Fast recovery circuit for heat pump water heater
AssigneeElectric Power Research Institute, Inc.
InventorsGlen P. Robinson, Jr., Carl C. Hiller
Life of this patent
Estimating the term…
Abstract
An external circuit that works in conjunction with the existing tank thermostatic controls to control both a water heating heat pump and the existing resistance elements in a water heater. The existing resistance elements are disabled to allow the heat pump to heat the water unless a large volume of hot water is quickly withdrawn whereupon the upper resistance element is re-enabled to heat the water for a faster recovery rate.
Claims10
A thermostatic control circuit connecting existing electric resistance upper and lower heating elements in an electric hot water heater and a water heating heat pump to line voltage to heat the water in the water heater tank, the resistance heating elements controlled by an existing thermostatic switch network having an upper switch responsive to the temperature of the water in the upper portion of the water tank to power the upper heating element from line voltage and disable the lower heating element in response to the temperature of the water in the upper portion of the water tank dropping below an upper prescribed threshold value, said thermostatic control circuit comprising:
- an impedance serially connecting said existing resistance heating elements to line voltage through said existing thermostatic switch network, said impedance having a sufficiently high impedance to reduce the current flow through said existing resistance heating elements to a level to substantially prevent the operation thereof when said existing thermostatic switch network connects the heating elements to line voltage;
- auxiliary control means operatively associated with said impedance and responsive to line voltage applied to said impedance to connect said water heating heat pump to line voltage to operate same;
- and
- bypass circuit means for shorting out said impedance in response to the upper switch in the existing thermostatic switch circuit applying power to the upper heating element to allow the upper heating element to heat the water in the upper portion of the water heater and to return said impedance to the circuit when the upper switch in the existing thermostatic switch circuit removes power from the upper heating element.
A method of disabling the electric resistance upper and lower heating elements in the existing tank circuitry of an electric hot water heater where the existing resistance heating elements are normally powered through an existing thermostatic switch network having a lower switch responsive to the temperature of the water in the lower portion of the water tank to close in response to the water in the lower portion of the water tank dropping below a lower prescribed threshold value and an upper switch responsive to the temperature of the water in the upper portion of the water tank to shift from a first position to a second position in response to the temperature of the water in the upper portion of the water tank dropping below an upper prescribed threshold value, where the lower heating element is connected to line voltage from an electrical power source through the lower switch and the upper switch in series in response to said lower switch being closed and said upper switch being in said first position, where the upper heating element is connected to line voltage from the electrical power source in response to said upper switch being the second position, and where the lower heating element is disabled in response the upper switch being the second position so as to produce an electrical power output upper switch being the second position so as to produce an electrical power output in response to the temperature of water in the lower portion of the water tank being below the lower prescribed threshold level comprising the steps of:
- (a) disconnecting the line voltage from the thermostatic switch network in the existing tank circuitry;
- (b) reconnecting the thermostatic switch network in the existing tank circuitry to line voltage through an impedance having a sufficiently high impedance value to reduce the current flow through the resistance heating elements to a level to substantially prevent the heating capability of the resistive heating elements responsive to the lower switch in the thermostatic switch network being closed while creating a voltage drop across the impedance above a prescribed threshold value;
- (c) connecting the primary winding of a step down transformer in parallel across the upper resistance heating element so that the secondary winding produces a detectable voltage output therefrom when the upper switch in the thermostatic circuit moves to the second position;
- and
- d) using the voltage output of the secondary winding to cause the impedance to be shorted out until the upper switch in the thermostatic network moves to the first position.
Dependencies are inferred from the claim text.