applications pm modulating pressure and temperature...

PM Modulating pressure andtemperature regulators

Applications

Refrigeration and Air Conditioning Controls

R E F R I G E R A T I O N A N D A I R C O N D I T I O N I N G

2 RA.4X.A2.02 � Danfoss A/S, 08-2001

Applications Modulating pressure and temperature regulators

Introduction

Danfoss PM regulators have been on themarket for more than ten years.During that period they have shown theirstrength in countless applications inrefrigerating, freezing and air conditioningsystems.

Today they show this strength even more; thecapacity range has been widened and theregulating performance has been enhancedwith electronics:The electronically controlled pilot valve CVQregulates the media temperature in systemsrequiring extremely accurate temperatureregulation.

PM regulators are supplied in two versions,PM 1 and PM 3:The PM 1 version is designed for the fitting ofone pilot valve, whereas it is possible to fitthree pilot valves to the PM 3 version.This gives several functions in the same valve.

PM regulators are also available as solenoidvalves, designated PML

The regulators may be used with all types offluorinated refrigerants and ammonia.

This publication deals with a number ofapplications that incorporate the PM.

If you have experience with other applications,please do not hesitate to contact Danfoss

� Danfoss A/S, 08-2001 RA.4X.A2.02 3


Contents Regulating Page

A Evaporating pressure 3

B Temperature of the medium 6

C Crankcase pressure 10

D Capacity 13

E Condensing pressure 15

F Defrosting 16

Heat recovery

G Condensers mounted in series (a) 21

H Condensers mounted in parallel (b) 23

4 RA.4X.A2.02 � Danfoss A/S, 08-2001


A1Evaporating pressureregulation

Maintains constant evaporating pressure andtherefore constant evaporating temperature.Prevents too low an evaporating pressure andhence the formation of ice in, for example,water chillers.

Product list(1) PM 1 Main valve(2) CVP Constant pressure pilot

SettingCVPWhen the adjustment spindle is turnedclockwise, the the the opening pressure(evaporating pressure/ evaporatingtemperature) will increase- and vice versa.

Type Range Factory Change per turnsetting of adjustment

spindle

CVP �0.66-+2 bar Lowest Approx. 0.5 baradjustment

CVP 0-7 bar setting Approx. 1 bar(spring slack)

CVP (HP) 6-22* bar Approx. 1.8 bar

* 28 bar on special order.

Fine adjustmentFine adjustment with pressure gauge.

� Danfoss A/S, 08-2001 RA.4X.A2.02 5


A2Evaporatingpressure regulation

In the processing industry differentevaporating temperatures/ air exhausttemperatures can be used with advantage.

When the parameters are fixed, one PM 3 withtwo CVP pilots in cascade control with forcedcontrol can perform such a task.

Product list(1) PM 3 Main valve(2) CVP Constant pressure pilot(3) CVP Constant pressure pilot(4) EVIVI On / off pilot

SizingCapacity table Suction vapour.

FunctionMain valve PM 3 (1) regulates as a function ofthe evaporating pressure, which is controlledby low-pressure pilots (2) or (3). The mainvalve will close when the pressure dropsbelow the preset pressure of the pilots.

ExampleControlling two evaporating pressures in heatexchangers

I IIOutlet air temperature +3°C +8°CEvaporating temperature �20°C +2°CChange In temperature, at 5 K 6 KRefrigerant R 22 R 22Evaporating pressure 3,6 bar 4,4 bar

I: EVM pilot (4) in position SI opens. Hence theevaporating pressure is controlled by CVP pilot (3),which is preset to the lowest pressure.

II: EVM pilot (4) closes. Now the evaporating pressure iscontrolled by CVP pilot (2), preset to the highestpressure.

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B1Media temperatureregulation

Maintains constant temperature of the mediumby evaporating pressure control.

Product list(1) PM 1 Main valve(2) CVT Temperature controlled pilot

SettingCVTLoosen the locking ring. When the setting ringis turned clockwise, the opening temperatureis reduced - and vice versa.

Type Range Factory Change per turnsetting of adjustment

spindle

M �40 - O°C �300°C Approx. 6°C

CVT �10 - +25°C 0°C Approx. 60°C

CVT +20 - +60°C +30°C Approx. 6°C

Note:The CV17 valve is a proportional regulator (P-band = 4°C).Its use for temperature control where high accuracy isrequired or where large load changes occur is therefore notrecommended.

� Danfoss A/S, 08-2001 RA.4X.A2.02 7


B2Media temperatureregulation

Regulates the temperature of the medium(water or air).

Frost protection.

Product list(1) PM 3 Main valve(2) CVT Temperature controlled pilot(3) CVP Safety pilot (constant pressure)

ExampleTemperature regulation of water chiller

Water temperature +2°CEvaporating temperature –3°CChange in temperature, �t 5 KFrost protection temperature +0.5°CRefrigerant R 134aEvaporating pressure 1.65 barSafety pressure 1.5 bar

(~0.5 bar –�t = –4.5°C)

The sensor for the CVT pilot valve (2) ismounted on the water outlet from the waterchiller.

When the water temperature drops, CVT pilotvalve (2) will begin closing main valve PM 3(1). The main valve will regulate in such a waythat the desired water temperature ismaintained.

The CVP pilot valve is fitted in position SI witha safety setting so that the evaporatingpressure cannot become lower than 1.5 bar -or the evaporating temperature not lower than0.50 C.

The CVP pilot valve thus operatessimultaneously with the CVT pilot and ensuresthat the lower limit of regulation is maintained.

Note:In the event of widely fluctuating coolingrequirements the evaporating pressure regulationmay cause the compressor to stop at low pressure,unless the compressor has capacity regulation.

8 RA.4X.A2.02 � Danfoss A/S, 08-2001


Maintains the temperature of the mediumconstant with an accuracy of ± 0.25°C (orbetter) by evaporating pressure regulation.

The system is very suitable for a large numberof applications in the freezing, refrigeratingand air conditioning sectors as well as inprocess industries with central control.

See also Refrigeration Controls catalogue, orCVQ manual, literature no. RS.4J.B1.02.

Product list(1) PM 1 Main valve(2) CM Electric pilot (actuator)(3) EKS 61 Electronic temperature regulator(4) AKS 21M Pt 1000D air sensor

SizingCapacity table: Suction gas.

B3Media temperatureregulationwith PI regulator

FunctionSensor AKS 21 M (4) is mounted in the cooledairstream after the evaporator.

Controller EKS 61 (3) compares the sensortemperature and the reference temperatureset on EKS 61.

On changes in temperature (changed coolingrequirement), EKS 61 will immediately performstepless adjustment of the energy supply toCV0 pilot valve (2). This causes the degree ofopening of the PM valve to change. Thus therefrigerant flow is changed and with K theevaporating temperature and roomtemperature.

SettingSee Refrigeration Controls catalogue,or CVQ manual, literature no. RS.4J.B-.02.

� Danfoss A/S, 08-2001 RA.4X.A2.02 9


B4Media temperatureregulation with P1regulator

Maintains the temperature of the mediumconstant with an accuracy of ± 0,25°C (orbetter). Frost protection and forced control.

Because it is capable of handling thecooling-down phase as well as the often longstorage phase, this type of regulation isparticularly suitable for the temperature controlof fruit storage cold rooms.

Product list(1) PM 3 Main valve(2) CVQ Electric pilot (actuator)(3) EKS 61 Electronic temperature

regulator(4) CVP Constant pressure pilot(5) EVM On / off pilot(6) AKS 21 M Pt 1000 ��air sensor


FunctionSensor AKS 21 M (6) is mounted in the cooledairstream after the evaporator.

Controller EKS 61 (3) compares the sensortemperature and the preset temperature.

On changes in temperature (changed coolingrequirements), EKS 61 will immediatelyperform a stepless adjustment of the energysupply to CVQ pilot (2).

The pilot then causes the degree of opening ofthe PM valve to change so that the flow ofrefrigerant and therefore the evaporatingtemperature and air temperature are changed.

In addition, EKS 61 takes care of the forcedopening of EVM pilot (5) so that thecompressor gives maximum output during thecooling-down phase of the fruit storage room.

CVQ pilot valve (2), together with CVP pilotvalve (4), prevents evaporating temperaturebecoming too low during the storage phase. Inthis way, drying-out of the air and storedproduce is prevented.

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C1Crankcase pressureregulation

Protects the compressor motor againstoverload caused by excessive suctionpressure during start-up after standstill forsome time or after defrosting.

Product list(1) PM 1 Main valve(2) CVC Suction pressure pilot

Fine adjustment

Type Range Factory Change per Number of turnssetting turn for protection at �20*C

of adjustmentspindle R 12 R 22 R 502

CVC �0.45 -+ 7 bar �0.45 bar (spring slack) Approx. 1.5 bar 2/3 1 1/3 1 1/2

FunctionWhen pressure p. exceeds the CVC setting,the PM valve closes and thus ensures that theupper limit of the compressor suction pressureis observed.

SettingCVC: When the spindle is turned clockwise,the opening pressure will increase - and viceversa.

Fine adjustment with pressure gauge

� Danfoss A/S, 08-2001 RA.4X.A2.02 11



Protects the compressor motor againstoverload caused by excessive suctionpressure with forced opening of the PM valveafter the start-up phase (min. pressure drop).

Product list(1) PM 3 Main valve(2) CVC Suction pressure pilot(3) EVM On / off pilot(4) Ext. External connection(5) KP 1 Pressure control


FunctionWhen the pressure ahead of the compressorexceeds the setting of CVC pilot (2), PM 3main valve (1) closes and thus maintains theupper limit of the suction pressure.

When the operating pressure has beenreached, pressure control KP 1 (5) starts theforced opening of PM 3 (1). PM 3 (1) is thenforced fully open by EVM pilot (3) and hot gasfrom the external connection, Ext. (4).

The hot gas regulation means that PM 3can be sized for a very small �p (as low as0.02 bar).

SettingSee application Cl.

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Protects the compressor motor againstoverload caused by excessive suctionpressure and at the same time regulates theevaporating pressure.

Product list(1) PM 3 Main valve(2) CVC Differential pressure pilot(3) CVP Constant pressure pilot

SizingCapacity table: Suction vapour.

FunctionWhen the compressor suction pressureexceeds the setting of CVC pilot (2), PM 3main valve (1) closes and thus maintains theupper limit of the suction pressure.

When the operating pressure has beenreached, PM 3 (1) will be fully open, and pilotvalves CVC (2) and CVP (3) will be open. Ifthe pressure ahead of PM 3 drops below theCVP pilot setting, PM 3 will close and thusensure that the evaporating pressure islimited.

SettingSee application Cl.

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SettingCVC:When the adjustment spindle is turnedclockwise, the main valve will open at a highersuction pressure.

Adapts the fixed compressor capacity to thecooling requirements.

PMC 3 (1) capacity regulator may be used onstandard compressors as well as oncompressors with relief and fixed outputincrements.

Product list(1) PMC 3 Main valve(2) CVC Differential pressure pilot(3) LG Liquid / gas mixer(4) EVM “Pump down" pilot

SizingCapacity table for PMC: See next page orRefrigeration Controls catalogue, literature no.RK.00.H-.02.

FeaturesThis type of hot gas supply offers manyadvantages:

� Instantaneous compensation for refrigerantsuperheat at the evaporator outlet.

� Increased hot gas velocity in the evaporatorand improved return of oil. This isparticularly important even 9 the evaporatoris placed lower than the compressor.

� Limitation of the refrigeration output bycompressor capacity adjustment to suit theevaporator capacity. This avoids shortcompressor operating cycles.

� Prevents too low an evaporating pressureand thereby ice formation in, for example,water chillers. With air coolers, the cooledair is prevented from becoming too dry.

FunctionMain valve PMC (1) opens when the pressureahead of the compressor drops below thereference pressure of CVC pilot (2).

Hot gas is injected between the thermostaticexpansion valve and the distributor through aliquid/gas mixer, LG (3).Adapts the fixed compressor capacity to thecooling requirements.

Capacity

Type Size Rated capacity* k,-value(= rated-R 12-cap.* kWin TR) R 12 R 22 R 502 R 717 m 3 /h

5 18 32 30 85 1.5

PMC8 29 52 48 140 2.5

12 44 77 72 210 3.6

20 72 130 120 340 6.0

* Rated capacity at te = 10°C, tc = 32°C, offset = 4°C

Fine adjustmentFine adjustment with pressure gauge.

Type Range Factory Change per(suction setting turnpressure) of adjustment

spindle

CVC �0.45 - + 7 bar �0.45 bar Approx. 1.5 bar

D1Capacity regulation

14 RA.4X.A2.02 � Danfoss A/S, 08-2001


Adapts the fixed compressor capacity to thecooling requirement.

PMC 3 (1) capacity regulator may be used onstandard compressors as well as oncompressors with relief and fixed outputincrements.

Product list(1) PMC 3 Main valve(2) TEAT Thermostatic injection valve(4) EVM *Pump down pilot(5) EVR/EVRA Solenoid valve

SizingCapacity table for PMC See application D1 orRefrigeration Controls catalogue, literature no.RK.00.H-.02.

D2Capacity regulation

FunctionIs often used in two-step compressor plant.

Main valve PMC 3 (1) opens when thepressure ahead of the compressor dropsbelow the reference pressure of CVC pilot (2).This causes hot gas to be led into the suctionline ahead of the HP compressor.

An excessive amount of hot gas may give riseto increased compressor outlet temperature. Ifthis occurs, thermostatic expansion valveTEAT (3) will inject a quantity of refrigerantinto the suction line, causing a suctiontemperature drop.

Setting and capacitySee application D1.

� Danfoss A/S, 08-2001 RA.4X.A2.02 15


E1Condensing pressureregulation

Maintains the condensing pressure constantand at a sufficiently high level in aircooledcondensers in low ambient temperature.

Product list

(1) PM 1 Main valve(2) CVP (HP) Constant pressure pilot(3) NRD Differential pressure valve(4) NRVA Check valve

SizingCapacity table Hot gas

FunctionMain valve PM 1 (1) regulates in proportion tothe compressor outlet pressure set onconstant pressure pilot (2). The main valvecloses when the pressure dops below thepreset value.

NRD differential pressure valve (3) with a fixedsetting of 1.4 bar ensures sufficient pressurein the receiver.

NRVA check valve (4) fitted next to the outletfrom the condensor, ensures increasedcondenser pressure by variable liquidcollection. This requires a sufficiently largereceiver.

The NRVA check valve also prevents liquidflowing from the receiver back towards thecondenser when the latter is colder duringcompressor shut-down periods.

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F1Hot gas defrostingfrom top ofevaporator - directexpansion

This defrosting system is used on commercialand industrial central refrigerating systemswith several evaporators and direct expansion.

Product list(1) PM 1 Main valve (shut-off valve)(2) EVM On/off pilot(3) TE 20 Thermostatic expansion

valve(4) PM 1 Main valve (shut-off valve)(5) EVM On/off pilot(6) PM 3 Main valve (modulating)(7) CVPP (HP) Differential pressure pilot(8) EVM On/off pilot(9) NRVA Check valve(11) NRVA Check valve(12) PM 3 Main valve (modulating)(13) EVM On/off pilot(14) CVQ Electric pilot (actuator)(15) EKS 61: Electronic temperature

regulator(16) AKS 21M Pt 1000 � air sensor

SizingCapacity table Hot gas.

FunctionRefrigerating phaseLiquid passes through shut-off valve PM 1 (1)kept open by its pilot EVM (2).

Liquid injection occurs through thermostaticexpansion valve TE 20 (3).

Main valve PM 3 (12) modulates theevaporating pressure in order to maintain thetemperature of the air being cooled. Thefunction is performed by CVQ pilot (14) whichis itself controlled by electronic regulator EKS61 (15) with air sensor AKS 21 M (16). Pilotvalve EVM (13) is open.

Main valve PM 3 (6) in the high-pressure lineis kept open by pilot E~ Defrosting valve PM 1(4) is kept closed by pilot EVM (5).

Defrosting phaseMain valves PM 1 (1), PM 3 (6) and PM 3 (12)are closed - each by their own EVM pilot.

Main valve PM 1 (4) is opened by EVM pilot(5) and feeds hot gas against the direction offlow to the evaporators that need defrosting.

NoteTo ensure that the evaporators are properlydefrosted, at least two thirds of the plant mustbe under cooling and at most one third underdefrosting - otherwise the output of hot gas willbe insufficient.

During the defrosting phase main valve PM 3(6), controlled by differential pressure pilotCVPP (HP) (7), will give priority to defrostingby creating sufficient differential pressure Apbetween hot gas pressure and receiverpressure.

This pressure drop ensures that the liquidwhich is condensed during defrosting ispressed out into the liquid line through NRVAcheck valve (11).

SettingExampleSystem with R 22The CVPP (HP) (7) is preset at between1 and 1.5 bar.

� Danfoss A/S, 08-2001 RA.4X.A2.02 17


This defrosting system is used on industrialrefrigerating systems with direct expansion.

The use of PML (9) in the suction lineprovides complete tightness during thedefrosting phase and a minimal pressure dropduring the refrigerating phase.

The combination of a PM 1 (7) and a CVP (8)keeps the pressure at a sufficiently high levelin the evaporator during defrosting.

Product list(1) PM 1 Main valve (shut-off valve)(2) EVM On/off pilot(3) TE 55 Thermostatic expansion

valve(4) PM 1 Main valve (shut-off valve)(5) EVM On/off pilot(6) NRVA Check valve(7) PM 1 Main valve (modulating)(8) CVP (HP) Constant pressure pilot(9) PML Main valve (shut-off valve)

with very low pressuredrop

(10) EVM (NC) On/off pilot(11) EVM (NO) On/off pilot

SizingCapacity table Liquid and hot gas.

F2Hot gas defrostingfrom top of vaporatordirect expansion

Function

Refrigerating phaseLiquid passes through main valve PM 1 (1)kept open by its pilot EVM (2).

Liquid injection occurs through thermostaticexpansion valve TE 55 (3). Vapour is led tothe liquid separator through main valve PML(9) kept open by on/off pilots EVM (10) and(11).

During the refrigerating phase check valveNRVA (6) prevents liquid flowback towards thedefrost tray heating element.

Defrosting phaseMain valves PM 1 (1) and PML (9) are closedand hot gas is led to the top of the evaporatorthrough main valve PM 1 (4) which iscontrolled by on/off pilot EVM (5).

Condensed vapour returns to the liquidseparator through main valve PM 1 (7),controlled by constant pressure pilot CVP(HP) (8), when the pressure in the evaporatorexceeds the CVP (HP) setting - normally apressure corresponding to approx. +5°C.

18 RA.4X.A2.02 � Danfoss A/S, 08-2001


This defrosting system is used on refrigeratingsystems with pump recirculation, including - inparticular - systems with several evaporatorsand separate defrosting.

Product list(1) PM 1 Main valve (shut-off valve)(2) EVM On/off pilot(3) NRVA Check valve(4) 6F Throttle valve(5) PML Main valve (shut-off valve)

with very low pressure drop(6) EVM (NC) On/off pilot(7) EVM (NO) On/off pilot(8) PM 1 Main valve (shut-off valve)(9) EVM On/off pilot(10) PM 1 Main valve (modulating)(11) CVP (HP) Constant pressure pilot(12) NRVA Check valve

SizingCapacity table: Liquid and hot gas.

F3Hot gas defrostingfrom top of vaporator- pump recirculation

Function

Refrigerating phaseLiquid is led from the pump and passesthrough main valve PM 1 (1), kept open by on/off pilot EVM (2); K then passes through checkvalve NRVA (3), which has a very lowpressure drop.

Liquid Injection Into the evaporator occursthrough throttle valve 6F (4). The liquid/vapourmixture is led to the liquid separator throughmain valve PML (5), kept open by hot gas andon/off pilots EVM (6) and (7). The main valveis therefore fully open, even when thepressure drop is very low. Main valves PM 1(8) and (10) are closed.

Defrosting phaseMain valves PM 1 (1) and PML (5) are closed,and hot gas is led to the top of the evaporatorthrough main valve PM 1 (8), controlled by on/off pilot EVM (9).

Check valve NRVA (3) prevents liquidflowback through main valve (1) into the pumpline.

Condensed vapour returns to the liquidseparator through main valve PM 1 (10),controlled by constant pressure pilot CVP(HP) (11); this makes it possible to maintainthe pressure necessary for defrosting theevaporator and at the same time ensures theexpansion of condensed vapour.

� Danfoss A/S, 08-2001 RA.4X.A2.02 19


Recovery of condenser heat inrefrigerating systems wholly orpartially without affecting theoperation of the plant.

15%In this case only 15% of thecondenser heat is recovered, but at ahigh temperature level. Thesuperheat is recovered.

Application exampleProduction of domestic hot water

50%This calls for a recovery systemconnected in series. The pressuredrop will be the loss in the heatrecovery condenser plus the loss inthe main condenser.

Application examples Heating of airPreheating of water in a hot-watertank

100%100 % recovery of condenser heat.The pressure drop is insignificant.However, it must be remembered that9 capacity is reduced, recovered heatis also reduced.

Application examples Heating of airin air conditioning systems Officeheating

Heat recovery

20 RA.4X.A2.02 � Danfoss A/S, 08-2001


Condensers mounted in series (a)

Liquid flow in main condenser= Liquid flow in recovery condenser.

Total pressure loss= pressure loss in recovery condenser+ pressure loss in main condenser.

Principle

Condensers mounted in parallel (b)

Several recovery condensers arrangedIn parallel.

Total pressure loss= pressure loss in recovery condenserorpressure loss in main condenser.

� Danfoss A/S, 08-2001 RA.4X.A2.02 21



This heat recovery system is applicable to airas well as water.

Product list(1) PM 1 Main valve (shut-off valve)(2) EVM On/off pilot(3) PM 1 Main valve (modulating)(4) CVP (HP) Constant pressure pilot(5) NRV Check valve(6) NRD Differential pressure valve(7) NRV/NRVA Check valve(8) EVR Solenoid valve

G1Heat recovery

FunctionRefrigerating phase without heat recoveryHot gas is led direct into the main condenserthrough main valve PM 1 (3) with constantpressure pilot CVP (HP) (4). Check valve NRV(5) prevents flowback towards the heatrecovery condenser.

Recovery phaseMain valve (3) is Closed and main valve PM 1(1) is opened by on/off pilot EW (2), activatedby an electric clock, a thermostat, etc.

If the pressure gets too high, constantpressure pilot CVP (HP) (4) will open mainvalve PM 1 (3) so that part of the hot gas canflow towards the main condenser.

In summertime the heat recovery condenser isidle for extended periods of time.

To avoid the risk of accumulation of liquid inthis condenser, a solenoid valve EVR (8) withcapillary tube or throttling orifice ensuresperiodic evaporation of any condensate in therecovery condenser.

Differential pressure valve NRD (6) and checkvalve NRV (7) operate as described inapplication E1 (Condensing pressureregulation).

SettingSee application E1 (Condensing pressureregulation).

22 RA.4X.A2.02 � Danfoss A/S, 08-2001



This heat recovery system is applicable tocentral refrigeration plant with severalcompressors.

Product list(1) PM 3 Main valve (modulating)(2) CVPP (HP) Differential pressure pilot(3) EVM On/off pilot(4) NRV Check valve(5) NRD Differential pressure valve(6) NRVA Check valve(7) RT Thermostat

G2Heat recovery

FunctionAs long as only a small proportion ofcompressor capacity is used, all gas will passthrough the recovery condenser and then tothe aircooled main condenser.

The greater the amount of compressorcapacity used, the higher becomes thepressure drop in the recovery condenser.When this pressure drop exceeds the settingof differential pressure pilot CVPP (2), mainvalve PM 3 (1) partially opens and excesspressure gas is led direct into the maincondenser.

When the desired water or air temperaturehas been reached by means of the heatrecovery condenser, thermostat RT (7)activates on/off pilot EVM (3), and main valvePM 3 (1) will open fully.

Valves (4), (5) and (6) operate as described inapplication E1 (Condensing pressureregulations).

SettingSee application E1(Condensing pressure regulation)

� Danfoss A/S, 08-2001 RA.4X.A2.02 23


Condensers mounted in parallel (b)

This heat recovery system is applicable tosystems with several compressors - e.g for theheating of central heating water.

Product list(1) PM 3 Main valve (modulating)(2) CVP (HP) Constant pressure pilot(3) EVM On/off pilot(4) NRVA Check valve(5) NRVA Check valve(6) RT Thermostat(7) KVD Modulating high-pressure

regulator

H1Heat recovery

FunctionIn normal operation main valve PM 3 (1) iskept open by on/off pilot EVM (3), activated byan external control connected to thermostatRT (6).

In wintertime, when the heating demandnecessitates heat recovery, on/off pilot EVM(3) is closed, which in turn causes main valvePM 3 (1) to close.

If the condensing pressure exceeds thesetting of constant pressure pilot CVP (HP)(2), main valve PM 3 (1) will open and excesspressure gas will be led to the maincondenser.

Check valves NRVA (4) and (5) preventflowback of refrigerant to the condensers.

SettingSee application E1 (Condensing pressureregulation).


24 RA.4X.A2.02 � Danfoss A/S (RC-RCM/mwa) 08-2001

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