Air handling units with heat recovery for a private house

The issue of increasing energy efficiency is necessarily considered when designing and overhauling private residential buildings. An air handling unit in a ventilation system is one of the most effective solutions to save on energy costs.

Types of ventilation systems

Household recuperator for ventilation

Air change in residential and utility rooms, in the kitchen and in the bathroom is a prerequisite for maintaining a healthy microclimate.

Ventilation is natural and forced.

In the first case, streams of clean air come from outside and are removed into the atmosphere due to physical processes of thrust in a high pipe.

In winter, cold air enters the house through windows, doors, supply ducts, and leaves the premises heated to room temperature - thus up to 15% of the energy is wasted on heating the street.

Forced systems use fans installed in the air supply or exhaust ducts to circulate flows.

In the supply and exhaust ventilation, both processes are forced.

The principle of operation of systems with recuperation

The principle of ventilation with a recuperator

Ventilation with recuperation works according to a simple scheme:

  1. In a place convenient for installation and maintenance, a recuperator is installed - a heat exchanger, to which the inlet and outlet ventilation ducts are connected.
  2. Warm room air from the room heats up the cold air coming from the outside.
  3. Heated clean air masses are blown into the house.
  4. Then the process is repeated.

It has been experimentally verified that at a temperature of the exhaust air of 23 ° C and the air entering from the outside -20 ° C, in the best samples of recuperators, the incoming flows are heated up to 18 ° C. In this way, energy savings are achieved.

Cold and polluted air in the recuperator does not mix - clean air from the street enters the building.

To increase the efficiency in different operating conditions, a wide variety of recuperator models have been developed.

Design features

High power industrial recuperator

Heat exchangers are classified according to various criteria:

  • technical characteristics;
  • method of placement;
  • body material and internal elements;
  • the principle of action;
  • design of working elements;
  • the physical medium used for heat transfer;
  • automation and control scheme.

The choice is made after a thorough analysis of all the features.

Place of installation of equipment

Floor-standing ventilation unit with heat recovery

When choosing the installation site for the main unit of the recuperator, take into account where the fans or pumps are installed. The noise generated by the device can be very disturbing.

They do not install recuperators above bedrooms and nurseries.

According to the method of installation, floor and pendant devices are distinguished, the choice is influenced by the surface. If there are no solid main walls, it is better to choose a model that is installed on the floor.

Suspended devices can be hidden behind false ceilings, but such solutions are suitable for industrial buildings. The vibration generated by the fan and the housing is transmitted and amplified by the building structure.

The heat exchanger body can be horizontal or vertical. This does not affect the technical characteristics, but it allows you to choose a model for convenient connection of air ducts. The fewer corners and turns, the less noise from air currents and less energy is spent on moving air masses by fans.

Typical construction schemes

Chamber recuperator

All recuperators are conventionally divided into models of direct heat transfer and devices with an intermediate heat carrier.

The first class includes heat exchangers:

  • chamber;
  • rotary;
  • lamellar cross-flow and counter-flow;
  • tubular.

Devices with an intermediate heat carrier use freon or water-glycol liquid.

Chamber

The device consists of two isolated chambers. The flows are automatically controlled by a movable flap.

At the first stage, warm air is directed into chamber No. 1, while the walls are heated. After a certain time automatically, the damper changes the air flow - the street damper is directed to the heated chamber and heats up there, and the room damper at this time to the chamber No. 2.

The process repeats cyclically as the compartments warm up and cool down. The efficiency of the devices does not exceed 50 - 60%.

Rotary

Rotary recuperator

The heat exchanger in the air handling unit with a rotary recuperator is the plates attached to the wheel. The shaft rotates slowly in the drum, the axis coincides with the air flows. The drum is divided into two parts, on one of which the apartment air moves, on the other street air. The impeller of the wheel, moving in the first segment, heats up. Further, by means of rotation, the heated blades move to another part of the drum, where they give off heat to the street air.

The control equipment allows you to turn off the heating mode in the warm season. Installation efficiency is about 80%.

The disadvantage of the model is the technical impossibility of completely separating the flows - about 5% of the air masses are mixed. The peculiarity does not allow the use of devices of this type in rooms where SNiP have established maximum permissible values ​​of contamination.

Lamellar

Plate recuperator

Models are produced in two types: counterflow and crossflow, the name depends on the direction of air movement.

Aluminum plates accumulate and release heat, from which narrow guide channels are formed.

The manufacturing scheme makes it possible to achieve mixing of air masses at a level of about 0.1%, which serves as a basis for considering the device as sealed.

The efficiency of counter-flow recuperators directly depends on the geometric dimensions. Bulky equipment has a high cost and is rarely used for private houses.

In cross-flow heat exchangers, air flows cross the device perpendicularly.

Cross-counterflow recuperators are the most efficient with small dimensions. A large number of components reduces the mechanical strength, therefore, such units are used only with small pressure drops.

Tubular

Tubular recuperator

Structurally made of one large-diameter pipe, inside which there are many pipes of a smaller cross-section.

Warm streams passing through thin tubes heats them up. A stream of street air heats up from the walls, which is fed into the house by means of a blower fan.

Ventilation with freon recuperator

Freon recuperators belong to the class of devices with an intermediate heat carrier.

The work is based on two physical principles:

  • a change in the state of aggregation of freon during heating-cooling cycles - the coolant, cooling down, turns into a liquid state and turns into a gas fraction when heated;
  • the property of a gas to be higher than a liquid due to a different specific gravity.

The design is a set of annular tubes filled with freon refrigerant.

The pipes pass through the ducts of the ventilation unit, and the exhaust duct must always be lower than the supply duct. Warm air heats the lower part of the tubes, freon boils and rises into the upper cavity through which cold street air passes. In the upper chamber, the freon in the tube gives off heat, while it cools itself, passes into the liquid fraction and goes down through the tube.

Freon system advantages:

  • lack of compressors for pumping coolant, which means high reliability of the device;
  • complete absence of mixing of clean and polluted air, which is achieved by sealing the transition points of the tubes through the walls of the chambers.

Duct recuperator with intermediate heat carrier

Recuperator with intermediate heat carrier

The device consists of two heat exchangers that can be spread over long distances.

The equipment is suitable for the reconstruction of ventilation systems, the design of which was not originally designed for the possibility of heat exchange.

Work algorithm:

  1. The air in the exhaust duct passes through a heat exchanger consisting of tubes through which an ethylene glycol liquid circulates.
  2. The coolant is pumped by means of a circulation pump into the same radiator installed in the supply duct.
  3. The fluid transfers heat to the supply air passing through the radiator grill.
  4. The pumping process takes place continuously.

To regulate the degree of heat transfer, valves are installed between the transporting tubes. In principle, this is similar to the scheme for regulating the heat transfer of heating radiators.

With any design of recuperators, condensate forms in the device. To remove it, a collection container and a path for further disposal outside the house or into the sewage system must be provided.

The main elements of ventilation systems

Recuperator in the ventilation system

Ventilation with heat recovery in a private house does not only consist of a heat exchanger unit.

The system includes:

  • protective grilles;
  • air ducts;
  • valves;
  • fans;
  • filters.
  • automation and control bodies.

The grilles prevent large objects, birds and rodents from accidentally entering the system, which can cause accidents. This option is possible when a foreign object falls on the fan impeller. The consequence may be:

  • deformed blades and increased vibration (noise);
  • jamming of the fan rotor and combustion of the motor windings;
  • unpleasant odor from dead and decaying animals.

The total cross-section of the grille openings should not be significantly less than the cross-section of the air ducts, this leads to a decrease in the performance of the entire system.

Air ducts and fittings (bends, tees, adapters) are bought at the same time, they are trying to purchase products from one manufacturer. The difference in size leads to gaps in the joints, disruption of flow and turbulence.

In severe frost, you can temporarily shut off the supply valve

Corrugated air ducts are not used for ventilation with a recuperator, which create resistance to air flows and increased noise during operation.

Air valves are needed to temporarily change the parameters of air movement, for example, they can be used to close the inlet channel during a particularly frosty period of time, when the recuperator cannot cope with heating the air to the required temperature.

Filters are installed in all models of ventilation with recuperation. They protect the equipment from street dust and tree fluff, which quickly clog the heat exchangers.

The fans can be built into the recuperator unit or installed in ducts. When calculating, the required power of the device must be determined.

You cannot save on buying fans - cheap, low-quality products are not designed for long-term operation.As the fans wear out, they make noise, lead to vibrations of the ventilation components, which causes discomfort when being in rooms.

Microclimate regulation

Automatic control panel for ventilation with recuperator

The recuperator is an integral part of the overall supply and exhaust ventilation system. The system operation cannot be configured once and not changed during the entire period of operation.

The modes are changed depending on the season, air temperature and wind strength, the desired climate parameters in the rooms.

The control systems include:

  • Temperature, humidity, smoke detectors installed in rooms and inside the equipment. By commands from sensors, fans and other control equipment are turned on or off.
  • Actuators and their drives that control the operation of valves, dampers, gate valves.
  • Devices for controlling the operation of fans, pumps, rotational speed of rotor plates.
  • Controllers of control devices that analyze the situation in the house, voltage regulators for stable and accurate operation of the equipment.
  • Backup power units in case of power outages.

Main functions of control systems:

  • supply air temperature control, taking into account microclimate parameters, external conditions, sensor readings;
  • monitoring and changing the temperature intensity of the flows before and after the heat exchanger;
  • air quality management, including CO2 content;
  • protection against freezing of the recuperator;
  • fan control;
  • switching off the supply ventilation in the event of a fire and switching on the smoke exhaust system;
  • monitoring the status and issuing information about the status of filters.

Control panels are created individually, taking into account the operating conditions, the size of the building and the requirements of the property owners.

Selection rules

The equipment must meet the requirements for air exchange in a particular room

The main criterion when choosing a plant is its performance. It is very difficult to make calculations on your own, so it is better to contact specialists.

Parameters that are important when choosing:

  • Coefficient of efficiency, which indicates how the temperature of the streams is redistributed, rather than heat savings. Real numbers are approaching 65-80%. Claims about 90% and higher are no more than marketing ploys. About 15% of heat is lost through ventilation, so the figures about 50% energy savings cannot be true.
  • Case material and thickness - Thin metal devices are subject to vibration and increased noise.
  • Reliable information about the fan performance, it should be selected with a margin of about 20%. At the maximum power indicated in the passports, the fan stops creating the pressure required for air circulation.
  • Composition and characteristics of automation systems, period of serviceability in case of power outage.
  • Additional automation capabilities for controlling an air conditioner, an air humidifier, an electric heater (if necessary).

A ventilation unit with a recuperator, correctly selected and configured, will reduce energy bills by 10-15%. There is no point in expecting more savings. At the same time, the comfort in a private house or apartment will noticeably increase. Components from well-known companies work for a long time and trouble-free with the correct calculation and adherence to the installation rules.

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