| Parameter | Outdoor | Conditioned (after ERV) |
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Energy Recovery Ventilators: Total Enthalpy Recovery for Canadian Climates
An ERV passes heat and water vapour between the exhaust and supply airstreams through a moisture-permeable core. In many commercial units that core is a rotating enthalpy wheel, and in most residential units it is a membrane or treated-paper plate. An HRV moves heat only. Add the sensible and latent parts together and you have the total enthalpy recovered, the quantity that the enthalpy calculator reports for any dry-bulb and humidity pair.
The direction of the benefit flips with the season. In summer the core takes heat and moisture out of hot, humid incoming air and hands them to the cooler, drier exhaust, so the cooling coil has less sensible and latent load to carry. In winter it warms the cold supply air and returns part of the indoor moisture to it, which spares a dry house some humidifying and adds to the moisture load of a tight, humid one.
Sensible and Latent Efficiency
Sensible efficiency is how far the supply air temperature moves from the outdoor value toward the indoor one, and latent efficiency does the same for the humidity ratio. Certified units in Canada are rated to CAN/CSA C439, and ENERGY STAR's specification for HRVs and ERVs requires a sensible recovery efficiency of at least 65% at 0 °C and 60% at -25 °C. That figure is measured on net supply airflow and adjusts for leakage and fan heat, so it is not identical to the simple temperature effectiveness this calculator applies, and it makes a slightly conservative input. Latent figures vary more from product to product than sensible ones, so take them from the data for the exact model.
What the Calculator Does
It moves the outdoor state toward the indoor state by the two efficiencies to find the air leaving the core, then converts the enthalpy difference to a load using the mass flow of dry air. That mass flow comes from the air density at the outdoor state, so it falls with elevation and with outdoor temperature instead of using a fixed 1.2 kg/m³. With 45 L/s, 70% sensible and 55% latent efficiency, 33 °C and 55% RH outdoors, and 24 °C and 50% RH indoors, the supply leaves the core at 26.7 °C and 59% RH. The ventilation load of 1.52 kW drops by 0.91 kW, made up of 0.33 kW sensible and 0.58 kW latent, leaving 0.61 kW. The latent share is the larger one because humid summer air carries so much of its energy as moisture. Winter mode counts only the sensible heat as load avoided.
Choosing Between ERV and HRV for Your Canadian Climate
Most of Canada is heating-dominated, and there an HRV is the usual choice because it exhausts indoor moisture, which suits tight new houses and busy households. An ERV makes more sense where summers are humid and air conditioning runs for long hours, or where winter indoor air is so dry that keeping some moisture matters. Natural Resources Canada's guide to heat and energy recovery ventilators says the right choice depends on the climate, the home and the people in it, and that either type should be ENERGY STAR certified. Run summer mode to see the cooling benefit, then winter mode to see the heat and moisture returned, and compare the winter figures with the HRV calculator.
Wheels, Plates and Cross-Contamination
A rotating wheel can reach high latent recovery, but the rotating media carries a small amount of exhaust air into the supply stream unless a purge section limits it. Fixed plate and membrane cores have much lower carryover. That matters when the exhaust comes from kitchens, washrooms, labs or patient rooms, and ASHRAE 62.1 restricts how much exhaust from higher-contaminant spaces an energy recovery device may carry back into the supply. For large rotary wheels, the energy wheel calculator covers the wheel side in more detail.
Frequently Asked Questions
An HRV moves only sensible heat between the exhaust and supply airstreams. An ERV also moves water vapour through its core. In summer that pulls moisture out of humid incoming air before it reaches the cooling coil. In winter it returns part of the indoor moisture to the cold, dry supply air instead of exhausting all of it, which can spare a dry home some humidifying and can add to the moisture load in a tight, humid one. The HRV calculator shows the sensible-only comparison.
Mainly where cooling is a real load and summers are humid, such as southern Ontario and Quebec (Windsor, Toronto, Ottawa, Montreal) and Winnipeg. Where summers are mild or dry, as on the BC coast or in much of Alberta, the latent benefit in summer is small. An ERV can still earn its place in a dry prairie home in winter by keeping some moisture indoors. Run summer mode with your own design conditions to put a number on it.
Sensible efficiency is how far the supply air temperature moves from outdoor toward indoor temperature. At 70%, 33 °C outdoors and 24 °C indoors, the supply leaves the core at 26.7 °C. Latent efficiency does the same for the humidity ratio. ENERGY STAR Canada requires a certified sensible recovery efficiency of at least 65% at 0 °C and 60% at -25 °C, tested to CAN/CSA C439. Latent figures come from the manufacturer, so use the value for the exact model.
It can in a tight home with many moisture sources, because less moisture leaves with the exhaust than with an HRV. If windows fog or indoor humidity stays high through the cold months, an HRV is the better fit. Winter mode here shows the heat the core adds to the supply air, and the latent line shows how much of the moisture is returned. Moisture return is not counted as a load avoided, since it only saves energy if you would otherwise humidify.