ある太陽・大気熱源ヒートポンプの特性と制御方式の提案

抄録

In colder districts, water is not to be-used, because of the possible freezing hazard, as the heat transfer medium for a heat pump, which is operated with the solar and atmospheric heat as its high temperature source. Thus, the low pressure refrigerant after the expansion valve is directly sent to the outdoor heat collecting panel for evaporation. This results in an elongated pipe line and which, in turn, tends to cause cycling in the control system.
Such a pump is operated during colder seasons and the dynamic responses are observed. As the results, some of the seemingly important characteristics of the system in connection with the cycling are detected. The inverse response of the refrigerant flow rate to a sudden change in solar input and the unstable fluctuation of the state variables in the evaporator side of the refrigerant system are the most remarkable ones.
The conventional expansion valve is replaced by a needle valve manipulated by a microcomputer through a step motor. The temperature signal right after the evaporator is processed to cut the harmful fluctuation by a nonlinear digital filter. Direct measurement of the degree of superheat through the pressure sensor is avoided to suppress the inverse response of the refrigerant flow rate. Instead, use is made of a model for the static characteristics, extracted from the observed data, to estimate the drgree of superheat and to manipulate the valve based on it.