 working as an assistant professor in Department of Mechanical Engineering, Walsh University of Technology, in this session of a vapour compression cycle, we will study methods to improve COP, learning outcome. At the end of this session, students will be able to describe sub-cooled vapour compression cycle and describe superheated vapour compression cycle. Now there are three methods to improve COP. First one is known as sub-cooled VCC, second superheated VCC and third one regenerative VCC. Here we will see first two only. In the first method to improve COP, improvement in COP requires either to increase in the refrigerating effect or decrease in the work consumption. So first one is sub-cooled VCC. In the sub-cooled VCC, the cooling of refrigerant is to be done in the liquid region. As we know on the pH plot, this is the pressure enthalpy plot and this is the saturation curve. Standard VCC we have plotted in which 1 to 2 is the isentropic compression, 2 to 3 is the isobaric condensation, 3 to 4 is the isenthalpic expansion process that is the throttling process, 4 to 1 is the refrigerating effect. Now point number 3 is on the saturated liquid curve as this is the critical point. So after leaving the condenser, if we will be able to move this liquid refrigerant which is at high pressure that is condenser pressure in the sub-cooled region. This region is the liquid region but the temperature of this region that is liquid refrigerant will be less than the saturation temperature as this is the isothermal line. So if I will be able to cool the saturated liquid on the sub-cooled side then that VCC we can call it as sub-cooled VCC. And this refrigerant is in the sub-cooled region. Now how to, can you think over the cooling of refrigerant which methods are there by means of which we can cool this liquid refrigerant for same size of the condenser we can spray for air-cooled condenser the water by means of that we can absorb more amount of heat than air-cooled condenser this is the first method. In the second method we can increase the length of condenser tube. So for that enlarge size of the condenser by increasing the length of the condenser tube we will be able to get sub-cooled liquid refrigerant at same pressure. So 3 to 3 bar will be sub-cooling process and the total condensation process will happen from point number 2 to point number 3 dash. This is known as sub-cooled 3 to 3 dash. Then this sub-cooled liquid refrigerant will be passed through the expansion wall either capillary tube or thermostatic expansion wall. There will be expansion up to u operator pressure. Let use 4 dash as the notation then 4 dash to 1 will be the evaporation process. So what happens by sub-cooling the liquid refrigerant for theoretical COP we had written refrigerating effect divided by worker consumption. So refrigerating effect was during process 4 to 1 so h1-h4 divided by worker consumption was h2-h1. By getting the sub-cooled refrigerant that means for sub-cooled VCC suppose the notation is COP dash will be equal to qr dash divided by WC dash. Now there is change in refrigerating effect from 4 to 1 to 4 dash to 1 that is why here the refrigerating effect will get changed from h1-h4 to h1-h4 dash by worker consumption is same that is h2-h1. For same worker consumption there is increase in the refrigerating effect. There is increase in the refrigerating effect sorry this is increase in the refrigerating effect. So numerator is increased, denominator is same so overall effect is increase in the COP. Though depending upon the type of the refrigerant that is r134a, r22, r717 the effect may be minimum or measurable. So this is all about the sub-cooled VCC. Second type of the increase in the COP method is superheated VCC. So what we are going to do in the superheated VCC on pH plot suppose this is the theoretical VCC 1, 2, 3, 4 this is the theoretical VCC. To avoid weight compression, weight compression practically the superheating of the refrigerant before entering to the compressor is recommended. Now how to achieve that superheating? So just increase the size of the E operator tubes. Here we increase the condenser tube, here we have to increase the E operator tubes. Just increase the length keep the diameter same so we will get the superheating from 1 to 1 dash. Now recommended practical values for sub-cooling and superheating is by 5 to 10 degree Celsius. For example if the E operator temperature is 10 degree Celsius then we should heat it, we should superheat it up to plus 20 degree Celsius maximum. This is the practical recommendation. So this 1 to 1 dash is known as superheating superheating the refrigerant. This 1 dash will enter into the compressor there will be compression from 1 dash to 2 dash and 2 dash to 3 will be actual condensation actual condensation. So what will be its effect on the COP? Let COP double dash denotes the change in the COP. This was the theoretical COP. Now by superheating the vapor refrigerant before entering to the compressor isobarically the change will be qr double dash divided by wc double dash. Now here new refrigerating effect is h1 sorry here double dash will be the notation h1 double dash minus h4 this is the change in the refrigerating effect to actual work that is h2 double dash minus h1 double dash. Now here as the specific volume increases there will be change in the compression work also there is increase in the refrigerating effect. For the selected refrigerant we have to find out the change that is increase in the refrigerating effect and increase in the work consumption. So the increase or decrease in the COP for superheating depends upon the type of the refrigerant filled or charged or used in that particular appliances means the superheated VCC COP may be greater than less than or equal to this is not possible but we will consider equal to theoretical COP. By these two methods we will get improvement in the COP. For further study you can refer refrigeration and air conditioning by CPR aurora and WF Stoker. Thank you.