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298 Mirela Panaite et al. BY GRAŢIELA MARIA ŢÂRLEA ∗2 , ION ZABET 1 , MIOARA VINCERIUC 2 and ANA ŢÂRLEA 2 1 Romanian General Association of Refrigeration of Bucharest 2 Technical University of Civil Engineering of Bucharest Received: September 20, 2012 Accepted for publication: November 10, 2012 Abstract. Several natural refrigerant alternatives are compared on the basis of their cycle coefficient of performance and TEWI factor (Total Equivalent Warming Impact – in respect with SR EN 378-1). These natural alternatives: ammonia and mixtures have zero or low global warming potential (GWP). The theoretical study uses as reference a single stage refrigeration system which works with R 404A. To implement the international Legislation, in the future it is necessary to retrofit HFC refrigerants with ecological refrigerants (with zero ODP and zero GWP). Energy efficiency is directly related to global warming and greenhouse gases emissions Key words: energy efficiency, TEWI, natural refrigerants, refrigeration system. 1. Introduction The retrofitted single stage refrigeration system is used for chilled products in a cold storage (0…4°C). Initial refrigeration system is composed by: condenser, scroll compressors, evaporators, refrigerant vessel and thermostatic valves. The single stage refrigeration system was upgraded by replacing the scroll compressor (working with R404A) with open drive screw compressor (working with R717). The new refrigeration system is composed by: condenser, open drive screw compressor, ammonia vessel, ammonia pump, cooling oil vessel, and equalization column and ammonia evaporators. In the following lines the eco-efficiency comparative study between three refrigerants (R717, R404A and R507A) are described. The eco-efficiency comparative study consists in performance coefficient, annual energy consumption and TEWI factor (Ţârlea et al., 2010). 2. Study Case ∗ Correspon<strong>din</strong>g author: e-mail: gratiela.tarlea@gmail.com
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 4, 2012 299 In this section, the method and step calculation for eco-efficiency of single stage refrigeration system will be described. Fig. 1 shows the schematic representation of the single stage refrigeration system which must be retrofitted from R404A to R717. The R404A refrigerant from the discharge compressor port goes to the condenser (where appear the condensation process), then from the condenser outlet it goes into liquid receiver. From the liquid receiver the refrigerant enter in evaporator 1 and 2 (where appear evaporation process) and after the evaporator the refrigerant goes to suction port of the compressor. First the working conditions are described; secondly the theoretical ecoefficiency parameters (presented in the introduction) and thirdly the results of the theoretical study are shown. The working conditions are given in Table 1. The refrigeration system works 8 hours/day (nhours) and 261 days/year (ndays). The life cycle of the refrigeration system is 15 years (nyears). The refrigerant charge (m) is: R404A – 14kg, R717 – 6.45 kg and R507A – 14.11 kg. The requirement electrical power (Pe) is shown in Table 1. The carbon dioxide emission (β) is 0,6kg/kWh. The recovery factor (αrec) is 75%. The refrigerant leak (msc) is 8%. The electrical power values were calculated and established by each refrigeration system, depen<strong>din</strong>g on properties and evaporation temperature (Zabet, 2011). Table 1 Working conditions Refrigerant Φ0 (kW) M (kg) Tc (K) TSH (K) TSUB (K) T0 (K) 263.2 273.2 Pe (kW) 278.2 R404A 12.3 14 3.70 5.25 5.47 R717 10 6.45 308.2 10 3 3.55 4.00 3.85 R507A 10 14.11 3.80 3.94 4.07 where: Φ0 is refrigerant capacity, T0 evaporation temperature; TC condensing temperature, TSH superheating temperature; TSUB subcooling.
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