Heating Sources and Refrigeration Flashcards
Natural gas is
Most common
Electricity is
Most expensive
Fuel oil/diesel may be used
in rural locations and is more common outside US
Liquefied Petroleum (LP)
may be used in rural locations
Steam
used in some urban areas (and on Cornell campus by Statler Hotel)
Centralized for heating
for heating, use a boiler to produce hot water and sometimes steam
Heat exchange or heat transfer
when two objects (typically liquid) come near each other and exchange heat
Centralized for chilled water
supplies cold water for water-based centralized HVAC systems
Secondary water
water used for heating and cooling
-chilled water supply and return
-condenser water supply and return
Refrigeration or vapour compression cycle
a circulating refrigerant removes heat from one location and transfers this heat to another location where it is rejected
Heat removal occurs in
the evaporator
Heat is rejected in
the condenser
The compressor provides
the energy necessary to accomplish this heat transfer
The expansion valve controls
the flow of refrigerant through the system
Chillers (and all refrigeration equipment) rely on the
refrigeration cycle
Refrigeration components
- expansion valve (controls flow of refrigerant)
- evaporator (liquid to vapour – super cools)
- compressor (vapour to compressed to hot, high pressure gas)
- condenser (vapour to liquid, hot gas cooled –condenses into liquid state)
Expansion valve/metering device
controls the flow of the refrigerant into the evaporator
Evaporator
refrigerant expands (to fill the space), boils, and evaporates
-refrigerant becomes very cold (below 0ºF) and is now able to absorb heat from space (air or water) you want to cool
-the refrigerant gets warmer and returns to the compressor
Compressor
refrigerant gas is compressed into a hot, high-pressure gas (around 125ºF)
Condenser
compressed gas travels to the condenser where it is cooled by either water or an air fan
-as it cools, it condenses into a liquid state
-refrigerant is now warm, high-pressure liquid (around 110ºF) leaving condenser
Lower pressure is
easier to boil
Higher pressure is
harder to boil
CFC. Chlorofluorocarbons. (“Freon”)
-often hear of R-11, R-12
-very detrimental to the ozone (at 100%)
-Montreal accords. Can no longer be produced. Phased out
of usage in new equipment. (But it is still being used)
HCFCs. Hydrochlorofluorocarbons
-often hear of R-22
-somewhat detrimental to the ozone (at around 5%)
-slated for phaseout by 2020
HFCs. Hydrofluorocarbons
no ozone impact
Other “refrigerants”
Ammonia, sulfur dioxide, carbon dioxide, methane
“Recharge” or Refill refrigerants
Cooling tower
equipment that transfers waste heat into the
atmosphere
-supply cooled water to the condenser in
the Chiller
Cooling tower fill
Forces the hot condenser water (return) to mix with air, promoting evaporation, which cools the condenser water
Cooling towers are large consumers of water because of the
evaporation and “blowdown” loss
