Danfoss 120U7018 User guide

Danfoss Inverter scroll

compressor, VRJ

For Residential Applications - R410A

Application Guidelines

http://danfoss.us.com/

Application Guidelines

4 FRCC.PC.019.A2.22

Contents

Introduction ...............................................................................................6

Scroll compressor components ................................................................................................................................. 6

Compressor size .............................................................................................................................................................. 6

Performance ..................................................................................................................................................................... 6

Compressor model designation ...............................................................7

Nomenclature ..................................................................................................................................................................7

Label .................................................................................................................................................................................... 7

Serial number ................................................................................................................................................................... 7

Technical specications ............................................................................ 8

Compressor specications ..........................................................................................................................................8

Performance data ..........................................................................................................................................................8

Variable speed drive specications .......................................................................................................................... 8

Bearings lubrication ....................................................................................................................................................... 8

Dimensions ................................................................................................9

VRJ 028 - 035 - 044..........................................................................................................................................................9

Electrical data, connections and wiring ..................................................10

Supply Voltage ............................................................................................................................................................... 10

Compressor electrical specications ......................................................................................................................10

LRA (Locked Rotor Amp) .............................................................................................................................................10

MCC (Maximum Continuous Current) .................................................................................................................... 10

Winding resistance ........................................................................................................................................................ 10

Wiring connections ...................................................................................................................................................... 11

Terminal cover mounting ...........................................................................................................................................11

Terminal cover removal ...............................................................................................................................................11

IP rating .............................................................................................................................................................................11

Internal motor protection ...........................................................................................................................................11

Phase sequence and reverse rotation protection .............................................................................................. 11

Approvals and certicates .......................................................................12

Approval and certicates ............................................................................................................................................12

Pressure equipment directive 97/23/EC ............................................................................................................... 12

Low voltage directive 73/23/EC, 93/68/EC ...........................................................................................................12

Internal free volume .....................................................................................................................................................12

Operating conditions ...............................................................................13

Refrigerant and lubricants .......................................................................................................................................... 13

Motor supply ...................................................................................................................................................................13

Compressor ambient temperature ..........................................................................................................................13

Application Guidelines

5FRCC.PC.019.A2.22

Contents

Application envelope ................................................................................................................................................... 14

High and low pressure protection ...........................................................................................................................15

Crankcase heating .........................................................................................................................................................15

Oil return management ...............................................................................................................................................15

On/o cycling (cycle rate limit) .................................................................................................................................16

Start-up sequence .........................................................................................................................................................16

System design recommendations ..........................................................17

General ..............................................................................................................................................................................17

Essential piping design considerations .................................................................................................................17

Refrigerant charge limit ..............................................................................................................................................18

Reversible heat pump systems .................................................................................................................................18

Minimum sump superheat .........................................................................................................................................18

Preventing liquid ood back ....................................................................................................................................18

Water utilising systems ...............................................................................................................................................19

Loss of charge protection ...........................................................................................................................................19

Oil level checking and top-up ................................................................................................................................... 19

Sound and vibration management .........................................................20

Starting sound level ...................................................................................................................................................... 20

Running sound level ..................................................................................................................................................... 20

Stopping sound level ...................................................................................................................................................20

Sound generation in a refrigeration system and air conditioning system ...............................................20

Installation ................................................................................................22

System cleanliness.........................................................................................................................................................22

Compressor handling and storage ..........................................................................................................................22

Compressor mounting .................................................................................................................................................22

Compressor holding charge ......................................................................................................................................22

Tube brazing procedure .............................................................................................................................................. 22

Brazing material .............................................................................................................................................................22

Compressor connection .............................................................................................................................................. 23

Vacuum evacuation and moisture removal .........................................................................................................23

Liquid line lter driers ..................................................................................................................................................24

Refrigerant charging .....................................................................................................................................................24

Insulation resistance and dielectric strength ......................................................................................................24

Compressor replacement after motor burn out ................................................................................................. 24

Ordering information and packaging ....................................................25

Packaging ........................................................................................................................................................................25

Ordering code numbers .............................................................................................................................................. 25

Application Guidelines

6 FRCC.PC.019.A2.22

Introduction

Scroll compressor

components

Compressor size

Performance

Danfoss VRJ for residential applications

developed by Danfoss is a complete package

consisting of a dedicated variable speed

compressor, variable speed drive, application

controller, electronic expansion valve (EEV), EEV

controller and sensors. Three nominal system

sizes are available (3, 4 and 5 TR), based on three

compressor models.

These Selection & Application Guidelines focus

on the variable speed scroll compressor.

The motor stator is rigidly attached to the shell.

The rotor is shrink-t onto the eccentric shaft. The

shaft is supported by two bearings, one in the

crankcase and the second below the motor.

Variable speed technology oers more exibility

in compressor selection than xed speed

compressors. Selection of the right variable

speed compressor size can be done by dierent

methods:

• Maximum cooling capacity: select a

compressor size that achieves the peak

load system cooling capacity demand at its

maximum speed.

• Nominal cooling capacity: select a

compressor size that achieves the nominal

system cooling capacity at a rotational

speed of 3000-4200 rpm (50-70Hz).

• Best Seasonal Eciency Ratio: select a

compressor size that achieves the minimum

system cooling demand at its minimum

speed. Ensure that the compressor is able to

cover the peak load system cooling capacity.

This selection makes the compressor to run

for a maximum of time at part load where

the system eciency is highest.

Danfoss scroll compressors are manufactured

using the most advanced machining, assembly,

and process control techniques. In design of

both the compressor and the factory, very high

standards of reliability and process control

were rst priority. The result is a highly ecient

product with the highest reliability obtainable,

and a low sound level.

The Danfoss VRJ compressors referenced in this

guide is a fully compliant scroll and actually

improves with run time in its early commissioning.

A seventy-two hour run-in is recommended to

meet performance expectations.

Application Guidelines

7FRCC.PC.019.A2.22

Compressor model designation

Label

Serial number

KS 1234509

Production year

Production week

Manufacturing location

Incremental number

Application, Family

& refrigerant

V: Variable speed

R: Residential

J: R410A, PVE lubricant

Swept Volume

Displacement in cc/rev

Model Variation

U: Design optimised for high SEER

Other features

6: No other features

Equipment version

P: Brased connections,

spade terminals

Motor protection

N: No internal motor

protection (protection by

drive)

Voltage

K: 420V DCL IPM

Model

Variation

028

Swept

Volume

VRJ

Application,

Family

& Refrigerant

Voltage

Motor

Protection

Equipment

Version

Other

Features

Nomenclature

Application Guidelines

8 FRCC.PC.019.A2.22

Technical specifications

Performance data

Variable speed drive

specications

Bearings lubrication

Compressor

model

Swept

volume

Displacement Oil charge Net weight

cu.in/rev

Min speed 30 Hz 60 Hz Max speed

oz lb

900 rpm 1800 rpm 3600 rpm 4200 rpm

VRJ028 1.64 51 103 206 240 36 68

VRJ035 2.12 66 133 265 310 45 71

VRJ044 2.65 83 166 332 387 45 71

Compressor specications

For dedicated variable speed drive specications,

refer to “Danfoss VRJ Installation and Operation

instructions”.

A specic oil pump ensures optimal bearing

lubrication at all compressor speeds. This to have

sucient bearing lubrication at low speeds as well

as avoid excessive Oil Circulation Ratio (OCR) at

high speeds.

Conditions

Compressor

model

Nominal

Tons

Compressor speed Compressor capacity

Compressor

isentropic eciency

rpm Hz Btu/hr Ton

High SEER

conditions

(H)

VRJ028 3 Tons

3600 60 36700 3.06 66.2

4200 70 42700 3.56 64.9

VRJ035 4 Tons

3600 60 46400 3.87 67.6

4200 70 53400 4.45 65.1

VRJ044 5 Tons

3600 60 57800 4.82 68.3

4200 70 68100 5.68 67.0

CHEER

conditions

VRJ028 3 Tons

3600 60 36500 3.04 65.9

4200 70 42300 3.53 64.3

VRJ035 4 Tons

3600 60 46200 3.85 67.3

4200 70 53000 4.42 64.6

VRJ044 5 Tons

3600 60 57900 4.83 68.8

4200 70 68300 5.69 67.5

Heat Pump

conditions

VRJ028 3 Tons

3600 60 25100 2.09 59.7

4200 70 29300 2.44 58.8

VRJ035 4 Tons

3600 60 31800 2.65 61.0

4200 70 36700 3.06 59.0

VRJ044 5 Tons

3600 60 40200 3.35 62.2

4200 70 47300 3.94 61.2

SEER

conditions (I)

VRJ028 3 Tons 1800 30 21000 1.75 68.5

VRJ035 4 Tons 1800 30 26800 2.23 69.7

VRJ044 5 Tons 1800 30 34500 2.88 70.9

Conditions

Evaporating

Temperature

(°F)

Condensing

Temperature

(°F)

Superheat

(°F)

Subcooling

(°F)

High SEER

conditions (H)

50 115 20 15

CHEER

conditions

45 100 20 15

Heat Pump

conditions

30 110 20 15

SEER

conditions (I)

55 100 20 15

Application Guidelines

9FRCC.PC.019.A2.22

Dimensions

VRJ 028 - 035 - 044

Mounting grommet

0.067

1.614

Ø 1.614

1.161

5/16” - 18 UNC

self tapping

Recommended torque for mounting bolts:

8 ft.lbs (±1ft.lbs)

Ø 0.433

9.40

4 x Ø 0.75 - 0.78

3.750

5.06

4.38

2.74 - 2.80

34°

31°

45°

14°

4.32

3.750

7.491 - 7.509

9.40

7.491 - 7.509

15.53

Suction port

3/4” ODF

6.438 - 6.515

2.84 - 2.95

14.19

7.76

9.09

0.42

0.75

Discharge port

1/2” ODF

All dimensions in inch

Application Guidelines

10 FRCC.PC.019.A2.22

Electrical data, connections and wiring

Supply Voltage

VRJ compressors must not be connected directly

to the mains supply. They must only be powered

through the dedicated Danfoss variable speed

drive.

Compressor model Variable Speed Drive Model

VRJ028 176L7000

VRJ035 176L7001

VRJ044 176L7002

Nominal voltage 208-230V – 1Ph – 60Hz

Voltage range 187 – 253 V

Refer to “Danfoss VRJ Installation and Operation

instructions” for more details about supply

voltage.

Compressor electrical

specications

Compressor model LRA MCC Winding resistance

A A Ohm

VRJ028 10.2 18 0.255

VRJ035 12 23.5 0.210

VRJ044 12 30 0.210

LRA (Locked Rotor Amp)

MCC (Maximum Continuous

Current)

Winding resistance

LRA is the higher average current as measured

on a mechanically blocked compressor tested

under nominal voltage. LRA is printed on the

nameplate, according to UL requirements. With

VRJ compressors, the LRA value is low because the

variable speed drive reacts very rapidly (far below

1 second).

The MCC value is the maximum at which

the compressor can be operated in transient

conditions and out of the operating envelope. The

MCC value is measured based on UL conditions

(max load) and at low voltage.

VRJ scroll compressors are equipped with an IPM

(permanent magnet) motor.

Winding resistance is the resistance between

indicated terminal pins at 77°F (resistance value ±

7%).

Winding resistance is generally low and it requires

adapted tools for precise measurement. Use

a digital ohm-meter, a ‘4 wires’ method and

measure under stabilised ambient temperature.

Winding resistance varies strongly with winding

temperature ; If the compressor is stabilised at a

dierent value than 77°F, the measured resistance

must be corrected with following formula:

tamb

= R

77°F

a + t

amb

a + t

77°F

: reference temperature = 77°F

amb

: temperature during measurement (°F)

77°F

: winding resistance at 77°F

tamb

: winding resistance at t

amb

a: Coecient a= 390

Application Guidelines

11FRCC.PC.019.A2.22

Electrical data, connections and wiring

Terminal cover mounting The terminal cover and gasket should be installed

prior to operation of the compressor. The terminal

cover has two outside tabs, 180 degrees apart, that

engage the terminal fence. When installing the

cover, check that it is not pinching the lead wires.

Terminal cover removal

Internal motor protection

Phase sequence and reverse

rotation protection

IP rating

Wiring connections

VRJ scroll compressors are not equipped with

an internal motor protector. Motor protection

is provided by the variable speed drive. All

motor para-meters are factory preset in order to

guaranty optimal locked rotor or overload current

protection.

The compressor will only operate properly in a

single direction. If electrical connections are done

correctly between the drive and the compressor

terminals (compressor and drive terminals T1, T2

and T3 matching), the drive will provide correct

phase supply to the compressor, and reverse

rotation will be not possible.

If compressor and drive T1, T2 and T3 terminals are

not matching, the compressor can go in reverse

rotation. This results in excessive noise, no pressure

dierential between suction and discharge, and

suction line warming rather than immediate

cooling. The compressor can be rapidly severely

damaged in these conditions.

The compressor terminal box IP rating according to CEI 529 is IP22 for all models. This IP rating is only

valid when correctly sized cable glands with the same IP rating are applied.

• First numeral, level of protection against contact and foreign objects

2 protection against object size over 1/2 inch (ngers of similar)

• Second numeral, level of protection against water

2 protection against dripping water when tilted up to 15°

VRJ scroll compressors will only compress gas

while rotating counter-clockwise (when viewed

from the compressor top).

The drawing shows electrical terminal labelling

and should be used as a reference when wiring the

compressor.

T1, T2 and T3 of the drive and the compressor

must be connected accordingly.

Refer to “Danfoss VRJ Installation and Operation

instructions” for details and cable sizes.

Quick connect spade terminals

P terminal box type

push

Application Guidelines

12 FRCC.PC.019.A2.22

Approvals and certificates

Approval and certicates VRJ scroll compressors comply with the following

approvals and certicates.

Pressure equipment

directive 97/23/EC

Low voltage directive

73/23/EC, 93/68/EC

Internal free volume

Manufacturer's declaration of incorporation

ref. EC Machines Directives 98/392/CE

Contact Danfoss

Products Internal free volume at LP side without oil (in.

)

VRJ028 - 035 - 044 179

Refrigerating uids Group 2

Category PED I

Evaluation module no scope

(Underwriters Laboratories)

All models

Other approvals / certicates Contact Danfoss

Application Guidelines

13FRCC.PC.019.A2.22

Operating conditions

Refrigerant and lubricants

Motor supply

Compressor ambient

temperature

General information

High ambient temperature

PVE

Low ambient temperature

Residual moisture

When choosing a refrigerant, dierent aspects

must be taken into consideration:

• Legislation (now and in the future)

• Safety

• Application envelope in relation to expected

running conditions

• Compressor capacity and eciency

• Compressor manufacturer

recommendations & guidelines

Additional points could inuence the nal choice:

• Environmental considerations

• Standardisation of refrigerants and

lubricants

• Refrigerant cost

• Refrigerant availability

In case of enclosed tting and high ambient

temperature, it is recommend to check the

temperature of power wires and conformity to

their insulation specication.

Polyvinyl ether (PVE) is an innovative refrigeration

lubricant for HFC refrigerant systems. PVE is as

hygroscopic as existing polyolester lubricants

(POE), but PVE does not chemically react with

water; no acids are formed and compressor

evacuation is easier.

The compressor technology applied in Danfoss

VRJ scroll compressors in combination with PVE

lubricant provides the best possible result in

terms of reliability and compressor lifetime.

Although the compressor itself can withstand

low ambient temperature, the system may

require specic design features to ensure safe

and reliable operation. See below sections for

recommendations.

Prior to shipment from the factory, every

compressor is dehydrated, evacuated, and

charged with dry nitrogen. Maximum residual

moisture levels are 0.0082 oz. for model VRJ028,

and 0.0120 oz. for VRJ035 and VRJ044.

VRJ scroll compressors can be operated only

connected to the dedicated variable speed

drive, at nominal voltages as indicated in “supply

voltage” section. Under-voltage and over-voltage

operation is allowed within the indicated voltage

range.

VRJ scroll compressors can be applied from

-13°F to 125°F ambient temperature. The

compressors are designed as 100 % suction gas

cooled without need for additional fan cooling.

Ambient temperature has very little eect on the

compressor performance

VRJ scroll compressor application range is

inuenced by several parameters which need to

be monitored for a safe and reliable operation.

These parameters and the main

recommendations for good practice and safety

devices are explained hereunder:

Refrigerant and lubricants

Motor supply

Compressor ambient temperature

Application envelope (evaporating

temperature, condensing temperature, return gas

temperature)

Application Guidelines

14 FRCC.PC.019.A2.22

Operating conditions

The operating envelope for VRJ scroll

compressors is given in the gure below, where

the condensing and evaporating temperatures

represent the range for steady-state operation.

Under transient conditions, such as start-up

and defrost for heat pump applications, the

compressor may operate outside this envelope

for short periods.

The operating limits serve to dene the

envelope within which reliable operations of the

compressor are guaranteed:

• Maximum discharge gas temperature: +275°F

• Suction superheat is dedictated by the

minimum sump superheat (see graph p16).

• Maximum superheat of 40°F

• Minimum and maximum evaporating

and condensing temperatures, as per the

operating envelopes.

All the below limits, temperatures and speeds,

are secured by the parameters in the drive and

application controller software’s.

The discharge temperature depends mainly on

the combination of evaporating temperature,

condensing temperature and suction gas

superheat and speed. Discharge gas temperature

should be controlled with an insulated sensor

attached to the discharge line, 6 in. from the

compressor shell. Maximum discharge gas

temperature must not exceed 275°F when the

compressor is running within the approved

operating envelope.

Refer to “Danfoss VRJ Installation and Operation

instructions” for connection details, and to

“Sensor Selection Guideline” manual for

selection details and technical brochures about

temperature sensors.

Application envelope

Maximum discharge gas

temperature

105

115

125

135

145

155

900 - 4500 RPM

2100 - 3750 RPM

2200 - 3300 RPM

2300 - 2850 RPM

2400 RPM Derated

1100 - 4500 RPM

1300 - 4500 RPM

1500 - 4200 RPM

1800 - 4200 RPM

-40 -30 -20 -10 0 10 20 30 40 50 60 70 80

Saturated evaporating temp. (°F)

Saturated condensing temp. (°F)

-40 -36 -32 -28 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24

(°C)

Application Guidelines

15FRCC.PC.019.A2.22

Operating conditions

Pressure settings

High pressure

Low pressure

High pressure ratio

Crankcase heating

Oil return management

R410A

Working pressure range high side psig 119 - 645

Working pressure range low side psig 28 - 202

Maximum high pressure safety switch setting psig 653

Minimum low pressure safety switch setting 

psig 22

: LP safety switch shall never be bypassed

According to UL requirements, a high pressure

safety switch is still mandatory in any system,

even with high pressure transmitters connected

and used via the variable speed drive.

HP switch settings shall not exceed the maximum

service pressure of any system components. The

high-pressure switch can be set to lower values

depending on the application and ambient

conditions. The HP switch must either be placed

in a lockout circuit or consist of a manual reset

device to prevent cycling around the high-

pressure limit. If a discharge valve is used, the HP

switch must be connected to the service valve

gauge port, which must not be isolated.

A low pressure (LP) safety switch is

recommended. Deep vacuum operations of a

scroll compressor can cause internal electrical

arcing and scroll instability. Danfoss scroll

compressors exhibit high volumetric eciency

and may draw very low vacuum levels, which

could induce such a problem. The minimum

low-pressure safety switch (loss of charge safety

switch) setting is given in the above table. Either

the LP safety switch must be a manual lockout

device or an automatic switch wired into an

electrical lockout circuit. The LP switch tolerance

must not allow for vacuum operations of the

compressor.

Scroll compressors are machines with xed

volume ratio, and operate more eciently

near the design pressure ratio. In the extreme,

do not exceed a 7.5:1 pressure ratio (absolute

discharge pressure to absolute suction pressure)

for extended periods. The Danfoss VRJ scroll

compressor is equipped with an internal pressure

relief valve for protection against blocked

condenser and fan failure conditions.

A crankcase heating function can be provided

by injecting a DC current in the motor of the

compressor, to keep the compressor warm, and

avoid liquid migration during o cycle.

Refer to “Danfoss VRJ Installation and Operation

instructions” for details.

A specic function can be enabled to secure

the oil return to the compressor. When the

compressor is running at minimum speed for

extended periods, every half hour, speed will be

increased to 2400 rpm for a 80 seconds period.

Suction and discharge pressure transmitters have

to be installed and connected to the variable

speed drive to ensure the compressor operates

within the application envelope described above.

Refer to “Danfoss VRJ Installation and Operation

instructions” for connection details, and to

“Sensor Selection Guideline” manual for selection

details and technical brochures about pressure

transmitters.

High and low pressure

protection

Application Guidelines

16 FRCC.PC.019.A2.22

Operating conditions

Start-up sequence To ensure correct lubrication of all the

mechanical parts, VRJ compressors start with

a dened ramp-up, and stay at a xed speed

for some seconds. Then the compressor speed

increases up to the desired set point according to

capacity request.

On/o cycling

(cycle rate limit)

The on/o cycling protection is included in the

variable speed drive. There is no need for extra

on/o cycling protection.

Application Guidelines

17FRCC.PC.019.A2.22

System design recommendations

Proper piping practices should be employed to

ensure adequate oil return, even under minimum

load conditions with special consideration given

to the size and slope of the tubing coming

from the evaporator. Tubing returns from the

evaporator should be designed so as not to trap

oil and to prevent oil and refrigerant migration

back to the compressor during o-cycles.

It is particularly important and critical with

variable capacity systems, where very low

velocities can be achieved for long periods of

time, generating oil return issues.

If the evaporator lies above the compressor, as

is often the case in split or remote condenser

systems, the addition of a pump-down cycle

is strongly recommended. If a pump-down

cycle were to be omitted, the suction line must

have a loop at the evaporator outlet to prevent

refrigerant from draining into the compressor

during o-cycles.

If the evaporator were situated below the

compressor, the suction riser must be trapped so

as to prevent liquid refrigerant from collecting at

the thermal bulb location (see g. 1).

When the condenser is mounted at a higher

position than the compressor, a suitably sized

«U»-shaped trap close to the compressor is

necessary to prevent oil leaving the compressor

from draining back to the discharge side of the

compressor during o cycle. The upper loop also

helps avoid condensed liquid refrigerant from

draining back to the compressor when stopped

(see g. 2). The maximum elevation dierence

between the indoor and outdoor section

cannot exceed 26 feet. System manufacturers

should specify precautions for any applications

that exceed these limits to ensure compressor

reliability.

Piping should be designed with adequate three-

dimensional exibility. It should not be in contact

with the surrounding structure, unless a proper

tubing mount has been installed. This protection

proves necessary to avoid excess vibration, which

can ultimately result in connection or tube failure

due to fatigue or wear from abrasion. Aside from

tubing and connection damage, excess vibration

may be transmitted to the surrounding structure

and generate an unacceptable noise level within

that structure as well (for more information on

noise and vibration, see the section on: “Sound

and vibration management” section.

Essential piping design

considerations

Successful application of scroll compressors

is dependent on careful selection of the

compressor for the application. If the compressor

is not correct for the system, it will operate

beyond the limits given in this manual. Poor

performance, reduced reliability, or both may

result.

General

0.5 % slope,

13 ft/s or more

0.5 % slope,

13 ft/s or more

U-trap

U-trap, as short as possible

max. 13 ft

g.1

max. 13 ft

26 to 40 ft/s

To condenser

Evaporator

Condenser

U-trap

3D exibility

Upper loop

g. 2

Application Guidelines

18 FRCC.PC.019.A2.22

System design recommendations

Reversible heat pump

systems

Minimum sump superheat

Preventing liquid ood back

Transients are likely to occur in reversible heat

pump systems, i.e. a changeover cycle from

cooling to heating, defrost or low-load short

cycles. These transient modes of operation may

lead to liquid refrigerant carryover (or ood

back) or excessively wet refrigerant return

conditions. As such, reversible cycle applications

require specic precautions for ensuring a long

compressor life and satisfactory operating

characteristics. Specic tests for repetitive ood

back are required to conrm whether or not

special system design considerations should be

considered.

The minimum sump temperature is in the range

from 10°F to 30°F above saturated suction

temperature. Refer to the ood back test criteria.

Danfoss recommends the use of an electronic

expansion valve for all air conditioning and heat

pump applications with VRJ compressors. An

EXV has two key benets: it provides modulating

control of the system under varying load

conditions, and it protects the compressors from

ood back during adverse running conditions.

Exceptions to the use of EXV’s with Danfoss

VRJ must be approved by Danfoss application

engineering.

Scroll compressors can tolerate liquid refrigerant

up to a certain extend without major problems.

However, excessive liquid refrigerant in the

compressor is always unfavourable for service

life. Besides, the installation cooling capacity may

be reduced because of the evaporation taking

place in the compressor and/or the suction line

instead of the evaporator. System design must be

such that the amount of liquid refrigerant in the

compressor is limited. In this respect, follow the

guidelines given in the section: “Essential piping

design recommendations” in priority.

Refrigerant charge limit

-10 0 10 20 30 40 50 55

Acceptable

Unacceptable

Floodback requirement

Sump superheat, °F

Saturated suction temp. °F

Application Guidelines

19FRCC.PC.019.A2.22

System design recommendations

Oil level checking and

top-up

Loss of charge protection

In installations with good oil return and line

runs up to 50 ft, no additional oil is required. If

installation lines exceed 50 ft, additional oil may

be needed. 1 or 2% of the total system refrigerant

charge (in weight) can be used to roughly dene

the required oil top-up quantity.

Always use oil from new cans.

Top-up the oil while the compressor is idle. Use

any accessible connector on the compressor

suction line and a suitable pump.

VRJ scroll compressors together with the variable

speed drive include a loss of charge protection

function. This protection is ensured if pressure

and temperature sensors are connected to the

drive.

Water utilising systems Apart from residual moisture in the system

after commissioning, water could also enter the

refrigeration circuit during operation. Water in

the system shall always be avoided. Not only

because it can shortly lead to electrical failure,

sludge in sump and corrosion but in particular

because it can cause serious safety risks.

Common causes for water leaks are corrosion and

freezing.

Corrosion: Materials in the system shall be

compliant with water and protected against

corrosion.

Freezing: When water freezes into ice its volume

expands which can damage heat exchanger

walls and cause leaks. During o periods water

inside heat exchangers could start freezing when

ambient temperature is lower than 32°F. During

on periods ice banking could occur when the

circuit is running continuously at too low load.

Both situations should be avoided by connecting

a pressure and thermostat switch in the safety

line.

Application Guidelines

20 FRCC.PC.019.A2.22

Sound and vibration management

Running sound level

Stopping sound level

Sound generation in a

refrigeration system and air

conditioning system

Compressor sound radiation

During start-up transients, it is natural for the

compressor sound level to be slightly higher

than during normal running. Danfoss scroll

compressors exhibit very little increased start-up

transient sound.

VRJ scroll compressors are designed with

optimised discharge ports and wrap geometry

to reduce the sound level when a compressor is

running.

VRJ scroll compressors have very low shutdown

sound due to minimal volume of discharge

volume to push scrolls in reverse at shutdown.

Due to this small re-expansion, there is no

internal break mechanism required to prevent

reverse spin of the scroll set.

Typical sound and vibration in refrigeration and

air conditioning systems encountered by design

and service engineers may be broken down into

the following three source categories.

Sound radiation: This generally takes an

airborne path.

Mechanical vibrations: These generally extend

along the parts of the unit and structure.

Gas pulsation: This tends to travel through the

cooling medium, i.e. the refrigerant.

The following sections will focus on the causes

and methods of mitigation for each of the above

sources.

For sound radiating from the compressor, the

emission path is airborne and the sound waves

are travelling directly from the machine in all

directions.

The VRJ scroll compressor is designed to be quiet

and the frequency of the sound generated is

pushed into the higher ranges, which not only

are easier to reduce but also do not generate the

penetrating power of lower-frequency sound.

Use of sound-insulation materials on the inside of

unit panels is an eective means of substantially

reducing the sound being transmitted to the

outside. Ensure that no components capable

of transmitting sound/vibration within the unit

come into direct contact with any non-insulated

parts on the walls of the unit.

Because of the Danfoss unique design of a full-

suction gas & oil cooled motor, compressor body

insulation across its entire operating range is

possible.

Starting sound level

Sound level vs Speed

45/130

4200

45/130

3600

45/100

3600

45/100

2400

45/100

1800

45/100

900

Condition (Tsat(suction) / Tsat (discharge) and speed (RPM)

Sound power level (dBA)

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Danfoss 120U7018 User guide

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