Patent GB-1437195-A (GB)
Title: Ventilating and airconditioning apparatus
IPC: F24F11/08
Filed: 1973-10-02
Abstract: 1437195 Automatic control of temperature ZENTRA ALBERT BURKLE KG 2 Oct 1973 [2 Oct 1972] 45920/73 Headings G3N and G3R In the automatic control of an air conditioning and ventilating plant wherein a servomotor 12 Fig. 1 controls the mixing in a chamber 31 of recirculating air 11 drawn from a space 12 (which is to be air conditioned) with external (outdoor) air 11, by means of adjustable flaps 20, 22, 17, the motor is controlled by a circuit which effects proportional control up to a first threshold temperature value T e1  during winter operation so as to  decrease the proportion of external air as either the sensed external air temperature TA or the mixed air temperature TM decreases. During summer operation proportional control is effected when the sensed temperature exceeds a second threshold value T e2 , which is equal to or higher than the first, whereby to decrease the external air proportion as the sensed temperature increases. The plant includes heat-exchangers 25, 26 for respectively heating or cooling air as it is passed by a fan 24 into the space 12. Control of the heat exchangers is not described. In the control circuit Fig. 4, a first channel 35 including an operational amplifier 50 produces an output proportional to the difference between the threshold temperature T e1  and the temperature sensed by an NTC resistor 30 (i.e. the mixed air temperature TM in the plant of Fig. 1) up to the threshold temperature T e1  (e.g. between 0 and 30C) set by a bias resistor 33. The rectified output of amplifier 50 is either zero or negative and is applied to an adder 40 together with the output of a second channel including an operational amplifier 51. The first channel output is zero when the sensed temperature is at T e1 . The second channel provides proportional control above the second threshold T e2  (which is between 10C and 30C) set by a resistor 34. The rectified output of amplifier 51 is zero or positive with respect to earth and is proportional to the difference between the threshold temperature T e2  and the sensed temperature T M ; furthermore it is inverted at 59 before application to adder 40. The adder output is applied to an amplifier 61 controlling the servomotor 27 together with an input from the servomotor angular position repeater 62. The motor 27 rotates to reduce to zero the difference between the inputs to amplifier 61. Thus up to the first threshold T e  1  the motor will control the external air flaps 19, 20 and 22. At this threshold and between T e1  and T e2  the flap is fully open and no adjustment is effected. Above threshold T e2  the flaps are again controlled by the servomotor. The operational characteristic relationship between the sensed temperature TA or TM and the servomotor adjusted flaps is illustrated in Figs. 2, 3 (not shown) wherein a slope (45) pertains to the winter and a slope (46) to the summer. In an embodiment Fig. 5 (not shown) a circuit (70) provides automatic adjustment of either the second or first threshold level in dependence upon the exhaust air temperature sensed by an NTC resistor 31 Fig. 1. In an embodiment Fig. 6 (not shown) each channel is connected to a respective temperature sensor 30, 30'. The second channel sensor may be a PTC or NTC element.  In an embodiment Fig. 7 (not shown) complete closure of the flaps 22 is prevented by a circuit (74) which imposes a limit position for the servomotor 27. Humidity and air cleaning control may also be effected, by means not described.