There are several types of soil heat exchangers that can be used at present. The ability to do it yourself, good efficiency, as well as the simplicity of the design itself made this type of ventilation very popular for arranging in a private house.
System description
To date, it is known for sure that in the territory of all CIS countries the temperature of the soil at a depth of about two meters remains almost unchanged. Year round, the approximate temperature of the soil is +10 degrees Celsius. Small changes are observed depending on the region, but they usually do not exceed two degrees. Installation of soil heat exchangers implies the use of this free energy. Thus, in the warm season, such ventilation will cool the air inside the room, and in winter, on the contrary, heat it. In addition, additional heat can help save the temperature that is created by other heating elements.
To date, a soil heat exchanger is most often used together with a recuperator. A recuperator is a heat exchange device that is designed to heat cold air due to warm exhaust air. In addition, its system includes fans, filters, piping and a heating device.
System use
Such a scheme of the soil heat exchanger allows you to get air from the soil already slightly warmed up, which helps to save some amount of energy that would go to the work of the recuperator. The presence of such an air heating system will also help save energy and the design of the recuperator. In this case, it is understood that no condensation will form inside the pipeline, since the temperature of the air that will pass through the pipes will be approximately the same all the time. A condensate problem can occur only when the recuperator is turned on, but initially frosty air will enter it.
Climate Impact on Ventilation
The effectiveness of the soil heat exchanger for ventilation is quite dependent on the climate that is observed in the region. If we talk about the climate in the CIS countries, then installing a heat exchanger can help in heating or cooling the air in the region from 5 to 20 degrees Celsius. The effectiveness of the system itself will directly depend on how large the temperature difference between the soil and air is. The greater the difference, the more efficient the system is. Due to this effect, a soil heat exchanger for ventilation is an effective tool both in winter and in summer. During the heat, the system can provide a reduction in temperature from 30 to 20 degrees. In frosty weather, the temperature can increase from -20 to 0 degrees.
When calculating the soil heat exchanger for ventilation, it is necessary to take into account the fact that in spring and autumn the effect of such ventilation on temperature is practically absent. This is justified by the fact that the temperatures of the surrounding air and soil are too close in value, due to which the air exchange is significantly slowed down. In some cases, such a system may even work in a negative mode. For example, the room temperature is 12 degrees Celsius, and the presence of a heat exchanger will reduce it to 8 degrees. Taking this fact into account, it is necessary to equip the soil heat exchanger with your own hands in such a way that it can be turned off or closed for direct air passage.
The main types of system
Currently, two main types of such a system are known - this is a tube and non-channel heat exchanger. When arranging a channel-free type of system, an underground layer will be used through which air will pass. Tubular, or channel type implies the presence of pipes for mounting a soil heat exchanger through which air will pass. They must also be laid underground.
What unites these two types is that the main channel of the supply type must be connected to the ventilation. The main requirement to keep in mind is that the system must have a mechanism that allows you to switch between the two modes. In the first mode, direct air flow from the street will be used; in the second mode of operation, a heat exchanger will be used.
Duct heat exchanger
When choosing between airy ground heat exchangers for a private house, it is better to choose this option. It, of course, requires more time and money, but is also more effective. In order to produce this type of ventilation, it is necessary to lay the pipe system in a prepared trench in the ground. On average, the length of the pipeline is from 15 to 50 meters. The choice depends only on the capabilities and area.
It is important to remember that the pipes for the soil heat exchanger can rotate, since this practically does not affect the movement of air. In addition, the longer the system is, the more efficient it will work, which is also very important to consider. Arranging a short exchanger makes little sense.
Choice of pipes for laying
As already mentioned, for the effective use of the system, it must have a large length. If the area around the house allows, then you can lay just one pipe around the house. If space is limited, then parallel laying can be used. The diameter of the pipes for the normal functioning of the system should be from 200 to 250 millimeters.
An excellent choice are polypropylene pipes. When calculating the soil heat exchanger, you also need to know that it is possible to improve the heat exchange process by reducing the wall thickness and increasing their area. Based on this, corrugated material can be used. In this case, the heat will not be retained at all in the soil system. It is also very important to equip the system bias by about 2% in any direction. A slight slope in this case is necessary so that condensate, which will form in very hot weather, can drain without problems.
Stock and other elements of the system
In order to effectively remove condensate from the system, it is necessary to equip the pipeline not only with a slope, but also create a small hole at the bottom mark of the pipe. To drain the liquid, it is necessary to equip a drainage well or draw a conclusion directly to the ground. If the site has a low level of groundwater, it is necessary to manufacture a sand cushion for the system. The end of the pipe, which is located on the site, must be equipped with a filter. In addition, it must be set above the level of snow that falls in winter.
When arranging a soil heat exchanger with your own hands, you need to know that if snow is a rare occurrence in the region, then the height of the pipe that protrudes above the ground should be at least 1.5 meters. This must be done as protection against radon - radioactive soil gas.
An air intake must be installed at the end of the pipe. This element should also be equipped with a filter and a strong metal mesh. The end of the pipe must be installed and protected in such a way that rain, leaves, and no animals, birds, etc. can get into it. If possible, this element is installed as far as possible from any sources that may affect air quality. The minimum required removal is 10 meters.
Channelless type
In order to equip this type of heat exchanger with your own hands, you need to dig a recess, the length of which should be 3-4 meters and a depth of 80 cm. In addition, this foundation pit must be filled with gravel and covered with a foam concrete top. This design is necessary so that the temperature inside the pit does not differ from the temperature of the soil at a recess of up to 5 meters. After this stage is completed, it is necessary to equip the outlet of the pipe through which air will pass.
As for the manufacture of this pipe, this process is no different from its manufacture in the previous version. Naturally, another pipe should connect a special heat-exchange layer of the pit and the ventilation of a private house. After this, air circulation will begin according to the simplest scheme. In addition, the air will not only be humidified, but also cleaned. Based on this, it can be argued that the channelless type is better in terms of air filtration, and the pipe, or channel type is more effective for heating or cooling.
System features
The channelless type, or gravel heat exchanger, is characterized by the fact that it needs to restore its functions. In addition, it is forbidden to mount it in those places where the influence of external loads is observed, for example, in the place of passage of automobile transport. Another feature is that if the gravel, which is intended for laying, is not washed out, then after arranging the system and the beginning of air circulation in the room, an unpleasant "basement" smell can occur. The same problem may arise if the gravel layer gets wet due to precipitation or because of the rise of groundwater, for example.
disadvantages
If you damage the surface layer of such an exchanger, this will lead to a decrease in its efficiency, as well as to possible saturation with moisture. All this will require repairs. When arranging the exchanger with your own hands of precisely this type, you also need to know that the layer of gravel is both a heat exchange point and an obstacle to air passage. Because of this, the system will need to install an additional source of air injection - a fan with enough power (several hundred watts). Naturally, this is an additional cost for both installation and purchase, as well as for subsequent payment of electricity. Because of this, it is necessary to carefully carry out system calculations. Here it can be added that the calculations of a liquid soil heat exchanger are somewhat simpler than gravel, although its arrangement and design are more complicated.
Membraneless type
To date, there are such types of soil heat exchangers (TRP) as membraneless. They are a combination of the two previous types of systems. The main point of installing such a device is that you need to mount an even layer of polymer slabs on top of an even layer of gravel.
System installation
Plates must be mounted on the "legs", which will rest on the gravel layer. Thus, it turns out that the air will not move through a layer of gravel, as with a channel-free type, but between a layer of plates and a layer of gravel. The main advantage is that it is possible to use such a heat exchanger for a sufficiently long period without regeneration of the gravel layer.
An ordinary layer of gravel can work only 12 hours, after which 12 hours of “rest” are necessary. During this rest, a layer of gravel will take heat from the soil, and then transfer it to ventilation. When using plates, these frames are greatly simplified. Another difference of the membraneless TRP is that there will be no strong obstacle to air circulation. With a channelless type of exchanger, gravel will be a natural obstacle to the air flow, which is why it is necessary to equip the system with additional fans most often.
The main problem of using such a ground-based heat exchanger for ventilation with your own hands is that the system is not continuous, and therefore it is completely forbidden to use it in those regions where there is an increased level of groundwater or there is a chance that the system will be flooded by atmospheric precipitation.