6.2 Full experiment Part 2: Enclosed heating system

6.1.4 CONCLUSION

The ventilated experiment concludes that the system requires human intervention after the solar energy is not available from 16:00 pm. The system needs to be closed from 16:00 pm till 8:00 to limit the heat loss from the rock bed heat collector. Smaller rocks or gravel can be used during the same experiment to heat the core of the rock faster, which will also increase the heat loss rate of the rocks. The study will test the heat storage capacity of the rocks utilised in part 1 of the full experiment, further in part 2 by testing the possibility of seasonal charging to heat the core of the rocks and not only the surface.

6.2 FULL EXPERIM ENT - PART 2: ENCLOSE D HEATING SYSTEM 6.2.1 INTRODUCTION

The enclosed system will focus on the heating system’s performance by circulating the air through the solar heating system and rock bed heat collector to limit the amount of heat loss. The system will not be able to provide fresh air into the interior space/ room.

Figure 57 illustrates the typical diagram of the enclosed heating system. The air within the solar heating system continues to recirculate through the system, which will heat the already heated air through the solar energy from the solar air heater.

Figure 57: Diagram of enclosed heating system

6.2.2 M ETHODOLOG Y

The rock bed heat collector is filled to full capacity with 0.25m³ of rock. The outlet solar air heater will be connected to the rock bed heat collector’s inlet with 2 x 50mmØ UPVC pipes. The inlet of the solar air heater, 2 x 50mmØ UPVC pipes, will be connected to the outlet of the rock bed heat collector to recirculate the air. The solar air heater is placed at a 26° angle facing north with full solar exposure.

Figure 58: Pipes of enclosed heating system (Author, 2021)

The circulation fan will be powered by a solar panel during the day, 8:00 am till 16:00 pm and after 16:00 pm till 8:00 am; the circulation fan will be powered by a 5000mah power bank. The experiment was conducted for a duration of 168 hours/ 7 days from 8:00 am on 5 July 2021 till 8:00 am on 12 July 2021 during the winter season.

Four data loggers are used during the experiment. The results from each will be compared to determine the system’s efficiency. One data logger is placed at the outlet of the solar air heater, one within the rock bed heat collector, one at the outlet of the rock bed heat collector. One logger is placed on top of the rock bed heat collector box to track the ambient temperatures during the day and night.

6.2.3 RESULTS

Figures 59 to 65 illustrate the results from the enclosed heating system. Each figure illustrates the results for seven day from 6:00 am to 6:00 am (24 hours). Figure 66 illustrates the combined results for the 7-day experiment.

Figure 59: Enclosed heating system experiment results – Day 1

Figure 60: Enclosed heating system experiment results – Day 2

80 70 60 50 40 30 20 Heat storage Day 2

10 0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

Figure 61: Enclosed heating system experiment results – Day 3

Figure 62: Enclosed heating system experiment results – Day 4

80 70 60 50 40 30 20 Heat storage Day 3

10 0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

80 70 60 50 40 30 20 10 Heat storage Day 4

0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

Figure 63: Enclosed heating system experiment results – Day 5

Figure 64: Enclosed heating system experiment results – Day 6

80 70 60 50 40 30 20 10 Heat storage Day 5

0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

80 70 60 50 40 30 20 Heat storage Day 6

10 0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

Figure 65: Enclosed heating system experiment results – Day 7

Figure 66: Enclosed heating system experiment results – Combined 7 Days

80 70 60 50 40 30 20 10 Heat storage Day 7

0 06:00:00 08:30:00 11:00:00 13:30:00 16:00:00 18:30:00 21:00:00 23:30:00 02:00:00 04:30:00 Amient Temperature Ambient Temperature Top of SAH Rockbed Outlet

The results from the 7-day experiment indicate that the solar air heater generated a maximum of 79°C during the day. The temperature within the rock bed reached a maximum of 49°C during the same time the solar air heater reached its peak. The solar air heater is charged from 8:00 am till 16:00 pm each day. The results indicate that the heat storage from the rock bed heat collector proved to store sufficient heat, which is 5°C or more, compared to the ambient temperature, from 6:00 am to 6:00 am (24 hours). From the 7 days combined figure, the temperature stored within the rock bed heat collector increased each day. All the heat is not lost by 8:00 am when the solar energy becomes available for the next day.

At 13:00 pm when the ambient temperature reached its peak at 22,2°C, the rock bed heat collector’s temperature was 45,4°C, 52% higher than the ambient air and the air temperature from the solar air heater was 72°C, 70% higher than the ambient temperature.

At 5:30 am, when the ambient air was at the lowest temperature of 11,2°C, the heat from the rock bed heat collector was still at 19,4°C, 43% higher than the ambient temperature.

Figures 66 and 67 illustrate the minimum temperature the rocks increase each day. Due to the flywheel effect, the rock’s core temperature increases and stores additional heat in incremental portions. The results illustrated in Figure 66 indicate the possibility of seasonal charging, which can be explored in more detail through further study. It is anticipated that when the core of the rocks is at its optimum temperature, the rock will be able to discharge sufficient heat to the air passing through the system. This can be confirmed by further studies by testing the system for more extended periods.

6.2.4 CONCLUSION

The enclosed system proved to store sufficient heat during the day to discharge warm air into a room/ space during the evening. The enclosed system can be tested further to establish the results when tested for extended periods. The results from the enclosed system indicate that the solar heating system can be charged seasonally during the summer to improve the heat supply during the winter season. By charging the solar heating system seasonally, the core of the rock can be heated by the time the winter season starts, and the heat required to heat the rock bed heat collector will be less.

Figure 67: Rock diagram of enclosed heating system ( Author, 2021)