Heating with air handling units
Heating Types for Air Handling Systems
Customers can choose from a variety of popular heating mediums including hot water coils and gas-fired or electric heaters.
Hot water coils are suitable for low, medium and high pressure hot water and steam applications. They are fabricated by expanding copper tube to aluminium collar spaced fins at a suitable pitch to meet key design performance parameters. These fins, which are staggered in the direction of the airflow, are mechanically bonded to deliver excellent heat transfer characteristics and are available in special materials and finishes such as copper and electro tinning to meet particular specifications.
Positioned in a rigid galvanised formed section, the coil tubes are brazed to copper headers with flow and return screwed or flanged connections. Coils feature an air vent and drain plug as standard and all pipe and drain connections are fitted with flexible bushes to ensure an airtight seal and good vibration isolation.
Direct gas-fired heaters are manufactured in accordance with European Standard EN525 and are CE certified. With combustion efficiencies of 93% gas firing provides the most efficient means of heating. The burner is a cast steel manifold with perforated stainless steel mixing plates which progressively mix fresh air and so provide optimum combustion at all levels of operation. In accordance with CE requirements, the burner has its own combustion fan. Fully modulating control with up to 25:1 modulation is provided using a microprocessor controller that monitors the space temperature and heater discharge temperature. Burner controls are fitted with an automatic ignition and an airflow system with safety controls to provide automatic safety shutdown.
Indirect gas and oil
Suitable for natural gas, LPG or oil, Jet's indirect gas-fired units are manufactured from heavy gauge, high quality stainless steel (316 grade) and feature a combustion chamber/heat exchanger. CE-marked for quality, they will deliver heater efficiencies of in excess of 86% across the output range, with condensing heater modules providing even higher combustion efficiencies.
For output units of up to 920kW, a forced draught burner is supplied, complete with controls to meet the particular specification requirements. For smaller output duties, single or multiple atmospheric burner modules can be provided. Exhaust gases are expelled using a flue fan with an in-built draught diverter.
Gas-fired coils are available as multi-tubular heat exchangers in aluminiumised steel or stainless steel, with the large surface area delivering high thermal efficiency. Heaters are equipped with full safety controls including gas pressure proving, flame detection, airflow proving and high temperature cut-out. Burner control is available as on/off, high/low/off or modulating as appropriate, facilitating optimum burner efficiency at all times.
Designed for black heat operation, the electric heater elements are manufactured from 80/20 nickel/chrome resistance wire centred in a protected metal tube packed with magnesium oxide. While element tubes are of copper-coated mild steel tubular or finned construction as standard, stainless steel or incoloy can also be supplied.
The AHUs are delivered complete, with safety cut-out and manual reset facilities, while the control enclosure complies with IP42 and special terminal boxes are available to IP/NEMA specification. The control system operation is via remote thermostat or step control with pre-wired switching and overheat protection. Thyristor/SCR control is also available with energise and de-energise cycling capabilities.
Thermal wheel exchangers incorporate a rotating wheel to recover both sensible and latent heat with efficiencies of up to 85%.
Plate heat exchanger
Cross flow type heat recovery provides up to 80% efficiency. Warm discharge air is passed through the heat exchanger to atmosphere with heat transfer to the cooler fresh air passing through the heat exchanger. Summer bypass facilities are installed. While waste heat exchanger plates are typically manufactured in aluminium, special epoxy coatings or stainless steel plates are also available.
Run around coils
Waste heat recovery is facilitated by liquid coupled run around coils constructed to the same specification as the heating coils. A water-glycol medium is pumped through the coupled coil circuit to provide 65% heat recovery. This facility can be provided in a number of ways, including via a pump set within the air handling unit with a control interface.