Question

design and their source water heat pump using simulation of software Photon 77 and explain step-by-step the theoretical as well as experimental steps to be carried out in order to design linear compressor technology in the air source heat pump using split evaporator

Answer 1

Design of System

Cakir et al. [4] designed a multifunctional heat pump system using just one scroll compressor and which can be run in four different modes, namely air to air, air to water, water to water and water to air, in order to make an experimental energetic and exergetic performance comparison. Experimental system uses R22 as working fluid. Results show that the heat pump unit which has the maximum COP (coefficient of performance) value is water to air type with 3.94 and followed by water to water type with 3.73, air to air type with 3.54 and air to water type with 3.40. Ranking of four heat pump types with respect to their mean exergy efficiency is as follows; water to air type with 30.23%, air to air type with 30.22%, air to water type with 24.77% and water to water type with 24.01%. Exergy destruction rates of the systems were investigated in this study and the results revealed that the heat pump type which has the maximum exergy destruction is air to air type with 2.93 kW. The second highest one is air to water type with 2.84 kW. The third highest one is water to air type with 2.64 kW and last one is water to water type with 2.55 kW.

Zhang et al. [7] studied the system optimization of ASHPWH. The ASHPWH system consisted of a heat pump and a water tank with the condenser coil installed inside the tank to release heat to the water side by natural convection. The capillary tube length, the filling quantity of refrigerant, the condenser coil tube length and system component matching were discussed accordingly. From the testing results, it could be seen that the system performance COP could be improved by optimizing the stated parameters.

Fu et al. [17] presented a dynamic model of air-to-water dual-mode HP with screw compressor having four-step capacities. The dynamic responses of adding additional compressor capacity in step-wise manner were studied and compared to experimental measurements that revealed good agreement.

MacArthur and Grald [18] put forward a model of vapor-compression heat pumps. The heat exchangers were modeled with detailed distributed formulations, while the expansion device was modeled as a simple fixed orifice.

Techarungpaisan et al. [19] presented a steady state simulation model to predict the performance of a small split type air conditioner with integrated water heater and validated it experimentally.

Fardoun et al. [20] developed a quasi-steady state model using MATLAB and used to predict the system parameters of interest such as hot water temperature, condensing and evaporating pressures, heating capacity, electrical power input and coefficient of performance (COP) of an air source heat pump water heater (ASHPWH). Based on the developed model, results showed that about 70% of energy consumption and financial cost is reduced comparing it to conventional electrical water heaters as well as 70% of environmental pollution is reduced based on calculating the amount of CO2 produced.

Hasegawa et al. [21] proposed a two-stage compression and cascade heating heat pump system for hot water supply. Using R12, it could heat water from 10 0C directly to 60 0C. The inlet and outlet water temperatures of evaporator are 12 0C and 7 0C, and the system COP is 3.73.

Harris et al. [22] and Sloane et al. [23] have developed two HPWH models. One model was designed as a complete unit, consisting of a HP assembly mounted at top a 0.31 m3 water tank. The second model was a retrofit unit, designed to be used with an existing water heater installation.

Zhifang and Lin [24] modelled a variable speed hermetic scroll compressor that describes various factors such as, the drive frequency, suction pressure, and discharge pressure as a function of the compressor speed. The model was validated experimentally using R22 and R134a in an experimental water source heat pump with variable speed control using frequency conversion. The results show that the analytical model properly describes the variable speed characteristics and provides a control strategy for adjusting the capacity of scroll compressors to match the heat pump or air conditioner operating conditions.

Madonna et al. [25] developed a model that simulates the hourly efficiency of air-to water heat pump based on thermodynamic considerations and on data coming from a field trial monitoring campaign. The model used to predict the behaviour of air source heat pumps installed in a set of residential buildings located different Italian cities, in both heating and cooling mode. The obtained results show that the climate plays the leading role on annual performance. The unit has recourse to excessive cycling in the less severe season, causing a seasonal efficiency reduction up 25%. Moreover, the benefits coming from a weather compensation strategy are investigated, showing an annual performance improvement up to 19%.

2.2 Experimental Studies Conducted on Heat Pump

Ma Guoyuan et al. [26] presented an improved ASHP for relatively cold regions. The dynamic performances of the prototype were tested in a laboratory test that could control all the parameters and the outcomes show that this new improved ASHP can work very well under ambient temperatures and great energy can be saved through the improved system with increased efficiency.

M. Mete Ozturk et al. [27] have done an experimental analysis of air source heat pump water heater. They concluded that the performance of entire system is directly proportional with environment conditions. While the highest ambient condition which is obtained with 30 0C and 80% humidity percentages is providing highest performance value, the poor weather which is obtained with 5 0C and 80% humidity percentages causes the performance of the system to diminish.

Hiller [28] led a group studying dual-tank water heating system from 1991. Continuous tests suggest that the efficiencies of 38 kinds of dual-tank water heating systems are higher than single-tank system HPWH with the same volume. Huang and Lin [29] also studied the dual-tank HPWH. The water tank volume was 100 L. Results showed that heating water form 42 0C to 52 0C need 10 –20 min, and the all-year COP reached 2.0–3.0. Compared with electrical water, the energy saving fraction was 50 –70%, and the hot water discharge efficiency was 0.912.

Ji et al. [30] combined heat pump water heater and conventional air conditioning, and realized a multi-functional domestic heat pump (MDHP). This equipment could implement multi functions in moderate climate areas, and operate long time with high efficiency. When refrigeration and heating run simultaneously, the average of COP and EER could reach 3.5.

Mei et al. [31] studied, experimentally, different HPWHs with natural convection immersed condensers. The described set of experiments demonstrated the viability of this type of HPWHs that is aimed to eliminate the application of electric resistance heating completely.

Ito and Miura [32] investigated the mechanism of heat pump for hot water supply using dual heat sources of the ambient air and water and the operating conditions of selecting either one or both heat sources. Then, the performance of a heat pump, which used water and the ambient air as the heat sources to heat water, was experimentally studied. When the temperature of the water heat source was decreased, the heat from the water as well as the heat from the air was used for the heat pump efficiently until its temperature became approximately that of the evaporation temperature of the heat pump using the ambient air alone as the heat source. When the temperature of the water dropped further, only the heat from the air was absorbed by the evaporators like an ordinary heat pump, which used only the evaporator of the air heat source at the same ambient air temperature.

An experimental setup and simulation model were constructed by Guo et al. [33]. Experimental results indicated that the average COP ranged from 2.82 to 5.51 under typical conditions. The recommended outside area ratio of condenser coil to evaporator is 0.14-0.31 when the evaporator outside area is between 6.0 and 6.5 m2 for this set-up. The optimal start-up time was between 12:00 and 14:00 if there was no electricity price difference between day and night, or it was near 22:00. The optimal setting water temperature should be adjusted according to the variation of seasonal ambient temperature. It was suggested that, based on this set-up, setting water temperature should be set higher than 46 ⁰C in summer and 50 ⁰C in other seasons.

Byrne et al. [34] presents the concepts of an air-source heat pump for simultaneous heating and cooling heat pumps designed for hotels and smaller residential, commercial and office buildings in which simultaneous needs in heating and cooling are frequent. The main advantage of the heat pumps is to carry out simultaneously space heating and space cooling with the same energy input unlike conventional air source heat pumps, defrosting is carried out without stopping the heat production. A R407C heat pump prototype was built and tested. Its performance on defined operating conditions corresponds to the data given by the selection software of the compressor manufacturer.

Gang et al. [35] established a comparative experiment prototype of an air source heat pump water heater system for the comparative study between instantaneous and cyclic heating modes. The air source heat pump water heater system worked at ambient temperatures of (19 ± 0.5C) in final set temperatures of 30, 35, 40, 45, 50, and 55 0C in the two modes. After calculating the coefficient of performance of the air source heat pump water heater system, it was found that the average COP of the instantaneous heating mode was 25.6, 19.0, 20.0, 21.1, 22.9, and 24.0% higher than that of the cyclic heating mode in the obtained final set temperatures of 30, 35, 40, 45, 50 and 55 0C of heated water, respectively. The results show that the instantaneous heating mode not only has a higher COP, but also a higher heating capacity, saving power consumption and decreasing heating time.

Liu et al. [36] proposed system utilize the gray water as heat source and sink for heating and cooling of residential buildings, respectively. Laboratory testing is performed with a prototype consisting of an outdoor heat pump, an indoor air handler, a gray water tank and a hot water tank. This system is set in two environmental chambers that they represent: the outdoor and indoor environments respectively. The system is designed to allow four combinations of two heat sources that they are a water-source evaporator and an air-source evaporator. The four combinations consist of air source only, water source only, air source and water source in parallel and air source and water source in series, in the refrigerant cycle. Performance of the four combinations of heat sources is experimentally investigated at a typical indoor air temperature of 21.1 ⁰C and various outdoor air temperatures at 1.1, 8.3, and 15.6 ⁰C. The results show that the heat source combinations influence the heating capacity and coefficient of performance of the system. As outdoor temperature decreases, the variation of system performance among different combinations becomes small. The COP of the system in the space heating plus hot water supply mode increases in all heat source combinations, compared with that in space heating only mode. The performance of the system for heating hot water from 30⁰C to 48.9⁰C is also studied. This proposed system can provide significant energy savings in space heating and hot water supply.

Kim et al. [37] designed a dynamic model of a water heater system driven by a heat pump to investigate transient thermal behaviour of the system which was composed of a heat pump and a hot water circulation loop. From the simulation, the smaller size of the water reservoir was found to have larger transient performance degradation, and the larger size caused additional heat loss during the hot water storage period. Therefore, the reservoir size should be optimized in a design process to minimize both the heat loss and the performance degradation.

Harata et al. [38] used thermoelectric technology. The thermoelectric technology changing electric energy into the heat energy was commonly known to be used as the heat pump. In this thermoelectric technology, they used a HP utilizing the latent heat of the atmosphere. The other characteristic was to collect the heat occurring from the power supply equipment of the thermoelectric technology device in effect a combined heat and power (CHP) device. In this thermoelectric technology, an improvement of the energy efficiency could be expected. Initially they examined for a basis a bench scale model. As for examination condition, the capacity of the tank was 3.7 Litres, the temperature of hot water was 85 0C, the environment temperature was 23 0C and the efficiency of the power supply was 80%.

Rankin et al. [39] presented a study about demand side management for commercial building using an inline heat pump water heater methodology. Rousseau and Greyvenstein [40] also performed enhancing the impact of heat pump water heater in the South African commercial sector.

Ji et al. [41] introduced a novel air-conditioning product that could achieve the multifunction with improved energy performance. They reported the basic design principles and the laboratory test results. The results showed that by incorporating a WH in the outdoor unit of a split-type air-conditioner, so that space cooling and water heating could take place simultaneously, the energy performance could be raised considerably. Two prototypes of slightly different design were fabricated for performance testing. Averaged COP, for space cooling and water heating, water heating only and space heating only was obtained 4.02, 2.91, 2.00 (ambient temperature at 4.5 ⁰C) and 2.72 respectively.

Ji et al. [42] presented a distributed model of an air-source heat pump (ASHP) system and its experimental setup using an immersed water condenser. Dynamic performance of the ASHP was then evaluated by both simulation and experiment. The results indicated that the system COP (coefficient of performance) decreased as the condenser temperature increased, ranging from 4.41 to 2.32.

Morrison et al. [43] presented a procedure for annual load cycle rating of ASHPWHs where two condenser designs were studied, a separate heat exchanger design with water pumped to it from the storage tank and a wrap-around condenser coil on the tank. The results showed that the second design had a higher annual COP (coefficient of performance). Furthermore, the study indicated that the effect of ambient temperature on the system performance is more significant than the effect of initial water temperature during the heating process.

Castro et al. [44] carried out study on an air to water reversible heat pump unit using two different fin-and-tube heat exchanger coil designs and propane (R290) as the working fluid. In the coil-2 design, the length of refrigerant circuit is increased about 17% and the refrigerant cross-sectional area decreases approximately 26% with respect to coil-1 design. From the calculation it was found that in both modes of operation coil-2 design gives higher heat transfer coefficient and pressure drops for the refrigerant side. The experimental result indicates that the performance (COP) of the heat pump find an optimal value at a superheat of 6–8 K depending on the heat exchanger design. An increment of the superheat leads to a deterioration of the COP.

Liang and Wong [45] analyzed the simultaneous heat and mass transfer on the evaporator coils, a new concept, i.e. sensible and latent fin efficiencies, is introduced. The result shows that the latent fin efficiency is generally not equal to the sensible or the overall fin efficiencies. The proposed 1-D wet fin efficiency model has been validated by the extensive comparison of the model predictions against the experimental data on evaporator coils with various configurations that include simple and complex refrigerant circuitry.

Palmiter et al. [46] studied the effect of improper airflow and refrigerant charge on the seasonal performance of a typical 10.6 kW, R410A residential heat pump with a thermostatic expansion valve. Heating and cooling tests were performed in combinations of three refrigerant charges of 75%, 100%, and 125% of nominal value and two airflows of 75% and 100% of rated airflow. In addition, cyclic tests were performed to estimate the heating and cooling seasonal coefficient of performance at six climate zones. Results showed that, in each climate zone, increases in refrigerant charge at the rated airflow could improve the unit’s heating seasonal COP. by as much as 5%. However, combined decreases in airflow and refrigerant charge could penalize the unit’s heating seasonal COP by as much as 10%.

Li et al. [47] proposed a frost free air source heat pump water heater system with integrated solid desiccant, in which frosting can be retarded by dehumidifying air before it enters the air source heat pump water heater evaporator. The system consists of a conventional heat pump water heater and an extra heat exchanger coated by a solid desiccant. A numerical simulation is carried out at a dry bulb temperature of - 7˚C to 5.5˚C and a relative humidity of 60% - 80% depending on the frosting conditions. The results show that the coefficient of performance is within the range 3.3-3.8, which is 5-30% higher than that of the air source heat pump water heater system using the hot-gas defrosting method.

2.3 Studies Conducted on Alternative Refrigerants

Laipradit et al. [48] investigated theoretical performance analysis of heat pump water heater using CO2 as refrigerant. For rated capacities of a 4 kW compressor with a 10 kW condenser and a 6 kW evaporator, the coefficient of performance is found to be between 2.0 and 3.0. The mass flow rate ratio of water and CO2 between 1.2 and 2.2 is the most suitable value for generating hot water temperature above 60 ˚C at 15 - 25 ˚C ambient air temperature.

Zhiqiang et al. [49] studied the dynamic performance characteristics of the air source heat pump with refrigerants R22 and R407C during frosting and defrosting. The results show that both refrigerant systems have similar performance characteristics, except that the performance of the R407C system deteriorated faster than that of the R22 system under frosting, and the performance of the R407C system attains its steady state faster than that of the R22 system after defrosting. R407C refrigerant can be used in either existing systems or in new systems that were originally designed for R22.

Zali et al. [50] studied thermodynamic properties of refrigerants, condenser and evaporator Secondary fluid using artificial neural network. They used Wilson-Plot method to compare performance of refrigeration cycle with R22 and R407C refrigerants. The result shows that decreasing evaporator temperature, behaviour of R407C approach to R22. Therefore R407C can be a suitable alternative for replacing R22 in all the refrigeration systems with low evaporation temperature.

Fard et al. [51] developed a numerical model for detailed simulation of the air-source residential heat pump. The model is validated by using the experimental and numerical data available in the literature. A group of pure refrigerants was selected as potential mixture components and their corresponding refrigerant mixtures are compared. It is seen that the mixture of R-32/CO2 (80/20) has the best performance among the mixtures studied. This mixture has both advantages of the CO2 and R-32; while, the flammability effect of R-32 and high pressure effect of CO2 are minimized. This mixture can increase the heating capacity of a conventional heat pump that runs on R-410A by 30% and it is shown that if the heat exchangers sizes are increased, the heating capacity can be increased by 45% and the COP by 8.5%. Moreover, the GWP of this mixture is 25% of R410A.

Liebenberg [52] evaluated heat pump water heater in terms of the viability of employing capacity control using non-azeotropic refrigerant mixtures (NARMs). By using (NARM) and changing the composition (x) of the circulating mixture, continuous capacity control could be offered. Computer simulations showed that, when operating between compositions of 100% R22 and 70% R22, the capacity-controlled heat pump showed a 29.6% improvement in energy conversion compared with a conventional R22 heat pump water heater.

According to the experiment, Mei VC [53] also found that it was feasible that R-407C could be used to replace R22 with improvement in water heating capacity without sacrificing the system energy efficiency.

Cao Feng [54] had done some experiment on heat pump hot water system by R417a; an experimental prototype was tested under different conditions by changing the temperature of the in fall or changing the quantity of the water or changing the evaporating temperature. According to the result, the system pressure of R417a was reduced contrasted with R22.

Neksa [55] did some research on CO2 hot-water heat pump system; he found a heating-COP of 4.3 was achieved for the prototype when heating tap water from 9 °C to 60 °C, at an evaporation temperature of 0 °C. The primary energy consumption could be reduced with more than 75% compared with electrical or gas fired systems.

Li Xiaoyan [56] had done some analyses on theoretical refrigeration cycle when using the mixture refrigerant R417a, a comparison test on using R407C to replace R22 was also performed. The result indicated the heat output of mixture refrigerant R417a was lower than R22, however, COP of R417a system were superior to R22 system.

C PROGRAM FOR CALCULATION OF LENGTH OF CAPILLARY TUBE in (R-22)

   IMPLICIT NONE

   Real :: t,p,Vf,Vg,V,hf,hg,h,uf,ug,u,Area,Vel,x1,x2,x,d,a,b,c,Re,
*fm,f,inc_length. cum_length

   REAL::e=2.718281828,pie=3.141592654,dia=1.63E-3,w=0010,tc=40,te=5
  
   t=tc

10   p=1000*E**(15.06-(2418.4/(t+273.15)))
   print*, "Pressure=", p/1000

   Vf=(0.777+0.002062*t+0.00001608*t**2)/1000
   PRINT*, "specific volume of saturated liquid=", Vf

   Vg=(-4.26+(94050*(t+273.15))/p)/1000
   print*, "Specific Volume of saturated vapour=", Vg

   hf= 200+1.172*t+0.001854*t**2
   print*, "enthalpy of saturated liquid=", hf

   hg=405.5+0.3636*t-0.002273*t**2
   print*, "enthalpy of saturated vapour=", hg

   uf=0.0002367-(1.715E-6*t)+(8.869E-9*t**2)
   print*, "viscosity of saturated liquid=", uf

   ug=11.945E-6+50.06E-9*t+0.2560E-9*t**2
   print*, "viscosity of saturated vapour=", ug

   Area=(pie*dia**2)/4
   print*, "Area=", Area

   d=(4*w)/(pie*dia**2)
   print*, "d=", d
  
   t=t-1

   V=d*V1
   print*, "velocity=", V

   a=0.5*(Vg-Vf)*(Vg-Vf)*d**2
   print*, "a=", a
   b=1000.0*(hg-hf)+Vf*(Vg-Vf)*d**2
   print*, "b=", b
   c=1000.0*(hf-h)+(0.5*d*d*Vf**2)-(0.5*V**2)
   print*, "c=", c
   x1=(-b+ SQRT(b**2-4*a*c))/(2*a)
   x2=(-b- SQRT(b**2-4*a*c))/(2*a)
   x=max(x1,x2)
   print*, "dryness fraction=", x

   h=hf*(1-x)+x*hg
   print*, "enthalpy=", h
   V=Vf*(1-x)+x*Vg
   print*, "specific volume=", V
   u=uf*(1-x)+x*ug
   print*, "viscosity=", u

   Re=(V*dia)/(Vf*uf)
   print*, "Reynolds Number=", Re
   f=0.33/(Re)**0.25
   print*, "Friction Factor=", f
c   inc_length=
  
  
  
   Vel=d*V
   print*, "velocity=", Vel
   Re=(Vel*dia)/(V*u)
   print*, "Reynolds Number=", Re
   f=0.33/(Re)**0.25
   print*, "friction factor=", f
  
   fm=(f+f)/2
   print*, "fm=", fm
   Vm=0.5*(Vel+Vel)
   print*, "Vm=", Vm

   inc_length=2*Area*dia*(p-p)-w*(V-V)/(fm*Vm*w)
   print*, "inc_length=", inc_length
   cum_length=inc_length+inc_length
   print*, "cum_length=", cum_length
10 continue
   stop
   end