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Encore Technical Director David Davis
Encore Technical Director David Davis.

Free—and Green—Toilet Flushing

Encore Cistern is described as “the most environmentally friendly cistern, as it uses a free, sustainable water supply that has previously been drained to waste.”

Here in Broward County, Fla., the mechanical and plumbing codes require the collection of condensate from cooling coils and evaporators in air-conditioning systems larger than 5 tons. If there is a cooling tower on site, the condensate is to be returned to the tower as makeup; if there is no cooling tower, the condensate is to be discharged to “an approved place of disposal.” As I wrote in July 2013, the idea is to avoid discharging condensate to the sanitary sewer system, which wastes water and energy and adds load to wastewater-treatment facilities. Landscape irrigation is one obvious use of condensate not being returned to a cooling tower. Now a UK-based company has introduced what it describes as the world’s first toilet cistern—what we commonly refer to as the tank—that uses air-conditioning condensate for flushing.

In a press release dated July 6, 2017, Encore Cistern (Encore is an acronym for Environmental Condensate Recovery) is described as “the most environmentally friendly cistern, as it uses a free, sustainable water supply that has previously been drained to waste.” The manufacturer claims it would save 4.7 billion liters (1.2 billion gal.) of water annually—the equivalent of the water in more than 1,800 Olympic-size swimming pools—if installed in the 191,832 rooms in the 1,477 hotels currently being built in the United States. Other target markets include commercial office buildings, condominiums and apartment buildings, public buildings, and any other new or existing building with relatively large numbers of concealed-installation toilets. Also, toilets equipped with the Encore Cistern apparently would qualify for LEED and Green Globes points.

The device’s theory of operation appears fairly straightforward. The cistern holds 18 liters (4.8 gal.) of water in two stacked chambers. The bottom chamber, which is connected to the building’s potable-water supply, holds 6 liters (1.6 gal.), which compares to the 6-liter (1.6-gal.) maximum flush rate of U.S.-manufactured toilets (with 4.8 liters [1.28 gal.] preferred for green buildings). The top chamber holds 12 liters (3.2 gal.) and is connected to the condensate drain. When the toilet is flushed, the bottom chamber empties and refills with condensate from the top chamber. In the case of multiple flushes close together or when no condensate is available, the cistern uses potable water, as in a conventional toilet. During periods of inactivity, any excess condensate simply is drained through the sanitary connection. The system is gravity-fed, requiring no pump.

Other benefits cited by the manufacturer include easy installation, just as a conventional cistern; compatibility with industry-standard rack mounting; and—unlike other reclaimed-water options, such as municipal systems and rainwater harvesting—relatively low first cost resulting in short payback periods. To comply with Florida code, greywater (including rainwater) must be filtered and colored (with special dye) to be used in a building. Condensate being used for cooling-tower makeup, however, has no such requirements, and several of my colleagues who are very conversant with the applicable codes are of the opinion condensate connected to the Encore Cistern would require no special treatment and could be piped using Schedule 40 PVC. If there are any Florida mechanical/plumbing-code experts reading this who don’t agree, please comment below.

Encore Technical Director David Davis.

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