10 Passive House design tips for keeping cool in summer Our advice for best bang for buck

14 March 2024 by Jason Quinn

The high temperatures this past summer have served to sharpen everyone’s focus on how to design Passive House buildings to remain comfortable for longer when the temps spike. The team at Sustainable Engineering Ltd is working on detailed energy modelling in order to produce building specification guidelines. We’ve also been thinking about what could be implemented right away: finding the low-hanging fruit, you might say. 

Here’s 10 things Passive House designers could usefully explore in the energy model for any project they are working on currently.  

  1. External shading is not optional. Use overhangs on the north side to exclude summer sun and invite winter solar gain. Overhangs on east/west orientations are almost useless, external shading or shutters are needed to block the low sun angles. Solar mesh that doubles as insect screening on opening windows is another option but not readily available yet in New Zealand. We need suppliers to step up and import it. 
  2. Specify Low SHGC glass or glass with a low g-value, eg Metro SunX Grey or Xtreme.
  3. Pay careful attention to g-values or SHGC glass area numbers in relation to the room’s floor area. Focus your attention on those spaces where the ratio of glass to floor area is high.
  4. Consider from the outset which windows will open in order to provide cross ventilation, which makes for fast and effective purging of heat at night. 
  5. Ceiling fans have been used for generations because they work. Some people don’t like the air movement in their bedroom while sleeping, so check in early with your client.
  6. Ensure security stays are specified so windows can be safely left open overnight. The tilt function on inward opening windows achieves this goal but consider if windows will stay tilted open in high wind zones.
  7. A two-story house ideally needs a heat pump downstairs for most efficient winter heating and upstairs for summer cooling. Either specify at least two heat pumps or investigate a ceiling fan in the stairwell to mix air from a central heat pump location.
  8. Ducted central heat pumps are another option, correctly sized and ducted. Remember the air split is fixed and so accordingly is the heating and cooling split. If you have 10% of the air to the master, then you can only deliver 10% of the cooling. Achieving optimal cooling in the master bedroom may require over-cooling the rest of the house.
  9. Mini ducted heat pump units allow cooling to be delivered to several rooms from a single unit, another option for delivering coolth specifically to bedrooms.
  10. Generally large volume builders really don’t want to deal with orientation-specific glazing or shading solutions. This leaves low g-value glass selection as the only option. However it will increase winter heating costs due to reducing solar gain year round.

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