How to reuse the condensate water from air conditioners?

Air conditioners release varying amounts of water, depending on the relative humidity of the room in which they are located. This condensation water is produced when humid ambient air passes through the air conditioner’s evaporator: the surface temperature of this exchanger being lower than the dew point temperature (temperature at which the water vapor present in the air turns into liquid water), the moisture in the air condenses and flows into the condensate tray.

On mobile systems, this condensate can easily be collected. In fixed installations, an evacuation system is provided.The quality of the condensation water produced by air conditioners can be reused for crop irrigation, for certain industrial processes requiring water or for various domestic applications (watering plants, supplying water for irons, or supply of toilet flushes). According to recent studies, after disinfection, this water can even be drinkable!

 

In a study published in August 2019 ^[1], a team of researchers studied the quality of condensate water to assess the different possibilities for reusing it. The study was carried out in two cities in Palestine, where water resources are precious.

 

The water samples were taken in plastic bottles, and the sampling locations were chosen randomly in two different cities: in shops, restaurants, residential buildings. Two series of tests were carried out.

In the first, performed immediately after sample collection, temperature, pH, electrical conductivity, dissolved oxygen and dissolved solids were measured.

 

In the second, carried out in a laboratory, the researchers measured the turbidity of the water, the biological oxygen demand, the chemical oxygen demand as well as the levels of different chemical elements (including among others arsenic, sulfate, copper, selenium and aluminum). Heavy metals have also been sought.

 

The results obtained were compared with the recommendations provided by the Palestinian Standards Institute (PSI) for drinking water and irrigation water. The results are presented in the following table:

 

 

These results show that the quality of condensate water is good enough to be reused as irrigation water. With regard to drinking water, the measurements carried out on turbidity and biological and chemical oxygen demand do not fully correspond to the national recommendations.

 

The researchers also assessed the amount of heavy metals contained in the samples. In some of the samples, the following elements were found: Cu, Fe, Al, Cr, Ba, Zn and Mn.

 

The study concludes that apart from a sample where the manganese contents were too high, the reuse of condensate water for irrigation or even for drinking does not present any particular risks.

The large amounts of water collected (between 8.63 and 15.1 L per day per air conditioning unit), if reused, could help reduce the demand for fresh water in Palestine.

 

Another study published in Renewable Energy and Environmental Sustainability ^[2] investigates the possibility of reusing condensate water as drinking water. The study was also conducted in a hot country where natural water resources are scarce: Oman.

 

Different water disinfection techniques are reviewed: ultraviolet radiation, chlorination, heating water to 63°C, ozonation, and finally solar disinfection. It is the latter technique that has been explored in the article.

 

According to the researchers, sun rays can contribute to the destruction of germs, viruses and other bacteria due to the presence of infrared and ultraviolet rays, after a filtration process to remove suspended materials.

 

For the experiment, condensation water was collected in Pyrex bottles previously sterilized using an autoclave. Samples were collected in three cities at different dates.

 

Different samples were taken in the three cities. During the analysis, the duration of exposure to sunlight as well as the temperature were considered.

The results show that the properties of the collected water are close to those of distilled water and that all Coliform and E-Coli bacteria are destroyed after 2 hours of irradiation at 43°C.

The sun disinfection method could therefore be used to make condensed water safe to drink in places where other disinfection methods are not available. This technique has the advantage of being particularly economical.

 

Sources :

 

^[1] Lubna Siam, Issam A. Al-Khatib, Fathi Anayah, et al. Developing a Strategy to Recover Condensate Water from Air Conditioners in Palestine. Water, 2020. doi: https://doi.org/10.3390/w11081696

^[2] Iessa Sabbe Moosa, Laila Masoud Rashid Al-Iessi, Hussein A. Kazem. Freshwater production and solar disinfection of water released from the air-conditioning cooling system: an experimental investigation. Renewable Energy and Environmental Sustainability, vol. 5, n. 9, 2020. doi : https://doi.org/10.1051/rees/2020004