Apricus Solar Water Heating System Installation and Operation ...

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Apricus Solar Collector Installation & Operation Manual - USApotable water, but because the pressure is independent of the water main pressure, fluctuations in pressurewill not occur.Refer also to 3.6.2 for more information about pressure and water boiling.3.5. Pump Selectiona) Pump Size: For most domestic installations, using a 3-speed pump is advisable in order to chose aspeed to suit the pressure drop of the piping. Speed 1 is generally suitable for a short pipe run, such as on asingle story house. Speed 3 (~90-100Watts) can normally service a 3 story, 90 tube, pressurized system(not necessarily a drain-back). If the pipe run is very long or there are more than 90 tubes, a larger pumpmay be needed. The Apricus Closed Loop Pump Station uses a 3-speed Grundfos UPS 15-58 FC cast ironbody pump and the Apricus Direct Flow Pump Station has a single-speed Grundfos UP 15-29 SFC stainlesssteel body pump.If multiple banks of collectors are installed in parallel, the head loss should be calculated based on thelongest pipe run through a single bank of collectors and then, the pump can be sized to meet the total flowrate requirements.b) Pump Body Material: Cast iron pumps may ONLY be used for closed loop or systems; they will rust andfail if used with potable water. Brass/bronze or stainless steel body pumps are suitable for direct flowsystems because the material has good corrosion resistance and is suitable for potable water use.c) Pressure Drop Curve: The Apricus 30 tube solar collector header has the following pressure drop curve.The pressure curve will be slightly less for Apricus 10 and 20 tube collectors.d) Use a Flow Meter: Always install a flow meter after the pump to ensure that flow rates are at suitablelevels and can be monitored. Most flow meters will incorporate a restrictor valve allowing the flow to be set.If significant restriction is required, a slower speed or smaller pump can be used, which will save electricity.e) Variable Speed vs ON/OFF: The most efficient option is to use a controller with a variable speed pumpfunction that can regulate the pump speed to achieve the desired temperature rise (delta-t). With a normalON/OFF delta-t setting, “shunting” of water can occur. Shunting is when the pump shuts down before all ofthe heated fluid can reach the tank. The hot fluid sits in the return line and looses heat until the next ONcycle, before it finally is delivered back to the tank. This is especially true when high flow rates are usedand when there is a long pipe run. A variable speed control helps to prevent this from happening bysending the heat back into the tank as it is produced and results in higher overall system efficiency and heatoutput.f) Direct Flow - Flow Rate: A high flow rate in a direct flow system may cause turbulence in the solarCopyright 2011 – Apricus Inc Doc: A7-05.4.1.4-PB-1.9 Page 20 of 126
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
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