Page 176 - Boiler_Operators_Handbook,_Second_Edition

Refrigeration & AC 161

it necessary to cover two of the fan discharge screens ers are readily damaged by the plastic strings of weed
to restrict airflow enough to maintain an adequate con- eaters; I even investigated one problem site where the
denser pressure. Wax coated cardboard hinged on one Yard workers had elected to write their initials into the
side with some duct tape did a good job of it but the fins using a weed eater; needless to say the culprits were
cardboard had to be flipped back over in cold weather if easy to identify. The grass and weed eater damage has
the fan of that section was operated. the same effect as debris accumulation on the condenser
Regular inspections of condensing units are re- outlet. Unless the damage is so extensive that the fins
quired because so many things can happen to them. are torn, bent fins on an air cooled condenser can be re-
During each inspection of the condensing unit you paired readily with a device called a fin comb. Even if
should always look for oily spots around the unit base none of these obvious conditions of condenser blockage
and connecting piping; those spots would be refriger- are evident a regular annual cleaning of the condenser
ant oil indicating a system leak. Sometimes the units are coils is recommended.
mounted on the roofs of buildings which requires a roof
hatch and/or ladder for access and it’s not uncommon Water Cooled Condensers
for the latter to be one that’s carried on a truck. These are Every source of water for a water cooled condens-
less susceptible to damage than units mounted at grade ers can be counted upon to be colder than air except
level but at the same time are the ones that are frequent- in the winter. Even water cooled by a cooling tower is
ly overlooked during normal inspection rounds. Prob- colder than the temperature of the air. Heat transfer be-
lems with rooftop condensing units normally fall in the tween metal and flowing water is considerably higher
range of blockage of the coils and fins of the condensing than the heat transfer between metal and flowing air. So,
unit by airborne contaminants. Cottonwood tree and water cooled condensers are preferred because they per-
oak tree pollen is a common problem when the trees are mit lower saturation temperatures inside the condenser
blooming and leaves can block the coils in the fall. which reduces the horsepower requirements of the com-
Newer condensing units mounted at ground level pressor.
are exposed to other hazards. All new units are similar You may ask, “Okay, why isn’t my home air condi-
to a residential unit (Figure 5-31) because the three sid- tioner water cooled?” Well, if you live in the Southwest,
ed coil and vertical air discharge make them more effi- it actually may be water cooled. We call them evapo-
cient. A common problem is the accumulation of leaves, rative condensers (Figure 5-16), and they can be found
seeds, and small branches that fall onto the condensing almost anywhere. The refrigerant is piped or connect-
unit and managed to drift past the fan to settle behind ed with tubing to coils in a casing where water drips
the condenser. The bottom tubes of the condenser then on them to absorb heat as the water evaporates and is
act as a receiver because tubes higher up have to serve carried off by air drawn through the evaporative con-
as that portion of the heat exchanger dedicated to sub- denser. It requires a pump to circulate the water from
cooling. The result is an apparent loss of refrigerant the catch well at the bottom of the condenser to the top
because more liquid is held in the condenser. Always where it’s distributed over the tubes. A makeup water
look through the fan to check for accumulations that can flow control valve is required to add water from a water
cause this problem. It’s not unusual for the discharge supply to replace the water that is evaporated. And, a
screen to be readily removed for access to remove any small amount of water must be removed by blowdown
accumulations; however, always turn the unit off and to limit the concentration of solids in the circulated wa-
disconnect power to the condensing unit before you ter. The operation and maintenance of an evaporative
reach your hands and arms through the fan to remove condenser is very similar to cooling towers which are
any accumulation. Don’t forget to put the discharge discussed later.
screen back on before restoring power and control. The Construction of a water cooled condenser is highly
inlet side of the condenser can also be plugged up with dependent on the quality of water used to absorb the
mown grass and debris drawn into the fins by the air- rejected heat. The condensers for my shipboard refrig-
flow with the assistance of a lawn mower, weedeater, or eration plants used seawater that is highly corrosive
wind. More frequent inspections in the spring when the and contains all forms plant and animal life. It had to
pollen and seeds are falling and in the fall when leaves be filtered before the section of the circulating pump
are falling should be made to ensure the condenser inlet that forced salt water from the ocean through the filter,
is clean. Yard workers prove to be a hazard for most con- the pump, condenser, and condenser water flow con-
densing units because the fins on the air cooled condens- trol valve then back to the ocean. The shell, heads, and