Apricus Solar Water Heating System Installation and Operation ...

Apricus Solar Collector Installation & Operation Manual - USAstorage tank and disturb stratification, which can lower the entire tank temp during low solar productionperiods. A variable speed pump control will ensure that the flow rate matches the heat output and limit tankde-stratification.g) Correct Pump Choice: Any pump used for solar loop circulation must be able to handle continuous useto at 232°F (110°C) and higher, if required by system design. The solar pump should always be installed onthe Supply (aka Flow) Line (i.e. pumping to the collector and away from the heat exchanger or tank) thuslimiting exposure to high temperatures. In addition, a check valve should always be installed after the pumpto prevent back flow, and nighttime thermo-siphoning, UNLESS the system is a drain-back, which shouldnever have a check valve installed in the solar loop. See Apricus system diagrams for reference. TheApricus pump stations incorporate a flow meter, pump and check valve. Refer to section 7 and 8 for moredetails on pump station operation.h) Flow Rate: The flow rate through the collectors should be determined under the following considerations:i) Turbulent flow through the header is provides for optimal heat transfer during high solar output and isachieved at flow rates of 0.8 gpm (3 Lpm) and greater. This is commonly exceeded in commercialapplications when 2 to 5 collectors are connected in series. In a single collector installation, this flowrate will generally only be achieved during summer. Running a high flow rate during the winter toachieve turbulent flow is NOT recommended or required as the solar heat output is not as high, andexcessive ON/OFF cycling of the pump will occur which can cause premature pump failure.ii) Temperature rise of the heat transfer fluid during each pass through the collector manifold(s) can beadjusted by changing the flow rate. Reducing the flow rate by half will double the temperature rise perpass. Normally, a temperature rise of 10-30°F is an acceptable range. Lower delta-t levels(temperature rises) attained at higher flow rates may cause the pump to turn ON/OFF too often.Extremely high delta-t levels produced by low flow rates will decrease collector efficiency. Thisdecrease is far less acute with evacuated tubes than that experienced with a flat plate collector andmay be acceptable, especially if pressure drop is an issue.iii) Pressure drop will increase at higher flow rates. For example, if installing 5 collectors in series, aflow rate of 4 gpm will result in a pressure drop of equal to 15 ft of head, while 2.5 gpm will result inmuch lower pressure drop of 6.25 ft of head pressure and, therefore, would allow a smaller pump to beused. When using a lower flow rate of 2.5 gpm (0.5 gpm per 30 tube collector), a higher temperaturerise will result per heat transfer fluid cycle, but even during clear summer conditions will only result in a40°F rise at the outlet of the final collector of a row of 5, which will not result in significant efficiencylosses.iv) The following table provides estimated temperature rises at various flow rates:Flow Rate per 30 tubes2Temp Rise @ 150Btu/ft(Clear Winter Day)2Temp Rise @ 320Btu/ft(Clear Summer Day)0.2 gpm (0.75 Lpm)° °30 F (16.4 C)0.4 gpm (1.5 Lpm)° °15 F (8.2 C)0.6 gpm (2.3 Lpm)° °10 F (5.5 C)0.8 gpm (3 Lpm)° °7 F (4.1 C)1 gpm (3.8 Lpm)° °6 F (3.3 C)° °85 F (35 C)° °42 F (17.5 C)° °28 F (11.7 C)° °21 F (8.7 C)° °17 F (7 C)v) As a general rule the ideal average flow rate for Apricus evacuated tube solar collectors is:0.026gallons/tube/min so AP-10 = 0.25gpm, AP-20 = 0.5gpm, AP-30 = 0.8gpm.Copyright 2011 – Apricus Inc Doc: A7-05.4.1.4-PB-1.9 Page 21 of 126