Comfort performance during winter

Zero Energy House

The process the Zero Energy House followed, from even before the site was purchased until the move-in date, was carefully thought of by its owners, Shay Brazier and Jo Woods. They knew what they wanted to achieve, they articulated their aspirations and requirements to their design team and made sure their goals were not forgotten during the design and construction stages. The couple’s paramount motivation for building a house was having a place where they could live comfortably and, to make sure they got what they were looking for, they defined three key goals around comfort:

  • Achieving a stable internal temperature range year-round.
  • Achieving consistency of temperatures between the living and bedroom areas.
  • Achieving the above using passive-design strategies, avoiding the use of mechanical systems.

They also defined acceptable temperature ranges for sleeping and living areas that needed to be met 95% of the occupied time: between 16℃ and 24℃ for bedrooms, and between 18℃ and 28℃ for living areas.

Actual temperatures inside the Zero Energy House

After moving in and with the help of a building-wide monitoring system, Shay and Jo recorded interior temperatures in bedrooms and living areas. The chart below presents half-hourly temperature readings over a six-week period during winter (June 1 - July 10) for the lounge (downstairs), master bedroom (upstairs) and outside.

The results indicate:

  • Temperatures inside were significantly higher than outside (average outside temperature was 11.2℃, whereas inside was 19.6℃).
  • Lower overall fluctuations of temperatures inside (9°) compared with outside (17℃).
  • Consistency of temperatures between living area and bedrooms (average upstairs temperature of 19.8℃, average downstairs temperature of 19.4℃).

These indoor temperatures were achieved without the use of any heating sources other than passive heat provided by the sun, captured during the day in the concrete slab on the ground floor and then released overnight. Thermal mass, together with an extremely efficient building envelope keep temperatures relatively stable through the day and night. The chart below shows, in more detail, internal and external temperatures in a typical winter day:

The graphs show:

  • Internal temperatures drop by around 3℃ overnight, from when the sun sets (20℃ at 6:00 p.m.) until when it rises (17℃ at 7:30 a.m.).
  • Once the sun begins to heat up the inside of the house, there is a jump in internal temperatures (between 9:00 a.m. and 10:30 a.m. temperatures increase from 17.2℃ to 18.6℃).  
  • Temperature drops inside the house are less variable than outside due to the absorbed heat being released by the concrete slab overnight and retained by the tight building envelope.

Keeping track of the temperatures inside the house over winter allowed Shay and Jo to objectively measure whether they were successful or not in achieving the comfort goals they had set early in the design process. Overall, the recorded data shows the house remained within the temperature range initially specified, with stable indoor temperatures, and warm throughout, avoiding the cold pockets typically created in mechanically heated buildings. The best part is that all of this was achieved without the need for active heating systems, using only the sun’s heat and thoughtful design.

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