Sunnovations developed a new Solar Hot Water (SHW) system. It uses solar thermal energy to create fluid circulation, which transfers heat from the collectors to the tank (which is located up to 33 feet below the collectors). The Sunnovations pump unit is directly connected to the collector(s) and is fully passive (i.e. no electric pumps or moving parts). As soon as the sun warms up the fluid in the collectors, the system starts circulation. The maximum temperature and pressure in the system are passively limited - making it a very safe system.
The circulation is based on the geyser pumping effect (also known as bubble pump). The solar heat on the collectors causes circulation through solar loop (i.e. the pipe runs and heat exchanger) that in turn transfers heat to water in the tank. The flow rate is adaptive to the solar radiation (insolation) to achieve optimal system efficiency.
1) Steam bubbles are formed once the fluid in the collector riser reaches its boiling point. The initial boiling point temperature is low (~100 F) because the system operates under a vacuum.
2) The rapid volume expansion of the bubbles force hot fluid up through the exit tube to a higher level (this is the geyser pumping effect).
3) This causes a difference in fluid levels. The principle of a fluid gravity balance causes circulation through the solar loop. Heat is transferred to the solar storage tank and cool fluid returns to the pump unit.
4) The cool fluid keeps a low dew point, which maintains a low pressure (vacuum) in the system. This maintains low temperature operation.
5) Condensation of steam preheats fluid returning to the collector - effectively recovering the energy used for pumping.
6) The pressure in the system adapts to increased insolation. This results in adaptive flow rate and operating temperature.
Temperature Limiting and Overheat protection Operation and Automatic Vacuum Restore System
The Sunnovations system is passively temperature limited - so the storage tank can never overheat (max 165 F). This also makes the system safe for use of PEX tubing.
The Sunnovations system has an unique passive overheat protection system - which purges all fluid from the collectors to avoid high temperature & high pressure. This protects the glycol from excessive temperatures which is the main cause for glycol breakdown (which turns acidic and causes leaks - a known problem in other closed loop glycol systems).
Another unique feature of the Sunnovations system is that is automatically (and passively) restores/revitalizes the vacuum to ensure optimal performance.
The heat transfer fluid offers freeze protection to -30C/-22F.