THE CANADIAN WELL: A PASSIVE AIR CONDITIONING SYSTEM
How can we harness the ground's thermal potential and climatize the air at low costs
As you already know, we are passionate about sustainability when it comes to buildings. We are always looking to find better solutions to make a building more efficient from all points of view. Another thing we focus on is also how to harness the energy from renewable sources available around us. One of these is geothermal energy (or earth's energy), that is available in abundance and without interruption, whether it is day or night, winter or summer, hot or cold climate.
It can be harnessed either for industrial applications, such as geothermal power plants that produce electricity and heating, as well as in residential applications. The most common systems for homes are ground-to-water or geothermal heat pumps, equipment that uses the shallow thermal potential of the ground to heat/cool a home. These systems are very efficient and have a coefficient of performance (COP) between 5.3-5.4. Its primary disadvantage, however, is the high investment cost, mainly due to drilling, which can even reach tens of meters deep, depending on the type of soil and underground waters.
The Canadian Well
Another method of harnessing the ground's thermal potential is the ground-to-air heat exchanger, or generically called the "Canadian Well" (you can guess its origin). The working principle is quite simple: the fresh outdoor air is pulled through a pipe buried in the ground, gets heated up or cooled down due to the heat exchange with the ground, and then introduced inside the building. Throughout the year, the temperature variation in the ground is directly proportional to the pipe's depth. The deeper we go into the ground, the temperature becomes stable regardless of the season.
The system consists of a tube buried at 2-3 m depth, a fan that circulates the air, and a grille at the end of the pipe outside, to prevent rodents or dust from entering the tube. The tube must be provided with a slope of 2-3% necessary for the discharge of condensate, which is installed at the lowest end of the tube.
The system's efficiency is primarily determined by the tube's depth, length, and type of soil. All these parameters are taken into account when designing the system. For example, in the summer scenario, if the outside temperature is 35 °C, the system can cool the air up to 20 °C. In the winter scenario, the outside air at -5 °C can be heated up to 7-8 °C. The energy consumption required for this whole process is the fan, let's say a maximum of 40Wh. Now let's imagine how much it would cost us in the summer to cool the air by 15 °C by conventional methods such as the AC (Air Conditioner) that has an energy consumption of 2000Wh. It's 50 times more.
However, the Canadian Well also has some disadvantages. One of them is the investment cost because the tube must be a special one, treated with silver ions inside to prevent the appearance of bacteria. Another disadvantage is related to the quality of the air circulated and the possibility of radon infiltration.
Radon is a toxic radioactive gas that results from uranium decomposition, a process that occurs naturally in the earth's underground layers. It is odorless and colorless and penetrates buildings through porous elements such as concrete foundations, water wells, and pipes. It does not take into account the building, either old or new, or with a concrete or earth foundation. Radon is found in soil, rocks, and water and can be detected by humans only through special measuring devices. It is a radioactive gas, and consequently carcinogenic. It is considered by the World Health Organization to be the second leading cause of lung cancer after smoking.
Canadian Well combined with Heat Recovery Ventilation (HRV) System
To prevent the air quality-related problems, the Canadian Well can be connected to a heat recovery ventilation system. Thus, the preheated/cooled air from the tube reaches the interior, first passing through the heat recovery unit, where it is again warmed up or cooled down, without mixing. In this way, in the summer scenario, for example, the fresh air circulated through the pipe enters the heat recovery at 20 °C, instead of 35 °C, and after the heat exchange with the evacuated air from inside at 26 °C, gets warmed up at 23-24 °C. Therefore, the system ensures a constant supply of fresh air, in proper thermal comfort parameters, with minimum energy consumption.
If the outside air temperature is within comfort parameters, the Canadian Well is by-passed, and the fresh air enters the heat recovery ventilation unit directly through an adjacent duct. In this configuration, there is also a need for basic automation that controls the system's operation according to the outside air temperature.
CLAGHE (Closed Loop Air Ground Heat Exchanger)
But things can be taken further. The whole system can be improved and optimized to increase the heat exchange efficiency and ensure a constant supply of fresh air, at optimal comfort parameters, both in summer and winter, without additional cooling or heating. Therefore, CLAGHE was developed, an innovative mechanical ventilation system with a closed-loop geothermal exchanger.
Our colleague, Architect Daniel Barbu-Mocănescu has designed and developed CLAGHE, which has been successfully implemented in various eco-friendly projects in Romania. CLAGHE consists of a closed-loop geothermal exchanger buried in the ground at a certain depth, an air-to-air heat exchanger, and a heat recovery ventilation system.
The working principle is similar, though extra equipment is added, and the geothermal exchanger has a closed-loop. In this way, the air in the tube is circulated in a closed-loop, and thus there is no need for special piping or condensate drainage solution. The fresh outside air is preheated/cooled by the air circulated in the geothermal exchanger, without mixing, and is then heated up/cooled down again by the exhaust air from inside, in the heat recovery unit, again, without to be mixed. More details about CLAGHE can be found on the dedicated page.
Judging by recent years' events, we tend to believe that only sophisticated and technologically advanced systems can increase the performance of a building. This is true, but there are alternatives that our ancestors successfully used thousands of years ago. We can combine with today's technology to obtain an efficient and cost-effective solution. We believe that such an alternative is the Canadian Well, in its various configurations. A worthwhile investment not only if we look at its efficiency, but also at the fact that it helps to reduce the impact that buildings have on the environment.