Working Principle
Heat recovery ventilation (HRV) or energy recovery ventilation (ERV) is an energy-saving technology that uses a heat exchanger to recover energy (heat or cooling) from exhaust air and pre-treat incoming fresh air. It is widely used in residential, office, hospital, and other building ventilation systems.
Transfer energy between exhaust and fresh air via a heat exchanger without mixing the airstreams
- Sensible heat recovery (HRV): Transfers only temperature (suitable for temperate climates).
- Total heat recovery (ERV): Transfers both temperature and humidity (ideal for humid or dry climates).
Heat transfer methods
- Cross-flow (Plate Heat Exchanger): Fresh and exhaust air flow perpendicularly, exchanging heat through metal/plastic plates.
- Counter-flow: Airflows move in opposite directions, achieving higher efficiency (up to 90%).
- Rotary Wheel (Thermal Wheel): A rotating wheel with hygroscopic material alternately absorbs and releases heat and moisture, suitable for ERV.
Core strengths
Exhaust Side
Stale indoor air is extracted by a fan, passing through the heat exchanger to release heat (winter) or cooling (summer).
Fresh Air Side
Outdoor air enters the heat exchanger, absorbing energy from the exhaust air for pre-heating (winter) or pre-cooling (summer).
Air Separation
The two airstreams remain physically separated to prevent cross-contamination.
Supply to Indoor
Treated fresh air is distributed indoors via ductwork.
Advantages
High Energy Efficiency: Recovery rates of 50–90%, significantly reducing HVAC load.
Improved Air Quality: Continuous filtered fresh air reduces CO₂, VOCs, and other pollutants.
Humidity Control (ERV): Retains moisture in dry climates and reduces humidity transfer in humid regions.
Low Operating Cost: Only requires fan power, no additional energy input.
Wide Applicability: Suitable for homes, offices, hospitals, labs, etc.
Disadvantages
Higher Initial Cost: More expensive than standard ventilation (requires heat exchanger, dual fans, etc.).
Airflow Balance Dependency: Exhaust and fresh air must be balanced for optimal efficiency.
Frost Risk in Cold Climates: May frost below -5°C, requiring electric preheating or bypass mode.
Maintenance Needs: Regular cleaning of filters and heat exchangers to prevent clogging and mold.
Increased Air Resistance: Heat exchangers add pressure drop, potentially requiring more powerful fans.