Thoughts to Combat Both ‘Water Mixing' and ‘Freeze Protection' in Water Storage Tanks

By: Kenneth A. Eichenberger, Caldwell Tanks, Inc.

1.  There are two types of mixing systems in place in the market today: PASSIVE and ACTIVE, and they each succeed really well in their proper environments.

2.  PASSIVE systems are hydrodynamic mixing systems and other jet aeration types of systems and products. These systems cause water movement or 'mixing' only during the filling of the tank and for short durations thereafter when warmer water entering rises to the top.

3.  ACTIVE systems are Pulse Hydraulics' 'Hydro Pulse' and SolarBee's GS-12 unit. These ACTIVE systems are truly ‘reactive’ because they can be programmed to respond to water system needs as seasonal weather moves in and out as well as water quality variations dictate. These systems are either controlled (PHI) or on full-time (SolarBee). Both systems can be equipped with SCADA outputs if the water system already has this feature. The PHI system has no moving parts inside the tank and all items requiring maintenance or possible service can be well protected inside the base of the CET, FLC, & PED shaft plus has a broad capability of providing visual or audible of operable function. For the LEG or FB style of tank, this unit can be provided inside of a small vandal-resistant building. The SolarBee product is an electric motor submerged in the tank with apparently not much maintenance requirements (options) and no immediate visual or audible feedback of operable function on the base unit.

4.  MIXING the tank is different from FREEZE PROTECTION. Mixing is for water quality while Freeze Protection requires water movement and sometimes insulation or heaters to prevent or help reduce ice build-up. The industry acceptance is that total volume of tank turn-over to provide the best opportunity of preventing ice-buildup is more than 30% of the total volume should be replaced each day (depending on ambient conditions of inlet water temperature and air temp of tank).

5.  With very little turn-over for the initial few years of some large capacity tanks in the colder climate areas, then a passive mixing system alone will not be sufficient to address the freezing of the water inside the tank. It is our understanding that you wish to hand over to the city a tank in 'as good of a condition as when it was first built'. With Caldwell also having a 'Tank Asset Preservation' division, it is in the best interest of all parties to build and maintain a tank that will make it to and beyond the prestigious 'Century Club'.

6.  The bottom line is that if the environment is right, simply moving water alone is not a guarantee that the top portion of water is not going to freeze. The goal, then, should be to minimize tank damage from ice buildup in extreme cold climates while also preventing stagnation, stratification, and short-circuiting issues of the water quality.

7.  I would be remiss if I did not mention that there are also heater systems (probably the least efficient) used in dedicated fire protection tanks as well as pump-recirculation systems that are also common to extreme cold weather applications. The heaters usually add many tens of thousands of dollars to the total cost of ownership but have other benefit/trade-offs. The pump-recirculation systems have been used in the coldest climates, but to our knowledge, there is not an independent third-party company actively marketing a 'packaged' product similar to other active mixing sytem providers in the marketplace. We can further investigate this avenue if desired as we have constructed numerous tanks with this type of solution, but the total cost of ownership seems significantly higher than the previously listed Active system solutions presented.

8.  We try to provide fair and open competition by laying out several options and letting your future owners decide what they want. The passive mixing systems are used in hundreds of tanks a year. The Pulse Hydraulics ACTIVE system has been used in small and large capacity ground and elevated water tanks as well as hundreds of water-treatment tanks. The SolarBee product mentioned above is brand new to the marketplace but they also offer more comprehensive products. We have provided links below to each system for your owner's consideration.

SOLARBEE's Active System (just released the GS-12 to the market late March 2011): and

Caldwell Connect