Exploring the Passive House Framework in Cooling-Dominated Climates
The energy used in buildings, primarily for heating and cooling, represents approximately 1/3 of the world’s energy use. In many locations, this is unsustainable as the current energy sources used are non-renewable and often linked to global warming and climate change. This is why it is important to study the Passive House concept (Passivhaus), and certification framework established in 1996. Passive Houses have been reported to save between 70 - 90% of the energy typically used in (residential) buildings, whilst maintaining acceptable comfort conditions. However, whilst such buildings have been demonstrated in heating-dominated climates such as northern and central Europe; there appears to be limited development of the concept in cooling-dominated climates (climates that require significantly more cooling than heating), where approximately 40% of the world's population currently live.
Considering this, this study set out to explore how the Passive House concept might behave in cooling dominated climates. Using computational simulations, the study showed that a certified Passive House could not simply be adopted from another climate and that a Passive House must be designed for the specific climate in which it will be located. Subsequently, parametric computational analyses sought to achieve a Passive House in cooling-dominated climates by implementing four main strategies (super-insulation, highly performance glazing, airtightness, and mechanical ventilation with ‘heat’ recovery).
It was shown that super-insulation and low-thermal transmission windows could result in energy savings of approximately 30% due to reduced heat transfer. Furthermore, it was shown that such savings could be achieved whilst maintaining comfort conditions considered acceptable to ASHRAE 55. Conversely, airtightness was found to have no significant effect on energy due to the minimal differences in outdoor and indoor temperatures in predominantly hot climates (with no heating requirement). It can, however, ensure a stable thermal condition in a conditioned building.
Furthermore, ensuring the peak load does not exceed 10W/m2 (a requirement of the Passive House certification), a mechanical ventilation system with ‘heat’ recovery at an average ventilation rate of 1 ACH could be sufficient to maintain acceptable comfort conditions and save up to 50% of the energy used in high-performance buildings. Otherwise, a conventional heating, ventilation, and air conditioning system (HVAC) would be required to maintain thermal comfort range and prevent overheating. Additionally, whilst not considered a primary strategy in heating-dominated climates, it was shown that minimising internal heat gain is a significant factor in meeting the Passive House standard in cooling-dominated climates.
In summary, the research has shown that achieving the Passive House standard in some cooling-dominated climates can be challenging due to extreme weather conditions (i.e., high solar insolation) for most of the year. That said, buildings that incorporate Passive House strategies such as super-insulation, highly insulated windows, and minimal internal heat gain, combined with other strategies such as shading, building orientation, and thermal mass, can save up to 70% of their energy whilst maintaining acceptable comfort conditions.
In conclusion, this work suggests that the Passive House standard could be enhanced with consideration for cooling-dominated climates (PH-CDC). This might include setting a target of saving at least 70% energy when compared to a reference building/s in the specific climate, whilst also requiring it to maintain acceptable comfort conditions throughout the year. Such a modification would ensure energy efficiency and thermal comfort are the metrics, rather than an impractical or generalised kWh/(m2a) or W/m2 metric.