While at Solar Power International 2011 I had the chance to stop by and speak with Lochinvar and learn about their thermal storage tank for solar applications.
The manufacturer of water heaters, boilers and pool heaters says their Strato-Therm+ is three appliances in one because it acts as a storage vessel for solar thermal systems, an indirect water heater and a buffer tank for hydronic applications. The storage tank uses the natural buoyancy of heated water to efficiently stratify the hydronic heating water that is stored in the tank.
A solar heat exchanger is connected at four points to the storage vessel, which allows for the water heated by the solar collector array to naturally heat the tank. A corrugated stainless steel coil in the storage vessel houses potable water and acts as a instantaneous water heater for generating domestic hot water.
Stratification Process
Lochinvar says its Strato-Therm + uses the natural stratification of hot and cold water to create the layering effect within the external heat exchanger and storage vessel. Because hot water is less dense than cold water it rises to the top of the vessel while the cooler water will sink to the bottom.
As solar thermal energy is added to the external spherical heat exchanger the stored water will follow the laws of physics and begin to stratify in the tank. As heat is added, the water will begin to “layer” with the heated water rising to the top and the cooler water sinking to the bottom. The external spherical heat exchanger utilizes four distinct connection points to drive the stratification process in the storage tank.
The hot water in the top of the tank allows domestic hot water to be generated instantaneously to meet the temperature demand through the corrugated stainless steel coil and allows for the space heating system to access the hottest possible water for distribution to the heat emitters. The cooler water in the bottom of the tank allows for greater collector efficiency and greater opportunity for solar thermal heat generation
How it Works
1. Solar Thermal heat is transferred to the storage vessel by way of a copper tube spherical heat exchanger.
2. As domestic water is drawn through the stainless steel corrugated coil it is indirectly heated. An ASSE mixing valve ensures that the water delivered is at the proper temperature. (ASSE mixing valve – by others)
3. A back-up hydronic heat source such as a boiler ensures that the storage vessel is at a suffi cient temperature to generate domestic hot water and meet heating demands.
4. As demand for space heating is initialized, the Strato-Therm+ acts as a hydraulic separator, decoupling the system demand from the boiler output. Decoupling the system and boiler demands allows for extended boiler on times and constant system delivery temperatures.
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