Condensate Water Introduction


The Science

When water vapor in the air (often described as humidity) comes in contact with a colder surface, the water changes from a gas to a liquid and collects onto the cold surface.  This is most often observed with an ice cold beverage container on a humid day, where water droplets collect on the outside surface of the glass full of iced tea or cold ale.  The water vapor in the air that becomes liquid is referred to as condensate.  While the condensate collected on a cold beverage is small and mostly considered a nuisance, the condensate that collects on refrigeration equipment is of significant volume and a potential alternate water source.

Condensate from Air-Conditioning Equipment

Air-conditioning uses a closed-loop compression-decompression cycle of a refrigerant (freon, CFC, HCFC, etc.) to absorb heat from inside a building, then transfer that heat to the outside.  With central air-conditioning, the cold refrigerant passes through the heat exchanger coil inside the building (often “A-coils” inside the plenum), where a fan blows air from inside the building through the coils, cooling the air, and returning the cold air into the occupied space.  As the air passes through the cold A-coil, water vapor in the air turns to liquid when it comes in contact to the cold coils.  This condensate water must be removed to prevent water damage to the equipment and the building structure.   Most often, the central Air Conditioner (AC) condensate drains off of the A-coil into a drip pan; then runs into a hose connected to the sewer system.  A central AC for an entire home can collect 5 to 20 gallons (18.9 L to 75.7 L) of condensate water per day, equating to more than 300 gallons (1135.3 L) per month in the summer.  Depending on the location of the central AC A-coils, this water can be easily captured, stored and utilized.

On a window AC, the condensate water can often be observed dripping out the back of the AC, from the outside portion of the equipment.  A window AC will collect only 1 to 2 gallons (3.78 L to7.57 L) of condensate water per day; often too small of a quantity to invest in a method to capture and use the water.   Sometimes, simply placing a bucket underneath the window AC can collect enough water to irrigate a few shrubs and flowers around the home.

Non-residential buildings are also potential sites to collect and use condensate water.  Wherever there is air-conditioning, there is condensate water collecting on the cooling coils; and this water must be diverted out of the building.  Like in homes, the condensate is most often sent to the sewer drain.  Depending on the HVAC design, the condensate water might be collectible for alternate uses on the building site.  The amount of condensate water can range form 3 to 10 gallons/day per 1,000 square feet of air-conditioned space( 11.35 L to 37.84 L /day per 92.9 square meters); largely dependant on local climate, HVAC design and type of use for the building.   A 10,000 square foot (929 square meters) office building can produce more than 15,000 gallons (56.8 m3) of condensate water per year.

Condensate Water Quality and Uses

The quality of this water is essentially the same as distilled water; mineral free and a Total Dissolved Solids (TDS) level of near zero.  The water should NEVER be used for human consumption as it may contain heavy metals from contact with the cooling coils and other HVAC equipment.  The lack of minerals in the water (similar to distilled water) also makes it corrosive to most metals, especially steel and iron. 

The water’s low-mineral quality and lack of sanitizers (chlorine, chloromine, etc.) makes it excellent for the purposes of irrigation.  In the residential sector, this water should be used similar to harvested rainwater; irrigation for plants not intended for human consumption.   Although condensate water does not have the health risk of containing biological pollutants commonly found in rainwater (bird feces), there is a slight risk of lead contamination (from solder joints in the evaporative coils) building up to dangerous levels in soil continually irrigated with the water.

In non-residential sites, one of the best uses is make-up water for the cooling tower.   For most cooling towers, a portion of cooling tower water is dumped several times each day to remove the build-up of minerals. (See Cooling Tower Section for more information.)  The dumped water requires replacement in the system, and the replacement water is usually potable water from the local water utility.  The amount of water removed and replaced is highly dependant on the level of minerals, measured as Total Dissolved Solids (TDS) contained in the potable water supply.  The greater TDS level of the source water, the greater the water use of the cooling tower.  Not only can condensate water be used instead of potable water (TDS levels of 150 to 800), the condensate water has virtually no minerals (TDS level of 0 to 25).   This allows the cooling tower to dump water less often.

In commercial and industrial processes, there are a myriad of applications to use condensate.   One should look beyond just irrigation and cooling towers.  It may be possible to use condensate water for water cooled equipment, decorative fountains and water features, evaporative coolers, rinse water for washing vehicles and equipment, water for laundry operations, and industrial processes.   Some newest generation of air-conditioners actually use the condensate to help cool the hot condenser coils of the AC itself.  As water efficiency concerns increase, the variety of uses for condensate water will grow.