5 SWIMMING POOL SYSTEMS
5.1 The Need for Low-Friction Piping and Filtration
CAUTION A low-friction piping and filtration system is essential to satisfactory solar pump
performance.
In a retrofit situation, be prepared to replace some components where appropriate. Plan
the pump installation with this in mind. You may need to leave space for a larger filter, larger pipe and/or
longer-radius (sweeping) pipe bends.
Conventional pool pump systems are often built with a relatively small filter and piping system. This
imposes substantial resistance to water flow. To compensate, a relatively large pump is installed – one
that has sufficient power to overcome the resistance. This reduces the INITIAL cost, but increases the
power requirement. With a solar pump, power is paid for up-front, so this is false economy.
SunCentric P
is not sized to handle a high-resistance piping system (with back-pressure greater than 15 PSI).
SunCentric P
swimming pool systems are sized for relatively efficient filters and piping, to minimize the
size and cost of the solar array. Before installing the pump, it is important to consider the efficiency of the
filter and piping, and to consider some simple methods to optimize its performance.
Reducing pipe friction and back-pressure
Resistance (friction) in the filter and piping loop causes
back-pressure, which is indicated by a pressure gauge. It is desirable for the back-pressure to be low.
This causes the flow rate of the system to increase. Typical back pressure for a pool system is around 15
psi (1 bar). Consider these suggestions to reduce the back-pressure and increase the flow rate.
Efficient filtration
Choose the filter carefully. A large filter will resist the flow less than a small one.
The filter maker's specifications will show the back-pressure vs. flow rate.
There are three common types of filters:
1. Cartridge
filter
This is the best. It works well at low and variable flow rates, has low pressure-drop, and no need to
be backwashed.
2. Sand
filter
This works well at low and variable flow rates, but check the specifications for pump requirements for
backwashing. The solar pump (by itself) may not produce sufficient backwash. If you have an AC
backup pump, this is not a problem.
3. Diatomaceous earth (DE) filter
This has the highest pressure drop and does not work well below a specific pressure. It may not
function consistently with a solar pump.
Double filter to reduce pressure drop
Two filters can be piped in parallel, to split the flow. This is the
equivalent of having one filter of twice the size. It will cut the resistance in half.
Efficient piping
Large pipe will minimize friction. 2" pipe has much less resistance than 1.5" pipe.
Anything smaller is not acceptable. Avoid sharp 90° elbows where possible. Instead, use long-radius 90°
elbows, 45° elbows, or flexible pipe This is especially true if 1.5” pipe is used. Even if part of the system
uses 1.5” pipe, it will help to step up to 2” pipe in places, especially where there are elbows.
Solar heating
Design a system for minimum friction, and calculate the pumping requirement carefully.
Installing a backup pump
See Section 4.9.
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