Installation, starting and adjustment of ventilation and air conditioning systems A Guide
Шрифт:
Heaters are often grouped into several pieces, both with a parallel installation through the air, and with a sequential or combined one. If the heat carrier is steam, then the heaters are installed with a vertical arrangement of tubes and steam supply to the upper branch pipe; if the heat carrier is water, then the position of the tubes should be horizontal, which ensures the removal of air when filling the heaters with water and draining water from it when the system stops working.
Electric heaters are also available (Fig.10).
Fig.10. Electric heater
Electric heaters consist of a steel casing with tubular heating elements: 1.6 or 2.5 kW each. To increase the heating surface area, the heating elements have ribs with a diameter of 42 mm. Electric heaters can work both in manual and automatic mode, maintaining a constant temperature of the air at the outlet or in the room.
3.6. Duct heaters
The duct heater is used to heat the supply (outdoor) air in the ducts (conventional circular section). In central ventilation systems, duct heaters are used as auxiliary heaters, and in decentralized ones – as the main air heaters.
The heater body is made of galvanized steel. Air heating is carried out by heating elements. It is mandatory to have protective and regulating thermostats, which provides the product with high safety and the ability to function in automatic mode at the same time.
Channel heaters are equipped with two thermostats for overheating protection: heat-protective with automatic restart (operating temperature +50
3.7. Air coolers
Duct air coolers (Fig. 11) are designed for cooling and dehumidification of supply, recirculating air or a mixture thereof in ventilation and air conditioning systems of industrial, public or residential buildings.
Fig. 11. Air cooler with ducted water and freon coolers
Water or non-freezing mixtures can be used as a refrigerant in ducted water coolers. The maximum allowable liquid pressure in them is 1.6 Mpa.
Freons are used as a refrigerant in ducted freon coolers. Upon delivery, the heat exchangers are filled with inert gas, which must be removed during connection to the refrigeration circuit.
The design of the cooler is a housing made of galvanized steel, inside which a heat exchanger, a drop trap and a pallet are installed.
The heat exchanger is made of copper tubes with aluminum fins arranged in a staggered order.
The freon cooler is distinguished by the design of the distribution unit ("spider") and the specifics of the refrigerant supply.
The collectors of the freon heat exchanger are made of copper tubes.
The drip trap (Fig. 12) is a set of special plastic plates that effectively trap condensate and collect it into a tray located in the lower part of the cooler body.
Fig. 12. The shape of the droplet trap plates.
The pallet is additionally thermally insulated and equipped with a discharge pipe for draining condensate
When installing the air cooler, it is necessary to ensure its horizontal position.
3.8. Filters
Filters are divided into three classes according to their effectiveness. Class I filters trap dust particles of all sizes (the cleaning coefficient is not less than 0.99), Class II filters – particles of more than 1 micron (cleaning coefficient is more than 0.85), class III filters – particles of more than 10–50 microns (cleaning coefficient is not less than 0.60).
3.9. Noise suppression equipment
The noise level generated by ventilation systems is an essential criterion of ventilation quality. The sources of noise in ventilation installations are fans and electric motors, as well as the movement of air in the ducts and its exit from the holes. Two types of noise are considered: aerodynamic and mechanical.
The reasons for the appearance of aerodynamic noise in fans are: the formation of vortices and their periodic disruption from the blades of the impeller, local air flows at the entrance to the wheel and at the exit from it, leading to unsteady flow around the blades of the wheel, perturbation of the medium by rotating blades. Mechanical noise occurs in bearings, in the drive, in the installation sites (fasteners) of the ventilation unit on building structures, etc. The degree of noise increases with insufficient balancing of the fan impeller.
Of all the sources of noise generation, the dominant ones are fans that create aerodynamic noise. The noise generated by the ventilation system can be reduced by the following measures: installation of fans with the most advanced acoustic characteristics, in particular, fans with blades bent backwards; the choice of fans with the highest efficiency (not less than 0.9 of the maximum), with a minimum angular velocity of the impeller (not higher than 30 m/s), i.e. fans with a small diameter of the impeller and a small number of revolutions (at the same time, you should not overestimate the pressure against the calculated one, since this causes an increase in noise level); careful balancing of the impeller.
Noise reduction along the path of its propagation is achieved by limiting the speed of air movement in the ducts or lining the inner surfaces of the ducts with a sound-proofing material.
In order to reduce the transmission of fan vibration to the ducts, the latter must be connected to the fan nozzles using soft inserts made of rubber, rubberized tarpaulin.
Vibration noise reduction is achieved by installing ventilation units on vibration isolators. Standard designs of spring and rubber vibration isolators are used (Fig. 13).