Experimental apparatus and measure instruments

The solar installation with special monitoring and controlling system is built in South-West University “N. Rilski” (SWU) — Blagoevgrad. The scheme and description of installation is presented in [6]. The main target of monitoring and controlling system is to ensure possibility to: work in direct and indirect regime with different heat exchange area and location of serpentine unit in the tank; change angle of collectors toward by horizon and azimuth; regulate some operating parameters (fluid flow rate); measure all important parameters, influenced the system performance.

The test tank is a vertical cylindrical tank made of stainless steal material. In the tank are built three copper serpentines along all the height of the tank. Serpentines are 10 meters each in length. They can be switched on or off as a heat exchange unit by system of valves. So the system can work with one, two or three serpentines situated in different regions of the tank. Installation can work also in direct regime, when all three serpentines are turned off.

Monitoring system includes 12 thermo sensors assembled in accumulation vessel, 6 thermo sensors in collector circle, one thermo sensor for measuring the ambient air temperature. Solar meter, located near the solar collectors measures solar radiation. The inflow rate, heat energy and heat power are measured by combined heatmeter. All observed parameters are registered by automatic monitoring system. It includes a special electronic module for converting the analog data from sensors to digital signals. Digital data from converting module is collected by computer system. After that, stored data can be used for detailed analysis of thermal and economical efficiency of system and preparing the statistical calculation for long-term analysis.

Measuring module includes also a control unit, which governs the pump performance. It starts pump, if the temperature difference between inlet and outlet temperature of working fluid is above preliminary defined value. Ordinarily, the systems work stable and efficiently with control temperature difference between 2 and 5oC.

Consumption of hot water is realized by simulation of a typical consumption regime for small restaurant hot water system and domestic (family) hot water system.