Abstract: Apparatus and methods are provided for thermal energy metering by measuring the average temperature of fluid in a tank, such as a hot water storage tank. Average temperature is measured with an elongated temperature sensor spanning the vertical height of the tank. A controller collects measurements from the temperature sensor and computes changes in thermal energy, from which the system can more accurately attribute gains of thermal energy to sources such as thermal, electric, or gas production, or losses of thermal energy to ambient losses and consumption.

Abstract: Solar collectors heat and self pump heat transfer fluid at reduced system pressure without mechanical intervention for heat exchange with hot water in a storage tank. Slugs of hot fluid are pumped by steam bubbles formed in solar collector tubes through an upper manifold and an exit-tube into an upper hot fluid reservoir. Hot fluid flows downward through a heat exchanger at the tank. Cold fluid returns to a lower reservoir. Vapor flows from the upper reservoir and is condensed by cooler water and walls of the lower reservoir. The cool fluid returns from the lower reservoir to a lower manifold supplying the collector tubes. Below ambient pressure is automatically established in the system. When heat build-up increases pressure in the system, fluid flows to a third closed variable volume reservoir. A float valve in the bottom of the third reservoir allows liquid to return to the system when it cools.

Abstract: Solar collectors heat and self pump heat transfer fluid at reduced system pressure without mechanical intervention for heat exchange with hot water in a storage tank. Slugs of hot fluid are pumped by steam bubbles formed in solar collector tubes through an upper manifold and an exit-tube into an upper hot fluid reservoir. Hot fluid flows downward through a heat exchanger at the tank. Cold fluid returns to a lower reservoir. Vapor flows from the upper reservoir and is condensed by cooler water and walls of the lower reservoir. The cool fluid returns from the lower reservoir to a lower manifold supplying the collector tubes. Below ambient pressure is automatically established in the system. When heat build-up increases pressure in the system, fluid flows to a third closed variable volume reservoir. A float valve in the bottom of the third reservoir allows liquid to return to the system when it cools.