The Prediction of Nominal and Off-design Characteristics of Economised Vapour Injection Scroll Compressor-driven Heat Pump

Transcription

1 Te Pediction of Nominal and Off-design Caacteistics of Economised Vapou Injection Scoll Compesso-diven Heat Pump Min Q. Nguyen 1* and Neil J. Heitt 2 1 College of Tecnology, Univesity of Danang, Danang City, Vietnam 2 Cente fo Sustainable Tecnologies, Univesity of Ulste, UK Abstact Economised vapou injection tecnology based on te integation of a emetic scoll compesso and a bazed plate eat excange is capable of geatly impoving vapou compession eat pump efficiency. Hoeve tee as been a lage diffeence in inceased level of pefomance beteen off-design and nominal conditions due to te oveall eat pump system being designed and built fom seveal components ic cetainly inteact it eac ote duing opeation pocess. Te size and configuation of eac component ae paticulaly impotant factos causing te oveall system pefomance to be deviated fom nominal condition-based values and subsequently enegy losses because of components to be eite ovesized o undesized unexpectedly. Expeimental investigation as conducted to estimate tese efficiency deviations in eac individual component as ell as te ole system unde a ide ange of oking conditions. In compaison it te pefomance efeence pedicted by te Copeland Selection Softae, te expeimental esults so a tendency of inceasing deviation beteen te measued and pedicted pefomances en te compesso poe is inceased ile te expeimentally measued eating capacities ae sligtly deviated fom te nominal values tougout te opeating ange. Keyods: Heat pump, Scoll compesso, Economised vapou injection, Heating capacity, Coefficient of pefomance 1. Intoduction Electic eat pumps ae one of a ange of eating devices tat can be tougt of as enegy-efficient and envionmentally fiendly systems. Tey offe lage enegy savings due to te fact tat a ell-designed system ill delive consideably moe eat enegy tan te pimay enegy used to dive it ile also contibute to significant eduction of CO 2 emissions compaed to ote eating systems. If te electicity is poduced fom eneable souces, tis benefit is fute inceased. Hoeve te enegy savings and potential envionment benefits offeed by electic eat pump ave been insufficient to enable tem to become te fist-coice eating system fo domestic and commecial buildings because of ineent enegy losses of vapou compession cycle on ic eat pump is opeated. Teefoe impoved vapou compession cycles including economised vapou injection (EVI) tecnique ave been developed to ovecome estictions and limitations of te conventional vapou compession cycle in ode to eliminate temodynamic losses and enlage te opeation ange of eat pump. 2. Heat pump it EVI tecnology Te economised vapou injection tecnology applying to vapou compession eat pump is a novel design concept using eite an intenal subcooling eat excange o a flas tank connected to an immediate pessue injection line of single to-stage scoll compesso. By subcooling te liquid efigeant te flas gas fomed duing te expansion pocess is educed and subsequently inducing a loe quality of efigeant enteing te evapoato contibuting to impoved eat tansfe pefomance in te evapoato. On te ote and, by injecting cooled vapou into te scoll compesso at immediate pessue, te compesso ok input and discage tempeatue ae educed, esulting in deceased poe consumption of te compesso and inceased eat tansfe effectiveness of te condense. Figue 1 descibes scematic pinciple of suc to EVI eat pump cycles it intenal subcooling eat excange and flas tank and its P- diagams. Fig. 1 EVI cycles and P- diagams Many studies ave been conducted bot teoetically and expeimentally to enance te pefomance of conventional eat pump by using EVI tecnology integated it eite intenal eat excange o flas tank [1-5]. Te esults soed significant lage augmentation in oveall efficiency, especially en opeating in ig tempeatue lift conditions ic ae disadvantageous fo taditional eat pump. Some ote intensive eseaces also demonstated muc fute benefits obtainable fom efigeant injection as ell as te effect of vaying injection conditions on oveall pefomance and compesso stability [6-7]. Hoeve te expeimental systems developed in above mentioned *Coesponding Auto: ngmin@ud.edu.vn, Tel: +84Z0X , Fax: + 84 Z0X Vol. 1 No.2 TSME Jounal of Reseac and Applications in Mecanical Engineeing

2 JRAME Te pediction of nominal and off-design caacteistics of economised vapou injection scoll compesso-diven eat pump studies ae pobably constucted and tested based on offdesign conditions ic ae entiely diffeent fom nominal values povided fom manufactue. Te pesent pape pedicts expeimentally tis deviation beteen nominal and off-design pefomances of EVI ai-souce eat pump fo eating applications. 3. Expeimental appaatus and data eduction Te eat pump pototype tested in te pesent study as developed based on vapou compession efigeation system ic consists of a Copeland EVI scoll compesso, to bazed plate-type eat excanges fo condense and intenal subcoole, a cylindical finned tube eat excange fo evapoato and to temostatic expansion valves fo main and subcooling cicuits. Refigeant R407C as selected it a citical tempeatue at o C coesponding to a citical pessue of ba. Te instumentation as designed to measue tempeatue, pessue, umidity and flo ate of efigeant, ate and ai as ell as to monito opeational stability of te oveall system duing test pocesses. Data collection and system contol ee acieved by using a data acquisition system connected to a pesonal compute. A scematic diagam of suc a test appaatus and measuing equipment as ell as component layout in te test bed ae illustated in Figues 2 and 3. Table I. Test conditions Ode of test Ai-on tempeatue ( o C) Wate-off tempeatue ( o C) Fig. 2 Scematic diagam of test appaatus Test conditions and pocedues ae in accodance it Euopean Standads EN and EN espectively, egading te ating and pefomance of an ai-to-ate eat pump it an electically diven compesso. Details of test conditions ae listed in Table I. Te opeating effectiveness of eat pump system is epesented by eating capacity Q and coefficient of pefomance COP on te ate-side tat bot ae calculated based on measued data as follos: out in Q m C dt m ( t t ) (1) p Q COP (2) W Fig. 3 Layout of components in test bed In ode to veify te validity of te measued data on te ate-side, an enegy balance using te temodynamic las is establised in eac test to calculate eating capacity Q and coefficient of pefomance COP on te efigeant-side as follos: out in Q m C dt m ( i i ) (3) p Q COP (4) W 10

3 Jounal of Reseac and Applications in Mecanical Engineeing (JRAME) Vol.1 No. 2 Te eo in eating capacities calculated on te ate-side and efigeant-side can be detemined by te folloing equation and sould be less tan 5%: Q Q Q (%) 100 (5) Q It as also found tat on aveage te electicity actually used by compesso is appoximately 7% geate tan tat specified by manufactue. Tis is due to ige mass flo ate of efigeant toug EVI subcoole tat leads to ige EVI capacity in compaison it te efeence value obtained fom te CSS. Figue 6 sos tis capacity incease ic means tat EVI subcoole is sligtly ovesized fo integating to te cuent EVI compesso unde off-design conditions. 6 Poe fom Select softae (kw) Measued poe (kw) Fig. 5 Measued and pedicted compesso poe Fig. 4 Test bed of EVI eat pump Figue 4 sos a potogap of te expeimental appaatus installed and commissioned in a test cambe along it all measuing equipment ic ae calibated befoe embedding to te test system. 4. Results and Discussion A eat pump system in pactice is nomally designed and assembled fom a numbe of components povided by seveal diffeent manufactues. Fo instance, it test facilities of eat pump system in tis study, EVI scoll compesso is povided by Copeland ile SWEP bazed plate eat excanges ae used as te main condense and intenal subcoole. Evapoato and expansion valves ae a cicula saped coil eat excange and Alco TISE types, espectively. So te opeating paametes of eac individual component ae measued in association it te opeation of te oveall system. Tei pefomance ill be compaed it te efeence data available in te Copeland Selection Softae (CSS) at te same oking conditions in ode to evaluate ete te opeation of eac component eacing to its nominal caacteistics. Figue 5 illustates a compaison of compesso poe beteen te actual measued values and efeence values pedicted by te CSS. Expeimental measuements so ige measued values compaed to te pedicted values deived fom te CCS. Te tendency as lage deviation en te compesso poe is inceased. EVI capacity (kw) Pedicted value Measued value Ai-on tempeatue ( C) Fig. 6 Measued and pedicted eat capacities of EVI subcoole Te pefomance assessment of SWEP bazed plate eat excange as also caied out ove a ide ange of opeating condition. Due to te tempeatue glide of te efigeant R407C, te efigeant tempeatue fo pefomance evaluation is ated at midpoint state. Figue 7 sos te vaiation of condense mid-point tempeatue diffeence at seveal diffeent test conditions of ate-off tempeatue. Due to te condense designed at te ate tempeatue of 60 o C coesponding to te condensing mid-point tempeatue of 62 o C, te measued pefomance beaviou of te bazed plate eat excange ave not canged significantly fom off-design condition-based pefomance. Te deviation of condense mid-point tempeatue diffeence ove ide ange of test conditions is elatively small. Tis means tat te plate eat excange used fo condense is designed and sized popely unde off-design conditions despite sligtly 11

4 JRAME Te pediction of nominal and off-design caacteistics of economised vapou injection scoll compesso-diven eat pump ovesized EVI subcoole causing ige efigeant flo ate toug bot EVI compesso and condense tat is not still muc to affect te condense opeating beaviou. Te compaison of eating capacity basing on te measued values and te efeence data pedicted by te CSS is illustated in Figue 8. Bot measued and pedicted values seem to emain appoximately te same duing te ange of test conditions. Te deviation ate is seen to be small, appoximately aound ±3%. Condense mid-point tempeatue diffeence ( C) Heating capacity fom Select softae(kw) Wate off tempeatue ( C) Fig. 7 Condense mid-point tempeatue diffeence Measued eating capacity (kw) Fig. 8 Measued and pedicted eating capacities of condense Hoeve te deviation beavio is diffeent fo evey diffeent test condition. Fo te cases of ig eating capacity ic is geate tan 12kW, te measued value ee found to deviate by maximum 3% ove te pedicted value ile te invese tendency as obseved at te ange of lo eating capacities. Tis may be contibuted by te pefomance of EVI subcoole ic is moe ovesized en opeating in ig ai-on tempeatue conditions. Figue 9 descibes te deviation in te oveall system pefomance beteen actual COP calculated fom measued data and nominal COP pedicted by te CSS. Te esults so a significant degadation in te actual pefomance tougout te ange of test conditions. As seen in Figue 5, on aveage te actual COP is educed about 5.5% compaed to te nominal COP specified by manufactue. Te educed pefomance of te oveall system is cetainly induced by igly inceased actual COP fom Select softae input of compesso poe ove te pedicted poe value as aleady pesented above, ile te actual eating capacity seems to be kept appoximately te same as te pedicted value. Measued COP Fig. 9 Actual and pedicted COPs of oveall system 5. Conclusions Te economised vapou injection tecnique utilizing in vapou compession cycle as contibuted to significant impovements in te pefomance of aisouce eat pump, especially en opeating at ig tempeatue lift. Hoeve actual inceased levels of pefomance ae entiely not simila to tose specified by manufactue unde nominal conditions. Altoug all components of te eat pump system ae designed and commissioned basing on off-design conditions ic ae te same as nominal conditions, te oveall system pefomance is still deviated significantly fom te nominal value. Tis is due to opeational inteaction among components of system tat induces degadation in pefomance of eac individual component and subsequently te oveall system. Te system modification afte design and commission pocesses is teefoe extemely essential to obtain te igest possible efficiency. 6. Refeences [1] Beeton, W. and Pam, H. (2003). Vapou-injected scoll compesso, ASHRAE Jounal, pp [2] Guayuan, M., Qinu, G., and Yi, J. (2003). Expeimental investigation of ai-souce eat pump fo cold egions, Intenational Jounal of Refigeation, vol. 26, pp [3] Huang, M., Heitt, N., and Nguyen, M. (2007). Field testing of an economised vapou injection eat pump, Pape pesented in te Intenational Congess of Refigeation, Beijing, Cina. [4] Winkle, J., Wang, X., and Rademace, R. (2008). Simulation and validation of to-stage flas tank cycle using R410A as a efigeant, Pape pesented in te Intenational Confeence of Refigeation, Pudue Univ., USA. [5] Guayuan, M. and Huaxia, Z. (2008). Expeimental study of a eat pump system it flas-tank coupled it scoll compesso, Enegy and Buildings, vol. 40, pp [6] Winandy, E. and Lebun, J. (2002). Scoll compessos using gas and liquid injection: expeimental analysis and modelling, Intenational Jounal of Refigeation, vol. 25, pp

5 Jounal of Reseac and Applications in Mecanical Engineeing (JRAME) Vol.1 No. 2 [7] Dutta, A., Yanagisaa, T., and Fukuta, M. (2001). An investiagtion of te pefomance of a scoll compesso unde liquid efigeation injection, Intenational Jounal of Refigeation, vol. 24, pp [8] Heitt, N., Huang, M., Adeson, M., and Quinn, M. (2011). Advanced ai souce eat pumps fo UK and Euopean domestic, Applied Temal Engineeing, vol. 31, pp