mechanical home ventilation

Mechanical ventilation can be as simple as a set of exhaust fans: a kitchen exhaust fan and a bathroom exhaust fan. But there are other more sophisticated mechanical systems. And modern homes, with good insulation levels, demand those other systems, namely mechanical HRV and ERV ventilation systems.

Indispensable

In tightly air sealed buildings, mechanical ventilation is highly advantageous. Since highly insulated and sealed homes can no more rely on air leakage to supply their fresh air needs, and natural ventilation can't simply supply enough and constant fresh air, mechanical ventilation is the only alternative.

Thats the only way to protect people from unhealthy indoor pollutants and odors, supplying fresh air to the building, or to protect the home from excess moisture and excess heat and cold.

The simpler systems: exhaust ventilation systems

Kitchen and bathroom exhaust fans are a typical exhaust ventilation system. They are the most common and the most simple exhaust ventilation systems. They belong to the spot and intermitent ventilation systems.

Supply ventilation Systems

Supply ventilation systems provide fresh-air distribution, instead of exhausting stale air (like exhaust ventilation systems). They can complement simple exhaust ventilation systems. Systems combining exhaust ventilation and supply ventilation (HRV and ERV systems) are more common than supply-only ventilation systems.

HRV and ERV systems

HRV and ERV systems allow to exhaust stale air from homes and also to bring fresh air into them. They combine these two features. They demand a duct system (see diagram below for a HRV system. Source: Energy Star).

HTV Mechanical Ventilation

HRV systems

Heat Recovery Ventilators (HRV) systems more common than ERV systems in colder climates. In HRV systems, as stale-warmer air is expelled by the system, the heat recovery core warms the incoming fresh-colder air, recovering that heat.

ERV Systems

Energy Recovery Ventilators (ERV) systems are a refinement of HRV systems, and are particularly suited for warmer climates and high-humidity environments.

While HRV systems transfer heat between the airstreams, ERV systems also transfer moisture, which means lower air conditioning costs in hot and humid climates.

HRV/ERV installing

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

Costs vary with the model and the needs of the building. There are models with and without moisture transfer, defrost control, pre-heater system to prevent ice buildup (a must needed feature in cold climates); there are single speed models and multiple speed models, models with pollutant sensor controls, with high efficiency air filter, etc.

Costs depend also on the size of the system (often based on a total ventilation capacity equal to 0.05 CFM/square foot). Costs around $1,000 to $2,500 are very common… in new constructions.

Energy Operating costs

HRV/ERV operational costs are very low: below $1.00 per day even for more complex and continuously working systems.

Comparing the performance of HRV/ERV models

Prefer Energy Star and other officially rated systems. To compare performances, take into account the loudness of the model (expressed in Sones) and its power to filter out the volume of pollutants, measured in CFMs (Cubic Feet per Minute). Models with higher Sones and higher CFM are better options.