Passive cooling

There will always be times when outside temperature will be higher than people find comfortable. The environmental cohesion of our designs means that it is possible to achieve a great deal of control without the need for active cooling systems. We always install a passive cooling systems as our homes are so thermally efficient. If additional cooling capability is required then there are three active cooling systems that are available to us.

We always create a central stair well so that air can be drawn through the building by a solar chimney or wind catcher. Ports in the internal walls allow air to flow from rooms to the staircase. A mixture of fresh and recycled air is ducted to the extremities of every room. Heat recovery ventilation removes heat or coolth from air as it is discharged from a building to the outside to be replaced with fresh incoming air. This equipment has the effect of extending the life of the energy stores. We have a hierarchy of methodologies available to us. Starting from the simplest they are;

Earth Tubes
We bury pipes in the ground or run pipes through cooling ponds. In warm weather the surrounding soil or water cools any air that passes through the tube. In cold weather incoming air is warmed when it passes through the same tubes. The force that is necessary to draw fresh air through the pipes is provided by negative air pressure which is created by a Solar Chimney or Wind Catcher, or by the kitchen and bathroom exhaust vents. The earth warming/cooling tubes are usually 200 mm in diameter and extend up to 100m from the building. They are buried at a depth of 1.5 m. These pipes permit a slow airflow which results in a high level of energy transfer. We prefer to introduce ducted air to a dwelling rather than unconditioned outside air.
Wet Wall
When the weather is not excessively hot we use the cooling wall to lower the temperature inside the building. Outside air passes down the back of the wet wall before it enters the building through low level vents. Air rises up the stairwell and is expelled via a solar chimney or a wind catcher. Since hot air rises cooler air flows in to replace it. When the temperature rises above the human comfort range the cooling vents in the walls are closed and the following active cooling systems are employed
Active Solar Cooling
In locations where extremely hot weather is the norm we install a range of active cooling systems to lower the temperature of the re-circulated air. The collectors concentrate the sun’s energy and this is used to power the cooling systems. We usually install the cooling equipment in the roof void of the house.
- Absorption Cooling
  This uses solar energy to drive the cooling process. A liquid refrigerant evaporates in a low partial pressure environment and in so doing extracts heat from its surroundings. The gaseous refrigerant is absorbed in another liquid so reducing the partial pressure in the evaporator and allowing more liquid to evaporate. The refrigerant-laden liquid is heated, causing the refrigerant to evaporate out. It is then condensed through a heat exchanger to replenish the liquid refrigerant in the evaporator.
- Desiccant Cooling
  A refrigeration condensing unit
  
  Moisture is extracted directly from the air without the use of complicated machinery. As the humidity falls so the air cools. The desiccant is usually calcium chloride. As the desiccant absorbs ever more water its ability to dry the air declines. The desiccant is then regenerated by warming the desiccant The water in the desiccant then evaporates to the outside air. The desiccant is then ready to dry more indoor air. We use heat from the solar collectors to regenerate the desiccant.
- Vapour Compression Cooling
  This uses solar energy to power a Rankine-cycle heat engine. The system has four components – a compressor, a condenser, a thermal expansion valve and an evaporator. The circulating refrigerant enters the compressor as a saturated vapour and is compressed to a higher pressure, resulting in a higher temperature. The hot compressed vapour passes through a condenser where it is cooled and condensed into a liquid by passing through a coil of pipes which have cold water flowing over their surface. The rejected heat is carried away by the water. The condensed liquid refrigerant passes through an expansion valve where it undergoes an abrupt reduction in pressure. The drop in pressure results in adiabatic evaporation of the liquid refrigerant. The auto-refrigeration effect of the evaporation lowers the temperature of the liquid and vapour refrigerant mixture and makes it colder than the temperature of the space to be refrigerated. The cold mixture is then passed through a coil of tubes in the evaporator. A fan draws the air across the coil. The warm air in the building evaporates the liquid part of the cold refrigerant mixture. The cooled air is then returned to the living area. In the evaporator the circulating refrigerant removes heat which is then drawn out in the condenser and carried away by the water. The fans and pumps are mechanically driven by a wind turbine or by electric motors that are powered by electricity that is generated on site.