Patent Application
20080173034
This invention relates to the field of heat pumps. More particularly, this invention relates to the field of air source heat pumps having a primary compressor and a booster compressor connected in series, the heat pumps being suitable for heating operation at temperatures down to zero degrees Fahrenheit and lower.
In accordance with the present invention, a primary compressor and a booster compressor are connected to operate in series in a heat pump system. The primary compressor is a variable capacity or partially unloadable compressor, and the booster is preferably a single speed compressor. The system also incorporates a temperature sensor for sensing the temperature of outdoor ambient air, a two stage indoor thermostat and a microprocessor. For heating operation, the system is capable of operation in any one of three modes, M1, M2, M3, depending on outdoor air temperature and the heating load on the system. M1 is partial capacity operation of the primary compressor; M2 is full capacity operation of the primary compressor; and M3 is full capacity operation of each of the primary compressor, the booster compressor, and an economizer. For outdoor temperatures in a first range between about 60° F. and up (i.e., up to where heating operation is no longer allowed), only operation in M1 is allowed. For outdoor air temperatures in a second range of from about 38° F. to about 59° F., operation in M1 is allowed, and, if M1 operation does not provide enough heat, operation in M2 is also allowed. For outdoor air temperatures in a third range of from about 31° F. to about 37° F., operation in only M2 is allowed. For outdoor air temperatures in a fourth range of from about 19° F. to about 37° F., operation in M2 is allowed, and, if M2 operation does not provide enough heat, operation in M3 is allowed. For outdoor air temperatures in a fifth range of from about 18° F. and below, operation in M3 is allowed, and, if M3 operation does not provide enough heat, the system may also include an M4 mode in which electrical resistance heat is added to the system.
The temperature sensor delivers signals to the microprocessor, and the microprocessor enables or allows operation in M1, M2 and M3 (and M4), i.e., conditions are created wherein operation in those modes will occur if the thermostat calls for heat. When the thermostat calls for heat, the microprocessor will generate signals to cause operation in M1, M2, M3 or M4 depending on the outdoor air temperature.
For cooling operation, only the primary compressor operates in either Mode 1 or 2 depending only on which indoor thermostat stage is calling for cooling operation.
The heat pump system also incorporates a demand defrost cycle in modes M2, M3 and M4 (if M4 is present). Outdoor air temperature is sensed by a temperature sensor external to the outdoor (evaporator) coil, and a signal representing that temperature is delivered to a system microprocessor. Based on the sensed outdoor air temperature, the microprocessor calculates a defrost trigger temperature T1 for each of modes M2 and M3 (M4 is identical to M3 for demand defrost purposes). A temperature T2 is also sensed that is commensurate with the temperature of the refrigerant boiling in the outdoor coil.
T2 is sensed by a sensor mounted on one of the tubes feeding an evaporator circuit directly downstream of the normal pressure reduction/flashing process. Whenever T2 then drops to a value equal to or less than the calculated T1 continuously for 10 minutes, a defrost cycle is triggered to defrost the outdoor coil. The defrost cycle continues until T2 rises to a predetermined defrost terminating value.
Referring to the drawings, where like elements are numbered alike in some of the figures:
Referring to
Primary compressor 22 is preferably a Bristol twin single (TS) compressor having two reciprocating pistons and cylinders. However, it can also be any multi-capacity or unloadable positive displacement or multi-speed compressor. Booster compressor 22 is any type of a positive displacement single speed compressor. The flow capacity of the primary compressor is preferably split 50%/100%, i.e., where 100% is the flow capacity when both cylinders are operating, and 50% is the percentage of total flow capacity when only one piston is reciprocating. In addition, the flow capacity of booster compressor is larger than the flow capacity of primary compressor, preferably by a ratio of from about 1.3/1 to about 1.7/1, depending on the climate where the system is to be used.
In initial operation of the system in the heating mode, a signal representing the ambient air temperature sensed by temperature sensor 48 is delivered to microprocessor 36, and the microprocessor will enable or allow partial capacity operation of primary compressor 24 upon receipt of a signal from thermostat 38 calling for heat if the outdoor ambient temperature is in a first range between about 60° F. and above. A signal calling for heat is delivered to microprocessor 36 from stage 1 of thermostat 38 when the temperature of the space to be heated falls below the set point of the thermostat by, e.g., 0.6° F.-1.2° F. If the temperature sensed at sensor 48 is in the first range of at or between about 60° F. and above, the microprocessor causes operation of one cylinder of primary compressor 24. That is, partial capacity operation of primary compressor 24 is effected. When that happens, compressed hot refrigerant vapor is circulated in conduit system 34 by delivery from primary compressor 24 through 4 way valve 32 and then to indoor condenser coil 26 where heat is extracted by air from an air handler passing over indoor coil 26 to be delivered to the space to be heated. On leaving the indoor condenser coil 26, the refrigerant is in the form of a warm liquid, and it flows through check valve 44, which is open, bypassing expansion valve 40. The warm refrigerant liquid then flows directly through the liquid side of economizer 30 and is delivered toward thermal expansion valve 42. Since direction of flow and pressure of the refrigerant close check valve 46, the warm liquid refrigerant is delivered to and flows through thermal expansion valve 42 where part of the refrigerant is flashed or boiled to vapor. The two phase refrigerant mixture then flows to outdoor coil 28 where the remaining liquid refrigerant is vaporized due to extraction of heat from the outside air. The resulting cool vapor is then delivered through 4 way valve 32 and through check valve 52 and conduit section 54 to the inlet to primary compressor 24. The refrigerant then goes through repeat cycles of compression; subsequent vapor cooling and condensation into liquid; then liquid flashing or expansion; subsequent boiling or evaporation while it is concurrently transferring heat energy into indoor air while cooling and condensing and extracting heat energy from the outside air while boiling or evaporating. The operating cycle described above with partial capacity operation of the primary compressor is termed Mode 1, or M1. When the set point of thermostat 38 is reached, a signal is sent from the thermostat to the microprocessor to terminate operation of primary compressor 24 in M1. If the temperature of the space to be heated again falls below the set point of the thermostat by 0.6° F.-1.2° F., the thermostat again delivers a heat calling signal to microprocessor 36, and if the temperature sensed by sensor 48 is still in the first range of between about 60° F. and up, the system is again cycled through operation in M1. As long as the outdoor ambient temperature sensed at sensor 48 is in the first range between about 60° F. and up, the microprocessor will only allow operation in M1, i.e., with partial capacity operation of primary compressor 24. Also, if the outside air temperature, as sensed by sensor 48 is not at or below a selected upper first range temperature of, e.g., about 75° F., the microprocessor will not allow operation of primary compressor 24, and heating operation will not occur. This prevents inefficient use of the heating system.
The system continues to operate in M1 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. When the setting of the thermostat is satisfied, a signal is delivered from the thermostat to the microprocessor, and operation of the compressor system is terminated. However, if sufficient heat has not been delivered to the internal space to be heated within a pre-programmed period of time (typically from 5 to 10 minutes) or if the rate of increase in temperature is not fast enough, the thermostat calls for stage 2 operation by sending a second signal to microprocessor 36 to call for more heating capacity from the system. If the outdoor ambient temperature sensed at sensor 48 is in a second and lower range of temperature between about 38° F. and 59° F., the microprocessor then delivers an enabling signal to primary compressor 24 to operate both pistons of the primary compressor 24 to effect operation of the primary compressor at full capacity. This full capacity operation of the primary compressor is termed Mode 2 or M2. In M2, the flow of refrigerant through the system is as in M1, but at a higher flow rate, whereby a greater volume of hot vapor is delivered to indoor condenser coil 26 to heat the indoor space to be heated. Note, again, that if the outdoor temperature sensed at sensor 48 is not at or below the upper limit of about 59° F. of the second operating range of outdoor temperatures, the microprocessor will not enable M2 operation of the system. Again, this prevents inefficient operation of the heating system. The system continues to operate in M2 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. When the setting of the thermostat has been satisfied, a signal is delivered from the thermostat to the microprocessor to terminate operation of the compressor system. If the temperature of the space to be heated again falls below the set point of the thermostat by 0.6° F.-1.2° F., the thermostat again delivers a heat calling signal to microprocessor 36, and if the temperature sensed by sensor 48 is still in the second range of between about 38° F. and 59° F., the system is again cycled through operation first in M1 and then in M2. As long as the outdoor ambient temperature sensed at sensor 48 is in the second range between about 38° F. and 59° F., the microprocessor will only allow operation in M1 and M2, i.e., first with partial capacity operation and then fall capacity of primary compressor 24.
At a third and lower range of outdoor ambient air temperatures, from about 31° F. to 37° F. the temperature signal delivered by sensor 48 to microprocessor causes the microprocessor to skip M1, and go directly to enabling or allowing M2 operation. Accordingly, upon receipt of a heat calling signal from stage 1 of thermostat 38 being delivered to microprocessor 36 (as the result of the temperature in the space to be heated falling below the set point of the thermostat), the microprocessor delivers a signal to primary compressor 24 to operate the primary compressor at full capacity. The system continues to operate in M2 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. If the setting of the thermostat is satisfied, a signal is delivered from the thermostat to the microprocessor, and operation of the compressor system is terminated. However, if sufficient heat has not been delivered to the internal space to be heated within a period of time (typically from 5 to 10 minutes), or if the rate of temperature increase is not fast enough, the thermostat calls for stage 2 operation by sending a second signal (calling for more heating capacity from the system) to microprocessor 36. However, in this third range of outdoor ambient air temperatures, from about 31° F. to 37° F., the microprocessor is programmed to still only allow M2 operation upon receiving the stage 2 signal from the thermostat. This prevents inefficient use of the heating system as higher capacity operation is not to be permitted by the microprocessor until it is really needed.
At a fourth and lower range of outdoor ambient air temperatures, from about 19° F. to about 30° F. the temperature signal delivered by sensor 48 to the microprocessor causes the microprocessor to again skip M1, and go directly to allowing M2 operation. Accordingly, upon receipt of a heat calling signal from stage 1 of thermostat 38 being delivered to microprocessor 36 (as the result of the temperature in the space to be heated falling below the set point of the thermostat by from about 0.6° F.-1.2° F.), the microprocessor delivers a signal to primary compressor 24 to operate the primary compressor at full capacity. The system continues to operate in M2 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. If the setting of the thermostat is satisfied, a signal is delivered from the thermostat to the microprocessor, and operation of the compressor system is terminated. However, if sufficient heat has not been delivered to the internal space to be heated within a period of time (typically from 5 to 10 minutes), or if the rate of temperature increase is not fast enough, the thermostat calls for stage 2 operation by sending a second signal (calling for more heating capacity from the system) to microprocessor 36. If the outdoor ambient temperature sensed at sensor 48 is still in the range of between about 19° F. and 30° F., the microprocessor then generates enabling signals to operate all of the booster compressor 22, the primary compressor 24 at full capacity, and the economizer at full capacity. This operation of the booster compressor, the primary compressor at full capacity and full capacity operation of the economizer is termed Mode 3 or M3.
Referring to
The warm liquid refrigerant discharged from indoor coil 26 is delivered to economizer 30. However, the economizer enabling signal from the microprocessor opens solenoid valve 31, whereby some of the liquid refrigerant is bled through bleed line 58 and expanded through an orifice in solenoid valve 31 thereby entering the boiling side of the economizer where it boiled (or evaporated) into saturated vapor. This boiling liquid in the boiling side of the economizer significantly subcools the warm refrigerant flowing through the liquid side of the economizer as it extracts the thermal energy originally present in the warm liquid. This results in significantly subcooled liquid refrigerant being delivered to expansion valve 42 of evaporator outdoor coil 28. This results in an increased refrigerant capacity (per unit of mass flow) which absorbs more heat energy from the ambient air passing over outdoor coil 28 thereby further increasing the heating capacity of the system.
The saturated refrigerant vapor from the boiling side of economizer 30 is delivered via conduit segment 60 to a location in conduit segment 56 between the discharge from primary compressor 22 and the inlet to primary compressor 24 where it joins and mixes with the vapor stream going form the discharge of the booster compressor to the inlet to the primary compressor.
In M3, the flow of refrigerant through the system is at a higher flow rate and pressure than in M1 or M2, whereby a greater volume of hot vapor is delivered to indoor condenser coil 26 to heat the indoor space to be heated. Note, again, that if the outdoor temperature sensed at sensor 48 is not at or below the upper limit of about 30° F. of the fourth operating range of outdoor temperatures, the microprocessor will not enable M3 operation of the system. Again, this prevents inefficient operation of the heating system.
The system continues to operate in M3 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. When the setting of the thermostat has been satisfied, a signal is delivered from the thermostat to the microprocessor to terminate operation of the compressor system. If the temperature of the space to be heated again falls below the set point of the thermostat by about 0.6° F.-1.2° F., the thermostat again delivers a heat calling signal to microprocessor 36, and if the temperature sensed by sensor 48 is in the fourth range of between about 19° F. and 30° F., the system is again cycled through operation first in M2 and then in M3. As long as the outdoor ambient temperature sensed at sensor 48 is in the fourth range between about 19° F. and 30° F., the microprocessor will only enable operation in M2 and M3, i.e., first with full capacity operation of primary compressor 24, and then adding in the operation of the booster compressor and the economizer.
For the sake of clarity, it should be noted that although the M3 enabling signal from the microprocessor calls for operation of both the booster compressor and the economizer, there is a slight delay in the operation of the economizer relative to operation of the booster compressor. The booster compressor operates at full capacity almost immediately upon receipt of the enabling signal from the microprocessor. However, there is a time delay in operation of the economizer because of the time needed to bleed the fluid through the orifice of solenoid valve 31 and deliver the saturated vapor from the boiling side of the economizer through conduit segment 60 to conduit segment 56.
When ambient air temperatures in a fifth range of 18° F. and below are sensed at sensor 48, and when thermostat 32 is calling for heat in stage 1, microprocessor 36 allows and effects operation of the heat pump system in M3, i.e., with full capacity operation of the primary compressor, and with operation of the booster compressor and with operation of the economizer. However, if sufficient heat has not been delivered to the internal space to be heated within a period of time (typically from 5 to 10 minutes) or if the rate of temperature rise is not fast enough, the thermostat calls for stage 2 operation by sending a second signal (calling for more heating capacity from the system) to microprocessor 36. The microprocessor then allows and effects operation of backup electrical resistance heater 62, which is positioned downstream of the air flow over indoor coil 26. This is designated as Mode 4 or M4 operation. Note, again, that if the outdoor temperature sensed at sensor 48 is not at or below about 18° F. of the fifth operating range of outdoor temperatures, the microprocessor will not allow M4 operation of the system. Again, this prevents inefficient operation of the heating system. The system continues to operate in M4 until sufficient heat has been delivered to the space being heated to satisfy the setting called for by thermostat 38. When the setting of the thermostat has been satisfied, a signal is delivered from the thermostat to the microprocessor to terminate operation of the compressor system. If the temperature of the space to be heated again falls below the set point of the thermostat by 0.6° F.-1.2° F., the thermostat again delivers a heat calling signal to microprocessor 36, and if the temperature sensed by sensor 48 is in the fifth range of between below 18° F., the system is again cycled through operation first in M3 and then in M4. As long as the outdoor ambient temperature sensed at sensor 48 is in the fifth range below about 18° F., the microprocessor will only enable operation in M3 and M4, i.e., first with full capacity operation of primary compressor 24 and booster compressor 22 and the economizer 30, and then adding in operation of electrical resistance heater 62 if the thermostat is not satisfied.
It will be understood that when the booster compressor and economizer are operating, the primary compressor is also operating at full capacity. That is, operation in M3 includes operation in M2. Also, when supplemental electrical resistance heat is operation, the primary compressor is operating at full capacity and both the booster compressor and the economizer are operating. That is, operation in M4 includes operation in M3.
Referring to
In an alternative embodiment of the heat pump system, an on-off booster operation may be utilized to reduce the net capacity being delivered to the system condenser when more heat capacity than M2 is needed, but when full M3 system capacity is not absolutely necessary. As an example, instead of allowing full Mode 3 operation as the outdoor temperature falls into the fourth range of temperatures (from about 19° F.-30° F.) and the thermostat is calling for heat, microprocessor 36 is programmed to first allow and effect booster compressor 22 to start and stop for pre-determined relatively short periods of time until the outdoor temperature eventually falls to a point where it is desirable to allow continuous M3 operation. This cycling mode of operation of booster 22 is designated as Mode 3-C (M3-C) and will be incorporated approximately half way down in outdoor temperature between where M2 operation and the full M3 operation are allowed as indicated previously (e.g., for a temperature range of from about 24° F. to about 30° F.). Full M3 operation would be enabled for the lower half of the M3 operating temperature range. The booster “on” and “off” intervals can be of equal time or unequal. Alternatively, the relative “on” and “off” times for the booster compressor can be made to vary in steps as outdoor air temperature falls through the entire outdoor door temperature range for M3 operation, with booster “on” time being lowest when outdoor air temperature is higher in the M3 enabling temperature range and booster “on” time being highest when outdoor ambient temperature is lower in the M3 enabling temperature range. This variable on-off time ratio inversely proportional to the outdoor temperature may further enhance operating efficiency.
Referring to
In another embodiment intended for use warmer winter climates such as in the southeastern or southwestern U.S., the heating demand on the system may be reduced. For use in such climates, economizer 30 can be eliminated from the system, and M3 or M3-C operation would then involve only full capacity operation of primary compressor 24 and operation of booster compressor 22
It is typical to incorporate a defrost cycle or operation in heat pump systems to prevent accumulation of ice on the outdoor evaporator coil. In the system of the present invention, temperatures are not low enough for icing of the evaporator coil to be a problem where only M1 operation is enabled. Accordingly, no provision is made for defrost operation whenever the system is enabled for operation only in M1.
However, whenever the system is enabled for operation in M2, (M3-C if that embodiment is incorporated), M3, or M4, provisions must be made for defrost cycling or operation. In the present invention, defrost cycling is accomplished on a demand basis, i.e., when defrosting is needed, as opposed to systems where defrosting operation is always initiated on a timed basis, whether needed or not.
In the present invention, microprocessor 36 uses an algorithm to calculate a defrost trigger temperature T1 based on the outdoor ambient temperature sensed by sensor 48. A second temperature sensor, sensor 50, is positioned on conduit 34 just upstream of the entrance to outdoor evaporator coil 28, whereby sensor 50 senses the temperature T2 of the boiling refrigerant entering the evaporator coil, and a signal commensurate with T2, i.e., the temperature of the boiling refrigerant entering the evaporator coil, is sent to microprocessor 36. When T2 is less than or equal to T1, i.e., T2≦T1, for a predetermined period of time, e.g., ten minutes, thus indicating a possible icing condition at outdoor coil 28, then defrost operation is triggered. In the present invention, separate algorithms are used to calculate the defrost trigger temperature (DTT) depending on whether the system is operating in M2 or M3.
When the system in operating in M2, a typical algorithm is as follows:
Mode 2 DTT (T1)=0.850×A° F.−10.50
When the system is operating in M3, a typical algorithm is:
Mode 3 DTT (T1)=0.7075A° F.−19.625
where, in both cases, A° F. is the outdoor ambient air temperature sensed by sensor 48 and delivered to microprocessor 36. These algorithms, which are linear functions of outdoor air temperature, are illustrated in
When microprocessor 38 determines that T2≦T1 for ten minutes, the microprocessor generates a signal to commence defrost operation. That defrost operation signal effectively puts the heat pump system in the cooling mode of operation (See
As shown in
The defrost cycle continues to operate until the condensed liquid refrigerant exiting the outdoor coil becomes sufficiently warm thus indicating complete removal of ice or heavy frost from the outdoor coil. At this point, responding to a now warm T2 (about 70° F.) the microprocessor sends a signal effecting 4 way valve movement to the position shown in
To operate the system in a cooling or air conditioning mode, thermostat 38 is moved to its air conditioning position, whereby a first stage signal is delivered from the thermostat to microprocessor 36 whereby a signal is delivered from the microprocessor to 4 way valve 32 to position the valve as shown in
In the preferred embodiment of this invention, neither M3 nor M3-C operation is enabled for cooling operation. However, for very hot climates, such as the southern or southwestern U.S. in summertime, an alternative embodiment would enable M3-C and/or full M3 operation of the system in cooling operation. In this embodiment, M1 and M2 operation are effected by the microprocessor when the signal from air temperature sensor 48 indicates an outdoor air temperature in a first range of temperatures, and the first and second stages of the thermostat call for M1 and M2 operation, respectively. For an outdoor air temperature sensed by temperature sensor 48 above the first range of temperatures, microprocessor 36 would effect full capacity operation of primary compressor 22, booster compressor 24 and economizer 30 for cooling operation (M3), or cyclical on-off (M3-C) operation of those components, if operation in M2 is not sufficient to satisfy the thermostat setting. The M3 or M3-C operation in cooling is shown in
The heat pump system may also include a refrigerant charge compensator that acts to reduce the refrigerant charge active in the system condenser during any operating mode causing booster compressor operation. Whenever the booster compressor is idle for any significant period of time, a significant amount of refrigerant vapor will condense into the booster oil in the booster sump. This occurs because the refrigerant is essentially 100% miscible in the oil. The refrigerant vapor condenses into the booster oil when agitation ceases upon shutdown of the booster compressor, and continues to condense as the booster oil temperature falls with the end result being that about 10% more refrigerant charge must be added to the system charge to ensure all operating modes without the booster will always have sufficient operating refrigerant charge. However, the refrigerant thus absorbed into the booster oil comes out of the booster oil-refrigerant solution very quickly upon booster startup and can overcharge the refrigerant system. This excess charge can cause a backup of liquid refrigerant in the condenser, thus reducing the effectiveness of condenser operation. This, in turn, can result in the primary compressor drawing more power and result in a reduction in the overall efficiency of the heat pump system. This problem can be avoided by incorporation of a refrigerant charge compensator 64 in the system (see
While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of this invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.
This application relates to heat pumps of the type disclosed and claimed in my previously issued U.S. Pat. Nos. 6,931,871, 6,276,148, 5,927,088, and 5,839,886 and my pending U.S. patent applications Ser. Nos. PCT/US05/34651 and 10/959,254. The entire contents of my said United States patents and patent applications are incorporated herein by reference.
