The arrangement of the tubes with the heating liquid can be consistent in the direction of air movement (corridor), staggered and offset along the corridor (most effectively). The tubes themselves can be either round or flat-oval in cross-section.

The best thermal engineering indicators have spiral-rolled bimetallic three- and four-row heaters for both steam (single-pass) and water (multi-pass) heater. The tubes for the heat carrier in these heaters are steel, the fins are rolled from aluminum.

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.

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 °C) and fire-fighting with manual restart (operating temperature +110 °C). Channel heaters are designed for a minimum air flow velocity of 1.5 m/s and a maximum operating temperature of 40 °C of the outgoing air.

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