Now that another summer is upon us, it's time to think about greenhouse cooling systems. Here are some simple tips to help you maintain your evaporative cooling system operating at maximum efficiency. Most evaporative cooler problems can be avoided by a regular schedule of preventative maintenance.
Check Water Distribution System. Before the cooling season gets into high gear the entire system should be carefully inspected. The major areas to be concerned with are:
- Leaks. Check for leaks in the system, and take the necessary corrective measures.
- Pads. Inspect pads for damage and scale buildup. Scale can be removed by gently wire brushing dry pads. Pads with large holes or tears should be replaced.
- Distribution pipe. Check to see if any of the holes in the distribution pipe above the evaporative pad are blocked. One telltale sign that one or more holes are blocked is the appearance of dry streaks in the pad.
- Filters. Clean all filters of scale and algae. Filters with clear covers and exposed to sunlight will clog more quickly with algae than ones with opaque covers.
- Troughs and tanks. Troughs, tanks and sumps should be cleaned of sludge. This sludge contains sufficient organic matter to support abundant alga growth.
Control of Algae Growth. The growth of algae on the evaporative pads greatly reduces their efficiency. For your system to operate at its maximum cooling capacity it is necessary to make sure that alga growth on the pads is kept at a minimum. Fortunately this can be accomplished rather easily by keeping in mind that algae are simple plants that, like the plants in your greenhouse, have three basic requirements for growth: light, moisture, and nutrients.
- Reduce light. Don't use translucent hoses or tubing, and make sure that tanks and sumps are covered. In addition a layer of shade cloth above the cooling pad will also help to reduce algae growth.
- Dry pads daily. Regular drying of the pads for several hours each day can retard the growth of algae. This can be easily accomplished installing a timer on the pumps, which will turn the water off all night, especially between midnight and sunup when there is little cooling by pads. In addition the controls for the cooling system can be set so that the fans operate for a short time after the water to the pads is turned off. This allows the pads to dry out between cooling cycles.
- Reduce nutrient supply. Algae use dissolved nutrients in the water for growth. By reducing the sources of these nutrients alga growth can be inhibited. The primary sources of nutrients are dirt and dead, decomposing algae. If using chemicals to control alga growth, make sure that the entire system is flushed to remove dead and decaying material from the system and not allowed to accumulate in sumps or tanks. If this material is not removed it will serve as a "fertilizer" for the next crop of algae. Also try to reduce the amount of dust from nearby farm fields, potting benches, and incinerators from being drawn into the pads.
Reduction of Scale Formation. Scale and mineral deposits form on cooling pads through the evaporation process and reduce the efficiency of the cooling system. Although scale formation is inevitable, several steps can be taken to slow the process:
- Increase the flow of water over the pad. This will allow of the minerals to remain dissolved in the water rather than be deposited as scale on the pads.
- Clean and flush the distributor pipe regularly. Uneven distribution of water over the pad will lead to greater flow of water over some areas than others. Minerals will precipitate out in the areas where the water is moving slow, particularly around dry streaks.
- Proper bleed-off. The addition of fresh make-up water to the system to replace that which was lost to evaporation introduces more minerals to the system. The concentration of these minerals will continue to increase until they precipitate out as scale on the pads. Therefore it is important to bleed off a portion of the water from the reservoir.
