Net-Zero Home: Passive Cooling from Natural Ventilation

In a previous article - link - was presented a case study that highlighted the benefits offered by our net-zero consulting service which allowed a single-family project, designed by the environment friendly architectural firm OWN*, to save 52% in energy and provide 76% sDA, climate-based daylight calculation. In this article we will discuss a specific topic excluded from the previous one: natural ventilation for passive cooling.

Our client wanted to validate the possibility of natural ventilation cooling instead of mechanical, thus we identified that almost all days of the year around mid-day there is higher internal gain and solar gain. It was clear that there is a requirement in load and hours of operation for cooling and there could be savings in initial investment (equipment and installation) and energy saving (2%-5% annual energy consumption). 

​The method used to evaluate the design was to measure the thermal comfort (statistical person comfort considering temperature, radiation, humidity level, air velocity, clothing, and people activity). Our first evaluation considered the original design openings configuration (see left image below) which showed us that the natural ventilation cooling allows the living spaces to reach an acceptable comfort by reducing the apparent temperature 2-3 degrees Celsius. However, there was some undesirable hot spot (temperature of 30 degrees Celsius) which showed that even if on average space should be comfortable the ventilation is not sufficient. Thus, we proposed to take advantage of the modified design additional glazing, which provide better solar panel generation and increase daylight, to maximize the ventilation and natural cooling efficiency (see right image below).

Original Design

Optimized Design

​The modified design with higher glazing on the south façade allows the fresh air to enter from lower level windows and escape from higher level windows after having cooled the spaces. The reason why this is more efficient than the original design is that the supply cool air has a greater distance from the escaping hot air. As well, there was added openings on the first-floor north façade which increase the suction of cool air from the ground floor which passed from the stairway and escape from the first-floor common corridor. Increased air flows from increased higher openings and the reduced mixing of supply/escape air by strategically placing high openings resulted in a reduction of apparent temperature of 1 degree Celsius and reduction of hot spots only to few wall surfaces. Below is presented the comparison for the 2 design of temperature distribution at 1.3m from finished floor of the two floors.

Initial Design - Ground floor temperature distribution from CFD.

Initial Design - 1st floor temperature distribution from CFD.

Optimized Design - Ground floor temperature distribution from CFD.

Optimized Design - 1st floor temperature distribution from CFD.

Finally, please take a look at the whole simulation results:

Please share your opinion below, your participation means a lot to us.​

* OWN, Architectural Firm with focus on balance between human and nature, www.thisisown.com/.