The first shows a large percentage overshoot to approximately 29°C, and the system is not capable of settling on the desired temperature. Through using the three relays, it can be clearly seen that the response has been improved by the additional complexity of the control system. The temperature takes slightly longer to change, but once it reaches the desired value it is able to maintain itself with significantly lower deviations from the desired value.

 

Finally, having shown that the temperature from a stable indoor source could be controlled, an unstable outdoor source was used. The fan was situated outside to draw in cold fresh air, and the system was set to heat it to 22°C. While the system was capable of delivering this output, there were a number of problems. The measurement noise increased greatly, primarily due to gusts of wind being picked up by the system, and accompanying this was an audible increase in noise level. Also the use of outside air meant that there were inevitable natural leakages into the room, which was negating the effect of the PV system. For the purposes of the experimental phase, air was therefore taken from inside, this removed the negative effects of the use of outside air and allows a much greater degree of control. However, it limited the overall potential performance of the system.