While the system is capable to output 17°C air, it has not been able to decrease the temperature of the Auditorium below 26°C, when the outdoor temperature has been over 30°C. The reasons could be:

Poor insulation due to low quality windows. While the system sizing has been carried out for a particular number of windows with particular parameters, another, “real quality” parameter should have been taken into account as well. In the system design and sizing stage it was difficult or impossible to take into account the bad quality of the windows that have evident gaps (fig. 5).

Stratification effect due to the high ceiling (6.5 meters) of the Auditorium and almost laminated flow of the cooled air from the ducts on the ceiling placed over the windows did not allow the cold air to reach to the vitally important zone, where public is seated. The used ducting provided 8 outlets to the Auditorium, all above the second row of the shaded windows that face east-south (C on fig. 2.). We think that the shaded windows, in summers have been always so warm that most of the energy from the system has been spent on cooling down the air in the top half of the Auditorium, enormously decreasing the efficiency of the operation.

In order to address the situation, a much shorter and direct ducting from the DEC machine has been constructed (D on fig. 2.). This measure immediately positively effected the system operation. However soon the machine was stopped due to a problem related to filters (see below), thus no monitoring data is available illustrate the change.

3.1. Reliability

During the five years of operation three major malfunctions occurred.

The first one is related to the breakage of the gear transmission due to intense use of the heat recovery wheel during the first year of system operation. Since we have felt a need in a more efficient operation, we have enforced high rpms (around 40 cycles per minute) of the heat recovery wheel (HRW) rotation for very long times. Naturally this caused an accelerated wear out of one of the main gears of the HRW drive. The drive has been repaired, and a lower limit of HRW rotation has been set, along with modification of the control program to a less intense operation. In subsequent years no such a “casualty” has been recorded.

The second major problem has been relating to rather rare need in functioning of the three-way valves that switch the circuits of the water, both hot and cold. The rare rotation causes salts sedimentation from water on the friction surfaces of the valves that bring to unacceptably excessive tightness. Unfortunately, this phenomenon is only revealed by the malfunction of the valves. In this case too, the problem was addressed through a change in the control program, by enforcing all three-way-valves to rotate at least once a day, thus prevent the sedimentation.

The third major failure is related to ice formation in the main solar heat exchanger in wintertime. The reason was a very low atmospheric air temperature that has been transferred by the heat recovery wheel to the solar heat exchanger (in the exhaust channel). While in winter the solar heat exchanger was idle, however it was full of water and was frozen below water melting point causing fracture of the heat exchanger pipe-work. And again the problem was addressed through an appropriate change in the control algorithm of the machine operation, after which mentioned problem did not occur. Currently the control program stops the system operation if the temperature when the solar heat exchanger reaches 0°C, and signals about the need to empty the solar heat exchanger loop when the outdoor temperature reaches 6°C. It signals back to fill the aforementioned loop, when for the first time in a particular year the outdoor temperature reaches 24°C.