GB2033621A - Air conditioning unit with heater biased control - Google Patents

Abstract

Apparatus and a method of controlling an air conditioning unit with a dual bulb thermostat (30) combination with an anticipator heater (38). A first bulb (34) of the thermostat is mounted to sense the temperature of the return air to the air conditioner. The second bulb (36) of the thermostat is mounted in heat exchange relationship with the anticipator heater (38). The anticipator heater (38) is energized when the air conditioning unit is not supplying conditioned air to the enclosure to bias the control. The compressor and evaporator fan of the air conditioner are simultaneously operated in response to the temperature sensed by the dual bulb thermostat (30). <IMAGE>

Description

SPECIFICATION Air conditioning unit with heater biased control The present invention relates to apparatus and a method for controlling compressor motor and evaporator fan motor operation of an air conditioning unit adapted to supply cooling to an enclosure. More particularly the present invention relates to control apparatus and the method within a room air condi tionerfor maintaining a given level on the temperature humidity index with a reduced input of energy.

A dual bulb, heater biased, temperature sensing element is used to cycle the evaporator fan motor simultaneously with the compressor motor to achieve an energy savings.

Many room air conditioning units when operating in the cooling mode of operation are designed to have the evaporator fan motor operate continuously and the compressor of a vapor compression refrigeration system to operate when a cooling need is sensed. Often a temperature sensing bulb connected to a thermostat is mounted in the incoming return air stream such that the temperature of the room air is ascertained. Compressor operation is then cycled on or off depending on the temperature of the incoming air. The evaporator fan runs continuously to provide a constant flow of room air over the thermostat so that the thermostat may sense a change of room air temperature without undue delay.

It has been found that atmosphere in an enclosure is comfortable as a human environment if the temperature humidity index level is less than or equal to 75. The temperature humidity index is calculated by multiplying the sum of the dry bulb and wet bulb temperatures (Farenheit) of the air being sensed by 0.4 and then adding 15. It has been found through experimentation and general usage that whenever this calculation results in a number less than or equal to 75 the average person is in a comfortable state. Should either the dry or wet bulb temperatures increase such that the temperature humidity index exceeds 75 then discomfort increases and air conditioning becomes desirable.

Often in a room air conditioner a temperature sensing element is mounted in the return air stream to sense the dry bulb temperature of the return air.

Consequently, the unit cycles on and off solely on dry bulb temperature. Since wet bulb temperature is ignored one of the two elements comprising the desired temperature humidity index level is not measured. The present invention uses an anticipator heater in combination with a second bulb of the same temperature sensing element to bias the bulb towards operating the unit at a lower temperature.

This manner of operation at a lower temperature acts to decrease the relative humidity and thus the wet bulb temperature as well as the dry bulb temperature and to consequently lower the temperature humidity index level. Additionally, with the use of the heater element it is possible to cycle the evaporator fan with the compressor motor such that the energy may be conserved by not operating the evaporator fan continuously. The anticipator serves to initiate an on cycle without the necessity of the evaporatorfan constantly circulating air in a heat exchange relation with the thermostat.

The preferred embodiment of the invention includes a thermostat having a dual bulb temperature sensing element. The first bulb is mounted in the return airstream from the room to be conditioned such that the dry bulb temperature of the entering air may be sensed. The second bulb is mounted in heat exchange relation with the anticipator heater such that the temperature sensing element may be biased by providing heat to the element through the anticipator. The compressor motor and evaporator fan are energized when the thermostat is closed indicating a cooling need. The heating anticipator is energized during off cycles of the compressor motor and evaporator fan to bias the thermostat such that unit operation is initiated at a relatively low temperature.By maintaining a lower room temperature and by cycling the evaporator fan only with the compressor it is possible to achieve energy savings in overall operation of the unit while maintaining a satisfactory temperature humidity index level.

Figure 1 is a top view of a room air conditioner.

Figure 2 is a partially cutaway front view of a room air conditioner showing the dual bulb temperature sensing element.

Figure 3 is a partial wiring schematic of an electrical control system with the anticipator heater.

Figure 4 is a graph of temperature humidity index versus room load percentage (percent of unit capacity required to cool the room) through various modes of operation.

Figure 5 is a graph of kilowatts consumed in a twenty-four hour period versus room load percentage for various modes of operation.

Figure 6 is a graph of temperature in degrees Farenheit of the room air at the inlet area of the room air conditioner, the temperature humidity index level of said air, and the watts consumed during unit operation all compared on a running time basis.

The embodiment described hereinafter is adapted for use with a room air conditioning unit. It is to be understood that the dual bulb thermostat and the heater anticipator together with the cycling of an evaporator fan motor with the compressor motor will find equal applicability in other types of air conditioning units. The present invention is not limited in scope to room air conditioners but might find utilization with other types of air conditioning and refrigeration systems and humidification or dehumidification systems including heat pumps.

Referring now to the drawings it can be seen in Figure 1, which is a top view of a typical room air conditioner, that room air conditioner 10 is divided by partition 5 into an evaporator section 8, and a condenser section 6. Within condenser section 6 are mounted compressor 18, condenser 14, fan motor 20 and connected thereto condenser fan 16. Within evaporator section 8 are shown evaporator fan 22 and evaporator 24. Base pan 12 (Figure 2 also) is shown as the bottom of the unit to which the various components are mounted.

In a typical room air conditioning unit refrigerant is compressed such that its temperature and pressure are increased in the compressor. This gaseous high temperature refrigerant is circulated through the condenser in heat exchange relation with the outdoor ambient air being forced therethru by the condenser fan such that heat is transferred from the refrigerant to the outdoor ambient air and the refrigerant changes state to a liquid. The high pressure liquid refrigerant is discharged from the condenser through an expansion device (not shown) such as a capillary tube or an thermal expansion valve wherein the pressure of the liquid refrigerant is decreased.The refrigerant is then conducted to evaporator 24 where under decreased pressure it changes state from a liquid to gas absorbing heat from the air being circulated in heat exchange relationship with the evaporator by the evaporator fan. As the refrigerant absorbs heat it changes from a liquid to a gas and is then drawn into the compressor where it is recompressed to start the cycle anew.

When the liquid refrigerant in the evaporator changes state to a gas heat is absorbed from the air in communication therewith such that the temperature of that air is lowered. If the temperature of the air is lowered below the dew point of the air, water condenses from the air onto the evaporator surface such that the overall amount of water contained by the air is reduced. Depending upon the relative humidity of the returned air entering the air conditioner and the discharge temperature of the air conditioner this removal of water may result in dehumidification of the room air by the air conditioner as well as a reduction in dry bulb temperature.

Referring now to Figure 2 there can be seen a partially cutaway front view of a room air conditioning unit. Evaporator 24 is shown mounted to base pan 12 with temperature sensing element 32 in front thereof. Evaporator fan 22 is mounted behind evaporator 24 and has the appropriate shroud arrangement (not shown) such that air from the room is drawn over the temperature sensing element through the evaporator coil and then discharged at the top of the unit above the evaporator coil indicated as discharge area 26. Selector switch 39 mounted in control area 40 is utilized to select the appropriate mode of operation for the unit. Thermostat 30 is shown with the control knob beneath selector switch 39. Connected in series with thermostat 30 are tube 37, second bulb 36, tube 35 and first bulb 34.This thermostat is a conventional thermostat having a bellows type arrangement in combination with liquid filled tubes and bulbs such that a change in temperature of the fluid results in an expansion or contraction of the fluid within the bulb and acts on the bellows to activate the appropriate response by the thermostat. The first bulb 34 is shown mounted directly in the incoming or return air path such that it senses the temperature of the room air to be conditioned. Second bulb 36 is shown mounted remotely from the return air in the control portion of the room air conditioning unit adJacent to anticipator 38 which is used to supply heat to the second bulb portion of the temperature sensing element.

Figure 3 is a partial wiring schematic of a circuit for use with a present invention. Power is supplied to the circuit from lines L1 and L2. Line L1 affixed to wire 40 is connected to thermostat 30, heater anticipator 38 and selector switch contacts SS-3.

Thermostat 30 is connected by wire 44 to selector switch contacts SS-1, SS-2 and SS-4. Selector switch contacts SS-4 are connected by wire 46 to heater anticipator 38. The compressor motor 50 is connected by wire 49 to selector switch contacts SS-1 and to wire 42 connected to L2. Wire 48 connects selector switch contacts SS-2 to selector switch contacts SS-3 and to fan motor 52 which is connected to line L2 by wire 42.

If the unit is in the cooling mode of operation temperature sensing element 32 is utilized to ascertain the dry bulb temperature level of the air to be conditioned. if this temperature level is within a predetermined range thermostat 30 is energized and the compressor motor and evaporator fan are cycled on. The compressor acts to circulate the refrigerant through the vapor compression refrigeration system as described above and the evaporator fan acts to circulate room air through the evaporator. During this operation the air to be conditioned is brought in heat exchange relationship with the evaporator and heat is absorbed therefrom. When the temperature of the room air drops below the predetermined range, and the thermostat senses that the air to be conditioned no longer needs to be cooled then unit operation is discontinued.Heating anticipator 38 is energized during those periods the unit is not operating. Atwo watt heater which has a curved portion designed to mate with the cylinder of second bulb 36 comprises the anticipator. Notwithstanding that the dry bulb temperature of the air entering the unit is below the temperature at which the thermostat would commence operation, by the use of the heater anticipator, additional heat is supplied to the fluid within the temperature sensing element such that the thermostat senses what appears to be a higher temperature level for the air to be conditioned. Consequently, unit operation will be commenced prior to when it was started if there were no anticipator heater.The heat output of the anticipator heater is of itself insufficient to commence unit operation and only serves to bias the thermostat so that unit operation commences at a lower return air temperature. By using this anticipator it is not necessary to run the evaporator fan motor continuously to accurately sense the temperature of the air in the room in view of determining when unit operation is desirable.

Selector switch contacts SS-1, SS-2, SS-3 and SS-4 are all controlled by selector switch 39. When the selector switch is in the off position contacts SS-1 are open and compressor motor 50 may not be energized. When the selector switch is in the fan only mode of operation contacts SS-3 are closed such that fan motor 52 is energized thru wire 40, contacts SS-3, and wire 48. Fan motor 52 is connected to L2 by wire 42 to complete the circuit.

If air conditioning operation without the use of the heater anticipator is desired then when the selector switch is set in the appropriate position selector switch contacts SS-1 and SS-3 are closed. Fan motor 52 is constantly energized when the SS-3 contacts are closed. Compressor motor 50 is energized when contacts SS-1 are closed and when thermostat 30 is closed. Compressor motor 50 is energized thru wire 40, thermostat 30, wire 44, contacts SS-1 and wire 49. Consequently the combination of selector switch contacts SS-1 and SS-3 being closed provides for continuous fan motor operation and for the compressor motor to be cycled when the thermostat is closed.

If air conditioning operation with the use of the anticipator heater is desired then when the selector switch is set in the appropriate position selector switch contacts SS-1, SS-2 and SS-4 are closed. In this mode of operation when thermostat 30 is open then current flows thru wire 40, anticipator heater 38, wire 46, contacts SS-4, wire 44 and then either thru contacts SS-1, wire 40, and compressor motor 50 to wire 42 or contacts SS-2, wire 48 and fan motor 52 to wire 42. The heater anticipator has a large resistance to generate heat to be transferred to the temperature sensing element. As a result of this large resistance the potential across either the fan motor or the compressor motor is insufficient to operate either the fan motor or the compressor motor although current is flowing therethrough.When thermostat 30 is closed compressor motor 50 and fan motor 52 are both energized from wire 40 thru thermostat 30, wire 44 and the appropriate selector switch contacts.

Because of the high resistance of the heater anticipator current flow will primarily be thru the thermostat in parallel therewith such that the anticipator heater will omit negligible heat. Consequently in this mode of operation with selector switch contacts SS-1, SS-2 and SS-4 being closed, when the thermostat is open the anticipator heater is energized and the compressor and fan motors do not operate. When the thermostat is closed the compressor motor and fan motor are operated and the anticipator heater does not heat the temperature sensing element.

Referring to Figure 4 there can be seen various graphs comparing temperature humidity index level to room load percentages. The equivalent room air conditioners were operated on a preselected thermostat setting to achieve a temperature humidity index level of 75 for a given set of ambient conditions. There can be seen on the graph a line marked constant fan, no heaters which indicates the temperature humidity index level achieved by a unit when operated with the evaporator fan running continuously. Additionally, the temperature humidity index level for the same unit is recorded with the evaporator fan cycling with the compressor and without supplying additional bias heating with an anticipator. It can be seen on a graph that this mode of operation resulted in a temperature humidity index level of 78 and is indicated by the line marked cycling fan, no heater.

The same unit was operated cycling the fan motor with the compressor motor and with the addition of a two watt anticipator heater in heat exchange relationship with the second bulb of the thermostat.

Using this combination a temperature humidity index level of approximately 73.2 was achieved. This line on the graph is indicated by cycling fan, two watt heater, number 1 setting.

The combination of cycling the evaporator fan motor with the compressor motor and the use of the anticipator heater achieved a temperature humidity index level of less than the design level. A fourth line on Figure 4 indicates the comparision between the temperature humidity index level and a room load percentage when the thermostat of the unit was set at a higher level referred to as the number 2 setting.

When the unit was operated at the second thermostat setting level the line labeled cycling fan, two watt heater, number 2 setting being at approximately the temperature humidity level of 74.8 was achieved. The graph indicates that a higher sensible heat setting (the higher dry bulb temperature level sensed by the thermostat at the number 2 setting) could be utilized to achieve an appropriate temperature humidity index level and atthe same time conserve energy with the combination of the anticipator heater and cycling the evaporator fan with the compressor.

Referring to Figure 5 there can be seen a plot of the same four modes of operation as in Figure 4 showing the energy consumed within a twenty-four hour period, i.e. kilowatts per twenty-four hours as compared to percentage room load factor. Again it can be seen that constant fan, no heater operation uses the most energy; cycling the fan with the two watt heater in the number 1 setting uses the second most energy; and cycling the fan with a two watt heater in the number 2 setting used even less energy. Operating the unit by cycling the fan with no heater uses the least energy, however, as can be seen in Figure 4 an unsatisfactory temperature humidity index level of 78 was achieved.Consequently, from these various modes of operation it is apparent that the mode of operation maintaining the temperature humidity index level at the appropriate setting and using the least energy is that of setting the thermostat at the second level or higher sensible temperature and cycling the fan motor with the compressor motor and utilizing a two watt anticipator heater with a combination dual bulb thermostat.

In Figure 6 there can be seen some specific comparisons of unit operation at the same thermostat setting by comparing constant fan operation without a heater to cycling the fan motor with the compressor motor and using a two watt anticipator heater both against running time. In portion A of the graph the watts consumed versus time of operation are shown for the two units. It can be seen by providing the unit without constant fan operation, that during those times when the compressor is not operated the fan is also not operated and consequently almost no wattage is used by the unit during that period. It can also be seen from portion A of Figure 6 that the length of time the unit operates for each cycle is slightly longer for the unit with a two watt heater. In the B portion ofthe diagram it can be seen that a much lower temperature humidity index level is achieved using the cycling fan and two watt heater than with the constant fan operation and no heater. The C portion of the diagram shows that the temperature of the return air entering the unit is also considerably lower using the cycling fan and the two watt heater as opposed to the constant fan and no heater.

Also from the graph it can be calculated that the unit with the constant fan and no heater actually used 18.93 kilowatts in a twenty-four hour period whereas the same unit with the two watt aniticpator heater and cycling fan used 17.29 kilowatts in a twenty-four hour period. All measurements shown in Figure 6 were taken with a unit operating at a 66% sensible cooling room load.

It is postulated that the combination of using an anticipator with a dual bulb thermostat and cycling the evaporator with the compressor motor results in energy savings while maintaining the same temperature humidity index level for several reasons. The anticipator heater allows evaporator fan motor operation to be discontinued during off periods saving fan motor energy. Additionally, the heater serves to commence unit operation at lower return air temperatures. Operating at lower temperatures may provide for some additional dehumidification which will reduce the wet bulb factor of the equation for determining the temperature humidity index level.

As compared to the unit with constant evaporator fan operation the individual run cycles using the present invention are slightly longer decreasing the number of cycles and cycling losses.

Claims (11)

1. A control for an air conditioning unit having a compressor, condenser and evaporator forming a vapor compression refrigeration circuit, and an evaporatorfan for circulating airto be conditioned in heat exchange relationship with the evaporator comprising a temperature actuated switch; a dual bulb fluid filled temperature sensing element con nected to the temperature actuated switch such that a predetermined level of heat energy within the element will actuate the switch, a first bulb of the element being mounted in heat exchange relation with the air to be conditioned and a second bulb being mounted remotely from the air of the enclo sure an anticipator heater mounted in heat exchange relation with the second bulb of the temperature sensing element; and an electrical circuit having means to energize the compressor and the evapor ator fan when the heat energy level of the fluid in the temperature sensing element as detected by the temperature actuated switch is above a preselected level and means to energize the anticipator heater when the heat energy level of the anticipator heater is below a predetermined level, the anticipator heater acting to supply heat energy to the dual bulb temperature sensing element when energized to bias the temperature actuated switch.

2. The apparatus as set forth in claim 1 wherein the first bulb of the temperature sensing element is located in the return stream of air to be conditioned entering the unit and the second bulb of the temperature sensing element is located remotely from said airstream in heat exchange relation with the anticipator heater.

3. The apparatus as set forth in claim 2 wherein the bulbs are cylindrical in configuration and where in the anticipator heater is an electric resistance heater having a curved mating surface adapted to receive the second bulb of the temperature sensing element.

4. The apparatus as set forth in claim 1 where the first bulb is joined to the second bulb with a tube and the second bulb is joined to the temperature actuated switch with a tube such that there is serial liquid communication between the temperature actuated switch and the first and second bulbs.

5. A control for a vapor compression air conditioning system having a compressor, a condenser, an evaporator motor and a fan motor for circulating the air to be conditioned in heat exchange relation with the evaporator, comprising switch means for energizing and de-energizing the compressor motor, and the evaporator fan motor together upon the temperature of the air to be conditioned being within a predetermined range; and an anticipator heater for supplying heat energy to the switch means remote from the air to be conditioned such that the switch means may detect an amount of heat energy equivalent to the heat energy present if the temperature of the air to be conditioned is within the predetermined range, notwithstanding the actual temperature of the air to be conditioned; and means for energizing the anticipator heater during those periods of time the compressor motor and evaporator fan motor are not energized through the switch means.

6. The apparatus as set forth in claim 5 wherein the anticipator means comprises a heating anticipator and the switch means comprises a temperature actuated switch connected to a liquid filled temperature sensing element having two liquid filled bulbs connected in series thereto, the anticipator being in heat exchange relation with one of the bulbs of the temperature sensing element.

7. A method of controlling operation of an air conditioning system having a compressor, a condenser and evaporator, forming a refrigeration circuit and an evaporator fan powered by an evaporator fan motor for circulating airto be conditioned in heat exchange communication with the evaporator which comprises the steps of sensing the temperature of the air to be conditioned with a temperature sensing element having dual bulbs; energizing the evaporator fan motor and the compressor motor when the temperature detected by the step of sensing is within a predetermined range; and supplying heat to a bulb of the temperature sensing element with a heating anticipator during those periods when the evaporator fan motor and the compressor motor are not energized such that the step of sensing may detect a heat energy level within the predetermined range although the air to be conditioned is not within that range.

8. The method as set forth in claim 7 wherein the step of sensing includes locating a first bulb of the temperature sensing element in heat exchange relation with the stream of return air from the enclosure to be conditioned and locating the second bulb of the temperature sensing element in heat exchange relation with a heating anticipator mounted remotely from the air to be conditioned.

9. The method as set forth in claim 7 wherein the step of energizing includes switching based upon the overall heat energy level sensed by temperature sensing element to operate the compressor motor, evaporator fan motor and the anticipator, the compressor motor and evaporator fan motor being energized when the anticipator is de-energized, and the anticipator being energized when the compressor motor and evaporator fan motor are de-energized

10. A control for an air conditioning unit substantially as described herein with reference to the drawings.

11. A method of operating an air conditioning unit substantially as described herein with reference to the drawings.