PERFORMANCE COMPARISON WITH OPTIMAL CYCLE TIME AND COLLECTORS IN DIFFERENT MONTHS
6.2 Results and Discussion
In chapter 5, it was noticed that based on available solar insolation, 16 collectors each of area 2.415m2 with cycle time 1100s is optimum. At that time the climate data for the month of April was chosen. The chilled water outlet temperature was kept fixed at 7°C by adjusting the chilled water flow rate. Since solar insolation differs with different seasons of the year, a standard number of collectors should be chosen to install for the year. In this chapter the program is allowed to run with 16 collectors and optimum cycle time 1100s for several months during the hot summer season and dry winter season, that is the month of March, April, June, August, October and December.
For silica gel-water pair the driving temperature should be more than 80°C. First the driving temperature needs to be adjusted and then performance can be analyzed. The driving heat to the chiller comes from the collector outlet. The heat absorbed by the collector material depends both of the available insolation and the ambient temperature.
Available insolation, maximum and minimum temperature varies for different seasons.
The climate data for several months is given in Table 3.4.
Figure 6.1 shows the temperature histories of the collector outlet for several months. It is seen that the collector outlet temperature is within the range of the driving
temperature that is around 85°C in the month of March. It could be also observed that the cycle time 1100s is required for March which is similar as for April. However, with the change of climate data there is change in the system performance. Figure 6.1 also shows that for the same number of collectors and cycle time the collector outlet temperature reaches to 77°C for the month of June. In the month of august the insolation increases, but due to rainy season it is not consistent and the average insolation data appears is less than that of the month of April. For the month of December the collector outlet temperature is very little and the chiller performance is very low with that choice. This study has been conducted considering optimum projected area and cycle time considered in the previous chapter for the typical hot day of the month of April. Thus the highest collector outlet temperature is observed as 92°C in April and the lowest temperature is 70°C in December at the peak hour.
Figure 6.2 illustrates the performance of the chiller for different months. It is observed that cyclic average cooling capacity (CACC) of month of April is higher than that of other months due to the higher solar insolation in April. In the month of March it is moderate and is maximum 7kW during the peak hours. The cooling capacity starts decreasing from June and in December is minimized and it is maximum 3.4kW whereas in April it is maximum 8.1kW. It is seen that with the change of climate data there is a change in system performance.
It is also understood that at the peak hours there is a very little variation in the values of COPcycle for different months. The fluctuation in the performance is observed here as the solar insolation data decreasing from the month of June. The maximum COPcycle is 0.39 in the month of December which is minimal, whereas the maximum COPcycle is 0.5 in the month of April which is a maximal of all at the peak hours. At the peak hour it is 0.49 in the month of March.
The variation of chilled water flow rate for different months is also illustrated in Figure 6.3. Since, ceasing the heat from chilled water increased, with heat source temperature, chilled water flow rate is increased. The maximum flow rate is observed in April which is 0.28kg/s. In December the maximum flow rate is found 0.12kg/s, which is minimal of the maximum flow rates of the year. The chilled water outlet temperature profile for different months is depicted in Figure 6.4.
8 9 10 11 12 13 14 15 16 17 60
65 70 75 80 85 90 95
March April June August October December
Temperature ( o C)
Day Time (Hours)
Figure 6.1: Collector outlet temperature profile for different months with cycle time 1100s and 16 collectors
8 9 10 11 12 13 14 15 16 17
0 1 2 3 4 5 6 7 8 9
March April June August October December
CACC (kW)
Day Time (Hours)
Figure 6.2(a): Comparison on CACC of the chiller for different months
8 9 10 11 12 13 14 15 16 17 0.10
0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55
March April June August October December
COPcycle
Day Time (Hours)
Figure 6.2(b): Comparison on COPcycle of the chiller for different months
8 9 10 11 12 13 14 15 16 17
0.04 0.08 0.12 0.16 0.20 0.24 0.28
March April June August October December
COPsc
Day Time (Hours)
Figure 6.2(c): Comparison on COPsc of the chiller for different months
8 9 10 11 12 13 14 15 16 17 0.00
0.04 0.08 0.12 0.16 0.20 0.24
March April June August October December
COPsolar.net
Day Time (Hours)
Figure 6.2(d): Comparison on COPsolar.net of the chiller for different months
8 9 10 11 12 13 14 15 16 17
0.00 0.05 0.10 0.15 0.20 0.25 0.30
March April June August October December
Chilled water flow rate (kg/s)
Day Time (Hours)
Figure 6.3: Variation of chilled water flow rate for different months
8 9 10 11 12 13 14 15 16 17 5.0
5.5 6.0 6.5 7.0 7.5
March April June August October December
Chilled water outlet temperature(o C)
Day Time (Hours)
Figure 6.4: Average chilled water outlet temperature profile for different months 6.3 Conclusions
This study has been done to investigate the feasibility of the installation of the optimum number of collectors and cycle time, which is found in chapter 5, for different months in the year. The chiller is allowed to run by silica gel-water pair under the operating conditions given in chapter 3. It is seen that 16 collectors are optimum in summer season to keep the chilled water outlet temperature at 7°C while in winter season it is not appropriate to produce standard amount of cooling. In order to increase the cooling capacity we need to increase either the number of collectors or the cycle time.