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Glossary – Heat Transfer Terminology

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A

Across the line starter

Motor starter used to immediately change the input current from 0 to 100%.

Adiabatic fluid cooler

Outdoor equipment using forced air over air-to-fluid heat exchanger to cool a process fluid. Uses air drawn through water moistened medium. As water evaporates from medium, it cools before entering air-to-fluid heat exchanger. Used to achieve fluid temperatures lower than ambient air temperatures.

Air-cooled condenser

Condenser using forced air over air-to-fluid heat exchanger to reject heat from refrigeration circuit.

Alarm

Condition in process equipment that forces a stop in operation to avoid damage.

Ambient temperature

Temperature of the air surrounding an area or piece of equipment


B

Brazed plate heat exchanger

Variation of plate type heat exchanger with permanently fused plates eliminating need for frame. Extremely compact and energy efficient.

British thermal unit (BTU)

Unit of energy measure to increase 1 lb of water by 1°F - imperial system.


C

CE

Mark that designates compliance with European Union requirement for products sold in Europe.

Centrifugal compressor

Type of non-displacement compressor using a spinning impeller to create outward force in volute to achieve compression.

Chiller

Equipment using refrigeration as the means to reject heat from a process system.

Chiller or cooling ton

Nominal rating for heat rejection capacity of a chiller. Based on about of energy required to melt 1 ton (2,000 lbs) of ice in 24 hours. 12,000 Btu/hr

Compressor

Component of refrigeration circuit acting as a pump to circulate refrigerant and adds pressure and heat.

Condenser

Component of refrigeration circuit used to reject heat from chiller.

Cooling tower

Equipment using evaporation as the means to reject heat from a process system.

Cooling tower ton

Informal variation of cooling ton that accounts for heat of compression added by a refrigeration compressor. 15,000 Btu/hr

Cubic feet per minute (CFM)

Flow rate measurement of gas.


D

Delta T

Temperature differential measured across an item.

Dew-point temperature (DP)

The temperature when moisture leaves the air and will condense on objects that are at or below that temperature, just as dew forms on grass and plant leaves.

Dry-bulb temperature (DB)

Read from an ordinary thermometer equipped with a “dry bulb” is basically the temperature of “ambient air”, un-effected by moisture.

Dry fluid cooler

Dry fluid cooler designates that the design does not utilize an adiabatic system.

Dual circuit chiller

Chiller with two refrigeration and two water loops, completely independent and implemented for increased efficiency and redundancy.


E

ECWT

Entering condenser water temperature

Electronic expansion valve (EEV)

Component of refrigeration circuit controlling the amount of refrigerant released into the evaporator to regulate superheat of vapor leaving evaporator. Precisely controlled via programming logic and pressure sensors.

Evaporator

Component of refrigeration circuit used to transfer heat from process fluid into chiller.

Expansion valve

Component of refrigeration circuit used to meter refrigerant to the evaporator, removes pressure to change state from liquid to vapor. See electronic and thermostatic for types.


F

Full load amps (FLA)

Used for load calculations.

Fluid cooler

Outdoor equipment using forced air over air-to-fluid heat exchanger to cool a process fluid. Cooling capacity relies mainly on air flow, heat exchanger surface area, and ambient air temperature.

Full divider

Partition used in dual well tank to physically isolate the fluids in each well, eliminates any mixing.


G

Gallon per minute (GPM)

Flow rate measurement of fluid.

Glycol

Chemical added to water to protect from freezing. Percentage of concentration affects minimum allowable temperature.


H

Heat exchanger

Equipment used to transfer energy from one medium to another. See brazed plate, plate and frame, shell and tube for types.

Hot gas bypass

Method of capacity control to add false load on an evaporator. Ensures compressor operates continuously avoiding cycling and maintaining temperature control.

Human Machine Interface (HMI)

Display of PLC input and outputs for operator’s control.


I

Integrated part load value (IPLV)

Measurement of efficiency for chillers, fixed set point of 44°F.


J

Joule

A basic unit of thermal energy equal to the work done by a force of one newton acting through a distance of one meter.


K

Kilowatt (kW)

Unit of measure of power (energy transfer rate) equal to joule/second - metric system.


L

Latent energy

Energy absorbed or released by a change of matter's state, i.e. - evaporation from liquid to gas absorbs latent energy.

Leaving water temperature (LWT)

also set point.

Low ambient design

Modifications made to a chiller to allow startup and operation in cold temperatures. Typically addresses temperatures from 65°F down to -20°F.


M

Magnetic bearings

Component used to eliminate contact surfaces of traditional bearings. Allows elimination of oil from system.

Maximum overcurrent protection (MOCP)

Used to determine maximum breaker or fuse rating.

Mechanical contactor

Relay using coils, magnetic fields, springs, and mechanical contacts to switch a supply.

Minimum circuit ampacity (MCA)

Used to determine main power wire size and guarantee wiring will not overheat under expected operating conditions.


N

Nominal capacity - Rating of chiller or cooling tower based upon agreed upon conditions such as set point and ambient air temperature.

Non-standard part load value (NPLV)

Measurement of efficiency for chillers, set point is selected.


O

Off Cycle

That time period of a refrigeration cycle when the system is not operating.


P

Partial divider

Partition used in dual well tank to thermally isolate the hot and cold wells while allowing equalization when the flow rates out of each well are unequal.

Pitch (piping)

Proper slope of gravity drain piping to ensure adequate flow.

Plate and frame heat exchanger

Heat exchanger using plates mounted on a frame that are mechanically sealed with tightened endplates. Cleanable and efficient.

Pounds per square inch (PSI)

Pressure measurement.

Pressure transducer

Sensor that converts pressure into an analog electrical signal, often used with variable speed drives for pumping systems.

Programmable Logic Controller (PLC)

Industrial computer control adapted for manufacturing or other automated applications.


R

Reciprocating compressor

Type of positive displacement compressor using piston(s) and cylinder(s) to achieve compression.

Relative humidity (RH)

The ratio of how much moisture is in the air divided by the maximum amount of moisture that air can hold. Note below that a fixed amount of moisture in the air changes the “relative” humidity based on the dry bulb temperature of that air. Warmer air can hold a greater volume of moisture.

Remote air-cooled condenser

Air-cooled condenser separated from chiller, installed in a different location, typically outdoors, to allow heat rejection in a preferred location.

Resistance temperature detector (RTD)

Probe that uses linear resistance change to measure temperature.

Return water temperature (RWT)

Riser drain

Piping used to protect the supply line to an elevated cooling tower from freezing. Installed before the supply line exits the building to gravity drain fluid exposed to outside ambient temperatures when system is off.


S

Screw compressor

Type of positive displacement compressor using rotary screws in a continuous sweeping motion to achieve compression.

Scroll compressor

Type of positive displacement compressor using circular motion of two scroll plates (one moving, one fixed) to achieve compression.

Sensible energy

Energy absorbed or released by the change in temperature of a matter state without change the state, i.e. - raising temperature of water from 50°F to 60°F absorbs sensible energy.

Set point

Desired temperature exiting a chiller, cooling tower, or fluid cooler. Input by user and controlled to by equipment.

Shell and tube heat exchanger

Heat exchanger using shell vessel with internal pipes (or tube bundles). Large passageways allow contaminated fluids without risk of clogging.

Short cycling

Occurs when a compressor regularly experiences low load and must shut off to avoid over cooling.

Single circuit chiller

Chiller with one refrigeration and one water loop.

Soft start starter

Motor starter used to ramp up the current into the motor, avoid peak amperage spikes.

Solid state relay (SSR)

Relay with no moving parts using electrical and optical properties of solid state semi-conductors to perform input and output isolation.

Strainer

Device used to provide filtration for medium.

Sub-cooling

Cooling of refrigerant liquid below its boiling temperature.

Superheat

Heating of refrigerant gas above its boiling temperature.


T

Tank residency

Amount of time water is designed to remain in a tank, used to predict turnover period for tank volumes.

Thermal conductivity

Property of a material's ability to conduct heat.

Thermostatic expansion valve (TXV)

Component of refrigeration circuit controlling the amount of refrigerant released into the evaporator to regulate superheat of vapor leaving evaporator. Controlled via sensing bulb logic mechanically actuating expansion valve.


U

Underwriters Laboratories (UL)

A third party approval agency for components and finished goods.


V

Variable frequency drive (VFD)

Component used in motor speed control by modulating frequency.

Variable speed control

Method of capacity control to adjust a motor's input frequency to match the demand. Commonly used for pumps, fans, and compressors in process cooling systems.

Viscosity

Measure of a fluid's resistance to flow.


W

Warning

Condition in process equipment that notifies operator of potential condition for pending alarm scenario.

Water-cooled condenser

Condenser using water-to-fluid heat exchanger to reject heat from refrigeration circuit.

Wet bulb temperature (WB)

Using the same thermometer as a dry bulb, but now equipped with a dampened wick on the bulb. The difference between the wet bulb and dry bulb temperatures is caused by the cooling effect of the evaporation of moisture from the wick. This evaporation effect reduces the temperature of the bulb’s temperature reading.