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Toolbox, thepossibility of the occurred ambiguity explanation has been given.1.2. The research purpose and domainThe determination of the dynamic properties of the heat ex-changer as the element of the control system was the purpose ofthis work.The changeability of this properties was observed during reali-zation of the purpose. In some cases the heat exchanger indicatedthe inertial object properties (corresponding to the theoreticaldependencies), but in the other – the properties of the oscillatoryobject. The necessity of the explanation of this oscillation causesoccurred.The domain of the study included the heat exchanger of the low(24 kW) and high (124 MW) power and the laboratory model ofthe heat exchanger of the power equal about to 160W.2. The experimental stands and methods of the measurement2.1. The plate low power heat exchangerThe hybrid system of renewable resources is rich in measuringinstruments. The conditions of an external surroundings and thesystemwork parameters have been recorded in the real time. Anal-ysis presented in this paper is restricted to conclusions based onthe temperature inlet (the primary side of an exchanger) and thetemperature outlet (the second side of the exchanger) measure-ments. The primary side working agent (the mixture of waterand glycol) has been heated in the liquid collectors and the second-ary side working agent (the water) driving to the heat water tank.The measurements of the temperature have been carried out usingthe PT 1000 thermometers with the time interval equal to 1 minand then (with the rest of the dates) recorded in the files closedevery day in the midnight. The scheme of the hybrid system withthe measurements and regulation systems is presented in Fig. 1.The measurement results of the plate exchanger were used forthe presented analysis. This is the soldered plate exchanger of theCB26 type produced by the Alfa Laval. The maximum of the heatpower is equal to 24 kW, the area of the exchanger is equal to0.45 m2. The flow in the exchanger is variable, regulated by thedelivery of a pump; it sometimes is a little higher than recom-mended by the producer. The exchanger works in the counter-current.2.2. The shell-and-tube high power heat exchangerThe first stage of the analysis was carried out for the little powerexchanger. The next stage was analogical, but for the exchangersworking by the other work parameters. The rendered accessibleresults of the full day’s monitoring of the high power industrialexchanger were taken into consideration in order to determine a high power exchanger dynamic. It is a shell-and-tube heat exchan-ger produced by MICo. Their max thermal power is equal to124 MW and the heat exchanger area is equal to 2680 m2. Thewater flows in tubes and the condensing steam flows in the shell.The water vapour flows perpendicular to the tubes. The heat ex-changer is presented in the Fig. 2a and the exchanger withoutthe shell (during the conservation) in the Fig. 2b.Thewater flowvalue is between the 2500 and 20,000 [t h 1], butthe input and output water temperatures are equal to 45 62 Cand 63 80 C. For the maximum value of the flow the Reynoldsnumber Re ffi 15,300 and Nusselt number Nu ffi 80. The measure-ments values, their units and the kinds of the sensors are presentedin the Table 1.2.3. The model of heat exchangerThe elements from copper and kanthal having different shapes(bar and spiral) have been prepared for the next experiment. Theseshapes have been selected in order to obtain physically similarmodel of an exchanger. The primary side has been modeling as a resistance heating element and the secondary side has been mod-eling by the next element in the very close neighborhood of thefirst without contact. The energy exchange has been made by theair (Fig. 3). The process of the resistance heating of the differentelements has been investigated also in order to analyze the charac-teristic quality of the conduction (without convection).The measuring position for an examination of the resistanceheating has been prepared as well as the elements from copperand kanthal. For the experiment these elements have been used: The kanthal spiral – 240 mm length, 1000 mm – the length ofthe straightened spiral, diameter£= 6 mm, the number of coils10 (Fig. 4a), The kanthal or copper bar – 1000 mm length, diameter£= 6 mm, The two copper spirals with dimensions the same as for thekanthal spiral, coiled as a two-start thread without contact(Fig. 4b).The temperature has been measured in selected points everysecond. For the temperature measurements the thermocouplesTP200 (£0.25 mm) and TP201 (£0.5 mm) of 800 mmlength wereused. The type K thermocouples (Ni–Cr–NiAl) with insulated andnon-insulated terminal were chosen. The time constant of the sen-sors are equal: for TP200: T0.5 = 0.9 s; T0.9 = 2 s, for TP201:T0.5 = 1.8 s; T0.9 = 6 s. For registering and archiving the measure-ments results the ScreenMaster 3000 produced by ABB was used.It gives the possibility of registering results every second [20].