Unsteady State Simulation of Vapor Compression Heat Pump Systems With Modular Analysis (This paper will not be presented.)

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1 Purdue University Purdue e-pubs nternational Refrigeration and ir Conditioning Conference Scool of Mecanical Engineering 0 Unsteady State Simulation of Vapor Compression Heat Pump Systems Wit Modular nalysis (Tis paper will not be presented.) Kuniyasu Matsumoto matsumoto.kuniyasu@d3.kepco.co.jp Kiyotaka Ueno Kiyosi Saito Keisuke no Follow tis and additional works at: ttp://docs.lib.purdue.edu/iracc Matsumoto, Kuniyasu; Ueno, Kiyotaka; Saito, Kiyosi; and no, Keisuke, "Unsteady State Simulation of Vapor Compression Heat Pump Systems Wit Modular nalysis (Tis paper will not be presented.)" (0). nternational Refrigeration and ir Conditioning Conference. Paper 93. ttp://docs.lib.purdue.edu/iracc/93 Tis document as been made available troug Purdue e-pubs, a service of te Purdue University Libraries. Please contact epubs@purdue.edu for additional information. Complete proceedings may be acuired in print and on CD-RM directly from te Ray W. Herrick Laboratories at ttps://engineering.purdue.edu/ Herrick/Events/orderlit.tml

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3 4, Page Unsteady State Simulation of Vapor Compression Heat Pump Systems Wit Modular nalysis Kuniyasu Matsumoto *, Kiyotaka Ueno Kiyosi Saito, Keisuke no Kansai Electric Power Co., nc., Energy Use R&D Center, kuno-ku, saka, Japan Waseda University, Scool of Fundamental Science and Engineering, Sinjuku-ku, Tokyo, Japan BSTRCT Due to worldwide demand for energy saving, many new tecnologies ave been developed in te air conditioning field. Packaged indoor unit and outdoor unit vapor compression refrigerating eat pump system using te cange of refrigerant s condition between liuid and gas is a recently developed air conditioning system. Te cooling cycle is composed of an evaporator, a condenser, a compressor, an accumulator, pipe and an expansion valve. Tese components are controlled by te euation of continuity, te euation of energy and te euation of motion and so on. We can solve tese euations by giving numerical boundary conditions. n tis study, we create te simulation model applied te cooling cycle using teory of modular analysis. n tis teory we classify te components into some kinds of module and we structure euations of eac component individually and connect by pysical continuity and initial condition. To verify te accuracy of simulation model, we tested tis system in te stable environmental facility. We set more tan 300 sensors of temperature, pressure and uantity of flow. We can analyze te cange of te conditions of refrigerant per a couple of seconds. Compared to experimental data and te solution of simulation model, we certain accuracy of model and analyze te influence of te ability of macinery and CP. s a result, we made sure tat te constructed simulation model could predict actual beavior of systems. Now we focused te eat excangers at indoor units and outdoor unit, and we calculated te adeuate foam of refrigerant flowing pats by cooling cycle and eating cycle.. NTRDUCTN Most of Japanese area belong to te temperature zones and ave rainy season called TUYU from middle of June to July. n Japan in te summer time it is too ot and umid, and in te winter time it is too cold and dry because of continental air flow. Because of environmental cange we Japanese are used to use air conditioners wic can control to adeuate air environmental bot summer and winter season. Limited of residential buildings, more tan 90% families install tem. n tis report we focus air-conditioners for office buildings and sops and ospitals especially VRF (Variable Refrigerant Flow) systems. By Japanese geograpical caracteristic residence space is narrow because of surrounding mountains and population is too big, alf of Japanese people live in just 4% land space. So in te urban area buildings tend to be iger and iger. Because of tendency office buildings and sops are composed of different tenants tat differ from business ours. n tis background building users tend to install VRF systems wic can be controlled individually. n Japan VRF systems soulder important role of air-conditioner market wic are manufactured 800 tousands per year for domestic buildings. Te ratio of installing VRF systems increases gradually. n 983 it sowed only 30%, but it rose 58% in 005. f tis tendency continues, VRF systems will monopolize alf of all stock of buildings at 030. Lately it is popular to use air-conditioners 4 ours for te reason wy cut te peak energy load, but commonly airconditioners turn N and FF freuently per a day. enerally speaking, on te way to design te planers considerate safety margin wic facilities can manage it te worst circumstances. Piling tese reasons, facilities

4 4, Page 3 seldom drive maximum load. Te result of survey VRF system s annual load factor in te office building said tat only 0~50% VRF systems manage load factor. Te new VRF systems ave improved and canged until now for te reason wy save energy or increase useful function or progress in ig cost performance and so on. n Japan, tere are standards for te consumers easy to evaluate te capacity of VRF systems. Japanese most famous standard is JS (Japanese ndustrial Standards), it consist of tree parts of standards te standard of fundamental and te standard of metod and te standard of product, in te standard of metod it is defined to measure and test and analyze. VRF systems standard is JSB866. t was establised in 006, and in tis standard it was mentioned tat te VRF systems lord factor is low and it was proposed te way ow to evaluate of PF (nnual Performance Factor).. Modular nalysis Metod t is important to evaluate VRF systems capacity and efficiency and actual management, but it is difficult to evaluate all VRF systems for consumers in te experimental room. So we ave developed simulation program called Modular nalysis Metod by using computers, instead of testing VRF systems. Tis metod is te way to analyze te complicated system. Te more VRF systems fundamental factors increase, te more complex te system are, because of improving te products. But it is uncanging te matematical model for VRF systems. Concretely we make a simulation model by tree steps. t first we separate te system for every element called Module composed of VRF systems. Secondly we connect eac element by pysical euations and initial conditions. f te number of variable uantity and te number of euations is same, we can solve te problem step by step. Finally we calculate te VRF systems for parameter study in case of many kinds of initial conditions and many kinds of te eac elemental form in steady and unsteady conditions on te computers. n tis report we sow te VRF systems model, tere are little difference of te products, basically VRF systems consist of 6 elements. Figure sows te model of wole VRF system. Tis model as one outdoor unit and four indoor units wic are same capacity. ndoor unit euips expansion valve independently. EEVsub HEX EEV4 EV4 EEV3 EV3 EEV EV EEV EV EEVmain CN REV CM CM CC Figure : model of VRF System. Pipe VRF systems compressed te refrigerant directly, and te pipe is role of te pat of refrigerant between two elements. Wen we create te matematical model, we assume te two premises. Firstly te refrigerant never eliminate, secondly tere is not energy excange (te pipe is covered by te perfect insulation). We create te matematical model of tree type of te pipe depending on te number of inlet and outlet. Te straigt pipe as only one inlet and outlet, and te mixing pipe as multiple inlets and one outlet, and te diverging pipe as one inlet and multiple outlets. Figure sows te model of mixing pipe wic as two inlets and one outlet. Tis element is restricted by euations ()~(4).

5 4, Page 4, P,, P, V, P,, d V du V P P Figure : model of mixing pipe () () P P (3) (4). Compressor Compressor is te macine for compressed refrigerant, and it is role of canging pressure conditions. Many kinds of compressors are used for te VRF system, and tere forms and pysical caracteristics vary individually. We focus on te single vapor compressed type. Wen we create te matematical model, we assume te two premises. Firstly, wen te refrigerant is compressed, it occurs tat te loss of entropy and mass volume and energy wic te ratio of loss is stable. Secondly, compressor can be controlled among wide range of output, and te refrigerant mass volume depends on te rotational speed of compressor relatively. Figure 3 sows te model of compressor. Tis element is restricted by euations (5)~(3). V, P,, o o o ' ` ', P,, Figure 3: model of compressor d V du ' ' V ' ad ' (5) (6) (7) s ' ad s nv 60 (8) (9) ' (0) ' ' W ()

6 4, Page 5 P P () (3).3 Heat excanger Heat Excanger is te macine for transferring eat from ig temperature medium to low temperature medium, and it is role of promote canging te conditions of refrigerant. Depending on te cooling cycle and eating cycle, it is used for an evaporator and a condenser. enerally speaking, teir forms and pysical caracteristics vary individually. We focus on te fin and tube type. Wen we create te matematical model, we assume te two premises. Firstly, eat transfer coefficient is cangeable depend on te case of refrigerant conditions. We treated tree types of euation. n case of single pase refrigerant, we adopted Dittus-Boelter euation, and in case of double pase refrigerant, we adopted Yosida euation and Nozu euation. Secondly, te loss of pressure passing troug te eat excanger is cangeable depend on te case of refrigerant s conditions. We treated two types of euation. n case of single pase refrigerant, we adopted Blasius euation, and in case of double pase refrigerant, we consider Lockart-Martinelli parameter. Figure 4 sows te model of eat excanger. Tis element is restricted by euations (4)~(3). R S t ( Ru t PR x Mu t v x R R Figure 4: model of eat excanger R x ) ( RvR SR x v f D M S S P M R R l l d MRxR M x R M _ in m R MR M ) S MR R l d M xr M _ in M MR (4) (5) (6) (7) (8) P (9) (Dv x M MR m M ) S l M x M (0) M ( T TM ) mm pase () ( T TR) () MR M ( X X ) M (3) M

7 4, Page 6.4 Expansion valve Expansion valve is te macine for decreasing te pressure from ig pressure refrigerant to low pressure refrigerant, and it is role of canging condition from ig pressure gas to low pressure liuid. Wen we create te matematical model, we assume te two premises. Firstly wen te refrigerant passes troug te expansion valve, te refrigerant s entalpy is stable. Secondly, te refrigerant flow volume ratio is constant according to te pressure. Tis element is restricted by euations (4)~(8)., V, P,, Figure 5: model of expansion valve V o t du V oo ( P P ) Ca (4) (5) (6) P P (7) (8).5 ccumulator ccumulator is te macine for separating between gas and liuid, and it is role of prevention of invasion of liuid refrigerant to compressors, and absorbing refrigerant flow volume wen te cooling output decrease. Wen we create te matematical model, we assume te premise. Te outlet of refrigerant is controlled by inside te accumulator s conditions. f in case of partial lord tere is liuid refrigerant inside te accumulator, outlet is decided te saturated gas. f tere is no liuid refrigerant in te accumulator, outlet is decided te supereated gas. Tis element is restricted by euations (9)~(3).,, Figure 6: model of accumulator V o t du V o P P P o (9) (30) (3)

8 4, Page 7.6 Reversing valve Reversing valve is te macine for canging te route of refrigerant, and it is role of canging cooling cycle and eating cycle, because indoor unit s role canges between cooling cycle and eating cycle. Wen we create te matematical model, we assume te premise. Wen te refrigerant passes troug te reversing valve, te refrigerant s pressure is constant. Tis element is restricted by euations (3)~(37)., P, V, P, V, P,, P,, P,, P, Figure 7: model of reversing valve d V o (3) du V o o (33) P P (34) o d V o (35) du V o o (36) P P (37) o 3. Facility of experimental room We simulate te VRF system by using te modular analysis metod using computers, and analyze an actual VRF system in our experimental rooms to verify te accuracy of te simulation results. Te experimental rooms consist of two boxes, and te temperature and umidity can be controlled separately in eac box. Table sows te specifications of te rooms. Two different sizes of manometers are installed in te upper box: tey take in air for te indoor units and outdoor unit, and measure pysical conditions. Figure 4- sows te diagram of experimental rooms. Table : Room conditions Two room Scale 7.9m(W) 6.8m(D) 6.3m(H) (Same) Dry bulb -0~40 (minimum range : ±0. ) Range Humidity 40~90% (minimum range:±%) nsulation Main 00mm + air + Sub 40mm For outdoor unit 0~440m 3 /min ir flow For indoor unit 5~85m 3 /min bility ir-conditioners.5hp~0hp

9 Pressure MPa s =.0kJ/kgK T =0 o C , Page 8 Brine tank Steam Boiler Brine Ciller D.B.Controller W.B.Controller irflow-measuring pparatus Room Brine piping Steam piping Manometer irflow-measuring pparatus Room B Manometer D.B.Controller W.B.Controller Room conditioning apparatus Room Temperature-measuring instruments utdoor-unit under experiment Room ndoor-unit x4 under experiment Room B Figure 8: Experimental room 4. Results and simulation and experiment We simulated te VRF system by using te modular analysis metod for varying patterns of initial conditions. Te test conditions were rougly classified into two groups: steady-state simulation under constant conditions, and unsteady-state simulation under varying conditions suc as te number of active indoor units. Te former was used to compare te results of simulation and measurement data in a stable environment, and te latter to test te response to canging situations. no and Saito (00) simulated evaluation of different capacity of VRF System using tis model. We conducted simulations of various conditions of cooling and eating, and reported te cooling conditions wic te JS standard proposes for measuring an air-conditioner s cooling capacity. Table sows te temperature conditions of te indoor units and outdoor unit. Table : Measurement Condition for cooling system (JSB866) ir temperature Dry bulb ( ) Wet bulb ( ) Electrical condition ndoor unit utdoor unit Hz / 00V Note : Simulation Results : Tested Results Entalpy kj/kg Figure 9: P diagram under cooling cycle.

10 4, Page 9 5. Evaluation of eat excanger by simulation analysis n tis study we focus on te VRF system, it is used for bot eating cycle and cooling cycle, and eat excanger s role differ from bot cycles. n te cooling cycle, indoor units are role for evaporators, and in te eating cycle, indoor units are role for condensers. Because of canging te operation, we tink tat te adeuate eat excangers facilities are different bot cycles. enerally speaking, wen te refrigerant flows into te eat excanger, it passes troug te distribution element, and refrigerant s route separates two more pats. Depending on te number of pats, refrigerant flow speed and eat transfer area cange, and it effects eat transfer coefficient and te loss of pressure. So Ten, we focus on te numbers of refrigerant pats wic are important factor of designing of eat excangers, and we evaluate by te simulation model by Modular analysis. Table 3 sows te facility of eat excangers. Table 3: Facility of eat excanger utdoor unit ndoor unit (per one unit) Tube Diameter (mm) 7.48/ /7.00 Tube Lengt (m) Te number of Pats (-) 8 5 Fin Pitc (mm).3.5 nterval of Tube (mm) 5 0 Fin Tickness (mm) Wi of fin (mm) We do te parameter study wit simulation model by canging te initial conditions of te number of pats. Table 4 sows te input conditions of case. Figure sow te result of simulation. Table 4: Parameter study of canging te number of pats of eat excanger Cooling Cycle Case te number of Pats te number of Pats Case utdoor unit ndoor unit utdoor unit ndoor unit Heating Cycle

11 CP CP 4, Page Heating Heating 4 Cooling 4 Cooling te number of pats (indoor unit) te number of pats (outdoor unit) Figure : Results of simulation 6. CNCLUSNS We constructed a simulation model for analyzing te VRF system under te unsteady state. We sow te results of te simulation and experimental data, te results were similar. We evaluated te influent of CP by canging te eat excanger s number of pats. ccording to figure, in case of increasing evaporator s pat (cooling cycle at indoor unit and eating cycle at outdoor unit) CP increase about 0%, but in case of increasing condenser s pat, CP is almost stable. We consider te reason wy CP increase at evaporator because of decreasing te loss of pressure. ncreasing te number of pat occurs decreasing refrigerant flow per pat, and te refrigerant flow speed decrease. But it as a peak because of eat transfer coefficient. n te oter and, t condenser, te refrigerant gas almost control te condition, canging te number of pat effect subtly. By te way, we recognize tis simulation results are small different compared to experimental data, because we assume some kind of premises in order to finis te calculation. n te future, we will improve te accuracy of te model, and add a eat recycle model, and analyze oter systems suc as gas eat-pumps, to identify te most suitable VRF system. NMENCLTURE Mass flow rate ( kg s ) Subscripts Specific entalpy ( kj kg ) nlet 3 Density ( kg m ) utlet 3 V Volume ( m ) ad Compressed gas adiabatically P Pressure ( kpa ) ir u Specific internal energy ( kj kg ) M Tube s Entropy ( J K ) R Refrigerant n Rotational speed ( rpm) W Work ( kw ) S rea ( m ) Specific eat flux ( kw m ) l Lengt ( m ) Heat transfer coefficient ( kw m K T Temperature ( K ) )

12 4, Page REFERENCES no, K., Saito, K., 009, JSRE nnual Conference : lobal unsteady state simulation of eat pump using modular analysis -st report: ntermittent driving of compression type eat pump- p no, K., Saito, K., 0, 0 t E Heat Pump Conference 0 : Unsteady State simulation of VRF Systems p4 Matsumoto, K., Saito, K., 0, 3 rd CR: Unsteady State Simulation of VRF Systems wit modular analysis p7