Energy audits may help greenhouse businesses save money

Is your greenhouse utility bill getting you down? Consider an energy audit to evaluate potential energy savings.

Are your greenhouse energy bills getting you down this winter? Do you wish you could find a way to lower your energy usage and thus save you money? Even some of the simplest and inexpensive repairs can do just that. According to University of Massachusetts Extension, fixing a fan louver that doesn’t close correctly – leaving 1-inch gaps, allowing 23,000 BTU per hour of heat loss – can save you $0.46 per hour, assuming a national average cost of $2.798 of fuel oil per gallon. In addition, Pennsylvania State Extension advises greenhouses to simply fill cracks, holes and openings in the structure to potentially reduce the heating bill by 5-10 percent. To evaluate these and other potential energy savings, consider a formal or informal energy audit.

To start, perform your own very informal energy audit by simply walking through your greenhouses and evaluating potential improvements. One tool to help you is a document titled “Conduct an Energy Audit of Your Greenhouses,” written by John W. Bartok Jr. This quick checklist provides a list of energy improvements to consider as you walk through your greenhouses.

A slightly more involved self-assessment tool is offered from the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). The Greenhouse Energy Self-Assessment Tool allows you to enter detailed information about your greenhouses, including dimensions, types of coverings, type of heaters, etc. A portion of the resulting report when using this tool is shown in Figure 1. In this case, a fictitious greenhouse (consisting of two 100-foot x 36-foot bays with 12-foot side walls) was used that had no thermal curtains, was covered in traditional double-poly and used forced air gravity vented unit heaters. The results of the program suggested multiple changes, including a 29 percent energy savings by switching from double poly to IR-inhibited double poly. More savings could be seen by adding thermal curtains or upgrading to high efficiency condensing heating systems.

Figure 1. Potential savings estimated from the USDA NRCS Greenhouse Energy Self Assessment Tool, using data entered in by you. In this case, a fictitious greenhouse consisting of two 100-foot x 36-foot bays with 12-foot tall side walls was used that had no thermal curtains, was covered in traditional double-poly and used a forced air gravity vented unit heater.

Glazing Materials

The following glazing changes would reduce energy usage.

Location

Current Glazing Materials

Recommended Replacement

Roof Area

Poly, Double

Poly, Double, IR inhibited

Side Walls

Poly, Double

Poly, Double, IR inhibited

End Walls

Poly, Double

Poly, Double, IR inhibited

Est. Energy Savings

162,639,700

Btu

Fuel Savings

1,626

Therm or CCF

Est. Annual Savings

$569

 

% Savings

29%

 

Greenhouse Gas Reduction

19,029

lbs. CO2/year

Thermal Curtain

The potential savings for installing a thermal curtain that will provide 52% energy savings (semi-porous 55% light transmission) covering 100% of the roof area and 50% of the gable ends.

Est. Energy Savings

143,585,944

Btu

Fuel Savings

1,436

Therm or CCF

Est. Annual Savings

$503

 

% Savings

26%

 

Greenhouse Gas Reduction

16,800

lbs. CO2/year

Heating System Efficiency

The energy savings if your current heating system was replaced with a new high efficiency condensing heating system (90% seasonal efficiency).

Est. Energy Savings

154,966,376

Btu

Fuel Savings

1,550

Therm or CCF

Est. Annual Savings

$542

 

% Savings

28%

 

Greenhouse Gas Reduction

18,131

lbs. CO2/year

Finally, consider paying for a formal energy audit by a Michigan State University-trained third party auditor, especially if you intend to seek government loans or rebates that require such an audit. Depending on the size of your business, the audit may take up to four hours to complete. The auditor will ask for detailed information before the audit takes place, including a year of your utility bills, structural layouts and coverings of your structures, temperature set points throughout the year and types of heaters, motors, fans and lighting. The auditor will then sit down with you for a two- to four-hour meeting to go over the data you provided and then tour your greenhouses. The final report will list detailed energy use by individual energy consuming appliances and options to save energy for each.

For more details on how a formal audit works and for an example of the resulting audit document, see “Greenhouse Energy Audit Overview” written by Thomas Dudek and Jeanne Himmelein from Michigan State University Extension.