Danfoss Automation of Commercial Refrigeration Plant

Automation of Commercial Refrigeration Plant

REFRIGERATION AND AIR CONDITIONING

Automation of commercial Automation commercial Refrigeration Plant The purpose o this manual is to show some examples o the use o Danoss automatic controls or commercial rerigeration plants. A simple, hand-regulated plant is used as the starting point o a step-by-step automation and a short description o the unction o each control is given. For additional training material we reer to http://rc.danoss.com/SW/RC_Training/En/Index.htm

Contents

Page

Hand-regulated rerigeration plant .....................................................................................................................................................................................................2 Rerigeration Rerigeratio n plant with thermostatic expansion valve and air-cooled air-cooled condenser ................................................................................ .......................... 3 Rerigeration with Finned evaporator ................................................................................................................................................................................................4 Thermostatic expansion valve .......................................................................................................................................................................................................5 Thermostatic expansion valve with distributor .......................................................................................................................................................................5 Expansion valves .................................................................................................................................................................................................................................6 Thermostatic expansion valve, method o operation ...........................................................................................................................................................7 Thermostatic expansion valve with MOP charge....................................................................................................................................................................8 Combined high and low pressure control .................................................................................................................................................................................9 Low-pressure and High-pressure control ..................................................................................................................................................................................9 High-pressure control, control, method o operation operation .................................................................................... .................................................... .................................0 Thermostat .......................................................................................................................................................................................................................................... Filter drier ............................................................................................................................................................................................................................................ Sight glass ........................................................................................................................................................................................................................................... Automatic water valve ....................................................................................................................................................................................................................2 Finned evaporator ............................................................................................................................................................................................................................3 Rerigeration Rerigeratio n plant with oil separator and heat exchanger............................................... ..................................................... .................................................. 4 Oil separator .......................................................................................................................................................................................................................................5 Heat exchanger .................................................................................................................................................................................................................................5 Rerigeration plant or a larger cold store .......................................................................................................................................................................................6 Shut-o valve .....................................................................................................................................................................................................................................7 Solenoid valve ....................................................................................................................................................................................................................................7 Key diagram, control control current or rerigeration rerigeration plant, g. 20 .................................................................................. ..................................................... ......8 Motor starters.....................................................................................................................................................................................................................................9 Central rerigeration rerigeration plant or cold store temperatures temperatures above reezing point .................................................................................. ................................20 Evaporating pressure pressure regulator regulator ................................................ ..................................................... ..................................................... .........................................2 Check valve .........................................................................................................................................................................................................................................2 Key diagram, control control current or rerigeration rerigeration plant g. 25 ................................................................................... ..................................................... ......22 Rerigeration Rerigeratio n plant or reezer display counter counter ............................................................................... .................................................... ..........................................23 Dierential pressure control .........................................................................................................................................................................................................24 Crankcase pressure pressure regulator.................................................... ..................................................... ..................................................... .........................................25 Condensing pressure pressure regulator regulator ................................................ ..................................................... ..................................................... .........................................25 Dierential pressure valve .............................................................................................................................................................................................................26 Evaporator thermostat ...................................................................................................................................................................................................................26 Key diagram, rerigeration rerigeration plant or reezer display counter, counter, g. 29 ................................................. .................................................... ........................27 Main wiring diagram or contactors ..........................................................................................................................................................................................28 Rerigeration plant or ventilation air................................................................................................................................................................................................29

© Danoss A/S (RC-CMS / MWA), MWA), 03 - 2004

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Manual

Hand‑regulated rerigerationplant

Automation o Commercial Rerigeration Plant

Fig. 

A hand-regulated rerigeration rerigeration plant is usually built up o these components: Compressor

()

Condenser

(2)

Evaporator

(3)

In order to maintain the cold store temperature t r at the desired level, it is necessary to equip the plant with adjustable valves (4) and (5) in that changes in the loads on the evaporator and condenser under varying rerigera rerigeration tion demands can be reckoned on. For example, example, the plant will be unable to maintain the same temperature summer and winter with permanently set regulating valves and a continuously operating compressor. This can easily be shown graphically, as illustrated in g. .

temperature t o. The E-curves represent evaporator capacity, which rises with the increasing temperature dierence t r - to between room temperature (t r) and evaporating temperature (to). Where the C-curve (winter operation) and E-curve (summer operation) intersect each other, compressor, condenser and evaporator capacities are in equilibrium. As can be seen rom g. , the room temperature will all rom tr to tr' when reriger rerigeration ation demand alls rom Qo in summer to Q o' in winter. To meet this condition the capacities o the compressor, condenser and evaporator must be adjusted, or example by regulating the compressor operation, operation, and by throttling the water ow to the condenser and rerigerant liquid ow to the evaporator.

The ull lines represen representt summer operation and the dotted lines winter operation, (e.g. condensing temp. winter +25°C, summer +35°C). The C-curves represen representt compressor capacity, which rises with increasing evaporating

© Danoss A/S (RC-CMS / MWA), 03 - 2004

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Manual

Rerigerationplantwith thermostaticexpansion valveandair‑cooled condenser


Fig. 2

Thermostatic expansion valve Automatic expansion valve

In this plant an air-cooled unit has replaced the water-cooled condenser. Air-cooled condensers are normally used where no cooling water is available or where the use o cooling water is orbidden. Replacing the manual valve ahead o the evaporator with a thermostatic expansion valve (pos. ) ensures that the evaporator is continuously supplied with the amount o rerigerantt necessary to keep a constant rerigeran superheat in proportion to the load.

Superheat in an evaporator is dened as t – ps = °C superheat, where t  is the temperature measured at the point on the evaporator where the expansion valve sensor is placed, and p s is the pressure measured measured at the same point. ( The relevant pressure is converted to °C). For urther details on superheat, see page 7.

This o course presupposes that the selected expansion valve suits the evaporator concerned. A actor here is that in conditions o maximum load the expansion valve supplies precisely the amount o rerigerant the evaporator is able to evaporate.. In addition the superheat setting o evaporate the valve must match the evaporator. Superheat is generally understood as being the number o °C the evaporator has minus the boiling point o the medium at the existing pressure and with all liquid evaporated.


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Manual

RerigerationwithFinned evaporator


Fig. 3

Thermostat type KP 6 () cuts the ans (2) in and out depending on the room temperature. Thermostatic expansion valve type TE (3) with Thermostatic external pressure equalization regulates liquid injection in the evaporator, dependent on the superheat but independent o the pressure drop across the evaporator.

Sight glass type, SGN (6) indicates too high moisture content in the rerigerant and too little ow to the thermostatic expansion valve. The indicator changes colour when the moisture content is too great. Vapour bubbles in the sight glass can mean insufcient charge, insufcient sub cooling or partial clogging o the strainer strainer..

Liquid distributor type 69G (4) distribute rerigerant liquid equally to the individual evaporator sections. The compressor is cut in and out on the lowpressure side o the combined high and low pressure control control type KP 5 (5) depending on the suction pressure. In addition, the high-pressur high-pressure e side o this control gives protection against too high a condensing pressure by cutting out the compressor i it becomes necessary (e.g. when the ventilator is deected or the airow is blocked (dirt)).


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Manual

Thermostaticexpansion valve


Fig. 4

T 2

Thermostatic expansion valve type T 2, the bulb o which is placed immediately ater the evaporator, opens on rising superheat. Pressure on the diaphragm () increases as bulb temperature increases and pressure under the diaphragm increases as the evaporating temperature increases. The pressure dierential, which corresponds to the rerigerant superheat, maniests itsel as a orce, which tries to open the valve against the

Thermostaticexpansion valvewithdistributor

opposite orce o the spring (2). I the dierenti dierential, al, i.e. superheat, exceeds the spring orce the valve will open. The orice assembly, with orice (3) and valve cone (4) can be changed. To suit capacity requirements, there are eight dierent sizes to choose rom.

Fig. 5

TE 5 + 69G

Distributor type 69G ensures an equal distribution o rerigerant to the parallel sections o the evaporator. The distributor can be installed either direct on the thermostatic expansion valve as shown or in the line immediately ater it. A distributor ought always to be tted so that the liquid ow through the nozzle in the distributor pipes is vertical. This ensures that the eect o gravity on liquid distribution is as little as possible. All distribution pipes must be exactly the same length.


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For evaporators with a large pressure drop, thermostatic expansion valves with external pressure equalization must always be used. Evaporatorss with liquid distributors will always Evaporator have a large pressure drop; thereore always use external pressure equalization.

5

Manual

Expansionvalves


Fig. 6

Upperdiagram: The diagram shows an evaporator, which is ed by a thermostatic expansion valve with internal pressure equalization. The degree o opening o the valve is regulated by: Pressure pb in the bulb and capillary tube acting on the upper side o the diaphragm and determined by the bulb temperature. Pressure po in the valve discharge connection acting under the diaphragm and determined by the evaporating temperature. Spring pressure ps acting under the diaphragm and manually adjustable. In the example shown, the pressure drop in the evaporator ∆p is measured in °C rerigerant pressure –5 – (–20) = 5°C. Provided that the valve spring has been manually adjusted to a pressure p s corresponding to 4°C, it ollows - in order to achieve equilibrium between the orces acting over and under the diaphragm - that pb = po + ps ~ –5 + 4 = –°C. That is, the rerigerant has to be superheated by –  – (–20) = 9°C beore the valve begins to open.

Lowerdiagram: The same evaporator coil, but this time ed by a thermostatic expansion valve with external Pressure equalization connected to the suction line ater the bulb. The degree o opening o the valve is now regulated by: Pressure pb in the bulb and capillary tube acting on the upper side o the diaphragm and determined by the bulb temperature. Pressure po - ∆p in the evaporator outlet acting under the diaphragm and determined by the evaporating temperature and the pressure drop in the e vaporator vaporator.. Spring pressure ps acting under the diaphragm and manually adjustable. Provided that, as stated above, pressure drop ∆p in the evaporator corresponds to 5°C and spring pressure ps in the valve to 4°C rerigerant pressure, it ollows that pb = po – ∆p + ps ~ –5 – 5 + 4 = –6°C. That is, the rerigerant now has to be superheated by –6 – (–20) = 4°C beore the valve begins to open. The amount o charge in the evaporator and hence its capacity become higher since a smaller portion o the evaporator surace is used or superheating.

Conclusion: Thermostatic expansion valves with external pressure equalizing must always be used or evaporators with a large pressure drop. Evaporators with a liquid distributor will always have a large pressure drop; thereore always use external pressure equalization. © Danoss A/S (RC-CMS / MWA), 03 - 2004

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Manual

Thermostaticexpansion valve,methodooperation


Fig. 7

The thermostatic expansion valve is controlled by the dierence between bulb temperature t b and evaporating temperature t o. The valve opens when the temperature dierential rises, t b – to = rerigerant ant superheat rises the valve ∆t, i.e. when reriger will have a larger opening rate. See g. 6. Solid curve po and dotted curve p b gives vapour pressure or the rerigerant and charge respectively.. Chain-dotted curve p o + ps respectively represents represen ts the rerigeran rerigerantt vapour pressure curve po oset in parallel with a constant spring pressure ps, the actory setting or example. At a given evaporating temperature, t o, a pressure po + ps acts under the valve diaphragm and tries to close the valve. Pressure p b acts over the diaphragm and tries to open the valve. The gure shows equilibrium between p o + ps and pb at evaporating temperature t o and bulb temperature t b respectively respectively.. Practically speaking, dierentiall tb – to, the static superheat, is the dierentia same within the entire working range o the valve rom to' to t o".


RG00A502

That is to say, irrespective o the evaporating temperature operated with inside the working range, the thermostatic expansion valve will regulate liquid injection so that rerigerant superheat ater the evaporator is held to the value determined by spring pressure p s. I the dierential between bulb temperature t b and evaporating temperature t o is less than the static superheat ∆t, the valve is closed (t b – to < ∆t; pb < po + ps) I the dierential between bulb temperature t b and evaporating temperature t o is greater than the static superheat ∆t, the valve is open (t b – to > ∆t; pb > po + ps). I the dierential between bulb temperature t b and evaporating temperature t o is equal to the static superheat ∆t, the valve is just about to open or just about to close (t b – to = ∆t; pb = po + ps).

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Manual

Thermostaticexpansion valvewithMOPcharge


Fig. 8

It can sometimes be desirable to use a thermostatic expansion valve with a limited working range - or example, in rerigeration plant with only one evaporator where cooling rom a completely or partially temperature equalized condition occurs only as an exception (ater repair or derosting). For such plants it may be cheaper to use a smaller compressor motor dimensioned in accordance with the load ater cooling down. However, during cooling down such a motor will become overloaded overloade d and cut-out on the thermal overload protection.


RG00A502

To eliminate this risk, a thermostatic expansion valve with a MOP (Maximum Operating Pressure) Pressure) charge can be used. This pressure-limite pressure-limited d valve will only begin to open at a low evaporating temperature, tMOP, since the charge is adapted to produce a bend in the vapour pressure curve P b. This means that static superheat ∆t is very high at evaporating temperatures higher than t MOP, i.e. in practice the valve will remain closed until the compressor has reduced the suction pressure sufciently to ensure that the electric motor is not overloaded.

8

Manual

Combinedhighandlow pressurecontrol


Fig. 9

Combined high and low pressure control type KP 5 has a single-pole changeover switch (2). KP 5

Low‑pressureside(LP): The LP connector (0) is connected to the suction side o the compressor. When pressure alls on the low-pressure side the circuit between terminals 2 and 3 is broken. Turning Turning the LP spindle () clockwise adjusts the unit to cut out (break the circuit between terminals 2 and 3) at a higher pressure. Turning the dierential spindle (2) clockwise adjusts the unit to cut in again (make the circuit between terminals 2 and 3) at a smaller dierentia dierential.l. Start pressure = stop pressure + dierential. LP signal unction between terminals A and B. Low‑pressureandHigh‑ pressurecontrol

Fig. 0

Low‑pressurecontroltypeKP1 Contains a single pole changeover switch (SPDT), which breaks the circuit between terminals 2 and 3 when pressure in the bellows element (9) ails (on ailing suction pressure) pressure),, i.e. the connector (0) must be connected to the suction side o the compressor. Turning the range spindle () clockwise adjusts the unit to cut in - to make the circuit between terminals 2 and 3 at a higher pressure. Turning the dierential spindle (2) clockwise adjusts the unit to cut out again - to break the circuit between terminals  and 2 at a smaller dierential. Start pressure = stop pressure + dierential.


High‑pressureside(HP): The HP connector () is connected to the discharge side o the compressor. When pressure rises, on the high-pressure side the circuit between terminals 2 and 3 is broken. Turning the HP spindle (5) clockwise adjusts the unit to cut out (break the circuit between terminals 2 and 3) at a higher pressure. The dierential is xed. Stop pressure = start pressure + dierential.

RG00A502

High‑pressurecontroltypeKP5 Is built up in the same way. Bellows, spring and scale are o course suitable or the higher working pressure. pressure. In this case, the switch breaks the circuit between terminals  and 2 when pressure rises in the bellows element (9), i.e. when condensing pressure rises (the connector must be connected to the discharge side o the compressorr ahead o the shut-o valve). compresso Turning the range spindle clockwise adjusts the unit to cut out - to break the circuit between terminals  and 2 at a higher pressure. Turning Turning the dierential spindle (2) clockwise adjusts the unit to cut in again - to make the circuit between terminals  and 2 at a smaller dierential. Stop pressure = start pressure + dierential.

9

Manual

High‑pressurecontrol, methodooperation


Fig. 

High-pressure control type KP 5 is connected to High-pressure the high-pressure side o the rerigeration plant and stops the compresso compressorr when the condensing pressure becomes too high. The control contains a pressure-controlled single- pole changeover switch (SPDT) where the contact position depends on the pressure in the bellows (9). See g. , drawings A and B. Via the adjusting spindle () the main spring (7) can be set to exert a suitable counter- pressure to the bellows pressure. The down-ward resultant o these two orces is transerred by a lever (2) to the main arm (3), one end o which is tted with a tumbler (6). The tumbler is held in position on the main arm by a compressive orce, which can be adjusted by using the spindle (2) to change the pull rom the dierential dieren tial spring (8). The orces rom the bellows pressure, main spring and dierential spring are thus transerred to the tumbler (6), which will tilt when the orces come out o equilibrium because o changes in the bellows pressure, i.e. the condensing pressure.

Conversely, the main arm moves instantaneously Conversely, rom the g. , drawing B position to the g. , drawing A position when the bellows pressure has risen to the stop pressure = start pressure + dierential dierent ial pressure. See also text or gs. 9 and 0 regarding adjustment o type KP. The contact system is specially designed so that the make contact travels at the initial speed o the snap action until it reaches the xed contact, while the break contact separates rom the xed contact at the maximum speed o the snap action. The system has been made possible by the use o a small striker (9) and accurately matched contact springs. The contacts (20) make with a smaller orce than they break, which means that in practice bounce during make is eliminated eliminated.. The holding orce during make is exceptionally high. At the same time the system gives an instantaneous break unction so that the holding orce is maintained 00% right up to break. For these reasons the system is able to operate with high currents and its unction is not impaired by shocks. Compared Compared with traditional designs, the system has given exceptionally good results in practice.

The main arm (3) can only take up two positions. In one position a orce is exerted on each end o the arm and creates opposite torques around its pivot (23). See drawing A. I the bellows pressure decreases, decrease s, the main spring exerts an increasing orce on the main arm. Finally, when the counter torque rom the dierential spring is overcome, the main arm tilts and the tumbler (6) instantaneously change position so that the compressive orce o the dierential spring lies on a line near the arm pivot point (23). The counter-torque rom the dierential spring thus becomes almost zero. See g. , drawing B. The bellows pressure must now rise to overcome the orce rom the main spring because the spring orce torque around the pivot point (23) must also all to zero beore the snap system can return to its initial position. On alling bellows pressure (see g. , drawing A), the main arm moves instantaneously to the position shown in g., drawing B when the bellows pressure is reduced to the stop pressure minus the set dierential pressure. pressure. © Danoss A/S (RC-CMS / MWA), 03 - 2004

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Manual

Thermostat


Fig. 2

KP 6

Thermostat type KP 6, which has a single pole changeover switch (2), makes the circuit between terminals 2 and 3 when bulb temperature rises, i.e. when room temperature rises. Filterdrier

Turning the range spindle () clockwise, increases the cut-in and cut-out temperature o the unit. Turning the dierential dierential spindle (2) clockwise decreases the dierential between cut-in and cut-out temperatures.

Fig. 3

DML / DCL

Filter drier type DML / DCL has a sintered charge, a so-called solid core (3). This is pressed by the spring (2) against the polyester mad (4) and corrugated corrugate d perorated per orated plate (5). Sightglass

The charge or core in the lter drier consists o material which eectively removes moisture, harmull acids, oreign particles, sediment and the products o oil breakdown.

Fig. 4

SGI

Sight glass type SGI / SGN has a colour indicator () that changes rom green to yellow when the moisture content o the rerigerant exceeds the critical value. The colour indication is reversible reversible,, i.e. the colour changes back rom yellow to green when the plant has been dried, e.g. by replacing the lter drier.


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Sight glass type SGI is or CFC, sight glass type SGN is or HFC and HCFC (R 22).



Manual

Automaticwatervalve


Fig. 5

WVFX

Automatic water water valve type WVFX opens on rising pressure in the bellows element (), i.e. when condensing pressure increases (the connector on the bellows housing must be connected to the rerigerant side o the condenser).


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Turning the hand wheel (2) counter clock-wise tightens the spring, which means that the valve will open at a higher condensing pressure. pressure. I the hand wheel is turned clock-wise the valve will open at a lower condensing pressure.

2

Manual

Finnedevaporator


Fig. 6

The nned evaporator is designed or orced air circulation over the parallel evaporator coils. The air circulation should always be on the counter ow principle so that the evaporator coils are uniormly loaded. Thereore the relation between airow and rerigerant ow ought always to be as shown in the upper gure. In this way the largest temperature dierence (see right hand gure) is ensured between the air t l and the evaporator surace t  at the rerigerant outlet o the evaporator. That is to say, rerigerant superheat ∆t will be rapidly aected by a change in the temperature o the incoming air (the load) and will thereby rapidly give a signal to the thermostatic expansion valve to change the liquid injection.

The thermostatic expansion valve bulb must not be inuenced by alse eects; such as air ow through the evaporator and the bulb must thereore thereor e be placed on the suction line outside this airow. I this is not possible, the bulb has to be isolated. Notethat a thermostatic expansion Notethat valve with external pressure equalization is used.

It is important that the evaporator coils are uniormly loaded. For example, with a downward vertical airow through the evaporator evaporator,, the incoming air will load the rst evaporator coils more than subsequent coils. The rear coils will be the least loaded and will thereore determine to what degree the thermostatic expansion valve opens. I a small amount o rerigerant liquid rom the rear evaporator coils passes the point where the bulb is located, the valve will close despite the act that the rst coils require a supply o rerigerantt liquid because o a larger load, i.e. rerigeran brisker evaporation.


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Manual

Rerigerationplantwith oilseparatorandheat exchanger


Fig. 7

In principle, in rerigeration plant the oil should remain in the compressor. Out in the system it will do more harm than good because it will impair the capacity o the evaporator and condenser.. Also, i the oil level in the crankcase condenser becomes too low, there will be a risk o insufcient compressor lubrication. The best protection against these disadvantages is the installation o an efcient oil separator, separator, type OUB ().

Furthermore, a heat exchanger type HE (2) oers the ollowing advantages: Superheating the suction gas provides greaterr protection against liquid k nock in greate the compressor and counteracts ormation o condensate or rost on the surace o uninsulated suction lines. Sub cooling the reriger rerigerant ant liquid counter-acts the ormation o vapour, which will reduce the capacity o the thermostatic expansion valve. Operating economy will oten be improved because sources o loss such as unevaporated evaporate d liquid drops in the suction gas and insufcient sub cooling o the rerigerant liquid are completely or partially eliminated.


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Manual

Oilseparator


Fig. 8

OUB

Hot high-pressure gas is supplied to the oil separator type OUB through the connector (). 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 oil separator through the upper connector (4).

Heatexchanger

Separated oil is collected in the bottom o the oil tank (2), which is kept heated by the incoming vapour. In this way the separated oil is stored in a warm condition, i.e. with the lowest possible rerigerant content. A oat valve (5) regulates oil return to the compressor.

Fig. 9

HE

Heat exchanger type HE has been designed with a view to achieving maximum heat transmission at minimum pressure drop. The outer spiralormed chamber (4) leads hot reriger rerigerant ant liquid in a ow counter to the ow o cold rerigerant liquid in the inner chamber (3). Built in to the inner chamber are oset n sections. Heat exchanger type HE is manuactured in brass and copper and has very small dimensions in relation to its heat transmission capacity. The


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spiral ormed outer chamber (4) orces the hot rerigerant liquid over the entire heat transmission surace and prevents the ormation o condensate on the outer jacket. The built-in oset n sections in the inner chamber (3) produce turbulent ow in the rerigerant vapour. Heat transmission rom liquid to vapour is thus very eective. At the same time, pressure drop is kept down to a reasonable level.

5

Manual

Rerigerationplantora largercoldstore


Fig. 20

Complete rerigeration plant or a larger cold store with temperature above reezing point

To ensure eective eective shut-o o the liquid line during compressor standstill periods, solenoid valve EVR () has been installed since bulb temperature may be expected to rise more rapidly than evaporating temperature and cause the thermostatic expansion valve to open. Protection against overcharging the evaporator during compressor standstill periods is provided by making the solenoid valve close at the same time as the compressor is stopped.


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The liquid line is equipped with type GBC (2) or BML manual shut-o valves to make replacement o the lter drier easy. Pressure on the high and low-pressure sides o the compressor can be read on the pressure gauges shown. The pressure gauges can be shut o with the three-way valves type BMT (3).

6

Manual

Solenoidvalve


Fig. 2

EVR

Solenoid valve type EVR is a servo-controlled electromagnetic electromag netic shut-o valve. Through equalizing holes (2) the upper side o the diaphragm () is pressure-equalized with the valve inlet pressure on the underside. When When current energizes energizes the coil (3) the pilot orice (4) is opened. This orice has a larger through-ow through-ow area than the total area o the equalizing holes. Shut‑ovalve

Pressure over the diaphragm is reduced by the ow through the pilot orice to the valve outlet side and the larger inlet pressure on the underside lits the diaphragm. When the coil is de-energized,, the pilot orice closes and the de-energized diaphragm is drawn onto the valve seat as the pressure over it increase through the equalizing holes.

Fig. 22

BM

Shut-o valves types BM have a triple diaphragm seal () o stainless steel. A thrust shoe (2) prevents direct contact with the spindle (3). The spring (4) together with the pre-stressed diaphragm is able to hold the valve open at operating pressures down to Pe = – bar.


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The counter seat in the cover (5) prevents the ingress o moisture. The valves are available in straight, and  /4" T versions. Flow through the side port o the T version can be shut o leaving the end ports permanently open.

7

Manual

Keydiagram,controlcurrent orrerigerationplant,fg.20


Fig. 23

The diagram must be read rom top to bottom and rom let to right. The individual circuits are drawn so that no leads cross. Power-consuming components are shown at the bottom o the diagram. These These include relay coils in the motor starters, solenoids coils, regulation motors, motors, etc. Motor starter thermal relays F are shown adjacent to the contacts between terminals 95 and 96. Manual reset S is also shown. Relay auxiliary contacts K between terminals 3 and 4 are shown at the top o the diagram. Designations Designations 3, 4, 95, 96, etc. correspond to those contained in Danoss inormation on contactors and motor starters. Relay coils K serve the auxiliary contacts between terminals terminals 3 and 4. The auxiliary contacts are drawn in their de-energized coil position. Under the neutral wire and each relay coil there is an indication o in, which circuit the associated auxiliary contacts, can be ound.


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Terminal designation 3-4 is, by denition, Terminal always a make contact (NO), while terminal designation -2 is always a break contact (NC). The key diagram should be read as ollows: When, on rising cold store temperature, thermostat type KP 6 cuts in (when switches S and S2 are made) between terminals terminals 2 and 3, relays K and K2 in motor starters type CIT pull in and start the evaporator ans. At the same time the associated auxiliary contacts in circuits 3 and 4 are made. Relay K3 in compressor motor starter type CIT pulls in i the combined high and low pressure control type KP 5 is made between terminals terminals 2 and 3, and i switch S3 is made. The compressor compressor starts and at the same time the auxiliary contact in circuit 5 connects current to coil E in the EVR solenoid valve in the liquid line. The solenoid valve opens and rerigerant liquid is injected into the evaporator, regulated by thermostatic expansion valve type TE.

8

Manual

Motorstarters


Fig. 24

The Danoss motor starter range up to 420 A is made up o modules. It consists o a basic module (contactor type Cl) onto which up to our auxiliary contact blocks (type CB) can be clipped as necessary. There There is also a range o thermal relays (type TI). The let-hand diagram shows a motor starter with start- stop / reset unction. The start contact (type CB-S) carries the terminal designation 3-4. The right-hand diagram shows a motor starter with stop/reset unction, controlled via a thermostat, pressure control, or similar.

The motor starters are available in several versions. The examples shown are tted with a manually lockable stop and reset or the thermal relay, i.e. the starters must be manually reset ater thermal cut-out. The modules are based on thermoplastic (CI) and Bakelite/thermoplastic Bakelite/ther moplastic (TI), and all main and auxiliary contacts are made o a special silver alloy. All steel parts are eectively corrosion protected. Sot starter type MCII and circuit breaker type CTI are also available rom Danoss.

The motor starters are equipped with a thermal relay having three indirectly heated bimetals. Through a cut-out mechanism the bimetals break the bounce-ree switch between terminals 95 and 96 in the event o overloading overloading.. Large current asymmetry between the three motor phases activates a built-in dierent dierential ial cut-out, which ensures an accelerated accelerated trip - as distinct rom what occurs under a normal symmetrical overload. The cut-out is partly temperature-compensated; temperature-compensated; up to a temperature o 35°C it compensates or any rise in the ambient temperature temperature not arising rom overloading. © Danoss A/S (RC-CMS / MWA), MWA), 03 - 2004

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9

Manual

Centralrerigerationplant orcoldstoretemperatures abovereezingpoint


Fig. 25

Temperature and relative humidity play a signicant role in the keeping o oodstus and the various categories o ware must be stored in the most avourable conditions. There is use thereore or cold stores having dierent temperatures and humidities; not only the room temperature but also the evaporating temperature must be under control. In the example shown, the ollowing temperatures might be considered: Room Ro om te temp mp..

Evap Ev apor ora ati ting ng temp mp..

Vegetable store

+8°C

+3°C

Sliced meat and salad store

+5°C

–5°C

Meat store

0°C

–0°C

The room temperature in all 3 cold stores are controlled with KP-62 thermostats opening and closing the EVR solenoid valves.


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Two evaporating temperature regulators type KVP () throttle the suction line ater the evaporator in the +8°C and +5°C stores so that the evaporating temperatures are maintained at +3°C and –5°C respectively. Combined high and low pressure control type KP 5 (2) cuts the compressor in and out at a suitably low suction pressure to maintain evaporating temperature in the 0°C store at –0°C. During compressor standstill, check valve type NRV (3) prevents rerigerant rom the evaporators in the +8°C and +5°C stores condensing in the coldest evaporator, i.e. the one in the 0°C store. Check valve type NRV (4) aords protection against rerigerant condensing in the oil separator and compressor top cover i these components become colder than the evaporator during plant standstill periods.

20

Manual

Evaporatingpressure regulator


Fig. 26

KVP

Evaporating pressure regulator regulator type KVP opens when pressure rises on its inlet side, i.e. when pressure in the evaporator rises (increasing load). Turning the regulating screw () clockwise compressess the spring (5) and increases the compresse opening pressure, i.e. evaporating temperature rises. The regulator regulator has a bellows (0) o the same diameter as the valve plate (2). This means that pressure variations on the outlet side o the regulator have no eect on the automatic regulation o the degree o opening since Checkvalve

pressure on the top o the valve plate is balanced by pressure on the bellows. The regulator also incorporatess a damping device () so that incorporate pressure pulsations in the plant do not aect the unction o the regulator. To make adjustment o the valve easier, it is tted with a special pressure gauge connection (9), which makes it possible to t or remove a pressure gauge without rst having to empty the suction line and evaporator. evaporator.

Fig. 27

NRV

Check valve type NRV is available in straight or angle versions with are as well as solder connections. Solely the pressure drop controls the unction o the valve across it. NRV straightway version: The valve plate is tted to a brake piston (), which is held against the valve seat by a weak


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spring (2). When the valve opens, the volume behind the brake piston becomes smaller. smaller. An equalizing hole (slot) allows the reriger rerigerant ant to slowly escape to the outlet side o the valve. In this way the movement o the piston is broken; an arrangement that makes the check valve well suited or lines where pressure pulsations can occur.

2

Manual

Keydiagram,controlcurrent orrerigerationplantfg.25


Fig. 28

Thermostat type KP 62 in the +8°C room controls solenoid valve E type EVR in the liquid line while the two other thermostats type KP 62 in the +5°C and 0°C rooms respectively control motor starters K and K3 type CIT or the evaporator ans, and solenoid valves K2 and K3 type EVR in the liquid lines. Combined high and low pressure control type KP 5 controls motor starter K4 type CIT or the compressor motor. A condition or this unction is that manual switches S, S2, S3 and S4 must be made.

However, since it is unlikely that all the room thermostats will cut out at the same time, this orm o control will result in some ater-evaporation, which can be advantageous as regards liquid hammer in the compressor but disadvantageouss as regards the end o a disadvantageou rerigeration period. When a room thermostat cuts out, slight evaporation will still continue and the charge in the evaporator concerned concerned will become smaller. When the room thermostat cuts in again, the eect o the smaller charge will be to make it more difcult or un-evaporated rerigerant reriger ant to enter the suction line during the sudden priming at the beginning o the evaporator-operating evaporator -operating period.

The compressor motor is thus only indirectly controlled by the room thermostats and is able; or example, to run or some time ater all the thermostats have cut out.


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22

Manual

Rerigerationplantor reezerdisplaycounter


Fig. 29

As this plant operates most o the time at low evaporating temperatures, interrupted only by automatic derosting once or twice every 24 hours, it is advantageous to have an electric compressor motor o a size corresponding to normal operating conditions, i.e. relatively small load at low suction pressure. However, ater a derosting this small motor would be overloaded and there would be a risk o motor burn-out. As a saeguard against this risk a crankcase pressure regulator regulator type KVL () is installed which rst opens when suction pressure in ront o the compressor has been reduced sufciently to avoid overloading the motor. Regulating system KVR (2) + NRD (3) is used to maintain a constant and sufciently high condensing pressure in the receiver on air-cooled condensers at low ambient temperatures. During winter operation the ambient temperature ails and with it the condensing pressure pressure o the air-cooled condenser. The KVR regulates dependent on the inlet pressure and begins to throttle when the pressure drops below the set value. As a consequence consequence,, the condenser becomes becomes partly charged with liquid and its eective area is reduced. In this way the required condensing pressure is re-established. Since the actual regulating task during winter operation is to maintain the receiver pressure at a suitably high level, the KVR is combined with a type NRD dierential pressure valve installed in the bypass line shown. The NRD begins to open at a dierential pressure o .4 bars. When the


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condensing pressure pressure ails, the KVR begins to throttle. This increases the total pressure drop across the condenser + KVR. When this pressure drop reaches .4 bars, the NRD begins to open and thus ensures that the receiver pressure is maintained. As a rule-o-thumb, it can be assumed that the pressure in the receiver is equal to the pressure set on the KVR minus  bar. During summer operation, operation, when the KVR is ully open, the total pressure drop across the condenser and KVR is less than .4 bars. Thereore the NRD remains closed. The charge can collect in the receiver during summer operation. Thereore the plant must be equipped with a sufciently large receiver. The KVR can also be used as a relie valve between between the high-pressure side and low pressure side to protect the high pressure side against too high a pressure (saety unction). The pressure-lubricated compressor compressor with oil pump is protected against oil ailure by dierential dierent ial pressure control type MP 55 (4). The control stops the compressor i the dieren dierential tial between the oil pressure and suction pressure in the crankcase becomes too low. A type 077B thermostat is installed in the counter, counter, with its sensor located in the cold room. I the temperature rises above the set value, a signal lamp lights up.

23

Manual

Dierentialpressurecontrol


Fig. 30

MP 55

Dierential pressure control type MP 55 is used as a saety pressure control on pressure-lubricated rerigeration compressors. Ater a xed time delay the control stops the compressor in the event o oil ailure. The oil pressure element “OIL” () is connected to the oil pump outlet and the low-pressur l ow-pressure e element “LP” (2) is connected to the compressor crankcase. I the dierential between oil pressure and pressure in the crankcase becomes less than the value set on the control, current to the time relay is cut in (contact T  - T2 made, see wiring diagram). I contact T  - T2 remains made or a lengthy period because o a all in pressure in relation to the pressure in the crankcase (suction pressure) pressure),, the time relay cuts out the control current to the compressor motor starter (time relay contact changes over rom A to B, i.e. control current is broken between L and M).


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The minimum permissible dierential pressure, i.e. the minimum oil pressure at which under normal operation the dierential pressure control sustains current to the time relay cut o (contact T - T2 broken), can be set on the pressure adjustment disc (3). Clockwise rotation increases the dierential, i.e. increases the minimum oil pressure at which the compressor can still run. The contact dierential is xed at 0.2 bars. Thereore, current to the time relay will be rst cut o during start, when the oil pressure is 0.2 bars higher than the minimum allowable dierential pressure. This means that at compressor start the oil pump must be capable o increasing the oil pressure to 0.2 bars more than the set minimum permissible oil pressure beore the end o the time delay. Contact T  - T2 must break so quickly ater start that the time relay never reaches it’s A to B changeover point (break between L and M). See also key diagram, g. 35.

24

Manual

Crankcasepressure regulator


Fig. 3

KVL

Crankcase pressure regulator regulator type KVL opens on spindle () clockwise tightens the spring (5) and alling pressure on the outlet side, i.e. on alling Condensingpressure regulator

the regulator then begins to regulate at a higher pressure ahead o the compressor. Turning the pressure on the outlet side.

Fig. 32

KVR

Condensing pressure regulator regulator type KVR opens when pressure on its inlet side rises, i.e. when condensing pressure rises. Turning the spindle () clockwise tightens the spring (5) and increases

the opening pressure so that the condensing pressure rises.

Like the previously mentioned evaporating pressure regulator type KVP, all regulators are tted with a pressure-equalizing bellows (0) to eliminate pressure pressure variations on the inlet side o type KVL and the outlet side o type KVL All regulatorss are also tted with a damping device regulator () so that pressure pulsations in the plant do not aect regulator unction.


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25

Manual

Dierentialpressurevalve


Fig. 33

NRD

Dierential pressure valve type NRD begins to Dierential open at a pressure drop o .4 bars and is ully open at 3 bars. When the valve is installed as a bypass, it ensures that the receiver pressure is maintained.

Evaporatorthermostat

Fig. 34

077B

The contact system in evaporator thermostat thermostat type 077B makes on rising temperatures. temperatures. Turning the range spindle clockwise increase the cutin temperature o the thermostat, i.e. the temperature at which the signal lamp lights up.


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26

Manual


Keydiagram,rerigerationplantorreez Keydiagram,reri gerationplantorreezerdisplaycount erdisplaycounter,fg er,fg.29 .29 Fig. 35

Time switch P controls changeover contact t, circuit 2, which makes or breaks control current to contactors K and K2 type Cl or the respective electric heating elements under the evaporators, and or the evaporator ans. When K2 is cut in, K is cut out, i.e. the evaporator ans are stopped during derosting. At the same time, motor starter K3 type CIT or the condenser an is cut out via the auxiliary contact (brake contact between 2 and 22) in circuit 4. A signal lamp H is switched on via the auxiliary contact (make contact between 3 and 4) in circuit 6. When motor starter K3 cuts out, the auxiliary contact (make contact between 3 and 4) in circuit 5 breaks and motor starter K4 type CIT or the compressor is cut out. Thus, the compressor also remains at a standstill.

evaporators while derosting was taking place, evaporators beore the evaporator ans are started. Low-pressure control type KP  (II) is connected to control the rerigeration plant during normal operation. High-pressure High-pressure control type KP 5 stops the compressor but not the condenser an when condensing pressure becomes excessive. A thermostat type 077B switches on signal lamp H3 i the temperature in the display counter exceeds –8°C. The signal lamps are connected to a 2 V battery system so that lamp H3 is able to unction even i a mains supply ailure occurs.

Pressure control control type KP () is connected so that it cuts out on rising pressure. This This cuts out derosting when the suction pressure has increased to such an extent that there is no more rost on the evaporator evaporator.. When contactor K2 is cut out, motor starter K3, and with it motor start K4 are cut in via the auxiliary contacts (make contact between 2 and 22) in circuit 4 and in circuit 5 (make contact between 3 and 4). Assuming switches S and S2 are made. This starts the condenser an and the compressor. compressor. At the same time, signal lamp H is switched o via the make contact between 3 and 4 in circuit 6 and signal lamp H2 is switched on via the auxiliary contact (make contact between 3 and 4) in circuit 7. The evaporator ans are started ater a period by time switch P cutting in contactor K. During this delay the compressor is able to remove the heat accumulated in the


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27

Manual

Mainwiringdiagramor contactors


Fig. 36

Wiring diagram or contactors contactors K and K2 type Cl or the display counter rerigeration plant, g. 29. For key diagram see g. 35.


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The changeover switch or time switch P controls the contactors so that one is cut in while the other is cut out. The main contacts -2 and 3-4 in contactor K2 are each connected to an electric heating element. Contactor K has our main contacts, each o which is connected to a single-phase an (-2, 3-4, 5-6,3-4).

28

Manual

Rerigerationplantor ventilationair


Fig. 37

An electronicallycontrolledsuctionpressure regulatortype regulator type KVS () is installed in the suction line. The electronic regulato regulatorr receives signals rom a central control unit, e.g. a PLC, which in turn receives signals rom a temperature sensor located in the return air ow rom the room in which the ventilation air is to be cooled. The KVS valve opens i the temperature temperature o the return air rises. I the temperature registered by the sensor rises, the valve opens a little more, and suction pressure rom the evaporator is increased. At the same time, the pressure drop across the valve is reduced as a result o reduced evaporation temperature temperatu re and increased suction pressure. This increases the capacity o the evaporator and compressor. I the temperature registered by the sensor alls, the valve closes a little more, and suction pressure rom the evaporator is reduced. At the same time, the pressure drop across the valve is increased as a result o increased evaporation temperature temperatu re and reduced suction pressure. This reduces the capacity o the evaporator and compressor. As plant such as this must be capable o running irrespective o load, compressor capacity must be adjustable.

that the compressor is either shut o by the lowpressure cut-out or is subjected to suction pressure below the acceptable minimum. This is achieved by the KVC valve being set to start opening in order to prevent the abovementioned limits rom being crossed. This hotgas bypass transers some high-pressure gas rom the pressure side o the plant to the suction side, thus reducing rerigera rerigeration tion capacity. This type o capacity regulation results in a certain degree o suction gas superheating. As a result, the temperature o the high-pressure gas increases, thus increasing the risk that oil in the compressor pressure valves will become coked. In order to prevent this, a thermostatic expansion valve type T (3) is installed in a bypass between the liquid line and the suction line. The valve sensor is installed in the suction line immediately ahead o the compressor. In case o excessive superheating superheating in this region, the valve opens and some liquid is injected into the suction line. When this liquid evaporates, superheating is reduced and thus also the highpressure gas temperature. A solenoid valve type EVR (4) is installed immediately immediate ly ahead o the thermostatic expansion valve (3) in order to prevent liquid rerigerant reriger ant rom entering the suction line when the rerigeration plant is shut down.

A capacityregulator type KVC (2) is suitable or this purpose as this regulator is able to prevent suction pressure rom dropping to such an extent Continued overleaf... © Danoss A/S (RC-CMS / MWA), MWA), 03 - 2004

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29

Manual


Fig. 38

KVS

Electronicallycontrolledsuctionpressure regulator KVS () is a suction pressure regulator, regulator, activated by a stepper motor. It alters the degree o opening in response to signals rom the EKC 368 regulatorr which transmits pulses that cause the regulato valve motor to rotate in one direction or the other depending on whether the valve is to be opened more or closed more.


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Fig. 39

KVC

Capacityregulator The capacity regulator type KVC opens in response to alling pressure on the discharge side, i.e. alling suction pressure ahead o the compressor.

30

Manual



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3

Manual



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32

Manual



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33

TheDanossproductrangeorthe rerigerationandairconditioningindustry Compressorsorrerigerationandairconditioning These products include hermetic reciprocating compressors, scroll compressors and an-cooled condensing units. Typical applications are air conditioning units, water chillers and commercial rerigeration systems. CompressorsandCondensingUnits This part o the range includes hermetic compressors and an-cooled condensing units or household rerigerators and reezers, and or commercial units such as bottle coolers and drinks dispensers . We also oer compressors or heat pumps, and 2 and 24 V compressors or rerigerators and reezers in commercial vehicles and boats. Appliancecontrols For the regulation o rerigeration appliances and reezers Danoss supplies a product range o electromechanical thermostats produced according to customer specications; electronic temperature controls comprising models with and without displays; service thermostats – or servicing on all rerigerating and reezing appliances. Rerigerationandairconditioningcontrols Our ull product range covers all control, saety, system protection and monitoring requirements in mechanically and electronically controlled rerigeration and air conditioning systems. The products are used in countless applications within the commercial and industrial rerigeration and air conditioning sectors.

RG00A502

Produced by Danoss RC-CMS. 03.2004 .MWA

Danfoss Automation of Commercial Refrigeration Plant

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