Building owners are turning to site-recovered energy technologies such as ERV.
By: Stephen J. Pargeter
Building owners are caught between two powerful forces — the need to lower energy costs and
the need to meet or exceed outdoor air ventilation regulations for occupant health and comfort.
Large amounts of energy are wasted each day from commercial, institutional and government
building sites as heating, ventilation and air conditioning (HVAC) systems replace indoor air
with fresh outdoor air multiple times per day. Heating or cooling energy is continually wasted in
the exhaust air stream while new energy must be generated and used to condition entering
outdoor air. Building owners who fail to capture this wasted energy will continue to incur high
energy costs, negatively impacting property values, profitability, and the ability to attract tenants
with corporate or federally directed energy-efficiency mandates
To address this challenge, many building owners are turning to site-recovered energy
technologies such as Energy Recovery Ventilation (ERV). Designed to operate with new or
existing HVAC units, ERV technology provides an affordable means to simultaneously cut
HVAC energy costs without compromising outdoor air ventilation requirements.
Important Energy Efficiency and HVAC Energy Trends
The commercial building energy sector represents 20 percent of all U.S. energy costs and is
growing more rapidly than the residential energy sector. With HVAC systems consuming an
average of 40-60 percent of commercial building energy, owners are searching for ways to
reduce these expenses.
As for government buildings, various local, state and federal policies encourage, and in many
cases mandate, “greener” construction and renovation. For example, the Energy Independence &
Security Act of 2007 (EISA 2007) established energy management goals and requirements for
federal buildings. Section 431 adopts the energy intensity reduction goals of Executive Order
13423, which calls for energy consumption to be reduced by 30 percent by fiscal year 2015
(relative to a 2003 baseline). Section 434 requires every federal agency to ensure that major
replacements of installed equipment (such as HVAC systems) or renovations or expansions of
existing space employ the most energy-efficient equipment that is life-cycle cost effective. And,
with certain exceptions, Section 435 (effective Dec.19, 2010) prohibits federal agencies from
leasing buildings that have not earned an ENERGY STAR label.
As the nation’s largest energy user, the federal government is leading by example, through the
Federal Energy Management Program (FEMP). This program promotes energy efficiency
through recommendations and incentives for the private sector as well as through guidelines and
mandates for federal agencies. The FEMP mandates ERV systems for federal buildings and
recommends these systems be considered for schools and businesses.
To help federal agencies comply with all pertinent mandates, the 2010 Facilities Standards for
the Public Buildings Service (known collectively as the P100) establish design standards and
criteria for the construction, repair, alteration and modernization of federal buildings.
Administered by the U.S. General Services Administration (GSA), these standards state that heat
recovery equipment must operate at a minimum of 70 percent efficiency at winter and summer
outdoor design conditions.
Many private organizations are also aggressively working to increase building efficiency. The
American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) — the
organization that established the benchmark national energy standard 90.1 — recently raised
energy efficiency levels in its 2010 standard by 30 percent and proposed the first “green
building” standard in 2009. When formally adopted by building codes, these increased
efficiency standards will significantly impact HVAC equipment selection and design.
In addition, many corporations are recognizing the financial and marketing advantages of green
building design, prompting many owners to pursue LEED Certification or the U.S.
Environmental Protection Agency’s ENERGY STAR rating. With increased focus on energy and
the environment, building owners are constantly challenged to improve HVAC efficiency
without compromising indoor air quality or the company’s bottom line.
Building owners seeking to maximize the profitability of their investments face several HVACrelated challenges and opportunities including: minimizing wasted energy, replacing existing
HVAC equipment and cost effectively meeting or exceeding outdoor air ventilation
1. Minimizing Wasted Energy: A large portion of HVAC energy can be attributed to
conditioning outdoor air ventilation. As fresh air is drawn into the building, stale air is expelled
along with site-generated energy used to condition it. This energy-rich exhaust air represents the
largest source of wasted energy in most commercial buildings. By failing to recapture this site
energy, owners will continue to face rising energy costs, lower profitability, and missed
opportunities to reduce greenhouse gas emissions.
2. Existing HVAC Equipment: Upgrading HVAC equipment provides an opportunity to lower
building energy use, however many energy efficient technologies are perceived to be expensive.
Fortunately, proven technologies are available to improve HVAC system efficiency and provide
attractive returns. Building owners willing to apply these technologies can successfully reduce
energy consumption and greenhouse gas emissions in existing buildings, often with local utility
3. Outdoor Air Ventilation versus Energy Cost: Studies have proven that outdoor air ventilation
creates a healthier work environment. According to the EPA, “Indoor air can be 2-5 times more
polluted than outdoor air … [and] that increased amounts of outdoor air supply is generally
better for indoor air quality.”
However, as outdoor air rates increase, so does the size, cost and operating expense of HVAC
systems. Attempts to reduce these costs by lowering ventilation rates in the 1980s led to Sick
Building Syndrome and multiple indoor air quality complaints and law suits, resulting in
building codes to protect the health and comfort of occupants. Recognizing that more ventilation
is beneficial, building owners must find a solution to provide for the health of its building
occupants while also controlling energy costs.
The Solution: Energy Recovery Wheel Technology
Energy recovery wheels, also known as enthalpy wheels, resolve the conflict between indoor air
quality and energy conservation by recovering site energy contained in building exhaust air. Up
to 80 percent of this energy is recycled to precondition outdoor air, resulting in reduced HVAC
load and operating cost.
For new and replacement projects, energy recovery costs are typically offset by lower HVAC
system first costs while up to 80 percent reductions in outdoor air fuel consumption provide
healthy returns for the life of the HVAC system.
Energy recovery wheels may also be used to improve the efficiency of relatively new HVAC
systems by up to 40 percent providing 1-3 year paybacks when supported by the local utility.
Finally, energy recovery wheels enable building owners interested in marketing green, healthy
buildings to increase outdoor air levels above minimum code, earning LEED points and reducing
the risk of indoor air quality complaints.
How Energy Recovery Wheels Work
Enthalpy wheels transfer energy by rotating between outdoor air and exhaust airstreams to
transfer heat and moisture from one airstream to the other. AHRI certification verifies the
effectiveness of this energy transfer.
Total energy saved depends on the wheel’s effectiveness and the difference in temperature and
humidity between the two air streams. A bigger differential drives larger energy savings.
Benefits of Energy Recovery Wheels
Energy recovery wheels offer many benefits, including:
– Reduce outdoor air energy costs 60-80 percent
– Reduce capital equipment cost by minimizing HVAC design loads
– Increase outdoor air levels 2-3 times without adding load to existing HVAC system
– Cost effectively improve HVAC system’s control over indoor humidity to prevent mold and
– Maintain building values by maximizing outdoor air ventilation and building health, thus
creating positive public relation opportunities
– Enable building owners to participate in energy programs such as ENERGY STAR
– Provide instant to two year paybacks in most North American climate zones
Case Study: School District Triples Ventilation and Saves Energy
The Port St. Lucie, Fla., school district was faced with having to upgrade HVAC systems in five
school buildings to meet changing air quality regulations. Upgrading to the revised code would
require adding 479 tons of air conditioning to accommodate increased levels of outdoor air.
The district considered installing additional chillers and air handling systems, however, this
method was determined to be impractical and costly due to space constraints and the complexity
of the retrofit, which meant the project could not be completed during school break.
Instead, the district chose a simpler, more energy efficient and less costly approach: standalone
ERVs with energy recovery wheels. The use of ERVs minimized installation costs by utilizing
existing ductwork and eliminating the need for additional chillers saving 335kw in peak demand.
A 70 percent reduction in outdoor air energy load saved the district an estimated $700,000 over
Energy Recovery Ventilation System Options
Energy recovery wheels are available from most HVAC OEMs and distributors in a variety of
– Energy Recovery Ventilators: Mounted indoors or outdoors. May include heating or cooling to
provide neutral air. Ducted separately or tied into existing ductwork.
– Rooftop Accessories: Bolt to rooftop units, no roof penetration required.
– Integrated Rooftop Packages: ERV wheel, fans, filters, and controls integrated into a standard
packaged rooftop unit.
– Air Handler Options: Energy Wheel modules for custom, semi-custom, and standard air
handler designs enabling a reduction in chiller and boilers size.
– Wall Mounted Packaged Units: Vertically mounted indoor or outdoor units with integrated
What to Look for in Energy Recovery Ventilation
1. AHRI-certified: Products that are rated and certified by the Air-Conditioning, Heating and
Refrigeration Institute (AHRI) ensure that building owners and engineers design HVAC
solutions based on verified performance data.
2. Temperature and humidity transfer capability: Look for ERV solutions that efficiently
transfer both heat and humidity, as this maximizes energy and capital equipment savings for the
3. Easy cleaning and low maintenance: Seek a solution that is easily accessible for cleaning and
maintenance. Energy wheels that cannot be cleaned are less effective over time, resulting in
shorter life spans and unrealized energy savings.
4. Performance Modeling: Look for a solution with computerized modeling software that
predicts performance and savings. The most accurate programs incorporate weather trends and
5. Trusted provider: Choose AHRI 1060 performance certified providers to ensure the highestquality equipment and strong customer service.
The high energy cost of outdoor air ventilation is a pressing issue among building owners eager
to save money while providing a clean, healthy building. Energy recovery wheels offer an
environmentally friendly solution to cut energy costs, provide fresh outdoor air ventilation, and
guarantee a high return on investment.
 Site-recovered energy is any energy recovered on site and re-used to reduce the demand for
 (2011). FlexYourPower. HVAC system.
 Scott, J. (July 7, 2010). ASHRAE. Standard 90.1: Setting the energy foundation in buildings
for 35 years. News release.
 (November 30, 2009). ASHRAE Standard Project Committee 189.1. Standard for the design
of high-performance, green buildings except low-rise residential buildings.
 EPA, IAQ Design Tools for Schools