In the next few posts, we are going to break down some of the key elements of Passive House Design. Today we examine the part of the mechanical system—proper ventilation and energy recovery.

Passive House Design Process

No One Likes Stale Air.

Passive buildings are designed to be air tight. Really air tight. But we want clean air to breathe, and keep our home feeling fresh. So how do we efficiently bring it in? In the northeast, the outside air is too hot and humid in the summer, and far too cold in the winter. This predicament traditionally necessitates the use of furnaces and air conditioners—the darlings of your utility bill.

Passive Building Design takes a more clever approach.

[box] Summer = hot air outside/cool air inside

⇒ use outgoing stale air to cool down incoming fresh air

Winter = cold air outside/warm air inside

⇒ use outgoing stale air to warm up incoming fresh air[/box]

And never the twain shall meet. Incoming and outgoing air streams are kept completely separate from each other, so stale air doesn’t end up back in your environment.

What Sorcery is This?

Let me introduce the star of the show—  ERV, or for those not into architecture acronyms Energy Recovery Ventilator. This is the preferred system here in the northeast US, due to our high humidity and wide temperature range. The beauty of an ERV is that is can harvest heat in the winter and reduce heat in the summer, while effectively manage humidity. The humidity component increases the energy harvesting efficiency of ERV and creates a more comfortable living environment.

Schematic of an Energy Recover Ventilator (ERV) for Passive Buildings.

In the summertime (cooling season), the system conditions incoming warm, humid air by passing it over coils or channels containing stale, cool air being exhausted from the house. Desiccants are used to remove humidity from the fresh air intake, which adds to the cooling effect. In the winter, the system uses warm, stale air being exhausted from the house to pre-heat the incoming fresh air. Humidity can be added to incoming air in order to maintain a comfortable level, preventing humans from drying out!

Mechanical ventilation diagram for Passive House Design.

Typical ventilation systems are set up to extract stale air from the “wet” areas of the house—kitchens, bathrooms and storage rooms—through the use of ventilation ducts that channel air though the ERV and exhaust it outside. Incoming air is ducted from the outside of the building, into the ERV, and then into bedrooms, living rooms and dining rooms. Inline filters can be added to the incoming air stream to remove pollen and other particulates.

For typical homes, only a single ERV  and blower are required and they reside inside the house for a low maintenance operation.  Heat exchange efficiency can range from 50 to 90%, depending on the type of system and manufacturer. It is generally accepted that ERV can cut energy usage by 50%.

High-efficiency ERV systems ensure optimal indoor air quality and comfortable living for energy-efficient and passive building construction. The whole house ventilation system really is like the heart and lungs of a passive building.

[box type=”bio”] Eric Davenport, LEAP’s founder is Passive House Certified, and understands the ins and outs of these systems. If you are considering a new build, or even a retrofit, leverage our expertise to get the most out of your project.[/box]