6-14-09 variable refrigerant flow handbook-1

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    Variable Refrigerant Flow

    ASHRAE Handbook Chapter XX

    VARIABLE REFRIGERANT FLOW (VRF) DEFINED2GENERAL DESIGN CONSIDERATIONS...16

    User Requirements17

    Diversity and Zoning.18Installation..20Refrigerant Pipe Design.20Maintenance Concerns...20Sustainability23

    TYPES OF VRF SYSTEMS...16EQUIPMENT AND SYSTEM STANDARDS...23

    AHRI Certification Programs....23Ventilation Standards.....23Refrigerant Management30Green Buildings.....34

    COMPONENTS AND SYSTEM LAYOUT34Software for Designing Systems.....23Indoor Unit Styles....23Controls....23Refrigerant Circuit and Components23Typical System Layout23

    SYSTEM OPERATION..36Explanations of P-H Diagram (Refrigerant Characteristics Table) .................. 36Concept of Basic Refrigeration Cycle ............................................................... 37Points of Refrigerant Control of VRF System ................................................... 38Cooling Operation............................................................................................... 38Heating Operation............................................................................................... 39Control of Electronic Expansion Valve.............................................................. 41Heating and Defrost Operations..43Heat-recovery Operations43

    APPLICATIONS BUILDING TYPES (NEW CONSTRUCTION AND RETROFIT)...43

    Offices.43Schools and Universities.43Limited Care Facilities; Nursing Homes.43Multi-tenant Dwellings, Apartments...43Hotel and Motel...43Churches..43Residential...43Hospitals..43

    REFERENCES... 44

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    VARIABLE REFRIGERANT FLOW DEFINEDMany HVAC professionals are familiar with mini-split systems: an air conditioner or heat pumpwith more than one factory-made assembly (e.g., one indoor and one outdoor unit). A variation ofthis product, often referred to as a multi-split or a variable-refrigerant flow (VRF) system, typicallyconsists of:1. A condensing section housing compressor(s) and condenser heat exchanger,

    2. Multiple indoor direct-expansion (DX) evaporator fan-coil indoor units with electronicexpansion devices, temperature sensing capabilities, and a dedicated microprocessor for individualcontrol,3. A single set of refrigerant piping that interconnects the condensing unit and the evaporator units,4. A zone temperature control device that may or may not be interlocked with a system controller.

    VRF multi-split products are fundamentally different from unitary or other types of traditionalHVAC systems in that heat is transferred to or from the space directly by circulating refrigerant toevaporators located near or within one conditioned space. In contrast, conventional systemstransfer heat from the space to the refrigerant by circulating air (in ducted unitary systems) orwater (in chillers) throughout the building. The main advantage of a VRF system is its ability to

    respond to fluctuations in space load conditions by allowing each individual thermostat tomodulate its corresponding electronic expansion valve to maintain its space temperature set point(see Tables 1 and 2 for a comparison of VRF to other systems).

    Table 1 Comparison of VRF and Unitary HVAC Systems

    Item Description VRF System Unitary System

    1 Condensing units components1.1 Single or multiple compressor Yes Yes1.2 Oil separator for each compressor or for all

    compressorsYes Yes

    1.3 Oil level control Yes Yes1.4 Active oil return Yes In some units

    1.5 Option for heating and cooling Yes Yes for hot gas defrostSimultaneous heating / cooling Yes No

    1.6 Air cooled or water cooled condenser Yes Yes1.7 Liquid receiver Yes Yes1.8 Control of the refrigerant level in the liquid receiver Yes Yes1.9 Condensing temperature control Yes It is an option1.10 Capacity control by the suction pressure Yes Yes1.11 Compressor cooling capacity control by speed

    (RPM) or stepsYes Yes

    1.12 Suction accumulator Depending on the System Yes2.0 Refrigerant lines2.1 Long liquid lines to many evaporators Yes Yes2.2 Refrigerant pipes special design procedure due to

    pressure drop and oil return

    Yes Yes

    3.0 Internal units3.1 Several units any size Yes Yes3.2 Independent control for each evaporator by an

    electronic expansion valveYes Yes

    3.3 Mechanical sub-cooling Provided for pressure drop(if necessary) and to

    improve performance

    Provided to improveperformance

    3.4 Expansion valve able to handle different coolingcapacities and pressure differential

    Electronic expansion valve Thermostatic or electronicexpansion valve

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    3.5 Coil and drain defrost Only necessary for theexternal unit heating

    Operational and protection

    3.6 Air filter Yes Not necessary3.7 Drainage pump Depends Depends4.0 Controls4.1 Microprocessor control condensing unit Yes Yes4.2 Microprocessor in the evaporator Yes Yes

    4.3 BMS available Yes Yes4.4 Inverters for power Yes Yes4.5 Alarm codes Yes Yes

    Table 2 Comparison of VRF and Chiller Systems

    Item Description Chilled Water System VRF System Comments

    1.0 Sensible coolingcapacity

    OK selection willalways meet the thermalload and air flow

    There is no option toselect equal to thethermal load and air flow

    Usually sensible cooling load forVRF is lower than the air flow,you may have to oversize the unit

    1.1 Latent coolingcapacity

    OK selection willalways meet the thermalload. It will be necessaryto add a heating device tocontrol humidity

    There is no option toselect equal to thethermal load

    Usually latent cooling load forVRF is a consequence from thesensible load it will be necessaryto add electrical heating forhumidity control

    1.2 Total coolingcapacity

    OK selection willalways meet the thermalload

    There is no option toselect equal to thethermal load and the airflow

    Usually total cooling load forVRF is lower than the thermalload or you may have to oversizethe unit

    1.3 Capacity Increaseor adjustment forSensible HeatFactorAir CooledCondenser

    Possible new coil andcontrol valve selection orchange in chilled watertemperature

    There is no option, itshould be anotherequipment or anotherrefrigerant lines

    Chilled water is more flexible.VRF was design to be compatiblewith usual Offices and comfortjobs SHF from 0.70 to 0.80

    1.4 Capacity Increase

    or adjustment forSensible HeatFactorWater CooledCondenser

    Possible new coil and

    control valve selection orchange in chilled watertemperature

    It should be provide

    room for expansion orcapacity increase easy tobe done.Difficult to change thesensible heating factor

    VRF was design to be compatible

    with usual Offices and comfortjobs SHF from 0.70 to 0.80

    2.0 Air flow in m3/h Adjustable it may needa motor change

    There is a band foradjustment between amaximum and minimumvalue

    Usually you should oversize thecooling capacity to match airflow

    2.1 Air flow pressuredrop

    Adjustable it may needa motor change

    There is a tap in themotor for adjustment fora higher value

    Very narrow band to adjust forVRF. If there is duct, the ductshould be calculated according tothe external pressure of the

    internal unit2.2 Air filter efficiency Compatible with almost

    air filter efficiencyIt uses a standard a lowefficiency filter 50%efficiency gravimetrictest not better thanMERV 4

    VRF there are options up to 85%efficiency dust spot test MERV11, but will reduce the externalpressure and will have a highercost

    2.3 Electrical motor efficiency internalunit

    Higher efficiency, couldbe better than 90%

    Lower efficiencyDepends on the modelminimum 60%

    There is no option to change themotor for VRF. Not good forASHRAE Standard 90.1-2004

    3.0 Condensate water Inside the machine room, It may need pump and Very unreliable for VRF

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    drainage no problem needs proper insulation Equipment may be over electricaldevices

    4.0 Long pipes - Air Cooled Condenser

    Increase chilled waterpump power but doesntchange capacity

    It reduces the capacityfor long lines up to 75%.It reduces the latentcooling capacity

    Very important to verify the realcapacity, including the suctionpressure drop for VRF. Greatissue

    4.1 Long condensingwater lines

    Increase condensingwater pump power butdoesnt change capacity

    Increase condensingwater pump power butdoesnt change capacity

    Both are very similar

    4.2 Refrigerant linessafety and leakageAir cooled units

    Only in the machineroom or in the outside air

    It is all over the buildingdifficult to control and tolocate the leakage. Highrisk for the occupants

    Very difficult to certified theVRF system according toASHRAE 15/1999

    4.3 Refrigerant linessafety and leakageWater cooled units

    Only in the machineroom or in the outside air

    It is all over the samefloor not so difficult tocontrol and to locate theleakage. High risk for theoccupants

    VRF system may be possible tocertified according to ASHRAE15-2007.

    5.0 Coefficient of performance

    Easy to calculate itdepends on the %cooling capacity and theoutside air

    Condensing unit isalmost constantregarding the coolingcapacity, but depends ofthe outside air

    High efficiency Chilled Plantcould be 0.8 kW/Ton and VRFcondensing units could be 0.95kW/Ton all year around averagefor Sao Paulo, Brazil

    5.1 Capacity control Leaving water temperature keepconstant, by the capacitycontrol on thecompressor

    Suction pressure of thecompressor keepconstant by the capacitycontrol on thecompressor speed orstages

    Constant pressure control in thesuction line near the compressorkeeps the COP constant, but itdoesnt gives the same value forthe evaporator due to the pressuredrop. Reduces the latent coolingcapacity for VRF

    5.2 Water cooledCondenser

    Shell and tubecondensers, standardprocedures and easy toclean

    Plate heat exchanger ortube in tube, it needs aclosed circuit with theuse of an intermediate

    heat exchanger

    Higher initial cost but very lowmaintenance for VRF

    6.0 Heating and cooling Needs four pipes to heatand cool at the same timewith heat recovery

    Almost standard easy todo and low cost

    Advantage for the VRF

    6.1 Cooling andHeating Control

    Very sophisticate not soeasy to use for thecostumer

    Easy to use is the sameas the mini-split

    Advantage for VRF, it doesntneed trained personal to operate

    There are two basic types of VRF multi-split systems: heat pump and heat recovery (see Figure 1).Heat pumps can operate in heating or cooling mode. A heat-recovery system, by managing therefrigerant through a gas flow device, can simultaneously heat and coolsome indoor fan coilunits in heating and some in cooling, depending on the requirements of each building zone. The

    majority of VRF systems are equipped with variable-speed compressors. Often called variable-frequency drives (VFD) or inverter compressors (Figure 2), this component responds to indoortemperature changes, varying the speed to operate only at the levels necessary to maintain aconstant and comfortable indoor environment. Due to this flexibility, VRF systems that includeinverter compressors are inherently energy efficient. Heat-recovery systems increase VRFefficiency because, when operating in simultaneous heating and cooling, energy from one zone canbe transferred to meet the needs of another.

    Figure 1: Heat-recovery and Heat-pump Systems

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    Figure 2: Compressor Frequency

    VRF outdoor units can have cooling and heating capacities from 12,000 Btu/h (3,508 W) to300,000 Btu/h (87,692 W); VRF indoor units can have cooling and heating capacities from 5,000Btu/h (1,462 W) to 120,000 Btu/h (17,538 W). The outdoor unit may support up to 50 indoorevaporator units with capacities that collectively add up to 150% capacity of the condensing unit.

    VRF equipment is divided into three general categories: residential, light commercial, and applied.Residential equipment is single-phase with a cooling capacity of 65,000 Btu/h or less. Lightcommercial equipment is generally three-phase, with cooling capacity greater than 65,000 Btu/hand is designed for small businesses and commercial properties. Applied equipment has coolingcapacities higher than 135,000 Btu/h and is designed for large commercial buildings.

    Definitions

    Heat pump multi-split. An encased, factory-made assembly or assemblies designed to be used as permanentlyinstalled equipment to take heat from a heat source and deliver it to the conditioned space when heating is desired.It may be constructed to remove heat from the conditioned space and discharge it to a heat sink if cooling and

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    dehumidification are desired from the same equipment. It normally includes multiple indoor conditioning coils,compressor(s), and outdoor coil(s). Such equipment may be provided in more than one assembly, the separatedassemblies of which are intended to be used together. The equipment may also provide the functions of cleaning,circulating and humidifying the air.

    Variable Refrigerant Flow (VRF) System. An engineered direct exchange (DX) multi-split system incorporating atleast one variable capacity compressor distributing refrigerant through a piping network to fan coil units eachcapable of individual zone temperature control, through proprietary multiple indoor zone temperature control

    devices and common communications network.

    VRF heat-recovery multi-split system. A split system air-conditioner or heat pump incorporating a single refrigerantcircuit, with one or more outdoor units at least one variable-speed compressor or an alternate compressorcombination for varying the capacity of the system by three or more steps, multiple indoor fan coil units, each ofwhich is individually metered and individually controlled by a proprietary control device and commoncommunications network. This system is capable of operating as an air-conditioner or as a heat pump. The system isalso capable of providing simultaneous heating and cooling operation, where recovered energy from the indoor unitsoperating in one mode can be transferred to one or more other indoor units operating in the other mode.Variablerefrigerant flow implies 3 or more steps of control on common, interconnecting piping.

    VRFmulti-split system. A split system air-conditioner or heat pump incorporating a single refrigerant circuit, withone or more outdoor units, at least one variable speed compressor or an alternative compressor combination for

    varying the capacity of the system by three or more steps, multiple indoor fan coil units, each of which isindividually metered and individually controlled by a proprietary control device and common communicationsnetwork. The system shall be capable of operating either as an air conditioner or a heat pump.

    GENERAL DESIGN CONSIDERATIONSUser Requirements

    The user primarily needs space conditioning for occupant comfort. Cooling, dehumidification, andair circulation often meet those needs, although heating, humidification, and ventilation are alsorequired in many applications. Components other than the base outdoor and indoor units may needto be installed for VRF systems to satisfy all requirements.

    ApplicationsVRF systems have many advantages over more traditional HVAC units. The advantages anddisadvantages for a VRF system, when compared to a chilled system, are presented in Table 1.

    Table 1: VRF System Advantages and DisadvantagesItem Description Variable Refrigerant Flow AC

    System

    Chilled Water AC System

    1 Human Comfort Partial no humidity control,not so good air distribution

    Good true air conditioning

    2 Process cooling, heating,humidification anddehumidification

    Not applicable - no humiditycontrol, not so good airdistribution

    Good - May by designed for anycondition

    3 Internal Air Quality Partial needs a auxiliary air make-up system and specialfiltersNo duct work is good

    Good may be designed for anycondition.Ducts need to be cleanable

    4 Initial Cost Similar Similar 5 Operational Cost Little higher at full load 1.25

    kW/tonAt full load 1.18 kW/ton

    6 Cooling capacity Good performance until 100 mequivalent lengthPoor performance above 100 m

    Distance is only a matter ofpumps selection and operationalpower consumption

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    equivalent length7 Increasing cooling capacity Not so easy, it may be necessary

    to change the refrigerant linesand the condensing unit

    It could be done by changing thecontrol valves and or the coils.Chiller plant doesnt change orchilled water pipes

    8 Operation at partial load Good performance and control Good performance and control9 Customer or tenant control on

    the operational cost

    Good - full control

    Very important

    No control on the operational and

    maintenance cost10 Compatibility with standards,guides and regulations

    Partial. It is necessary to solvethe compatibilities issue duringthe design

    Fully compatible

    11 Long distance pipes Up to 100 m is OK, more thereis a cooling capacity reductionup to 75%

    No problem.

    12 Refrigerant management Difficult it depends on thedesign of the system formonitoring, identification andrepair

    Concentrate in a single equipmenteasy and simple Good

    13 Customer operation Easy and simple GoodVery important

    Not so clear to customer -Acceptable

    14 Malfunction Possibility To many parts and componentsand long refrigerant lines Acceptable

    More reliable, just a few parts andequipment Good

    15 Operational life expectation Up to 15 years - Acceptable Up to 25 years Good16 Maintenance Depends on the design, access

    may be a problemNo problem - Good

    17 Sales strategy It is necessary to verify, the saywhat the customer would like tolisten, but not all is true

    To much engineering stuff,difficult for the costumer tounderstand

    VRF systems are not suitable for all applications. Some limitations include:

    There is a limitation on the indoor coil maximum and minimum entering dry- and wet-bulbtemperatures, which makes the units unsuitable for 100% outside air applications especiallyin hot and humid climates.

    The cooling capacity available to an indoor section is reduced at lower outdoortemperatures. This limits the use of the system in cold climates to serve rooms that requireyear-round cooling, such as telecom rooms.

    The external static pressure available for ducted indoor sections is limited. For ductedindoor sections, the permissible ductwork lengths and fittings must be kept to a minimum.Ducted indoor sections should be placed near the zones they serve.

    Diversity and Zoning

    The complete specification of a VRF system requires careful planning. Each indoor section isselected based on the greater of the heating or cooling loads in the area it serves. In cold climateswhere the VRF system is used as the primary source for heating, some of the indoor sections willneed to be sized based on heating requirements.

    Once all indoor sections are sized, the outdoor unit is selected based on the load profile of thefacility (Example 1). The combined cooling capacity of the indoor sections can match, exceed, orbe lower than the capacity of the outdoor section connected to them. An engineer can specify an

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    outdoor unit with a capacity that constitutes anywhere between 70% and 130% of the combinedindoor units capacities. The design engineer must review the load profile for the building so thateach outdoor section is sized based on the peak load of all the indoor sections at any given time.Adding up the peak load for each indoor unit and using that total number to size the outdoor unitlikely will result in an unnecessarily oversized outdoor section. Although an oversized outdoor unitin a VRF system is capable of operating at lower capacity, avoid oversizing unless it is required for

    a particular project due to an anticipated future expansion or other criteria. Also, when indoorsections are greatly oversized, the modulation function of the expansion valve is reduced orentirely lost. Most manufacturers offer selection software to help simplify the optimization processfor the systems components.

    Sizing Example 1

    Peak cooling load for Zone 1 3 tonPeak cooling load for Zone 2 2.5 tonPeak cooling load for Zone 3 4 tonZones peak load = 3 + 2.5 + 4 9.5 tonBuilding peak load 7.0 tonAvailable sizes for outdoor unit 7.5 ton and 10 ton

    Selection: Unless additional indoor units are planned for the future, select a 7.5 tonoutdoor section.

    Installation

    In deciding if a VRF system is feasible for a particular project, the designer should considerbuilding characteristics; cooling and heating load requirements; peak occurrence; simultaneous

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    heating and cooling requirements; fresh air needs; electrical and accessibility requirements for allsystem components; minimum and maximum outdoor temperatures; sustainability; and acousticcharacteristics. The physical size of the outdoor section of a typical VRF is somewhat larger thanthat of a conventional DX condensing unit, with a height up to 6 ft. (1.8 m) excluding supports.The chosen location should have enough space to accommodate the condensing unit(s) and anyclearance requirements necessary for proper operation.

    Refrigerant Piping Design

    Building geometry must be studied carefully so that refrigerant piping lines are properly designed.The system should not be considered if the expected pipe lengths or height difference exceed thoselisted in the manufacturers catalog. In buildings where several outdoor locations are available forthe installation of the outdoor units, such as roof, setback, and ground floor, each condensingsection should be placed as close as possible to the indoor units it serves.

    Although manufacturers routinely increase the maximum allowable refrigerant pipe run, the longerthe lengths of refrigerant pipes, the more expensive the initial and operating costs. For most VRFunits, the maximum allowable vertical distance between an outdoor unit and its farthest indoor unit

    is approximately 164 ft ( m); the maximum permissible vertical distance between two individualindoor units is approximately 49 ft ( m); and the maximum refrigerant piping lengths allowablebetween outdoor and farthest indoor units is up to 541 ft. ( m) (see Figure 2 and Table 2).

    Figure 2: Maximum Allowable Distances and Piping Lengths

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    Table 2: Maximum Allowable Distances and Piping Length Ranges

    Maintenance Considerations

    Ductless VRF indoor units have some considerations in reference to maintenance: Draining condensate water from the indoor and outdoor units Changing air filters Repairs Cleaning

    Ease of maintenance depends on the relative position of the indoor and outdoor units and the roomto ensure access for changing filters, repairing, and cleaning. The installer must make sure there isenough slope to drain condensate water generated by both the indoor and outdoor units. Dependingon the location where the indoor unit is installed, it may be necessary to install a pump so thatwater drains properly.

    Sustainability

    VRF systems feature higher efficiencies in comparison to conventional heat pump units. Lesspower is consumed by heat-recovery VRF systems at part load, which is due to the variable speeddriven compressors and fans at outdoor sections. The designer should consider other factors toincrease the system efficiency and sustainability. Again, sizing should be carefully evaluated.Environmentally friendly refrigerants such as R-410A should be specified. Relying on the heatpump cycle for heating, in lieu of electric resistance heat, should be considered, depending onoutdoor air conditions and building heating loads. This is because significant heating capacities areavailable at low ambient temperatures (e.g., the heating capacity available at 5F ( 15C) can beup to 70% of the heating capacity available at 60F (16C), depending on the particular design ofthe VRF system).

    TYPES OF VRF SYSTEMSBoth heat-pump and heat-recovery VRF systems are available in air-to-air and water-source(water-to-refrigerant) configurations (see Table 1). Air-cooled condensing units contain a propellerfan to transfer heat from the refrigerant to the air; water-cooled condensing units, which are usuallyinstalled indoors, uses a closed or open water loop to transfer heat from the refrigerant .

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    Closed Loop ConfigurationsWater-loop heat pump application: Water-to-air heat pump using liquid circulating in a commonpiping loop functioning as a heat source/heat sink.NOTE: The temperature of the liquid loop is usually mechanically controlled within a temperaturerange of 59F [15C] to 104F [40C].

    Ground-loop heat pump application: Brine-to-air heat pump using a brine solution circulatingthrough a subsurface piping loop functioning as a heat source/heat sink.NOTES

    1.The heat exchange loop may be placed in horizontal trenches or vertical bores, or besubmerged in a body of surface water. ANSI/ARI/ASHRAE ISO Standard 13256-1:1998

    2.The temperature of the brine is related to the climatic conditions and may vary from 23 to104F [5 to 40C].

    Water-to-air heat pump and/or brine-to-air heat pump: Heat pump which consists of one or morefactory-made assemblies which normally include an indoor conditioning coil with air-movingmeans, compressor(s), and refrigerant-to-water or refrigerant-to-brine heat exchanger(s), includingmeans to provide both cooling and heating, cooling-only, or heating-only functions.NOTES

    1.When such equipment is provided in more than one assembly, the separated assembliesshould be designed to be used together.

    2.Such equipment may also provide functions of sanitary water heating, air cleaning,dehumidifying, and humidifying.

    Open Loop ConfigurationGroundwater heat pump: Water-to-air heat pump using water pumped from a well, lake, or streamfunctioning as a heat source/heat sink.NOTE: The temperature of the water is related to the climatic conditions and may vary from 41 to77F (5 to 25C) for deep wells.

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    Table 1. Classification of VRF Multi-Split Systems

    System Identification

    Attribute

    VRF Heat-pump Multi-split VRF Heat-recovery

    Multi-split

    Refrigerant Circuits 1 Shared to all indoor units 1 Shared to all indoor unitsCompressors 1 or More Variable Speed or

    alternative method resulting in3 or more steps of capacity

    1 or More Variable Speed or

    alternative method resulting in3 or more steps of capacityIndoorUnits

    Qty. Greater than one indoor unitOperation Individual

    Zones/TempIndividualZones/Temp

    OutdoorUnit(s)

    Qty. 1 or multiple-manifoldedoutdoor units with a specificmodel number.

    1 or More

    Steps of Control 3 or More 3 or More

    Mode of Operation A/C, H/P A/C, H/P, H/R

    Heat Exchanger One or more circuits of shared

    refrigerant flow

    One or more circuits of shared

    refrigerant flowClassification

    Air-Conditioner(air-to-air)

    MSV-A-CB

    Air-Conditioner(water-to-air)

    MSV-W-CB

    Heat Pump (air-to-air)

    HMSV-A-CB HMSR-A-CB

    Heat Pump (water-to-air)

    HMSV-W-CB HMSR-W-CB

    NOTES:1 A suffix of -O following any of the above classifications indicates equipment not intended for usewith field-installed duct systems (6.1.5.1.2).2 A suffix of -A indicates air-cooled condenser and -W indicates water-cooled condenser.3 For the purposes of the tested combination definition, when two or more outdoor units are connected,they will be considered as one outdoor unit.

    Heat Rejection. VRF condensers may be air-cooled or water-cooled; the letters A or W follow the Air-ConditioningHeating and Refrigeration Institute (AHRI) designation.Heat Source/Sink. Unitary heat pump outdoor coils are designated as air-source or water-source by an A or W,following AHRI practice. The same coils that act as a heat sink in the cooling mode act as the heat source in theheating mode.Unit Exterior. The unit exterior should be decorative for in-space application, functional for equipment room andducts, and weatherproofed for outdoors.

    EQUIPMENT AND SYSTEM STANDARDS

    AHRI Certification ProgramsAHRI is developing a certification program for VRF multi-split air-conditioning and heat-pumpequipment up to 300,000 Btu/h that will be based on AHRI Draft Standard 1230 and ASHRAEStandard 37. The certification program includes all VRF multi-split air-conditioning, air- andwater-source heat-pump equipment rated up to 300,000 Btu/h (88,000 W) at AHRI StandardRating Conditions.

    The following Certification Program ratings are verified by test:VRF Multi-Split Air-Conditioning and Heat Pump Equipment

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    a. For VRF Multi-Split Air-Conditioners < 65,000 Btu/h (19,000 W)1. ARI Standard Rating Cooling Capacity, Btu/h (W)2. Seasonal Energy Efficiency Ratio, SEER, Btu/(W h)

    b. For VRF Multi-Split Air-Conditioners 65,000 Btu/h (19,000 W)1. ARI Standard Rating Cooling Capacity, Btu/h (W)

    2. Energy Efficiency Ratio, EER, Btu/(W

    h)3. Integrated Part-Load Value, IPLV/IEER

    c. For all VRF Multi-Split Heat Pumps < 65,000 Btu/h (19,000 W)1. ARI Standard Rating Cooling Capacity, Btu/h (W)2. Seasonal Energy Efficiency Ratio, SEER3. High Temperature Heating Standard Rating Capacity, Btu/h (W)4. Region IV Heating Seasonal Performance Factor, HSPF, Minimum Design Heating

    Requirement, Btu/(W h)

    d. For VRF Multi-Split Heat Pumps 65,000 Btu/h (19,000 W)

    1. ARI Standard Rating Cooling Capacity, Btu/h (W)2. Energy Efficiency Ratio, EER, Btu/(W h)3. Integrated Part-Load Value, IPLV/IEER4. High Temperature Heating Standard Rating Capacity, Btu/h (W)5. High Temperature Coefficient of Performance, COP6. Low Temperature Heating Standard Rating Capacity, Btu/h (W)7. Low Temperature Coefficient of Performance, COP

    e. For VRF Multi-Split Heat Recovery Heat Pumps1. Ratings Appropriate in (c) (d) above2. Simultaneous Cooling and Heating Efficiency (SCHE) (50% heating/50% cooling)

    f. For VRF Multi-Split Heat Pumps Systems that Use a Water Source for Heat Rejection1. ARI Standard Rating Cooling Capacity, Btu/h (W)2. Energy Efficiency Ratio, EER, Btu/(W h)3. Integrated Part-Load Value, IPLV/IEER4. Heating Standard Rating Capacity, Btu/h (W)5. Heating Coefficient of Performance, COP6. Simultaneous Cooling and Heating Efficiency (SCHE) (50% heating/50% cooling)

    (Heat Recovery models only)

    Energy Efficiency RatingsDefinitions

    Coefficient of performance (COP). A ratio of the heating capacity in watts [W] to the power input values in watts[W] at any given set of rating conditions expressed in watts/watts [W/W]. For heating COP, supplementaryresistance heat shall be excluded.

    Energy efficiency ratio (EER). A ratio of the Cooling Capacity in Btu/h to the power input values in watts at anygiven set of rating conditions expressed in Btu/Wh.

    Heating Seasonal Performance Factor (HSPF). The total heating output of a heat pump, including supplementaryelectric heat necessary to achieve building heating requirements during its normal annual usage period for heatingdivided by the total electric power during the same period, as determined in Appendix C expressed in Btu/[W h].

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    Integrated Energy Efficiency Ratio (IEER). A single number that is a cooling part-load efficiency figure of meritcalculated per the method described in paragraph 6.5.

    Integrated Part-Load Value (IPLV). A single number that is a cooling part-load efficiency figure of merit calculatedper the method described in Appendix H.

    Seasonal Energy Efficiency Ratio (SEER). The total cooling of a systems covered by this standard with a capacity

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    o Those filters have a higher cost and reduce the static external pressure availableand can only be used in ducted units and select ductless units.

    o Higher efficiency filters are available for: Ceiling Mounted Cassette Type double flow Ceiling Mounted Cassette Type multi-flow Ceiling Mounted Built-in Type Ceiling Mounted Duct Type Slim Ceiling Mounted Duct Type, can be installed with field supplied

    return air grill + filter Console Ceiling Suspended Type

    o Higher filter arent available for: Ceiling Mounted Cassette Corner Type Console Ceiling Suspended Type Wall Mounted Type Floor Standing Type/Concealed Floor Standing Type Ceiling Suspended Cassette Type

    Refrigerant Management Standards

    HVAC systems must comply with ASHRAE Standard 15-2007Safety Standard for RefrigerationSystems (ANSI approved).

    Refrigerant leak detector to activate alarms and mechanical ventilation systemo Difficult to provide, because you dont know where the leaks may occuro If machine room is for an air cooled VRF systems, it is external OKo If machine room is for an water cooled VRF systems, it is internal and needs the

    leak detector and ventilation OKo Refrigerant lines between the floors are external, usually in the corner of the

    building OKo Refrigerant lines inside the roof and the ceiling may need a refrigerant leak detector

    OKo Mechanical ventilation system shall be provided by the installation, could be

    provided OKo All the items above are possible, but they mean more cost

    Machinery room shall be vented to the outdoors, utilizing mechanical ventilation.o Machine room are for air cooled VRF systems external OKo Machine room for water cooled VRF systems needs the leak detector and

    ventilation OKo The air supply and exhaust ducts for the machinery room shall serve no other area

    OKo All the items above are possible, but they means more cost

    Refrigerant Quantity Limits. The quantity of refrigerant in each independent circuit of highprobability systems shall not exceed the amounts shown in Table 1, except as provided in7.2.1 and 7.2.2, based on volumes determined in accordance with 7.3. For refrigerantblends not listed in Table 1, the amount of each component shall be limited in the samemanner and the total of all components in each circuit shall not exceed the quantity thatwould equal 69,100 ppm by volume upon release to the volume determined by 7.3.

    o It is possible to accomplish seems to be OK

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    Declaration. A dated declaration of test shall be provided for all systems containing 55 lb(25 kg) or more of refrigerant. The declaration shall give the name of the refrigerant andthe field test pressure applied to the high-side and the low-side of the system. The testdeclaration shall be signed by the installer and, if an inspector is present at the tests, theinspector shall also sign the declaration. When requested, copies of this declaration shall befurnished to the authority having jurisdiction.

    o It is possible to accomplish - OK

    Since introduction, interest has been generated in regards to designing R410A VRF systems tomeet ASHRAE Standard 15 (Safety Standards for Refrigerant Systems) requirements. Specificdesigns must focus on the refrigerant flow attributes of these systems, and ASHRAE 15 instructsdesigners in many aspects of refrigerant safety.

    ASHRAE Standard 15

    ASHRAE 15 is a National Voluntary Consensus Standard; but, equipment listed by a NationallyRecognized Testing Laboratory (NRTL) and identified as being in compliance with Standard 15meets the applicable provisions of the Standard (ASHRAE Standard 15-2007, Section 13). Also,

    regulatory language was incorporated in the 2001 revision and, by adoption, can be made part oflocal code requirements. This is specific to each jurisdiction, so it is important for the designer tobe familiar with local codes and regulations.Applying ASHRAE Standards 15 and 34 to R410A

    R410A is the refrigerant used in newer and more energy-efficient systems. Though ASHRAE 15was last revised in 2007, it does not directly reference R-410A refrigerant except by footnote aunder Table 1 Refrigerant and Amounts that states:aThe refrigerant safety groups in Table 1 are not part of ASHRAE Standard 15. The classifications

    shown are from ASHRAE Standard 34, which governs in the event of a difference. Therefore,system designers must refer to Standard 34 when applying Standard 15 safety principles to R410Arefrigerant.

    The overall purpose of ASHRAE Standard 34 is to establish a simple means of referring tocommon refrigerants It also establishes a uniform system for assigning reference numbers andsafety classifications to refrigerants. The standard identifies requirements to apply for

    designations and safety classifications for refrigerants, including blends, in addenda or revisions

    to this standard. (Designation and Safety Classification of Refrigerants ASHRAE Standard 34-2007, Section 1).A main point of discussion under ASHRAE Standard 34 is Refrigerant Concentration Limit(RCL) (ASHRAE Standard 34-2007, Section 7), which is defined as the refrigerantconcentration limit, in air, determined in accordance with this standard and intended to reduce the

    risks of acute toxicity asphyxiation and flammability hazards in normally occupied, enclosed

    spaces

    RCL can be expressed in: ppm v/v g/m3 lb./Mcf (or lb./1,000 ft3)

    Limits have been developed as indicated (ASHRAE Standard 34, Section 7.4.1):Mass per Unit Volume. The following equation shall be used to convert the RCL from avolumetric ratio, ppm by volume, to mass per unit volume, g/m3 (lb./Mcf):

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    RCLM= RCL a MwhereRCLM= The RCL expressed as g/m3 (lb./Mcf)RCL = the RCL expressed as ppm v/va = 4.096 10-5 for g/m3 (1.160 x 10-3 for lb./Mcf)M= The molecular mass of the refrigerant in g/mol (lb./mol)

    RCL values are the lowest of the following three factors:Acute Toxicity Exposure Limit (ATEL): The refrigerant concentration limit determined inaccordance with this standard (34-2007) and intended to reduce the risks of acute toxicity hazardsin normally occupied, enclosed spaces (ASHRAE Standard 34-2007, Section 7.1.1).ATEL includes consideration of mortality, cardiac sensitization, anesthetic or central nervoussystem effects and other escape impairing effects and permanent injury.Oxygen Deprivation Limit (ODL): The concentration of a refrigerant or other gas that results ininsufficient oxygen for normal breathing (ASHRAE Standard 34-2007, Section 7.1.2).Flammable Concentration Limit (FCL): The refrigerant concentration limit, in air, determinedin accordance with this standard and intended to reduce the risk of fire or explosion in normallyoccupied spaces which is 25% of the Lower Flammability Limit (LFL) (LFL is the minimum

    concentration of refrigerant that is capable of propagating a flame) (ASHRAE Standard 34-2007, Section 7.1.3).12 RCL for R-410A is based on the ATEL (Acute Toxicity Exposure Limit) because it islower than the ODL (Oxygen Deprivation Limit). Toxicologists considered the elderly andchildren when determining the RCL values for refrigerants. (No discussion on this in Standard.The toxicology subcommittee of SSPC 34 includes toxicologists from Honeywell, DuPont, andArkema, PhD Consulting and representatives from Trane and IIAR.)3

    ASHRAE Standard 34-2007

    Table 10 Data & Safety: Classifications for Refrigerant Blends

    Refrigerant Safety Data from Table 1 of ASHRAE Standard 34-2007

    Refrigerant Safety Group RCL lb./Mcf Highly Toxic or Toxic UnderCode Classification

    R-22 (CHCIF2) A1 13 Neither

    R-134A (CH2FCF3) A1 13 Neither

    R-407C (Blend) A1 17 Neither

    R-410A (blend) A1 25 Neither

    R410A Qty per Occupied Space = RCL =130,000 ppm v/v or = 390 g/m3 = 25 lb./MCF.Designing VRF Systems with ASHRAE 15 and 34

    Occupied SpacesStandard 15 guides designers on how to apply a refrigeration system in a safe manner, and detailsinformation on the type and amount of refrigerant allowed in an occupied space, defined as thatportion of the premises accessible to or occupied by people, excluding machinery rooms(ASHRAE Standard 15-2004, Section 3).

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    Standard 15 also lists occupancy classifications (Section 4) with recommendations of allowableconditions for each class:1 Institutional Occupancy2 Public Assembly3 Residential Occupancy4 Commercial Occupancy

    5 Large Mercantile Occupancy6 Industrial Occupancy7 Mixed Occupancy

    Standard 15 (Section 5) also defines Refrigerating System Classifications with guidance forapplications for:

    Direct Systems, which are systems having evaporator, condenser, or refrigerant lines indirect contact with the material (air) to be cooled or heated

    Indirect Open Spray Systems Double Indirect Open Spray Systems Indirect Closed Systems

    Indirect Vented Closed Systems

    In reviewing specific applications, the designer must look at the space any HVAC system serves,as well as the refrigerant line paths. If system components are located in normally occupied spaces,then they must be evaluated for safety and suitability. Corridors and lobbies especially points ofegress - should be evaluated as well since their volume is, by definition, part of the connectedspaces volume and the restrictions in the Standard limit refrigeration concentrations in these areasto specified amounts. In most cases such system components including refrigerant piping donot pose a safety or suitability issue. ASHRAE 15 requires factory testing on all refrigerantcontaining components; as a result, the likelihood of subsequent failure is remote. Field fabricatedconnections also require inspection and evaluation. VRF systems require evacuation of the

    complete system and all piping, including field fabricated connections, and vacuum must be heldwith no leaks as a part of the commissioning process for every system installed.

    Refrigerant Leaks in Occupied Spaces

    Leaks are not defined in Standard 15, but it generally addresses a catastrophic event where fullcircuit refrigerant volume is to be considered as available for discharge into the occupied space.Standard 15 also does not address any time period over which a leak might occur. Even in theunlikely event of a line rupture, the amount of refrigerant in a circuit would require a significantperiod to escape from the system.The design professional should keep in mind that ASHRAE 15 was primarily developed andwritten for the catastrophic release of the entire contents of a pressure vessel thru a safety valve of

    large diameter in a short time.There is a clearly defined relationship between the amount of refrigerant in a system and thevolume of the occupied space into which the refrigerant could flow. According to Standard 15,the volume used to determine the refrigerant quantity limits for refrigerants in 7.2 shall be basedon the volume of space to which the refrigerant disperses in the event of a refrigerant leak(ASHRAE Standard 15-2007, Section 7). Occupied space is not necessarily a single room or area.If a group of rooms or spaces (offices, corridors, other spaces off the corridor, etc.) are connectedby ductwork or other means, then all of their connected volumes are counted in calculating theaffected volume. These connected spaces could also include louvers or permanent openings to

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    adjacent spaces or to the outside, as in a ventilation source or exhaust, and even undercuts onconnecting doors, provided there is forced movement of air (Note that R-410A is heavier than airand would spread along floor surfaces as a free gas). Standard 15 specifically lists ventilation as aremedy in establishing occupied space, but does not quantify the amount or type of ventilationrequired only, the smallest volume in which the leaked refrigerant disperses... (ASHRAEStandard 15-2007, Section 7.3.2).

    Fig. 4

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    Table 11 VRF System Volume Example (Using a CITY MULTI System)

    To further illustrate the design options, a system with a P72 outdoor unit is shown in Table 11. Thespace is a single bay tenant upfit within a strip mall located in a mild climate. The space is 30 feetby 70 feet with 14 feet from the floor to the underside of the roof deck. The interior walls shownextend 18 inches above the dropped ceiling.

    The 72,000 Btu/h capacity unit contains 23 lbs 3 oz of R410A refrigerant. ASHRAE Standard 34lists the refrigerant concentration limit (RCL) as 25 lb./Mcf for R410A. As shown in Table 11, theminimum room volume needed to handle the full refrigerant charge of the system can be easilycalculated.RCL (R410A) = 25 lb./McfRefrigerant Charge (Rc) of a P72 = 23 lbs 3 oz = 23.1875 lbs

    MRV = Minimum Room Volume (cubic feet)MRV = Rc/RCLMRV = (23.1875 lbs)/(25 lbs/1000 cu ft)MRV = 927.5 cu ft

    Table 12To summarize the above equation, the smallest space which any of the indoor units could belocated in would have to be capable of dispersing the refrigerant charge into 927.5 cu ft.As per Table 11, the only spaces of concern would be-Mens Bathroom-Womens Bathroom-Electrical Room

    -Janitor Closet-Office 2There are several options available to deal with the smaller spaces. In cases such as the bathrooms,the code required ventilation will likely be all that is required to maintain conditions in the space.Should extra cooling be required, a ducted unit located in the workroom corridor would solve theproblem. The electrical room/janitor closet area provides another opportunity for the architect tohelp the mechanical design team. An opening located low along the common wall between the twospaces would increase the available volume from 504 cu ft minimum to over 1000 cu ft. Should theelectrical closet require a rated enclosure as required by NFPA-70 a fire damper could be installed.

    TENANT UPFIT SPACESRoom Name Room Area (sq ft) Ceiling Height (ft) Room Volume (cu ft)

    Lobby/WaitingRoom

    450 10 4500

    Conference Room 235 12 2820

    Office #1 115 10 1150Office #2 70 10 700Open Work Room 944 12 11328

    Break Room 127 10 1270Men's Bathroom 42 9 378

    Women's Bathroom 42 9 378

    Electrical Room 39 14 546

    Janitor Closet 36 14 504

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    Office 2 was provided with a ducted unit located in the corridor to meet the requirements of theStandard. Another option for office 2 would be to omit the ceiling entirely or install it at a levelwhich provides the needed volume. It shall be noted that ASHRAE 15 Section 7.3.2 clearly statesthe space above a suspended ceiling shall not be included in calculating the refrigerant quantitylimit in the systemAs illustrated by the example, the only requirement to meet the standard was an understanding of

    the language and not major accommodations or changes. With the application of soundengineering practice, any design professional can easily integrate VRF technology into his or herdesign.Conclusion

    Engineers and designers have great flexibility in applying VRF systems to ensure the design isASHRAE 15 compliant. Examining the project spaces and determining the occupied andconnected spaces needs to be a primary consideration, and care must be taken in the location andlayout of refrigerant lines and indoor units.

    Green Buildings

    The U.S. Green Building Council (USGBC) is the nations foremost coalition of leaders from

    across the building industry working to promote buildings that are environmentally responsible,profitable, and healthy places to live and work. The core purpose of USGBC is:To transform the way buildings are designed, built, and operated enabling an

    environmentally and socially responsible, healthy, and prosperous built

    environment that improves the quality of life in communities.In order to further that purpose, USGBC developed the LEED (Leadership in Energy andEnvironmental Design) Green Building Rating System. The LEED Green Building RatingSystem is a voluntary, consensus-based national standard for developing high-performance,sustainable buildings.VRF systems can be used to help buildings to achieve LEED certification in many ways; thecredits discussed in the paragraphs below are based off of the LEED New Construction (NC) v2.2rating system.

    Energy and AtmospherePrerequisite 1: Fundamental Commissioning of the Building Energy SystemsRequiredA VRF controls system assists building commissioning by allowing easy testing, setting, andadjusting of the entire HVAC system.Prerequisite 2: Minimum Energy PerformanceRequiredAll buildings must be designed at a minimum to meet both the mandatory and prescriptive orperformance requirements of ASHRAE 90.1-2004. VRF equipment has many energy savingfeatures, further described under EAc1, which helps with meeting this prerequisite.Prerequisite 3: Fundamental Refrigerant ManagementRequiredNewer VRF systems use R410A, which is a HFC based refrigerant, CFC free and has no ozonedepletion potential.Credit 1: Optimize Energy Performance 1-10 points (2 Points Required)Some VRF systems, in addition to the variable refrigerant flow through the indoor units, use aninverter drive on the compressor and the outdoor fan motor, feature simultaneous heating andcooling operation, and include an integrated control system allowing for scheduling of equipmentin each room to maximize energy performance. VRF systems can be coupled with an energyrecovery ventilator (ERV) to further reduce energy usage. Building energy savings can bedemonstrated by performing a building energy model using the EnergyPro software available fromEnergySoft, LLC. and comparing the building design with a baseline building as defined by

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    ASHRAE 90.1 2004. Energy Pro has been approved by the USGBC as acceptable for EAc1calculations.Credit 5: Measurement and Verification (1 point)Some VRF system manufacturers offer software to provide for the ongoing accountability andoptimization of building energy consumption over time, monitoring and logging energyconsumption, heat-recovery cycles, static pressure and ventilation air volumes, and other building

    specific systems and equipment. Energy usage data obtained from such software can be comparedwith a building energy model prepared in Energy Pro in order to verify the energy savings shownby the model.Indoor Environmental Quality

    Prerequisite 1: Minimum IAQ PerformanceRequiredVRF systems can often meet minimum outside air requirements through the ventilationconnections of the indoor units. In applications where more outside air is required and the indoorunits capacity is exceeded, an ERV can bring in outside air by using the exhaust air from thebuilding and transferring energy and moisture to or from the outside air before delivering it tooccupied zones.Credit 1: Outdoor Air Delivery Monitoring (1 point)

    The ERV can be fully integrated within a VRF controls systems, which allows the unit to beprogrammed based on occupancy. An ERV can also be integrated with a C02 sensor to energizethe unit and or vary the airflow based on C02 levels within the space.Credit 2: Increased Ventilation (1 point)An ERV can be used to exchange a high percentage of air, which when used with adequate airdistribution from ducted units, can increase the ventilation rates above the requirements ofASHRAE 62.1-2004.Credit 3.2: Construction IAQ Management Plan: Before Occupancy (1 point)An ERV can be used to flush the building prior to occupancy.Credit 5: Indoor Chemical and Pollutant Source Control (1 point)Many VRF system indoor units can be installed with a filter. A design professional should beconsulted to ensure that adequate static pressure is available to provide desired airflowperformance.Credit 6.2: Controllability of Systems: Thermal Comfort (1 point)VRF systems can be controlled by the occupant via the wall-mounted remote controller that can beprovided in every room, or centrally via web-based control. The occupant has the ability to controlairflow direction, fan speed and temperature set points.Credit 7.1: Thermal Comfort: (1 point)When VRF systems are properly designed into a building, temperature and humidity control can beprovided in accordance with the ASHRAE 55-2004 guidelines.Credit 7.2: Thermal Comfort: Verification (1 point)The trending software that many VRF system manufacturers can install provide verification of thespace temperature, set temperature and mode of operation. The data obtained can be used incongruence with the thermal comfort surveys, required by this credit, to develop a plan to correctzones that present thermal comfort issues.

    Note: The LEED rating system is a measure of whole building sustainability and to effectivelypursue a LEED certification for any building, the entire team (owner, architect, engineer,contractor, etc.) must work together to maximize potential. No single equipment selection canassure any level of certification.

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    COMPONENTS AND SYSTEM LAYOUTSoftware for Designing SystemsMost VRF manufacturers provide software that makes designing for VRF systems quick and easy. Insome systems, the designer just needs to drag and drop components to complete the design. The programhas built in safeguards against exceeding limitations and shows if there is an error. Assuring line lengths,maximum connected capacities, component selection, control scheme, etc. are within the systemrequirements.

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    Indoor Unit Types

    Condensing units (or outdoor unit) of an air conditioning system contains the compressor, circuitboard, and heat exchanger coil; pumps refrigerant to the evaporator coil (or indoor unit).These indoor units are available in multiple configurations such as wall-mounted, ceiling-mountedcassette suspended, and concealed ducted types. Multiple types of indoor units can be combinedwith a single outdoor unit.

    Controls

    Each individual indoor unit can be controlled by a programmable thermostat or a multiple indoor

    units serving the same zone can be controlled by the same thermostat. Most VRF manufacturersoffer a centralized control option, which enables the user to monitor and control the entire systemfrom a single location or via the Internet.System Controls

    An integral network operations and communications system with sensors to monitor and forecastthe status of items such as temperature, pressure, oil, refrigerant levels and fan speed.A micro-processor, algorithm-based control scheme to: (1) communicate with an optimallymanaged variable capacity compressor, fan speed of indoor units, fan speed of the outdoor unit,solenoids, various accessories; (2) manage metering devices; and (3) concurrently operate variousparts of the system.These controls optimize system efficiency and refrigerant flow through an engineered distributed

    refrigerant system to conduct zoning operations, matching capacity to the load in each of the zones.

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    Refrigerant Circuit and Components

    VRF systems use a sophisticated refrigerant circuit that monitors mass flow, oil flow, and balanceto ensure optimum performance. This is accomplished in unison with variable-speed compressorsand condenser fan motors. Both of these components adjust their frequency in reaction to changingmass flow conditions and refrigerant operating pressures and temperatures. A dedicatedmicroprocessor continuously monitors and controls these key components to ensure properrefrigerant is delivered to each indoor unit in cooling or heating.

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    VRF heat-pump systems include either a two-pipe (liquid and suction gas) or three-pipe (liquid,suction gas, and discharge gas) configuration. Heat-recovery systems use similar pipeconfigurations, but add a gas flow device that determines the proper routing of refrigerant gas to aparticular indoor unit.

    Typical System Layout

    Figure 1 illustrates a standard VRF configuration, while Figure 2 shows a heat recovery unitproviding simultaneous heating and cooling.

    Fig. 1: Typical VRF Configuration in an Office Building.

    Fig. 2 Typical VRF Water Source Heat Pump Application

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    Fig. 3: Heat Recovery VRF System.

    Designing Refrigeration LinesA New Approach.Calculating the refrigerant lines for VRF systems introduces new issues in reference to the liquidand suction lines:

    Diameter Its always the same; it doesnt matter the distance Liquid line Pressure drop isnt important, the expansion valve will handle it Suction line Have the same diameter to ensure oil return during the active oil return cycle

    and inform the cooling capacity reduction.

    Liquid Line

    The liquid line should be selected for the minimum refrigerant charge with a smaller diameter (less

    refrigerant charge), and minimum pressure drop, larger diameter (bigger refrigerant charge). Theoption was to choose the smaller diameter for less refrigerant charge and as a penalty the higherpressure drop in the liquid line.

    Manage the higher pressure drop plus vertical line risers in the refrigerant lines following thesesuggestions:

    Mechanical liquid sub-cooling to avoid flash gas, with less refrigerant in circulation andpumped by the compressor;

    o Increase the sub-cooling by increasing the condensing pressure: Refrigerant flash gas reduction is OK Higher condensing pressure means increase in the power consumption for

    the same capacity not acceptableo Heat exchange between the liquid line and the suction line:

    Refrigerant flash gas is OK Using almost all the exchange in the internal unit for evaporation is OK No increase in cooling capacity or in power consumption acceptable

    o Liquid evaporation from the liquid line to cool down the liquid line: Refrigerant flash gas is OK

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    Cooling capacity is almost the same by increasing the refrigerant specificenthalpy difference but reducing the mass flow acceptable

    Expansion valve operates together with the liquid line pressure drop to keep the condensingpressure in reasonable level. Flash gas refrigerant gas is acceptable, but the design of theliquid line is more difficult (refinet);

    o The total pressure drop between the high pressure and low pressure is part pressure

    drop and part expansion valve;o It keeps the condensing pressure always in its minimum value - OKo Refrigerant flash gas is OK;o It is necessary to use electronic expansion valve acceptable but with higher cost;o The design of the liquid line needs closer attention to keep the same ration of vapor

    mass and total mass needs attention;o Best control to be usedo

    Liquid Line Pressure Drop and Expansion Valve

    Note: No problems Usually maximum capacity loss 2% Total pressure drop is the sum of liquid line and expansion valve Enthalpy is the same, it doesnt matter the pressure drop Its necessary an electronic expansion valve

    Fig. 3 Refrigerant P&h diagram

    28

    PressureMPa

    Enthalpy kJ/kg

    Liquid line pressure drop

    Expansion valve pressure drop

    Refrigerationeffect

    Total pressure drop

    Compressor

    Condenser

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    The refrigerant lines in current VRF systems can have up to 50 m rise and 190 m equivalent lengthconsidering that the equipment is operating with full capacity and we have the following data:

    Table 4 Differential Pressure for Vertical RiseOutside air

    dry bulbSaturatedpressure

    Bubbletemp. Dew temp.

    Liquid linetemp. Density

    Differential Pressure in kPa VerticalRise

    C kPA C C C kg/m3 10 m 20 m 30 m 40 m 50 m34.1 3000 48.99 49.1 38.99 914.5 90 179 269 358 44836.9 3200 51.81 51.91 41.81 892.6 87 175 262 350 43739.6 3400 54.49 54.59 44.49 870.0 85 171 256 341 426

    Note: The difference between the saturated temperature and the dry bulb outside air temperature is15.0C.

    50 m Vertical Rise:o Pressure differential 448 kPa for dry bulb outside air 34.1C;o Liquid line sub-cooling 10C;o Equivalent saturated temperature difference 7.8 Co Liquid sub-cooling due to the 50 m vertical rise 2.2 C

    Table 5 Equivalent Temperature Difference Due to the Pressure Loss Equivalent Length

    Coolingcapacity

    Liquidline Dia.

    ASHRAETable

    0.,02C/m Equivalent length liquid linekW Ton inches mm kW 20 60 100 140 180

    70.32 20 3/4 19,1 47.3 0.82 2.45 4.08 5.72 7.3587.90 25 3/4 19,1 47.3 1.22 3.66 6.10 8.54 10.98105.48 30 3/4 19,1 47.3 1.69 5.08 8.47 11.86 15.25

    123.06 35 3/4 19,1 47.3 2.24 6.71 11.18 15.65 20.13140.64 40 3/4 19,1 47.3 2.84 8.53 14.22 19.91 25.59Note: Calculated according to the ASHRAE table 8 ASHRAE 2006 Refrigeration Handbookchapter 2 System Practices for Halocarbon Refrigerants.

    Equivalent length 180 m plus 50 m vertical rise for 40 tons and 19.1 mm tube diameter: Pressure drop

    o Vertical rise: 448 kPa or 7.8Co Equivalent length 180 m: 1525 kPa or 25.6Co Total pressure drop: 1973 kPa or 33.4 Co Minimum sub-cooling to assure only liquid 5C

    o Natural sub-cooling 10Co Mechanical sub-cooling necessary 28.4Co Total pressure differential 2005 kPao Pressure differential available for the expansion valve 32 kPa for condensing

    pressure 3000 kPa and evaporating pressure 950 kPa Mechanical sub-cooling should be at least 28.4C and natural sub-cooling 10C, with a

    final sub-cooling 5C If flash refrigerant gas is used, there may be natural sub-cooling 10C and the refrigerant

    will have 25% mass of refrigerant vapor

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    Mass flow will be the same, because enthalpy is the same.Its important to remember that these numbers are for full cooling capacity, at partial load thiswont be an issue. Most of the time, the system is operating at partial cooling capacity.

    The following tables show the pressure drop.

    Table 6 Pressure Drop for a Vertical Rise Liquid Line Refrigerant HFC 410A

    DB Out-side Air

    SaturatedPressure

    BubbleTemp.

    DewTemp

    LiquidLine

    Temp.Liquid

    Saturated DensityVertical liquid line rise pressure increase for - HFC

    410AC kPA C C C kPa kg/m3 10 20 30 40 50 60 70 80

    28.0 2600 42.9 43 34.9 2100 957 94 188 281 375 469 563 657 75031.1 2800 46.02 46.14 38.0 2300 935.8 92 183 275 367 459 550 642 73434.1 3000 48.99 49.1 41.0 2500 914.5 90 179 269 358 448 538 627 71736.9 3200 51.81 51.91 43.8 2700 892.6 87 175 262 350 437 525 612 70039.6 3400 54.49 54.59 46.5 2800 870.0 85 171 256 341 426 512 597 68242.2 3600 57.05 57.15 49.1 3000 846.3 83 166 249 332 415 498 581 66344.6 3800 59.5 59.59 51.5 3200 821.0 80 161 241 322 402 483 563 644

    46.9 4000 61.85 61.93 53.9 3400 793.5 78 156 233 311 389 467 544 62249.2 4200 64.1 64.17 56.1 3500 762.6 75 149 224 299 374 448 523 598

    Note:A - Liquid sub-cooling 10C or 650 kPa, minimum sub-cooling 5C or 325 kPaB Blue columns liquid sub-cooling is OKC Yellow columns liquid sub-cooling near zeroD Gray columns no more liquid sub-cooling, flash gasE The maximum vertical rise liquid line without mechanical sub-cooling is 40 mF It doesnt consider the pressure drop of the equivalent length

    At least 10C sub-cooling is necessary to ensure only liquid in all branches for vertical rise.

    Table 7 Pressure Drop in C for the Equivalent Length of Liquid Line at Same LevelCooling Capacity Diameter Equivalent length liquid line in meters

    kW Tr pol Units 20 40 60 80 100 120 140 16070 20 3/4 C 0.82 1.63 2.45 3.27 4.08 4.90 5.72 6.5387 25 3/4 C 1.22 2.44 3.66 4.88 6.10 7.32 8.54 9.76

    105 30 3/4 C 1.69 3.39 5.08 6.78 8.47 10.17 11.86 13.56123 35 3/4 C 2.24 4.47 6.71 8.95 11.18 13.42 15.65 17.89140 40 3/4 C 2.84 5.69 8.53 11.38 14.22 17.06 19.91 22.75140 40 3/4 kPa 169 339 508 678 847 1017 1187 1356

    Note:A - Liquid sub-cooling 10CB Blue columns liquid sub-cooling is OKC Yellow columns liquid sub-cooling near zeroD Gray columns indicate the lack of liquid sub-cooling, flash gasE Liquid line diameter (19.05 mm)F The maximum equivalent length for the liquid line without mechanical sub-cooling for 100% cooling capacity is40 mG The maximum equivalent length for the liquid line without mechanical sub-cooling for 50% cooling capacity is140 m

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    As indicated, there is a possibility of using flash gas or increasing the mechanical cooling to ensureunit performance.

    Pressure drop in the liquid line doesnt reduce the cooling capacity or increase the powerconsumption. If the expansion valve is properly sized, the cooling capacity is reduced only 2% to3% due to design of the liquid line.

    Suction Line

    Suction line is different. The pressure drop in the suction could be responsible for up to 20%reduction of cooling capacity. VRF system manufacturers decided to maintain the COP as high aspossible by keeping the suction pressure near the compressor constant.

    To keep the performance and compensate for the pressure drop, it is usually necessary to reducethe pressure at the compressors suction. This will keep the evaporator cooling capacity, butreduces the compressor cooling capacity and with the same power consumption, will lower theCOP.

    VRF system manufacturers decided to maintain the compressor suction saturated temperaturealways near 5.5C. (42F) It doesnt matter how the evaporators are operatingthe saturated

    temperature at the evaporators will be always the compressor suction saturated temperature plusthe pressure drop.

    For the compressor, maintaining the temperature near 5.5C (42F) is perfectthe COP is almostconstant. But for the evaporator that means higher saturated temperature, which results in:

    Small sensible cooling capacity variation 10% so dry bulb will be OK 100% latent cooling capacity variation problems with humidity Large variation in total cooling capacity due to the latent cooling capacity variation

    problems with humidity Evaporators arent operational for evaporating temperature above 10C

    Table 8 Coil Cooling Capacity Different Evaporating Temperature

    Coil Cooling Performance Cooling CapacitySaturated Sensible Percentage Latent Percentage Total Percentage

    Condition C kW % kW % kW %1 4 15.4 110% 6.8 139% 22.2 117%2 6 14 100% 4.9 100% 18.9 100%3 8 12.8 91% 3 61% 15.8 84%4 10 12.7 91% 0 0% 12.7 67%

    Coil Specifications: Application Cooling Tube Diameter Copper Fin Material Aluminum 0.006 thick Fin length 30 Fin Height 20 Rows 4, 12 FPI 8 circuits Air Flow 3400 m3/h or 2000 CFM EAT-DB 26.7C and EAT-WB 19.4C Refrigerant HCFC-22 Suction Temperature: 4C, 6C, 8C, and 10C

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    Table 9 Suction Line Pressure Drop in C HFC-410ADiameter Suction Line - Equivalent length

    kW pol mm 20 40 60 80 100 120 140 160 180Refrigerant

    Charge kg 1-5/8 42 1.01 2.02 3.04 4.05 5.06 6.07 7.08 8.10 9.11Cooling Capacity Tr Pressure Drop in C saturated temperature equivalent

    70.32 20 1-5/8 42 0.28 0.55 0.83 1.10 1.38 1.66 1.93 2.21 2.48

    87.90 25 1-5/8 42 0.41 0.82 1.24 1.65 2.06 2.47 2.89 3.30 3.71105.48 30 1-5/8 42 0.57 1.14 1.72 2.29 2.86 3.43 4.01 4.58 5.15123.06 35 1-5/8 42 0.76 1.51 2.27 3.02 3.78 4.53 5.29 6.04 6.80140.64 40 1-5/8 42 0.96 1.92 2.88 3.84 4.80 5.76 6.72 7.68 8.65

    Note:A Pressure drop suction line in equivalent temperature CB Blue columns pressure drop is up to 2C, good performance OKC Yellow columns pressure drop is from 2C up to 3C, acceptableD Pink columns pressure drop from 3C up to 5C not acceptable latent cooling is zero

    E Red columns pressure drop above 5C equipment wont cool, totally wrongE Suction line diameter 1-5/8 (42 mm)F The maximum equivalent length 180 m, cooling capacity shouldnt be greater than 75% of thenominal cooling capacityG For full cooling capacity maximum equivalent length should be not greater than 100 mH DOAS Dedicated outside air is mandatory for VRF with pressure drop higher than 3C

    If the hypothesis is that the compressor cooling capacity is controlled by the suction pressure at thecompressor, for lines greater than 100 m, the unit will never be at full capacity and probably thehighest cooling capacity will be 75% of the nominal.

    Active Oil ReturnActive oil return is well known. The equipment opens all the expansion valves, the compressorsoperate at the manufacturers predefined speed, and the refrigerants high velocity through thesuction line will return the oil.

    Ducts No Longer Necessary

    In small jobs or jobs with small rooms, its easy to use a ductless system. In large systems usuallywith chilled water (high temperature differential; variable flow) and the air side (variable flow withVAV; diffusers for variable air flow), the cost of the air side is so high that is an issue for acomplete system:

    Equipment: 18% Chiller Plant +1% Splits +9% F&C = 28%;

    Air Distribution: 5% VAV +6% Sound attenuation +24% Ducts = 35%; Electrical Installation = 10%; Hydraulic Installation = 10%; Controls: = 9% Exhaust and Ventilation = 3% Fire protection system = 3% Engineering = 1%

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    Air distribution system that includes ducts, VAV box, controls air side, grilles, diffusers and laborrepresents 35% of the total system price, which is why using ductless VRF systems isadvantageous. VRF system equipment will cost more than air distribution system equipment, butwhen the total cost is compared, it could be less expensive. Another advantage for ductlesssystems is the reduced electrical power consumption. VRF will push harder for ductless system.

    SYSTEM OPERATIONExplanation of P-H Diagram (Refrigerant Characteristics Table)

    The following P-H (pressure, enthalpy) diagram shows characteristics of various refrigerants withpressure on the vertical axis and enthalpy on the horizontal axis.

    The change of state from gas to liquid is called condensing and that from liquid to gas iscalled evaporating. The boundary state of each change is called saturation, and thetemperature generating saturation is called the saturation temperature.

    Saturation temperature depends on the kind of refrigerant and pressure. Thecharacteristics of saturation temperature are shown on P-H diagrams of variousrefrigerants, and are called the saturation curve. The characteristics of temperature gradients for pressure and enthalpy are shown on P-H diagrams, called isothermal lines. By knowing the zone divided with saturation curve inwhich the intersection point of pressure and isothermal line is included, the information onthe state of refrigerant can be provided. The intersection above can be obtained bymeasuring pressure and temperature of refrigerant at a certain point. For single refrigerants such as R22 and R134A, the isothermal line has no gradient inthe saturated area, that is, the saturation temperature under certain pressure is the same atboth the liquid side and the gas side. For mixed or blended refrigerants such as R407C and

    R410A, in which multiple refrigerants with different boiling points are mixed, theirisothermal lines have gradients in the saturated area, so the saturation temperatures undercertain pressure are different at the liquid side and the gas side. They are called zeotropicrefrigerants, with the exception that R410A is called an quasi azeotropic refrigerant.

    States of refrigerants are classified in the following three categories: Superheated vapor: state that refrigerant exists as gas Saturated vapor: state that is a mixture of liquid and gas (this is also called wet vapor) Subcooled liquid: state that refrigerant exists as liquid.

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    Concept of Basic Refrigeration Cycle

    The following P-H diagram shows characteristics of various refrigerants with pressure on thevertical axis and enthalpy on the horizontal axis. Theoretical refrigeration cycle neglectingpressure loss is shown.

    The difference between temperature and pressure equivalent saturation temperature iscalled theSuperheated Degree.

    The difference between discharge pipe temperature and condensing temperature iscalled theDischarging Superheated Degree (DSH).

    The difference between suction pipe temperature and evaporating temperature is calledSuction Superheated Degree (SH). Generally, superheated degree means suction-superheated degree.

    The difference between temperature andpressure equivalent saturation temperaturein subcooled liquid is calledSubcooled Degree (SC).

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    In order to prevent wet operation (*), the superheated degree is calculated at the evaporatoroutlet, and the refrigerant flow rate into the evaporator is regulated with the expansion valve,so that the superheated vapor only is returned to the compressor.

    * Wet operation is a state of operation where wet vapor not completely vaporized in theevaporator is sucked by the compressor, causing liquid return or liquid hammering.

    Points of Refrigerant Control of VRF SystemCooling Operation

    Influenced by the number of operating (thermostat-on) units, capacity, airflow rate, return-airtemperature, and humidityof indoor units:

    Load on total system changes.Loads on every indoor unit are different.

    Compressor Capacity Control

    In order to maintain the cooling capacity corresponding to the capacity of evaporator and load

    fluctuation, based on the pressure detected by low pressure sensor of the outdoor unit (Pe), thecompressor capacity is controlled so as to put the low pressure equivalent saturation temperatures(evaporation temperature = Te) close to target value.

    Superheated Degree Control of Indoor Electronic Expansion Valve

    To maintain the superheated degree in the evaporator and to distribute proper refrigerant flow rateregardless of different loads on every indoor unit, based on the temperature detected by thermistorson the liquid pipes and gas pipes, the indoor electronic expansion valve is regulated so as to putsuperheated degree at the evaporator outlet close to target value.

    * Superheated degree SH = (indoor gas pipe temperature - indoor liquid pipe temperature)

    *1. When sizing indoor units, caution should be taken to ensure that the unit is not oversized forthe calculated load; otherwise, large temperature swings, poor comfort levels, and overall systeminefficiencies may occur.

    Heating Operation

    Influenced by change the number of operating (thermostat-on) units, capacity, airflow rate, andreturn-air temperature of indoor units:

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    Load on total system changes.Loads on every indoor unit are different.

    Compressor Capacity ControlTo maintain the heating capacity against condenser capacity and load fluctuation based on thepressure detected by high-pressure sensor control (Pc), compressor capacity is controlled so as toput the high pressure equivalent saturation temperature (condensing temperature = Tc) close totarget value.

    Superheated Degree Control of Indoor Electronic Expansion Valve

    To maintain the superheated degree in the evaporator, based on the pressure detected andcalculated low pressure sensor equivalent saturation temperature (Te) & the temperature detectedby the suction pipe thermistor, the outdoor unit electronic expansion valve is controlled to maintainthe superheat value of the evaporator outlet close to the target value.

    * Superheated degree SH = (outdoor suction pipe temperature - outdoor evaporatingtemperature)

    Subcooled Degree Control of Indoor Electronic Expansion Valve

    To distribute proper refrigerant flow rate regardless of different loads on every indoor unit, basedon the pressure detected, and calculated high pressure equivalent saturation temperature of theoutdoor unit (Tc) and the temperature detected on the thermistor of indoor liquid pipe, the indoorelectronic expansion valve is controlled so as to put subcooled degree at condenser outlet close totarget value.

    * Subcooled degree SC = (outdoor condensing temperature - indoor liquid pipe temperature)

    *1. When sizing indoor units, caution should be taken to ensure that the unit is not oversized forthe calculated load; otherwise the phenomenon of the EEV not fully closing can cause the zone toheat up even during thermostat-OFF, causing user discomfort and an ineffective system.

    Compressor Capacity Control

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    Using the compressor capacity controller of the VRF system, the pressure detected (Pe or Pc)by the pressure sensor installed in the outdoor unit is converted into the equivalent saturationtemperature, and the evaporating temperature (Te) while cooling, or the condensingtemperature (Tc) while heating, are controlled with PI control so as to put them close to the

    target value. This maintains stable capacity regardless of incessantly varying loads. Refer tothe following target value table. All target temperatures represent mean saturationtemperatures on the gas side

    The pressure loss in piping increases depending on connected pipe length and operationcapacity of the compressor. In order to compensate the reduction of capacity caused by thepressure loss in piping the following correction is made:

    The target value can be adjusted with a field setting. Long connection piping at the installation site may increase pressure loss in piping and an

    inverse installation (outdoor unit placed lower than indoor unit) may increase liquid pipe

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    inside resistance. In this event, a lower setting of target evaporation temperature byusing field setting helps to give stable operation.

    For short connection piping, a higher setting enables stable operation. In addition, samplings of evaporating temperature and condensing temperature are made so

    that the pressure detected by pressure sensors of high/low pressure are read every 20seconds and calculated. With each reading, the compressor capacity (INV frequency or

    STD ON/OFF) is controlled to eliminate deviation from target value.

    Control of Electronic Expansion Valves

    Electronic Expansion Valve of Outdoor Unit:

    In Cooling Operation

    In cooling operation, the outdoor electronic expansion valve is basically in the fully openposition.Note: The valve can be fully closed when a bridge circuit is included.

    In Heating Operation = Superheated Degree Control

    Superheated degree [SH] is calculated from the low-pressure equivalent saturation temperature

    (Te) converted from the pressure detected by the low pressure sensor of the outdoor unit (Pe) andtemperature detected by the suction pipe thermistor (Te). The electronic expansion valve openingdegree is regulated so that the superheated degree [SH] becomes close to target superheateddegree [SHS].

    When SH > SHS, adjust to make opening degree of the electronic expansion valve largerthan the present one.

    When SH< SHS, adjust to make opening degree of the electronic expansion valve smallerthan the present one.

    SH : Superheated degree (Ts Te)SHS : Target superheated degree (Normally 9 F / 5C)

    REFERENCE: Control range of outdoor electronic expansion valve:R410A unit ... 0 to 1400 pulses

    Electronic Expansion Valve of Indoor Unit

    In Cooling Operation = Superheated Degree Control

    Superheated degree [SH] is calculated from temperature detected by the gas pipe thermistorof indoor unit (Tg) and the temperature detected by the liquid pipe thermistor (Tl). Theelectronic expansion valve opening degree is controlled so that the superheated degree[SH] is close to the targeted superheated degree [SHS].The compensation is made based on the temperature difference between set-point

    temperature and the return-air thermistor temperature (T). When SH > SHS, adjust to make opening degree of the electronic expansion valve

    larger than the present one. When SH< SHS, adjust to make opening degree of the electronic expansion valve

    smaller than the present one.o SH : Superheated degree (Tg Tl)o SHS : Target superheated degree

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    Normally 9 F (5C), but when the temperature difference (T)decreases, SHS increases. Even when SH is large, the openingdegree of the electronic expansion valve becomes small.

    o (T): Remote controller set-point temperature return-air thermistordetection value

    In Heating Operation = Subcooled Degree ControlSubcooled degree [SC] is calculated from the high pressure equivalent saturationtemperature (Tc) converted from the pressure detected by high pressure sensor of theoutdoor unit and the temperature detected by the liquid pipe thermistor of the indoor unit(Tl). Electronic expansion valve opening degree is regulated so that the subcooled degree[SC] is close to target subcooled degree [SCS].The compensation is made based on the temperature difference between set-pointtemperature and the return-air thermistor temperature (T).

    When SC > SCS, adjust to make opening degree of the electronic expansion valvelarger than the present one.

    When SC < SCS, adjust to make opening degree of the electronic expansion valvesmaller than the present one.

    o SC : Subcooled degree (Tc - Tl)o SCS : Target Subcooled degreeo Normally 9 F (5C), but when the temperature difference (T) decreases,

    SCS increases. Even when SC is large, the opening degree of the electronicexpansion valve becomes small.

    o (T): Remote controller set-point temperature - return-air thermistordetection.

    Heating Operation

    Using VRF heat pump units for heating and cooling can increase building energy efficiency,especially when the heating obtained from the heat pump mode replaces an electric resistanceheating coil. Most VRF units provide higher heating capacities than conventional DX heat pumpsat low ambient temperatures. The designer must evaluate the heat output for the units at theoutdoor design temperature. Manufacturers indicate the heating capacities at catalog minimumoutside temperature, after which point, a low ambient kit is sometimes offered as an option. Whenthe outdoor temperature drops below the temperature indicated in the catalog, the heating outputfrom the heat pump cycle decreases. Supplemental heating should be considered when the heatingcapacity of the VRF units is below the heating capacity required by the application. Sequence ofoperation and commissioning must specify and prevent premature activation of supplementalheating.

    Simultaneous Heating and Cooling Operation

    In heat-recovery VRF systems, although several indoor sections are connected to one outdoorsection, some indoor sections can provide heating, while others provide cooling. The prices forthose units and their installation are higher than that of cooling- or heating-only units. Moreeconomical design can sometimes be achieved by combining zones with similar heating or coolingrequirements together. When zones with different cooling/heating requirements are connected tothe same outdoor section, consider units that are capable of providing simultaneous heating andcooling. Examples of zones that may require simultaneous heating and cooling when combined are

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    interior and exterior zones; exterior zones with different exposures; and zones requiring comfortcooling with rooms requiring close environmental control. Units capable of providingsimultaneous heating and cooling are not available in smaller sizes (e.g., capacities below 6 tons[21 kW]).

    Heating and Defrost Operation

    In heating mode, VRF systems typically must defrost like any mechanical heat pump, usingreverse cycle valves to temporarily operate the outdoor coil in cooling mode. Oil return andbalance with the refrigerant circuit is managed by the microprocessor to ensure that any oilentrained in the low side of the system is brought back to the high side by increasing the refrigerantvelocity using a high-frequency operation performed automatically based on hours of operation.The DX fan coils are constant air volume, but use variable refrigerant flow through an electronicexpansion valve. The electronic expansion valve reacts to several temperature-sensing devices

    such as return air, inlet and outlet refrigerant temperatures, or suction pressure. The electronicexpansion valve modulates to maintain the desired set point.

    APPLICATIONSBUILDING TYPES (NEW CONSTRUCTION AND RETROFIT)

    Offices

    Schools and universities

    Limited care facilities; nursing homes

    Multi-tenant dwellings; apartments

    Hotel and motel

    Churches

    Residential

    Hospitals

    REFERENCESRefrigerants (from ASHRAE Standard 34)

    R-22 Single Compound - HCFC Methane-based, Contains Chlorine - Safety Group A1 (S34-Table 1)R-32 Single Compound HFC No Chlorine Safety Group A2 (S34-Table 1)R-125 Single Compound HFC No Chlorine Safety Group A1 (S34-Table 1)

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    R-134A Single Compound - HFC Ethane-based, No Chlorine - Safety Group A1 (S34-Table1)R-407C Zeotropic Blend (23.0% R-32, 25.0% R-125, 52.0% R-134A) HFC No chlorine(S34-Table 2)R-410A Zeotropic Blend (50% R-32, 50% R-125) HFC No chlorine (S34-Table 2)Safety Group Classifications (from ASHRAE Standard 34)

    Classification consists of two alphanumeric characters. The capital letter indicates toxicity and thenumeral indicates flammability (S34-6.1.1).Class A signifies refrigerants for which toxicity has not been identified at concentrations less than400 ppm (S34-6.1.2).Class 1 indicates refrigerants that do not show flame propagation, Class 2 indicates refrigerantsthat have a low flammability limit (S34-6.1.3)Some Related Standards: UBC - Chapter 11 and ISO 5149Code Documents: OSHA 29 CFR 1910.119 and EPA 40 CFR 68

    1-Green Buildings show higher rents, occupancy Building Operating ManagementJuly 2008. http://www.facilitiesnet.com/bom/a