It’s almost July, and that means it’s hot.  In a greenhouse, it’s even hotter.  We’ve been flying through shade cloth as if there were some kind of national shortage.  But chances are pretty good that, this time of year, a simple shade cloth may not cut it.  With some shade and no other form of ventilation or cooling, temps in your building can still soar above 100°F; more than enough to torch your precious plants.  Exhaust fans and shutters can help a ton, but even with fans, shutters, and shade your greenhouse can only reasonably attain the outside temperature +/- a few degrees.

For heavy duty cooling, you need to call in heavy artillery.  By that I mean evaporative cooling, called variously a water wall, cool cell, wet wall, or swamp cooler.  With these systems you can actually lower the temperature inside your greenhouse 10-20 degrees below outside temperture, possibly more, depending on your specific environmental variables.

Evaporative cooling works kind of like a filter.  All of the air coming into your building passes through the pads of the cooler.  The cooler must be sealed properly so this is the case.  These pads have water running down them driven by a pump.  As the air passes through, water evaporates into it.  The evaporation process pulls heat out of the air, thus cooling it.  This air then flows into your building and is usually circulated with the help of circulation fans.  Something to keep in mind with evaporative cooling is that since it relies on water evaporation, efficiency is greatly increased in dry climates.  This is because humid air is already chock full of water, and cannot easily take on much more.

There are two main types of evaporative cooling systems, along with simple portable coolers.  The portable ones simply cool and recirculate the air inside your building and require only a water source and standard wall plug.  These are great for small hobby greenhouses, and can be coupled with a plug-thermostat to give you by-the-degree control.

The first kind of evaporative cooler is a negative pressure system.  Known as a cool cell, water wall, or wet wall, these are wall-sized systems that work in conjunction with your fans and shutters.  They are typically installed inside your building along one wall and sealed to the building.  Inlet shutters are located on the outside of the same wall, and exhaust fans stand opposite both.  When the exhaust fans kick on they pull air out of the building, and in through the shutters and cooler.

Two kinds of cool cell systems are available from us: an aluminum system and a PVC system.  Both are excellent options for your cooling needs.

The second kind of evaporative cooler is a positive pressure cooler, commonly called a swamp cooler.  These are used often in lieu of true air conditioning in hot, dry locations such as the American Southwest.  They are small, box-shaped units that sit external to your building.  Inside is a round fan, often called a “squirrel cage.”  As the fan rotates, it pulls air into the unit through the cooling pads.  This air is then pushed into your building, and shutters located opposite the cooler allow for the hot air already inside your building to escape.  Again, circulation fans help move this air around a more consistent temperature.

Any of these options can help make the summer months bearable and productive in the greenhouse, and as always the efficiency of any cooling system can be increased by a simple shade cloth.  So analyze your situation, and if it calls for more ammo to fight the heat, consider an evaporative cooling solution.