HVACR UNIT 14
How much would system capacity be increased by subcooling the liquid refrigerant leaving the condenser an extra 12°F?
12°F × 0.5%/°F = 6% increased capacity
How much heat is rejected through condensation?
80%
If the refrigerant condensing saturation temperature is 100°F at the start of the process, what would the entering water temperature be?
80°F
If the temperature of the refrigerant in a water-cooled system is 95°F, what is the temperature of the leaving water?
85°F
If the water entering a water-cooled condenser is 80°F, what would the leaving water temperature be?
90°F
How many BTUs does each pound of water evaporating remove?
970
Which type of condenser uses a fan to push air across the condenser?
A forced-draft air-cooled condenser
Which type of condenser is on the back of a non-frostfree refrigerator?
A natural-draft air-cooled condenser
What is the difference between the compressor operating temperatures in an air-cooled condenser and a water-cooled condenser?
A water-cooled condenser operates 15°F below an air-cooled condenser.
The three basic types of condensers used with HVACR systems are:
Air cooled, water cooled, and evaporative.
Compared to other coil constructions, microchannel coils:
Are much smaller for the same capacity.
What is the best pH level to maintain in a water tower?
Between 6.5 and 9
Cooling towers in which the water circulating in the tower is separate from the water circulating through the condenser are called:
Closed-loop cooling towers.
Why do some commercial buildings need air conditioning in the winter?
Commercial buildings often have large internal heat loads from people, lights, and machines.
Fan cycling, fan speed control, damper control, and condenser flooding are different types of:
Condenser low ambient controls.
The first check to make whenever working on a water-cooled system is:
Condenser water flow.
How can tube-in-tube condensers become contaminated?
Cross-contamination can occur if the inside tube leaks.
As it passes through the condenser, the refrigerant is:
Desuperheated, condensed from a gas to a liquid, and subcooled.
The main cause of high condensing temperature and pressure in air-cooled condensers is:
Dirty condensers.
Subcooling the liquid refrigerant increases system efficiency by:
Ensuring a solid stream of liquid to the metering device.
The heat rejected by the condenser:
Equals the heat absorbed by the evaporator plus the heat added by the compressor.
The fins on finned tube coils increase heat transfer by:
Increasing the surface area exposed to the air.
What is the purpose of a cooling tower?
It cools the water flowing through it by evaporating a small portion of the water.
In a water-cooled condenser, what do an increase in head pressure and an increase in temperature difference across the condenser indicate?
Low water flow
The purpose of the condenser in a refrigeration system is to:
Reject heat from the refrigerant.
The primary cause of high condensing temperatures in water-cooled condensers is:
Scaled and fouled condenser surfaces.
In a water-cooled condenser, what do an increase in head pressure and a decrease in temperature difference across the condenser indicate?
Scaling on tubing
What is the primary difference between air-cooled condensers on lower-efficiency systems and those on high-efficiency systems?
The coil size is increased to increase the heat-transfer area.
What is the primary advantage of a remote air-cooled condenser on an ice machine?
The heat generated by the ice machine is expelled outside instead of into the kitchen.
If the refrigerant is recovered improperly from a water-cooled condenser:
The water may freeze.
How can scaling be reduced in water towers?
There is a small amount of water drained off the cooling tower sump.
How can water-tubing fouling be prevented in tube-and-shell water-cooled condenser systems?
Through annual draining of the water, removing access plates, and running brushes through the water tubes
Why do water and refrigerant flow in opposite directions in tube-in-tube condensers?
To increase efficiency
What is the purpose of low ambient controls for air-cooled condensers?
To maintain a minimum head pressure, even at lower-than-normal operating conditions
Why are biocides added to cooling-tower water?
To reduce biofilm
The three types of air-cooled condenser coil construction found on residential air-conditioning units today include:
Tube-and-fin, spine-fin, and microchannel.
Why are wastewater systems no longer allowed in some areas of the country?
Water resources are becoming increasingly scarce.
Which type of condenser generally operates with a lower discharge pressure?
Water-cooled condensers
Which type of condenser requires the most maintenance?
Water-cooled condensers
Tube-in-tube, shell-and-coil, and shell-and-tube are all different types of:
Water-cooled condensers.
An evaporative condenser:
Works by evaporating water to cool the condenser coil.
Water conditions that must be monitored to keep a cooling tower system working properly include:
pH, mineral content, and biological growth.
