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The Reznor ML Series gas-fired warm air heaters, specifically models ML 1511, 1515, and 1520, are designed as axial fanned, forced convection air heaters. They incorporate automatic ignition and fanned flues, making them suitable for use as Type B22, C12, or C32 appliances. These heaters are primarily designed for free-blowing use, providing efficient space heating for commercial and industrial applications.
The core function of the Reznor ML series air heaters is to provide space heating through the combustion of gas. They operate on a direct burner ignition principle, meaning a separate ignition burner is not used to light the main burner. Instead, a hot surface igniter heats and glows, initiating combustion. Flame failure protection is achieved through an ionization principle, where a suitable flame passes an electrical current between an electrode and the earthed burner assembly.
When the external controls, such as a room thermostat or time switch, call for heat, an electrical circuit is made to an electronic burner control. This control first performs a safety check, ensuring that the combustion air induced draught fan (venter) is stationary, as monitored by a differential pressure switch. If no airflow is proven, the venter is switched on, and the proving switch moves to the airflow position, indicating adequate airflow. This mechanism safeguards against blocked flues or faulty flue fans.
Following the airflow proof, a pre-purge period of approximately 18 seconds commences to ensure no unburnt gas is present in the combustion chamber. If a flame or simulated flame is detected during this period, the system will lock out. After the pre-purge, the ignition sequence begins: the hot surface igniter heats up for about 23 seconds until ignition temperature is reached. Subsequently, the main gas valves open, and the burner lights within a maximum of 5 seconds. As long as the flame remains adequate, sensed by a nominal flame ionization current of 1.5-3.2 µA, the burner stays lit until the external controls are satisfied.
Simultaneously with the ignition circuit and gas valve activation, electrical power is supplied to an anticipator within the air circulation thermal fan control. This anticipator accelerates the warm-up of the thermal fan control, ensuring that the airflow from the fan is temperate (around 45°C) when it switches on. The air circulation fan continues to run after the burner switches off to cool the heat exchanger, preventing residual heat build-up.
Safety against overheating is a critical feature, managed by two thermal overheat controls. The first, LC1, is an automatic recycle control that switches off the burner upon overheating and automatically resets upon cooling. This protects against low airflow conditions, such as clogged airways or fan failure. The second control, LC3, is a super overheat control that operates at a higher temperature setting. If activated, it locks out the burner, requiring manual intervention to reset. The electronic burner control may also require resetting in such events.
The heaters are designed to take combustion air from outdoors, improving operational efficiency. This is typically achieved through two round pipes/ducts connected to the rear of the air heater. The products of combustion are vented to the outdoor atmosphere via a permanently connected forced draught flue.
The Reznor ML series heaters are designed for straightforward operation. To light the air heater, users must first ensure the gas supply is turned on, including the heater's manual valve. Next, the electrical supply to the heater must be switched on. If a time switch is fitted, it should be set to an ON cycle. Finally, the room thermostat should be adjusted to the desired temperature. The heater will then light automatically when the room thermostat calls for heat. If the heater does not light, users should check if the burner control or thermal overheat (limit) control requires resetting, indicated by a glowing indicator light on the heater or remote control panel. Manual reset buttons are available for these controls.
For short periods of turning off the heater, the room thermostat can be adjusted to its lowest setting. For prolonged periods, the room thermostat should be set to low, the heater manual gas valve turned OFF, and after five minutes or when the fan has stopped, the electricity supply to the heater should be turned off. The gas supply to the air heater should also be turned off. It is important to note that the gas service tap should only be operated in emergencies or for servicing/prolonged shutdowns.
Some Reznor unit air heaters may include a remote override switch for the fans, allowing cool air circulation during warmer months when heating is not required. To use this feature, the mains electricity supply to the air heater must be ON, and the manual override switch (which may be on a remote control panel) must be switched ON.
The appliance is supplied with external control circuits bridged, meaning it will operate continuously unless these bridges are removed and time and temperature controls are substituted. This allows for flexible integration with various external control systems.
Regular maintenance and servicing are crucial for the safe and efficient operation of the Reznor ML series air heaters. It is recommended that servicing be carried out by suitably qualified persons at least once a year, or more frequently depending on the environmental conditions where the heater is installed. Initial regular inspections are advised, especially in dirty areas, to determine the appropriate service frequency.
Before commencing any servicing, the main gas supply and electricity supply to the air heater must be turned OFF (after the air circulation fan has stopped).
Maintenance tasks include:
The manual also emphasizes the importance of ensuring that any combustion air vents fitted to the building are unblocked and that the outer casing of the air heater is clean to prevent hazards from excessive dust. If converting to a different gas type, a Reznor conversion kit must be used, involving changing the gas valve, burner injectors, resetting the burner ribbon aeration shutter, and applying new over stickers. The commissioning procedure must be followed after conversion.
General| Model | ML 1511 |
|---|---|
| Category | Heater |
| Phase | 1 |
| Input BTU/h | 150000 |
| Gas Type | Natural Gas/Propane |
| Mounting | Suspended |
