Table of Contents
- Any heated or cooled air carries energy in two forms. Sensible heat changes the dry-bulb temperature of the air without changing its moisture content. Latent heat is the energy tied up in water vapour: it moves when moisture condenses or evaporates, and it can change without any temperature change at all. Air-to-air heat recovery matters because the two forms are recovered by different hardware. A plate heat exchanger only touches sensible heat; an enthalpy wheel or membrane core recovers both. Getting this distinction right is the first step in choosing between sensible and total-energy recovery.
- The sensible energy in a flow is: Q_sensible = mass_flow x specific_heat x temperature_difference For air, specific heat is about 1.006 kJ/kg.K and density about 1.2 kg/m3 at 20 degC. A stream of 1 m3/s cooled by 10 K releases roughly 1.2 x 1.006 x 10 x 1 = 12 kW of sensible heat. This is the number most recovery calculations start from, and it is what efficiency metrics report as temperature effectiveness.
- When air is cooled below its dew point, vapour condenses and releases its latent heat of vaporisation (about 2450 kJ/kg of water). In ventilation, exhaust air in a humid building can carry more energy as latent heat than as sensible heat. Recovering it requires a desiccant-coated wheel or a membrane that passes water vapour, not just a metal plate.
- Dry, cold climates (heating dominated): sensible recovery (HRV) is usually enough; adding latent recovery can over-dry the supply. Hot, humid climates (cooling dominated): latent loads dominate, so an ERV / enthalpy wheel cuts both cooling and reheat coil duty. Contamination-sensitive spaces: sensible-only plates keep streams fully separated.
- Can a plate exchanger recover humidity? No. A sensible plate transfers heat through the wall but does not pass water vapour, so indoor moisture stays in the exhaust. Is latent recovery always better? Not in dry climates, where it adds cost and can cause over-drying. Match the recovery type to the local psychrometrics. Need help specifying the right air-to-air heat recovery for your project? Contact the QIYU engineering team - WhatsApp +86 157 5335 5505, or email kuns913@gmail.com. Frequently Asked Questions What is the practical difference between sensible and latent heat in HVAC recovery? Sensible heat changes air temperature without changing its moisture content, while latent heat changes moisture at essentially constant temperature. A plate sensible exchanger moves only temperature; an enthalpy wheel also moves moisture. Why does latent recovery matter for energy recovery? In humid climates exhaust carries a large latent load; recovering it with a desiccant or enthalpy wheel can cut cooling and dehumidification energy, but it also transfers moisture and risks cross-contamination, so plate exchangers are preferred where the air streams must stay separate.
Any heated or cooled air carries energy in two forms. Sensible heat changes the dry-bulb temperature of the air without changing its moisture content. Latent heat is the energy tied up in water vapour: it moves when moisture condenses or evaporates, and it can change without any temperature change at all.
Air-to-air heat recovery matters because the two forms are recovered by different hardware. A plate heat exchanger only touches sensible heat; an enthalpy wheel or membrane core recovers both. Getting this distinction right is the first step in choosing between sensible and total-energy recovery.
The sensible energy in a flow is:
Q_sensible = mass_flow x specific_heat x temperature_difference
For air, specific heat is about 1.006 kJ/kg.K and density about 1.2 kg/m3 at 20 degC. A stream of 1 m3/s cooled by 10 K releases roughly 1.2 x 1.006 x 10 x 1 = 12 kW of sensible heat. This is the number most recovery calculations start from, and it is what efficiency metrics report as temperature effectiveness.
When air is cooled below its dew point, vapour condenses and releases its latent heat of vaporisation (about 2450 kJ/kg of water). In ventilation, exhaust air in a humid building can carry more energy as latent heat than as sensible heat. Recovering it requires a desiccant-coated wheel or a membrane that passes water vapour, not just a metal plate.
- Dry, cold climates (heating dominated): sensible recovery (HRV) is usually enough; adding latent recovery can over-dry the supply.
- Hot, humid climates (cooling dominated): latent loads dominate, so an ERV / enthalpy wheel cuts both cooling and reheat coil duty.
- Contamination-sensitive spaces: sensible-only plates keep streams fully separated.
Can a plate exchanger recover humidity? No. A sensible plate transfers heat through the wall but does not pass water vapour, so indoor moisture stays in the exhaust.
Is latent recovery always better? Not in dry climates, where it adds cost and can cause over-drying. Match the recovery type to the local psychrometrics.
Need help specifying the right air-to-air heat recovery for your project? Contact the QIYU engineering team - WhatsApp +86 157 5335 5505, or email kuns913@gmail.com.
Frequently Asked Questions
What is the practical difference between sensible and latent heat in HVAC recovery?
Sensible heat changes air temperature without changing its moisture content, while latent heat changes moisture at essentially constant temperature. A plate sensible exchanger moves only temperature; an enthalpy wheel also moves moisture.
Why does latent recovery matter for energy recovery?
In humid climates exhaust carries a large latent load; recovering it with a desiccant or enthalpy wheel can cut cooling and dehumidification energy, but it also transfers moisture and risks cross-contamination, so plate exchangers are preferred where the air streams must stay separate.