Layout construction of installations
Panel construction of air conditioners
Outdoor air conditioners
Main technological sections of air handling units:
Air heaters (air coolers)
Heat and mass transfer apparatus
In the last decade, a lot of new equipment has appeared on the heating and ventilation equipment market, the use of which in the practice of design and construction requires generalization and analysis. In this work, the task is to acquaint specialists involved in the design and operation of fan installations and air conditioning systems, on the basis of systematization and generalization, with the trends in the development of ventilation technology. Without claiming to be an exhaustive presentation of the material on this topic, the author hopes that the material presented in the article will be useful and will facilitate the work of specialists. In this review, due to its limited volume, only information is given regarding the equipment of ventilation and air conditioning systems: air conditioners, supply chambers, air heaters, heat exchangers, fans, etc.
The main equipment for the systems is the equipment of supply, exhaust, air handling units and central air conditioners. This is due to the versatility of the equipment that can be used in most industries and premises, their high performance in terms of air, heat, cold, efficiency and low specific energy consumption.
The global trend in air conditioning equipment production is in line with the general trend towards complete installations in order to move the main production operations to factories and minimize the cost of installation and assembly of equipment on site. The units are delivered to the customer in the form of separate sections, assembled according to one scheme or another during installation at the installation site. Such a desire is economically justified.
Let us note one more trend: the transition in Russia to a new economic system leads to an increase in the power supply, an increase in the utilization rate of equipment, obtaining as many products as possible from a unit area of industrial premises, etc. This predetermines an increase in thermal loads. And if earlier many workshops managed with ventilation means, now air conditioning systems are needed.
The air conditioning industry is characterized by a high level of production specialization, the use of materials with high mechanical, thermal and other indicators, the use of efficient components and devices, etc.
The analysis shows that the main direction is the individual design and manufacture of installations. Particular attention is paid to the efficiency of installations, since their implementation and operation require significant costs. At the same time, it turns out to be advisable to provide a certain margin for the capacity of the installed equipment. Changes in technology, intensification of production require design flexibility so that capacity can be increased during operation at the lowest cost. These activities ultimately pay off in the long run.
Designing the most economical systems is possible only with a thorough feasibility study of projects, comparing the cost of their options and taking into account local conditions. This, in turn, requires a clear understanding of the capabilities, cost of equipment and its operation, as well as the economic efficiency of the systems.
Technical and economic calculations show that with an increase in the volume of air moving through the ducts, its optimal (economical) speed should fall. When switching to economical speeds, the sections of the main air ducts of large ventilation units become commensurate with the section of the unit itself. Naturally, ducting and air distribution become a major design problem that does not take into account the optimization of the speed in the ducts, which in turn leads to energy overruns.
It can be noted that there is a downward trend in the unit capacity of ventilation units and central air conditioners. Many companies produce the main size range of units with an air capacity of up to 100-120 thousand m3/h, while, as a rule, it is indicated that units with a higher air capacity can be delivered by special order. As a performance series, a sequence of numbers is taken
[аj-1 + (i-1)·dh1].
The decrease in the overall air throughput of ventilation and air conditioning systems goes in several directions.
1. Introduction in a number of countries of energy consumption standards for buildings. Such standards are established in England, Sweden, the USA, Finland, etc. Naturally, in order to meet the strict standard, the designer needs to implement the whole range of measures to reduce air exchanges, and at the same time energy costs for installations.
The introduction of an energy consumption standard for buildings for various purposes and engineering equipment has a significant economic effect.
2. In a number of countries, thermal protection standards for buildings for various purposes with high heat transfer resistance for external enclosing structures have been adopted.
Increasing the thermal insulation properties of buildings (especially those with air conditioning) also leads to a decrease in air capacity and energy consumption of installations.
3. Increased attention to the issues of recirculation of air removed from the premises. This is most simply carried out for exhaust systems, where there is no air pollution by gases and vapors of harmful substances. For example, during the mechanical processing of metal, woodworking, etc., air is cleaned from solid particles, after which it is returned to the room. High-efficiency filters are produced for air purification during welding, soldering and other similar processes.
Companies that produce such equipment advertise them as heat recovery units with 100% efficiency, since all the air is returned in a purified form to the working room, while the heating load and air capacity of ventilation units are reduced.
Traditional schemes and systems, calculated on the basis of the gross inflow of harmful substances into the entire volume of the room and for the air exchange of the entire volume of the room, become uneconomical due to significant capital investments and operating costs.
4. Almost complete coverage of all technological devices with harmful emissions by local exhaust ventilation systems, with the supply of supply, often conditioned air to work stations. This is especially true for flexible automated industries in mechanical engineering, instrumentation, electronic industries, etc. In combination with exhaust air regeneration devices, heat recovery units and other air conditioning systems, they approach waste-free technology installations.
Layout construction of installations
An analysis of the air conditioning industry shows that over the past 20-30 years, the layout of central installations has not undergone major changes. The basis of the production of most companies is sectional, block-sectional and block installations according to the following layouts:
direct-flow — with one- and two-stage heating; with a surface and (or) contact heat and mass transfer device; with a dry air filter made of bulk filter materials; with a heat recovery unit (Fig. 1);
recirculation (in addition to direct-flow layouts) — with mixing chambers; with a second fan unit;
It is possible to separate the supply and exhaust units into a separate layout scheme (Fig. 2), combining the supply and exhaust units and the heat recovery device in a single unit (recuperative plate air-to-air heat exchanger; regenerative rotating rotary heat exchanger; heat exchangers based on heat pipes).
For air conditioners and supply ventilation units, as a rule, service chambers, viewing, transitional and similar sections are not used. The main technological sections adjoin directly to each other. For repair work, opening sealed doors or removable panels are provided, and in the lower part of the section there are guides for rolling out elements from the section. Such a layout solution reduces the overall length of the installation (sometimes by several meters).
Refusal from the service chambers and the introduction of layouts of reduced length are possible only with the transition to the panel design of air conditioners.
At the same time, monoblock air handling units and air handling units are widely produced (as a rule, with a small capacity — up to 10 thousand m3/h), combining all the equipment in a single unit; at the same time, the elements of the automation system are placed in the installation case and the internal installation of cables is performed (Fig. 3).
Rice. 3. Monoblock air handling unit
Panel construction of air conditioners
In recent years, panel construction has become predominant in foreign and domestic air conditioning.
The principle of building air conditioners panel design is as follows.
On the base (as a rule, a frame made of profiled rolled steel), an air conditioner frame is installed in the form of a U-shape with modules for placing technological sections (Fig. 4). All load-bearing elements of the frame are formed from special aluminum or steel profiles. Panels (thickness 20-60 mm) are multi-layered (at least three-layered) plates. Galvanized steel 0.6-0.7 mm thick, unpainted or coated, is used as the facing layers of the panel. The inner space of the panel is filled with a material with high heat and sound insulation properties (Fig. 5).
The panels are very light. The panels are fastened in the frame in different ways, mainly with the help of special profiles, the joints between the panels are sealed with an elastic sealant.
Manufacturers use panels of various design sizes, which is associated with the unification of the parametric range of air conditioners within the company.
The transition to panel structures of air conditioners allows to reduce the labor intensity of assembly operations during installation and dismantling. In addition, the panel design significantly improves the aesthetic appearance of the air conditioner.
Rice. 4. Layout of panel air conditioners
Rice. 5. Structural elements of panel air conditioners
Outdoor air conditioners
It should be noted that in recent years the production of outdoor units has increased. This is due to the significant cost of production space, including those occupied by ventilation and air conditioning systems. This situation predetermined the main directions of work in this area.
1. Reducing the overall length of the air conditioner layout and the dimensions of all related equipment (pumping and storage facilities, refrigeration, etc.) in the overall reduction in the area of the machine room for ventilation equipment.
2. Complete removal of the air conditioner installation outside the building. For foreign construction with private land ownership and high cost of land, the removal of the air conditioner from the premises is carried out only on the roof of the building (“roof-top”), while the basements and technical floors are equated by foreign experts with production areas.
The air conditioners are delivered fully factory-ready, i.e. in a frame with panel fencing (Fig. 6). The base is supplied separately and ordered according to the roof pitch. Air conditioners are placed in a panel frame made of 1 mm thick steel sheet with a multilayer water-repellent coating. A heat-insulating layer (60-70 mm) is placed between two steel sheets. The entrance to the layout is through a watertight door. Joints between panels are sealed with sealant.
Air conditioners are run-in and pre-configured at the factory stands according to the parameters specified by the project. The connection of air conditioners to the heat-cooling mains, power supply, sewerage, etc., is carried out in the lower part of the frame.
Rice. 6. Installing the rooftop unit
Here is a brief description of the main technological sections of air handling units.
Air valves. For most air conditioners, valves with parallel and counter-movement of the flaps are accepted.
mixing chambers. All companies produce mixing chambers according to the scheme with free mixing of two streams. It should be noted that this design of the mixing chambers does not exclude temperature stratification that occurs when mixing two streams with different temperatures.
Air filters. Air filters are an essential element of any air handling unit. In an air handling unit or air conditioner arrangement, air filters perform a dual function: cleaning the treated air from dust and protecting the rest of the process sections from dust. The main emphasis is on the use of only dry filters, usually pocket filters. The use of such filters for air conditioners reduces their aerodynamic resistance, increases dust capacity and increases the service life of the filter until the required replacement (these filters are not subject to regeneration).
Unfortunately, self-cleaning oil filters are practically not used in the designs of air handling units and air conditioners, which have proven themselves well in cleaning air with a lot of dust.
Heat recovery units. Using the heat of the indoor (exhaust) air of the room along with recirculation and mechanical cleaning
is one of the main companies in energy saving programs and. Recuperative plate air-to-air and regenerative rotating rotary heat exchangers, heat exchangers based on heat pipes are used.
Air heaters (air coolers). Let us note the main directions of work in the field of surface heat transfer.
1. The use of new intensified surfaces, which, due to the successful combination of the design parameters of the fins and tubes, the length of the heat-releasing channel, etc. provide the maximum heat transfer coefficient with minimum energy costs for the movement of air and water.
2. Application for mass production of heat exchangers of highly efficient structural materials, primarily non-ferrous metals. The combination of “copper tube + aluminum plate” makes it possible to manufacture compact heat exchangers with high thermal and aerodynamic characteristics.
3. Reducing the thickness of the metal used for the manufacture of heat exchangers (for example, a tape of 0.1-0.2 mm is used for plates).
4. Wide application of refrigeration scheme with direct expansion air cooler. In this case, the evaporator of the refrigeration unit is built into the design of the supply unit or air conditioner.
Heat and mass transfer devices. The use of nozzle-type irrigation chambers has significantly decreased. This is due to their bulkiness, energy consumption and unreliability. The works carried out in this direction abroad have not found wide application, and the previously advertised high-pressure nozzles do not appear now in the main nomenclatures of firms. The main reason for this is the low operational reliability.
Humidifiers with irrigated nozzles (honeycomb) are mainly used, specially adapted for inclusion in the installations. Such humidifiers are used only for adiabatic air humidification with three nominal values of the adiabatic efficiency coefficient: 0.65, 0.85 and 0.95. The units are characterized by low power consumption compared to spray irrigation chambers.
Sections with rotating disk and pneumatic humidifiers appeared in the designs of central air conditioners.
Steam humidifiers are rarely used to humidify the air. The main reason for this is the high cost of electricity and, consequently, significant operating costs.
We note the need for further research in the field of application of irrigation chambers. It seems promising for the introduction of the principle of quantitative change in the water supply depending on the change in the parameters of the treated air, especially in combination with the quantitative regulation of the air-conditioning capacity (or the irrigation chamber during bypassing). At the same time: the heat consumption for the second heating can be reduced and the energy consumption of the air conditioner pump and fan can be reduced (for some modes). The transition to automatic control according to the “optimal modes” method can be considered a complete solution to the problem of optimizing the energy consumption of an air conditioner. In this case, the operation of the irrigation chamber, its pumping unit, bypass, etc., is considered together with the operation of the other sections, the climatological state of the outside air at the moment, the parameters of the conditioning object, and the static and dynamic characteristics of the regulated objects.
Fan units. Almost all companies have ceased to allocate separately fans for air conditioners and ventilation systems. Previously, such a division was explained by economic reasons (i.e. the cost of an air conditioner fan was much higher than the cost of a conventional fan), the number of hours of use, the specifics of the purpose, etc. various devices and machines.
Consider several areas of work to improve fans.
1. The range of equipment for ventilation and air conditioning systems is thousands of units; almost any air parameters required by the customer are provided, depending on the purpose of the systems and their operating conditions. The standard sizes of fans for application in installations, as a rule, correspond to the standardized series R20.
2. The variety of types of electric motors used, taking into account the peculiarities of the operation of fans in the network and the widespread use of quantitative regulation. Basically, squirrel-cage three-phase electric motors are used to drive fans. However, along with electric motors of the basic design, separate modifications of these motors are also installed: multi-speed, with a phase rotor, with increased slip, etc.
3. Firms are moving away from traditional spiral case fan designs and developing new aerodynamic case designs. Radial fans without casing are widely used (Fig. 7), allowing to reduce the length of the installation.
4. A feature of some fans is the placement of the electric motor inside the fan impeller (outer rotor motor). The fan in this case is compact, the engine is cooled by air flow (Fig. 8).
Rice. 7. Radial fan without shroud built into a panel air conditioner
Rice. 8. External rotor motor fan integrated in panel air conditioner
1. The analysis shows that the central installations of ventilation and air conditioning systems occupy the main place in the global and domestic air conditioning industry. In recent years, equipment manufacturers have limited the range of central units with an air capacity of 100-120 thousand m3/h This is due to economic factors, primarily the reduction of energy costs.
2. There is a trend towards a reduction in the terms of renewal of manufactured equipment for ventilation and air conditioning systems. Air conditioners are created with specific requirements for specific conditions of use: in the northern version, with blocks for chemical air purification, explosion-proof version, etc.
3. Most central air conditioners do not have service chambers, and therefore occupy a smaller area; At the same time, air conditioners have a panel structure with heat and sound insulating panels. Foreign air conditioning industry pays more and more attention to the production of outdoor air conditioners.
4. The main application for air purification from dust is dry pocket filters.
5. Surface heat exchangers made of non-ferrous metals are used in air handling units of ventilation systems and central air conditioners, as a rule, copper tube + aluminum plate.
6. In the configurations of central air conditioners, for efficient heat and mass transfer, spray chambers and packed humidifiers are used.
7. Changes in production technology for the main industries and an increase in the volume of reconstruction determine the need for the use of “modular installations” that serve a specific building module — a floor cell or a workshop volume, with their placement outside the building (on the roof) or outside the technological areas (on columns, in inter-farm space, etc.).
8. The general trend in the development of global and domestic air conditioning is the saving of energy and material resources while achieving and maintaining the required microclimate in the serviced object.