Mechanical Ventilation: HRV and ERV


Mechanical Ventilation

In cold climates and tightly air sealed residences, mechanical ventilation is usually mandatory. Natural ventilation devices - ceiling fans, window fans, exhaust fans, attic fans... – can't supply fresh air to your home, in such conditions. Mechanical ventilation systems (HRC and ERV systems) are the only solutions, in such cases.


HRV and ERV systems

HRV and ERV systems allow to remove stale air from homes and also to bring fresh air into them. Usually they involve a duct system (see diagram below for a HRV system. Source: Energy Star).


 

Heat Recovery Ventilators (HRV) are the most common solution in colder climates, where home heating is essential. As stale (and warm) air is expelled by the system, the heat recovery core warms the incoming fresh (and colder) air before it is distributed throughout the home, providing ventilation and controlling excess humidity.

Energy Recovery Ventilators (ERV) are the most common solution in warmer climates and high-humidity environments (though they are also used in cold climates) where the control of humidity is crucial.

Besides recovering heat, ERV systems also recuperate the energy present in moisture. The ERV systems regulate the amount of moisture coming into home or expelled from it.

Buying an HRV/ERV

HRV and ERV models are sold and installed by heating, ventilation and air conditioning (HVAC) contractors. They can be good advisors in the buying process.

Costs vary a lot. They depend on the model and the complexity of the installation. There are models with and without moisture transfer, with or without defrost control or pre-heater system to prevent ice buildup (a must needed feature in cold climates), models with single or multiple speed controls, models with or without pollutant sensor controls, or with or without high efficiency air filter on incoming air… Costs depend also on the size of the system (often based on a total ventilation capacity equal to 0.05 CFM/square foot).

Total costs around $1,000 to $2,500 for typical models and typical home uses are very common… in new constructions. These values may rise sharply for a retrofit.

Energy Operating costs

HRV/ERV operational costs are relatively low: electrical costs – the main cost - stand below $1.00 per day even for more complex and continuous systems.

Comparing the performance of HRV/ERV models

Energy Star labeled models are good options. To compare their performance take into account:

1) the ratings for airflow capacity in cubic feet per minute (CFM) and
2) the ratings for recovery efficiency (expressed in Sones).

Models with higher Sones and higher CFM are the best options.


HRV/ERV, humidifiers, bath and kitchen exhaust fans

HRV/ERV are what they are: ventilation devices. They aren’t heating and cooling equipment. They do not replace air conditioning needs or even bath fans, dehumidifiers, and other equivalent devices. It all depends on the environment of the house, HRV/ERV duct design, bathroom airflow requirements, etc.






See, for more information:
Energy Efficient House Basics
Home Air Leakage and Home Sealing
Good and Bad Indoor Air quality
Natural Ventilation: cross and stack


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