Benefits of using heating system booster pumps

by arslan_ahmed | July 28, 2023 11:00 am

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By Tom Soukup

Many heated pool and spa systems rely on a single pump or pump package to provide flow for the filtration system and heating units. While this simple approach has provided the bare necessity for circulation of pool water for decades, it is far from an optimum design. When properly sized and installed, providing a separate pump for the heating equipment extends the lifecycle of all system components, lowers power and fuel consumption, and reduces maintenance.

In commercial pool applications, filter pumps are specified based on the size of the pool and the turnover rate dictated by the local governing body or International Swimming Pool and Spa Code (ISPSC). For example, in Pennsylvania, a commercial pool requires a turnover once every six hours, and spas must turnover once every 20 minutes.

All too often, filter pumps are sized to meet the required flow rate and overcome filter head loss, with no consideration given to the flow requirements and head loss of the heat exchanger(s) in the system. This is an issue because heating equipment has a manufacturer-specified minimum flow rate requirement to protect the heat exchanger and attain maximum efficiency.

Most systems seen in the field use an insufficient means of providing flow to the heating unit(s). This almost always includes two tees with a manual diversion valve in between.

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This diversion valve is, in theory but rarely in practice, adjusted to provide the correct flow rate through the heaters. Often, the valve is not set correctly because the system lacks flow meters to indicate what the actual flow rate is through the heat exchanger(s).

Moreover, even if a valve is set to the correct flow rate a manual valve does not modulate to reflect whether the heaters are running or not, meaning water is constantly flowing through the heat exchangers. This not only wastes power, but constant circulation through the heat exchangers increases mineralization inside. This reduces the heat transfer efficiency of the heater and further increases pumping resistance, as the channels within the heat exchanger become narrower. It is similar to plaque buildup inside the arteries of the body.

In the less-than-desirable but all-too-common scenario described above, the issue is, the filtration system and the heating system are not hydraulically separated. Both loops are served by the same pump, and the pump is typically not sized for the additional head loss of the heat exchangers.

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Aside from the inadequate flow for both the filters and the heating appliance, this creates a scenario in which the pump draws more amperage than intended, leading to wasted energy and premature pump failure.

Marginal improvement

Some manufacturers have recognized this issue and have tried to make an improvement. Some larger commercial pool heaters ship with a built-in pump that serves the heat exchanger of the appliance. However, when you look at the specifications of the appliance, there is a very specific acceptable “developed pipe length” the provided pump can fit. Developed pipe length is the length of the pipe that can be accommodated by the pump, including the pressure drop created by elbows and other fittings.

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For example, the installation and operation manual of a pool heater may specify that no more than 4.5 m (15 ft) of developed pipe length can be accommodated. Some installers may use no more than 4.5 m of pipe, but when elbows and fittings are accounted for, the real head pressure of the loop equals about 18 m (60 ft) of developed pipe. In a real-world application, it is difficult to fall within manufacturer specifications when the pump is supplied with the heating unit. The manual rarely reflects a real-world application.

Custom solution

The author’s company customizes all their systems by hydraulically separating the filtration loop from the heating appliance loop and accurately sizing the pumps for each.

Instead of using a diversion valve to supply water to the heating appliance, the company provides hydraulic separation through closely spaced tees, so the flow rate through the heater loop does not affect the flow rate through the filtration system or vice versa. The independent heating loop is circulated with a variable frequency drive (VFD)-powered pump. The company calculates the developed pipe length and heat exchanger pressure drop to select a pump. This gives a number very close to the actual performance needed, but actual pump performance is perfected through one final step.

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By installing a flow meter on the effluent side of the heat exchanger, the VFD on the pump can be calibrated to perfectly match the specifications provided by the heating appliance manufacturer. If the heat exchanger is not getting enough flow, the speed of the pump is increased; if it is too high, the speed is reduced.

Through a unique control strategy, the company only runs the booster pump when there is a call for heat. As a fail-safe, they also provide secondary flow-proving, to ensure the heaters will not fire without flow through the heat exchanger.

Through the controls, a cool-down period is programmed after the call for heat, and it protects and extends the life of the heat exchanger. Often, a procedural problem in the field occurs when maintenance personnel backwash filters or turn off the pump off any reason, without either shutting off the heaters or giving them a cool-down period. A safe cool-down period can be determined by the temperature differential between the supply and effluent side of the loop, but five minutes is typically sufficient.

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Conclusion

Installing a heating system booster pump, hydraulically separating the filter loop and heating loop, and using a well-designed control system provides many significant benefits. Appliance heat exchangers are protected from corrosion, sooting, and mineralization, service life of the system’s filter pump is increased, electrical consumption is reduced, fuel efficiency is increased, and maintenance is reduced.

A vast majority of existing pool heating systems are not designed or installed as effectively as possible—this leaves a lot of room for improvement in the pool and spa industry.

Author

Tom Soukup is the principal of Patriot Water Works Co., with more than 20 years as a hydronic designer and installer. He specializes in high-efficiency and green technology and brings his expertise to custom commercial work, pool heating, and agricultural projects. He can be reached at twsoukup@patriotwaterworks.com.

Source URL: https://www.poolspamarketing.com/trade/features/benefits-of-using-heating-system-booster-pumps/

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