Manual de Instalação - Danfoss

8/14/2019 Manual de Instalao - Danfoss

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REFRIGERATION AND

AIR CONDITIONING

Automation of

Commercial Refrigeration Plant


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The purpose of this manual is to show someexamples of the use of Danfoss automatic

controls for commercial refrigeration plants.A simple, hand-regulated plant is used as thestarting point of a step-by-step automation and ashort description of the function of each control isgiven.

For additional training material we refer tohttp://rc.danfoss.com/SW/RC_Training/En/Index.htm

Automation of commercial

Refrigeration Plant


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Danfoss A/S (RC-CMS / MWA), 03 - 2004 RG00A502 1

Contents Page

Hand-regulated refrigeration plant.....................................................................................................................................................................................................2Refrigeration plant with thermostatic expansion valve and air-cooled condenser .............................................. .................................................... ........ 3

Refrigeration with Finned evaporator......... .................................................... ..................................................... ..................................................... ......................... 4

Thermostatic expansion valve ................................................... .................................................... ..................................................... ........................................... 5

Thermostatic expansion valve with distributor.......................................................................................................................................................................5

Expansion valves.................................................................................................................................................................................................................................6

Thermostatic expansion valve, method of operation ................................................... .................................................... .................................................... 7Thermostatic expansion valve with MOP charge....................................................................................................................................................................8

Combined high and low pressure control.................................................................................................................................................................................9

Low-pressure and High-pressure control ............................................... ..................................................... ..................................................... ......................... 9

High-pressure control, method of operation ................................................. ..................................................... ..................................................... ..............10

Thermostat..........................................................................................................................................................................................................................................11

Filter drier .............................................. ..................................................... .................................................... ..................................................... ................................11Sight glass ............................................. ..................................................... .................................................... ..................................................... ................................11

Automatic water valve....................................................................................................................................................................................................................12

Finned evaporator............................................................................................................................................................................................................................13

Refrigeration plant with oil separator and heat exchanger......................................................................................................................................................14

Oil separator...... .................................................... ..................................................... ..................................................... ..................................................... ..............15Heat exchanger.................................................... ..................................................... ..................................................... ..................................................... ..............15

Refrigeration plant for a larger cold store ............................................. ..................................................... ..................................................... ................................16

Shut-o valve.....................................................................................................................................................................................................................................17

Solenoid valve....................................................................................................................................................................................................................................17Key diagram, control current for refrigeration plant, g. 20 ............................................... ..................................................... .........................................18

Motor starters .............................................. ..................................................... ..................................................... ..................................................... .......................19Central refrigeration plant for cold store temperatures above freezing point............................................... ..................................................... ..............20

Evaporating pressure regulator...................................................................................................................................................................................................21

Check valve................................................... ..................................................... ..................................................... ..................................................... .......................21

Key diagram, control current for refrigeration plant g. 25 ................................................ ..................................................... .........................................22

Refrigeration plant for freezer display counter ............................................ ..................................................... ..................................................... .......................23

Dierential pressure control.........................................................................................................................................................................................................24Crankcase pressure regulator.......................................................................................................................................................................................................25

Condensing pressure regulator...................................................................................................................................................................................................25

Dierential pressure valve.............................................................................................................................................................................................................26

Evaporator thermostat ............................................... ..................................................... ..................................................... ..................................................... .....26

Key diagram, refrigeration plant for freezer display counter, g. 29 ................................................. ..................................................... .......................27

Main wiring diagram for contactors ................................................ ..................................................... ..................................................... ................................28Refrigeration plant for ventilation air ............................................. .................................................... ..................................................... .........................................29


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Manual Automation of Commercial Refrigeration Plant

Hand-regulatedrefrigeration plant

A hand-regulated refrigeration plant is usuallybuilt up of these components:

Compressor (1)

Condenser (2)

Evaporator (3)

In order to maintain the cold store temperature tr

at the desired level, it is necessary to equip the

plant with adjustable valves (4) and (5) in thatchanges in the loads on the evaporator andcondenser under varying refrigeration demandscan be reckoned on.

For example, the plant will be unable to maintainthe same temperature summer and winter withpermanently set regulating valves and acontinuously operating compressor. This caneasily be shown graphically, as illustrated in g. 1.

The full lines represent summer operation andthe dotted lines winter operation, (e.g.condensing temp. winter +25C, summer +35C).

The C-curves represent compressor capacity,

which rises with increasing evaporating

temperature to. The E-curves represent eva-

porator capacity, which rises with the increasingtemperature dierence t

r- t

obetween room

temperature (tr) and evaporating temperature

(to). Where the C-curve (winter operation) and

E-curve (summer operation) intersect each other,compressor, condenser and evaporator capacitiesare in equilibrium.

As can be seen from g. 1, the room temperaturewill fall from t

rto t

r' when refrigeration demand

falls from Qo in summer to Qo' in winter. To meetthis condition the capacities of the compressor,condenser and evaporator must be adjusted, forexample by regulating the compressor operation,and by throttling the water ow to the condenserand refrigerant liquid ow to the evaporator.

Fig. 1


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Refrigeration plant withthermostatic expansionvalve and air-cooledcondenser

In this plant an air-cooled unit has replaced thewater-cooled condenser. Air-cooled condensersare normally used where no cooling water isavailable or where the use of cooling water isforbidden.

Replacing the manual valve ahead of theevaporator with a thermostatic expansion valve(pos. 1) ensures that the evaporator iscontinuously supplied with the amount ofrefrigerant necessary to keep a constant

superheat in proportion to the load.

This of course presupposes that the selectedexpansion valve suits the evaporator concerned.A factor here is that in conditions of maximumload the expansion valve supplies precisely theamount of refrigerant the evaporator is able toevaporate. In addition the superheat setting ofthe valve must match the evaporator.Superheat is generally understood as being thenumber of C the evaporator has minus theboiling point of the medium at the existingpressure and with all liquid evaporated.

Superheat in an evaporator is dened ast

1 p

s= C superheat, where t

1is the temperature

measured at the point on the evaporator wherethe expansion valve sensor is placed, and p

sis the

pressure measured at the same point. ( Therelevant pressure is converted to C).

For further details on superheat, see page 7.

Fig. 2

Thermostatic expansion valve

Automatic expansion valve


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Refrigeration with Finnedevaporator

Thermostat type KP 61 (1) cuts the fans (2) in andout depending on the room temperature.

Thermostatic expansion valve type TE (3) withexternal pressure equalization regulates liquidinjection in the evaporator, dependent on thesuperheat but independent of the pressure dropacross the evaporator.

Liquid distributor type 69G (4) distribute refri-gerant liquid equally to the individual evapo-

rator sections.

The compressor is cut in and out on the low-pressure side of the combined high and lowpressure control type KP 15 (5) depending on thesuction pressure. In addition, the high-pressureside of this control gives protection against toohigh a condensing pressure by cutting out thecompressor if it becomes necessary (e.g. whenthe ventilator is defected or the airow is blocked(dirt)).

Sight glass type, SGN (6) indicates too highmoisture content in the refrigerant and too littleow to the thermostatic expansion valve. Theindicator changes colour when the moisturecontent is too great. Vapour bubbles in the sightglass can mean insucient charge, insucientsub cooling or partial clogging of the strainer.

Fig. 3


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Thermostatic expansionvalve

Thermostatic expansion valve type T 2, the bulbof which is placed immediately after theevaporator, opens on rising superheat. Pressureon the diaphragm (1) increases as bulbtemperature increases and pressure under thediaphragm increases as the evaporatingtemperature increases.

The pressure dierential, which corresponds tothe refrigerant superheat, manifests itself as aforce, which tries to open the valve against the

opposite force of the spring (2). If the dierential,i.e. superheat, exceeds the spring force the valvewill open.

The orice assembly, with orice (3) and valvecone (4) can be changed. To suit capacityrequirements, there are eight dierent sizes tochoose from.

Fig. 4

T 2

Thermostatic expansionvalve with distributor

Fig. 5

TE 5 + 69G

Distributor type 69G ensures an equal distri-bution of refrigerant to the parallel sections ofthe evaporator.

The distributor can be installed either direct onthe thermostatic expansion valve as shown or inthe line immediately after it. A distributor oughtalways to be tted so that the liquid ow throughthe nozzle in the distributor pipes is vertical. Thisensures that the eect of gravity on liquiddistribution is as little as possible. All distributionpipes must be exactly the same length.

For evaporators with a large pressure drop,thermostatic expansion valves with externalpressure equalization must always be used.Evaporators with liquid distributors will alwayshave a large pressure drop; therefore always useexternal pressure equalization.


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Expansion valves

Upper diagram:The diagram shows an evaporator, which is fed by athermostatic expansion valve with internal pressureequalization.

The degree of opening of the valve is regulated by:Pressure p

bin the bulb and capillary tube acting

on the upper side of the diaphragm anddetermined by the bulb temperature.

Pressure po

in the valve discharge connectionacting under the diaphragm and determined bythe evaporating temperature.

Spring pressure ps

acting under the diaphragmand manually adjustable.

In the example shown, the pressure drop in theevaporatorp is measured in C refrigerant pressure15 (20) = 5C. Provided that the valve spring hasbeen manually adjusted to a pressure p

s

corresponding to 4C, it follows - in order to achieveequilibrium between the forces acting over andunder the diaphragm - thatp

b= p

o+ p

s~ 15 + 4 = 11C.

That is, the refrigerant has to be superheated by 11 (20) = 9C before the valve begins to open.

Lower diagram:The same evaporator coil, but this time fed by athermostatic expansion valve with external Pressureequalization connected to the suction line after thebulb.

The degree of opening of the valve is now regulatedby:

Pressure pb

in the bulb and capillary tube actingon the upper side of the diaphragm anddetermined by the bulb temperature.

Pressure p

o- p in the evaporator outlet acting

under the diaphragm and determined by theevaporating temperature and the pressure dropin the evaporator.

Spring pressure ps

acting under the diaphragmand manually adjustable.

Provided that, as stated above, pressure drop p inthe evaporator corresponds to 5C and springpressure p

sin the valve to 4C refrigerant pressure, it

follows that pb

= po

p + ps

~ 15 5 + 4 = 16C.That is, the refrigerant now has to be superheatedby 16 (20) = 4C before the valve begins to open.

The amount of charge in the evaporator and henceits capacity become higher since a smaller portion ofthe evaporator surface is used for superheating.

Fig. 6

Conclusion:Thermostatic expansion valves with external pressure equalizing must always be used for evaporators with alarge pressure drop. Evaporators with a liquid distributor will always have a large pressure drop; thereforealways use external pressure equalization.


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Thermostatic expansionvalve, method of operation

Fig. 7

The thermostatic expansion valve is controlled bythe dierence between bulb temperature t

band

evaporating temperature to. The valve opens

when the temperature dierential rises, tb

to

=t, i.e. when refrigerant superheat rises the valvewill have a larger opening rate. See g. 6.

Solid curve po

and dotted curve pb

gives vapourpressure for the refrigerant and chargerespectively. Chain-dotted curve p

o+ p

s

represents the refrigerant vapour pressure curvep

ooset in parallel with a constant spring

pressure ps, the factory setting for example.

At a given evaporating temperature, to, a pressure

po

+ ps

acts under the valve diaphragm and triesto close the valve. Pressure p

bacts over the

diaphragm and tries to open the valve.

The gure shows equilibrium between po

+ ps

and pb

at evaporating temperature to

and bulbtemperature t

brespectively. Practically speaking,

dierential tb

to, the static superheat, is the

same within the entire working range of the valvefrom to' to to".

That is to say, irrespective of the evaporatingtemperature operated with inside the workingrange, the thermostatic expansion valve willregulate liquid injection so that refrigerantsuperheat after the evaporator is held to thevalue determined by spring pressure p

s. If the

dierential between bulb temperature tb

andevaporating temperature t

ois less than the static

superheatt, the valve is closed (tb

to

< t; pb

t; pb

> po

+ ps).

If the dierential between bulb temperature tb

and evaporating temperature to

is equal to thestatic superheat t, the valve is just about toopen or just about to close (t

b t

o= t; p

b=

po

+ ps).


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Thermostatic expansionvalve with MOP charge

Fig. 8

It can sometimes be desirable to use athermostatic expansion valve with a limitedworking range - for example, in refrigerationplant with only one evaporator where coolingfrom a completely or partially temperatureequalized condition occurs only as an exception(after repair or defrosting).

For such plants it may be cheaper to use a smallercompressor motor dimensioned in accordancewith the load after cooling down. However,during cooling down such a motor will becomeoverloaded and cut-out on the thermal overloadprotection.

To eliminate this risk, a thermostatic expansionvalve with a MOP (Maximum Operating Pressure)charge can be used. This pressure-limited valvewill only begin to open at a low evaporatingtemperature, t

MOP, since the charge is adapted to

produce a bend in the vapour pressure curve Pb.

This means that static superheat t is very high atevaporating temperatures higher than t

MOP

, i.e. inpractice the valve will remain closed until thecompressor has reduced the suction pressuresuciently to ensure that the electric motor isnot overloaded.


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Combined high and lowpressure control

Low-pressure side (LP):The LP connector (10) is connected to the suctionside of the compressor. When pressure falls on

the low-pressure side the circuit betweenterminals 2 and 3 is broken. Turning the LPspindle (1) clockwise adjusts the unit to cut out(break the circuit between terminals 2 and 3) at ahigher pressure. Turning the dierential spindle(2) clockwise adjusts the unit to cut in again(make the circuit between terminals 2 and 3) at asmaller dierential.Start pressure = stop pressure + dierential.LP signal function between terminals A and B.

High-pressure side (HP):The HP connector (11) is connected to thedischarge side of the compressor. When pressure

rises, on the high-pressure side the circuitbetween terminals 2 and 3 is broken. Turning theHP spindle (5) clockwise adjusts the unit to cutout (break the circuit between terminals 2 and 3)at a higher pressure. The dierential is xed.Stop pressure = start pressure + dierential.

Low-pressure and High-pressure control

Fig. 9

KP 15

Combined high and low pressure control

type KP 15 has a single-pole changeover

switch (12).

Fig. 10

Low-pressure control type KP 1Contains a single pole changeover switch (SPDT),which breaks the circuit between terminals 2 and3 when pressure in the bellows element (9) fails(on failing suction pressure), i.e. the connector(10) must be connected to the suction side of thecompressor.

Turning the range spindle (1) clockwise adjuststhe unit to cut in - to make the circuit betweenterminals 2 and 3 at a higher pressure. Turningthe dierential spindle (2) clockwise adjusts theunit to cut out again - to break the circuitbetween terminals 1 and 2 at a smallerdierential.

Start pressure = stop pressure + dierential.

High-pressure control type KP 5Is built up in the same way. Bellows, spring andscale are of course suitable for the higherworking pressure. In this case, the switch breaksthe circuit between terminals 1 and 2 whenpressure rises in the bellows element (9), i.e.when condensing pressure rises (the connectormust be connected to the discharge side of thecompressor ahead of the shut-o valve).

Turning the range spindle clockwise adjusts theunit to cut out - to break the circuit betweenterminals 1 and 2 at a higher pressure. Turningthe dierential spindle (2) clockwise adjusts theunit to cut in again - to make the circuit between

terminals 1 and 2 at a smaller dierential.Stop pressure = start pressure + dierential.


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High-pressure control,method of operation

High-pressure control type KP 5 is connected tothe high-pressure side of the refrigeration plantand stops the compressor when the condensing

pressure becomes too high. The control containsa pressure-controlled single- pole changeoverswitch (SPDT) where the contact positiondepends on the pressure in the bellows (9). Seeg. 11, drawings A and B.

Via the adjusting spindle (1) the main spring (7)can be set to exert a suitable counter- pressure tothe bellows pressure. The down-ward resultant ofthese two forces is transferred by a lever (21) tothe main arm (3), one end of which is tted with atumbler (16).

The tumbler is held in position on the main armby a compressive force, which can be adjusted byusing the spindle (2) to change the pull from thedierential spring (8).

The forces from the bellows pressure, main springand dierential spring are thus transferred to thetumbler (16), which will tilt when the forces comeout of equilibrium because of changes in thebellows pressure, i.e. the condensing pressure.

The main arm (3) can only take up two positions.In one position a force is exerted on each end ofthe arm and creates opposite torques around itspivot (23). See drawing A. If the bellows pressuredecreases, the main spring exerts an increasing

force on the main arm. Finally, when the countertorque from the dierential spring is overcome,the main arm tilts and the tumbler (16)instantaneously change position so that thecompressive force of the dierential spring lieson a line near the arm pivot point (23). Thecounter-torque from the dierential spring thusbecomes almost zero. See g. 11, drawing B.

The bellows pressure must now rise to overcomethe force from the main spring because thespring force torque around the pivot point (23)must also fall to zero before the snap system canreturn to its initial position.

On falling bellows pressure (see g. 11, drawingA), the main arm moves instantaneously to theposition shown in g.11, drawing B when thebellows pressure is reduced to the stop pressureminus the set dierential pressure.

Conversely, the main arm moves instantaneouslyfrom the g. 11, drawing B position to the g. 11,drawing A position when the bellows pressure

has risen to the stop pressure = start pressure +dierential pressure. See also text for gs. 9 and10 regarding adjustment of type KP.

The contact system is specially designed so thatthe make contact travels at the initial speed ofthe snap action until it reaches the xed contact,while the break contact separates from the xedcontact at the maximum speed of the snapaction. The system has been made possible bythe use of a small striker (19) and accuratelymatched contact springs.

The contacts (20) make with a smaller force thanthey break, which means that in practice bounceduring make is eliminated. The holding forceduring make is exceptionally high. At the sametime the system gives an instantaneous breakfunction so that the holding force is maintained100% right up to break. For these reasons thesystem is able to operate with high currents andits function is not impaired by shocks. Comparedwith traditional designs, the system has givenexceptionally good results in practice.

Fig. 11


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ThermostatFig. 12

KP 61

Thermostat type KP 61, which has a single polechangeover switch (12), makes the circuitbetween terminals 2 and 3 when bulbtemperature rises, i.e. when room temperaturerises.

Turning the range spindle (1) clockwise, increasesthe cut-in and cut-out temperature of the unit.

Turning the dierential spindle (2) clockwise

decreases the dierential between cut-in andcut-out temperatures.

Filter drierFig. 13

DML / DCL

Filter drier type DML / DCL has a sintered charge,a so-called solid core (3). This is pressed by thespring (2) against the polyester mad (4) andcorrugated perforated plate (5).

The charge or core in the lter drier consists ofmaterial which eectively removes moisture,harmfull acids, foreign particles, sediment andthe products of oil breakdown.

Sight glassFig. 14

SGI

Sight glass type SGI / SGN has a colour indicator(1) that changes from green to yellow when themoisture content of the refrigerant exceeds thecritical value. The colour indication is reversible,i.e. the colour changes back from yellow to greenwhen the plant has been dried, e.g. by replacingthe lter drier.

Sight glass type SGI is for CFC, sight glass typeSGN is for HFC and HCFC (R 22).


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Automatic water valveFig. 15

WVFX

Automatic water valve type WVFX opens onrising pressure in the bellows element (1), i.e.when condensing pressure increases (theconnector on the bellows housing must beconnected to the refrigerant side of thecondenser).

Turning the hand wheel (2) counter clock-wisetightens the spring, which means that the valvewill open at a higher condensing pressure. If the

hand wheel is turned clock-wise the valve willopen at a lower condensing pressure.


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Finned evaporatorFig. 16

The nned evaporator is designed for forced aircirculation over the parallel evaporator coils. Theair circulation should always be on the counterow principle so that the evaporator coils areuniformly loaded. Therefore the relation betweenairow and refrigerant ow ought always to be asshown in the upper gure.

In this way the largest temperature dierence(see right hand gure) is ensured between the airt

land the evaporator surface t

fat the refrigerant

outlet of the evaporator. That is to say, refrigerantsuperheatt will be rapidly aected by a changein the temperature of the incoming air (the load)and will thereby rapidly give a signal to thethermostatic expansion valve to change theliquid injection.

It is important that the evaporator coils areuniformly loaded. For example, with a downwardvertical airow through the evaporator, theincoming air will load the rst evaporator coilsmore than subsequent coils. The rear coils will bethe least loaded and will therefore determine towhat degree the thermostatic expansion valveopens. If a small amount of refrigerant liquid fromthe rear evaporator coils passes the point wherethe bulb is located, the valve will close despitethe fact that the rst coils require a supply ofrefrigerant liquid because of a larger load, i.e.brisker evaporation.

The thermostatic expansion valve bulb must notbe inuenced by false eects; such as air owthrough the evaporator and the bulb musttherefore be placed on the suction line outsidethis airow. If this is not possible, the bulb has tobe isolated.

Note that a thermostatic expansionvalve with external pressureequalization is used.


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Refrigeration plant withoil separator and heatexchanger

Fig. 17

In principle, in refrigeration plant the oil shouldremain in the compressor. Out in the system itwill do more harm than good because it willimpair the capacity of the evaporator and

condenser. Also, if the oil level in the crankcasebecomes too low, there will be a risk ofinsucient compressor lubrication.

The best protection against these disadvantagesis the installation of an ecient oil separator, typeOUB (1).

Furthermore, a heat exchanger type HE (2) oersthe following advantages:

Superheating the suction gas providesgreater protection against liquid knock in

the compressor and counteracts formation ofcondensate or frost on the surface ofuninsulated suction lines.

Sub cooling the refrigerant liquid counter-actsthe formation of vapour, which will reduce thecapacity of the thermostatic expansion valve.

Operating economy will often be improvedbecause sources of loss such as un-evaporated liquid drops in the suction gasand insucient sub cooling of the refrigerantliquid are completely or partially eliminated.


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Oil separator Fig. 18

OUB

Hot high-pressure gas is supplied to the oilseparator type OUB through the connector (1).

The gas then ows around the oil tank (2) and

through the lter (3) where the oil is separated.The vapour, now poor in oil, leaves the oilseparator through the upper connector (4).

Separated oil is collected in the bottom of the oiltank (2), which is kept heated by the incomingvapour. In this way the separated oil is stored in a

warm condition, i.e. with the lowest possiblerefrigerant content.A oat valve (5) regulates oil return to thecompressor.

Heat exchangerFig. 19

HE

Heat exchanger type HE has been designed witha view to achieving maximum heat transmissionat minimum pressure drop. The outer spiral-formed chamber (4) leads hot refrigerant liquid ina ow counter to the ow of cold refrigerantliquid in the inner chamber (3). Built in to theinner chamber are oset n sections.

Heat exchanger type HE is manufactured in brassand copper and has very small dimensions inrelation to its heat transmission capacity. The

spiral formed outer chamber (4) forces the hotrefrigerant liquid over the entire heattransmission surface and prevents the formationof condensate on the outer jacket. The built-inoset n sections in the inner chamber (3)produce turbulent ow in the refrigerant vapour.Heat transmission from liquid to vapour is thusvery eective. At the same time, pressure drop iskept down to a reasonable level.


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Refrigeration plant for alarger cold store

Fig. 20

Complete refrigeration plant for a larger cold store with temperature above freezing point

To ensure eective shut-o of the liquid lineduring compressor standstill periods, solenoidvalve EVR (1) has been installed since bulbtemperature may be expected to rise morerapidly than evaporating temperature and causethe thermostatic expansion valve to open.Protection against overcharging the evaporatorduring compressor standstill periods is providedby making the solenoid valve close at the sametime as the compressor is stopped.

The liquid line is equipped with type GBC (2) orBML manual shut-o valves to make replacementof the lter drier easy.

Pressure on the high and low-pressure sides ofthe compressor can be read on the pressuregauges shown. The pressure gauges can be shuto with the three-way valves type BMT (3).


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Solenoid valveFig. 21

EVR

Solenoid valve type EVR is a servo-controlledelectromagnetic shut-o valve. Throughequalizing holes (2) the upper side of thediaphragm (1) is pressure-equalized with thevalve inlet pressure on the underside. Whencurrent energizes the coil (3) the pilot orice (4) isopened. This orice has a larger through-owarea than the total area of the equalizing holes.

Pressure over the diaphragm is reduced by theow through the pilot orice to the valve outletside and the larger inlet pressure on theunderside lifts the diaphragm. When the coil isde-energized, the pilot orice closes and thediaphragm is drawn onto the valve seat as thepressure over it increase through the equalizingholes.

Shut-o valveFig. 22

BM

Shut-o valves types BM have a triple diaphragmseal (1) of stainless steel. A thrust shoe (2)prevents direct contact with the spindle (3). Thespring (4) together with the pre-stresseddiaphragm is able to hold the valve open atoperating pressures down to P

e= 1 bar.

The counter seat in the cover (5) prevents theingress of moisture. The valves are available instraight, and 1/

4" T versions. Flow through the side

port of the T version can be shut o leaving theend ports permanently open.


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Key diagram, control currentfor refrigeration plant, g. 20

Fig. 23

The diagram must be read from top to bottomand from left to right. The individual circuits aredrawn so that no leads cross. Power-consumingcomponents are shown at the bottom of thediagram. These include relay coils in the motorstarters, solenoids coils, regulation motors, etc.Motor starter thermal relays F are shown adjacentto the contacts between terminals 95 and 96.Manual reset S is also shown. Relay auxiliary

contacts K between terminals 13 and 14 areshown at the top of the diagram. Designations13, 14, 95, 96, etc. correspond to those containedin Danfoss information on contactors and motorstarters.

Relay coils K1 serve the auxiliary contactsbetween terminals 13 and 14. The auxiliarycontacts are drawn in their de-energized coilposition. Under the neutral wire and each relaycoil there is an indication of in, which circuit theassociated auxiliary contacts, can be found.

Terminal designation 13-14 is, by denition,always a make contact (NO), while terminaldesignation 11-12 is always a break contact (NC).

The key diagram should be read as follows: When,on rising cold store temperature, thermostat typeKP 61 cuts in (when switches S1 and S2 are made)between terminals 2 and 3, relays K1 and K2 inmotor starters type CIT pull in and start theevaporator fans. At the same time the associated

auxiliary contacts in circuits 3 and 4 are made.Relay K3 in compressor motor starter type CITpulls in if the combined high and low pressurecontrol type KP 15 is made between terminals 2and 3, and if switch S3 is made. The compressorstarts and at the same time the auxiliary contactin circuit 5 connects current to coil E in the EVRsolenoid valve in the liquid line. The solenoidvalve opens and refrigerant liquid is injected intothe evaporator, regulated by thermostaticexpansion valve type TE.


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Motor startersFig. 24

The Danfoss motor starter range up to 420 A ismade up of modules. It consists of a basic module(contactor type Cl) onto which up to fourauxiliary contact blocks (type CB) can be clippedas necessary. There is also a range of thermalrelays (type TI). The left-hand diagram shows a

motor starter with start- stop / reset function. Thestart contact (type CB-S) carries the terminaldesignation 13-14. The right-hand diagram showsa motor starter with stop/reset function,controlled via a thermostat, pressure control, orsimilar.

The motor starters are equipped with a thermalrelay having three indirectly heated bimetals.

Through a cut-out mechanism the bimetals breakthe bounce-free switch between terminals 95and 96 in the event of overloading. Large currentasymmetry between the three motor phasesactivates a built-in dierential cut-out, whichensures an accelerated trip - as distinct from what

occurs under a normal symmetrical overload. Thecut-out is partly temperature-compensated; upto a temperature of 35C it compensates for anyrise in the ambient temperature not arising fromoverloading.

The motor starters are available in severalversions. The examples shown are tted with amanually lockable stop and reset for the thermalrelay, i.e. the starters must be manually reset afterthermal cut-out.

The modules are based on thermoplastic (CI) andBakelite/thermoplastic (TI), and all main andauxiliary contacts are made of a special silveralloy. All steel parts are eectively corrosionprotected.Soft starter type MCII and circuit breaker type CTIare also available from Danfoss.


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Central refrigeration plantfor cold store temperaturesabove freezing point

Fig. 25

Temperature and relative humidity play asignicant role in the keeping of foodstus andthe various categories of ware must be stored in

the most favourable conditions. There is usetherefore for cold stores having dierenttemperatures and humidities; not only the roomtemperature but also the evaporatingtemperature must be under control.

In the example shown, the followingtemperatures might be considered:

The room temperature in all 3 cold stores arecontrolled with KP-62 thermostats opening andclosing the EVR solenoid valves.

Two evaporating temperature regulators typeKVP (1) throttle the suction line after theevaporator in the +8C and +5C stores so that

the evaporating temperatures are maintained at+3C and 5C respectively.

Combined high and low pressure control type KP15 (2) cuts the compressor in and out at a suitablylow suction pressure to maintain evaporatingtemperature in the 0C store at 10C.

During compressor standstill, check valve typeNRV (3) prevents refrigerant from the evaporatorsin the +8C and +5C stores condensing in thecoldest evaporator, i.e. the one in the 0C store.

Check valve type NRV (4) aords protectionagainst refrigerant condensing in the oil

separator and compressor top cover if thesecomponents become colder than the evaporatorduring plant standstill periods.

Room temp. Evaporat ing temp.

Vegetable store +8C +3C

Sliced meat and

salad store

+5C 5C

Meat store 0C 10C


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Evaporating pressureregulator Fig. 26

KVP

Evaporating pressure regulator type KVP openswhen pressure rises on its inlet side, i.e. whenpressure in the evaporator rises (increasing load).

Turning the regulating screw (1) clockwisecompresses the spring (5) and increases theopening pressure, i.e. evaporating temperaturerises. The regulator has a bellows (10) of the samediameter as the valve plate (2). This means thatpressure variations on the outlet side of theregulator have no eect on the automatic

regulation of the degree of opening since

pressure on the top of the valve plate is balancedby pressure on the bellows. The regulator alsoincorporates a damping device (11) so thatpressure pulsations in the plant do not aect thefunction of the regulator.

To make adjustment of the valve easier, it is ttedwith a special pressure gauge connection (9),which makes it possible to t or remove apressure gauge without rst having to empty the

suction line and evaporator.

Check valveFig. 27

NRV

Check valve type NRV is available in straight orangle versions with are as well as solderconnections. Solely the pressure drop controlsthe function of the valve across it.

NRV straightway version:The valve plate is tted to a brake piston (1),which is held against the valve seat by a weak

spring (2). When the valve opens, the volumebehind the brake piston becomes smaller. Anequalizing hole (slot) allows the refrigerant toslowly escape to the outlet side of the valve. Inthis way the movement of the piston is broken;an arrangement that makes the check valve wellsuited for lines where pressure pulsations canoccur.


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Key diagram, control currentfor refrigeration plant g. 25 Fig. 28

Thermostat type KP 62 in the +8C room controlssolenoid valve E1 type EVR in the liquid line whilethe two other thermostats type KP 62 in the +5Cand 0C rooms respectively control motor startersK1 and K3 type CIT for the evaporator fans, andsolenoid valves K2 and K3 type EVR in the liquidlines.

Combined high and low pressure control type KP15 controls motor starter K4 type CIT for thecompressor motor.

A condition for this function is that manualswitches S1, S2, S3 and S4 must be made.

The compressor motor is thus only indirectlycontrolled by the room thermostats and is able;for example, to run for some time after all thethermostats have cut out.

However, since it is unlikely that all the roomthermostats will cut out at the same time, thisform of control will result in some after-eva-poration, which can be advantageous as regardsliquid hammer in the compressor butdisadvantageous as regards the end of arefrigeration period. When a room thermostatcuts out, slight evaporation will still continue andthe charge in the evaporator concerned willbecome smaller. When the room thermostat cutsin again, the eect of the smaller charge will be

to make it more dicult for un-evaporatedrefrigerant to enter the suction line during thesudden priming at the beginning of theevaporator-operating period.


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Refrigeration plant forfreezer display counter Fig. 29

As this plant operates most of the time at lowevaporating temperatures, interrupted only byautomatic defrosting once or twice every 24hours, it is advantageous to have an electriccompressor motor of a size corresponding tonormal operating conditions, i.e. relatively smallload at low suction pressure.

However, after a defrosting this small motorwould be overloaded and there would be a risk ofmotor burn-out. As a safeguard against this risk acrankcase pressure regulator type KVL (1) isinstalled which rst opens when suction pressurein front of the compressor has been reducedsuciently to avoid overloading the motor.

Regulating system KVR (2) + NRD (3) is used tomaintain a constant and suciently high

condensing pressure in the receiver on air-cooledcondensers at low ambient temperatures.

During winter operation the ambient tempe-rature fails and with it the condensing pressure ofthe air-cooled condenser. The KVR regulatesdependent on the inlet pressure and begins tothrottle when the pressure drops below the setvalue. As a consequence, the condenser becomespartly charged with liquid and its eective area isreduced. In this way the required condensingpressure is re-established.

Since the actual regulating task during winteroperation is to maintain the receiver pressure at a

suitably high level, the KVR is combined with atype NRD dierential pressure valve installed inthe bypass line shown. The NRD begins to openat a dierential pressure of 1.4 bars. When the

condensing pressure fails, the KVR begins tothrottle. This increases the total pressure dropacross the condenser + KVR. When this pressuredrop reaches 1.4 bars, the NRD begins to openand thus ensures that the receiver pressure ismaintained.As a rule-of-thumb, it can be assumed that thepressure in the receiver is equal to the pressureset on the KVR minus 1 bar.

During summer operation, when the KVR is fullyopen, the total pressure drop across thecondenser and KVR is less than 1.4 bars. Thereforethe NRD remains closed.

The charge can collect in the receiver duringsummer operation. Therefore the plant must beequipped with a suciently large receiver. The

KVR can also be used as a relief valve betweenthe high-pressure side and low pressure side toprotect the high pressure side against too high apressure (safety function).

The pressure-lubricated compressor with oilpump is protected against oil failure bydierential pressure control type MP 55 (4). Thecontrol stops the compressor if the dierentialbetween the oil pressure and suction pressure inthe crankcase becomes too low.

A type 077B thermostat is installed in the counter,with its sensor located in the cold room. If thetemperature rises above the set value, a signal

lamp lights up.


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Dierential pressure controlFig. 30

MP 55

Dierential pressure control type MP 55 is used asa safety pressure control on pressure-lubricatedrefrigeration compressors. After a xed timedelay the control stops the compressor in theevent of oil failure.

The oil pressure element OIL (1) is connected tothe oil pump outlet and the low-pressureelement LP (2) is connected to the compressorcrankcase. If the dierential between oil pressureand pressure in the crankcase becomes less thanthe value set on the control, current to the timerelay is cut in (contact T

1- T

2made, see wiring

diagram).

If contact T1

- T2

remains made for a lengthyperiod because of a fall in pressure in relation tothe pressure in the crankcase (suction pressure),the time relay cuts out the control current to thecompressor motor starter (time relay contactchanges over from A to B, i.e. control current isbroken between L and M).

The minimum permissible dierential pressure,i.e. the minimum oil pressure at which undernormal operation the dierential pressure controlsustains current to the time relay cut o (contact

T1

- T2

broken), can be set on the pressureadjustment disc (3). Clockwise rotation increases

the dierential, i.e. increases the minimum oilpressure at which the compressor can still run.

The contact dierential is xed at 0.2 bars.Therefore, current to the time relay will be rstcut o during start, when the oil pressure is 0.2bars higher than the minimum allowabledierential pressure. This means that atcompressor start the oil pump must be capableof increasing the oil pressure to 0.2 bars morethan the set minimum permissible oil pressurebefore the end of the time delay. Contact T

1- T

2

must break so quickly after start that the timerelay never reaches its A to B changeover point(break between L and M). See also key diagram,g. 35.


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Crankcase pressureregulator Fig. 31

KVL

Crankcase pressure regulator type KVL opens onspindle (1) clockwise tightens the spring (5) andfalling pressure on the outlet side, i.e. on falling

the regulator then begins to regulate at a higherpressure ahead of the compressor. Turning thepressure on the outlet side.

Condensing pressureregulator Fig. 32

KVR

Condensing pressure regulator type KVR openswhen pressure on its inlet side rises, i.e. whencondensing pressure rises. Turning the spindle (1)clockwise tightens the spring (5) and increases

the opening pressure so that the condensingpressure rises.

Like the previously mentioned evaporatingpressure regulator type KVP, all regulators aretted with a pressure-equalizing bellows (10) toeliminate pressure variations on the inlet side oftype KVL and the outlet side of type KVL Allregulators are also tted with a damping device

(11) so that pressure pulsations in the plant donot aect regulator function.


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Dierential pressure valveFig. 33

NRD

Dierential pressure valve type NRD begins toopen at a pressure drop of 1.4 bars and is fullyopen at 3 bars. When the valve is installed as abypass, it ensures that the receiver pressure ismaintained.

The contact system in evaporator thermostattype 077B makes on rising temperatures. Turningthe range spindle clockwise increase the cutintemperature of the thermostat, i.e. thetemperature at which the signal lamp lights up.

Evaporator thermostatFig. 34

077B


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Key diagram, refrigeration plant for freezer display counter, g. 29

Time switch P controls changeover contact t,circuit 2, which makes or breaks control currentto contactors K1 and K2 type Cl for the respectiveelectric heating elements under the evaporators,and for the evaporator fans. When K2 is cut in, K1is cut out, i.e. the evaporator fans are stoppedduring defrosting. At the same time, motorstarter K3 type CIT for the condenser fan is cutout via the auxiliary contact (brake contactbetween 21 and 22) in circuit 4. A signal lamp H1is switched on via the auxiliary contact (makecontact between 13 and 14) in circuit 6. Whenmotor starter K3 cuts out, the auxiliary contact(make contact between 13 and 14) in circuit 5breaks and motor starter K4 type CIT for thecompressor is cut out. Thus, the compressor alsoremains at a standstill.

Pressure control type KP (1) is connected so thatit cuts out on rising pressure. This cuts outdefrosting when the suction pressure hasincreased to such an extent that there is no morefrost on the evaporator. When contactor K2 is cutout, motor starter K3, and with it motor start K4are cut in via the auxiliary contacts (make contactbetween 21 and 22) in circuit 4 and in circuit 5(make contact between 13 and 14). Assumingswitches S1 and S2 are made.

This starts the condenser fan and the compressor.At the same time, signal lamp H1 is switched ovia the make contact between 13 and 14 in circuit6 and signal lamp H2 is switched on via theauxiliary contact (make contact between 13 and

14) in circuit 7. The evaporator fans are startedafter a period by time switch P cutting incontactor K1. During this delay the compressor isable to remove the heat accumulated in the

evaporators while defrosting was taking place,before the evaporator fans are started.

Low-pressure control type KP 1 (II) is connectedto control the refrigeration plant during normaloperation. High-pressure control type KP 5 stopsthe compressor but not the condenser fan whencondensing pressure becomes excessive.

A thermostat type 077B switches on signal lampH3 if the temperature in the display counterexceeds 18C. The signal lamps are connected toa 12 V battery system so that lamp H3 is able tofunction even if a mains supply failure occurs.

Fig. 35


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Main wiring diagram forcontactors

Fig. 36

Wiring diagram for contactors K1 and K2 type Clfor the display counter refrigeration plant, g. 29.For key diagram see g. 35.

The changeover switch for time switch P controlsthe contactors so that one is cut in while theother is cut out. The main contacts 1-2 and 3-4 incontactor K2 are each connected to an electricheating element. Contactor K1 has four maincontacts, each of which is connected to a

single-phase fan (1-2, 3-4, 5-6,13-14).


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Refrigeration plant forventilation air

Fig. 37

Continued overleaf...

An electronically controlled suction pressure

regulator type KVS (1) is installed in the suctionline. The electronic regulator receives signalsfrom a central control unit, e.g. a PLC, which inturn receives signals from a temperature sensorlocated in the return air ow from the room inwhich the ventilation air is to be cooled.

The KVS valve opens if the temperature of thereturn air rises.

If the temperature registered by the sensor rises,the valve opens a little more, and suctionpressure from the evaporator is increased. At thesame time, the pressure drop across the valve isreduced as a result of reduced evaporation

temperature and increased suction pressure. Thisincreases the capacity of the evaporator andcompressor.

If the temperature registered by the sensor falls,the valve closes a little more, and suctionpressure from the evaporator is reduced. At thesame time, the pressure drop across the valve isincreased as a result of increased evaporationtemperature and reduced suction pressure. Thisreduces the capacity of the evaporator andcompressor.

As plant such as this must be capable of runningirrespective of load, compressor capacity must beadjustable.

A capacity regulator type KVC (2) is suitable forthis purpose as this regulator is able to preventsuction pressure from dropping to such an extent

that the compressor is either shut o by the low-

pressure cut-out or is subjected to suctionpressure below the acceptable minimum. This isachieved by the KVC valve being set to startopening in order to prevent the above-mentioned limits from being crossed. This hot-gas bypass transfers some high-pressure gas fromthe pressure side of the plant to the suction side,thus reducing refrigeration capacity.

This type of capacity regulation results in acertain degree of suction gas superheating. As aresult, the temperature of the high-pressure gasincreases, thus increasing the risk that oil in thecompressor pressure valves will become coked. Inorder to prevent this, a thermostatic expansion

valve type T (3) is installed in a bypass betweenthe liquid line and the suction line. The valvesensor is installed in the suction line immediatelyahead of the compressor.

In case of excessive superheating in this region,the valve opens and some liquid is injected intothe suction line. When this liquid evaporates,superheating is reduced and thus also the high-pressure gas temperature.

A solenoid valve type EVR (4) is installedimmediately ahead of the thermostaticexpansion valve (3) in order to prevent liquidrefrigerant from entering the suction line whenthe refrigeration plant is shut down.


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Electronically controlled suction pressureregulator

KVS (1) is a suction pressure regulator, activatedby a stepper motor. It alters the degree ofopening in response to signals from the EKC 368regulator which transmits pulses that cause thevalve motor to rotate in one direction or theother depending on whether the valve is to beopened more or closed more.

Capacity regulatorThe capacity regulator type KVC opens in

response to falling pressure on the dischargeside, i.e. falling suction pressure ahead of thecompressor.

Fig. 38

KVS KVC

Fig. 39


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The Danfoss product range for therefrigeration and air conditioning industry

Compressors for refrigeration and air conditioningThese products include hermetic reciprocating compressors, scroll compressors and fan-cooled condensingunits. Typical applications are air conditioning units, water chillers and commercial refrigerationsystems.

Compressors and Condensing UnitsThis part of the range includes hermetic compressors and fan-cooled condensing units for householdrefrigerators and freezers, and for commercial units such as bottle coolers and drinks dispensers . Wealso oer compressors for heat pumps, and 12 and 24 V compressors for refrigerators and freezers incommercial vehicles and boats.

Appliance controlsFor the regulation of refrigeration appliances and freezers Danfoss supplies a product range ofelectromechanical thermostats produced according to customer specications; electronic temperaturecontrols comprising models with and without displays; service thermostats for servicing on all refrigerating

and freezing appliances.

Refrigeration and air conditioning controlsOur full product range covers all control, safety, system protection and monitoring requirements inmechanically and electronically controlled refrigeration and air conditioning systems. The products areused in countless applications within the commercial and industrial refrigeration and air conditioningsectors.

Manual de Instalação - Danfoss

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