When to use: Estimate how much energy an ERV (enthalpy wheel, total recovery) or HRV (plate-core/heat-pipe, sensible-only) recovers from outdoor ventilation air before it reaches the main AHU coil, and the resulting pre-conditioned supply air temperature. Use your unit's AHRI 1060-certified rated effectiveness for accurate results, or the representative defaults provided.
Disclaimer: Effectiveness values should come from the specific unit's AHRI-certified rating (AHRI Standard 1060) for accurate results. This tool illustrates the calculation method using either your input values or representative typical values — it is not a substitute for the manufacturer's certified performance data.
This calculator models how an energy recovery ventilator (ERV) or heat recovery ventilator (HRV) pre-conditions incoming outdoor ventilation air using the outgoing exhaust air stream, before that air reaches the main air handling unit's heating/cooling coil. It reports the resulting pre-conditioned supply air condition and the sensible, latent, and total energy recovered — using either your unit's datasheet-rated effectiveness or representative typical values.
An HRV (heat recovery ventilator) — typically a plate-core or heat-pipe exchanger — transfers only sensible heat between the outgoing exhaust air and incoming outdoor air; it does not transfer moisture. An ERV (energy recovery ventilator) — typically an enthalpy wheel or fixed-plate enthalpy core — transfers both sensible heat and latent moisture, which matters most in humid climates or buildings with high latent loads. Selecting HRV in this tool disables the latent effectiveness input and latent recovery calculation, since an HRV by design does not recover moisture.
The pre-conditioned supply air temperature is T_supply = T_out + εs × (T_in − T_out), where εs is the sensible effectiveness (as a fraction) — this moves the outdoor air temperature toward the indoor exhaust air temperature by the effectiveness fraction. For an ERV, the pre-conditioned humidity ratio is similarly adjusted using latent effectiveness εl. Sensible energy recovered is Qs = 1.08 × CFM × εs × ΔT (Btu/hr), and for an ERV, latent energy recovered is Ql = 0.68 × CFM × εl × ΔW, where ΔW is the humidity ratio difference in grains of moisture per pound of dry air. Total recovered energy is Qs + Ql, and the percent reduction compares that to what the main coil would have had to do with no recovery at all.
Every AHU with outdoor air ventilation must condition that air from outdoor design conditions to supply conditions. Energy recovery does part of that job upstream, using energy that would otherwise be exhausted, so the main heating/cooling coil only has to handle the remaining (1 − effectiveness) fraction. This is why ASHRAE 90.1 requires energy recovery on many systems above certain OA percentage and CFM thresholds — the fuel/electricity savings can be substantial, especially in climates with large outdoor-to-indoor design temperature swings. Always confirm your unit's actual rated effectiveness from its AHRI 1060 certified datasheet rather than assuming a typical default, since real effectiveness varies by exchanger technology, face velocity, and frost-control strategy.
An HRV (heat recovery ventilator) transfers only sensible heat between exhaust and outdoor air streams. An ERV (energy recovery ventilator) transfers both sensible heat and latent moisture, which is important in humid climates or spaces with high latent loads (pools, kitchens, gyms). Select the unit type in this tool to match your actual equipment — HRV disables the latent effectiveness input.
From the specific unit's AHRI Standard 1060-certified performance data sheet, which lists sensible and (for ERVs) latent effectiveness at rated airflow conditions. Typical published ranges are roughly 50–80% sensible and 50–75% latent for real ERV/HRV products, but actual values vary by exchanger technology (plate, heat-pipe, enthalpy wheel), face velocity, and frost-control operation — always use the certified datasheet value for real design.
This tool estimates the percent reduction by comparing the energy recovered (sensible + latent, scaled by effectiveness) to the total outdoor-air conditioning load that would exist with zero recovery. A unit with 65% sensible and 60% latent effectiveness roughly cuts the OA-conditioning load by that same order of magnitude — the exact percentage depends on the sensible/latent split of your specific outdoor and indoor design conditions.
The standard latent-load formula (Ql = 0.68 × CFM × ΔW) uses the humidity ratio difference directly in grains of moisture per pound of dry air. Asking for %RH would require an additional psychrometric conversion (saturation pressure/Magnus formula) that adds complexity without changing the underlying method — use the site's Psychrometric Calculator first if you only have dry-bulb temperature and %RH.
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