Smart Greenhouse Heating Saves Money
From energy curtains to barrels of water, heating the greenhouse doesn’t have to mean burning cash. Use these strategies to get a quick return on your investment.
September 5, 2012
As the days get shorter and temperatures drop, it’s a perfect time to start thinking about how to reduce your energy consumption this winter. There are a number of relatively simple methods you can use.
The installation of thermal energy curtains has been popular in recent years due to the substantial energy savings associated with them. They can serve double duty in the spring and summer as retractable shade curtains.
Energy curtains can be expensive. For example, a grower installed a 40-foot-by-78-foot energy curtain for the price of $12,000. If the grower heats the greenhouse without the curtain from January 1 to May 31 at a temperature of 65°F, it would cost almost $24,000 to heat. With the curtain, it only costs about $17,000. At the time of installation, heating oil cost $3.10 per gallon. The grower saved about $6,600 per year, making the payback on investment in less than two years.
Insulating hot water pipes can be a very inexpensive way of conserving heat. According to John Bartok of the University of Connecticut, you can save about $5 per linear foot per year if you insulate a 0.75-inch pipe, or up to $16 per linear foot per year on a 3-inch pipe.
Thermostats have been used extensively in greenhouses over the years but can be inaccurate and can only run one system. This can result in your heating and cooling systems running simultaneously. Upgrading to a computerized system has become more affordable and can run both heating and cooling systems more efficiently.
Cleaning or replacing glazing also has a number of benefits: better light transmission, which results in less disease, fewer PGRs needed and higher-quality plants. Plus, newer glazing often allows better heat retention, which means lower heating bills.
Explore Alternate Energy Options
Wood heat is an option with an outdoor boiler and cordwood. Some growers are investing in large-scale wood chip burners. Be sure to work with your local governments and abide by local ordinances associated with burning certain alternative fuels. Boilers can be run at maximum efficiency 24 hours a day, which creates excess heat during the day and under-produces heat at night. The excess heat from a boiler can be stored in water and extracted at night. One pound of water will store about 1 BTU for each degree increase in temperature. For example, one gallon of water weighs 8.35 pounds. If it is heated from 60°F to 100°F, it is a change of 40°F. (8.35 pounds × 40 degrees = 334) This means each gallon of water can hold 334 BTUs.
While large tanks can store more BTUs, they are not a viable option
for most growers. A low-tech option is filling 50-gallon drums with water and placing them in an unused space in the greenhouse, such as under benches.
The water heats passively from the surrounding air temperature and
returns the heat back to the air as the temperature drops. This method
can help moderate fluctuations in temperatures.
Crop Scheduling For Savings
Taking the time to schedule your crops can have a dramatic effect on your heating bill. When scheduling, be accurate. Don’t second guess the weather and add in extra weeks of production to compensate for poor growing conditions. Write down your schedule and make it accessible to your staff. Make sure you stick to it.
Consider a crop grown for Mother’s Day in a typical poly house. If the crop is accurately scheduled, it should take eight weeks to finish. It will cost about $2,700 to heat the poly house. If the schedule is overestimated by just two weeks, it will cost $3,600 to heat it — a difference of more than $900 for just two extra weeks.
Stop now to plan ahead for the coming spring season. While no means an all-inclusive list to conserve energy and save money, I recommend starting with the low-hanging fruit by targeting things that are the easiest to implement and have a short payback on investment.
Brian A. Krug is an Extension assistant professor at the University of New Hampshire Cooperative Extension. E-mail him at email@example.com.