Proper siting and knowledge of greenhouse design principles, including selection of appropriate materials, are the major factors in the efficiency of modern greenhouses. Along with siting, use of materials with the highest-possible R-ratings should be a priority. Higher insulation values, however, often mean higher cost, so the relationship between high efficiency and high costs can be a deciding factor. Proper glazing will boost efficiency, but in lieu of glass panels, there are other modern materials that can be used to boost the performance of even the simplest plastic film-covered greenhouses. Some fuels have higher efficiency ratings than others, so the fuel choice used is also a factor in the decision about supplemental heating and cooling methods. It's important to weigh the pros and cons of various options and estimate seasonal needs when planning greenhouse systems.
For hobby greenhouses, energy-efficiency is not as vital as it might be for commercial growers. In small-scale greenhouses, plants can often be protected from infrequent freezes with plant blankets and temporary shields rather than heating the entire structure. The same is true for shading in the summer. Deflective devices can be installed over grow beds to prevent leaf burn and mitigate any damage from too much sun. It's an individual choice, but heating and cooling needs should always be considered as part of the initial greenhouse design and specifications. If you're planning to build a greenhouse, consider providing initial rough-in for future plumbing and electrical needs. It's always easier and more cost-effective to plan ahead for possible contingencies rather than having to retrofit for additional heating and cooling at some future date.
