RACT Unit 22 Flashcards
The condenser is a heat exchange device that _______ heat from the system
rejects
What are the 3 main functions of a compressor in order of occurrence?
- De-superheating the vapour
- Condensing vapours to liquid
- sub cooling the liquid
What main function has the greatest amount of heat absorbed in the system?
When the refrigeration is changing state (vapour to liquid)
The condenser operates at _______ pressures and temperatures than the evaporator and is often located _______
higher, outside
Water cooled condensers can operate at much _____ condensing temps
lower
Because water has a _____ specific heat and density than air, water cooled condensers are more _______ than air cooled
higher, efficient
The condenser also rejects heat picked up in the ______ line, _______ and heat of ______ compression
suction line, compressor, and heat of compression
Three types of water cooled condensers are:
- Tube within a _____ condenser (double tube)
- Shell and ______ condenser
- Shell and ____ condenser
- tube within a tube condenser (double tube)
- shell and coil condenser
- shell and tube condenser
Tube-within-a-tube Condensers:
- Two styles: the ____ type and the _______ type with flanged ends
- Heat exchange takes place between the fluids in the ______ and _______ tube
- Refrigerant flows in the ______ tube
- Refrigerant and water flow in _______ directions to maximize the _______ rate
- coil type and cleanable type
- Inner and outer
- outer tube
- opposite, transfer rate
A tube within a tube condenser is constructed by sliding one tube through another tube. The tubes are _______ in such a manner that the inside tube is ________ from the outside tube
sealed, separated
Mineral deposits:
- Heat from the ________ gas causes minerals to come out of solution
1A) Form scale that adheres to the _____
1A) i) Scale acts as an _______, reducing heat transfer
1B) Water is chemically treated to reduce ______ formation on the interior pipe surfaces
1C) Dirty condensers lead to ____ ______ pressures
1D) Tube within a tube condenser can not be cleaned mechanically with ______
- discharge gas
1A) pipes
1A) i) insulator
1B) scale
1C) high head pressures
1D) brushes
Scale deposits are normally found on the inner ______ tube
water
Cleanable tube-within-a-tube condensers:
- Have end _______, which are removed to access the _______ circuit
- The _________ circuit remains sealed while the ________ circuit is open
- Straight tubes are more expensive, but more easily ________
- ________ pump and chemicals are used to ______ the water tube circuit
- flanges, water circuit
- refrigerant , water
- serviced
- circulator pump, descale
Cleanable Tube-within-a-tube Condensers: Cleaning brush
Parts;
- Rotating _____
- water _____
- flexible _____
- Nylon _______
- rotating brush
- water flush
- flexible shaft
- nylon casing
Shell and Coil Condensers:
- Coil of tubing enclosed in a ________ shell
- Water flows through the _______
- Refrigerant from the comp is discharged into the ______
3A) Shell also acts as a ________ storage tank
- When ref comes in contact with the cool coil, it _________ and falls to the bottom
- This condenser must be cleaned __________
- welded
- coil
- shell
3A) receiver
- condenses
- chemically
Shell and coil condensers:
The hot refrigerant gas is piped into the _______ and the water is contained inside the _______
shell , tubes
Shell and Tube Condensers:
- Most _________ type or condenser
- normally used in _______ installations
- Can be cleaned ____________ with _______
3A) Comp discharge gas is piped into the ______
3A) i) Water flows through the _____ in the cond.
3A) ii) The ends of the shell are removed for _______
3A) iii) The shell acts as a _______ storage tank
- Expensive
- Larger
- Mechanically, brushes
3A) piped
3A) i) tubes
3A) ii) cleaning
3A) iii) Receiver
Four-Pass Shell-and-tube Condenser:
- Water can be circulated back and forth through the condenser by using the ____ _____ to give the water proper direction
- The number of _____ passes will vary with the ____ plate design
- end caps
2. water, end plate design
Wastewater Systems:
- Water used once and then ______ down the drain
1A) Economical of water is _____ or system is _____
1B) Drawback: Water ______ can vary greatly
1C) Amount of water needed depends on the temp difference between the water ____ and _____ of the __________
- wasted
1A) free, small
1B) temperature
1C) in, out, condenser
Wastewater systems: Plentiful water;
Waste water systems are used when water is _______ and at a low _____ such as from a well or lake
plentiful, low cost
Refrigerant-to-water Temperature Relationship for Wastewater Systems:
- Water flow can be varied using a _____- ________ valve with a ________ tap
- Constant _______ pressure maintained by letting more or less water into the condenser as the head pressure changes
- Water ____ temperatures often vary with the ______
3A) Faster inlet when water is ______
3B) Slower inlet when water is _______
- water-regulating valve, pressure tap
- head
- inlet , season
3A) warmer
3B) colder
Re-circulating water systems:
- The water flowing through condenser pumped to a _______ location, ______ , and _______
1A) Design water temp is ___F
1B) A water flow rate of ___ gpm per ton of refrigeration is required to absorb heat
1C) There is a ___F split across the ______ circuit
- remote location, cooled, and reused
1A) 85F
1B) 3.0gpm
1C) 10F, water circuit
Recirculating Water Systems Described:
- The water cooled condenser absorbs _____ from the refrigerant, ______ the water to a cooling tower at a ______ location
- Condenser is located _____ to the compressor and tower is on the ____ outside the structure
- heat, pumps, remote
2. close, roof
Cooling Towers:
- Device that passes outside ____ over ______ to remove system _____
- Capacity limited by the amount of ________ that occurs at any given time
2A) Towers can cool the water to a temp within ___F of the ____ - _____ temp of the air surrounding the tower
- Types; (3)
- air, water, heat
- evaporation
2A) 7F, wet-bulb
- Natural Air, forced draft, evaporative
Forced-Draft Cooling Tower:
- The relationship of a forced-draft cooling tower to the _______ air.
- A) Cooling tower performance depends on the ___-____ temp of the air
1B) This relates to the ______ and the ability of the air to absorb _______
- ambient
1A) wet-bulb
1B) humidity , moisture
Natural-Draft Towers:
- Often made of ___wood, fibreglass or ________ sheet metal
- No ______ to move air through
2A) natural ______ move air through the tower - Water enters the tower from the ____ and is cooled as it falls to the ______
3A) Some _________ in the process, helping to cool the remaining ______ in the tower - Additional water added through a ______ valve
- redwood, fibreglass , or galvanized sheet metal
- No blowers
2A) natural breezes - top, bottom
3A) evaporates, remaining water - float valve
Forced - or Induced-Draft Towers:
- Uses ____ or _______ to move air through
1A) As ______ falls through the tower, air is moved across to air in _______ - Can be located almost ________
- The fan cycled ___ and ____ to maintain the desired ________ temperature
3A) Forced draft: air is _____ through tower
3B) Induced draft: air is _______ through the tower
- fan or blower
1A) water, aid in cooling - anywhere
- on and off, water
3A) pushed through
3B) pulled through
Evaporative Condensers:
- Located ______ cooling tower
- Uses the ______water over and over by means of a ______ located at the tower
- _______ system replaces evaporated water
- Both ___ and ______ used to desuperheat, condense, and subcool refrigerant
- Water allowed to escape on a regular bases to prevent ______ ________
5A) Water escaping is called ____down
- Inside
- same, pump
- Makeup
- air and water
- prevent mineral deposits
5A) blowdown
Air-Cooled Condensers:
- ____ absorbs heat rejected by the system in locations where water is difficult to use
- Horizontal, ______ or _____ intake and top discharge
- Hot gas enters the condenser from the ____
- For standard efficiency systems, the refrigerant will condense at a temp about ___F higher than the outside _______ temperature
- Air
- horizontal, vertical, or side intake and top discharge
- from the top
- 30F higher then outside ambient air temp
Air-Cooled Condensers: Function of Fins;
- Fins are designed to give the coil more _______ ____
- surface area
High-Efficiency Condensers:
- Have _______ surface areas than standard condensers
1A) Allow systems to operate at ______ pressure
1B) allow systems to operate more _________
1C) Can operate with ______ pressure as low as ___F higher than the outside ambient air temp
- large
1A) lower pressure
1B) more efficiently
1C) head pressure as low as 10F
The Condenser and Low Ambient Conditions:
- Condensing temperatures drop when the outside ambient temperature ____
1A) Reduces the ________ pressure on the ____ pressure side of the system
1B) A _______ evap coil may result
- drops
1A) reduces operating pressure on the high-pressure side
1B) starved evaporator coil
Head Pressure Controls: Practical Methods;
Methods to maintain correct head pressure:
- Fan-_____ controls
- Variable-_______ drive (VFD) condenser fan motor controls
- Da_____
- _______ flooding
- Condenser _______
- Fan-cycling control
- Variable-frequency drive
- dampers
- condenser flooding
- condenser splitting
Head Pressure Controls: Fan Cycling Devices;
- Used on _____- cooled condensers
- As head pressure drops, fan cycles ____
- As head pressure rises, fan cycles _____
- Can be added without much ______
- Causes _____ pressure to swing up and down
- Some condensers may have _____ then one fan
6A) May remain on at all times or _____ on/off
6B) Head and ______ pressures will decrease
- air cooled condensers
- cycles off
- cycles on
- without much expense
- head pressure to swing up and down
- more than one fan
6A) cycle on/off
6B) Receiver
Head Pressure Controls: VFD Condenser Fan Motors;
- Vary speed gradually according to _____ pressure or outside ambient temperature _____
- Motor speed changes as the incoming ______ frequency changes
- Keeps a more _______ head pressure
3A) prevents erratic head press changes seen in ____ motor _____ cycling
- head pressure, ambient temp changes
- voltage
- consistent
3A) seen in fan motor cycling
Head Pressure Controls: Air Shutters or Dampers:
- Located at the _____ or the _______
- Operated by pressure-controlled ______
- Provide ____ head pressure control
- Inlet or outlet
- piston
- even
Head Pressure Controls: Air Shutters or Dampers:
With a single fan:
1. Shutter installed over the ____ or over the _____ to the fan
With Multiple fans:
2. Shutter-covered fan operated ___ the _____
2A) Others _____ by pressure or temp
- over the inlet or outlet
- All the time
2A) cycled by press or temp
Head Pressure Controls: Condenser Flooding;
- Causes head pressure to ____
- Accomplished by having enough refrigerant in the system to flood the condenser in the ____ and ____ weather
2A) Requires a _____ ref charge and an _______ liquid receiver
2B) Also required a valve ________ that allows the refrigerant liquid to fill the condenser during mild and cold weather
- rise
- mild and cold
2A) large refrigerant charge and oversized liquid receiver
2B) valve arrangement that allows ref to fill cond during mild and cold weather
Head Pressure Controls: Condenser Splitting;
- Reduces extra refrigerant charge needed for ________ flooding
- ____ the condenser in two separate identical condenser ______
2A) ______/______ condenser, _______ condenser - _______ valve control energized/de-energized by controller sensing outside _____ temperature, an outdoor thermostats or a high-side pressure control
- condenser
- Splits, circuits
2A) Summer/Winter condenser, Summer Condenser
- Solenoid valve control, sensing outdoor ambient temp
Using the Condenser Superheat:
- ___-cooled condensers have ____ discharge temperatures
- Can be captured and redistributed as _____ for the structure in the ______ or to heat ______
- air cooled condensers have high discharge temps
2. captured and redistributed as heat for the structure in water or to heat water
Floating Head Pressures:
- Term used for attaining the _______ possible ________ temperature
- Allows the head pressure to follow the ______ temp without using head pressure _______
2A) TXV and some newer expansion devices can operate with pressure differences as low as ____psig
2B) Systems become ______ efficient since they operate at ______ pressure
- lowest possible condensing temperature
- follow the ambient temp without using head pressure controls
2A) as low as 30 psig
2B) more efficient since they operate at lower pressures
