Abstract: When waste liquid is concentrated using a radiant heat section and a heat absorbent section of a heat pump circuit, in the proper place of the heating region of the heat pump circuit, a detector for detecting the pressure and/or temperature of the heat transfer medium is provided, or a detector for detecting the value of an electric current flowing through or the amount of electric power consumed in a system which includes a compressor for the heat pump circuit, is provided, and by the provision of a control system which can halt the concentration operation when the detected value exceeds a set value, both with a liquid in which the concentration of the non-volatile component is low so that a comparatively long time is required for the concentration operation, and, conversely, with a liquid in which the concentration of the non-volatile component is high so that the concentration operation is completed in a comparatively short time, the concentration operation has good efficiency, and can always be halted at

Abstract: An ultrasonic humidifier for atomizing water in a vessel by an ultrasonic oscillator and supplying atomized water with air into a room by a blower comprising a humidity sensor detecting the humidity in the room and a thermosensor detecting the temperature in the room. The operation of said ultrasonic oscillator is controlled in such a manner that the value of the detected humidity compensated by said thermosensor may be set for the desired value.