Herrmidifier Load Calculator User Manual

Page 19

L o a d C a l c u l a t i o n G u i d e

w w w. h e r r m i d i f i e r- h v a c . c o m

Evaporation

This process actually evaporates the water to the vapor state

before it is discharged into the air. No droplets of water enter

the humidified air. Minerals contained in the water are left be-

hind in the humidification equipment and must be removed

by periodic cleaning. No mineral fallout is experienced with

this type of equipment. Generally a bleedoff or blowdown

mechanism is built in to flush away concentrated minerals

and lengthen maintenance periods. Evaporative equipment

will work well on any quality of water.

Evaporation will occur off the surface on an open pan of wa-

ter or off a saturated sponge. Since it requires 1000 BTU’s to

evaporate one (1) pound of water, heat is often added to the

water or air to enhance evaporation. There are four types of

evaporative humidifiers: heated water and media, pan-coil,

heated air and media and air washers.

HEATED WATER AND MEDIA humidifiers use a wetted

media through which heated water is poured and air blown

through to pick up the moisture. Although effective, large

amounts of heated water and energy are poured down the

drain in the necessary constant blowdown process. These

units are usually placed on a supply duct and therefore add

to the static pressure and blower costs. Overall energy ef-

ficiency of this type of evaporative humidifier is very poor.

AIR WASHERS use the evaporative process by passing

air over a continuous film of water flowing over deflectors

which present a large surface of water in contact with the air.

The resulting surface evaporation raises the R.H. of the air.

Because of the evaporative cooling and their large size and

cost, air washers are usually used as evaporative coolers,

purifiers AND humidifiers. It is necessary that efficient “de-

mistors” be placed in the air stream after the washer section

to remove and drain any water droplets that may have be-

come entrained in the air stream. This often results in high

static loss across the washer. High levels of R.H. usually

cannot be attained by this method of humidification. (Upper

limit is about 55% R.H.)

Steam

This process injects live steam into the air to be humidified

either via manifold in a ducted air system, or direct discharge

into the area. Where good quality steam is available in suf-

ficient quantities, a central steam humidification system will

have a very low “first cost.” Where a steam boiler must be

installed for humidification, its first cost is comparable to oth-

er forms of humidification. A steam boiler for humidification

must be able to supply good quality steam with very little

droplet entrainment. Any droplet entrainment will result in

mineral clogging of the humidification equipment since these

droplets contain the same chemical makeup as the water in

the boiler.

A central steam humidifier consists of a condensate sepa-

rator (to remove slugs of condensate) and a distribution

manifold (for insertion in ducts) or outlet (for area disper-

sion). Generally the steam flows through the control value

into the separator manifold. This is where any solid water

particles fall out of the steam providing a good quality steam

for humidification. The Herrmidifier Herricane CS Series is

designed for low steam velocities in the distribution tubes

resulting in very low noise levels. The distribution tubes are

also engineered to return any condensate to the header. The

stainless steel nozzles receive their steam from the middle

of the distribution tube where the driest steam is available.

Care must be taken to ensure that any spitting, caused by

heavy slugs of condensate, will not damage duct work or

materials positioned beneath an area steam humidifier.