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With summer upon us your, drycleaning machine’s cooling system will be under greater
stress.
It doesn’t matter if you are using a water tower, chiller or city water for cooling, conditions
that weren’t an issue during the cooler months may become problems as the ambient
(surrounding) temperature rises.
Most of the cooling problems will
rear their ugly heads during the
drying segment of the drycleaning
cycle.
Drying in the drycleaning machine
sense is all about moving heat
energy. The media which moves all
this heat is called a refrigerant (most
machines use R22 Freon while some
of the newer models and the K4 machines use R400 Freon as refrigerants) and some form of
coolant (generally water or a water and glycol mixture.)
It doesn’t matter which Freon is used, the process itself requires a device called a
refrigeration condenser which changes hot, vapor rich, Freon gas back into liquid Freon which is
constantly being recycled during the drying segment of the drycleaning cycle.
In almost every case, this condenser is cooled by a liquid (there are a few air cooled
condensers which are not the topic of this article). Hot, compressed Freon gas is forced by the
refrigeration compressor into the refrigeration condenser where it is cooled and condensed by
water (called a coolant)
In this case we are transferring the heat from a vapor rich, hot, compressed Freon gas into
the coolant flowing through the refrigeration condenser.
There are three methods of supplying water to the refrigerated condenser
1. City water. Water from the city main is forced through the drycleaning machine’s
refrigeration condenser propelled by existing city water pressure. The exiting water is then sent
down the drain.
2. Water tower. Water is circulated by a pump through the drycleaning machine’s
refrigeration condenser; over an evaporative cooling media (looks like corrugated plastic cubes)
which has air forced though it to aid in evaporation; into a sump where the suction inlet of the
pump is connected.
The evaporation of the water from the surface of the media cools the remaining water which
drops into the sump for recirculation through the drycleaning machine’s refrigeration condenser.
3. Chiller. Water or a mixture of water and glycol (this mixture is called a brine) is circulated
by a pump through the drycleaning machine’s refrigeration condenser; cooled by a separate
refrigeration system; then recirculated through the drycleaning machine’s refrigeration
condenser.
No matter what method is used for cooling and circulating the coolant through the
refrigeration condenser, the efficiency of the process is dependent on two factors:
• Coolant flow. The amount of coolant moving through the condenser.
• Heat transfer efficiency. The ability of the condenser coil to move heat to the coolant.
Each of the above factors can be easily monitored using pressure and temperature as
indicators of what is going on in the coolant system.
A pressure gage and a thermometer at the inlet and outlet of the coolant system located near
the drycleaning machine are vital for monitoring the cooling system performance.
Let’s take a look at what the pressure gage can tell us about the condition of the coolant
system.
The pump must supply enough pressure as well as flow in sufficient quantity to push coolant
through the components that require cooling on the drycleaning machine.
On most machines this would include not only the refrigeration condenser but also the still
condenser and solvent cooler. In the case of water towers and chillers, also enough pressure to
push it back to the tower or chiller sump which are often located on the roof.
Unfortunately there is no hard and fast rule for what the pressure readings should be.
The best method for obtaining the “numbers” is to note, for future reference, the drycleaning
machine inlet and outlet pressure and temperature readings when the drycleaning machine is
working properly .
The following are some possible scenarios for different combinations of qualitative data:
1. Inlet pressure high/outlet pressure low:
A. Check for blockage of the inlet flow path, a clogged Y strainer between the pump and the
drycleaning machine.
B. Heavy scale build up inside the piping of the drycleaning machine.
2. Inlet and outlet pressure rapidly changing:
A. Low coolant level in the pumping system.
3. Low inlet/high outlet pressure:
A. Open bypass valve on pumping system.
4. Low inlet/low outlet pressure:
A. Pump off.
B. Clogged inlet strainer.
5. High inlet temperature; high outlet temperature:
A. Water tower fan not working; chiller refrigeration system faulty.
B. Pump off.
6. Slightly higher than normal inlet temperature/high outlet temperature:
A. Heavy scale build up inside the piping of the drycleaning machine.
B. Excessive heat source — still boil over or steam sweep valve open; steam supply
valve to steam boost coil or carbon adsorber.
Back to the drycleaning machine operation.
Problems with the cooling system are most likely to appear during the dry cycle. To be more
specific, towards the end of the dry cycle when the drycleaning machine goes into cool down
mode.
During the drying mode the heat exchanger coil is transferring much of the heat from the
Freon to the air stream and only a small portion of the heat load is being dumped into the
refrigeration condenser.
In the cooldown mode, solenoids and dampers change and almost the entire heat load is now
dumped into the refrigeration condenser.
This type of problem is indicated by the refrigeration compressor going into a high pressure
condition and tripping the refrigeration high pressure safety switch.
Most of the time this would cause an error message on the programmer screen and require a
manual rest of the refrigeration high pressure safety switch. This condition is almost always
caused by either a clogged Y strainer or excessive scaling inside the refrigeration condenser.
On most drycleaning machines there is a refrigeration head pressure adjusting valve which
controls the refrigeration head pressure by varying flow of coolant to the refrigeration
condenser. This valve is adjusted to give sufficient refrigeration head pressure for efficient
refrigeration system operation.
When scale builds up in the refrigeration condenser past the point for which the normal
adjustment of the head pressure adjusting valve can compensate, many drycleaners simple
open the valve wider in the very mistaken belief they have actually fixed something.
What they have actually done is “kicked the can down the road” and pay a lot of extra money
in solvent and energy for the privilege.
The accompanying illustration shows a schematics for a typical cooling water installation for
use with a water tower or chiller with the addition of valves 1,2,3 which are used when a city
water hook-up is included in the installation. This city water hook-up provides an emergency
back-up for continuing operations when there is a failure in the normal cooling system It will not
help if excessive internal scaling is the cause of the problem.
Hot weather cooling problems
Bruce Grossman is chief
of R&D for EZtimers
Manufacturing, a
manufacturer of the
Sahara and Drop in the
Bucket line of high purity
separator water mister/
evaporators. For more
information on the
EZtimers product line
visit www.eztimers.com.
Questions can be
addressed to
bruce@eztimers.com or
call (702) 376-6693.
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