March 23 2008

What is Energy Recovery Ventilation? And why should I care?

Entropy Wheel_Image 05 Combined

Energy Recovery Ventilation (ERV) refers to the recapture of energy typically lost through the building ventilation process. Conditioned air that is routinely being exhausted from both residential and commercial buildings contains significant energy in the form of heat or coolth and humidity which is lost into the exterior environment. As part of a preconditioning process, ERV systems transfer the energy from the exhaust into the incoming air stream, which can also be described in terms of enthalpy. The use of ERV can have significant benefits both directly and indirectly in terms of energy efficiency, indoor air quality, and downsizing of the remaining HVAC equipment.

It is important to note the difference between Energy Recovery Ventilation (ERV) and Heat Recovery Ventilation (HRV). ERV exchanges both temperature and humidity between the exhaust and incoming air. HRV only exchanges thermal energy. The difference can also be stated as Total and Sensible or just Sensible energy exchange.

ERV systems are gaining popularity for a number of reasons. First, the technology and manufacturing processes are making the systems more affordable. Secondly, increased awareness of energy efficiency and sustainability both for environmental and economic reasons are causing more building operators to request such energy saving measures. Last and perhaps significant, increased ventilation to prevent Sick Building Syndrome (SBS) and promote healthy indoor environments results in a dramatic rise in energy consumption. Heavy ventilation or air changes requires the use of ERV technology, especially in the case of Passive Houses, high LEED certifications and most high performance buildings. In the United States ventilation standards are set by ASHRAE 62 which are used for both LEED and a general standard for high performance buildings. There is a growing body of data to suggest the health benefits of healthy indoor environments and updates to ASHRAE 62 are a recognition of that evolution.

An Opinion on ERV

ERV technology will likely develop further as awareness of occupant health, environmental sustainability, and energy cost grows. Right now we can recover up to 85% of the energy from the exhaust air, maybe in the future it will be possible to recapture even more. Costs will be reduced. The systems will be easier to integrate.

But to me the most exciting aspect of ERV technology is the idea that we can harvest latent, waste energy from our buildings, systems, occupants and environment. Renewable energy sources do roughly the same thing except they recover energy from the largest system of all, the planet itself. Wasting renewable energy supplies is unwarranted but probably inevitable. Entropy will occur in a system, but blatant waste of energy we have already generated elsewhere is shameful. Buildings use energy generated from coal fired plants, nuclear facilities, and other carbon and pollutant producing sources. This energy pollutes our environment when it is created. Costs real money. And therefore should not be thrown out into the environment. On a larger scale, projects like the Zollverein School and Hammarby Sjostad are have started to engage the idea that buildings can recover waste heat energy but the technology has not advanced far enough.

Who knows, maybe an adoption of ERV systems will cause a sea-change in the way people think about energy!

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March 24th, 2008 at 8:46 PM

Lloyd Alter

Thank you for reminding me of these. When I first graduated as an architect I wanted to use one, then they were called enthalpy wheels, but were too expensive and nobody understood the point.

March 25th, 2008 at 1:55 AM


No problem Lloyd. By the way I am a fan of the articles you post on Treehugger... you know where to hunt for good architecture stories... Hopefully one day someone will agree to let me design a high performance building and I'll get to install one of these... Actually when I was in grad school studying sustainable design at Carnegie Mellon I got to open up a Semco ERV... very interesting tech... Cheers, Jonas

March 25th, 2008 at 2:32 AM

Greenline » What is an Enthalpy Wheel?

[...] Enthalpy Wheel is a type of Energy Recovery Ventilator (transfers both heat and sensible energy) that uses a rotating air permeable energy exchanger to [...]

April 6th, 2008 at 9:38 PM

Greenline » Earth Tubes

[...] exhaust air to incoming ventilation air in the winter or vice versa in the summer.  (See Jonas Risen’s recent post on Energy Recovery Ventilation for an excellent primer on the topic. [...]

June 1st, 2009 at 10:12 AM

Greenline What is Energy Recovery Ventilation And why should I | Portable Greenhouse

[...] Greenline What is Energy Recovery Ventilation And why should I Posted by root 7 minutes ago ( Post a comment or leave a trackback trackback url response to the build up of greenhouse gases and explore the repercussions for today world and Discuss  |  Bury |  News | Greenline What is Energy Recovery Ventilation And why should I [...]

December 15th, 2010 at 6:37 PM


I was told an ERV system can greatly help in the winter to control condensation on windows. Is this a possible solution to go along with proper insulation?