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Clearing the mists that surround humidification

Humidifier projects don't come along very often for the average hvac contractor so building-up enough experience to overcome the common pitfalls can be difficult. Tim Scott offers 10 tips to ensure a smooth and successful humidifier installation
Installing humidifiers can be a tricky business. Here's a list of fitting tips.

1 - Steam pipes: Installing steam pipes incorrectly between the humidifier and the steam lance in the duct can cause a drop in humidifier efficiency and increased humidifier running costs. If steam piping is too long, the steam will condense prior to being released inside the duct. This results in the humidifier working harder to provide the correct amount of humidity to maintain the required room condition.

As a general rule, steam pipes should not exceed 5m of lagged copper pipe or 3m of flexible steam hose. Whenever there is an elbow in the pipe run, 1m should be taken off the overall length. So a lagged copper steam pipe with a bend should be a maximum length of 4m.

These distances will vary and can be influenced by the power of the humidifier, the diameter of pipe and the temperature of the room the pipe is located in.

Avoid sags in pipework or deadlegs where condensate can build-up without running to drain. This can restrict steam flow and a potentially dangerous buildup of steam pressure in the system.

2 - Steam lances: The steam lance's job is to disperse steam quickly and evenly in the airflow of the duct. It is important to consult the manufacturer's recommendations for the location of steam lances. Understanding the conditions of the airflow will determine the positioning and type of the lance used. A single lance will typically be positioned centrally in the duct, with the holes pointing upwards and at a right angle to the airflow. The lance must be angled to direct condensate into the lance's drain.

Common problems occur when steam lances are positioned too close to bends causing steam to condense on the duct prior to absorption. If it is necessary to mount a lance in a short run of duct, special lances are available with multiple pipes and tiny inner nozzles that take only the hottest, driest steam from the centre of the lance. These quick-absorption lances can provide an evaporation distance of just 60cm.

Care should be taken to avoid placing lances too close to stats, attenuators and air filters as wetting-out could occur. Locating a steam pipe too high or low in a duct may also cause a problem. Stratification of the air with different humidity levels in the airstream could result in condensation on
ductwork and poor humidity control.

3 - Drainage: The water being released from a steam humidifier could be between 60-100 deg C so consideration should be given to drain piping. Plastic pipes can melt and bend. Some steam humidifiers will temper water temperature prior to release so if this is an issue, select an appropriate model.

Don't position a humidifier above an open drain as steam rising from the drain can enter the unit, resulting in condensation and corrosion or electrical faults in the circuit boards. It's better to run a long drain and position the humidifier near the duct, so steam piping is an appropriate length, than position near the drain and have excessively long steam piping.

4 - Water quality: Running a steam humidifier on hard water will inevitably result in an increased maintenance schedule. Limescale left behind after the water evaporates will need removing from the
boiling chamber more frequently.

Careful consideration ought to be given to appropriate humidifier selection in hard water areas to reduce necessary servicing as much as possible. Installing an electrode boiler humidifier in such an area could cost the end-user dearly in replaceable boiling cylinders.

Using a resistive humidifier with an easy-to-service, cleanable cylinder will present better value, even with its higher capital cost. Cold water humidifiers could also be a more appropriate option.

Water treatment, such as reverse osmosis or water softeners, will reduce humidifier maintenance in hard water areas and also improve humidity control as steam humidifiers will be draining less to combat mineral build-up.

5 - Control strategy: Employ a fully considered control strategy that involves safety interlock protection. Care needs to be taken with the location of controlling and high limit sensors.

6 - Humidifier positioning: Humidifiers should be located where they can be easily accessed for servicing. Every humidifier needs to be maintained and inconvenient positioning may mean increased labour time or even a two-man job rather than one.

7 - Check the spec: The type of humidifier specified isn't always the most appropriate for the project. Check with the manufacturer that the model specified will do what the end-user requires. Check the output will meet the project's requirement given the AHU's actual conditions. Ensure the acceptable humidity control will be met by the model suggested. Ask whether the level of expected maintenance and annual cost of consumable components is acceptable to the end-user.

8 - Power: Always consider the full power requirements of the humidifier. Is there enough electrical or gas supply for the unit selected? Also, is there a requirement for single-phase power?

9 - Commissioning: When commissioning a humidifier it is important to consider it as part of the whole air handling system. The humidifier is often accused of under or over-humidifying when air volumes and temperatures have not been checked beforehand.

If an external commissioning engineer is being used, check that all services are installed and tested prior to him arriving on site. Scheduling in the controls company to be on site at the same time can
ensure speedy, accurate commissioning.

10 - Good advice: Seek good advice from a competent supplier when tackling a humidifier project. A quality humidifier supplier will work alongside the contractor to help them make the most from each project.

// The author is sales and marketing director at JS Humidifiers //

1 March 2012


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