Herrmidifier Herrmidicool Technical Guide - Manual (Page 2)

SECTION I THE HERMIDICOOL HUMIDIFICATION
SYSTEM
Answering the Need for New Technology
In the days of cheap fossil fuels, the easiest and most
often used solution to a humidification problem was the
installation of steam humidifiers, which, although
inefficient and often difficult and expensive to install,
provided a simple, trouble-free means of raising the
relative humidity. As fuels became more expensive,
awareness of energy efficiency increased and in the
1970's, with growing concern about cancer causing
agents contained in many boiler treatment chemicals,
engineers began to look actively at alternatives such as
electronic steam and atomizing humidifiers.
The electronic steam humidifiers promised increased
energy efficiency (most operate at an average of 94%
efficiency as opposed to as low as 60% efficiency for
conventional steam humidifiers) and freedom from the
need for carcinogenic boiler treatment chemicals.
However, as computers and electronic switching devices
proliferated (they tend to create high internal heat loads),
so did the requirement for a more efficient humidifier--
one that could deliver evaporative cooling as well as
efficient humidification. Air washers were considered,
but because of their large size and open tanks of water,
they could not easily be retrofitted to existing systems
and presented a hazard for clean environments. The
Herrmidicool is the only system able to answer all these
challenges!
According to thermodynamic laws, evaporating one
pound of water requires approximately 1075 BTU's. This
energy must be obtained either from direct input (as in
the case of steam humidifiers) or from the ambient air,
as a result of converting sensible heat to latent heat.
Quite simply, steam humidifiers increase enthalpy,
atomizing humidifiers do not. Therefore, during some
part of the year, the evaporative cooling provided by the
Herrmidicool system can be of great benefit, particularly
if the environment to be humidified has a relatively high
internal heat load, such as in a computer room. Chart 1
shows the psychrometric path of a steam humidifier
versus that of the Herrmidicool system. Pay particular
attention to the enthalpy lines, the temperatures and the
grains of moisture added.
The Psychrometric Chart is designed to show the
moisture content, volume, relative humidity and enthalpy
of air at various temperatures. The chart works
somewhat like a nomograph, in that intersections of the
lines represent various conditions. The vertical lines
correspond to scale A along the bottom of the chart,
which represents the dry bulb temperature of the air.
There are three sets of diagonal lines on the chart, one
set corresponding to scale B which represents the wet bulb temperature of the air, one set corresponding to
scale C which represents the enthalpy of the air in BTU's
per pound of dry air, and the other set representing the
volume of the air in cubic feet per pound of dry air. The
horizontal lines correspond to scale D, which represents
the moisture content of the air in pounds of moisture per
pound of dry air. Lastly, there is a set of parabolically
curved lines, which represent the relative humidity in %.
To read the chart, you simply choose your known
conditions, lay them out on the chart and read the
corresponding intersection from the appropriate scale.
Consider the following examples:
1. If you have air at 70
O
F bulb and 60% RH, what is
the resultant moisture content, enthalpy and wet
bulb temperature?
To find the moisture content, run up the vertical dry
bulb temperature line at 70
0
F until it meets the
parabolic % RH line at 60%. Now follow the
horizontal line from this intersection to scale D and
read the moisture content (.0094 pounds per pound
of dry air).
To find the enthalpy, again find the intersection of
70
0
F dry bulb and 60% RH and follow the diagonal
line from this intersection to scale C and read the
enthalpy (27.2 BTU's per pound of dry air).
To find the wet bulb temperature, again find the
intersection of 70
O
F dry bulb and 60% RH and follow
the diagonal line from this intersection to scale B and
read the wet bulb temperature (61
0
F).
2. If you start with air at 70 0 F dry bulb and 20% RH
and add steam humidification until you reach 60%
RH, what is the starting and final enthalpy?
To determine the starting enthalpy, locate the
intersection of 70
0
F dry bulb and 20% RH and
follow the diagonal line from this intersection to scale
C and read the enthalpy (20.3 BTU's per pound of
dry air).
Since steam humidification contains its own heat, to
determine the final enthalpy, locate the intersection
of 70
0 F dry bulb and 60% RH and follow the
diagonal line from this intersection to scale C and
read the enthalpy (27.2 BTU's per pound of dry air).
3. If you start with air at 70
0
F dry bulb and 20% RH
and use the Herrmidicool system to add
humidification until you reach 60% RH, what is the
starting and final enthalpy?
HERRMIDICOOL Technical Manual