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US 6,310,330 B1Granted
HVAC heater power and control circuit
AssigneeTransport International Pool, Inc.
InventorsLjubisa Dragoljub Stevanovic, Ahmed Elasser, Thomas Bernard Breen, Wayne William Mihailov, Rollie Richard Herzog
Life of this patent
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Abstract
An improved system and method for controlling the temperature of a resistance heater in a heating, ventilation and air-conditioning (“HVAC”) system is disclosed. The control circuit and method includes three separate thermostats per heater leg and are designed to trip at three, sequential pre-selected temperatures to address certain issues associated with prior art designs for thermal overload protection. One of the thermostats is of an automatically resettable type wherein the remaining two are of a “one-shot” design and will remain open until there is human intervention.
Claims33
A circuit for controlling the temperature of a resistance heater comprising:
- a power circuit including
- a dual thermostat having a first and second thermostat in series with each other,
- a first switch coupled to a first contactor for controlling the operation of the switch, and
- a resistance heater coupled in series between the dual thermostat and the switch, wherein the first thermostat cycles open and closed automatically and is set to trip at a first temperature T1 and the second thermostat is a manual thermostat and is set to trip at a second temperature T2, where T2 is higher than T1;
- and
- a control circuit including
- a third thermostat coupled in series with the first contactor wherein energizing and de-energizing the first contactor causes the first switch to close and open, respectively, and wherein the third thermostat is a one-shot thermostat and is set to trip at a third temperature T3, where T3 is higher than T2, and wherein when the temperature exceeds T3, the third thermostat trips, thereby de-energizing the first contactor, causing the first switch to open in the power circuit and preventing current from being supplied to one end of the resistance heater,
- whereby continual oscillation in the opening and closing of the first thermostat as a result of oscillation in the temperature above and below T1, but less than T3, is prevented by said second thermostat having a trip temperature above T1 but less than T3.
5 more elements
A circuit for controlling the temperature of a heater comprising:
- a power circuit including
- a first thermostat means in series with a second thermostat means for providing thermal overload protection,
- a first switching means coupled to a first contactor means for controlling the operation of the first switching means, and
- heater means coupled in series between the first switching means and at least one of the first and second thermostat means, wherein the first thermostat means cycles open and closed automatically and is set to trip at a first temperature T1 and the second thermostat means is a one-shot thermostat and is set to trip at a second temperature T2, where T2 is higher than T1;
- and
- a control circuit including
- a third thermostat means coupled in series with the first contactor means wherein energizing and de-energizing the first contactor means causes the first switch to close and open, respectively, and wherein the third thermostat means is a one-shot thermostat and is set to trip at a third temperature T3, where T3 is higher than T2, and wherein when the temperature exceeds T3, the third thermostat trips, thereby de-energizing the first contactor means, causing the first switch means to open in the power circuit and preventing current from being supplied to one end of the heater means,
- whereby continual oscillation in the opening and closing of the first thermostat means as a result of oscillation in the temperature above and below T1, but less than T3, is prevented by said second thermostat means having a trip temperature above T1 but less than T3.
5 more elements
A method for controlling the temperature of a resistance heater comprising:
- providing in a power circuit a dual set of thermostats having a first and second thermostat in series with each other, a first switch coupled to a first contactor for controlling the operation of the switch, and a resistance heater coupled in series between the dual set of thermostats and the switch, wherein the first thermostat cycles open and closed automatically and is set to trip at a first temperature T1 and the second thermostat is a one-shot thermostat and is set to trip at a second temperature T2, where T2 is higher than T1;
- and
- providing in a control circuit a third thermostat coupled in series with the first contactor wherein energizing and de-energizing the first contactor causes the first switch to close and open, respectively, and wherein the third thermostat is a one-shot thermostat and is set to trip at a third temperature T3, where T3 is higher than T2, and wherein when the temperature exceeds T3, the third thermostat trips, thereby de-energizing the first contactor, causing the first switch to open in the power circuit and preventing current from being supplied to one end of the resistance heater,
- whereby continual oscillation in the opening and closing of the first thermostat as a result of oscillation in the temperature above and below T1, but less than T3, is prevented by said second thermostat having a trip temperature above T1 but less than T3.
1 more element
Dependencies are inferred from the claim text.