Glossary for industrial handbook

A

Adsorption charge

In addition to refrigerant, the bulb also contains a solid adsorbent such as charcoal or silica gel. The adsorbed refrigerant reacts more slowly to temperature changes than direct-charged bulbs, and gives a slower response.

Alkalinity

The quantitative capacity of water to neutralize an acid, i.e. the measure of how much acid can be added to a liquid without causing a significant change in pH. Expressed as mg CaCO₃/l.

AMP

Adenosine monophosphate.

ASHRAE

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Asymmetric operation

When the temperature change in a fluid (or the flow) on one side of the brazed plate heat exchanger is much larger than on the other side.

B

B-model

SWEP's standard compact brazed heat exchanger, made of stainless steel 316 and copper.

Back pressure

Higher pressure in the system after the heat exchanger than in the heat exchanger. This pressure prevents the condensate from being drained in steam applications.

Boiling point

See: bubble point.

BPHE

Brazed plate heat exchanger.

Bubble point

The temperature (pressure related) where boiling starts. 100% saturated liquid.

Bulb

A pressure probe connected to the expansion valve in order to control the amount of superheating.

Burnout point

At this point in the boiling process, vapor will form to such an extent that it hinders contact between the liquid refrigerant and the heat transfer area, leading to lower heat transfer efficiency.

C

Carnot heat engine

A heat engine is an engine that uses heat to produce mechanical work by carrying a working substance through a cyclic process. The Carnot heat engine uses a particular thermodynamic cycle, which is a four stage reversible sequence consisting of: 1. Isothermal expansion of the gas at high temperature 2. Adiabatic expansion 3. Isothermal compression of the gas at low temperature 4. Adiabatic compression

Centrifugal compressor

Also called a turbo compressor. Compresses the gas by accelerating it with an impeller. The velocity is then transformed to pressure.

CFC

ChloroFluoroCarbon

CHP

Combined Heat and Power plant, producing both electricity and heat.

Circulation number

In flooded systems, the number of times a specific volume has to pass the evaporator to be fully evaporated.

Cleaning in place (CIP)

The mineral scaling and other fouling that may form in a brazed plate heat exchanger can be removed using this cleaning method.

Close temperature programs

When the primary and the secondary fluid temperatures are close to each other.

Compression ratio

Ratio of condenser and evaporator pressures.

Compressor

Removes refrigerant vapor formed in the evaporator and brings it to a higher pressure. The compressor is usually powered by electricity.

Compressor shut-off valves

Safety devices to protect the system from excessively high or low compressor pressures, i.e. low/high evaporation temperatures. Also: service valves.

Condenser

A heat exchanger turning gas into liquid.

Conduction

Heat transfer through a solid material.

Conductor

Conductors are materials that contain movable electrical charges. When an electrical potential difference is applied across separate points on a conductor, an electric current flows between those points. While many conductors are metallic, there are also many non-metallic conductors.

Convection

Heat transfer by eddies in a fluid.

COP

Coefficient Of Performance. COP is a measure of efficiency, and can be calculated for the chiller, the condenser and the heat pump. COPref = THA/W (=compressor work) and COPhp = THR/W. COPhp = COPref + 1

Critical heat flux

At this point, vapor will form to such an extent in the evaporator that it hinders contact between the liquid refrigerant and the heat transfer area, leading to lower heat transfer efficiency.

Cryogenic

Very low-temperature applications, e.g. liquid nitrogen at -120°C.

Cyclotrons

A cyclotron is a machine for accelerating beams of charged particles. It uses a high-frequency alternating voltage across a magnetic field to spiral the beam outwards and eventually to deflect it once the beam's radius equals it’s the container's. At this point the particles' speed is generally very high (approaching the speed of light). Cyclotrons are used today in the treatment of cancer, because the particles ionize tumors and help to stop or slow cancerous growth.

D

Detergents

Detergents are surface-active agents, substances that lower the surface tension of water.

Dew point

At the dew point, all liquid has evaporated and superheating starts. The gas is 100% saturated.

Direct expansion (DX) system

The basic compression cycle is a DX system. The expansion valve is mounted directly before the evaporator.

E

Electron gun

An electron gun is a component that produces an electron stream with a precise kinetic energy. It is used in all TVs and monitors using cathode ray tube (CRT) technology. The CRT has three electron guns, each producing a different stream of electrons. These make red, green or blue phosphors illuminate, each pixel of the TV screen being made by combining these three colors.

Electronically controlled ON/OFF valves

The electronic ON/OFF valve is actually an electronically controlled solenoid valve that functions both as an expansion valve and as a solenoid valve. When functioning as an expansion valve, ON/OFF control is used.

Evaporator

Heat exchanger turning liquid into gas.

EWT

Entering Water Temperature

Excited state

The energy state of each atom in the active medium (of a gas laser, for example) is characterized by a set of energy states in which it may exist. These states may be visualized as unevenly spaced steps on a ladder, with higher steps representing higher energy states. In stimulated emission, an atom in the excited state is stimulated by the presence of light to fall to a lower energy state, emitting additional light while doing so.

Expansion valve

A valve that maintains the pressure difference between the high-pressure and low-pressure sides in a condenser/evaporator system. See also: valves.

External pressure equalization

An expansion valve with external pressure equalization compares the bulb pressure with the suction line pressure in order to control the superheat. Recommended in connection with brazed plate heat exchanger evaporators due to the extra V-ring pressure drop.

Externally equalized expansion valve

An expansion valve with external pressure equalization compares the bulb pressure with the suction line pressure in order to control the superheat. Recommended in connection with brazed plate heat exchanger evaporators due to the extra V-ring pressure drop.

F

Flooded (wet) evaporator

Generic term for thermosiphons and forced-flow systems. The forcedflow system is similar to a thermosiphon, but the forced-flow system has a pump installed before the evaporator.

Flooded systems

Flooded evaporation is also called wet evaporation. In flooded systems, the refrigerant enters the evaporator as 100% liquid, and the outlet flow may contain liquid. The outlet flow must not be superheated.

Foaming

Droplets of refrigerant entering the oil sump, where they are immediately evaporated.

Footprint

In this context, the floor area underneath a heat exchanger.

Forced circulation systems

The forced-flow system is similar to a thermosiphon, but the forced-flow system has a pump installed before the evaporator.

Forwarding temperature

Temperature of the hot fluid when it enters the device in question (radiator, heat exchanger)

Fouling factors

Contamination factors. Used as a measure of the contamination of (amount of dirt in) a brazed plate heat exchanger.

G

Glide

With reference to refrigerants, glide is a phenomenon that occurs with some mixed refrigerants due to different refrigerants boiling off at different temperatures, i.e. at constant evaporation pressure, the temperature varies.

GWP

Global Warming Potential

H

Halons

Generic term for carbon compounds containing halogens (F, Cl, Br, I)

HCFC

HydroChloroFluoroCarbon

Heat flux

A measure to describe the heat transfer efficiency. The unit for this measure is transferred energy per unit area (kW/m2).

Hermetic compressor

Houses both motor and compressor house inside a welded shell, which provides a truly hermetic seal to the surroundings. The welded shell of a hermetic compressor does not open.

HFC

HydroFluoroCarbon

High-pressure float valve

Located on the high-pressure side of the system and in open connection to the condenser. It controls the evaporator level indirectly by maintaining a constant level of refrigerant inside the float chamber. Float valves can be found in flooded systems.

High-theta pattern

Large-angled "herringbone" pattern. The pressure drop is higher in a brazed plate heat exchanger with a high-theta pattern than in a brazed plate heat exchanger with a low-theta pattern. Increased pressure drop leads to increased turbulence in the fluid = higher heat transfer efficiency.

Hunting

A phenomenon that can happen in (e.g.) steam systems if the condensate drainage is incorrect. Condensate backs-up in the heat exchanger and induces on/off regulation. This leads to wear on the control valve, the risk of cavitation, and temperature fluctuations in the secondary fluid.

Hydraulic block

In a boiler, block consisting of connections to the brazed plate heat exchanger, instead of pipes, in order to save space. It contains a number of functions, such as threeway valve, bypass valve, fill-up valve and temperature sensors.

Hygroscopic

Absorbs water.

I

Indirect

In an indirect system, the fluid is not directly heated by the heating source. The heating source heats an intermediate fluid that heats the fluid by means of a heat exchanger.

Inhibitors

Compounds that make a chemical reaction go more slowly, by obstructing the reaction.

Instantaneous tap water

Hot tap water produced only when the demand occurs (no accumulation).

Internally equalized expansion valve

An expansion valve with internal pressure equalization compares the bulb pressure with the pressure in the gas/liquid line before the evaporator inlet in order to control the superheat. NOT recommended in connection with BPHE evaporators due to the extra V-ring pressure drop.

Isentropic efficiency

Isentropic efficiency = actual work/isentropic work. Isentropic work = no heat losses to the surroundings, no heat gained from the surroundings, no change in entropy during the work process.

L

Lag time

The time a process takes to react to various changes.

Latent energy

The energy that is absorbed or rejected when a phase change occurs between two states of aggregation (gas/liquid/solid).

Latent heat

The heat that is absorbed or rejected when a phase change occurs between two states of aggregation (gas/liquid/solid).

Legionella

Bacteria that develop in stagnant hot water and cause the deadly Legionnaires' disease.

Liquid cooler

Here, a brazed plate heat exchanger being used to cool liquid.

Liquid hammer

In compressors, if a considerable amount of liquid enters the compressor house, a very large pressure can be built up when the piston reaches its top position. This phenomenon is called liquid hammer, and may cause severe damage to the valves or crankshaft.

Liquid heat capacity

Amount of energy needed to increase the temperature of a specific liquid 1 Kelvin.

Liquid line

That part of the refrigeration cycle where the refrigerant is in the liquid phase (after the condenser, before the evaporator).

Liquid line filter driers

Positioned in the liquid line to protect the expansion valve from particle contamination and to absorb potential humidity in the refrigerant. N.B. Creates additional pressure drop.

Liquid static head

A pressure head created by liquid.

Liquid-charged bulb

A liquid-charged bulb has a large charge of refrigerant and will never "run dry". It will always contain both liquid and gaseous refrigerant (see: bulb).

LMTD

Logarithmic Mean Temperature Difference.

Low-pressure float valve

Controls the liquid level in the receiver, and is normally mounted in a chamber parallel to the liquid/vapor separator. Float valves can be found in flooded systems.

Low-theta pattern

Small-angled "herringbone" pattern. The pressure drop is lower in a brazed plate heat exchanger with a low-theta pattern than in a brazed plate heat exchanger with a high-theta pattern. Reduced pressure drop leads to reduced turbulence in the fluid = lower heat transfer efficiency.

LWT

Leaving Water Temperature.

M

Minimum stable signal (MSS)

Thermal expansion valves must always operate with a minimal working superheating to achieve stable regulation. The minimum stable signal (MSS) is sent to the TEV at theminimum superheating.

Modulating electronic expansion valves

Modulating electronic expansion valves are controlled by temperature or pressure sensors.

MOP bulb

An MOP (Maximum Operating Pressure) bulb, also called a gas-charged bulb, has a much smaller quantity of refrigerant mixture inside the bulb than a liquid-charged bulb (see: bulb).

Multi-pass

The fluid passes through more than one channel length before leaving the brazed plate heat exchanger.

N

Nominal operation point

The most usual operating case. The system design case.

NTU

Number of heat Transfer Units, an expression for the thermal length of a plate.

O

ODP

Ozone Depletion Potential

Oil filters

Often installed in the oil return line between the oil separator and the compressor to protect the compressor from contaminants. If this filter is blocked, it can lead to excessive oil carry-over, which affects heat transfer in the evaporator.

Oil separator

Separates oil from refrigerant and returns it to the compressor.

Open compressor

The motor and compressor house are mounted without a shell, although the shaft has a seal.

Opening superheating

The additional superheating (in addition to the static superheating) required to open the expansion valve for operation.

Operating point

In a refrigerant system: the equilibrium point, where the performance of the evaporator matches the performance of the compressor.

Oversurfacing

The overdimensioning of a heat exchanger as a percentage. A heat exchanger with oversurface is larger than is necessary to accomplish the thermal duty.

P

pAlk

The negative logarithm of the alkalinity, expressed as mg CaCO3 /L.

pCa

The negative logarithm of the calcium concentration, expressed as mg CaCO3 /L.

The pH of a solution is the negative common logarithm of the hydrogen ion activity, aH+: pH = -log10 (aH+)

Pinch

The minimum temperature difference between the refrigerant and the secondary fluid in a counter-current condenser.

Positive displacement compressors

Compressors where a certain volume of gas is trapped in a space that is continuously reduced by the compressing device (piston, scroll, screw or similar) inside the compressor.

Pressure gauges

Permanently installed to monitor compressor suction and discharge pressures.

Primary circuit

Intermediate fluid transporting the heat from the heating source to the fluid required to be heated (in heating systems).

The negative logarithm of the content of solid particles in a fluid.

Photovoltaic. A photovoltaic panel converts sunlight into electricity.

R

Radiation

No medium need exist between the two bodies for heat transfer to take place (cf. conduction and convection). In radiation, the intermediaries are photons that travel at the speed of light.

Receiver

Positioned after the condenser. Compensates for varying refrigerant flow in evaporator and condenser systems. Makes subcooling impossible.

Reciprocating compressors

Another name for piston compressors.

Recirculation type evaporator

Flooded evaporator.

Redox potential

The redox potential is a measure (in volts) of the affinity of a substance for electrons compared with hydrogen (which is set at 0), it is the electronegativity of a substance. Substances more strongly electronegative than (i.e., capable of oxidizing) hydrogen have positive redox potentials. Substances less electronegative than (i.e., capable of reducing) hydrogen have negative redox potentials.

Refrigerant

A fluid used in cooling systems, usually with a low boiling point at atmospheric pressure.

S

sSaturation point

A state where a phase change may occur without a change in temperature and pressure.

Scaling

A fouling phenomenon: the inorganic salts dissolved in water precipitate and form a scale on a surface.

Scroll compressors

These capture the gas in the volume formed between one fixed and one orbiting scroll.

Secondary distribution loop

Safety circuit between corrosive/explosive, etc., fluids and the primary circuit. In the event of leakage, the hazardous fluid is confined in an area where it will not do any harm.

Secondary heat exchanger

Transfers the heat from the primary to the secondary circuit.

Semi-hermetic compressor

The motor and the compressor house are located in a two-piece shell. The covers are bolted together.

Semi-instantaneous tap water

Hot water accumulated in a tank to ensure a short response time when a demand occurs.

Sensible energy

The energy added to or rejected from a gas, liquid or solid without a phase change.

Sensible heat

The heat absorbed by or rejected from a gas or liquid without any phase change.

Sight glass

Used for inspection of the refrigerant flow before the expansion valve.

Single-pass

A brazed plate heat exchanger where the fluids pass through the channels only once.

Single-screw compressor

A configuration of a screw compressor consisting of a single screw rotor.

Solenoid valve

The solenoid valve will maintain the pressure difference between the condenser and the evaporator sides during off periods and thereby prevent liquid from flowing into the evaporator.

SSP

The SWEP Software Package.

Stalling point

Condition where the steam pressure inside the heat exchanger is equal to the back pressure in the condensate system.

Static head

Liquid column in a vertical pipe.

Static superheating

The minimum level of superheating that is required to allow the pressure from the bulb to start pushing back the spring and thus opening the expansion valve.

Sub-cooled liquid

When saturated liquid is cooled at constant pressure, its temperature decreases and it becomes subcooled.

Substation

Installation transferring heat from the district heating/cooling network (primary system) to the building network (secondary system).

Suction line

The part of the refrigerant cycle that is located between the evaporator and the compressor. The refrigerant is usually in the state of superheated refrigerant here.

Suction line accumulators

Installed to avoid liquid carry-over to the compressor, which could affect lubrication and, in the worst-case scenario, lead to damage if liquid or oil foam enters the compression chamber.

Suction line filters

Protects the compressor from particle contamination and absorbs potential humidity in the refrigerant. N.B. induces additional pressure drop. The evaporation pressure must be measured before the filter.

Superheated gas

When a dry saturated gas is heated at constant pressure, its temperature rises and it becomes superheated.

Surfactants

Any substance that will reduce water's surface tension is called a surfaceactive agent, or surfactant. Using the analogy of the thin, elastic surface membrane, a surfactant cuts that membrane to ribbons.

System hunting

On-off regulation. See: hunting.

T

Tandem compressors

Two or more compressor working in parallel.

TDS

Total Dissolved Solids

TEV

Thermal Expansion Valve.

TEWI

Total Environmental Warming Impact

THA

Total Heat of Absorption.

Thermocouple

The junction between two metals generates a voltage that is a function of temperature. Thermocouples rely on this effect. Almost any metals can be used to make a thermocouple. Standard tables show the voltage produced by thermocouples at any given temperature.

Thermosiphon systems

A flooded system where no pump is needed.

THR

Total Heat of Rejection.

Triplet compressors

Three compressors in parallel (also called trio).

Twin-screw compressor

Consists of two rotors with matching profiles. The rotor profiles are designed to decrease the volume between them continuously from the inlet to the outlet of the compressor.

Two-pass over one-pass

A brazed plate heat exchanger where one of the fluids passes through the channels only once but the other passes through the channels twice.

Two-phase static head

A pressure head created by a liquid/gas mixture.

V

V-ring

A SWEP distribution device, securing a good distribution of gas and liquid in SWEP evaporators.

Volumetric efficiency

The ratio between the actual vapor volume and the maximum volume that can be theoretically contained in the compressor cylinder.

W

Wankel engines

In the Wankel engine, the four strokes of a typical Otto cycle engine occur sequentially around an oval, unlike the reciprocating motion of a piston engine. In the basic single-rotor Wankel engine, a single oval housing contains a three-sided rotor that turns and moves within the housing. The sides of the rotor seal against the sides of the housing, and the corners of the rotor seal against the inner periphery of the housing, dividing it into three combustion chambers.

Water hammer

Water propelled in the heat exchanger with a high velocity, which causes damage.

Water hammer arrester

Absorbs unstable pressure due to sudden closing of gate, and moderates the impact of the fluid inside the pipe.

Water heater

Provides only hot tap water (cf. boiler, which provides hot tap water and space heating).

Working superheating

The real superheating that can be measured in the system. Working superheating = opening superheating + static superheating.