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Solar Pool Panel Header Size Requirements

Residential and small commercial systems utilize 1.5” Headers for arrays up to 10 panels. Larger residential and commercial systems utilize 2” headers where arrays contain up to 16 panels, or where overall flow is critical and must be kept below the total flow rate of the commercial pool. Friction loss for water flow through plastic schedule 40 PVC pipe is based on the Hazen-Williams Equation with a Hazen-Williams coefficient c = 140. Velocities between 7 to 10 feet per second are common. In general velocities above 5 feet per second should be avoided when possible. With the Vortex solar panel system, the flow rate should be regulated between 3 (minimum) and 5 (preferred) gpm per panel to prevent excess increased pressure in the pool system while still delivering proper heat transfer. For a 10 panel system, this yields a flow rate of between 30 to 50 gpm. The header manifold distributes this flow across all of the headers as the water passes into each panel in the series; based on the average 25 gpm rate, the velocity in a 1.5” header is only 4 ft/sec with a friction loss of 1.7 psi/100ft through the header – this rate is acceptable for standard flow characteristics. Since the friction loss per panel is relatively low, it has a very small impact on overall system Friction Head. Utilizing the 1.5” header reduces overall system cost. Increasing the header size to 2” allows for the same velocity with more panels, but for residential systems where an array does not exceed 10 panels is not required. The PVC transport plumbing between the pump/filter area and the solar array(s) must be a minimum of 1.5” for systems up to 6 panels, and 2” for systems up to 10 panels – 2” is recommended even for less panels in order to minimize increased friction losses. This is because all of the flow for the solar panels must be transported in the single pipe, and there are generally a large quantity of elbows required to transition from the filter to the roof system and back. Fittings and valves have less friction loss as the size increases relative to the flow, so the larger 2” plumbing is required to keep the overall increase to system pressure at a minimum. The flow rate for 2” PVC at 5 ft/sec velocity is 50 gpm, and at 9.8 ft/sec is 100 gpm. Most pool systems have undersized plumbing, and often have a pump that is oversized – delivering flows that exceed the allowable velocity in the piping. Pools with 1.5” PVC and a pump larger than 1hp, should always increase the pipe size to the solar system to 2” in order to keep pressure losses reduced. Pools with 1.5hp and larger pumps should be evaluated for proper pipe size; it is generally impractical to increase underground plumbing; however, there is a definite advantage to increasing the size of the pipe and fittings at the equipment pad (from the ground level trough the pump and filter, and all valves back to the pool return at ground level) to 2.5” to 3”. This will greatly reduce overall system friction losses, and will result in decreased system pressure and reduced operating costs of the pump. 

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