Energy recovery ventilators can exchange both heat and moisture between the air streams. Photo provided by Carrier.The most basic approach to improve the indoor air quality within a space is to open the windows and let in some fresh air. According to Gord Cooke, president of Building Knowledge Canada, “The first building code stated in as many words, thou shalt have windows in every room and people should leave the windows open most of the time.”
This standard has been a fairly common practice for getting fresh air inside a home. And as much as this principle will likely be here to stay, as we all know, times change and evolve. Better solutions have come about with the improvement of mechanical ventilation. Since 1995, the National Building Code of Canada has had comprehensive requirements for continuous mechanical ventilation devices to provide fresh air capacity year-round. Around 22 years later, with the adoption of energy efficiency requirements within the Ontario Building Code, heat recovery ventilators (HRVs) became effectively mandatory in all new homes.
When HRVs are brought up in conversation, it is only natural to get into energy recovery ventilators (ERVs).
Differences
When discussing ERVs, we first need to understand the overall history of heat exchangers. “HRVs were referred to as heat exchangers and the first ones developed in Canada for residential applications were always associated with energy-efficient housing programs such as the R-2000 program. So, you’d have a sheet metal box with one fan taking stale stinky air out of the house and one fan bringing fresh air in from outside through the heat recovery core, recovering approximately 70 per cent of the waste heat from the exhaust air,” explains Cooke. “ERVs use the same two fans and pull new air into a home while taking stale air away, but in addition to recovering the temperature difference between the two air streams, the ERV core was able to transfer moisture from one air stream to the other which was an advantage specifically in hot, humid weather to reduce cooling loads.”
Both systems are very similar in construction and operation. However, the main difference between ERVs and HRVs is that essentially, “HRVs core can exchange heat, whereas an ERVs core can exchange both heat and moisture between the air streams,” explained Bruno Poitras, North American product manager of indoor air quality solutions at Fantech. Looking under the hood of an ERV system, “The core in an ERV is made of a permeable material that allows moisture to move from the higher humidity stream to the one with lower humidity, equalizing the incoming air’s humidity,” explains Poitras.
This or that
With ventilation required in all homes, some customers may ask, “Which system should I use? An HRV or ERV?” As Jean-Paul van Miltenburg, Carrier’s residential product manager, explains, “It all depends on your climate. Typically, ERVs are used more in warmer climates. Traditionally, Canada has fewer zones to use ERVs. There are a few zones that allow adequate energy transfer. For example, these zones would be in the southern areas of our provinces, and coastal provinces. But once we get further up north, we have shorter summers and less humidity in the air, and the ERV may not be used to its potential or be subject to the core freezing, and that’s where an HRV could be used instead. Ongoing research may change the currently recommended zones but it’s best to follow the manufacturer’s specifications.”
When it comes to which is the better choice for an application, the home’s needs to come into play, “Whether it is an HRV or an ERV, it will depend on the circumstances of the home and the climate conditions. Several factors must be taken into consideration — the number of people living in the home, the number of washrooms, and the amount of water used,” said Christian Romeroll, vice president of the HVAC division and sales at Napoleon. “For example, for a family with three teenagers who utilize a high amount of water, the home will need a unit with a higher number of CFM to correctly transfer ventilation and control humidity in the house.” He adds that HRV and ERV sizes range between 90 and 150 CFM.
An ERV can be seen in a home’s mechanical room as one part of a total home heating and cooling system.Benefits of an ERV
When trying to promote the benefits of an ERV system, an essential thing any contractor can do “is flat out ask their customer, how often do you want fresh air in your home? In most cases they will answer all the time, and that’s when you inform them on ERVs,” said Cooke. The benefits of an ERV system are apparent. They provide “fresh, clean air inside of a home. ERVs are recovering around 70 to 80 per cent of the temperature in the winter and around 60 to 70 per cent in the summer,” said Cooke. ERVs can be used in both seasons as, “The cold fresh outside air is humidified in the winter, preheated by the outgoing, warm interior air. In the summer, the fresh, warm, humid outside air is precooled and dehumidified by the outgoing air-conditioned interior air,” said van Miltenburg.
A home is always vulnerable to contaminated indoor air quality. “For the most part, the air outside is fresher than inside. Inside air becomes contaminated by various elements, for one, us humans. Then you have the various materials being spread throughout the house. Like your deodorants, pet dander, and also the toxins coming from carpets, paints, etc.,” adds Cooke.
The air found in homes is becoming staler and this is also a result of innovation, as “Homes are more airtight than ever, but this also increases the potential to have stale indoor air, and this is where HRVs and ERVs can help balance this out,” said Romeroll.
When trying to weigh the benefits of installing an ERV system, it’s crucial to understand which type of system you will install, as they all serve different purposes depending on the home’s needs. There are three types of installs regarding HRVs ERVs — “First, you can do a simplified install, which is ideal when you have a fully furnished heat pump that is fully ducted to your home. HRVs would be ideal in this scenario. Then you have a partially dedicated install, which an ERV would work best as you will pull from the bathrooms and the kitchen. Those often have more moist air. Lastly, there’s the fully dedicated install, where essentially, you’re pulling from the same areas, but you’re distributing the air from the HRV or ERV directly into the living spaces,” explained Poitras.
Potential challenges
While ERVs can provide homeowners with many benefits, the system can present some challenges for the contractor during the installation, especially in retrofit projects. “For example, when an HVAC system has already been set up, the contractor has to plan and think about where to put the ERV system and its connections,” explained Cooke.
Even in the more basic installs, both HRVs and ERVs require new ducting and low-voltage control systems, explains van Miltenburg. “You must plan where to put the drains, upsize existing fresh air intake, route new exhaust, and ensure you’re using properly insulated ductwork.”
Additionally, there are telltale signs homeowners should know when it comes to the maintenance of an ERV system, “If your system’s filters are dirty, your house will have no ventilation and you can tell when you get that musty smell. Also, suppose your unit is running at a higher speed, in that case, let’s say in the summer, sometimes your system can over-ventilate, and you’re going to notice your floor or building materials begin to swell because there is too much moisture inside the home,” explained Poitras.
No matter which system you choose, the first and most important thing to remember is your customer’s needs. “It’s about the relationship between a contractor or dealer and the homeowner. Homeowners want information, choices, and they want their needs met. Our job is to provide our customers with just that. We provide information, choices and help homeowners through dealers and distributors figure out what’s best for their needs,” said Romeroll.