Description:
Rooftop ventilation and heating units are autonomous units, the manufacture and assembly of which, including electrics and automation, are carried out by the manufacturer. Such units are transported and delivered as a single unit, ready for installation and commissioning. Since their inception, such systems have been intended to carry out the basic functions of ventilation with the possibility of complete or partial processing of supply air: heating, cooling, humidification, dehumidification, cleaning.
Rooftop ventilation and heating units are autonomous units, the manufacture and assembly of which, including electrics and automation, are carried out by the manufacturer. Such units are transported and delivered as a single unit, ready for installation and commissioning. Since their inception, such systems have been intended to carry out the basic functions of ventilation with the possibility of complete or partial processing of supply air: heating, cooling, humidification, dehumidification, cleaning.
The manufacturing technology of roof ventilation and heating units is constantly evolving in last years has reached a level where, in terms of methods of application, they fully meet today’s most complex and varied requirements. Accordingly, the scope of their application has expanded significantly.
The development of technology has contributed to a significant expansion of the range of functions performed. Today, their number includes those that just a few years ago were considered the exclusive prerogative of so-called “applied” installations, assembled directly on site according to individual projects.
In addition to the functions listed above, modern roof ventilation and heating systems, at least most high-performance systems, can include almost any equipment. For example, drying systems with a rotary heat exchanger, heating systems with natural gas equipped with a burner or heating boiler and battery hot water, heat exchangers for free cooling of outside air, units for mixing outside air with recirculated air and many others. As a rule, modifications with heat pumps are installed next to models that provide only cooling.
To the same extent, the range of methods for regulating the operation of these units has expanded. Now the installation can be controlled via the interface " Automatic systems life support of buildings and structures" (Building Automation) or from remote control centers via a telephone line via a modem.
All these functions, at least for medium and high power installations, can be selected and ordered by the customer or designer using the "mix and match" principle. a certain number components) in order to assemble an installation that meets the requirements of a specific project. The cooling capacity of rooftop units available today ranges from 5 to 600 kW per unit. Low-power systems are in greatest demand, since the user prefers that not one, but several systems be installed at the site. Most often, this is done for the purpose of rationally dividing the facility into service areas and for the purpose of ensuring reliability, in order to avoid the risk of complete shutdown of the facility’s ventilation and heating system in the event of a breakdown or accident.
If previously manufacturers offered quite a lot of rooftop ventilation and heating units with a wide coverage radius, now this offer has narrowed noticeably. Most of the units offered are of the zonal type. This has been facilitated by the introduction of variable air volume (VAV) systems and, more recently, variable air flow and temperature (VVT) systems, which allow zone-type units to cover all service areas of a facility.
In systems with adjustable air flow, supply fans can be equipped with motors with adjustable power or, even simpler, with air intake dampers that maintain air flow at a given level.
Most rooftop ventilation and heating units are equipped with sealed vapor compression cooling circuits. Until now, R22 is most often used as a refrigerant, although HFC compounds are also sometimes used.
The system provides priority cooling of the condenser over air.
Most wide application found alternative types of cooling capacitors, hermetic and semi-hermetic. Recently, capacitors with spiral fins (scroll) have become increasingly widespread.
One or more cooling circuits
The number of cooling circuits on the basis of which the ventilation and heating unit is built is determined by the indicator of the delivered cooling power and, therefore, the size of the installation itself. Most often, systems with one or two hermetic compressors are used to provide low capacities and with semi-hermetic compressors for large ones.
The design diagram of a rooftop ventilation and heating installation of medium-high power is shown in Fig. 1. The figure shows that the condenser drive unit is located at the end of the installation, while the evaporator unit, including the supply fan, is located on the opposite side. A mixer, an outside air intake unit, a heat exchanger and a restart fan are installed between them.
In Fig. 2 is presented in section real installation having the described characteristics. It is equipped with two sealed condensers and the same number of cooling circuits. The system is equipped with a gas air heater to ensure air heating. There is also exhaust fan, allowing you to remove up to 100% of the air flow.
Of course, the system configuration may vary depending on the cooling capacity and design features object, as shown in Fig. 3.
This unit is still sold on the market. This unit is of medium-low power, equipped with a gas air heater and only one compressor (scroll), and has one cooling circuit.
Almost always, when an installation has two cooling circuits, evaporators with two separate sections are used.
Sections can be divided vertically or installed face to face in order to cover the entire heat transfer surface in any case. As an alternative to this solution, sometimes the pipes of both circuits are arranged so that they cover the entire surface not only in height, but also in depth.
In essence, the choice of solution determines whether the system will be able to control the level of relative humidity even at partial load.
The cooling power of the system, which usually includes hermetic compressors (scroll), is controlled by stopping and starting the compressors at the command of a thermostat installed in the room being served.
But semi-hermetic compressors allow you to change power by turning off part of the cylinders. Another measure used, in particular, to ensure permanent job with low loads - heated gas bypass.
The combination of power control and compressor stopping allows the required thermal load in normal operating mode.
Need to take into account climatic conditions, when it is necessary to maintain a low level of relative humidity in the premises served (about 40%) - for example, in crowded restaurants or supermarket departments lined with refrigerated counters - the development of new technologies, which are based on the use of chemical adsorbents, liquid or solid (in particular , RCI mentioned above).
In addition, cooling loop technologies for mass-produced units have also been developed to make direct expansion systems energy competitive at low relative humidity levels. Cooling circuit in fig. 4 represents one of modern solutions organization of the system.
As can be seen in the figure, a coolant heat exchanger is installed under the evaporator at the outlet of the condenser. Cold air leaving the evaporator cools the liquid, which enters the evaporator in a form that is more suitable for removing the “latent” heat load. The cold treatment unit is switched on and off via a solenoid valve in the coolant circuit. The valve is controlled by a hygrostat installed in the room being served.
In this way, dehumidification is switched on at full power only when it is really necessary. With this configuration, according to the manufacturers, the installation can provide a relative humidity level of up to 40% and remain quite attractive in terms of energy consumption compared to other systems traditionally used for this purpose, in particular, heating pipes.
On the characteristics of roof ventilation and heating units, as well as all other units with air cooled, mounted on the roof of a building, are influenced by special conditions that form just at the roof level on hot days. On a black tar-coated roof, layers of still air can form that have a temperature 10 o C or more higher than the outside air temperature. As a result, on hot days, the operating efficiency of the units may drop by 10% compared to the rated values. In some cases, the system may stall or fail to start due to the high pressure switch tripping.
It should be taken into account that, taking into account the operating characteristics of air-cooled machines, the condensing temperature, as a rule, is 14 - 16 o C above the outside dry bulb temperature. At an air temperature of 32 0C, overheating of the lower layers, due to the effect of a dark roof, can reach 42 o C. Consequently, the condensation temperature of the unit will jump to 56 Є 58 o C, and in this mode few installations will be able to function.
For the same reasons, if units are equipped with electronic fan speed control units, such units must be equipped with an appropriate cooling system, since they are usually not designed for hard temperature regime roof systems.
Some measures taken during the phase construction work, can minimize the manifestations of this phenomenon. To cover roof areas in the area where roof units are installed, materials of light reflective colors should be used.
There are a variety of configurations of rooftop ventilation and heating units. The variety is determined by application conditions and special requirements for the power of units. Constructive choice in each individual case is determined by the specific life support requirements of buildings and structures.
High-power units are completely assembled at the manufacturing plant, where they are tested and pre-sold. They are then disassembled into individual units and delivered to the site.
The system shown in Fig. 5, was specially manufactured to ensure that 100% of the outside air is treated. In its composition - refrigeration machine air-cooled and the actual air treatment unit, equipped with filters, heat exchangers and a fan. Both units are mounted on the same platform. The installation provides control over the level of humidity in the serviced room and extraction of heat from the exhaust air. The production of installations with cooling power from 700 to 2000 kW (this may seem incredible, but in America there is one manufacturer of systems with such power) takes on completely different scales, as can be seen in Fig. 6.
In fact, these are several machine rooms under one roof that need to be installed on site. Screw compressors are used for installations of this size. Fan blades typically have a wing profile, which reduces noise levels.
They try to equip such installations as much as possible a large number building life support systems, such as air conditioning, ventilation, heating and hot water supply. Most often, such installations provide access and a certain inner space service personnel.
Typically, rooftop installations are protected on top by galvanized steel sheets coated with epoxy, which are insensitive to UV rays. Some manufacturers use peralluman for these purposes.
From the inside the system is equipped thermal insulation mats usually 25 to 50 mm thick in areas around the evaporator and supply fan to combat condensation and heat exchange with the external environment.
Some manufacturers offer such installations, where all the outer walls are made of two panels, between which thermal insulation material is laid. In these cases, the thickness of the panels also ranges from 25 to 50 mm.
Installations with double walls, although more expensive than conventional systems, more fully meet modern requirements for the hygiene of the processed air. In fact thermal insulation material on inside often saturated with moisture and dust and, therefore, creates an environment favorable for the growth of mold and mildew.
For all types of installations, tightness against air, precipitation and melt water must be ensured, since due to the peculiarities of their location and their rectangular shapes V winter period Significant amounts of snow accumulate on rooftop installations.
Finally, one should keep in mind the aggressive nature of the impact of atmospheric reagents on the materials used in the manufacture of units, especially taking into account the general pollution of the atmosphere.
On standard installations, access panels are secured with screws; on improved models, quick-release elements are used. In other cases, the panels are mounted on hinges and open easily, forming convenient entrance doors.
In installations of medium-low power, air supply and extraction from them is carried out, as a rule, in the horizontal direction. For systems of higher power, you can most often choose the direction of air supply yourself - horizontally or vertically down. In the latter case, the neck of the air ducts is covered by the dimensions of the system and passes through the frame of the installation.
Heat exchangers are typically made of copper (piping) and aluminum (fins). Taking into account the general pollution of the atmosphere, heat exchangers are often painted with special protective compounds based on phenolic or epoxy resins. For operation in coastal regions, all-copper batteries are recommended.
Rooftop ventilation and heating units of medium and medium-high power are mounted on a special platform. In the case when air intake and supply are carried out in a vertical direction, the air duct channels do not extend beyond the perimeter of the platform (Fig. 7).
The role of the platform is extremely important. In addition to forming a supporting area, it ensures sealing of the system, since it has bitumen base and increases the degree of water resistance of the roof. In all cases, the platform should be slightly elevated above the roof level so that in cases of heavy rain or snow, water cannot seep in in areas where the installation is not tightly installed on the platform.
Obviously, all work on compaction and sealing of fasteners must be carried out at the installation stage of the system in accordance with the recommendations of the manufacturer of the units.
It is recommended at the installation stage to work out a solution to the problem of noise penetration of operating units into the serviced premises. It should be taken into account that if the installation is located directly above the room being served, and the air ducts have a minimum length, then with noticeable cost savings, the operating noise of the units will be very noticeable. In these cases, it is recommended to equip the inlet and outlet pipes of the machines with appropriate mufflers. In general, to avoid problems of this kind, it is best to locate the units away from service areas, for example, above corridors or office premises. Another important aspect is the location of the system relative to the exhaust openings of kitchens and toilets. It seems necessary to determine the wind rose, after which the installation distances of the system are calculated taking into account the dominant directions of movement of air masses. Emissions should not be drawn into the units and sent back to the premises.
Winds can affect the operation of condenser fans and therefore the cooling efficiency of the units. When there is wind, the stationary fans begin to rotate. If the mechanism is electrically switched on during rotation caused by the wind, single-phase fans most often continue to rotate in the direction specified by the wind. Consequently, if the direction of such rotation is incorrect, the passage of air through the condenser will be blocked or very limited, with all the ensuing troubles.
With three-phase fans, something different happens: they have a fixed direction of rotation and, if the wind rotates in the opposite direction when the mechanism is not working, then when the engine starts, the force created to overcome the wind force can damage the drive or blades.
In this regard, in places where they blow strong winds, it is recommended to install additional protection capacitor assembly.
Air distribution from rooftop ventilation and heating units is carried out through low-velocity, low-pressure air ducts. From the vertical supply shaft exiting through the roof, horizontal air ducts are discharged, laid at the level of the ceiling slabs. The norms and rules for installation work do not differ from the installation and equipment of conventional ventilation systems. Conventional sheet steel, fiberglass and sandwich ducts are used. As a rule, air is removed from the room from the space between the ceiling and suspended ceiling and therefore does not require the installation of special air ducts.
Systems with adjustable air flow (VAV) or with adjustable flow and temperature (VVT) are widely used abroad, where special attention is paid to dividing the facility into service zones and, therefore, the possibility of regulating the air temperature in the room at the request of consumers.
In Fig. Figure 8 shows a diagram of a rooftop installation with adjustable air flow. The supplied air enters the VAV unit, equipped with mechanically driven dampers, from where the air is in turn supplied to the air distributors of the serviced room. A diagram of an installation with variable air flow and temperature VVT, equipped with electrically driven dampers, is shown in Fig. 9.
Devices of this type have two operating modes - cold and warm. Switching from one to another is carried out by a unit for adjusting the operation of the system in accordance with actual operational needs.
As with most self-contained direct expansion air conditioners, the average ratio of air flow to cooling power output is approximately 200 m 3 /h per kW of cooling output, with a tolerance of approximately ±20%. At the same values, installations with a lower air flow rate - about 160 m 3 / h - allow for higher moisture absorption and, therefore, are more suitable for loads mainly due to “latent” heat, including quite intense ones.
And, conversely, more powerful units - from 240 m 3 / h per kW - provide less dehumidification and can be recommended for operation under fairly significant loads.
Roof-mounted ventilation and heating units can rightfully claim to be successfully used for the implementation of very complex technological tasks. At civil facilities, such installations with high quality work as part of life support systems of buildings, while energy costs do not exceed those of traditional systems. The fact that this statement is true is evidenced by the widespread use of units of this kind in the United States. The appearance on the market of modern VVT systems with controlled air flow and temperature is further evidence in favor of choosing these installations, which provide the advantage of independent zone control. It would be logical to expect that in Italy, rooftop ventilation and heating units will find successful use among a wide range of users.
Reprinted from RCI Magazine, December 1997
Translation from Italian by S.N. Bulekov
Rooftop air conditioners BOX manufactured by VEZA perform various functions for air treatment and are designed to create and support decentralized general ventilation. Air conditioners from this line are available in four standard sizes with an air capacity of up to 13 thousand m3/h, and can be used at any facility, both civil and industrial.
We offer a wide range of options for BOX air conditioners, as well as various configurations, among which you can easily choose the best option. The variety of design options makes it possible to use these air conditioners as supply, exhaust, supply and exhaust systems, and as installations that provide heating and cooling of air. BOX units are equipped with a high-quality automatic control system, which allows you to maintain precise microclimate parameters at the site and makes the use of central air conditioners more economical and efficient.
BOX rooftop air conditioners - features and benefits
All BOX rooftop air conditioners consist of two key elements- external and internal blocks. The external unit is mounted on the roof (supplied with a roof plinth selected for the roof type) and is frame structure made of reliable and durable materials. The casing is based on galvanized steel panels filled with polyurethane foam. The panels provide good heat insulation and keep heat loss to the minimum possible.
External units are also equipped with convenient service panels that are sealed and can be dismantled for repair and maintenance in a minimum amount of time. In external unit usually includes the following elements:
The indoor unit works with air coming directly from the room. He gives it and takes it away, ensuring a constant and high-quality exchange. The indoor unit contains a heat exchanger, an air distributor, a counter element for the air duct or an air distribution grille. Since the heat exchanger is mounted inside this unit, you can not be afraid of freezing in winter and operate the air conditioner even in severe frosts. In addition, if desired, the air conditioner can be equipped with a separate air cooler through the internal unit.
The Smart Trading company offers a wide selection of BOX rooftop air conditioners, from which you can choose right size with the required air performance, and equipment that ensures the creation and maintenance of the required air parameters. At the moment, thanks to the design, which involves the location of the main unit on the roof, and thereby saving space in the room, this is truly the best option for most objects. Managers of our company will help you select and calculate the BOX rooftop air conditioner for specific operating conditions in a given room.
Ductless rooftop air conditioners INTAKT PRO are an advanced line of outdoor supply and exhaust recuperative units designed for installation on the roofs of buildings. The placement category corresponds to U1 (regular and insulated valves) and UHL1 (north valves) according to GOST 15150-69.
The units are intended for rooms with high ceilings and large open spaces, for example:
Rooftop ductless air conditioners are an innovative product on the market ventilation equipment. To create this series we used modern technologies, the latest design solutions and many years of experience, which made it possible to obtain a whole range of advantages.
Advantages of using INTAKT PRO air conditioners:
Heating mode. The supply air temperature is higher than the room air temperature. Consequently, the air, being distributed, rises. The greater the temperature difference between the supply air and the room air, the less swirling it should be to ensure optimal range and air supply directly to the work area.
Isothermal mode. The supply air temperature is equal to the room air temperature.
Cooling mode. The supply air temperature is lower than the room air temperature. The air is distributed horizontally parallel to the ceiling. Having been distributed, the air falls down into the work area, without creating the feeling of drafts.
When placing INTAKT PRO units, it is necessary to exclude the possibility of exhaust air from one unit getting into the intake of another unit. To do this, it is necessary to direct the exhaust grilles of the units towards each other. The exhaust grille must not be blocked by anything to ensure effective removal air from the room. To service the heat exchangers, it is necessary to leave free space on the side of the removable panels; the panels are completely removable and do not have hinges, so a minimum of space is required for maintenance. The supply air stream must be supplied to the working area completely unhindered, therefore, when locating the units, it is necessary to ensure that there are no obstacles in the direct air distribution zone. The units are supported on the mounting frame by their own weight. Silicone, polyurethane foam or a similar substance is required for sealing. The filter insert on the exhaust part is replaced through the external module (pulled up).
| Parameter | Unit. | INTAKT 90 | INTAKT 60 | ||
|---|---|---|---|---|---|
| Nominal air capacity | m3/h | 9000 | 6000 | ||
| Nominal power consumption total | kW | 7 | 4 | ||
| Minimum | Maximum | Minimum | Maximum | ||
| Mounting height (minimum configuration - recovery only) | m | 5 | 25 | 4 | 25 |
| Installation height (maximum configuration - recovery, noise reduction, heating, cooling) | m | 11 | 11 | ||
| Distance from the center of the unit to the walls | m | 6,5 | 14 | 5,5 | 11 |
| Distance between centers of units | m | 13 | 28 | 11 | 22 |
| Maximum processed area | m2 | 700 | 450 | ||
| Basic swirl distributor | /LSA.I80 | /LSA.I63 | |||
Elements indoor unit and climate control are options. The composition of these blocks must be selected depending on the operating conditions. The composition of the outdoor unit cannot be changed.
| Dimensional and weight characteristics | INTAKT 90 | INTAKT 60 | |||||||
|---|---|---|---|---|---|---|---|---|---|
| A, mm | B, mm | L, mm | Weight, kg | A, mm | B, mm | L, mm | Weight, kg | ||
| External module | |||||||||
| External module | OAT.E1 | 1400 | 2000 | 1700 | 550 | 1200 | 1600 | 1400 | 420 |
| Indoor module | |||||||||
| Indoor module without silencer | OAT.I1 | 1100 | 1100 | 1800 | 170 | 900 | 900 | 1800 | 145 |
| Indoor module with silencer | OAT.I2 | 1100 | 1100 | 1800 | 210 | 900 | 900 | 1800 | 175 |
| Climate module | |||||||||
| Water heater | HW.2 | 1100 | 1100 | 300 | 46 | 900 | 900 | 300 | 35 |
| Water heater | HW.3 | 1100 | 1100 | 300 | 54 | 900 | 900 | 300 | 38 |
| CW.3 | 1100 | 1100 | 550 | 64 | 900 | 900 | 550 | 49 | |
| Water cooler with drop eliminator | CW.4 | 1100 | 1100 | 550 | 70 | 900 | 900 | 550 | 54 |
| CF.3 | 1100 | 1100 | 550 | 64 | 900 | 900 | 550 | 49 | |
| Freon cooler with drop eliminator | CF.4 | 1100 | 1100 | 550 | 70 | 900 | 900 | 550 | 54 |
| Drop eliminator | AS.1 | 1100 | 1100 | 400 | 41 | 900 | 900 | 400 | 32 |
| Air distributor | |||||||||
| Vortex adjustable | LSA. | 1300 | 1300 | 560 | 35 | 1100 | 1100 | 400 | 27 |
| Nozzle | LCN.1 | 1100 | 1100 | 300 | 18 | 900 | 900 | 300 | 14 |
Important note: clause 10.5 of SNiP 41-01-2003 “emissions into the atmosphere from ventilation systems of industrial premises should be placed according to calculation or at a distance from receiving devices for outside air of at least 10 m horizontally or 6 m vertically with a horizontal distance of less than 10 m" refers to production premises with harmful emissions, does not apply to non-production premises. The placement of INTAKT PRO units “supply to supply”, “exhaust to exhaust” prevents exhaust air from entering the supply air.
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