Tech Talk 4
Efficiency versus Type ...
Select the right type of aerator for the application.
An aerator's standard aeration efficiency (SAE) is an important consideration when comparing one aerator with another.
The SAE can be calculated by measuring the aerator’s oxygen transfer and the amount of energy used per horsepower, per hour, under standard conditions. An SAE of 2.1, for example, means that 2.1 pounds of oxygen per horsepower, per hour, are transferred to the water under standard conditions. The higher the SAE, the higher the oxygen transfer, the higher the efficiency.
However, SAE numbers are a fair comparison only when comparing aeration equipment of the same exact type. You cannot use the SAE as your only tool in the selection of an aeration system. Before looking at the SAE numbers, choose the right type aerator or oxygenator for the job.
Here are some examples (analyze the differences):
- A surface aerator like our Kasco 3/4-hp (with an SAE rating of 2.9) may be a good choice where the volume of water is small and the stocking density is high, such as in a culture tank or small pond. It may be a poor choice, however, if cold water temperatures are required when air temperatures are warm (summer trout culture), because both the motor and the airborne water droplets will add unwanted heat.
- A surface aerator would be a poor choice for a large or deep pond. Without moving water away from the aerator, it will continue to pump the same water over and over again, adding no oxygen where it is needed.
- A surface aerator may be excellent in emergencies because it quickly raises the oxygen level in a small area. If trained, the fish will move to that location. Again, it will not be a good choice for full-time aeration because it will not disperse oxygen throughout the pond.
- A diffused air system (with an SAE rating of 2.7) may be the best choice for multiple tanks and ponds because the energy source (blower) can be centralized and just the right amount of energy (compressed air) can be easily directed where it is needed. What appears to be lower SAE efficiency (2.7) is more than offset by comparative application efficiency.
- Water-moving aeration devices like paddle wheel type aerators are excellent choices for medium and large ponds where movement of oxygenated water away from the aerator is most important.
- If destratification alone will solve a bottom oxygen problem, only a few air diffusers may be needed to accomplish this. For instance, a 10-acre lake, 15' deep, may need only 3/4 hp (see Lake Aeration). Only 1 cfm of air may be needed to aerate a 1/20-acre pool when raising tropical fish compared to 6 cfm per pool using airlifts.
- A destratification system, such as our Great Lakes® aeration system, should not be used as an emergency aerator because it very quickly mixes the water. Its rate of oxygen transfer is excellent; however, it cannot raise the oxygen level of such a large volume quickly enough to avoid a fishkill. It can actually aggravate the problem.
- Even noise is a consideration above and below the water surface. Pentair AES diffused air systems are preferred over agitators in bait stores, improving conditions for both the fish and the employees. As more of our research is conducted under water, we are increasingly aware of underwater noise produced by devices such as paddle wheels, agitators, airlifts and drilled pipe spargers (our Sweetwater® air diffusers have a barely audible hiss). Some fish breeders have reported that diffused air is the only aeration method they can use that will not disrupt breeding. The situations and considerations are virtually endless, so take some time to research the best aeration method for your particular application. For the price of a phone call, you can discuss your application with a Pentair technician and get an expert opinion (877-347-4788).
Standard aeration efficiency tests conducted at Auburn University showed that the Pentair AES Sweetwater® diffuser and 1-hp blower combination yielded a 2.71 SAE. Prior to rating our diffusers, Auburn gave air diffusers in general an SAE rating of only 1.6. That 70 percent increase illustrates how much efficiency can change when the right combination is used.