Abstract Outline:
As the planet warms, solutions to the growing crisis of climate change are evolving at a dizzying pace. Many of the solutions being proposed are mechanical in nature and may end up being part of the problems of the future. As is often the case with new and untested technologies, these new systems have been found to be just as harmful if not more harmful than their predecessors. Such is the case with regards to HFC’s (hydro fluorocarbons) when they replaced CFC’s in air conditioning units. The United Nations Environment Program (UNEP) later found that HFC’s were up to ten thousand times more harmful. In order to avoid these future problems, it has become important to research systems that are passive in nature, meaning they have few if any moving parts, and require no chemicals. An example of a passive building, The Eastgate Building in Harare, South Africa, uses biomimicry for its cooling system. The cooling system is modelled from a termite mound. The results of this passive system are astounding. The building uses only 10% of the energy that a conventional building of similar size would use, lessening the costs of construction, and contributing to a reduction in operating costs and even the costs of rent. This shows that often the simplest solution to a problem is the best solution.
How does an earth tube system perform with respect to the passive cooling of residential buildings in Kamloops, BC?
The Air Tube Concept:
Earth air tube systems were developed during the 1970’s and 1980’s as a method of providing natural cooling and air circulation to a home. The system is passive in nature and uses air circulation or more specifically air convection to power the air flow. In other words, there are no moving parts. The system is described as follows; one end of the pipe acts as an inlet for the ambient outdoor air. In a standard building, the other end of the pipe brings the air to the fresh air intake of an HVAC system. For the purposes of the research however, the air will simply enter the room through a vent in different locations throughout the cabin. The air is conditioned through conduction via the ground temperature, in the winter the conditioned air is warmer whereas in the summer it is cooler than the exterior temperatures. The system can be completely passive; however, a small fan can be used to augment the airflow. The warm air is then forced out of the building via a small air vent located near the top of the building. During the warm summer months, this is where the warm air escapes. The system remains working due to the convection of the warm air and cold air thus ensuring a steady supply of cooled air being brought into the house.
According to F. Al-Ajmi, in his research paper titled “The cooling potential of earth-air heat exchangers for domestic buildings in a desert climate”, earth tube systems can reduce cooling demands by up to 30% or by as much as 420 kWh.
Researching the cooling potential of Earth Tubes:
While there is much potential to reduce heating costs with an earth tube system, only the cooling potential shall be examined in this research. Small baseboard heaters, powered by photovoltaics, will be used to heat the cabin in the winter. The cabin is to be completely passive in its energy use. In order to determine the potential savings an earth tube system can provide, several factors will be examined and recorded. Thermometers shall be placed in several key locations and recorded using a data logger. One shall measure the outdoor air temperatures, another shall measure the temperature of the air entering the inlet of the earth tube, and a thermometer shall measure the temperature of the air entering the building, after it has been cooled. Another shall measure the air temperature inside the building. In order to determine the cooling potential of the earth tube system as a whole, other important qualitative factors shall be recorded, such as; pipe diameter, pipe length, air velocity, soil temperature, and pipe depth. According to research, “the model (earth tube system) can properly predict the performance of an earth tube system and the heating/cooling load reduction due to the earth tubes.”1
Building simulation:
Research will be performed on a system of earth tubes in Barnhartvale, where a small cabin will be constructed, and several earth tube runs shall be constructed. There will be two primary types of earth tube systems; the first two sets shall be buried under the ground at 8’-0” and 6’-0” in depth. The air intake for the 6’-0” depth system shall be placed in the shade where the air is always cooler, while the other intake shall be placed in full sun. A third run shall be placed under water. Several measurements shall be taken. The ambient outdoor air temperature shall be measured at the inlet of each tube, and the temperature of the air coming into the building from the individual tubes shall be measured. The difference of temperatures shall be plotted on a graph to determine the efficiency of the system.
Conclusion:
Air tubes alone cannot replace a mechanical air conditioner; however, in conjunction with smart passive designs, a well designed building envelope with good insulation, modern windows, and night-time venting, a passive system may be able to maintain indoor thermal comfort during the warm summer months. In addition to the reduction in cooling costs, an earth tube system can offset the cost of heating a building in the winter. The savings on heating will result in energy savings of about 25% or more. While extra cooling may be needed during peak summer days and extra heating will be needed during the cold winter days, Earth tubes can eliminate the need for cooling and heating during the spring and late into the fall.
