F LORIDA S OLAR E NERGY C ENTER Creating Energy Independence Since 1975 A Research Institute of the University of Central Florida Northern Climate System Types

System Types  Active  Uses a pump  Passive  Does not use a pump – relies on natural forces

Active System A pump circulates heat transfer liquid through the collector.

Solar collector

System types  Direct  City potable (or well) water is circulated from the tank to the collector and back  For warm climates  Indirect  Fluid circulating through the collector never comes in contact with the city potable water in the storage tank  A heat exchanger is used to transfer heat from the circulating fluid to the potable water  For cold climates - freeze

System types

Available System Types  Active indirect using a differential controller and flat plate collectors  Active indirect drainback using a differential controller  Indirect thermosiphon

Closer look at each system  What makes the system unique  Basic operation and components  Freeze prevention mechanisms  Maintenance requirements  Advantages and disadvantages of direct and indirect systems

Thermosiphon System

 Passive system  No pump or controller  Thermosiphon action  Simple, reliable system

Thermosiphon System  Considerations +  Simplicity, ease of understanding by service personnel  Most common system internationally  Considerations -  Installation  Weight on roof  Heat transfer fluids – periodic check

Active Indirect System

 Two types  Indirect using a Heat exchanger Heat exchanger Differential controller Differential controller Anti-freeze solution Anti-freeze solution  Indirect drainback using a Heat exchanger Heat exchanger Differential controller Differential controller Drainage of fluid from collector Drainage of fluid from collector

Indirect Drainback  Key feature is that the heat transfer liquid in the collector and collector loop drains back into a drainback reservoir  When drained, there is no liquid in the collector to freeze

Indirect Drainback  System includes a drainback reservoir  Also uses a differential controlled to regulate pump operation  Heat exchanger is also incorporated into the system. Can be:  Within the drainback reservoir  Within the solar tank  Collector and collector loop piping must be sloped to allow proper drainback

Indirect Drainback

Drainback reservoir

Indirect Drainback  Freeze protection  All fluid drains from the collector and collector loop  Fail safe method but piping and collector must be sloped to allow complete drainage  In colder climates glycol is mixed with water for added freeze security

Indirect Drainback  Considerations +  Positive freeze protection  Thermal energy from collector is conserved in drainback tanks – not lost in exposed collectors

Indirect Drainback  Considerations –  Collectors have to withstand dry stagnation  Required elevation differences between collectors and drainback tanks  Higher collector loop pump capacity required  Collector and piping must be carefully installed to provide positive drain

Indirect Pumped System

 Use where freezing is common  Anti-freeze heat transfer fluid  Heat exchanger  Internal or external  Expansion tank  Differential controller  Various valves

Indirect Pumped System

 Considerations +  Freeze protection provided by anti-freeze fluid glycols glycols  Collector loop remains full and pressurized  Careful sloping of piping is not critical

Indirect Pumped System  Heat transfer properties of antifreeze fluids inferior to water – reduced performance  Periodic maintenance required to ensure heat transfer fluid properties have not deteriorated  Collectors and antifreeze have to withstand stagnation when summer load is satisfied early in day  Venting through T-P valve under stagnation conditions  If excessive will require refilling of system to proper operating pressure

System Certification  Systems installed should be certified to insure product safety and proper design  Florida Solar Energy Center (Florida)  Solar Rating & Certification Corporation (National)

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