What is the heating potential of Sojol's solar ventilation?
Sojol's solar air heating can contribute a significant portion of the total heating requirements in winter. Two examples below show approximately what can be expected on a sunny or cloudy day in winter, but of course this will depend on variables such as solar radiation, flow rate, pitch and orientation. The examples given were from a 2m2 prototype on a roof. Solar radiation readings from these days are in the left images and the temperature readings are in the right images. Three temperature readings were measured - from the supply inlet near the outlet of the solar ventilator, the supply inlet to the room and the outside temperature. The average volume of air at the outlet was measured at 660m3/hr. (Since these results we have optimized the design even further by means of simulation iterations)
On the sunny day in winter in NZ, solar radiation reached nearly 1000Wh/m2 with the outside temperature starting at 11C and reaching 15C by about midday. The supply temperatures measured 35C near the solar ventilator and 32C entering the building at about midday. Over an 8 hour period, solar air heating raised the ambient temperature by an average of 14C.
On a cloudy and wet day in winter in NZ, solar radiation hovered around a low of 200Wh/m2. But even in these circumstances, temperature readings of the supply air still increased by an average of 5 degrees C above the ambient temperature.
How does it work?
Sojol's solar ventilator absorbs heat through 98% transmissive glass onto an absorbing panel formed of black anodized aluminum interlocking tubes. Air always enters the lower end and flows upwards through the tubes in both winter and summer modes. The rapid rate of increase in the heat differential between the outside temperature of air and the temperature in the solar ventilator causes air to be naturally pushed upwards. An inline fan in the ducted system also pushes through this heated air. So in winter solar heated fresh air is drawn into the building. One or two strategically positioned vents in the building allow solar heated air to cross ventilate the building.
In summer mode, it operates like a solar chimney extracting stale air. Since the ideal pressure in a building is slightly positive, this is controlled by pressure sensors that detect when the pressure drops below a certain threshold and this closes off the system allowing the solar ventilator to self-cool instead using fresh air.
The tubes that form the absorbing panel optimize solar heat extraction into the air stream while the space between the glass and the absorbing panel remains well sealed from any air flow in order to retain heat and to keep this area clean. The hinged lid can be opened from the top if access is ever required.
When the solar ventilator is operating in the winter mode, the damper blade positioned at the upper end directs fresh air into the building.
This example of a ducting system in a roof cavity shows how fresh air is supplied to the solar ventilator on the roof via a filter with the help of an inline fan.
Dampers direct the air flow either to the solar ventilator and electric air heater or by-passes the solar ventilator to another air heater depending on the availability of solar heat. The first air heater stores heat from the solar ventilator and occasionally boosts the temperature to the desired level. The second air heater by-passes the solar ventilator and efficiently heats air at night time.
The amount of fresh air is pre-programmed such that there will always be a reliably warm source of fresh air flow in winter when required 24 hours of the day.
When the solar ventilator is operating in summer mode, the damper blade directs stale air out of the building