- Humidity – Amount of moisture in the air.
- Calorie – The quantity of heat required to raise the temp of one gram of water one degree celcius.
- Absolute Pressure – psia – Pressure in pounds per square inch above a complete vacuum.
- Gage Pressure – psig – Pressure in pounds per square inch above normal atmospheric air pressure. 14.696 psi
What refrigerant is used in a centrifugal system?
Dielene, R11, R113, Methylene chloride
What is a hermetic compressor?
Motor and compressor in a gas tight housing.
What is a hermetic system?
A closed centrifugal system to include the compressor, condenser and cooler. The refrigerant cools the m
What is a safety head?
A space designed in the head to increase clearance and capacity control.It lifts or expands when a liquid slug of refrigerant enters the cylinder of the compressor and has a discharge valve on a separate plate.
How would you control a compressor capacity?
With the bypass capacity control.
Name three different types of compressors.
Centrifugal, Rotary and Piston type.
What is gallon degrees per minute per ton?
Heat required to raise the flow of one gallon of water per minute one degree Fahrenheit or 8.33 BTUs.
Name 5 types of condensers.
Shell and tube, shell and coil, double pipe, atmospheric, evaporative and air cooled.
How would you control water levels in cooling tower?
Water regulating valve or float valve.
What is the main concern in cooling tower water treatment?
Name the types of evaporators.
Dry or flooded.
What are the two types of refrigeration?
Direct and indirect.
Name the different types of expansion valves.
Hand expansion, cap tube, automatic, thermostatic, high side float and low side float.
- Latent heat – Heat added to or removed from a substance to cause a change of state but not a change in temperature.
- Conduction – Heat transfer by contact.
- Convection – Heat currents between hot and cold.
- Vacuum – Pressure below atmospheric pressure.
- Standard ton of refrigeration – Amount of heat needed to melt one ton of ice in 24 hours or 200/btu per minute or 1200/btu per hour.
- Wet bulb – Temp to include moisture in air.
- BTU – Measurement of the quantity of heat. Amount of heat needed to raise one pound of water one degree. 778 foot/lbs.
- PSIG – Gauge pressure above atmospheric pressure.
What should your temperature rise from the inlet to the outlet of the evaporator be?
About 16 to 18 degrees.
What would be the evaporator pressure of R11 at standard Ton?
What would be the evaporator pressure of ch3cl at standard ton?
What would frost on the evaporator cause?
It would like an insulator and prevent heat transfer.
Give some reasons for low evaporator pressures.
Low refrigerant charge, light load, clogged strainer, bad expansion valve.
What is a liquid seal and where would you find it?
It is a pipe to be extended down in the receiver from the king valve to be submerged in liquid at all times.
Can a safety device and fire valve be on the same pipe?
How is a safety device piped?
From the receiver to the atmosphere / From the compressor to the receiver.
What is the latent of ?
- R11 – 84 BTUs per LB at 5 degrees
- R22 – 93.21
- R717 — 565
- R764(SO2 / Sulfur dioxide) – 169.38
Name some types of compressor valves.
Feather, reed, ring, poppet, diaphragm
What two types of dryers are there and what is there purpose?
Absorbers absorb moisture in the refrigerant and Adsorbers mix and dilute the moisture in the refrigerant.
A cut view of a rooftop package unit.
Cooling Tower Terminology
Approach – difference between cold water temperature and the measured wet-bulb temperature.
Bleed Off – is the circulating water in the tower which is discharged to waste to help keep the dissolved solids concentration of the water below a maximum allowable limit. As a result of evaporation, dissolved solids concentration will continually increase unless reduced by bleed off.
Blowdown – water intentionally discharged from the cooling system to control concentrations of salts and other impurities in the circulating water
British Thermal Unit (BTU) – the heat energy required to raise the temperature of one pound of water one degree Fahrenheit in the range from 32° F to 212° F
Cell – smallest tower subdivision which can function independently
Cold water temperature – temperature of the circulating water leaving the cooling tower
Counterflow tower – design in which air flows upward through the fill section and interfaces counter currently with the down coming hot water.
Crossflow tower – design in which air flows horizontally across the fill section and interfaces perpendicularly with the falling hot water
CTI – Cooling Tower Institute. Organization for testing and certification of cooling towers
Cycles of Concentration – compares dissolved solids in makeup with solids in the circulating water
Drift – water lost from the tower as liquid droplets entrained in the exhaust air stream
Drift eliminators – baffling to control the drift loss in towers
Heat load – heat removed from the circulating water within the tower
Makeup – water added to the circulating water to replace water lost from the system by evaporation, drift, blowdown and leakage
Mechanical draft tower – tower in which a fan moves the air through the fill
Natural draft tower – hyperbolic design in which air moves through the fill because of pressure difference between top and bottom of tower, creating a chimney effect
pH – number between 0 and 14 indicating degree of acidity (below 7) and alkalinity (above 7)
Pumping head – minimum pressure required to lift water from basin level to tower top and force it into the water distribution system
Recirculation air – portion of the exhaust air which reenters the tower measured on the basis of the increase in entering wet-bulb temperature compared to the ambient
TDS – total dissolved solids contained in solution in cooling system water
Ton – an evaporative cooling ton is 15,000 Btu / hr
Water loading – circulating water flow expressed in gal / min per square foot of effective horizontal wetted area of the tower
Wet-bulb temperature – temperature indicated by a psychrometer
This is the formula used to calculate the heating surface of a power plant boiler:
An HRT boiler is 5 ft in diameter and 16 ft long. It contains 60 tubes of 3 inch outside diameter and 2.732 inch inside diameter. Find the boiler-heating surface. Take the inner surface of tubes, half of the shell surface, and two-thirds of the tube plate area, less the area of the tube holes.
Circumference of shell = 5 * 3.14 = 15.700 ft
Half circumference of shell = 15,700 * ½ = 7.850 ft
Area of half of shell = 7.850 * 16 = 125.60 sq. ft
Inner circumference of fire tube = 2.732 * 3.14 = 8.578 in or 8.578 / 12 = 0.7148ft
Surface of one tube = 0.7148 * 16 = 11.437 sq. ft
Surface of 60 tubes = 60 * 11.437 = 686.2 sq. ft
Total area of one tube sheet = 0.785 * 5 * 5 = 19.625
Two-thirds area one tube sheet = 2/3 * 19.625 = 13.083 sq. ft
Area of one tube hole = 0.785 * 3 * 3 = 7.065 sq. in
Area of 60 tube holes = 60 * 7.065 = 423.9 sq. in or 423.9 / 144 = 2.94 sq. ft
Net heating surface of one tube sheet = 13.08 – 2.94 = 10.14 sq. ft
Net surface of two tube sheets = 10.14 * 2 = 20.28 sq. ft
Total net area = 125.60 + 686.2 + 20.28 = 832.08 sq. ft
832 sq. ft