Page 194 - Boiler_Operators_Handbook,_Second_Edition

Refrigeration & AC 179

atmospheric temperature is colder, fan speed is adjusted cilities that only receive heating and ventilation. Since
to maintain a minimum temperature, unlike the typical most people today expect complete air conditioning it’s
water-cooled condenser where water flow is controlled. not necessarily an applicable label anymore. Air condi-
Variable speed drives on cooling tower water pumps tioning is the best overall label.
can reduce power costs but are limited to ensure good While they’re not as common as they used to be
distribution of the water in the cooling tower. the typical window unit (Figure 5-40), is a packaged air
The water vaporized in a cooling tower has to be conditioning system that incorporates a complete refrig-
replaced with makeup. In addition, because the vapor eration cycle within it to transfer heat from the room to
doesn’t carry off the solids that were dissolved in it, the atmosphere outside the window, is still familiar to
blowdown of the cooling tower is required to prevent most of us. Air from the room (A) is drawn into the unit
scaling and deposits of mud on the fill. Small towers through a filter (B) that cleans the air, the air passes over
commonly have a float valve in the sump that adds an evaporator coil (C) with fins that removes the heat
makeup water to maintain the level. Larger towers can from the air and condenses some of the moisture in the
have level controls using an electric probe system that air then a fan (D) blows the air back into the room (E) at
senses the water level to open and close a solenoid or a high velocity so that it mixes with the rest of the room
motorized makeup water valve. Blowdown control can air to produce the comfortable condition. To achieve all
be manually set or automatic and except for cooling the the requirements for air conditioning there’s usually a
water they work the same as a boiler’s continuous blow- small damper (F) in the barrier between the indoor and
down. Any large system will also have meters on the outdoor air that can be opened to admit outside air into
makeup and blowdown water flows to produce a dif- the flow of room air to be conditioned to achieve ven-
ference between the two that equals water lost to vapor- tilation. Condensate which is moisture removed from
ization and drift so the owner doesn’t pay to for sewage the room air drips (G) into a drain pan at the bottom
treatment of water that wasn’t dumped down the sewer. of the unit and passes through a trap (H) formed in the
Just like a boiler the cooling tower water chemistry bottom of the casing to the outdoor side of the unit. A
has to be monitored and maintained to prevent damage slinging ring attached to the outside of the condenser
to the tower, the condenser, the pumps, and piping. In fan (I) picks up the condensate and hurls it at the con-
addition to scale and corrosion protection chemicals are denser (J). Heat from cooling the air and condensing the
added to control the growth of bacteria and algae in the moisture is absorbed by the refrigerant with flow into
cooling tower water. the evaporator controlled by a metering device, in Fig-
ure 5-40 a capillary (K) and, for the typical window unit
with R-134a into the evaporator (C) at a pressure of 35
AIR CONDITIONING psig which corresponds to a saturation temperature of
40°F. The boiling refrigerant absorbs the heat from the
Normally we think of air conditioning as cooling room air and condenses some of the moisture from the
the air in a space, a room, or building. More appropri- room air to cool it from a design room temperature of
ately air conditioning should be considered to be the 75°F to approximately 55°F. Once all the refrigerant has
heating or cooling plus adding or removing moisture evaporated (L) the gas is heated to a leaving tempera-
and removing airborne contaminants from the space to ture of 50 to 60°F (10 to 20 degrees of superheat). The
maintain conditions in that space that are comfortable refrigerant passes through the insulated barrier between
for the occupants. That definition covers more than the room and outdoors to the inlet of the compressor
what we typically think of. In many zoos around the (M). The gas is compressed by the compressor to a pres-
country there are spaces where the conditions are not sure of 100 psig raising the temperature of the gas that
necessarily comfortable for humans but are enjoyed by enters the condenser to 200°F. The condenser (O) trans-
the occupants. With few exceptions air conditioning is fers the heat removed from the room along with the heat
accomplished by removing air from the space, altering added by the compressor to outside air drawn into the
its conditions, then returning it to the space where it is outside casing by the condenser fan (I) through louvers
mixed with the air in the space to produce the comfort- in the side (P), passing over the condenser and out grills
able conditions for the occupants. (Q) at the back and top of the unit. The grill at the top of
Another term you should hear is HVAC, standing the unit permits admission of rain water that can assist
for heating, ventilating, and air conditioning. I would in cooling when the moisture contributed to the room
dissuade the use of the term if it were not for many fa- air by the moisture from the rain penetrating the room