Natural recuperator or free air conditioner for a country house

Recommendation points

• Stable energy source
• International practice
• Why a natural heat exchanger is good
• Simple and straightforward system
• We create an internal system of ventilation ducts at home
• An example of calculating the consumption of materials for the device of internal channels at home
• Tube heat exchanger
• We create a recuperation field
• Bunker heat exchanger
• We fill the tank
• Installing the fans
• Estimated operating cost
• Perspectives

Cooling the air in the summer is one of the homeowner’s primary concerns. How to use the energy that surrounds us for this purpose and make air conditioning practically free, this article will tell..

The importance of ventilation can hardly be overestimated. We will not repeat what has been described many times and will focus on our own task – to cool and refresh the air in the house. Traditional ventilation systems can be quite expensive for the device due to the cost of components and assemblies, as well as the cost of qualified installation work.

During operation, they consume a significant amount of electricity, especially for cooling the air mass, generate a lot of heat and create noise. The system described in this article is easy to install, energy efficient, requires no special skills, and is intuitive. It should be noted right away that due to its simplicity, it has limited functions, however, it provides for modernization at any site at any convenient moment..

In our case, the term “recuperation” is a synonym for the word “heat exchange”, therefore the concepts “recuperator” and “heat exchanger” are interchangeable. At the physical level, the process consists in cooling / heating air, in changing its temperature due to the consumption of thermal energy, and then mixing. How and why this happens, we will consider further..

Stable energy source

In pursuit of the goal of lowering the temperature in the room in the summer, it is reasonable to ask the question: “Where to give the energy of the heated atmospheric air? How to cool it? ” Here the forces of nature come to our aid. The fact that at a certain depth the ground temperature is constant will be our main argument when justifying the energy efficiency of the system..

The soil is capable of endlessly exchanging energy – to cool and heat any medium (air, water), but only to its own temperature at a given depth, which remains constant due to the relative stability of the earth’s core.

International practice

Of course, we are far from the first who decided to use the infinite and free energy of the Earth. In European countries, which are usually called developed (Germany, Sweden, Belgium, etc.), this energy has been used since the beginning of the last century. The successes achieved in this field are impressive.

Heat transfer systems for water below ground level are called “heat pumps”. These underground and underwater devices heat and cool the entire home. Standard projects have been developed for any building and it is possible to transfer a house from a traditional (gas, electric) air-conditioning system to heat pumps. In a similar, but more primitive way, this energy is used in our country, arranging underground storage of products (cellars).

Why a natural heat exchanger is good

The operation of our recuperator is based on the same physical process as in heat pumps. Focusing on economy, we use this principle, summing it up to our own needs and local realities.

Tasks that an adapted autonomous recuperator can solve:

1. Constant natural ventilation with closed doors and windows.
2. Quick replacement of indoor air with fresh air.
3. Indoor air cooling.
4. Preparing the air mixture for subsequent actions.

Benefits:

1. Absolute environmental friendliness. During the installation and operation of the basic system, toxic materials are not used and no thermal emissions into the atmosphere occur.
2. Safety. The recuperator does not use electric motors (more than 100 W), chemical agents, high voltage.
3. Simplicity and low cost. For forced ventilation, only low-power 100 W fans are used. Ventilation takes place naturally.
4. Oxygen is not burned during operation.
5. Low noise level.

Disadvantages:

• the basic system does not provide for filtration, humidity control, heating or other processing of the air mixture (but allows the possibility of installing the corresponding equipment later).

Simple and straightforward system

An autonomous heat exchanger for a country house is a ventilation duct system, partially laid underground, included in the supply and exhaust ventilation circuit. In order to create such a “conditioner”, it is not necessary to understand the intricacies of physical phenomena. You just need to know that it works. You can verify this by going down in the heat to any basement, well or metro.

The principle of operation is as follows:

1. Atmospheric air passes through pipes laid in the ground with a constant temperature (usually from +4 to +10 ° С).
2. In the underground part, the cool soil absorbs the thermal energy of the heated air.
3. Cooled air is delivered through ventilation ducts to the premises of the house.
4. At the same time, the exhaust fan removes the saturated and heated air mixture (“old air”) from the room.

According to the construction principle, such systems are divided into two main types: pipe and bunker.

Pipe – consists entirely of pipes. The design can be varied depending on the site conditions. Suitable in case of reconstruction of a house without a spacious basement, but it will take a lot of earthworks.

Bunker or stone – the heat exchanger is a bunker filled with large stones. Takes up less space than pipe (you can arrange it in the basement of the house). Requires a basement or underground room. The best option for new construction.

We create an internal system of ventilation ducts at home

In both cases, the ventilation ducts inside the house will be approximately the same. Let’s start with them.

A primitive supply and exhaust ventilation system represents external and internal ventilation ducts connected into one network. Air outlets are located in the upper diagonally opposite corners of the rooms. In one – the inflow, in the other – the exhaust. In a one-story building, the main ducts can be located in the attic. In a two-storey building, the supply and exhaust air ducts of the first floor will run in ducts that fit into the interior decoration, and on the second floor – through the attic. The location of the main air ducts should be determined for each house individually, taking into account the layout (location of walls and partitions).

Council. Premises where supply and exhaust ventilation is recommended: living room, bedroom, nursery, kitchen, dining room, offices, storeroom, recreation rooms, gym. In bathrooms and toilets – only an exhaust. Not needed at all in corridors, vestibules, halls and loggias.

Rules for calculating the system of internal ventilation ducts:

1. Sewer pipe with a diameter of 250 mm for distributing supply and combined outlet channels. Estimated consumption – two lengths of the house + height along the upper floor + 20%.
2. Sewer pipe (gray) with a diameter of 150 mm. Estimated consumption – three times the length of the house + 20%. For a two-story house with equal floor area + 50%.
3. Pipe fasteners (based on the wall material) at the rate of 1 pc. 70 cm.
4. Insulation (rolled mineral wool) – 1 roll.
5. Foam, sealant, decorative grilles.
6. Knees, revisions, couplings (1 piece per 70 cm).

Attention! Do not use 90 ° elbows, this will obstruct the passage of air and create noise. Combine 45 ° elbows (similar to sewers).

If it is planned to arrange a pipe recuperator in a one-story building, the supply duct will go out from the ground into a heat-insulated box outside the building and enter the attic. In a two-story one, it is better to bring it into the building at the bottom of the first floor and install an internal vertical (distribution) channel, which will then be led into the attic space.

When installing a bunker option in the basement of a building, the vertical distribution channel will exit the bunker directly into the room. It is possible to mount it outside.

An example of calculating the consumption of materials for the device of internal channels at home

Let’s take as an example a one-story house with an estimated ventilated area of ​​60 m2², which will have approximately 100 m² total area and approximate dimensions 8×12 m:

1. Pipe 250 mm: 2 x 12 + 3 + 20% = 32 m.
2. Pipe 150 mm: 3 x 12 + 20% = 43 m.
3. Fasteners: 32 + 43 / 0.7 = 107 pcs.
4. Elbows, revisions, couplings – take for 1 piece per 3 m: 32 + 43/3 = 55/3 = 20 pcs.
5. Lattices: 8 pcs. (2 for each room).
6. Switches: 4 pcs.
7. Foam, sealant.

Name	Unit rev.	Qty	Price	Total, rub.
Pipe 250 mm	run. m	32	200	6400
Pipe 150 mm	run. m	43	150	6450
Elbows, revisions, couplings	PCS.	20	40	800
Fasteners	PCS.	one hundred	thirty	3000
Lattice decor	PCS.	4	one hundred	400
Switches 2-cl.	PCS.	4	120	500
Insulation	pack.	1	1000	1000
Foam, sealant, other	1000
Total material	19550
Job	5000
Total material and work	24550

Tube heat exchanger

In order not to complicate the calculations with mathematical calculations, we will provide the data of the tests already carried out in an averaged form, or rather, their results.

The basic principle that must be observed when creating a system of pipes is that at least one pipe of an underground channel must fall on one room. This will facilitate the operation of the fans due to atmospheric pressure. Now it remains to place the required number of pipes in the underground part of the site. They can be laid separately or combined into a common channel (250 mm).

In this description, we propose to take into account not the maximum load, when all rooms are forcibly ventilated at the same time, but the average load, which will be supplied with regular periodic ventilation of different rooms (as is the case in real life). This means that there is no need to output a separate channel for each room. It is enough to bring 150 mm air ducts from each room to one common 250 mm channel. The number of common channels is taken from the calculation of one channel per 60 m².

We create a recuperation field

Recommended layout of the underground part of the tube heat exchanger:

Diagram of the tube recuperator device: 1 – fan; 2 – channel in a trench? 250 mm; 3 – rows of pipes? 250 mm; 4 – recuperation field.

First, you need to choose the location of the pipes (recuperation field). The greater the length of the laid pipes, the more efficient the air cooling will be. It should be noted that after work, this area can be used for planting plants, landscaping or a playground. Under no circumstances plant trees in the recovery field:

1. We excavate soil to the freezing depth plus 0.4 m.
2. We lay pipes 250 mm with a step of at least 700 mm along the axis.
3. We bring the air intakes to a height of 1 m.It is desirable that they are in a shaded, but well-ventilated place.
4. With the help of elbows and adapters, we combine them into a common channel of 250 mm, which is connected to the ventilation system of the house (see above).

Attention! In the underground part, use special thick-walled earthen sewer pipes. They do not need to be thermally insulated, but simply covered with soil, spilling water. Only concreting is allowed if necessary.

Calculation of the amount of work and material consumption:

1. For the recovery field we take a 15×6 m area with an area of ​​90 m².
2. The volume of the foundation pit with a freezing depth of 0.8 m will be: V_cat = (0.8 + 0.4) x 60 = 72 m³.
3. Trench volume 40 cm wide (10 m from the house): V_tr = 1.2 x 0.4 x 10 = 4.8 m³.
4. Total volume of earthworks: V_total = V_cat + V_tr = 72 + 4.8 = 77 m³.
5. Sections of 15 m: N_neg = a / 0.7 = 6 / 0.7 = 9 pcs., where a is the field width.
6. Total pipe length: L = N_neg x 15 + 10 = 9 x 15 + 10 = 145 linear meters. m.
7. The consumption of elbows, couplings, adapters is accepted 2 pcs. x 15 m = 30 pcs.

Council. The deeper the heat exchanger is laid, the more efficient its operation will be. More than one tier is allowed.

Name	Unit rev.	Qty	Price	Total, rub.
Sewer pipe 250 mm soil	run. m	150	250	37500
Elbows, couplings, adapters	PCS.	thirty	50	15000
Excavation:
excavation	cub. m	77	300	23000
backfilling	cub. m	70	150	10500
Pipe installation work		3000
Total material		52500
Total work		36500
Total work and material		89000
The cost of 1 sq. m	89000/60	1500

Bunker heat exchanger

If the house has unoccupied basements, they can also be used to build a bunker (air or heat exchange tank) for a stone heat exchanger. Its action is based on the energy content of the stone – it gradually picks up the ambient temperature and balances the flow of passing air. If there is no free space in the basement, the bunker can be arranged on a site outside the house.

Bunker heat exchanger device diagram: 1 – fan; 2 – pipe O250 mm; 3 – protection; 4 – stone O200-450 mm; 5 – brick walls; 6 – cover

At a certain place, a pit is digging about 2x3x3 m in size.A trench is made from the exit of the common channel of the ventilation system of the house to the pit of the future reservoir, a 250 mm pipe is laid into it to a depth of 140 cm, through which cooled air will be discharged from the bunker. Along the wall, to which the trench came, a vertical groove is laid to the bottom for a pipe with a diameter of 250 mm. Then the bottom is laid out with bricks or concreted. The bottom of the air tank should be at least 1 meter deeper than the level of soil freezing.

Attention! After the installation of the bottom of the hopper, a 250 mm branch pipe should be laid.

The beginning of the branch pipe protrudes from the wall by 1/3 of the distance to the opposite wall and is lined with brick protection. A protective grid is installed on the inlet.

We fill the tank

It is better to lay the walls out of bricks or cast from concrete (no slag!), Since these materials conduct the temperature better than others. The cinder block will not work because of its thermal insulation properties. The walls and bottom must be thoroughly waterproofed (roofing material) from the outside and plastered from the inside to prevent the penetration of organic matter or moisture. The height of the walls is up to the ground level minus 20 cm. An inlet is arranged at the top of any wall and air intake pipes are installed. To facilitate the operation of the fans, we recommend installing 3 pcs..

After the mortar has hardened, the hopper must be filled with large pebble stones. Sizes from 200 to 450 mm in diameter. The stone must be clean of organic matter, washed.

The reservoir is covered with a “lid” made of solid plank flooring on wooden beams, covered with waterproofing materials. Sod is laid on top. Then the branch pipe is connected to the ventilation system of the house (to the common ventilation duct) and backfilling is performed.

Calculation of the amount of work and material consumption:

1. With an air tank size of 2×3 m and a depth of 3 m, the volume of soil (earthworks and stone for filling) will be: V = 2x3x3 = 18 m³ + V_tr = 22.8 m³.
2. Volume of brickwork: V_treasure = S_walls + S_bottom x 0.125 = ((2×3) x 2 + (3×3) x 2 + 2×3) x 0.065 = 36 x 0.065 = 2.34 m³.
3. Total pipe length (10 m from the house): L = (10 + 3) + 10% = 15 m.
4. Number of knees – 6 pieces.

Name	Unit rev.	Qty	Price	Total, rub.
Solid red brick	cub. m	2,3	7000	16000
Pipes 250 mm	run. m	15	250	3750
Knee	PCS.	6	50	300
A rock	cub. m	18	1500	27000
Cement / sand / treasure. grid	–	–	–	2000
Cap	–	–	–	1000
Job:
excavation	cub. m	22.8	300	7000
tank masonry	cub. m	2,3	1000	2300
pipe laying	run. m	15	one hundred	1500
cover device	PCS.	1	1000	1000
Total material		50,000
Total work		12000
Total material and work		62000
The cost of 1 sq. m	79550/60	1000

The cost of the stone for filling the tank may vary depending on the region of construction.

As can be seen from the calculations, the final cost of air conditioning 1 m² is different for both options. The main selection factor is the level of groundwater occurrence. If it is high, less than 3 m, then it will not work to build a bunker heat exchanger. Pipe fit even with a GWL of 1.5 meters.

Installing the fans

The system presented here provides for the synchronous operation of two duct fans – supply and exhaust – installed in each air outlet of the room. This makes it possible to quickly deliver cool fresh air to the room and remove heated air. For effective ventilation, a fan power of 100 W each is sufficient. When choosing a fan, pay attention to the noise level during its operation..

Estimated operating cost

If you ventilate each room three times a day for 20 minutes, then we get 1 hour of operation of 8 0.1 kW fans. This is less than 1 kWh per day. Per month – 30 kW. At a price of 5 rubles / kW, this will be 150 rubles / month.

The service life of recuperators and ventilation ducts at home is limited by the service life of the material. For underground elements – from 50 years, for internal – unlimited.

The system does not require maintenance (except for fans – every 5 years).

Perspectives

The described scheme can become the basis for a more complex air conditioning system. Additional elements can be gradually included in it – filters, heating and cooling tents, more powerful fans, automatic control units and others. The air mixture prepared underground has a stable temperature not only in summer but also in winter, therefore it can be used for heating..