How does a gas-powered steam humidifier work?

How a gas-fired steam humidifier works

The combustion system of a gas-fired steam humidifier is based on a modulating premix gas forced-draft burner and a gas pressure regulating valve. When humidity is required, the burner fan starts up and creates a vacuum at the air inlet. The fan runs briefly to purge the system. The igniter is then activated for 15 seconds. During this time, the electronic ignition system performs a diagnostic check of the safety systems, which includes testing the pressure switch that monitors the negative pressure at the air inlet. If the safety systems are functioning correctly, the gas pressure regulating valve opens and the gas-air mixture is ignited by the igniter.

The gas pressure regulating valve ensures a constant ratio of air to natural gas or propane, regardless of the fan speed or external environmental conditions. The air and gas are thoroughly mixed in the blower and passed through the burner openings, where combustion takes place.

The hot combustion gases flow over a baffle inside the heat exchanger to the flue gas outlet.

The level in the water tank is continuously monitored by the level sensor. When the unit is started for the first time, the control system checks the function of the level sensor. During this test, the tank is first filled to level ‘A’, then emptied to level ‘C’ and subsequently refilled to level ‘A’. As soon as level “B” is reached during the refilling process and the level sensor test has been successful, the humidifier is ready for operation. As soon as a humidity requirement is detected, the heating process begins and steam production starts.

Exhaust gas heat recovery via the HVAC system

Channelling exhaust gases through the HVAC system’s exhaust air ductwork offers significant advantages. Firstly, installation is made considerably easier, as a chimney is no longer required. The heat from the exhaust gases is reused via the HVAC unit’s heat recovery system without adversely affecting the quality of the exhaust air. The energy in the flue gas is available free of charge and the savings achieved can be offset against the ventilation heating requirement. The different performance levels allow for a precise selection of units to suit a wide range of applications. As the steam volume increases, so does the heating output generated within the air handling unit.

The total usable exhaust gas heating capacity results from sensible heat due to the high exhaust gas temperature and latent heat in the form of water vapour. The values in brackets represent the sensible heat gain excluding condensation heat.

With a steam output of 40 kg/h, the exhaust gas heat is 4.5 kW; with 65% heat recovery: 2.9 kW (1.5), with 70% heat recovery: 3.2 kW (1.6), with 75% heat recovery: 3.4 kW (1.7).

At 80 kg/h, the exhaust heat is 9.0 kW; with 65% heat recovery: 5.8 kW (3.1), with 70% heat recovery: 6.4 kW (3.3), with 75% heat recovery: 6.8 kW (3.5).

At 120 kg/h, the exhaust heat is 13.5 kW; with 65% heat recovery: 8.7 kW (4.6), with 70% heat recovery: 9.6 kW (4.9), with 75% heat recovery: 10.2 kW (5.2).

At 160 kg/h, the exhaust heat is 18.0 kW; with 65% heat recovery: 11.6 kW (6.1), with 70% heat recovery: 12.8 kW (6.6), with 75% heat recovery: 13.6 kW (7.0).

At 200 kg/h, the exhaust heat is 22.5 kW; with 65% heat recovery: 14.5 kW (7.6), with 70% heat recovery: 16.0 kW (8.2), with 75% heat recovery: 17.0 kW (8.7).

At 240 kg/h, the exhaust heat is 27.0 kW; with 65% heat recovery: 17.4 kW (9.2), with 70% heat recovery: 19.2 kW (9.9), with 75% heat recovery: 20.4 kW (10.5).