Gardeners' Dirt: Condensate irrigation strategy
By Alex White - Victoria County Master Gardener InternEdited by Charla Borchers Leon
May 31, 2012 at 12:31 a.m.
Air conditioner (A/C) condensate is pure water, moisture condensed from air passing over cooling coils of an air conditioner. Condensate is free of minerals and impurities and a valuable by-product of modern climate control systems in large buildings where it is recycled into cooling towers and used to irrigate the landscape.
Cost offset by reduced domestic water requirements
Large, air-conditioned buildings generate lots of condensate in long, humid summers. In buildings more than 100,000 square feet, the added cost of condensate recovery is offset quickly by reduced domestic water requirements for cooling towers and irrigation. Return on investment remains strong even when rainwater collection costs are added.
Mainstream technology for large, environmentally-conscious systems
Condensate recovery (CR) is mainstream building technology now. It's an Environmental Protection Agency requirement for larger federal buildings and retrofits, a best practice for building designs trying to replace domestic water with recycled water for cooling and a standard practice in building designs seeking to achieve green building certifications.
The Texas Water Development Board stipulates condensate recovery for industrial, commercial and institutional users in their sustainability guide (Best Management Practices) and recognizes excellent building examples like the Texas A&M Life Sciences Center and the Hays Consolidated School District for their Annual Rain Catcher Awards.
Practical for small applications?
So, condensate recovery is practical for big buildings and related landscapes, but is it practical for small applications like a residential or community garden? I had volunteered to lead a garden building effort in a neglected residential lot next to our church in Refugio this spring.
We wanted to grow vegetables and fruit for a local food pantry and flowers for the church. The garden site was in plain view along a well-traveled street. It was a good opportunity to show our community commitment and demonstrate best gardening practices recommended by Master Gardeners, including water conservation.
We chose raised beds rather than furrow to demonstrate good production, diversity and easy maintenance in a small intensely cultivated space. We planned a large compost facility with drive-in access to encourage neighbors to bring leaves in the fall and see how compost grows the garden the following spring. Finally, we want to build a CR/RWC collection system to promote water conservation as we face drought and sustained hot weather again this summer.
Fortunately, we have experienced consultants for perspective and technical advice. Master Gardeners Paul and Mary Meredith have built practical, small garden CR and RWC systems in Victoria. These are do-it-yourself projects to keep costs in an affordable range and we hope to model our effort on theirs.
8-10 gallons per day for average A/C unit
Condensate production is determined by temperature, humidity, the size of conditioned space and the capacity of the A/C unit. Production varies considerably over time, but eight to 10 gallons a day for the average residential A/C unit is a useful rule of thumb for sizing the storage container and planning utilization. While this seems small, the best production is likely to occur when most needed and total production builds to a significant volume over time. Paul Meredith reports collecting more than 2,700 gallons of condensate last year - enough for all their container plants plus extra for their native plant garden. Our raised beds are well-mulched and, we think we can water at least one of the four from the new CR system. We hope to water the other three from the RWC system augmented by domestic water. The citrus grove in a grassy 30-by-40 foot area is likely to remain 100 percent domestic water.
Control algae, bacteria
Condensate water will grow algae if the storage container is not dark or painted to keep out sun light. It can harbor bacteria if allowed to sit unused as well. We were given a 400-gallon molded plastic carboy to use as our storage container, and it will need to be painted. Large CR systems use chlorine injection to kill bacteria, but our practical approach will be to add a cap or two of bleach per 100 gallons to the storage container each week. Best practice is that even treated condensate water is not recommended for human consumption.
The community is interested and involved in our garden project, but we expect more questions when we start building the CR/RWC system shortly. Our Master Gardener consultants can help with those answers, but we wonder, like everyone else, whether this summer will be as long and hot as last year or if we will get a break. In either case, we expect to have our alternative water collection system in place to help.
The Gardeners' Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas AgriLife Extension - Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or firstname.lastname@example.org, or comment on this column at VictoriaAdvocate.com.