Numeric model of a direct expansion solar assisted heat pump water heater operating with low GWP refrigerants (R1234YF,R290, R600A and R744) for replacement of R134A

Autor: Duarte, Willian Moreira
Přispěvatelé: Luiz Machado, Antonio Augusto Torres Maia, Sinthya Gonçalves Tavares, Ralney Nogueira de Faria, Rudolf Huebner, Matheus Pereira Porto
Rok vydání: 2018
Předmět:
Zdroj: Repositório Institucional da UFMG
Universidade Federal de Minas Gerais (UFMG)
instacron:UFMG
Popis: O uso de bomba de calor para o aquecimento de ´agua reduz o consumo de energia el´etrica devido ao uso de energia t´ermica dispon´vel no meio ambiente. Este trabalho explora a falta de estudos de bomba de calor solar de expansao direta utilizando refrigerantes com baixo GlobalWarmingPotential(GWP).Omodelonum´ericopropostoutilizamodelosdeparametros concentrados para os trocadores de calor e um modelo semi emp´rico para o compressor. Esse modelo foi validado experimentalmente a partir de uma bomba de calor solar que usa o R134a, equipada com dois tipos de condensadores, comparando resultados experimentais e te´oricos de Coefcient of Performance (COP). Esses resultados experimentais estao dispon´veis na literatura e foram obtidos sob radiac¸ao solar de 0 e 1100 W/m2, temperatura ambiente entre 24.8 e 34.5oC, temperatura nal da ´agua em torno de 45oC e velocidade do vento entre 0 e 2.4 m/s. A diferenc¸a m´edia entre o COP medido e calculado ´e de 2%. Os refrigerantes com baixo GWP analisadosforamoR290,oR600a,oR744eoR1234yf. OR290temmelhorCOPpararadiac¸ao solarentre50W/m2 e700W/m2,bemcomoparatemperaturaambienteentre10oCe35oC.Por outro lado, para radiac¸ao solar menor que 50 W/m2, o R134a tem melhor COP que o R290. A an´alise ambiental indica que as emissoes indiretas ´e o efeito mais importante e os resultadosdeTotalEquivalentWarmingImpact (TEWI)quaseseguiramoresultadodoCOP.Omenor TEWIfoiobtidousandooR290eumaan´aliseeconomicafoirealizadausandoesterefrigerante. Uma ´area ´otima para o coletor e um comprimento para o condensador foram encontrados nas simulac¸oesamdereduzirotempoderetorno. Otamanho ´otimodocondensadoraumentacom o aumento da radiac¸ao solar, mas o tamanho ´otimo do coletor ca aproximadamente constante com o aumento da radiac¸ao solar. O tempo de retorno de uma bomba de calor solar a R290 em Belo Horizonte ´e de 3.9 anos e ´e 13% maior que o tempo de retorno dispon´vel na literatura para o uma bomba de calor solar a R134a Heating water through of heat pump has a reduced consumption of electric energy duetotheuseoftheenergyavailableintheenvironment. Thisworkexploresthelackofstudies of direct expansion solar assisted heat pump (DX-SAHP) using refrigerants with low Global Warming Potential (GWP). The numeric model proposed uses a lumped parameter model for the heat exchangers and a semi-empirical model for the compressor. This model was validated fromanexperimentalsetuprunningwithR134a,equippedwithtwotypesofcondenser,comparing the experimentaland theoretical results ofCoefcient of Performance (COP). These results are available in the literature and were obtained under a solar radiation from 0 to 1100W/m2, an ambient temperature between 24.8 and 34.5oC, a nal water temperature around 45oC, and a wind velocity between 0 and 2.4 m/s. The mean difference between measured and calculated COP is 2%. The refrigerants with low GWP analyzed are R290, R600a, R744, and R1234yf. R290 has better COP for solar radiation between 50 W/m2 and 700 W/m2, as well as for environment temperature between 10oC and 35oC. On the other hand, for solar radiation less than 50 W/m2, the R134a has better COP than R290. Environmental analysis indicates that the indirect emissions are the most important effect, and then, the Total Equivalent Warming Impact (TEWI)resultsalmostfollowedtheCOPoutcome. ThelowestTEWIwasobtainedusingR290 and an economic analysis was performed usingthis refrigerant. An optimum collectorarea and condenser length were found in the simulations to reduce the payback time. The optimum size of the condenser increases with the augment of solar radiation, but the optimum collector size remains approximately constant with the increase of solar radiation. The payback time of a R290 DX-SAHP in Belo Horizonte is 3.9 years and is 13% higher than the payback time available in the literature for R134a DX-SAHP
Databáze: OpenAIRE
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