - January 2013