Patent GB-634204-A (GB)
Title: Improvements relating to humidity control
IPC: F24F3/14
Filed: 1947-04-30
Abstract: 634,204. Automatic humidity control systems. STONE & CO.; Ltd., J., READ, F. H. E., and SMITH, W. M. April 30, 1947, Nos. 11644/47 and 11042/48. [Class 38 (iv)] Apparatus for the automatic control of humidity consists of two thermostats 1, 2, Fig. 1, exposed to wet and dry-bulb temperatures and set to operate in unison when the relative humidity has a required value, and a humidity correcting device which is responsive to out-of-unison operation of the thermostats. The correcting device may comprise a spray, the rate of delivery of which is controlled by a reversible motor or a spray intermittently operates to deliver water at a fixed rate when open, the duration of opening being varied to effect the necessary correction ; alternatively the air flow past the spray may be varied. As shown, the thermostats 1, 2 are biassed by auxiliary heaters 3, 4 supplied through a common circuit which is interrupted periodically by the dry bulb thermostat 2. The temperature settings of the thermostats are such that for a predetermined value of the relative humidity they open and close their contacts in unison, adjustment being effected by variable resistances 14, 14<1>. Closure of the contacts of of the web bulb thermostat 1 energizes a relay 13, and closure of the contacts of the dry bulb thermostat 2 operates a relay 7, one contact 7<1> of which is connected in the auxiliary heater circuit. A second contact 7<2> is connected in series with a contact 13<1> of the relay 13 and one field winding 10 of the reversible motor 12, while a third contact 7<3> is connected in series with a contact 13<2> of the relay 13 and the other field winding 11 of the motor 12, the connections being such that as long as the thermostats operate in unison no current is supplied to the motor 12. If, however, the value of humidity falls the contacts of the wet bulb thermostat 1 will close late and open earlier than those of the dry bulb thermostat 2, so that for certain periods the field 10 of the motor will be energized to control a spray (Fig. 4, not shown), or an air flow damper in a sense to increase humidity. If the humidity rises, the field 11 is energized so as to operate the motor in the reverse direction so as to decrease humidity. At high temperatures the correctional rate of action to increase humidity tends to increase, whilst the action to reduce it decreases. To ensure a more constant rate of correction under these conditions further regulation is provided by an additional thermostat (Fig. 2, not shown), having contacts in series with a relay which interrupts the heater circuits of all three thermostats at a higher rate. Alternatively, a large capacity condenser (Fig. 3, not shown), may be connected to additional contacts on the relay 7 so that it is alternately charged through further contacts on the relay 7 in parallel with the heaters 4 and discharged through a separate resistance, ensuring a more constant rate of correction by reducing the effectiveness of the heaters. In a further embodiment (Fig. 5, not shown), a spray device, which delivers water at a fixed rate when open is opened intermittently for periods of varying duration, by a relay operated by the wet bulb thermostat 1. In this case the dry bulb thermostat 2 merely effects control of the current to the heater circuits 3, 4.