- Why ventilation control is so important
- Existing solution set
- Differences between zonal and general ventilation
- Related videos:
- Heat recovery units
- Air exchange calculation and system configuration
- Related videos:
The current trends in construction oblige to take care of the energy efficiency of buildings. High-quality insulation is almost impossible to perform without providing a high-quality thermal cutoff between the internal microclimate and the external environment, which requires the correct organization of the ventilation system.
Why ventilation control is so important
The rapid rise in the cost of energy resources requires the adoption of measures to reduce the cost of heating and air conditioning buildings. From the point of view of building technologies, these tasks are relatively easy to solve, but a number of problems arise. The fact is that at the moment no material has been invented that ideally combines bearing and thermal insulation properties. Because of this, the enclosing structures of most buildings have a multilayer structure: a load-bearing base is located inside, and an insulating shell outside..
Such an arrangement of layers is especially beneficial from the point of view of heating inertia: a more massive layer accumulates enough heat to smooth out temperature differences between active work and downtime of the heating system. However, because of this, steam that seeps through the supporting structure due to the difference in partial pressures inside and outside has a high temperature and can condense inside the insulation. Therefore, a continuous vapor barrier is arranged inside the building, forming a shell impermeable to atmospheric moisture..
On the one hand, high-quality insulation of the indoor environment from the outdoor environment helps to eliminate convection heat transfer. This is extremely important in houses with zero and positive energy balance, where the insulation of the main enclosing structures is performed at the highest level and the main heat leaks occur through glazing and gas exchange with the outdoor environment. However, on the other hand, one should not overlook the fact that only one person secretes through the lungs and skin up to 1.5 liters of water every day, and you need to add to this the moisture evaporated during cooking and wet cleaning, house plants and pets. As the relative humidity rises, the temperature of dew formation also rises, due to which condensation on the windows can fall out even if there is no frost outside.
The other side of the issue is the suitability of the room atmosphere for breathing. The normal proportion of carbon dioxide in the air is 0.025%, which corresponds to 250-300 PPM (parts per million). The concentration of 1400 PPM is considered to be the limit and dangerous for human health, however, raising the CO2 concentration to 500-600 PPM causes noticeable discomfort: painful sensations appear in the respiratory organs, and you simply cannot get enough sleep at night. By the simplest calculations, it can be established that in a normal state in a house with an internal volume of 300 m3 contains only 75 liters of carbon dioxide. That is, even one person will be able to increase concentration to an uncomfortable level within 6-8 hours, and not in a single room, but in the whole house!
Existing solution set
Regulation of the room atmosphere is carried out by means of limited air exchange with the outdoor environment. When installing a ventilation system, a compromise must be found between the effective removal of excess moisture with carbon dioxide and the saving of heated room air. For these purposes, three variants of systems can be used:
Breathers are point ventilation points installed zonally on the outer walls. These ventilation devices are electronically controlled and can operate in several modes, including heating the supply air.
Natural exhaust ventilation – one or several ducts in the central part of the building, most of which are straight booster sections without horizontal branches. Due to the natural vacuum, draft is created, due to which air is removed through the ventilation duct. Air enters the house through unsealed junctions, for example, gaps in window frames. If the house is carefully sealed, air enters through the sashes of the windows in contour ventilation mode.
Forced supply and exhaust ventilation uses air pumps to move air. The pressure difference they create allows not only distributing the supply of fresh air over the area of the house through channels, but also organizing its intake from one point. With such a device, the user knows exactly the real volume of air exchange and has full control over the operation of the system..
From the point of view of convenience and efficiency, forced-type ventilation systems are considered optimal, having an accelerating section, which allows them to work with limited performance in the absence of power supply. But for the device and the correct functioning of such systems, careful research work must be carried out, during which the air flow organization scheme is determined, as well as the economic justification, because controlled ventilation must first of all meet the energy efficiency requirements.
Differences between zonal and general ventilation
Breather and duct ventilation are comparable in functionality. Systems of both types allow you to regulate the intensity of air exchange, can operate on daily and weekly schedules, provide filtration, recirculation in order to provide forced convection, heating and heat recovery from the exhaust stream.
The most important differences between these types of systems lie in the nuances of installation and ergonomics. Breathers can be installed at any stage of construction and even after finishing work is completed. They have a hidden connection system and a fairly low noise level comparable to domestic air conditioners. At the same time, breathers belong to the category of “smart” household appliances: they can be controlled from mobile devices and combined into a common home network. This makes it possible to realize their alternating mode of operation: half of the breathers provide inflow, half of them operate in the exhaust mode, which eliminates the problem of excessive vacuum and achieves high efficiency.
With all its advantages, breather ventilation cannot be considered a panacea. Restricting installation exclusively on external walls almost always leads to the formation of blind spots, especially in large and multi-storey buildings. It is rather difficult to coordinate the operation of more than 4–5 breathers, and in the absence of an internal sealed environment, it is practically impossible. The organization of ventilation in large houses is mainly carried out according to a centralized principle: a single unit of air pumps, supply and exhaust ducts, as well as a distribution duct system.
There are few obvious advantages of a centralized system, of which the most obvious is the reduction in the cost of organizing additional points of air intake or inflow, while the placement of these points is practically not limited by anything. Another plus is the low maintenance cost and reduced energy consumption, which is especially important in the long term. However, ventilation ducts are the largest type of intra-building communications. The organization of the channel system requires a significant rise in the rough ceilings or the use of special technologies for the construction of partitions and floors. Plus, the calculation of a centralized system is more difficult to perform; errors are fraught with drafts and channel noise. Nevertheless, all these disadvantages are leveled by the main highlight of the supply and exhaust ventilation – the ability to fully recuperate the warm exhaust air..
Heat recovery units
The essence of recuperation is extremely simple: the exhaust and supply flows are passed through channels that have a common partition made of heat-conducting material with the largest possible contact area. At the same time, due to the equalization of temperatures between the two streams, the proportion of heat losses through ventilation is reduced and fresh air is heated to a comfortable temperature. To implement this principle of operation, a massive heat exchanger with channels of complex shape is required, therefore recuperation in breathers does not work as efficiently.
The use of recuperation in the northern regions of Europe has become firmly established in the practice of civil housing construction; there is no doubt about the profitability of these installations for a long time. Three types of recuperators have been developed for home use:
Heat exchangers are the simplest recuperators, which are two chambers with adjacent walls with fins like radiators. They can be easily integrated into small ventilation systems, but are not supplied with air pumps, due to which they remain a fairly budget solution.
In addition to fans and a heat exchanger, the recuperation and ventilation unit also has a control unit that allows you to monitor the operating parameters and make a fairly fine adjustment of the operating modes. Equipped with condensate removal systems and air filters, can be used as a single solution for organizing a central ventilation unit.
Recuperators with a secondary circuit – in fact, they are heat pumps, which, due to the low delta of temperatures, significantly increase the intensity of heat transfer. They allow not only to equalize the temperature between the two channels, but also to additionally heat the supply air, cooling the exhaust air more than usual. Like devices of the previous type, they represent a single turnkey solution, but they are more expensive, although they are guaranteed to pay off in regions with a cold climate..
Air exchange calculation and system configuration
Like many other components of individual construction, the organization of ventilation systems in private homes is not subject to strict government regulations. However, it is possible to rely on the norms of air exchange for apartment buildings, according to which the minimum supply of fresh air for each resident is at least 60 m3/ h at a nominal total air exchange rate in residential premises of 0.35 of their total volume per hour.
Also SNiP 41-01-2003 establishes the need to increase the intensity of the exhaust systems in non-residential premises: kitchens, bathrooms, laundries and storerooms – from 50 to 120 m3/ h depending on the purpose.
This data is often sufficient to determine the performance of a breather ventilation complex. The calculation of the central supply and exhaust system is carried out according to a more complex scheme. For example, it is necessary to ensure sufficient throughput of ventilation ducts and intake grilles in order to avoid the formation of noise, as well as to choose the right diffusers in order to maintain the normal air flow rate in each individual room. For buildings with more than two above-ground floors, it is also required to provide a fire emergency mode, in which the supply of supply air is stopped and smoke is removed from the main escape routes.
The placement of supply and air intake points in a private house is carried out according to a fairly simple scheme. A supply channel with the required throughput is introduced into each living room, while the number of inflow points is determined by the permissible dimensions and throughput of the diffusers. Indoor air intake point up to 50 m2 there may be only one, it is placed near the floor in a place diametrically opposite to the inflow. Channel branches for each room are included in a single highway running along the ceiling of the interior corridor and a common technical riser to the room where the central ventilation unit is located and it is possible to connect to external channels.
Only exhaust ducts are brought into technical rooms, this is done in order to exclude the penetration of unpleasant odors into the habitat. In general, practically all ventilation systems in private houses have excess exhaust system capacity – 20–30% higher than the intake capacity. When choosing a central unit of the ventilation system, you can start from the total area of the building: manufacturers provide for a sufficient power reserve, and the nominal performance is determined by automation based on the readings of humidity sensors, gas analyzers and a daily-weekly timer. You also need to remember that technical ventilation (clothes dryers, kitchen hoods) is organized separately from the general ventilation, although some central nodes have additional outlets for connecting technical ducts.