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This article was originally published in the September/October 1997 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.

 

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Home Energy Magazine Online September/October 1997


TRENDS

The Rage for Aquaria

Residential energy auditors often dismiss or overlook aquaria in their assessments. Yet nearly one in every 12 households owns at least one aquarium. Depending on the equipment used, the tanks can draw a surprisingly large load and occasionally qualify as the single largest end use in a home.

Most freshwater aquarium setups include fluorescent lighting, a filter, and an aerator. The three basic types of aquarium filters are:

  • Canister filters--large plastic canisters that have a powerful pump that forces water through a dense filter medium at high pressure.
  • Power filters--plastic cartridges that fit inside the aquarium. Water is drawn into the filter by a pump and allowed to trickle back into the tank.
  • Under-gravel filters (UGFs)--aerator creates a current that draws water through a gravel filter and up a pipe.
Aerators are commonly used in smaller tanks with UGFs or when there are few plants or lots of fish, requiring more dissolved oxygen in the water. Aerators are also used with bubble wands--decorative devices that create a stream of bubbles in the tank. Aerators are not necessary with larger tanks that have a power or canister filter, since these devices provide sufficient water movement during filtration to oxygenate the tank. Energy Use in Three Typical Types To estimate energy use in home aquaria, we surveyed shop employees and hobbyists about equipment size and run times. From this data, we constructed three different prototype aquaria and calculated the energy consumption of each (see Table 1).

Our prototypes' energy usage barely approached that of a microwave oven. Nevertheless, sometimes the loads can be much higher.

Table 1. Comparison of Aquarium Energy Use* 
Tank Category Capacity (Gallons) Energy Use (kWh/yr)
Small 10 90-120
Medium 30 160-200
Large 55 280-400
* Values are based on use of one or two 10W-20W fluorescent light tubes with 10 hour per day run times; 4W-15W filters with 24 hour per day run times; and 1.5W-4W aerators with 24 hour per day run times.
Sea Water and Plants Can Be Demanding Saltwater tanks have equipment needs similar to those of basic freshwater tanks. Many of these tanks also use power heads--pumps to increase water movement--which draw a substantial amount of energy and run constantly. Small tanks typically use two small power heads--each rated at 8W and using approximately 140 kWh per yr. Total energy consumption in these small tanks ranges from 250 to 280 kWh per year. Medium and large saltwater tanks may have two large power heads, each rated at 25W. Power heads in these tanks use 440 kWh per year. Medium saltwater tanks use 740 to 780 kWh per year, and large tanks use 1,000 to 1,100 kWh per year.

Some hobbyists go for a lush plant growth in their tanks. These densely planted tanks need extra lighting. A small tank will use 20 watts of lighting (approximately 2 watts per gallon), and the annual total energy consumption will range from 110 to 140 kWh. Medium tanks will require nearly 60 watts and will use 300 to 340 kWh per year. The lighting requirement of a large tank is more than 100 watts, and energy consumption will range from 570 to 650 kWh per year.

Coral Reefer Madness? Reef hobbyists build tanks that simulate the conditions of a tropical coral reef. These are the largest, most complex of all the aquaria. They also generally consume the most energy.

The typical reef setup uses a tank and gravity-fed sump combination. After the water flows down to the sump, a powerful pump returns it to the main tank. Another pump pulls water through a protein skimmer, removing amino acids, lipids, phosphates, and other nutrients needed by algae. Reef hobbyists also like to use power heads, which they frequently control with a wavemaker. Because corals do best when water surges in different directions, the wavemaker turns power heads on and off to recreate turbulent reef conditions.

Reef tanks use an average of 6 watts of lighting per gallon, which, in combination with the pumps, frequently creates tank temperatures well above the tropical temperature of 75°F. As a result, the tanks generally need cooling rather than heating. Cooling is often achieved with fans located below the lights that blow air across the water increasing evaporation and cooling the tank. Sometimes, a small air conditioning unit called a chiller is attached to the tank. The fans are relatively inexpensive and are cheaper to operate than the chillers (chillers are rated at approximately 1,800 watts); they are thus the favored option among hobbyists.

During the summer, the fans may run all day long. In other months, they run only when the lights are on. Some reef hobbyists have also been known to run the house air conditioning unit to keep room temperatures low.

So how much energy does a reef tank use? We compared two prototype tanks, a 55-gallon and 180-gallon tank, using typical setups. We found that the 55 gallon tank used around 3,000 kWh per year, while the 180-gallon tank used over 6,000 kWh per year. To put these numbers in perspective, the energy used by the smaller tank was greater than the energy used by a typical home's central air conditioning system and lighting combined. Energy used by the larger tank was greater than the energy used by a typical home's central electric heating and refrigerator combined.

Reef tanks, such as the one pictured here, have circulation, lighting, and cooling needs that can make them a household's single biggest energy consumer.
Something's Fishy Nationwide Ninety percent of all aquaria in the United States are freshwater tanks; 9% are regular saltwater tanks; and the remaining 1% are reef tanks. Based on a detailed breakdown using survey data from the Pet Product Manufacturer Trade Association, overall national energy use for these aquaria is estimated at 2.4 terawatt-hours per year. Freshwater tanks consume 56% of this energy, while saltwater tanks consume approximately 19%. Amazingly, reef tanks are responsible for 25% of aquarium energy consumption nationwide.

These numbers clearly indicate that auditors need to take careful stock of aquarium energy use. That's no fish story!

--Marla Sanchez and Alan Meier
Marla Sanchez is a senior research associate at the Lawrence Berkeley National Laboratory in Berkeley, California.

 


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