Various embodiments of the teachings herein include methods of estimating a heat transfer via one or more thermal energy exchangers. An example method includes: acquiring a signal for a setpoint temperature; acquiring a signal for an inside temperature at a site; acquiring one or more signals indicative of positions of valves of the thermal energy exchangers; producing a value of setpoint temperature from the signal; producing a value of inside temperature; producing a value of position from the one or more signals; providing a calibrated model with the value of setpoint temperature and inside temperature and position; and using the calibrated model to estimate the heat transfer via the one or more thermal energy exchangers.

The disclosed technology includes a controller for a cascade boiler system having both condensing and non-condensing boilers. The controller can receive supply water temperature data and return water temperature data to determine a current temperature differential in the system. The controller can determine a current load demand value using the current temperature differential and a set point temperature. If the current load demand value is less than or equal to a first load demand threshold, the controller can output a control signal for a condensing boiler to transition to a heating mode. If the current load demand value is greater than a second load demand threshold, the controller can output a control signal for a non-condensing boiler to transition to a heating mode.

The present invention improves the user-friendliness of a hot-water supply apparatus when using hot water supply and air conditioning. A switching control unit 27, which switches between heat medium flow paths 4 and 5 according to an air conditioning ready state or a hot-water supply ready state, switches a heat medium flow path to the hot-water supply ready state by a switching valve 21 in the case where air conditioning is not used by the time an air conditioning standby time elapses during standby in the air conditioning ready state.

A control system is provided for controlling heating and/or cooling with a conditioning load such as fan coils and chilled beams. Based on user input and ambient conditions, the control system determines a desired temperature for the liquid entering the load and combines fresh supply liquid (e.g., from a chiller or boiler) with a portion of the liquid that has passed through the load, to achieve the target load input temperature for the liquid. A recirculation pump may be used to return a portion of the liquid exiting the load for mixing with the fresh supply liquid and a control valve may be used to adjust the ratio of fresh supply liquid and recirculated liquid to achieve the targeted temperature. The control systems can be compatible with a variety of liquid supply systems such as two- and four-pipe systems.

A system and method for improving the responsiveness of forced hot water heat exchangers placed around the baseboards of conditioned living spaces and improving the efficiently of centralized hot water heating systems. The control system may comprise a convector baseboard heat exchanger or a replacement heat exchanger cover, and a blower, a diffuser and sensors which are mounted to one or more of the baseboard heat exchangers, the heating system influent and effluent loops, the fuel supply and the recirculation pump. When the heating system and forced hot water loop reaches its operating temperature, the blower activates to rapidly transfer energy from the-forced hot water loop into the air and disperse treated, heated air into the conditioned spaces. After the centralized heating system turns off, the system continues to transfer energy from the forced hot water into the air of the conditioned spaces until the latent heat of the centralized heating system has been extracted and the return loop temperatures are at levels consistent with optimal boiler performance.

In an aspect, an HVAC system includes an inducer motor to provide combustion airflow, and a pressure sensor to measure an output airflow pressure of the inducer motor. The HVAC system may initiate the inducer motor, and receive a pulse width modulation (PWM) signal from the inducer motor, wherein the PWM signal indicates a PWM signal of the inducer motor corresponding to a predetermined airflow pressure of the inducer motor and measured by the pressure sensor. The HVAC system may compare the PWM signal to a baseline value, and control the inducer motor based on the comparing of the PWM signal to the baseline value. The HVAC system may also generate a status notification of the combustion airflow of the HVAC system in response to the comparing the PWM signal to the baseline value.

A portable indirect fuel fired heater includes a burner assembly having a fuel burner to deliver fuel from a fuel supply to a combustion chamber of the heater and a combustion air blower to deliver combustion air to the combustion chamber with the fuel for combustion in the combustion chamber to produce exhaust gases. A heat exchanger receives air to be heated in heat exchanging relationship with at least a portion of the combustion chamber. A sensor senses an oxygen level as a partial pressure of oxygen in the exhaust gases. A controller operates an actuator operatively connected to the burner assembly to controllably vary the delivery rate of combustion air and thus vary the ratio of the air and fuel responsive to the oxygen level sensed by the combustion sensor so as to maintain the sensed oxygen level at a prescribed set point level stored on the controller.

A heat pump may include a compressor configured to compress a refrigerant, a first temperature sensor provided in heating pipes connected to a heating device that heats an indoor space to sense a temperature of fluid flowing through the heating pipes, and a controller. The controller may be configured to determine whether a boiler is operating to heat an indoor space or is operating to supply hot water based on a sensing value of the first temperature sensor. The compressor may operate when the controller determines that the boiler is not operating to heat the indoor space and/or determines that the boiler is operating to supply hot water.

A combination water heating, air conditioning refrigerant system is described. The combined system includes a plurality of independently adjustable electronic expansion valves. The expansion valves can independently modulate the delivery of high-temperature, high-pressure refrigerant to either a water heat exchanger or an outside condenser. A controller can receive input signals, including temperature signals from one or more temperature sensors that indicate the temperature at various locations of the system. The temperature signals include one or more of water temperature signals, ambient air temperature signals, or refrigerant super heat temperatures signals. In response to the input signals, the controller can output control signals to one or more of the plurality of electronic expansion valves.

A method of controlling a gas furnace system includes controlling a motor of a draft inducer coupled to a conduit to increase a speed of the motor from a stopped condition in response to a call for heat, and receiving pressure signals output by a pressure transducer responsive to pressure in the conduit. Signals indicating whether a pressure switch responsive to pressure in the conduit is in a first state or a second state are received. A first status of the pressure transducer is determined based on the received pressure signals from the pressure transducer and the signals indicating whether the pressure switch is in the first state or the second state. The method includes continuing to operate the motor when the first status does not indicate that the pressure transducer is unreliable, and stopping the motor when the first status indicates that the pressure transducer is unreliable.