Controller Savings For The Smaller Grower
An environmental control, even a simple one, can do so much more than a thermostat.
June 11, 2008
like DIF and night set-back.
A controller does not have to be elaborate or complicated to save you money and improve your crop quality. It does not have to control every operation of the greenhouse to be effective. Replacing thermostats with a simple controller that handles only the heating and cooling will save you energy and improve your crops. Many affordable controllers add settings like DIF, night set-back, humidity control and curtain control and still stay price competitive with thermostats.
Single Temperature Reading
One of the greatest cost savings that a controller produces versus thermostats is from the coordination of heats and cools from one temperature probe. It is almost universal that growers will tell you that in a greenhouse with thermostats, you will, sooner or later, get heats and cools running at the same time. This can happen when the heat thermostat is located too close to an inlet or when a thermostat loses its calibration, causing overlap between the heating and cooling ranges.
A controller uses one temperature reading and compares this to a set point to decide if heating or cooling is needed. The temperature cannot be in both the heating and cooling zone, so only heating or cooling will be
active - never both.
The accuracy of a controller will also lead to savings. Inaccurate thermostats often cause the temperature to be higher than the dial setting, causing energy waste through higher heat loss. The accuracy of controllers also makes the staging of appliances effective by using only equipment needed to maintain the desired temperature. In fact, Mark Lugibill of Lugibill's Greenhouses in Columbus Grove, Ohio, says when he originally installed his controllers, it took a little time to get used to the preciseness of the controllers because he was used to "sloppy thermostats."
Night Setback & DIF
Heat loss is a function of the temperature difference from the inside to the outside. Night is generally the time of lowest outside temperature, so dropping the night temperature (night set back) can save energy. Most decisions have trade offs. Be careful that your night set back does not affect your 24 hour average temperature so much that you extend your growing time and miss target dates. Raising your day temperature, when it is easier to heat due to warmer outside temperatures and solar gain, can help boost your 24 hour average temperature to compensate for the night set back.
Lowering the night temperature and raising the day temperature can lead to plant stretch so you can take advantage of the DIF feature of many controllers. DIF is the lowering of the temperature during the one to two hours just before sunrise. The early-morning drop of temperature can convince some plants to act as if the entire day is cooler than the night. This reduces stretch plus allows you to drop your temperature just prior to sunrise, which is usually the coldest time of the night.
Losing a crop to disease is a horrible waste of energy and labor! Humidity control is the first tool in fighting disease by keeping leaves and surfaces dry. Manual humidity control with thermostats can be tedious, time consuming and inconsistent. First, you adjust the cooling thermostats to purge the humid air. Next, you adjust the thermostats to stop the ventilation and start heating to capture more humidity. Then you repeat the first step to exhaust more humidity. Lastly, you adjust your thermostats back to their original settings and hope they control at the same temperature as before. Controllers with a built-in dehumidification cycle make automated humidity control easy and consistent. The cycle is triggered at a consistent humidity level, runs without any manual adjustments and returns to precisely the original set point. Humidity control does use energy, but saving a crop by controlling the humidity can keep you from being penny-wise and pound-foolish.
Energy/shade curtains are great energy saving devices but hard to control manually. Matt Mohrfeld, of Matt's Greenhouse & Flower Cottage in Fort Madison, Iowa, wanted to add an energy curtain and inquired about what additional controls he would have to add. He was pleased to find out the small controller he was using had the capability to extend the curtain at night with the timer and adjust the curtain during the day with an unused proportional output. When you are upgrading from thermostats to an affordable controller, make sure it has a timer function to close a curtain at night and a proportional output to move the shade curtain during the day.
Monitoring your greenhouse remotely with a computer interface is another indirect saving that controllers can provide over thermostats. Checking all your greenhouses from your desk or home will eliminate the cold, night-time walk to each greenhouse to check on the heaters and thermostats. You will know the temperature of each house without opening the door and letting more cold air in. Additionally, controllers generally have alarms to alert you of problems and prevent the awful surprise of opening a greenhouse and finding it frozen due to a heater that failed after your last check of the night.
A small, affordable controller can save you energy. "This is the best thing going for small growers," Richard Bodfish of Bodfish Farms in South Haven, Mich., says of his controllers. Growers who have indicated that the system paid for itself in one growing season have attributed the greatest saving to not running heats and cools at the same time. The great thing about controllers is they are installed for energy savings, and then quickly become a growing tool that will help produce better crops. Schlegal Greenhouse in Indianapolis purchased a controller for the energy benefits but, Terry Christian, a grower there, also commented that they had the best poinsettia crop in 20 years thanks to tight control and DIF. A controller will not solve all your greenhouse problems, but a small affordable controller can start saving energy dollars, provide growing tools not available with thermostats and free up time that was spent continually adjusting thermostats.
Dave Bartlett is president of Bartlett Instrument Company. You can reach him at firstname.lastname@example.org.