The disclosed technology includes an on-demand water heater which uses an electric heat source to heat the water. The on-demand water heater can have a low fluid capacity heating chamber which has an inlet and an outlet, an electric heat source for heating the water, and a controller to control the electric heat source and maintain the temperature of the water at a predetermined temperature setting. The on-demand water heater can be powered by a direct current power source. The on-demand water heater can also utilize a solar thermal system to provide additional heat to the water.

The disclosed technology includes an on-demand water heater which uses an electric heat source to heat the water. The on-demand water heater can have a low fluid capacity heating chamber which has an inlet and an outlet, an electric heat source for heating the water, and a controller to control the electric heat source and maintain the temperature of the water at a predetermined temperature setting. The on-demand water heater can be powered by a direct current power source. The on-demand water heater can also utilize a solar thermal system to provide additional heat to the water.

A water heater auxiliary heating system includes a heat pump. It further includes a first tap to circulate water from a water tank to a heat exchanger within the heat pump. It further includes a second tap to circulate water back to the water tank. The heat pump is controlled by an energy management system to preferentially operate based at least in part on a status of a site energy system that the energy management system is configured to manage. The water tank stores excess energy that is generated locally at the site energy system.

A water heater auxiliary heating system includes a heat pump. It further includes a first tap to circulate water from a water tank to a heat exchanger within the heat pump. It further includes a second tap to circulate water back to the water tank. The heat pump is controlled by an energy management system to preferentially operate based at least in part on a status of a site energy system that the energy management system is configured to manage. The water tank stores excess energy that is generated locally at the site energy system.

A multi-parallel carbon dioxide heat pump control method based on target load control, wherein the multi-parallel carbon dioxide heat pump comprises a carbon dioxide circulation loop, a heat source pipeline and a hot water pipeline, and the control method comprises: adjusting the opening degree of an electronic expansion valve (3) according to the temperature of an inlet of the hot water pipeline, the temperature of an outlet of the hot water pipeline, the flow in the hot water pipeline and a target outlet temperature set by a user, such that the steady-state change of system pressure can be realized by adjusting the electronic expansion valve (3) on the basis of the fluctuation of parameters such as user side temperature and flow, thus a target outlet temperature change curve is rapidly and stably converged to a target value, and the outlet temperature can be rapidly stabilized.

As a circulation pump is activated while a hot water supply faucet is closed, an immediate hot water supply circulation path is formed to bypass the hot water supply faucet on the outside of a water heating apparatus and to pass through a heat exchanger in the inside of the water heating apparatus. A controller determines in a test mode, whether or not the immediate hot water supply circulation path has been formed by connection of a thermal water stop bypass valve, based on whether or not a temperature detector senses increase in temperature to a predetermined criterion temperature while the circulation pump and a heat source apparatus are active.

A control device causes an air conditioning apparatus to execute a temperature adjustment operation of causing a first temperature to approach a first target temperature at a target time point and causing a second temperature to approach a second target temperature at the target time point. The first temperature is a surface temperature of a partition portion including at least one of a floor, a wall, and a ceiling facing a target space. The second temperature is an indoor temperature of the target space.

A heat pump water heater includes a tank, a first condenser, a second condenser, a heat pump, valving and a controller. The tank includes an interior cavity, an input port and an output port. The first condenser and second condenser each include an input port and an output port. The heat pump drives a fluid in a heated state through an output. A first setting of the valving fluidically couples the heat pump output to the input port of the first condenser, and fluidically disconnects the heat pump output from the input port of the second condenser. A second setting of the valving fluidically couples the heat pump output to the input port of the second condenser, and fluidically disconnects the heat pump output from the input port of the first condenser. The controller selectively directs the valving to the first or second setting.

Methods and systems for water heater system receiving electrical power from an electrical grid. The system includes an electronic processor configured to monitor an average water temperature of the water within a water tank of the system based on a first and second signal from an upper and lower temperature sensor, operate an upper heating element heating an upper portion of the tank and a lower heating element heating a lower portion of the tank in a first operation mode, receiving, via a transceiver, either an add load command or a shed load command from a grid controller, operating the upper heating element and lower heating element in a second mode in response to receiving the add load command, and operating the upper heating element and lower heating element in a third mode in response to receiving the shed load command.

An aspect of some embodiments of the current invention relates to an integrated system for heat distribution among a plurality of users. In some embodiments, the system includes a separate automatic control of heat distribution to each user and/or separate billing to each user. For example, a system may supply hot fluid to a plurality of apartments in a building and/or in multiple buildings. Optionally, each apartment has separate remote controlled valves controlling flow of heated fluid to the apartment and/or a sensor sensing how much heat enters and leaves the apartment in the hot fluid. In some embodiments, a processor controls the valve and/or receives data from sensors. The processor optionally controls devices that generate and/or store and/or dissipate heat. Optionally the processor predicts energy availability, costs and needs controls valves and/or devices to provide for predicted and/or unexpected needs while reduce cost of the energy.