A fresh air ventilation unit with energy recovery, an ERV or HRV, supplies filtered outdoor air while recovering 60 to 90 percent of the energy from the air it extracts, so you ventilate a building without paying full heating or cooling cost for the incoming stream. It is the standard solution for tight, energy-efficient buildings where opening windows is impractical and where mechanical ventilation is required by code to maintain indoor air quality. The unit continuously brings in outside air, filters it, and pre-conditions it using the outgoing stale air.
ERV vs HRV: The Core Difference
An HRV, or heat recovery ventilator, transfers only sensible heat between the exhaust and supply airstreams through a plate or rotary core. An ERV, or energy recovery ventilator, transfers both heat and moisture, using an enthalpy wheel or desiccant core that also balances humidity. In a cold climate, an HRV recovers warmth without adding indoor humidity; in a hot, humid climate, an ERV removes moisture from incoming air so the cooling coil works less. Both deliver the same fresh-air benefit, but the ERV adds latent control that matters where humidity drives comfort and mould risk.
How Energy Recovery Works
The two airstreams pass through a heat-exchange core without mixing. In winter, warm exhaust air pre-heats the cold incoming supply; in summer, cool exhaust pre-cools the hot supply. A rotary wheel can reach enthalpy effectiveness of 70 to 85 percent, while a fixed plate core typically delivers 60 to 80 percent sensible recovery. The recovered energy directly offsets the load on the building's heating or cooling system. For a unit moving 2,000 m³/h with an 80 percent effective core and a 20°C indoor-outdoor difference, the recovered heating power is roughly 11 kW, a figure that scales with airflow and temperature swing.
ERV vs HRV vs Simple Fresh Air Unit
| Unit type | Energy recovered | Humidity control | Typical effectiveness |
|---|---|---|---|
| Simple fresh air unit | None | None (uses main HVAC) | 0 percent |
| HRV (plate or rotary) | Sensible heat only | None | 60 to 80 percent |
| ERV (enthalpy wheel) | Heat and moisture | Yes, both directions | 65 to 85 percent |
The comparison shows why recovery units dominate modern ventilation: they cut the fresh-air energy penalty from 100 percent to 10 to 40 percent of the unrecovered load.
Key Numbers and Sizing
Three numbers guide selection. First, ventilation rate: residential units commonly supply 150 to 600 m³/h, while commercial AHUs scale to 5,000 to 50,000 m³/h. Second, recovery effectiveness, typically 60 to 90 percent depending on core type and face velocity. Third, fan power, often 0.3 to 1.5 W per m³/h of airflow, so a 2,000 m³/h unit may draw 0.8 to 2.5 kW total for both fans and controls. Filters are usually G4 prefilters plus F7 final filters, and supply heating or cooling coils are added when recovery alone cannot meet setpoint.
When to Choose ERV vs HRV
- Choose an ERV in hot-humid or mixed climates where controlling incoming moisture protects comfort and prevents mould.
- Choose an HRV in cold or dry climates where you want heat recovery without adding indoor humidity in winter.
- Choose a simple fresh-air unit only when energy recovery is impractical and the HVAC plant handles the full load.
- Choose a rotary wheel when space is tight and highest effectiveness is needed; choose a plate core for lower cost and no moving parts.
- Choose modular AHU-style recovery for large buildings above 10,000 m³/h.
Installation and Maintenance
Mount the unit with service clearance of at least 600 mm on the filter and core side, connect balanced supply and return ducts, and commission the airflow to the design 2,000 to 5,000 m³/h per zone. Set the bypass damper to free-cool during mild seasons, saving further energy. Maintain filters every 3 to 6 months and inspect the core annually; fouling can pull effectiveness from 80 percent down toward 50 percent. With proper care, the unit's service life reaches 15 to 20 years, and payback on the recovery feature typically lands within 2 to 5 years of operation.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Core Types and Airflow Paths
The recovery core defines performance and upkeep. A fixed plate core has no moving parts and reaches 60 to 80 percent sensible effectiveness with a pressure drop of 50 to 150 Pa; it is cheap and silent but cannot transfer moisture. A rotary enthalpy wheel spins at 8 to 20 rpm and reaches 70 to 85 percent total effectiveness, transferring both heat and humidity through a desiccant-coated matrix, though it needs a small motor and a purge sector to limit supply-to-exhaust leakage to under 5 percent. A run-around coil loop uses two coils and a fluid loop for separation where streams cannot mix. For a 2,000 m³/h home or small office unit, plate cores dominate; for 10,000 to 50,000 m³/h commercial AHUs, wheels are common.
Controls, Bypass, and Payback
Most units add a summer bypass damper that routes air around the core when free cooling is available, saving 10 to 30 percent of fan energy in mild weather. Supply and exhaust fans are often DC or EC types drawing 0.3 to 1.5 W per m³/h, so a 3,000 m³/h unit uses 1 to 4 kW total. With recovery of 60 to 90 percent, a building that would need 15 kW of heating for fresh air may need only 2 to 6 kW, and the payback on the recovery feature typically lands within 2 to 5 years where indoor-outdoor temperature differences exceed 10°C for much of the year. Filters are G4 plus F7, and the controller modulates flow to demand, keeping indoor CO2 near 600 to 1,000 ppm for good air quality.
Indoor Air Quality and CO2 Control
Because the unit supplies measured outdoor air, it lets the controller hold indoor CO2 near 600 to 1,000 ppm instead of diluting with full heating or cooling. Coupling recovery with a CO2 demand signal trims ventilation to actual occupancy, cutting the fresh-air load another 10 to 25 percent while meeting ventilation codes for schools, offices, and homes.
FAQ
What is the difference between an ERV and an HRV?
An HRV (heat recovery ventilator) transfers only sensible heat between exhaust and supply air, while an ERV (energy recovery ventilator) transfers both heat and moisture, controlling humidity as well. Choose an ERV in humid climates where latent load matters, and an HRV in dry climates where humidity transfer is unwanted.
How much energy can an ERV or HRV recover?
A well-designed unit recovers 60 to 90 percent of the energy in the exhaust air, with enthalpy effectiveness typically 65 to 85 percent. On a heating load of 10 kW, recovering 75 percent can cut fresh-air heating demand to about 2.5 kW, a major saving across a year of continuous operation.
Do I need an ERV if I already have a fresh air unit?
If your fresh air unit simply heats or cools incoming air, you pay full energy cost for conditioning it. Adding recovery cuts that load by 60 to 90 percent, so an ERV or HRV pays back through lower utility bills, usually within 2 to 5 years in climates with large indoor-outdoor temperature differences.
What maintenance does an ERV or HRV require?
Replace or wash filters every 3 to 6 months, inspect the heat-exchange core annually, and clean condensate paths to prevent mould. The enthalpy wheel or plate core should be checked for fouling, which can drop effectiveness from 80 percent toward 50 percent if neglected.