Question

design and experimental setup for Air source water heat pump develop its mathematical model using fortran 77 formulate the governing differential equation and solve it by Photon 77 only no other software as it is to be submitted for course work of Mtech and plot the results for various parameter such as outside air temperature and splitting the evaporator will increase the scope or will decreases that also you discuss and finally the conclusion on the whole experiments performed

Answer 1

Heat pumps are widely used for building thermal energy services, cooling, heating and water heating. Air source heat pump is one of the most cost effective option and may play a key role in the development of smart building in future. Air source heat pump does not have a constant temperature source like soil, ground water or surface water, also the efficiency of air-source heat pump decreases sharply at low source temperature.

As they compete with other heating and cooling equipment’s and in order to reduce the environmental impact of their use, it is very important that heat pumps should be energy efficient. The main purpose of this study was to experimentally investigate the performance of the ASHPWH under varying air source temperature, a prototype was developed and tested for different evaporator temperature conditions. Hence this chapter describes the heat pump design, construction, instrumentation and experimental procedure adopted.

Experimental Setup

An experimental setup for Air source heat pump water heater is developed for carrying out the specific experimental work.

In Fig. principle drawing of the experimental setup and main components of ASHP are illustrated. The ASHP has a scroll compressor using R407C as refrigerant. The condenser is plate heat exchanger consisting of 14 plates with 0.48 m² heat transfer area. The system consist of split evaporators of fin tube type with two rows of tubes each. The thermostatic expansion valve is used in this system as an expansion device. The volume of hot water tank is 500 liters.

During the ASHPWH system running, the working fluid absorbs heat from air, evaporates in the evaporator, then is compressed into the high pressure and temperature vapour, which is then condensed into liquid and release heat in the plate heat exchanger to heat up the water in the water tank. The liquid goes through thermal expansion valve turning into gas-liquid mixture with low temperature and pressure. The low temperature liquid is vaporized in the evaporator after absorbing heat from the air and the cycle continues.

In the experiment, a controller sets the final temperature of water in the tank. When the water temperature goes up to the set point, the system stops automatically and restarts once temperature lower down to the set limit. Suction fan is located at the top, which is used to force the air available at the evaporator side to pass over the evaporator coils helping refrigerant to gain heat. The sectional view of main components in heat pump and auxiliary components are as shown in Fig.

A centrifugal pump is used to circulate water in plate heat exchanger. It draws water from storage tank through rotameter then plate heat exchanger and brings water back to hot water tank. Rotameter is installed just after the pump which indicates the water supplied to plate heat exchanger.

A three phase energy meter is used which measures cumulative energy consumption of whole system i.e. compressor, suction fan and pump.

The air source heat pump water heater were tested under varying air source temperature. Temperature variations were obtained by setting the regeneration temperature of the air using temperature knob of dehumidifier. First set of experiment was carried out when air source heat pump is operating without dehumidifier, meaning that the ambient air at 30 ⁰C was sucked by the fan over the evaporator coil and the performance of heat pump under this condition was tested. In all cases initial water temperature was 30 ⁰C and final set temperature was 50 ⁰C.

In next set of experiment, heat pump was assembled with solid desiccant dehumidifier using ducts as discussed earlier. The temperature is varied using temperature knob located on dehumidifying apparatus. The heat pump was tested under 35 ⁰C, 40 ⁰C and 45 ⁰C hot air temperatures and power consumption, heating capacity, cooling capacity, compressor work, and COP of the system were evaluated.

C PROGRAM FOR CALCULATION OF AIR SOURCE WATER HEAT PUMP USING R407C REFRIGERANT

   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

Influence of Air Source Temperature on Heat Pump Performance

The influence of air source temperature is discussed in regards to suction pressure, discharge pressure, discharge temperature, heating effect, compressor work, COP and heating time etc. Also effect of increasing water temperature in the condenser is discussed.

Effect of Air Source Temperature on Heating Capacity

The effect of air source temperature on heating capacity is shown in Fig.4.2. The heating capacity of air source heat pump is dependent on the air source temperature. As the air source temperature increases, more and more heat will be gained by the refrigerant in evaporator. Hence discharged temperature increases, and ultimately it produces higher heating effect in the system

Effect of Air Source Temperature on Compressor Work

The effect of air source temperature on compressor work is illustrated in Fig. 4.3. Increase in air source temperature increases the evaporation temperature of refrigerant which increases refrigerating effect. There is decrease in suction volume of the vapour refrigerant and decrease in pressure ratio. Hence decrease in compressor work due to decrease in pressure ratio.

Effect of Air Source temperature on COP

The comparative graph of theoretical and actual COP of heat pump at different air source temperature is presented in Fig. 4.4. The growth of air source temperature led to the increase in evaporating temperature. The difference of the heat transfer between refregerant and air is enlarged. The energy gained by the refrigerant will be increased due to raised evaporating temperature and the COP will be enhanced.

Effect of Air Source Temperature on Heating Time

As the air source temperature increases, heating capacity increases which reduces the running time of the heat pump. The effect of increasing air source temperature on heating time is shown in Fig. 4.5.

Influence of Water Inlet Temperature to Condenser on Heat Pump Performance

Water inlet temperature to condenser affects the performance of heat pump. As the water temperature in water reservoir increases, the heating effect as well as COP decreases.

Effect of Water Inlet Temperature to Condenser on Heating Capacity and Compressor Work

The effect of increasing water temperature to condenser in a heat pump on its heating capacity and compression work is illustrated in Fig. 4.6 and Fig. 4.7 respectively.

As the water temperature increases, the refrigerant discharge pressure and temperature rises. With temperature of the water in the tank is gradually increased, the temperature difference between refrigerant and water becomes smaller leads to the decrease of heating capacity of the heat pump and the power consumption of the compressor is more to compress the refrigerant to a higher pressure.

Effect of Water Inlet Temperature to Condenser on COP

Effect of water inlet temperature to condenser on COP of heat pump is shown in Fig.

As the water inlet temperature to condenser increases, the heating capacity decreases due to drop in heat transfer properties of refrigerant in condenser and the refrigerant exit temperature in condenser increases which increases the vapour quality of the refrigerant at the evaporator inlet and hence cooling effect decreases. However compressor work is nearly invariant due to negligible change in refrigerant mass flow rate and degree of superheat and hence system COP decreases significantly.

Concluding Remarks

This chapter has presented experimental results to meet the objectives of this work. The following conclusions can thus be drawn;

Higher ambient temperature increased the discharge temperature, heating effect and COP of heat pump whereas compressor work was reduced.

Also it was observed that heating time required for heating water from 30 to 50 ⁰C was reduced considerably and hence the energy consumption.

Conclusions and Recommendations

Introduction

The objective of this study was to investigate the performance of an air source heat pump for the water heating purpose.

To achieve this objective, a comprehensive literature research was performed concerning currently available HP technologies and heat pump water heaters.

Laboratory experiments were carried out under diverse operating conditions by varying the air source temperature.

During the experimental test, data concerning the HP water heating system, such as ambient temperature, temperatures in the HP cycle and pressures in the HP cycle, were recorded.

These data were measured by using pressure gauges and thermocouples.

The experimental results indicated that the key advantages of an ASHPWH are: energy saving, efficient and environmental benefits through reduced air pollution. The results also showed the influence of air source temperature and increasing water temperature in condenser on the ASHPWH performance.

Conclusions

1. This integrated approach to heat pump water heating system has very good impacts and important aspect as a means for reducing the first cost and energy saving, especially in the application where simultaneous space cooling and water heating is to be achieved.
2. Hot and dehumidified air is cooled over evaporator and can be further process to air conditioning apparatus to reduce the load on the system and can be effectively use for air conditioning purpose.
3. The discharge and suction temperatures increased as the air source temperature increased due to the increased heat level exchanged at the evaporator between air and refrigerant. As the air source temperature rises, more energy can be pumped to the water reservoir and accordingly quite important savings in time and energy are obtained.
4. The COP increased as the air temperature over evaporator is increased due to an increase in the heating effect and a reduction in the compressor work.
5. Also it was observed that the dehumidified hot air reduces the problem of frosting on evaporator coil.

Recommendations

The experimental study addressed an initial structure for an ASHP water heating system and performance evaluation under different evaporator temperature.

Thoughts and proposals for focusing future efforts to clarify uncompleted aspects or to solve new issues are suggested below;

1. Detailed studies on energy and exergy analysis and the capital and economic feasibility of an air source heat pump water heater compared to other water heating methods.
2. Long term reliability test of heat pump water heater should be carried out to improve design.
3. Studying the effect of varying flow rate of water in condenser and flow rate of air on evaporator.
4. The existing system can also be tested for different humidity level and one can address frost formation issue on evaporator coils and the methods to reduce it.