Scholarly article on topic 'Parametric Studies of a Simple Direct Expansion Solar Assisted Heat Pump Operating in a Hot and Humid Environment'

Parametric Studies of a Simple Direct Expansion Solar Assisted Heat Pump Operating in a Hot and Humid Environment Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Lokesh Paradeshi, M. Srinivas, S. Jayaraj

Abstract In this paper the theoretical and experimental studies were carried out on a direct expansion solar assisted heat pump (DX-SAHP) under the metrological condition of Calicut located in the southern peninsula of the India continent. The system mainly includes a flat-plate solar collector of total are 2 m2, acting as an evaporator with refrigerant R22, a hermetically sealed reciprocating type compressor, an air cooled condenser and an electronic expansion valve. These performance parameters such as energy performance ratio, power consumption, heating capacity, solar energy input ratio and compressor discharge temperature of a DX-SAHP obtained from the experiment confirmed that, the experimental values were agreed well with simulation predicated results with average error of 1-2%. And The system COP is found to be vary from 1.8 to 2.8, power consumption from 1098 to 1305W, heating capacity from 2.0 to 3.6kW respectively. The effect of various parameters such as solar insolation, ambient temperature, collector area, wind speed has been theoretically analysed in order to understand the system performance.

Academic research paper on topic "Parametric Studies of a Simple Direct Expansion Solar Assisted Heat Pump Operating in a Hot and Humid Environment"

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Energy Procedia 90 (2016) 635 - 644

5th International Conference on Advances in Energy Research, ICAER 2015, 15-17 December

2015, Mumbai, India

Parametric studies of a Simple Direct Expansion Solar Assisted Heat Pump Operating in a Hot and Humid Environment

Lokesh Paradeshi% M. Srinivasb, S. Jayarajc

a Research Scholar, Department of Mechanical Engineering, National Institute of Technology, Calicut-673601, India b Assistant Professor, Department of Mechanical Engineering, National Institute of Technology, Calicut-673601, India c Professor, Department of Mechanical Engineering, National Institute of Technology, Calicut-673601, India

Abstract

In this paper the theoretical and experimental studies were carried out on a direct expansion solar assisted heat pump (DX-SAHP) under the metrological condition of Calicut located in the southern peninsula of the India continent. The system mainly includes a flat-plate solar collector of total are 2 m2, acting as an evaporator with refrigerant R22, a hermetically sealed reciprocating type compressor, an air cooled condenser and an electronic expansion valve. These performance parameters such as energy performance ratio, power consumption, heating capacity, solar energy input ratio and compressor discharge temperature of a DX-SAHP obtained from the experiment confirmed that, the experimental values were agreed well with simulation predicated results with average error of 1-2%. And The system COP is found to be vary from 1.8 to 2.8, power consumption from 1098 to 1305W, heating capacity from 2.0 to 3.6 kW respectively. The effect of various parameters such as solar insolation, ambient temperature, collector area, wind speed has been theoretically analysed in order to understand the system performance.

© 2016 The Authors.Publishedby ElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICAER 2015 Keywords: DX-SAHP; Parametric Studies;EPR.

• Corresponding author Tel.: 0495-2286477; Mob: +91-8136885455; E-mail address: lokeshpb@gmail.com

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICAER 2015 doi:10.1016/j.egypro.2016.11.232

1. Introduction

In view of the growing global energy demand and concern for environmental degradation, the possibility of running thermal system using the energy from the sun has received considerable attention in recent years. Solar energy is clean and most inexhaustible of all known energy sources. The low temperature thermal requirement of a heat pump makes it an excellent match for the use of solar energy. The combination of solar energy and heat pump system can bring about various thermal applications for domestic and industrial use.Since from last 25 years many researchers reported the performance of the solar assisted heat pump by experimentally and theoretically for water heating, desalination, solar drying, refrigeration, space heating and many other applications.

The concept of DX-SAHP was first proposed by Sporn and Ambrose from in West Virginia in the year 1955. Following their work O'Dell et al. [1] reported that 10-15% COP improvement and a general procedure is presented to estimating the seasonal performance refrigerant filled solar collector. Ito et al. [2] carried out the theoretical and experimental studies on the thermal performance of a heat pump that used a bare flat-plate collector as the evaporator. Theoretical results agreed well with experimental results presented, with average value of COP found to be 5.3. Morrison [3] experimentally investigated the thermal performance of solar boosted evaporators. A simulation model in the TRNSYS package is developed for assessing the annual performance. Morgan [4] presented the experimental and simulation of thermal performance of a direct expansion solar assisted heat pump system with R11 as a refrigerant, Average values of COP is found to be 2.5 to 3.5. Chaturvedi et al. [5] reported that COP and collector efficiency of a direct expansion solar assisted heat pump system working with R12 as a refrigerant in unglazed solar collector ranged from 2 to 3 and from 40 to 70%, respectively.

Huang et al. [6] carried out a modeling and system simulation of an integral type direct expansion solar assisted heat pump water heating (DX-SAHPWH). The simulation results agreed very well with experiment. Hawladar et al. [7] has been developed to study the thermal performance of solar assisted heat pump water heating system. The values of COP as high as about 9 and average collector efficiency of 75%. The thermal performance of refrigerant R134a based solar assisted heat pump studied by Saldo et al. [8] and reported that, the averaged values of COP ranged from 4 to 9 and solar collector efficiencies 60 to 85%. Mohanraj et al. [9] experimentally studied the performance of R22 and its alternative refrigerant mixture R407C- LPG and identified that RM30 (LPG10%+ R407C90%) as an optimum refrigerant composition, which has thermodynamic properties closer to that of R22 across the wide range of operating conditions.

Kuang et al. [10] have compared the analytical and experimental on DX-SAHP water heating system in which monthly averaged COP is found to vary between 4 to 6 while collector efficiency varied from 40 to 60%. Hawlader et al. [11] investigated the thermal performance of the solar assisted hat pump system for dryer and water heater application. The values of COP, obtained from simulation and experiment are 7.0 and 6.0, respectively. Li et al. [12] experimentally analyzed the performance of a direct expansion solar assisted heat pump water heater based on exergy analysis. Results indicate that exergy losses occur in the compressor and solar collector followed by condenser and expansion valve with total exergy destruction of 0.593 kW. Kong et al. [13] presented a simulation model to predict the thermal performance of direct expansion solar assisted water heater (DX-SAHPWH).Simulation results are well agreed with experimental results and simulation model also capable to effect of various parameters on the system performance. Mohanraj et al. [14] presented the suitability of artificial neural network (ANN) to predict the performance of a direct expansion solar assisted heat pump.

In this study, an attempt has been made to recover the condenser heat and utilize it in space heating with renewable heat sources: solar energy and ambient energy by developing experimental set up model of a direct expansion solar-assisted assisted heat-pump system. Results obtained from the experimentation are well agreed with the devolved simulation model. The simulation model can predict the system performance under various weather conditions and it can able to examine the effect of solar insolation, ambient temperature, wind velocity and collector area on the system performance.

Nomenclature

Ac Area of the collector (m2)

C Specific heat of air (J/Kg. K)

D External diameter of the tube (m)

F Fin efficiency

F' Collector Fin efficiency

hw Wind Heat transfer co-efficient (W/ m2. K)

It Total solar insolation (W/ m2)

m mass flow rate (Kg/s)

mair mass flow rate of air in the duct (Kg/s)

P Work input the compressor (W)

qc Heat rejected at the condenser (W)

qe Heat absorbed in the solar collector/evaporator (W)

S Solar insolation absorbed in the collector (W/ m2)

te Evaporating temperature (°C)

tc Condensing temperature (°C)

tamb Ambient temperature (°C)

Ui Overall Heat transfer co-efficient (W/ m2. K)

W Pitch of the tube (m)

Greek Symbols

a absorptivity

sp Plate thickness(m)

V Thermal conductivity of plate (m)

s emissivity

a Stefan Boltzmann Constant

2. Experiment

2.1. Experimental Set Up

A direct expansion solar assisted heat pump for space heating experimental set-up schematic diagram as shown in Fig 1. Experimental set up mainly consists of a glazed type solar collector with total area 2.0 m2 (2 x 1 m) was used as heat source device as well as evaporator for the refrigerant, Difloro-mono Chloro Methane (R22).The solar collector has 0.8 mm thick copper fins with 10mm length are attached with copper tube. The collector/evaporator surface was selective coated to improve its absorptivity of the incident solar radiation. An R22 reciprocating hermetic type compressor with rated input power 1020 W is used. A forced type air cooled condenser was made up of a coil copper tube (9 mm diameter) with face velocity 4.8 m/s. A liquid receiver and sight glass installed downstream of the condenser, followed by the, a filter-drier and a flow meter which are used to remove the moisture content in the refrigerant and measure the flow rate of the refrigerant respectively. The thermostatic expansion valve (external balance type) regulates refrigerant flow through the solar collector/evaporator.

2.2. Data Acquisition System

The pressures, temperatures, velocity and flow rate of working fluid (R22) were measured at the different locations in the experimental set up as shown in Fig. 1. Also, the ambient temperature, relative humidity, wind velocity and the incident solar insolation were measured. Suction and discharge pressure of the compressor are measured using mechanical bourdon type pressure gages and pressure transducer at inlet and outlet of the

compressor. Similarly, inlet and outlet of the expansion value, the bourdon type pressure gages and pressure transducer are used to measure the condenser outlet pressure and pressure of the refrigerant after expansion. Suction and discharge temperature of the compressor, outlet temperature of the condenser and temperature of after expansion of the refrigerant were measured with platinum resistance thermometers (RTDs). Another, similar RTDs are used to measure the inlet and outlet air temperature of the condenser. The ambient temperature was measured with the help of a thermometer. Relative humidity and wind velocity were measured with help of the Vantage-Pro weather station. Outlet air velocity of the condenser was measured using vane type anemometer and velocity sensor. A solar Pyranometer was mounted on the surface of the solar collector (evaporator) to measure the instantaneous solar radiation. A turbine flow meter was used to measure the refrigerant flow in system. A digital multi-function single phase power meter was used to measure the power consumptions of the compressor. All above temperature, pressure, velocity, solar insolation and power consumption were monitored and controlled by a personal computer-based data-acquisition system. The data was recorded at every 5 minutes interval in a data logger, which will be later used for the analysis.

The experiments in the DX-SAHP were carried out under the metrological condition of Calicut (Latitude of 11.15°N, Longitude of 75.49°E), located in the southern peninsula of the India continent.

Fig. 1 Schematic view of the experimental set up

3. Model Development

3.1. Assumptions

A system simulation model is developed to predict the thermal performance of the DX-SAHP system, based on the following assumptions:

• All the process are steady-state within the chosen time interval.

• Pressure drop is negligible in collector/evaporator, condenser as well as in piping.

• Compression of the refrigerant vapor is assumed to follow a polytropic process.

• Expansion of refrigerant liquid is considered to be isenthalpic.

Based on the above assumptions, governing equations describing the thermal performance of various components of the system have been formulated.

3.2. Mass and Energy Balance

In general, the mass balance equation can be expressed in the rate form as

mi =me (1)

Here, m is the constant mass flow rate. The mass flow rate of the refrigerant is assumed to be constant at all the typical locations in the system. The energy balance equation for the DXSAHP can be expressed as;

qe + P=qc (2)

Where qc is the heat rejected at the condenser, qe is the useful heat gain at the evaporator /solar collector and P is the work input to the compressor.

3.3. Compressor Power Consumption

The performance characteristics of a constant speed compressor will be expressed by their power consumption and cooling capacity. Based on the experimental data, the performance characteristics such as power consumption and cooling capacity can be expressed in terms of their evaporating and condensing temperature as follows;

P = -17854.2632 -2381.4993/ - 73.5881/ 2+870.29110/-9.9902/ 2-110.8510 // + 3.45881/ 2/ + 1.2900/2/ - 0.0404 / 2/ 2 (3)

e e 22 e 2 e 2 e e 2 v/

q = -76112.1029 + 10754.2169/ - 350.0243/ 2 + 3345.3171/ -36.9126/ 2-479.2131/ t +15.9065/ 2t +5.4086/ 2t - 0.180% 2t 2 (4)

e e e c c ececceec

Where te and tc are the evaporating and condensing temperatures. The constants applicable to the above equations are determined by a suitable equation fitting procedure.

3.4. Evaporator/Solar Collector Model

The useful energy gain from the flat plate collector qe, operating at steady state conditions can be evaluated as follows;

qe = AcF' (-Ui (te-tamb)) (5)

Where Ac is the area of the solar collector, S is the incident solar radiation on the solar collector, Ul is the overall heat loss coefficient from the collector to the ambient air, te is the average evaporating temperature of collector/evaporator unit, and tamb is the ambient air temperature.

Assuming that the thermal resistance of the bond between the collector plate and tube can be neglected, F' is given by

F' = F+(1-F)(D/W) (6)

Where F is the fin efficiency, D is the external diameter of the tube and W is the pitch of the tube. The fin efficiency F can be calculated using the following correlation.

F=-V ' P P -— (7)

(yjWÁpáp (W-D)/2) v y

Where, 8p are the thermal conductivity and thickness of the collector plate, respectively. And Eq. (5), the symbol S is given as follows

S = aIT (8)

Where IT is the total solar radiation intensity on the solar collector plate, a is the absorptivity of the collector. In Eq. (5), the symbol Ul is mainly due to convection and radiation heat transfer from the top surface of the collector to the surroundings, obtained by;

U, = h + 4oeT3 (9)

Where a is the Stefan Boltzmann constant, and hw is the wind heat transfer co-efficient, is given by

h = 5.7+ 3.8u (10)

Where uw is the wind speed 3.5. Condenser Model

Heat ejected at the condenser is the sum energy absorbed in the evaporator (solar collector) and the work in input in the compressor. It can also be expressed as

q = m C (t -1 ,) (11)

c air pa c amb

Where m is the mass flow rate of air through the duct area, Cpa is the specific heat of air, tc is condensing temperature of condenser unit and tamb is the ambient air temperature.

Finally Energy performance ratio (EPR) or performance coefficient of the system can be expressed as follows; EPR=qc/P (12)

3.6. Simulation Procedure

Based on the above expressions for each component of the DX-SAHP system experimented, a Matlab® (Version 9.1) program was written and developed to estimate the thermal performance of this system. The input data are ambient parameters (such as solar intensity and ambient temperature etc...). The technique chosen for the mathematical simulation was Newton-Raphson method, which is the most popular technique for solving the simultaneous equations. The information flow diagram of the simulation program carried out is shown in Fig. 2.

Fig. 2 Information flow diagram of the simulation

4. Result and Discussion

The experiments were carried out under the metrological condition of Calicut located in the southern peninsula of the Indian continent. The results obtained from the experimentation and system simulation model are compared and presented in this section. And also discussed the effect of solar insolation, ambient temperature, wind velocity and collector area on the system performance based on the simulation results.

4.1. Experimental Validation of Simulation

A plot of simulation predicted and experimental values for the heating capacity of the DX-SAHP with respect to solar intensity are depicted in Fig. 3. The comparison of results showed that simulation predicted heating capacity is found to be closer with the experimental heating capacity. The average deviation is in the range of 2%. The power consumption predicated by simulation and experimentally measured results against the solar intensity are compared in Fig. 4. In this case, these results confirmed that the experimental values are closer to simulation predicted results with an average error of 2.05%.

_ 3.400 <

eg «3

M 2.G00

1 2,200 1.800

0 200 400 600 800 1,000 u £lJU umJ c

Solar Insolation (W/m2) Solar Isolation (W/m2)

Fig. 3. Heating Capacity with respect to solar insolation

Fig. 4. Power Consumption with respect to solar insolation

The simulation predicted and calculated energy performance ratio values against the solar intensity are reported in Fig. 5. For this parameter, it is seen that, initially actual performance of the system is higher than simulation. It is because the collector was able to gain more latent heat from the solar and ambient, which improved the thermal performance of the system, and values varied from 1.88 to 2.72. Compared to the experimental results, the simulated values of the of the energy performance ratio have same trend with average error 1%. The SEIR varies between 0.20 and 0.80 with increase in solar intensity from 100 to 918 W/m2. Simulation predicted and experimental measured values of solar energy input ratio (SEIR) against solar intensity are shown in Fig. 6.

Solar Insolation (W/in2) Solar Insolation (W/m2)

Fig. 5. EPR with respect to solar insolation Fig. 6 Solar energy inPut ratio with respect to solar

insolation

4.2. Effect of various parameters on the system performance 4.2.1. Effect Wind Speed and Collector Area

Figure. 7, shows that effect of wind speed on the system performance, the increase in the wind speed enhances the heat transfer rate between collector and surroundings. When te is lower than ta, the rising the wind speed enhances the collector to obtain more useful energy gain from the surroundings and consequently increasing the system COP. It is observed that, the variation of wind speed from 1 to 4.5 m/s, for given solar intensity of750 W/m2, the system COP increases from 2.42 to 2.49, which increase the average system performance about 0.5% Similarly Fig. 8, Shows that for given ambient temperature and solar intensity of 750 W/m2, varying collector area from 0.5 to 3.5 m2, enable to increase the solar and air source heat in the collector. Hence the system co-efficient performance increases from 1.50 to 3.05. And similarly about 11% average increment in the system performance.

Fig. 7. Effect of wind speed on the system performance

Fig. 8. Effect of collector area on the system performance

4.2.2. Effect of Ambient Temperature and Solar Insolation

The system performance improves with increasing in the ambient temperature. This is because rising the ambient temperature lower the heat loss from the collector and increase the evaporating temperature of the working fluid in the collector; (as shown in Fig. 9)., With increasing the ambient temperature from 22 to 38°C, for given solar intensity of 750 W/m2, the system COP increases from 2.4 to 2.8. This increases the average system performance by about 2%. From the Fig. 10, it is clear that increase in the solar radiation at given ambient temperature and collector area, there will be increase in the system performance. This is mainly because of an increase in intensity enables to attain a higher evaporating temperature of the working fluid and also enhance the collector to obtain more useful energy gain, which results in a higher system COP. For a given ambient temperature 25°C and varying the solar insolation from 100 to 900 W/m2, the system COP increases from 1.7 to 2.6. And about 6% average increment in the system performance.

Fig. 9. Effect of ambient temperature on the system performance Fig- 1(0 Effect of solar Nation on the system pafornancx

5. Conclusion

Based on the experiment and developed system simulation model, the thermal performance of direct expansion solar assisted heat pump system has been studied under metrological condition of Calicut in India. It is found that Energy performance ratio (COP) to be vary from 1.88 to 2.72 with power consumption variation from 1110 to 1310W. The heating capacity range is from 2.09 to 3.57 kW while solar energy input ratio variation from 0.2 and 0.8 These performance parameters results indicate that, the experimental values agree well with the simulation results with an average error of 2%. According to the simulations, the thermal performance of the DX-SAHP system for different parameters are studied, which is shows that system performance affected considerably by variation of solar collector/evaporator area, solar insolation, ambient temperature and followed by the effect of wind speed. The system simulation technique presented in this paper is expected to contribute further studies and applications of DX-SAHP systems with inside ranging operating conditions and refrigerants in the future.

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