Energy Recovery Ventilation (ERV) and Heat Recovery Ventilation (HRV) systems are both designed to provide fresh air ventilation while recovering energy from the outgoing air, but they operate slightly differently and offer unique benefits. Here's a comparison between ERV and HRV systems:
1. HEAT RECOVERY VENTILATION (HRV):
Principle: HRV systems transfer heat energy from the outgoing stale indoor air to the incoming fresh outdoor air without the two air streams mixing.
Heat Exchange: HRV systems utilize a heat exchanger core made of a material that conducts heat well, such as aluminum. As the fresh outdoor air and stale indoor air pass through the heat exchanger core, heat from the indoor air is transferred to the outdoor air, preheating it in the winter.
Efficiency: HRV systems are highly efficient at recovering heat energy, typically recovering 70% to 90% of the heat from the outgoing air. This helps maintain a comfortable indoor temperature while reducing heating costs and energy consumption.
Application: HRV systems are well-suited for colder climates where maintaining indoor warmth is a priority. They are ideal for reducing heating energy demand and ensuring fresh air ventilation without compromising indoor comfort.
2. ENERGY RECOVERY VENTILATION (ERV):
Principle: ERV systems not only transfer heat energy but also moisture between the incoming outdoor air and the outgoing indoor air.
Moisture Exchange: In addition to heat transfer, ERV systems transfer moisture from the incoming outdoor air to the outgoing indoor air during the summer months. This helps reduce indoor humidity levels, improving comfort and indoor air quality.
Efficiency: ERV systems are highly efficient at both heat and moisture recovery, making them ideal for maintaining a comfortable and healthy indoor environment year-round. They recover heat and moisture simultaneously, minimizing energy consumption and improving indoor air quality.
Application: ERV systems are particularly beneficial in humid climates where controlling indoor humidity levels is essential. They are suitable for both heating and cooling seasons, providing balanced ventilation while mitigating humidity-related issues.
COMPARISON:
Heat vs. Heat and Moisture Recovery: The primary difference between HRV and ERV systems lies in their ability to transfer moisture. HRV systems only transfer heat, while ERV systems transfer both heat and moisture, making them more versatile in different climates.
Humidity Control: ERV systems offer additional benefits in humid climates by regulating indoor humidity levels, preventing moisture buildup and mold growth.
Climate Suitability: HRV systems are well-suited for colder climates where heating is the primary concern, while ERV systems are beneficial in both heating and cooling climates, particularly where humidity control is essential.
Summary: both ERV and HRV systems provide fresh air ventilation and energy recovery benefits, but ERV systems offer additional moisture transfer capabilities, making them more versatile in a wider range of climates and seasons. The choice between ERV and HRV depends on factors such as climate, indoor air quality needs, and humidity control requirements.
AIR DISTRIBUTION SYSTEMS FOR HRV/ERV:
Single-Point HRV or ERV:
• A single-point HRV/ERV system consists of a standalone unit installed in a central location within the building, typically the utility room or mechanical closet.
• The HRV/ERV unit supplies fresh air to the entire building and exhausts stale air, operating independently of the central air handling system.
• While simpler in design and installation, single-point HRV/ERV systems may be less efficient in distributing fresh air evenly throughout the building, particularly in larger or multi-story structures.
Multi-Point HRV or ERV (Fully Ducted):
• In a fully ducted multi-point HRV/ERV system, multiple HRV/ERV units are installed throughout the building, each serving specific zones or areas.
• Each HRV/ERV unit is connected to a dedicated set of supply and return ducts, providing localized ventilation to individual rooms or zones.
• This configuration offers precise control over ventilation in different areas of the building, allowing for customized airflow rates and air quality management.
• However, it may require more extensive ductwork and installation compared to centralized systems, increasing upfront costs and complexity.
Multi-Point HRV or ERV with Partial Connection to Central Air Handler:
• In this configuration, the HRV/ERV unit is partially connected to the central air handling system, typically serving specific zones or areas of the building.
• The HRV/ERV unit may supply fresh air directly to certain zones or rooms, bypassing the central air handler in those areas.
• This setup offers greater flexibility in ventilation control, allowing for targeted ventilation in areas with specific air quality or occupancy requirements.
• However, it may result in uneven ventilation distribution throughout the building, depending on the configuration and design of the system.
Multi-Point HRV or ERV with Full Connection to Central Air Handler:
• In this configuration, the HRV/ERV unit is fully integrated and connected to the central air handling system of the building.
• The HRV/ERV unit works in tandem with the central air handler to distribute fresh air throughout the building and exhaust stale air.
• Fresh air from the HRV/ERV unit is supplied directly into the central air handler, where it is mixed with conditioned air before being distributed to individual rooms.
• This setup allows for efficient ventilation and temperature control throughout the building, with the HRV/ERV unit playing a crucial role in providing fresh air supply and energy recovery.
ERVs & HRVs IN PASSIVE HOUSE:
ERV and HRV systems are indispensable in Passive House construction, where energy efficiency, indoor air quality, comfort, and health are prioritized. By recovering energy and providing continuous ventilation with heat and/or moisture exchange, these systems play a crucial role in creating sustainable, comfortable, and healthy living environments in Passive Houses.
1. Energy Efficiency:
In Passive Houses, where strict energy efficiency standards are upheld, this heat or cool air exchange significantly contributes to overall energy savings. By transferring heat (in HRV) or both heat and moisture (in ERV) between the indoor and outdoor air streams, these systems help maintain a stable indoor temperature, minimizing the workload on heating and cooling systems.
2. Indoor Air Quality:
Passive Houses prioritize superior indoor air quality, and ERV/HRV systems play a vital role in achieving this. By continuously supplying fresh outdoor air while expelling stale indoor air, these systems ensure a constant flow of clean, filtered air throughout the building. ERV systems, in particular, excel in humid climates by regulating indoor humidity levels. They transfer moisture between the incoming and outgoing air streams, preventing excessive moisture buildup that can lead to mold growth and other indoor air quality issues.
3. Comfort and Health:
A comfortable and healthy indoor environment is a core tenet of Passive House design. ERV/HRV systems contribute to this by providing a balanced ventilation solution that eliminates indoor pollutants, allergens, and odors while ensuring adequate fresh air supply. The continuous ventilation provided by these systems helps prevent the buildup of indoor pollutants, creating a more comfortable and healthier living environment for occupants.
Continue reading about my last Passive House building in New York City, here:
March 17, 2024
Written By Pebel Rodriguez, AIA, Licensed Architect, Principal at Atelier Essex.
Chair of the American Institute of Architects (AIA) Silicon Valley Committee on the Environment (COTE)
LEED Accredited Professional | Passive House Designer
M.Sc. Environmental Systems Management
