Principles of Passive House Design

A critical component of passive housing is the implementation of Mechanical Ventilation with Heat Recovery (MVHR) systems, which address the dual challenges of building airtightness and indoor air quality. Because a passive building envelope is meticulously sealed to prevent uncontrolled draughts and thermal leakage, natural air infiltration is virtually non-existent. Without an engineered ventilation strategy, stale air, excess humidity, and indoor pollutants would quickly accumulate to hazardous levels.

The MVHR unit resolves this predicament by continuously extracting moist, stale air from service rooms, such as kitchens and bathrooms, while concurrently drawing fresh air from the outside. Before the stale air is expelled outdoors, it passes through an internal counterflow heat exchanger. Here, the thermal energy from the warm exhaust air is transferred to the cooler incoming fresh stream without the two air currents ever physically mixing.

This thermal exchange mechanism typically recovers up to ninety percent of the heat that would otherwise be wasted through conventional window venting. In addition to conserving energy, the incoming air is passed through fine filtration media, which removes pollen, particulates, and external allergens. Consequently, the MVHR system maintains superior indoor environmental quality with minimal temperature fluctuations, decoupling fresh air provision from heating energy losses.

Passive solar architecture relies on the strategic orientation and specification of windows to harness solar radiation as a primary heat source. In temperate zones of the Northern Hemisphere, passive houses typically incorporate extensive glazing on south-facing facades to capture maximum solar energy during winter months, while minimising apertures on northern exposures where thermal losses exceed potential gains.

To make this approach viable, standard double glazing is replaced with triple-glazed units filled with inert gases such as argon or krypton, coupled with low-emissivity coatings. These technologies allow shortwave solar radiation to penetrate the interior while preventing longwave thermal radiation from radiating back outside. Furthermore, thermally broken window frames ensure that the perimeter of the glazing does not become a conduit for heat dissipation.

However, the capacity to capture solar gains presents an inherent risk of summertime overheating if solar geometry is not managed. Passive house designers address this vulnerability through architectural shading, including carefully calibrated overhangs, external louvres, and deciduous plantings. These elements obstruct high-angle summer sun while permitting low-angle winter rays to enter freely. As a result, the building maintains an optimal thermodynamic balance throughout shifting seasons without relying on energy-intensive air conditioning systems.