With new building codes in effect in Florida, I’ve been asked quite a lot about variable speed vs. variable flow pumps, especially with solar pool heating systems. The answer turns out to be a bit complex. The simple answer is that a variable speed pump will give you better trouble-free performance while still resulting in significant energy savings. The whole story is more complex.
At first glance, the features of a Variable Flow pump like the Pentair Intelliflo VF seem perfectly suited for a solar pool heating system. The pump would operate at a constant flow rate that is optimal for solar pool heating, adjusting the pump speed as necessary to meet changing pressures from water features or dirty filters. An automatic controller could further optimize performance by adjusting flow rates depending on the heating source and features being used. Unfortunately, there are two problems with this approach:
- Variable Flow pumps are designed to shut off when there is a significant flow rate change. In some cases the enabling or disabling of a solar pool heating system will result in a fault that shuts the pump off.
- Variable Flow pumps on the market do no meet the Safety Vacuum Release System (SVRS) requirements for the Virginia Graeme Baker Act and incorporated in the Florida Building Code 2010 that went into effect March 15, 2012.
The best solution is to install a variable speed pump like the Pentair Intelliflo VS. This pump varies in speed, which loosely translates into varying flow rates. Because in any given configuration a pool circulation system has a relatively stable pressure, we can set up a variable speed pump to act essentially like a variable flow pump. We “dial in” speeds for pool heating, features, and cleaners with a flow meter at the time of installation. Optimal flow rates are selected to optimize the performance of heaters and pool features with energy savings. Flow rates decrease when filters become clogged, but this is easily remedied by proper maintenance practices.
However, we need to again consider the Virginia Graeme Baker Act and SVRS systems. If your pool does not meet certain guidelines for safety, a SVRS system is now required when replacing a pool pump or pump motor. Fortunately, variable speed pumps come in SVRS models like the Pentair Intelliflo VS+SVRS. The downside is that nuisance tripping of the SVRS system can still occur with the solar pool heating system, particularly at low flow rates. In our experience, the corrective measure is to run the speed at slightly higher speeds than otherwise required to not trigger the SVRS. Unfortunately, you will not be able to take full advantage of the energy savings of the variable speed pump, but the savings will still be spectacular. The best capability is the ability to run the pump at optimal speeds based on heating source and pool features with an automatic controller. We can successfully integrate a variable speed pump, SVRS, and solar pool heating this way.
To recap, the ideal energy saving pool pump for solar pool heating systems is a variable speed pump without SVRS if your pool plumbing allows it, or a VS+SVRS pump if you must upgrade due to new codes. A Variable Flow pump may work, particularly at higher flow rates, but it is not advised with solar pool heating systems. If you don’t know whether a SVRS is required on your pool, your friendly Fafco Solar representative can tell you!