Abstract:
An atmospheric thermostat having an auxiliary humidity input, for controlling heating and cooling so as to provide a controlled temperature modified by the humidity present thereby to provide a desirable comfort level to humans within the controlled environment. The thermostat is of the type which controls heating and cooling equipment through the use of electronic logic or a microcomputer. The thermostat operates the controls of the heating and cooling equipment and, where necessary, humidifying or dehumidifying equipment.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a thermometer having an output signal which is processed in a computer, the said output being modified by a signal from a humidity sensor. 
     More recently temperature controlling thermostats have become fairly sophisticated with the incorporation of micro-computers. The micro-computers have enabled daily programming of say, four different selected temperatures, overriding of such temperature selections for week-end operation and of resuming of programmed operation after several weeks of operation at a single selected temperature, as for example, during a vacation period. A thermostat having the foregoing features is manufactured by Valera Electronics Inc.,® of Ottawa, Ontario, Canada and sold under the trade mark &#34;ENERSTAT&#34;.™ The &#34;ENERSTAT&#34; will now be well known to those skilled in the art. Another feature of the ENERSTAT™ is that it computes burn time. This eliminates droop which results from the use of more conventional anticipation methods. 
     It has been recognized that ambient temperature per se is not the sole criterion in the attainment of comfort. The humidity of the air has a corresponding effect on comfort. It has been known for many years that humans feel comfortable in light clothing, over a narrow range of temperatures, but the range of temperatures is significantly modified by humidity. When humidity is low there is excessive evaporation from the skin surface, and as a result the body is cooled and the apparent ambient temperature is lower. 
     An American Society of Heating and Air Conditioning Engineers (ASHAE) comfort chart indicates the temperature and humidity zones in which most persons feel relatively comfortable. The foregoing discussion of desirable comfort conditions will be known to those skilled in the art and forms no part of the present invention. 
     SUMMARY OF THE INVENTION 
     Reverting to the electronic thermostat, the present invention enables a fairly simple addition to a programmable type of thermostat. This enables a manufacturer to sell either a straight thermostat or the present humidity modified thermostats both utilizing the same micro-computer. However, the invention has application where a humidistat alone is required. 
     It is a feature of one object of the invention to provide a heat/cool programmable thermostat wherein the temperature control point is modified by a humidity input. 
     It is a feature of another aspect of the invention to provide a heat/cool thermostat which may utilize the same micro-computer as in a programmable thermostat. 
     It is a feature of another aspect of the invention to provide a micro-computer type humidity indicator or a programmable humidistat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a chart of wet-bulb v. dry-bulb temperatures indicating the respective relative humidities corresponding thereof, and the resultant effective temperature. 
     FIG. 2 is a circuit diagram which includes a capacitive humidity sensing element and a logarithmic resistive temperature sensor. 
     FIG. 3 is a diagram which indicates the change in pulse width, due to changes in humidity in response to a linear capacitive humidity sensor. 
     FIG. 4 is a diagram which indicates the changes in pulse width, due to changes in humidity in response to a logarithmic resistive humidity sensor. 
     FIG. 5 is a circuit diagram, similar to FIG. 2 but including a logarithmic resistive humidity sensing element. 
     FIG. 6 is a diagram which indicates changes in pulse width proportional to changes in temperature in response to a logarithmic resistive temperature sensor. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIG. 1, the chart indicates &#34;comfort&#34; conditions, for various wet and dry bulk readings, with an air movement of about 15-25 feet per minute. 
     An arbitrary index, known as the effective temperature, is the degree to which a human body feels the warmth or cold in response to the air temperature, moisture content and air motion. The diagonal temperature lines represent instant effective temperature. It will be observed that several combinations of wet and dry bulb temperatures with different relative humidities produce the same effective temperature. The curves at the top and bottom of the chart indicate the percentage of persons feeling comfortable for various effective temperatures. For example, about 98% of persons feel comfortable at an effective temperative of 71° F., in summer, and 97.7% at an effective temperature at 68° F. in winter. Other aspects of the comfort requirements will be obvious to those skilled in the art. 
     As previously mentioned, a programmable thermostat of the type sold under the trade mark &#34;ENERSTAT&#34;, requires an input which is pulse-width modulated. The computer per se forms no part of the present invention. 
     Referring now to FIG. 2, a temperature comparator 1 is provided with a low frequency square shaped input through resister R 8  to the negative input terminal thereof. The low frequency input, of say 2 Hz, is selected as it provides a longer pulse width so that computer has time to measure the resultant pulse width more accurately. The said resultant pulse width modulated output is provided at output terminal B which forms the input to the micro-computer. This output from terminal B in effect modulates a steady supply from V cc  through resister R 9 . The 2 Hz pulses applied to R 8  in series with C 4  provide a reference wave form at their junction to the negative terminal of comparator 1. 
     A temperature sensing resister RT. is connected to receive Vcc and Vcc is potentially divided by resistor RT, resistor R10 and patentiometer R11 to provide a signal to the positive terminal of comparator 1 and constitutes a temperature variable input, V T  to the comparator 1. As previously mentioned the output from terminal B provides the input to a suitably programmed computer thermostat. A feature of this circuit is that it maintains the pulse width which is proportional to temperature, independent of variations of V cc . 
     As previously discussed, the present invention modifies the temperature measurement of a suitably programmed computer thermostat so as to optimize comfort by applying an adjustment which is a function of the humidity. 
     With electronic thermostats there is a wide range of possible temperature detection means available. The most common are based on a change in resistance of a sensor with temperature; many other sensing elements are available some of which may be applicable to the concept outlined in this invention. 
     To apply temperature information to the computer, it is necessary to provide the information in a form which the computer will accept. This could be based, for example, on a thermocouple generating a voltage which is converted to a digital form through an Analog to Digital converter, thereby informing the computer of the temperature by means of a digital code, or one might communicate temperature to a computer in the form of frequency, asking the computer to determine the frequency and calculate the related temperature. 
     In the present invention temperature information is supplied to the computer in the form of a pulse width. The pulse is generated by means of a waveform which operates on the biased comparator (on and off) in a temperature dependent manner; the width of the resultant pulse at the output B of the comparator being temperature related and passed to the computer. The approach has the advantage of simplicity and, in addition, the waveform applied to the comparator 1 is adjusted to compensate for non-linearity of the detector and is independent of variations in V cc . 
     Referring again to FIG. 2, there is shown a DC supply Vcc through resistors R1 and R2 to provide a reference voltage, V ref , to the negative input to a comparator 2. 
     A square wave supply is applied via resistor R3 to the positive terminal of comparator 2. The shape of a square wave signal is modified by the network R3 and C RH  and applied to the biased comparator 2. As the value of C RH  changes with humidity the pulse appearing at output `A` will vary in width (see FIG. 3). If output `A` is to be used as a separate humidity output the value of R2 must be adjusted for calibration purposes. 
     FIG. 3 indicates the change in pulse width at the output of comparator 2 as a function of the change in relative humidity as determined by C RH . 
     It can be shown that these changes are in accordance with the following equation: ##EQU1## 
     It is, of course, desirable that the value of C RH  be substantially a linear function of humidity. 
     Referring again to FIG. 2, the 2 Hz square wave applied to comparator 1 through R8 produces a pulse width proportional to temperature at the output of comparator 1 as shown in FIG. 6. This output pulse is modified by the output pulse from comparator 2 by averaging the latter with resistor R4 and capacitor C2 thus correcting V T  in a manner proportional to the relative humidity. 
     FIG. 5 is a circuit similar to FIG. 2 but wherein the humidity sensor is resistor R RH . Those components functioning in a similar manner as in FIG. 2 have identical numerals. 
     The negative input terminal to the comparator 2 is provided with a reference waveform, V ref , generated by a 2 kHz signal through resistor R21 to which is connected a capacitor C21. The same 2 kHz signal is connected to one end of a humidity sensing resistor R RH  in parallel with R22 and through parallel diodes D21 and D22 to the positive terminal of the comparator 2. The diodes D21 together with capacitor C22 and D22 serve to convert the logarithmic signals developed in R RH  to a linear signal V RH . The combination of V ref  and V RH  produces a pulse width at output terminal A of comparator 2 which is proportional to RN (see FIG. 4). 
     It is to be observed from FIGS. 2 and 5 that the temp.T being sensed varies with RT as follows: 
     
         Tα1nR.sub.T 
    
     α pulse width at B 
     also pulse width at B X 1n (R 10  and R 11 ) 
     It is to be observed from FIG. 2 that RH being sensed varies with C RH  as follows: 
     
         RHαC.sub.RH 
    
     αpulse width at A 
     also pulse width at A modifies R 10  and R 11  in a logarithmic manner. 
     It is to be observed from FIG. 5 that RH being sensed varies with R RH  as follows: 
     
         RHαlog R.sub.RH 
    
     αa pulse width at A 
     also the pulse width at A modifies R 10  and R 11  in a logarithmic manner. 
     Hence the output at B is modified linearly with changes in temperature and humidity. 
     R 8  is selected to provide the correct change in pulse width with change in temperature. 
     R11 is adjusted to provide the resultant humidity/temperature pulse width to a selected calibration point. 
     For practical applications R 4  is selected to cause the measured temperature to change approximately 1° F. for 10% change in RH. 
     Other embodiments falling within the terms of the appended claims will occur to those skilled in the art. 
     
         __________________________________________________________________________APPENDIXNOMINAL CIRCUIT VALUESRESISTORS (IN OHMS)  CAPACITORS (IN FARADS)FIG. 2   FIG. 5      FIG. 2     FIG. 5__________________________________________________________________________R1 330K  R21 270K    C1  0.01 uF                           C21 1nR2 15K   R22 1 M     C2  2.2 u  C22 22 u    R4  4.7K    C4  0.68 u C2  2.2 u                           C4  0.6 uR3 470K  R8  237K    C.sup.RH                    110-144 p                           C4  0.68 uR4 1.8K  R9  4.7K        0%-90% RH    R10 5.6K    R11 2.2KR8 237K  R.sub.RH        15K-10 MR9 4.7K      90%-20% RHR10   5.6K              DIODES D21-D22 1N4148R11   2.2KR.sub.T   10K 25° C.__________________________________________________________________________