Page 190 - Boiler_Operators_Handbook,_Second_Edition

Refrigeration & AC 175

and chilled water, the level of the liquid over the tubes in not separated by the oil and rub stationary parts result-
the evaporator, lubricating oil level and oil temperature. ing in rubbing (wiping) metal off the bearings. Some
A centrifugal compressor takes some time to come centrifugal compressors have surge tanks for oil that
to a stop so a problem can occur if all power is lost to provide enough for lubrication on a power failure but
the plant. The result will be loss of lubricating oil pres- others require a UPS (uninterruptible power supply) to
sure before the motor stops turning with wiping of the keep the oil pump running until the shaft stops rotat-
bearings. By wiping I mean the moving metal parts are ing. Modern compressors with magnetic bearings will
also require a UPS. The backup power
in some facilities relies on startup of
emergency generators before the UPS
batteries lose their charge. A very few
units might even have a hand pump
that can be operated to keep the chiller
lubricated until it stops turning. Be
sure your SOPs and disaster plans in-
clude consideration for power loss to
large chillers if you have them.

Absorption Chillers
Every time my lovely wife and I
get ready for a trip I fire up the refrig-
erator in the RV and I do mean light a
fire. Seriously? Yup! That refrigerator
runs on propane. It boils a solution of
ammonia and water to evaporate the
ammonia which is then condensed in
Figure 5-33. Absorption chiller coils on the back of the refrigerator
and flows into the refrigerator where
it evaporates to absorb heat from the
freezer and refrigerator sections. It
uses the principle of partial pressures
to achieve the cooling. The cooling is
achieved because the liquid ammo-
nia enters the evaporator sections that
contain hydrogen gas which provides
a sensation of lower pressure so the
ammonia can evaporate. The evap-
orated ammonia is then absorbed in
water cooled by another coil and the
mixture returned to the furnace sec-
tion to be boiled again. The refrigera-
tor thermostat controls the firing of the
gas. It’s not an efficient cooling device
but it works wherever I go as long as
I keep propane in the tank and have a
charged twelve volt battery to power
the controls.
There’s not much difference be-
tween that RV refrigerator and an ab-
sorption chiller in concept. Size, con-
Figure 5-34. Absorption chiller rear view struction, only chilling water, and effi-