Whole House Energy Recovery Ventilators (ERVs) Explained, by Panasonic

Posted by: Rate It Green Team

We’d like to thank Ken Nelson at Panasonic for his terrific video explanation of how ERVs work and for introducing us to the features and benefits of the Intelli-Balance 200 as well.  Have you been wondering what an ERV is and how it really works, as in, how this techology adds fresh air to built spaces while preserving energy and leveraging heat, and how exactly air and water vapor move around in that enthalpic (or magic) core?  Do you want ideas on how to explain this technology to clients in terms everyone can understand?  Read below for a fairly detailed summary of this presentation, and then plan to sit down to watch Ken's video presentation and conversation to learn more.   

 

How we get clean air into our homes is especially important given a range of issues brought to the forefront recently, including wildfires and other pollution, and of course the COVID-19 pandemic.  In addition, we’re spending even more time indoors and at home in particular, and good indoor air quality is essential to our health as well as for maintaining our furnishings.    

 

 

What is an Energy Recovery Ventilator, or ERV?

 

An Energy Recovery Ventilator, or ERV is part of a complex HVAC system that manages air temperature, humidity and particulates in our built environment.  An ERV is energy-efficient ventilation equipment that brings fresh air into the home while exhausting some of that “bad” or stale air out, in equal measure.   The supply and exhaust airstreams pass each other divided by a specially designed capillary plate that enhances the enthalpic heat transfer process.  This transfer lets us keep humidity inside when it’s drier out, or shunt excess moisture back to the exhaust airstream when the outside air is more humid.  We also recapture heat, or expel unwanted heat. And finally, the ERV provides cleaner air as a part of this process as it also filters the supplied air.  We must realize that our HVAC systems can’t keep up when humidity and temperature differences are too extreme, and the ERV helps us moderate these extremes.  

 

 

As Ken explains, an ERV helps keep the air flows in our systems “predictable” and “uneventful.”  That is a primary ventilation goal.   Bringing in this fresh air through a supply fan dilutes toxins and improves indoor air quality, while keeping the system in balance by expelling the existing air through an exhaust fan.  This idea of balanced air pressure within the home is essential and beneficial.  It’s a key objective across the building industry to educate more builders and occupants about this technology as it moves from a leading-edge building practice to a code and healthy home requirement.  

 

Moderating or tempering the air helps prevent our HVAC systems from working too hard.  Think about it this way - would we want to carelessly expel humid air in the winter, only to bring in colder, drier air we that now needs to be heated and humidified?  Re-claiming heat energy and moisture saves us a good deal of energy.  The best practice for builders and occupants is to balance supply and exhaust air flows to recapture or expel the heat and humidity that is not optimal.  

 

There’s an interesting discussion about upfront costs and ERV ROI, but it depends on how one defines ROI. ERVs technically use energy, but they help the rest of our systems operate more efficiently.  Temperature and humidity extremes make people uncomfortable, and when we do not manage temperature and humidity properly, we risk all kinds of property and health problems.  Our property is exposed to mold, mildew and pest risk, while people are susceptible to respiratory and other illnesses from poor Indoor Air quality.  

 

Ken helpfully begins this awesome science lesson with a glossary of useful terms.  He also explains the ideas of ballistics and buoyancy as they apply to ventilation.  Ballistics is what happens to items like particulates after propulsion.  What happens to a droplet after someone sneezes, for example?  Buoyancy is the tendency of an object to sink, rise, or float.  We want to create predictable air flows in a house that will allow us to manage buoyant particulates in the air.  To bring in fresh air, we certainly don’t want to have to wait for someone to open a window and for the wind to blow.  Managing predictable airflow is preferable to waiting for items to fall to the ground or stick to surfaces and then get cleaned.  

 

Ken explains how ERVs differ from HRVs, or heat recovery ventilators, which are both parts of an HRVs, or heat recovery ventilation system.  In an HRV, heat recovery is similar in that (outside) supply air travels through the core, providing fresh air to the occupants, and return air also becomes exhaust air in balanced system.  But the HRV does not transfer moisture between the airstreams as it does not have a capillary system to allow water vapor movement between them. 

 

 

 

How does an Energy Recovery Ventilator, or ERV work?

 

Ken does a fantastic job explaining how an ERV works, and shares some cool history on how we got here. Apparently back in the 1930’s, Frank Rowley of the University of Minnesota conducted research on how water moves through building materials, and how temperature and materials affect this movement.  Frank determined that vapor diffusion could carry a thermal load, and that moisture actually has temperature associated with it.  Furthermore, he documented that the higher the temperature difference, the more moisture moves through materials.  

 

 

 

 

As we know, air moves from hot to cold, and moisture from more to less.  So as the airstreams pass by each other, the first way an ERV works is by conduction, from hot to cold.  When the two airstreams pass over the surface of the plate between them, the plate material absorbs the temperature differential.  So heat will move from the warmer airstream to the cooler airstream through the plate.  The second method is capillarity. The water vapor moves though the capillaries in the enthalpic core from the warmer airstream to the cooler airstream in an ERV.  The capillary paths through the core are small enough that actual liquid does not flow through, only the grains of moisture as they seek a balance between the two airstreams.  It is important to keep the airstreams moving so that the moisture isn't allowed to condensate and phase change from vapor to liquid.  Constant air movement through the core will prevent any moisture-related mold and mildew.  This is one reason Ken advocates for continuous ventilation.  Ken shares two great examples, from hot to cold and cold to hot, where we can understand how the system captures or recovers heat and humidity. 

 

 

Panasonic's Intelli-Balance 200

Ken shares some questions and aspects to consider when selecting an ERV. He also provides an excellent introduction and demonstration of the Intelli-Balance 200 ERV by Panasonic, including settings and controls.  The Intelli-Balance 200 is a 200 cfm (cubic feet per minute, the volume of air flowing for each minute it moves) application, part of a family of products including the Intelli-Balance 100 at 100 cfm and the WhisperComfort model at 20-40 cfm.  The Intelli-Balance 200 can service up to a 7500 sf home.  

 

 

 

Ken does such a great job explaining, it’s worth a listen to process information in the form it’s shared and may be best received.  But we can summarize some key Intelli-Balance features here for convenience:

 

• Two DC motors - custom pressurization strategies
• Boost function allows for an occupant controlled airflow increase based on demand, in times or areas of increased activity or occupancy 
• MERV 13 supply filter, with optional MERV 8 and HEPA filters available
• The unit does not require a condensate line or drain
• Designed for stand alone use or connect to existing ductwork 
• Carry handles for ease of installation and employee safety
• Optional remove LCD 
• Designed for single family homes and new air-tight homes built to meet energy efficiency standards
• Engineered for any North American Climate Zone
  • Can operate in areas where temperatures can drop as low as -22°F (-30°C). Defrost cycle function activates when the outdoor temperature drops to 14°F
• High efficiency capillary core
  • Recovers heat and balances moisture
  • Core material permeated with anti-mold treatment
  • Sensible recovery rate (SRE) of 83% at 67 CFM
• Separate control of continuous supply and exhaust airflow 
• External controls 
• Meets Ontario ENERGY STAR and Novoclimate requirements
• Three installation options - floor, wall or ceiling (chain mount and brackets included)
• Includes static pressure ports with balancing instructions
• Powder coat finish for a professional look from a professional installer. No fingerprints or rust
• 6 year warranty on ECM motor, 3 years on all other parts

 

The Intelli-Balance 200 comes with a MERV 13 supply-side filter, which is becoming standard for quality filtration without impeding efficiency.  MERV stands for the Minimum Efficiency Reporting Value and measures the performance of filters when intercepting particles of .3 to 10 micrometers in size. The higher the MERV filter, the better.  HEPA stands for High Efficiency Particulate Absorbing filters and is even finer.  HEPA filters can make sense in higher air pollution areas, or in the event of wildfires or other irritants.  Ken explains that a HEPA filter will need to be inspected and cleaned more often, as it’s working harder to trap more particulate matter.  

 

Panasonic prides itself in making quiet ventilation products and achieves this with the Intelli-Balance 200 by strategically locating the fan motors within the device and using an EPS insulation lining throughout.  This is efficient and encourages operations as noisy fans cause occupants to turn equipment off.  In additional, Intelli-Balance 200 is a relatively small unit for what it does, which may also contribute to its sound reduction.  

 

Ken recommends running ERVs continuously.  When this equipment is not running, it is theoretically possible for moisture to settle.  It is never a good idea for moisture to remain in the core, though Panasonic has added an anti-mold treatment, just in case.  

 

 

When is an ERV ideal?

 

An ERV balances air flows and moderates temperature and humidity differences.  It makes the rest of this complex system work less hard, and in non extreme differentials, it significantly helps manage both sensible (heat) and latent (moisture) loads.  But an ERV is not a dedicated heater, an air conditioner, or a humidification or dehumidification device.  It’s a part of a system, in which, when designed and built right, each part of the system contributes to energy efficient temperature, ventilation, filtration, and humidity management.  An ERV helps moderate the air and prevent needless energy loss.  An ERV is also best used in habitable space, where the occupants will be, where we typically heat or cool, where it’s worth conditioning our air for much or all of the time.   

 

It’s worth listening to Ken and Green Builder Matt Hoots discussing when an ERV makes the most sense and the current evolution of HVAC design and building thinking.  Matt brings up that many people are still working to understand HVAC systems.  He reviews the difference between balanced ventilation instead of exhaust ventilation (specifically exhausting problematic air in key areas, like kitchens and bathrooms) and supply-side ventilation (pressurizing the structure and pushing the air out).  The two discuss where certain elements or strategies might work better and not.  We hope and plan to continue this fascinating conversation, and everyone is welcome to add their voice.  It’s essential to consider the size of a home, the airtightness, and the climate zone in designing the right system.  

 

 

The Future of Ventilation Systems 

 

Ken reminds us that builders are responsible for moisture damage for the first couple of years, so this is another incentive to get it right.  With too much moisture in the air, it will seek out a cold surface and condense into a liquid.  As a result, walls and floors could get wet from condensation and be susceptible to damage. As Matt points out, using the condition of your hardwood cabinets and floors as a barometer of humidity management can be pretty costly.  Where humidity is not significant, an ERV might be sufficient.  Where humidity is consistently high, an ERV might better be the backbone of a more extensive system with dedicated dehumidification.  

The building industry is indeed evolving.  The two review that the best strategy for new construction is to “build tight and ventilate right,” meaning that we need to seal and insulate our buildings and then also make sure to control air flow and air quality.  And… understand that occupants do indeed have “huge expectations” of their new homes.  These challenges are all more easily addressed when we have the luxury of building new.  Before adding equipment in existing buildings, both agree that it’s best to tighten the envelope and stop energy loss.  Then, one can design or upgrade new systems based on the climate/conditions created.  

 

There’s a leading edge group of manufacturers and professionals delivering and installing equipment and whole systems of a type and quality we didn’t have available before.  As a result, we have a range of homes from leaky, new and built to code, or tight and even Passive level, at a wide range of square footages, and in every climate zone. We need to continue to talk about indoor air quality and ventilation and to incorporate these strategies as best we can in all houses and buildings.  As we continue to learn more and as leading thinkers like Ken continue to take the time to share their expertise, we will keep reporting what we know and learn to you!  We also welcome your comments.  

 

Balanced ventilation strategies are indeed on the rise.  The COVID-19 pandemic has made indoor air quality (IAQ) and ventilation household words to be sure.  Ken points out that “supply air is expensive air,” as it needs to be tempered and filtered and controlled.  So why not implement a strategy that reduces the energy required to manage this air? 

 

Ken points out that he loves talking about the best strategy for a particular situation.  We agree with him that we can all learn together and that our goal is "to create a better living environment for the occupant, for the earth.”  Ken’s closing question is powerful: "How do we raise the bar?”

 

What are your thoughts and recommendations on ERVs and Indoor Air quality generally?  What are your top questions?  We’d love to hear, and we bet Ken will be happy to reply. 

 

 

 

 

Additional Information:

 

Demystifying Ventilation and Energy Recovery Ventilators (ERVs)

A Look at How ERVs Work with Panasonic: How 80% Efficiency Might Work in Practice

The Benefits of an ERV + How it Works | Panasonic FV-04VE1+FV-WC04VE1 

Spot Energy Recovery Ventilation (ERV) - Designed for One Location (vs Whole House)

Humidity Control Master Class from Therma-Stor

Humidity, Hardwoods and Homes - The Building Science Approach to Protecting your Investment

Whole House Humidity Control - Dehumidification and Humidification, with Aprilaire

Whisper Green Fans from Panasonic Eco Solutions - Quiet Prevention for Moisture and Condensation (Video)

Green Building Myth Busting: Natural Ventilation - Do Your Walls Need to "Breathe?" (Video)

Walking and Talking about Fresh Air and Ventilation with Green Building Expert Matt Hoots - and Oliver

Your House May be Making You Sick!

What is the ideal humidity needed to help maintain hardwood flooring?

Indoor Air Quality (IAQ) 101 - An Introduction, and Starting a Wider Conversation