New Greenhouse Construction

Figure 18: Greenhouse under construction Source: A.J. Both, Rutgers University

Figure 18: Greenhouse under construction Source: A.J. Both, Rutgers University

If you are planning new greenhouses, keep in mind that different types of greenhouses use different amounts of energy (Figure 18). A gutter-connected greenhouse will have 15 to 20 percent less surface area (1.5 ratio of heat loss area to floor area), and therefore lower heat loss than a stand-alone greenhouse based on a half-acre of covered area. A gutter-connected greenhouse also will have better space utilization and higher labor efficiency.

Stand-alone greenhouses have a 1.7 to 1.8 heat loss area to floor area so they will use more energy for heating. However, stand-alone greenhouses allow for  isolated growing conditions, which can help with disease and pest control. Because of the narrow width, they can be easily ventilated naturally if roll-up side walls are used. Stand alone greenhouses can be heated one at a time as as needed and each can be maintained with different environmental conditions. In a gutter-connected greenhouse, plastic walls could be installed so only a portion of the greenhouse is heated at a time, but the heating and ventilation systems need to be designed in zones so it can be partitioned. The maximum recommended length for a greenhouse is 200 feet. Greenhouses longer than 200 feet may have problems with ventilation.

To illustrate the difference in energy use, let’s compare eight 30’ x 100’ stand-alone greenhouses with a five bay 150’ x 160’ gutter-connected greenhouse. All greenhouses are covered with double poly film that is treated with an IR inhibitor, have black fabric covering the dirt floors, cover 24,000 square feet and use heaters with a seasonal efficiency of 78 percent. The stand-alone greenhouses used 1793 gallons of LP gas per greenhouse for a total of 14,344 gallons for the spring growing season. The gutter-connected greenhouse used 11,929 gallons, which is 2415 gallons, or 18 percent less, LP for the same period.

Are you a small grower, with plans to eventually grow your business? Consider starting out with a small one- or two-bay gutter-connected greenhouse that you can add to as your business grows. Additions can include lengthening the existing greenhouse or adding additional bays or both. The cost is higher for the initial greenhouse, but the payback will come as you grow.

 

Figure 19: Greenhouse under construction Source: Scott Sanford

Figure 19: Greenhouse under construction Source: Scott Sanford

Greenhouse Orientation

For higher latitudes (most of the northern U.S. and Canada) the general recommendation is to orient stand-alone greenhouses with the length running east/west and gutter-connected/multiple-bay greenhouses north/south (Figure 19). Orienting the greenhouse east/west provides the most surface exposure to the winter sun. However, if the gutter-connected greenhouse were faced east/west, the shadow cast by the gutters would be basically stationary, causing lower growth in that area of the greenhouse. Orienting the gutter-connected greenhouse north/south is a compromise to overcome the shading issue.

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