What is a compressor-condensing unit: device and principle of operation
Almost all ventilation systems include a compressor-condensing unit responsible for heating or cooling the air. KKB is included in the class of non-autonomous air conditioners.
In it, the refrigerant in a liquid state goes through a preparatory stage, and then enters the heat exchanger and evaporates.
In this material we will talk about the principles of operation of this equipment, dwell in detail on the nuances of its selection and some installation features.
The content of the article:
Components of the compressor-condensing unit
KKB is a monoblock with compactly placed units. They are used in tandem with fresh air ventilation devices, with split systems any type equipped with indoor units or direct cooling systems. They can replace the chiller when installing the latter is impossible due to the heavy load on the roof.
The main elements of this important part of the ventilation system are:
- compressor;
- engine;
- centrifugal or axial fan;
- a heat exchanger that acts as a condenser;
- power supply system;
- control system.
Additionally, the KKB is equipped with connectors that enhance its performance and consist of a throttle, a special filter, a solenoid valve, and a sight glass. Modern KKB models operate on ozone-safe refrigerants. They can circulate highly environmentally friendly freon R-22, R-407C, R-410a.They are suitable for both ventilation units and duct coolers.
The internal elements of the KKB are insulated and grounded to avoid injury from electric shock. Manufacturers cover the surfaces of all components of the device with an anti-corrosion coating. This allows it to be used in wet conditions.
Advantages of a compressor-condensing unit
If we compare KKB with chiller, then we can note the clear advantages of the first:
- Producing one kW of cold is cheaper because There is no intermediate coolant here.
- Convenient adjustment. Each KKB is connected to one air supply unit, so control is carried out using standard controllers.
- Easy installation. No additional fans, air ducts or other elements are needed. Only installation of the evaporator heat exchanger is required.
The KKB can be a component of a large ventilation system and a separate unit built into the device. They come in stationary floor-mounted and wall-mounted types. Stationary blocks are placed near buildings and on the roof.
The modern KKB compressor is equipped with protection against unstable operation of the electrical network, the influence of moisture, mechanical damage, and critically high and low temperatures. All this disrupts the functioning of the unit. The housing in which the block is enclosed is made of galvanized steel, so it does not corrode.
To make the device cool faster, manufacturers often supplement the heat exchanger, condenser, and lines with aluminum inserts. The heat exchanger is also protected from harmful influences - a special anti-corrosion alloy is applied to its surface.
To be able to monitor the pressure inside the CCU, all elements in contact with the coolant are equipped with inspection nipples.
Despite such advantages, it often happens that after installation the KKB quickly fails or does not start working at all. Experts point to one reason. This is an illiterate selection of the compressor-compensation unit and evaporator.
Nuances of selecting KKB
Most often, a compressor-condensing unit based on power is selected that is suitable for specific circumstances. To do this, you will have to perform a standard calculation based on the performance of the ventilation unit in mᶾ/hour, temperature, air humidity outside in the summer, and supply air temperature. This parameter plus humidity is selected for a specific region according to SNiP.
The first parameter is taken 6 degrees less than the optimal room temperature. In addition to these values, you will have to use the i-d diagram. Then all the found parameters are substituted into the formula: Qcol = 1.2xLx(Inar-Iin)/3600.
To avoid calculations altogether, sometimes a simplified method is used. It has been established that for every 10 m² and a room height of 3 m, 1 kW of cold is required.If the room area is 200 m², a 20 kW unit is required.
Experts advise paying attention to several nuances that are important for choosing the right unit. To guarantee the effective operation of the KKB, it should be calculated not at the maximum temperature of the outside air, but at the minimum provided for by the range of operation of the KKB.
If you perform the calculation based on the maximum outside air temperature, the unit will be able to operate normally when the outside temperature is equal to the calculated value or rises above this value. When its value drops, a phenomenon such as partial boiling of the refrigerant in the evaporator will be observed. Liquid freon will return to the compressor suction. This will be followed by jamming of the latter.
For normal operation, the compressor capacity must be less than the maximum evaporator capacity. The connection kit is not always sold together with the compressor-condensing unit. Sometimes you need to select it yourself, but to do this you need to know the technical features of the elements included in this harness.
Recommendations for selecting a filter drier
This unit is necessary to absorb moisture and various unnecessary impurities from the freon line. It is selected according to the manufacturers' tables, taking into account the brand of refrigerant. In addition, it is important to know in advance how this element will be installed - by soldering, flanging, on fittings. The connecting dimensions will depend on this.
It affects the choice of filter and the fluid performance indicator, which affects the interval between replacements. It is also important how the KKB will function - exclusively for cold or for heat. In the first case, the freon will move in one direction, in the second - in both directions.
How to choose a sight glass?
This element is necessary to monitor the freon filling level, the condition of the filter, and the presence of moisture in the circuit. When choosing it, they take into account the brand of freon, the ambient temperature, the method of glass installation, the presence of a humidity indicator, and the critical level of humidity.
If R407C or R410A freon circulates through the circuit, then polyester oil for these brands can form acid and alcohol when interacting with water. This will be signaled by the changed color of the sight glass, which will help prevent the compressor from jamming as a result of oil decomposition. The normal state of the refrigeration circuit is indicated by the green color of the indicator.
A shift towards a yellow tint indicates that the refrigeration circuit needs to be monitored more closely. A completely yellow indicator indicates an unacceptable amount of moisture in the circuit. After taking measures to remove it, the filter will have to be changed.
Selecting a thermostatic valve
The expansion valve regulates the flow of refrigerant from the unit to the evaporator for cooling. It is selected according to the type of refrigerant, the nominal refrigeration capacity, boiling point, subcooling, and condensation. The temperature level of the working environment is also taken into account - maximum and minimum.
It influences the choice and method of pressure equalization - internal or external. You need to know how the expansion valve will be installed. It is usually installed for soldering, flanging or fittings.
Solenoid valve selection
The choice of this element is influenced by the brand of freon, maximum operating temperature and pressure. Another important parameter is the peak value of the opening pressure difference. You should pay attention to the connecting dimensions and performance.
The Ku coefficient must be taken into account, which takes into account the change in flow rate of the working medium when the pressure difference is solenoid valve will be 1 Bar.
Types of compressor-condensing units
The type of KKB is determined by the type of its own cooling. It can be carried out using air, water, or an external cooler. Units of the first type have a built-in fan that generates air flow.
If an axial fan is included in the design, then the unit is mounted outside the building. If there is a centrifugal fan, the unit is installed directly indoors.
The compressor-condensing unit, in which the condenser is cooled with water, is more powerful. It does not require a large volume of air for its operation, therefore it is compact and intended for indoor installation. Its installation is possible over a considerable distance.
KKB with a remote-type condenser are used less frequently, mainly when there is not enough space in the room. In this case, the block itself is installed inside the room. The heat exchanger is placed outside it.
Operating principle of KKB
The operation of the compressor-condensing unit is based on the law of physics about the absorption of thermal energy when the state of the refrigerant changes from a liquid state to another aggregate form. When the process occurs in the opposite direction, previously accumulated thermal energy is released and transferred to the consumer.
When the KKB operates for cooling, freon evaporates inside the heat exchanger, then condenses. When heating, the opposite is true.
While the installation of a chiller system allows you to individually set the temperature regime for each room, when using KKB, the temperature will have the same value everywhere. It is set on the main thermostat for the entire building.
Air-cooled KKB
The refrigeration circuit has 2 heat exchangers. One of them, the condenser heat exchanger, is located in the KKB itself. The second is the evaporator heat exchanger, located in the air cooler of the central air conditioner. In addition to these components, the refrigeration circuit includes a compressor enclosed in a KKB housing.
Its elements also include a filter drier, expansion valve, and sight glass. The last three elements are located on the interblock liquid line near the evaporator.
Unlike other components of the refrigeration circuit, the cross-section for the passage of freon in the thermal expansion valve is small.Its adjustment depends on the temperature of freon evaporation in the heat exchanger and the pressure value. Before the expansion valve, the compressed gaseous freon in the condenser heat exchanger has excess pressure, pumped by the compressor. After the expansion valve, the pressure in the evaporator heat exchanger decreases.
In the condenser, the refrigerant, having lost heat to the surrounding space, condenses. After releasing part of the thermal energy, the freon is still under increased pressure, but only until it passes through the thermal expansion valve. After this, the pressure drops sharply and cooling occurs.
Under the influence of the centrifugal fan of the main air conditioner, the heat exchange surface of the evaporator heats up. It acquires a high temperature and passes into the gaseous phase, the previously liquid refrigerant circulating in the evaporator. At the same time, it absorbs heat from the supply air, thereby cooling it.
Afterwards, the refrigerant in the form of a gas again ends up in the compressor, compresses, transforms into a liquid aggregate state and the circulation process resumes.
Water cooled unit
Installation of a water-cooled KKB requires preliminary hydraulic calculations and professional installation. The cost of these blocks is higher than that of their air counterparts. This is explained by the need for additional costs for the installation of a cooling tower, laying a circuit to it, and purchasing pumps.
These units are intended for installation inside a building.Cooling of the condenser here occurs with the help of a liquid that makes a circular revolution in a closed circuit. A cooling tower is installed outdoors - wet or dry, or running water is used.
This climate control equipment has an additional heat exchanger. It cools the refrigerant and, by partially taking away the heat, heats the circulating water, which can then be reused. Its use in the heating system for hot water supply justifies somewhat larger investments in the purchase of equipment of this type.
The advantage of water-cooled units is their higher power and the possibility and prospect of increasing the distance between the unit and the cooling tower as convenient as possible. If running water is used as a coolant, the cost of air conditioning drops significantly.
Features of KKB installation
The installation of a condensing unit must be preceded by careful preparation. First of all, check the compliance of such unit data as phase connection, voltage, current frequency with the corresponding characteristics of the power supply line.
There should be no dust in the place where the KKB is planned to be installed, otherwise it may get into the heat exchanger. The air flow leaving the condenser should not be returned to it.
If the unit is installed on the ground, it must be positioned so that rainwater and snow do not enter it. The space around the unit must be free, without obstructions for air movement and maintenance. Do not connect air ducts supplying or removing air from the unit.
The assembly and installation of compressor and condensing units is carried out by specialized companies whose employees have the appropriate qualifications and certificates. To connect the unit you need to have special tools and equipment. It also happens that the unit has to be refueled or completely refueled.
Reputable manufacturers of KKB
KKB with high performance characteristics is produced by the Italian company Aermec. The range includes professional air-cooled compressor and condenser units and equipment for home use.
KKB Aerotek, produced by the international company of the same name, founded in Switzerland, are popular. The equipment parameters are completely tailored to the Russian consumer.
The French company Airwell is famous for the quality of its equipment. No less popular are Carrier units, supplied to the air conditioning equipment market by the American Carrier Corporation. The company Daikin from Japan has its representative office, whose climate control equipment is also in great demand.
Conclusions and useful video on the topic
Components of the compressor-condensing unit:
Reasonable choice of compressor-condensing unit:
To ensure excellent ventilation in an office, home or other premises, a compressor-condensing unit will be the best solution. The unit itself is light in weight and dimensions, but this in no way reduces its functionality. It is important not to violate the operating rules and follow the instructions, then the unit will serve for many years.
If you have questions about the topic of the article, you can ask them in the comments section, and we will try to give them a very clear answer. There you can leave a comment on this article or share advice on choosing a KKB.
