Available online.jocpr.com Journal of emical and Parmaceutical Researc, 013, 5(1):55-531 Researc Article ISSN : 0975-7384 ODEN(USA) : JPR5 Performance and empirical models of a eat pump ater eater system it eat recovery of aste ater Handong Wang Scool of Mecanical & Electrical Engineering, Senzen Polytecnic, Senzen, ina ABSTRAT In order to save energy, te autor developed a type of air-asteater source eat pump (AWSHP) ater eater system. Wat presented ere is about te experimental performance and empirical models of te AWSHP system. Experiments and analysis soed tat en te temperatures of aste ater and city ater varied in te ranges of 16.9~35.1 and 18.3~3.6, respectively, te AWSHP system could produce 41.~53.9 ot ater it flo rate of 3.53 10-5 ~9.31 10-5 m 3 /s. Te coefficient of eating performance (OP ) varied from 3.89 to 5.35. On te basis of energy balance, syntetic degree of grey incidence (SDGI) and grey-box metods, it as found tat te OP and ot ater flo rate depended on te ratio of inlet and outlet temperature differences of aste ater and ot ater, i.e. /. Te input poer of compressor as proportional to te outlet temperature of ot ater. Tus, te empirical correlation equations ere obtained. Keyords: eat recovery; eat pump; aste ater; empirical model; energy saving INTRODUTION In families and oter fields suc as artificial arm springs, sauna rooms and HVA engineering, ot ater is generally required above 40. But in tese fields, especially in families and sauna rooms, te aste ot ater generated during soer bat or sauna is directly drained into te environment. Tis causes bot energy-asting and termal pollution to te environment. Measurements soed tat te temperature of aste ater generated by soer bat as in te range of 30~36, ic is still valuable for utilizing. In order to recover te eat of soer aste ater and provide local air-conditioning, on te basis of researc results of [1 4], te autor developed a type of air-ater source eat pump (AWSHP). It uses air and aste ater, especially soer aste ater, as eat sources. Te AWSHP could produce enoug ot ater for bating by recovering te eat from air and soer aste ater, and soed satisfactory performance of energy saving. Wat presented in tis paper is about te experimental performance and te data-based empirical models of te AWSHP ater eater system, ic is a furter study on te performance of AWSHP presented by [5]. FLOW HART AND EXPERIMENTAL SET OF THE AWSHP Te basic flo cart diagram of te AWSHP ater eater is son in Figure 1. It can be installed in batroom or elseere. Tere is no need of ot ater tank and tis makes it more compact. Its basic principle is te same as common ater-source eat pump ater eater. In tis type of AWSHP, te air source evaporator (AE) and ater source evaporator (WE) are arranged in serial instead of parallel to maintain te different evaporating temperatures. 55
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 Te AWSHP can efficiently recover eat from aste ater and air to save energy and avoid te eat pollution caused by directly drained ot ater. In te experimental set, te outlet temperature of ot ater is regulated by a condenser-pressure-dependent valve ic also controls te condenser pressure and temperature by regulating cooling ater floing troug te condenser. Te trottling part of te AWSHP is a set of capillary tubes. Te air source evaporator is a self-made eat excanger it a fan. A plate-type eat excanger and a sell-tube eat excanger are used as te condenser and aste ater evaporator, respectively. Te refrigerant is R and te input poer of aste ater pump is 5W. Figure 1. Diagram of flo cart and energy-excanging of AWSHP ater eater. omp compressor; ond condenser; ap capillary; AE air source evaporator; WE ater evaporator; WWHE ater-ater eat excanger; WWL aste ater collector. A data acquisition system based on LabVie virtual instrument tecnology is equipped to te experimental set. Te temperature sensors are T-type termocouples. Te flo rates of ot ater and aste ater are measured by intelligent electromagnetic flo meters it accuracy of ±1.0%. Te pressures are manually measured by refrigerant pressure gauges. Te input poer of te eat pump system is measured on line by a Fluke 43B poer quality analyzer. Te umidity of air floing troug te air source evaporator is measured by digital temperature-umidity meters it accuracy of ±3.0% (for relative umidity), and te velocity of air flo in te air source evaporator is measured by an anemometer it accuracy of ±.0%. ALULATION BASIS In te AWSHP ater eater, driven by input poer of compressor, te refrigerant only excanges energy it air, city ater and aste ater, as son in Figure 1. From te vie of energy balance, te performance of te AWSHP sould depend on input poer of compressor (N) and eat capacities of condenser ( ), air source evaporator ( AE ) and aste ater source evaporator ( WE ). Te coefficient of eating performance of te AWSHP is defined by Eq.1: OP = (1) N ere, N can be measured by te Fluke 43B poer quality analyzer. is also te eat transferred to ot ater. If te eat loss of condenser is neglected, can be calculated from te parameters of ot ater as Eq.: cv = ρ ( T, o T, m 3600 ) () 56
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 ere T,m is te temperature of ot ater leaving off te WWHE,. T,m is determined by te eat excanging efficiency of WWHE and te initial temperature of city ater named as T,in (as son in Figure.1). Based on te energy balance of te system, if te eat loss of te system is neglected, tere is Eq.3: = N + + (3) AE WE Were, WE cv = ρ ( T, m T, o 3600 ) (4) AE = ρ V ) (5) A A ( A, in A, o In Eqs.4 and 5, T,m is te temperature of aste ater leaving off te WWHE, (as son in Figure 1). T,m is determined by te eat excanging efficiency of WWHE and te initial temperature of aste ater named as T,in. V A is te volume flo rate of air floing troug te AE, m 3 /s. V A =v F, v and F are te velocity of air flo (m/s) and area (m ) of te air supplying section of te air source evaporator, respectively. Eq.3 also can be used to judge te eat loss of te system. PERFORMANE AND EMPIRIAL MODELS OF THE AWSHP Tere are many teoretical models based on matematic equations of compressor, condenser, trottle valve (or capillary tube) and evaporator to simulate te performance of eat pump system, suc as [, 6 9]. But all of te teoretical models need many parameters and sopisticated computer calculation. Tey are suitable for simulating and designing te system but not convenient for engineering evaluation on te fields. Yu (1995) [10] establised an empirical OP model solely depending on te temperature difference of condensing and evaporating temperature, but it is found not suitable for evaluating te performance of te AWSHP son in Figure 1. In order to investigate te performance and establis te empirical models of te AWSHP, experiments are carried out at various conditions suc as different inlet temperatures of aste ater and city ater, it or itout aterater eat excanger, different outlet temperature of ot ater, different volume of carged refrigerant (R), and so on. Experimental performance Experiments and analysis so en te temperatures of aste ater and city ater are in te range of 16.9~35.1 and 18.3~3.6, respectively, te AWSHP can produce ot ater it temperature of 41.~53.9, and te volume flo rate of ot ater varies in te range of 0.13~0.34 m 3 / (3.53 10-5 ~ 9.31 10-5 m 3 /s). Te OP varies in te range of 3.89~5.35. Wen te input poer of pump and fan are taken into account, te overall energy efficiency ratio (EER) varies in 3.74~5.10. It is also found tat te WWHE deteriorates te OP, but it can efficiently increase te ot ater flo rate. Terefore, te WWHE is necessary to provide enoug ot ater en te city ater temperature is loer suc as in inter. Experiments so te temperature and relative umidity of air at outlet of te AE vary in te range of 1.3~0.8 and 83.1~93.4%, respectively. But te refrigeration capacity of te AE is just 5.~13.% of tat produced by te WE. Terefore, te influence of te AE on te performance of AWSHP can be neglected in te present analysis. It also indicates tat te AE sould be redesigned to supply enoug cold air for local air-conditioning. Empirical models Te empirical models are based on energy-excanging and te affecting factors of te AWSHP. It can be deduced From Eqs.1 3 tat te OP of te AWSHP is te function of N, AE and WE. As AE and WE depend on te temperatures and flo rates of air flo and aste ater flo, te OP can be expressed by te f 1 function of te parameters as Eq.6: 57
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 OP =f 1 (N, A,in, A,o, V A, T,in, T,o, V ) (6) Because te experiments so tat te AE is very small and it takes little effect on OP, te parameters of te AE can be omitted by adjusting oter coefficients, e.g. T,in. It is also found tat te N is closely related to te outlet temperature of ot ater (T,o ). Tus, en te aste ater flo rate V is kept constant, Eq.6 can be simplified as Eq.7: OP =f (T,o, T,in, T,in, T,o ) (7) Furter analysis on experimental data sos tat OP of te AWSHP closely depends on te ratio of temperature difference / en V is constant. / can be calculated as Eq.8: T = T, in, o T T, o, in (8) Terefore, Eq.7 can be furter simplified as Eq.9: OP =f 3 ( / ) (9) Similar to OP, te influence factors of te performances of te AWSHP can be summarized as T,in, T,o, T,in, T,o,, and /. Based on te analysis metod of syntetic degree of grey incidence (SDGI) proposed by [11], te most important factors of te performances of te AWSHP can be determined as / and T,o. Tus, te empirical models can be proposed by coosing / or T,o as te variables. If te grey-box metod is used to determine te empirical models, en te aste ater flo rate is kept constant, te empirical regression equations of OP, V and N can be establised based on te experiment data and principle of te least square metod as Eqs.10 1: OP = A T + B + (10) V = D E (11) + N = m T, n (1) o + ere A, B,, D, E, m and n are constant coefficients determined by regression data. Te experiment data of OP, V and N are son in Figures 4. Te corresponding empirical regression equations of OP, V and N in Figures 4 are Eqs.13 15: OP.518 = + 5.704 + 3.1159 (13) = 0.454 + 0.0551 V (14) N 0.014, + 0.03 (15) = T o 58
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 6 5 4 OP 3 1 0 0 0.1 0. 0.3 0.4 0.5 0.6 0.7 / Figure. Relationsip of OP and / 0.4 0.35 0.3 V (m 3 /) 0.5 0. 0.15 0.1 0.05 0 0 0.1 0. 0.3 0.4 0.5 0.6 0.7 / Figure 3. Relationsip of V and / N (kw) 1.6 1.4 1. 1 0.8 0.6 0.4 0. 0 40 45 50 55 T,o ( ) Figure 4. Relationsip of N and T,o Validation and discussion of empirical models In order to investigate te validity of models expressed by Eqs.10 1, experiments ere carried out on te AWSHP it reduced carged refrigerant (R). Te results soed te perfect accordance of Eqs.10 1 and only te constant coefficients ere different. For example, te OP at tis condition is son in Figure 5, and te corresponding empirical regression equation of OP is expressed by Eqs.16. 59
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 OP 13.735 = + 11.895 +.3817 (16) It demonstrates te validity of empirical models expressed by Eqs.10 1. As te temperatures of ot ater and aste ater can be easily measured, tese models can be conveniently used to evaluate and modulate te performances of ater-source eat pump ater eaters on te field. It also indicates tat te OP as a maximum or optimal value at certain /. Tis provides an engineering guide to improve te eating performance of te AWSHP. Tus, designers sould keep in mind to set te / of AWSHP in close proximity to its optimal value to obtain te maximum OP. OP 5 4.9 4.8 4.7 4.6 4.5 4.4 4.3 0. 0.3 0.4 0.5 0.6 / Figure 5. Relationsip of OP and / in te AWSHP it reduced carged R. Above analysis sos tat te performance of te AWSHP ater eater can be determined using te inlet and outlet temperatures of asteater and ot ater, especially te ratio of temperature differences of asteater and ot ater (i.e., / ). Te variable of / makes te above empirical models different to te oters presented in literatures in most of ic te absolute, not te relative temperatures of fluids ere selected as model variables. Meanile, te empirical models presented in tis paper not only can be used to predict te OP, but also can be used to evaluate te ot ater flo rate and te compressor poer-consumption of te AWSHP ater eater. Tus, it te above empirical models, te performance of AWSHP ater eater can be investigated from different points of vie, but not only from te OP. Te above empirical models also provide an easy ay for engineers to analyze and evaluate te performance of te AWSHP ater eater because measuring te temperatures of asteater and ot ater is easier tan measuring refrigerant parameters. Te empirical models are also elpful for evaluating and optimizing operational conditions. Toug Eqs.10 1 are obtained from experiment data of te AWSHP, tey are also suitable for evaluating oter ater-source eat pump ater eaters because te influence of air-source evaporator as neglected. It sould be mentioned tat te constant coefficients in Eqs.10 1 depend on operating conditions, suc as carged volume of refrigerant, dimensions of capillary tube, it or itout ater-ater eat excanger, aste ater flo rate and so on. ONLUSION Experiments and analysis indicate tat te AWSHP ater eater as satisfactory energy saving performance. Tis system also provides a simple and efficient ay to obtain sustainable use of aste ater by recovering te lograde eat from it. Te main points of tis paper can be summarized as folloing: 1) Te coefficient of eating performance (OP ) varies in te range of 3.89~5.35. Toug te WWHE deteriorates te OP of AWSHP, it can efficiently increase te ot ater flo rate. But te AE in te system sould be redesigned to provide enoug cooling capacity. 530
Handong Wang J. em. Parm. Res., 013, 5(1):55-531 ) Based on te analysis of energy balance, SDGI and grey-box, empirical models are obtained and te models so tat te OP, V and N only depend on te temperatures of ot ater and aster ater, especially te ratio of temperature differences of asteater and ot ater (i.e., / ). 3) Te empirical models presented in tis paper can be used to predict te OP, te ot ater flo rate and te compressor poer-consumption of te AWSHP ater eater at te same time. It can be conveniently used to evaluate and modulate te performances of te AWSHP or oter ater-source eat pump ater eaters on te field. Furter researc on te performances of te AWSHP it improved air-source evaporator ill soon be carried out. Nomenclature c specific eat of ater, kj/(kg ) f 1, f, f 3 signs of functions specific entalpy, kj/(kg ) N input poer of compressor, kw eat capacity, kw T temperature, V volume flo rate, m 3 / Greek symbols temperature difference, ρ density, kg/m 3 Superscripts and subscripts A air A,in inlet air A,o outlet air c condenser ot ater ot ater,in inlet of ot ater,m middle status of ot ater,o outlet of ot ater ater WE aste source evaporator asteater,in inlet of asteater,m middle status of asteater,o outlet of asteater Acknoledgement Te autor ill be grateful to Senzen Baomei Ne-Energy Resource Ltd. ompany for supporting tis researc. REFERENES [1] GS en; F Li; Journal of Guangdong University of Tecnology, 00, 19(4), 47 49. [] GX Kou; H Wang; XL Wang; XL Li; HV&A, 004, 34(6), 43 45. [3] HP Tan; Y en; Fluid Macinery, 008, 36(6), 83 85. [4] HP Tan; Fluid Macinery, 009, 37(7), 65 68. [5] HD Wang; MAE011 Proceedings, IEEE Press, 011, 7, 5803 5806. [6] J Ji; G Pei; W He; J Dong; WP Zao; HV&A, 003, 33(), 19 3. [7] H Tian; YT Ma; Z Wen; Journal of Termal Science and Tecnology, 008, 7(4), 373 378. [8] GY Xu; SH Li; XS Zang; WB Wu; Journal of Harbin Institute of Tecnology, 009, 41(), 11 13. [9] J Li; S.M Jin; Fluid Macinery, 010, 38(8), 73 79. [10] L Yu; HV&A, 1995, 5(1), 1 14. [11] SF Liu; YG Dang; ZG Fang; Grey system teory and application, 3 rd Edition, Science Press, Beijing, 004. 531