Control for a combination furnace and heat pump system

• US 4,178,988 A
• Filed: 11/10/1977
• Issued: 12/18/1979
• Est. Priority Date: 11/10/1977
• Status: Expired due to Term

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Cann, Peter L., Honnold, Fred V., Karns, Phil J.
• Primary Examiner(s): Davis, Jr., Albert W.
• Assistant Examiner(s): Focarino, Margaret A.
• Application Number:
  US05/850,180
• Time in Patent Office: 768 Days
• Field of Search: 165/29, 165/17, 165/2, 62/156, 62/160
• US Class Current: 165/242
• CPC Class Codes: F24D 11/0271 combined with conventional energy
• CPC Class Codes: F25B 49/022 Compressor control arrangements
• CPC Class Codes: F25D 21/008 by timer
• CPC Class Codes: Y02B 10/70 Hybrid systems, e.g. uninterruptible or back-up power supplies integrating renewable energies
• CPC Class Codes: Y02B 30/13 Hot air central heating systems using heat pumps

Abstract

A control circuit for a combination furnace and heat pump wherein a temperature dependent relay is connected to a thermostat such that the heat pump is operated to supply heat to an enclosure when the outdoor temperature is above a predetermined level and the furnace is operated to supply heat to the enclosure when the outdoor temperature is below a predetermined level. To defrost the outdoor coil of the heat pump the furnace is operated to supply heat to the indoor coil of the heat pump and a reversing valve relay is energized whereby the heat pump is operated in a reverse direction to supply heat to the outdoor coil for defrost.

Claims

1. A control circuit for a combination heating means and heat pump for conditioning an enclosure wherein the heating means has an actuating device to commence the generation of heat and blower actuated by a blower relay which circulates air through the area to be conditioned and wherein the heat pump has a compressor motor for operating the compressor, an outdoor fan motor for circulating fluid in a heat exchange relationship with an outdoor heat exchanger means including a defrost relay for defrosting the outdoor coil, an indoor coil mounted in communication with the air circulated by the blower and a reversing valve actuated by a reversing valve relay which comprises:

a temperature sensing means for making an electrical connection when heating is required in the enclosure;

means for supplying an electric current to the temperature sensing means;

switching means electrically connected to the temperature sensing means for selectively energizing either the compressor motor of the heat pump or the actuating device of the heating means depending on the temperature of the ambient fluid in communication with the outdoor heat exchanger, including no delay other than that which naturally occurs between switching from heating means heating to heat pump heating and the means for actuating the heating means for defrost includes no delay other than that which naturally occurs through switching; and

means for actuating the heating means to provide heat to the indoor coil when the means for defrosting the outdoor coil is energized including termination means for discontinuing defrost before heat pump refrigerant temperature or pressure reached excessive levels.

2. The invention as set forth in claim 1 wherein the switching means includes a temperature sensitive switch which when the thermostat calls for heating energizes the heat pump compressor if the ambient air temperature is above a predetermined level and actuates the heating means if the ambient air temperature is below a predetermined level.

3. The invention as set forth in claim 2 wherein the means for actuating the heating means for defrost includes defrost relay contacts being mounted such that when the defrost thermostat senses a no frost condition the defrost relay will be disengaged allowing the heat pump to be operated to provide heat to the enclosure.

4. The invention as set forth in claim 1 wherein the termination means is a defrost thermostat mounted on the refrigerant discharge line from the outdoor coil preset to terminate heating means operation upon the completion of defrost prior to excessive refrigerant temperatures or pressures occuring in the heat pump system.

7. The invention as set forth in claim 4 wherein the heating means is a fuel fired furnace.

5. A system for conditioning air in an enclosure, said air having an indoor air temperature which may be different from the outdoor air temperature which comprises:

a heating means having a blower for circulating air through a duct to the enclosure and having heat exchanger means for heating said air;

a heat pump having an outdoor heat exchanger, an indoor heat exchanger mounted in heat exchange relationship with the air in the duct and reversing means for defrosting the outdoor heat exchanger;

a thermostat for determining if heating or cooling is required in the enclosure; and

control means for coordinately controlling the heat pump and the heating means, said control means being responsive to the thermostat and said control means selecting either the heat pump or the heating means to supply heating to the enclosure dependent on the temperature level of the ambient outdoor air, said control means activating the heat pump if the outdoor air is at a higher temperature than a predetermined level and the furnace of the outdoor air is at a lower temperature than a predetermined level, said control means including defrost means which automatically cycles the heating means on and reverses the heat pump notwithstanding the outdoor air temperature when the outdoor heat exchanger requires defrosting so that heat from the heating means is used with the heat pump for defrost and which automatically terminates heaing means operation upon the completion of defrost being detected and prior to excessive heat pump refrigerant pressures occurring as a result of the heat supplied to the indoor coil by the heating means after the outdoor coil is free of ice and the heat pump is unable to dissipate the heat received, wherein there are no built-in delays for cooling or heating between the switching among heating means operation, heat pump operation and defrost operation.

6. The invention as set forth in claim 5 wherein the defrost means includes a defrost thermostat in series with a defrost relay, said thermostat actuating the relay when defrost is required and said defrost relay closing the defrost relay contacts, to cycle the heating means on and to reverse the heat pump.

8. A method of controlling the synchronized operation of a combination heating means and heat pump with an outdoor coil in communication with outdoor air for conditioning air within an enclosure which comprises the steps of:

operating the heat pump to supply heated air to the enclosure when the temperature of the outdoor air is above a predetermined level;

energizing the heating means to supply heated air to the enclosure when the outdoor temperature is below a preselected level;

cycling the heating means such that the heating means is energized when the heat pump is reversed for defrosting, the heat pump utilizing part of the heat supplied by the furnace for defrost; and

terminating the step of cycling the heating means during defrost upon a defrost thermostat sensing no ice on the outdoor coil; and

switching the heating means and heat pump among the steps of operating, energizing, terminating and cycling without any thermal delays.

9. A control circuit for a combination heat pump and furnace for conditioning an enclosure, the furnace having a means for heating air being circulated therethrough by a furnace blower and the heat pump having an outdoor coil, an outdoor coil fan motor, a compressor motor actuated by compressor relay, and a reversing valve actuated by a reversing valve relay, the reversing valve being normally in the position for the heat pump to be operated in the heating mode, and defrost means including a defrost relay, and a thermostat for determining when heating or cooling is required which comprises:

a temperature sensitive relay connected to the thermostat for actuating either the furnace means for heating air or means for actuating the compressor, said temperature sensitive relay being dependent on the outdoor air temperature;

first defrost relay contacts in a normally open position connected to the reversing valve relay;

second defrost relay contacts in a normally open position connected to the furnace means for heating air such that when the defrost relay is actuated the heat pump will operate in the cooling mode and heat from the furnace will be used to defrost the outdoor coil; and

a defrost thermostat in series with the defrost relay for sensing the presence or absence of ice on the outdoor heat exchanger for discontinuing defrost operation, said switching between heat pump heating, furnace heating and defrost occurring without any thermal delays.

10. The invention as set forth in claim 9 wherein the thermostat is connected to the reversing valve relay such that when a cooling need is sensed the compressor will be operated through the temperature sensitive relay and the reversing valve relay will be operated through a separate thermostat connection.