As the spring season starts to wind down, it is never a bad time to look back at the last couple of months to evaluate what changes you might consider for next year. There is no better time than the off-season to make these changes for the next spring season. Few things you do will have a greater effect on your operation than how proficient you are with energy efficiency. In this installment of Basics and Beyond, we will look at a few items you should consider to save energy in the greenhouse, most of which will cost very little and will pay for themselves well within the first season if you implement them.
1. Tighten Exhaust Fan Belts
When was the last time you checked the tightness of your exhaust fan belts? Fan belts are an easily overlooked detail, and they are often not tightened to the proper tension. When fan belts are this loose (Figure 1), the likelihood that the fan is rotating at the speed it is supposed to is low due to belt slippage. Not only is this wasting electricity, but it also reduces the cooling effect the fan can create.
2. Check Louvers – Proper Opening And Closing
Figure 2 shows a set of louvers that are being propped open with an old pot. The propped open louver works against us in two ways. If the grower forgets to prop the louvers open during the day, the greenhouse overheats due to the fan running but not exhausting hot air. If the grower forgets to close the louvers at night, especially in the early spring, warm air will escape the entire night when the boiler is running. Making sure your louvers are well oiled will help, but ideally growers should invest in installing motors that open and close the louvers.
Check Louvers Cont.- Eliminate Gaps
Even a small gap in your louvers can add up. Taking the time to straighten any bent louvers can conserve a lot of heat. Figure 3 is an example of a very tight closing louver on an exhaust fan.
3. Eliminate Endwall Gaps
Another place where we lose a lot of heat is from gaps is in the end-walls, a few cans of spray insulation will easily close up minor gaps (Figure 4).
4. Reassess Placement Of Glazing Material
Many greenhouses have double-poly or polycarbonate all the way down to the ground. This makes perfect sense if you are growing your crops on the ground to maximize light exposure. However, if you are growing on benches ,the glazing material below the level of the bench is probably losing more energy than it is letting in light.
A simple solution is to add insulation to the kneewall (below the level of your benches) of your greenhouse (Figure 5). This can be done with inexpensive foil-lined bubble wrap or ridged foam insulation. Both can be purchased from most hardware stores.
5. Inflate Double-Poly Correctly
For growers using double-poly hoop houses, it is important to properly inflate the two layers of polyethylene. It is all too common to see a greenhouse inflated with inside air, that is, air being pulled from inside the greenhouse. This air is usually high in humidity and causes condensation within the two layers. As moisture collects between the layers of polyethylene, the efficiency of the dead air as an insulator decreases. Double-poly houses should always be inflated with outside air, which is typically drier.
6. Install An Environmental Controller
The final thing to consider in your off-season energy efficiency checklist is installing an environmental controller rather than any mechanical thermostats. Typically, each element of your heating and cooling system has its own mechanical thermostats. As these thermostats get out of calibration, you may find your heating and cooling systems working at the same time. The use of a fully integrated environmental controller manages all aspects of your heating and cooling system from a central controller and prevents any overlap from exhaust fans and heaters. There are many such controllers on the market that are ideal for hoop houses for only a few hundred dollars.
As we move into the summertime, look around your greenhouse to find ways to make simple and inexpensive improvements that will pay dividends when it is time to heat your greenhouse again.