Refrigeration – Automatic control – Of external fluid or means
Reexamination Certificate
1999-06-07
2001-04-24
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Of external fluid or means
C062S126000, C062S158000
Reexamination Certificate
active
06220043
ABSTRACT:
A microfiche appendix comprises 24 sheets of microfiche.
FIELD OF THE INVENTION
This application relates generally to heating, ventilating and air conditioning (HVAC) systems and more particularly to micro-controller based controls for heat pumps and electric furnaces.
A microfiche appendix is included totaling—microfiche and—frames
BACKGROUND OF THE INVENTION
The use of electronics in HVAC systems has become increasingly common in recent years and has grown to include heat pumps and electric furnaces. The use of electronics, with relays, to control electric heat, has only recently become practical through the use of zero, or near zero, voltage crossing switching techniques such as those disclosed and claimed in co-assigned U.S. Pat. No. 5,530,615, the contents of which is included herein by this reference. With respect to defrost controls, electronics have replaced electro-mechanical controls for a considerable period of time.
Conventional split systems for residential heat pumps have an indoor evaporator coil unit and an outdoor condenser coil unit with electronic controls for each unit receiving an input from a wall thermostat for either heating or cooling and for operating outputs such as electric resistive heat, fans, reversing valves and a compressor. Typically, some seven wires are required to interconnect the thermostat and the indoor control with six wires running out to the outdoor unit. It would be very desirable to reduce the wiring complexity from a standpoint of cost saving but also because many field failures occur due to miswiring during installation and decreasing the wiring connections would result in fewer failures. Even when the wiring is done correctly, however, there are undesirable functional limitations of the conventional control system. Ideally, the indoor fan should not be energized when the compressor is not operating, however, there are certain operational modes in which the indoor fan can be energized when the compressor is not energized such as in a lockout, either for a short or a long duration.
SUMMARY OF THE INVENTION
It is an object of the invention to provide apparatus and methods for controlling heat pumps and electric furnaces which overcome the above noted prior art limitations. Another object is the provision of such control apparatus and methods which result in improved efficiency of operation as well as an enhanced comfort performance. Yet another object of the invention is the provision of control apparatus and methods which result in fewer system components than conventional systems and with less complex wiring.
Briefly, in accordance with the invention, controls for the indoor and outdoor units are integrated into a single control with control of the evaporator (indoor) fan matched or synchronized with the compressor operation. The integrated control receives the defrost thermostat signal input from the outdoor unit and controls the reversing valve, condenser fan and compressor contactor by relays. This results in improved efficiency and comfort. For example, if the compressor has been shut off due to a pressure switch trip or anti-short cycle timer then the evaporator fan can be shut off during this period. This improves system efficiency because the heat convection transferal is maximized to a specific set point, a feature not available in conventional split system controls. In the heat mode, supplemental electric heat can also be energized. Additionally, the evaporator fan speed can be varied during defrost to improve comfort. Complete control of the electric heat, indoor fan, outdoor fan, reversing valve and compressor allows optimum control of the defrost operation in a manner not available in conventional systems. The electric heat can be initialized in anticipation of defrost, the outdoor fan can be enabled in anticipation of completion of defrost, and the reversing valve can be used to equalize system pressures at the end of each cycle.
Conventional heat pumps have been known to result in discomfort due to the limitations of the refrigerant. This problem is obviated by an integrated control made in accordance with the invention by synchronizing operation of the compressor and evaporator fan. For example, allowing the compressor to run allows the refrigerant to transfer heat to the heat exchanger. After the compressor has been running for a selected time, e.g., 30 seconds, the indoor fan is enabled thereby providing a warmer discharge air.
The control detects air flow problems due to improper installation, indoor (evaporator) fan failure and “stuck” on resistive heaters. If the thermal limit switch opens, the indoor blower fan is energized. If the switch opens for a continuous duration of a selected amount, e.g., 80 seconds, then the system is put into a hard lockout which maintains the indoor fan running and prevents the electric heat from being turned on. In addition, during any mode of operation, if the thermal limit switch opens and recloses four times, the system is put into a soft lockout which allows the evaporator fan to cycle with demand for heat/cool but prevents the electric heat from being turned on for a selected period, e.g., one hour. If, after one hour, the limit has not switched open, the counters are cleared and the heaters can be enabled.
The control is provided with on board diagnostics which can monitor all limit devices, pressure and thermal switches, and can provide a central location for troubleshooting.
REFERENCES:
patent: 2713250 (1955-07-01), Blatchford
patent: 3068661 (1962-12-01), McGrath
patent: 4563877 (1986-01-01), Harnish
patent: 4662184 (1987-05-01), Pohl et al.
patent: 5065593 (1991-11-01), Dudley et al.
patent: 5321957 (1994-06-01), Moore
patent: 5488218 (1996-01-01), Olsen et al.
patent: 5530615 (1996-06-01), Miller et al.
patent: 5743100 (1998-04-01), Welguisz et al.
patent: 5758507 (1998-06-01), Schuster et al.
Chaney, Jr. Robert K.
Miller Mark E.
Rowlette Mitchell R.
Baumann Russell E.
Tanner Harry B.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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