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  • Writer's pictureRydePassiveHouse

A Sydney Summer in a Certified Passive House

Updated: Jul 3, 2023

Our first experience of living in a passive house was in the heat of summer 2022-23. I include March in this because it was unseasonably hot. The house is located 11kms northwest of Sydney harbour, so the costal climate makes summer milder than in many other areas. However, we experienced 32 days with maximum temperatures of above 30°c. The competition winner was March 6th 2023, with a maximum temperature of 38.5°c.

I was happy with the performance of the house. During this period, the internal temperature on the sensor for the ducted dehumidifier showed between 17°c and 23°c. It sits at roughly the centre of the house on the first floor. We had temporary curtains and bed sheets on the windows at this stage, which have now been replaced with block-out, honeycomb blinds. We learned a few things during the period.

The a/c system is small at 7kw, which is what you would expect from a passive house. I was told to turn it on first thing in the morning on forecast hot days. Through experience, I also realised that you could leave the a/c off until 11am or midday on less hot days and that the house would still remain comfortable.

There were temperature variations between rooms. When I look back, I was naïve to think that the HRV would be adequate to move the cool air from the 2 a/c outlets on each floor to all parts of the house. We had 1 ceiling fan, which was in the main bedroom. We ran it on the fastest setting during the day to move as much air as possible and the house was kept relatively comfortable in all but 2 rooms. It was noticeably warm in a southwest-facing bedroom with a small section of brick veneer and a west facing office that missed out on an a/c vent. In April, I had ceiling fans installed in the other bedrooms and the office, which will no doubt make a difference this summer.

The goal of the large areas of glazing to the north is solar gain in the colder months and high levels of ambient light all year round. Despite the allowance we made for shading with a deep northern balcony, and even with sheer curtains, glare from the morning sun in the downstairs living areas was an issue. We had the same problem with afternoon sun on the western side of the house, but openings on that side are much smaller and are now being managed with blinds. We have opted for remote-controlled exterior roller blinds between the balcony posts, which are yet to be installed.

We intentionally designed the house to maximise cross-ventilation for heat purging at the end of the day. In order to take advantage of a possible pressure differential during summer evenings, window openings on the windward (SW) side of the house are much smaller than those on the leeward (N) side (see the historical BOM wind rose below). We were hoping to take advantage of a thermal stack effect by locating 2 small windows in the southwest wall of the internal stairwell void on the ground floor, which line up with a 1st floor balcony door in the centre of the northern wall. I hoped that airflow could also be diverted to 2 balcony doors in bedrooms on either side of this main door, if it was to be closed.

This all sounds good in theory, however there is a lot of concrete and masonry on the SW side of the house. If I open these windows before it has cooled down on a day where the breezes are light, I get relatively warm air pushing out the cooler, air-conditioned air. Oops. To compensate, I now to leave the windows closed and a/c running until after dark in this situation. There are extensive gardens planned for the brick planter boxes that are part of the retaining walls, so hopefully it will improve. The a/c is cheap to run and is at least partially powered by the solar system until well into the late afternoon. Our quarterly power bill was $99.95, most of which was the network connection fee.

I plan to monitor internal and external temperature and humidity levels more closely and will post for anyone who is interested.

small windows in the southwest wall of the internal stairwell void

balcony doors on the 1st floor to provide large openings

masonry and concrete on the SW side

Ducted dehumidifier sensor at (roughly) the middle of the 1st floor

The Bureau of Meteorology wind rose for Sydney Airport at 3pm in February from 1939 to 2016

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