HVACR416 - Design

Humidification

Relative Humidity

1.Air in the home is artificially dried out when it is heated.

2.Because warm air expands, this expansion lowers the moisture content.

3.The amount of moisture in the air is expressed in terms of relative humidity.

4.The relative humidity of the air decreases as the temperature increases because as the air temperature rises it can hold more moisture.

5.This dry warm air draws moisture from everything in the conditioned space.

Dry air causes more energy consumption than necessary

The air gets moisture from the human body through evaporation from the skin.

The person then feels cold and sets the thermostat a few degrees

higher to feel more comfortable. When moisture is in the air the person feels comfortable at a lower

temperature. Static electricity is also more prevalent in dry air.

Relative Humidity

The recommended relative humidity for a home isbetween 35 and 50%

Bacteria, Viruses, Fungi and so forth become more active when the relative humidity varies above or below these limits

Indoor air quality has become more and more important

Relative Humidity

Air Humidification

Years ago people placed pans of water on top ofradiators or stoves. Today more efficient ways and equipment producemoisture.

They add moisture to air by evaporation. The evaporation process is accelerated by using either power or heat. By passing air over large areas of water the area of the water can be increased by spreading it over pads or by atomization.

Types of Humidifiers Evaporative Humidifiers.

Evaporative humidifiers work on the principle of providing moisture on a surface called media exposing it to the dry air.

This is normally done by forcing air through or around the media.

Picking up the moisture from the media as a vapor.

Types of Humidifiers Evaporative Humidifiers.

Bypass Humidifiers

Rely on the difference in pressure between the supply and return side of the system. It can be mounted on either the supply or return side. A duct must be run from the plenum where the humidifier is mounted to the other plenum. The difference in pressure between the two plenums creates air flow through the humidifier

Bypass Humidifiers

The Plenum mounted humidifier is mounted in thesupply or return plenum.

The furnace fan forces air through the media where it picks up the moisture. The Under duct mount humidifier is mounted onthe underside of the supply plenum.

The media extends into the air flow where moisture is picked up.

Atomizing Humidifiers

Atomizing Humidifiers discharge tiny droplets of water into the air. Which evaporate rapidly into the duct air stream or directly into the conditioned space. These humidifiers can be spray nozzle or centrifugal types. They should not be used with hard water. The minerals in the hard water leave the air stream as dust. 8-10 grains of water hardness is the maximum recommended. Atomizing humidifiers should be mounted on the hot air supply plenum

Atomizing Humidifiers

Controlling Humidifiers They are controlled by a humidistat.

The humidistat controls the motor and or the heating element. The humidistat has a moisture sensitive element made of hair or nylon ribbon. This material is wound around two or more bobbins and shrinks and expands depending on humidity.

Dry air causes the element to shrink which activates a snap action switch.

Other devices are used to monitor the moisture content of the air including electronic components that vary in resistance according to humidity.

Sizing Humidifiers General factors involved in the sizing process.

The Number of cubic ft of space to be humidified this is determined by multiplying the number of heated square ft of the house by the ceiling height.

The construction of the building, this includes quality of insulation, storm windows, fireplaces, building tightness and so forth. The amount of air change per hour and the approximate lowest outdoor temperature.

The level of relative humidity desired

Troubleshooting Humidifier not running?

When the humidifier does not run the problem is usually electrical or a component is blocked because of mineral build up.

A blocked condition can cause a thermal overload to cut out.

Check over load protection circuit breaker and low voltage controls. Check whether the motor is burned out, clean and disinfect all components.

Excessive dust Excessive white dust is caused by the humidifier mineral build up on the media. Clean and replace the media. If excessive white dust occurs in a atomizing humidifier the wrong equipment has been installed.

Water overflow May indicate a defective float valve assembly It may need clearing or replacing.

Moisture in or around ducts Moisture in ducts is found only in atomizing humidifiers. Check the control to see if it operates at the wrong time. Restricted air flow may also cause low or high humidity levels.

Check the calibration of the humidistat. If it is off you need to adjust it.

You need a sling psychrometer.

Insure that the humidifier is clean and operating properly.