Cooler coil construction

There are three forms cooler coil: water-cooled, direct expansion, and cooled brine. The first and third types of use of heat absorbed by the chilled liquid as it spreads through the finned tubes coil to produce the necessary cooling and dehumidification of the air flow. The second form has a boiling point of liquid refrigerant in the pipes, and so the heat absorbed from the air flow provides the latent heat of evaporation of the coolant.

Heat exchanger, usually implemented outwardly, finned, horizontal pipes, arranged so as to facilitate drainage of condensed moisture from the fins. Pipe diameter range from 8 to 25 mm, and copper material, widely used, with copper or aluminium fins. Copper fins and copper tubes, usually offer better resistance to corrosion, especially if the whole Assembly of the electro-tinned after manufacturing. Fins are usually plate type, although spirally wound and circular ribs. Cross-flow heat exchange between the air and coolant happens for a specific line, but, line by line, " against " or parallel flow heat, may take place, depending on the way in which the pipeline was constructed. On Fig. 10.2(a) illustrates the case of a single streamer tube, but double serpentine, and other arrangements are also used. In a double serpentine form shown in Fig. 10.2(b), two trumpets, from the stream riser feed first and third rows with two tubes of second and fourth lines leading to the return of the header.

Reverse connection, it is important for the heat exchanger in all cases. In direct expansion coil, as refrigerant boiling point at a constant temperature, the surface temperature is more uniform and there is no difference between parallel and reverse logarithmic mean temperature difference being the same. However, with direct expansion cooler coils many problems that need to be taken pipelines in order to ensure the uniform distribution of liquid refrigerant is happening all over the surface of the coil. This is achieved by having a " guide " after the expansion valve, the function of which is to divide the flow of liquid refrigerant in the number of equal flows. Pipes of equal resistance join the exit distributor of the coil so that the liquid is fed evenly over the depth and height of the coil. It may be necessary to feed the coil on both sides, if it is very wide. Restrictions on the need to ensure effective distribution of liquid refrigerant during coil tend to discourage the use of very large direct expansion cooler coils. Control problems exist.

Steeper the coils must be partitioned horizontally, independently, drain the condensate collection tray running across their width and depth. Opinions may vary among manufacturers on the maximum vertical distance between the condensate drip trays. Obviously, it depends on the reasonable-General ratio of heat (the less the higher the rate of condensation)distance between the ribs (the smaller the interval, the more difficult to drain freely) and the rated speed (the speed of the air flow in the more probable transfer of condensate). Fin distances in common use are 316, 394 and 476 per meter (8,10 and 12 per inch thickness using lie between 0.42 and 0.15 mm (thinner fins, by the way, as a rule, to grab the receiver, less densely on their roots and perhaps give poorer heat transfer.) Fins may be corrugated or smooth, former reducing the risk of rolling while improved heat due to a small increase in the area of the fins. Analysis of the manufacturers ' data shows that for cooling coils, which have a reasonable-the total heat coefficients of not less than 0.65 person speeds listed in Table 10.1 must not be exceeded without the provision of drops of moisture.

Maximum vertical distance between the intermediate drainage trays should preferably not exceed 900 mm and more 394 fins on the meter should not be used with coils, which have a large latent loads when reasonable-the total heat coefficients less than 0.80. For sensible-General indicators of less than 0.65 and sprayed coils are 316 fins on the meter should not be used. When sober-General relationship between 0.8 and 0.95, perhaps, it is safe to drain trays 1200 mm from each other, provided the person speed and fin is consistent with the proposals in Table 10.1. Coil with a reasonable-General indicators, greater than 0.98 almost makes sensible cooling only and the risk of condensate rolling a little. The velocity of water use, - from 0.6 to 2.4 m s-1, in which range coils are self-purification of air. Water pressure drop is typically between 15 and 150 kPa air pressure drops and depending on the number of rows and finning of tubes and mechanisms. Roll that makes no hidden provides around one-third less resistance to airflow. Typical air-pressure falls within four rows of coils 2.25 m s-1 person speed from 60 to 190 PA when wet with condensation.

Condensate trays should slope towards the drainage point and there should be adequate access for regular cleaning. It is important that the connection of the pipeline from the drainage point should be provided to trap outside the coil. It must be deep enough to provide water seal of condensate and prevent air being sucked into the drainage trays in the case of a tie through the coil, or is blown in the event of a strike-through the coil. Condensate will drain freely away if there is no airflow through the exit point. The trap must feed gas condensate through the air gap in the bucket, to condensate being piped sewer system. Air gap is needed to ensure the presence of a condensate drain can be observed in hygienic purposes, to ensure that there is no direct connection between the main collector and an air conditioning system. Cm. Fig. 10.5.

After installing the aluminum fins, and in the cold coils not provide uniform condensation throughout its area until they were at the age of about a year of use. ASHRAE (1996) mentions the development of hydrophylic coating for aluminium plates, which reduces the surface tension of condensate and gives a more even distribution on the fins from the very beginning.

Rough handling in the production, delivery and installation often causes damage to the coil face, leaving large areas of the turned back edges, that spoil the air, collect dirt from accumulating stream of air and increase the air pressure. The fins in such damaged areas must be combed out after installation, before the system is installed.

Other materials are sometimes used for cooler air coils, but ordinary steel coils should never be used because of the rapid corrosion is likely. Stainless steel is sometimes used, but it is expensive, and because its thermal conductivity is less than that of copper, more heat transfer surface is required.

Cooler air coils, as a rule, wide and short, not narrow and high. This is because it is cheaper to do coil with this form, because there is less return bend connection do (where there are traffic jams from the coil and housing). This is because short coil condensate drains away easily: high coil there is a probability of condensate development, between the ribs, at the bottom of the coil, blocking the airflow and heat transfer, and increases the risk of condensate entrainment in the duct system. The consequence of the broad shape of the cooler coil faces is that the air flow over them, is likely to be uneven airflow tendency to flow in the middle of the coil face. This is usually dealt with ventilation installations using multiple fans in parallel.

Strike-through the coil is used, but can sometimes lead to poor results, because the air flow discharged from the fan very rough and even if a few fans in parallel are used, air distribution system coil person will be uneven. The coil should be as far from the fan outlet, is to give turbulent air flow chance to become smoother.

With the draw through the coil, smooth holes having advanced edges are usually provided in the membranes, where there are traffic jams join headers or return bends. Hole slightly larger than the outside diameter of the pipe to provide free space for thermal motion. It follows that, with the blowing of the coils, condensate will be blown out of such design of the premises. This cannot be allowed, and the coils used for blow-through applications must have clearance spaces seal manufacturer.

Galvanized steel membranes are often used for coils with copper tubes and copper or aluminum plates. This is a bad combination, since copper and zinc in combination with sour condensate favor of electrolytic corrosion. If possible, materials should be used for cooler coil shell. Drain valves and vent holes must be given for cooling coils using chilled water or in brine...