By Chris Guntermann
The opportunity now to grow in greenhouses versus traditional indoor facilities brings up the question of how best to design such environments and how to scale up from the knowledge base of indoor culture.
There are many similarities between indoor and greenhouse cultures but there are significant variables — most of which can be decided as business decisions based on capital utilization and profitability, tempered with risk management.
As any new market stabilizes, the winners will always be those with the lowest costs of production for a product of acceptable quality within a price category. Much like wines, there will be low-end and high-end products. Knowing your target niche may be difficult right now because new demand is hard to forecast.
Advantages of indoor production include having complete control over the environment, which allows production costs to be forecast. However, the disadvantages are that those production costs are high, and very intensive on capital and energy. Indoor growing can also be difficult to scale up as demand increases.
The energy equation comes down to the cost/benefit of indoor HID lighting versus sunlight. If there are linear relationships between light levels, plant growth and quality, then your local energy costs will dictate which direction to go.
Greenhouses may offer “free sunlight,” but at the expense of dark nights and higher heat loss. Properly selected equipment is needed to maintain a steady environment against an unsteady energy input. For example, as weather and sunlight intensity changes it will change everything from heating and cooling, to irrigation and feeding.
Our well-established and competitively efficient greenhouse industry already grows all kinds of floral, vegetable and research crops in every world climate, so there is no question a greenhouse will work well when designed to meet your parameters. Many of those parameters will be answered by the business plan. There can be equal success with low production from low-cost facilities as from high production from high-cost facilities.
Because of that, designers must be provided with very specific environmental requirements from which they can help with capital and operating cost comparisons. A very useful — and free — tool for lighting, growth and energy-use comparisons is the USDA’s downloadable “Virtual Grower 3.0.”
So, while sunlight is free, a properly designed greenhouse will bring in the maximum available light, through a structure strong enough for your weather. Please, don’t skimp on the steel frame. It is the only thing that you cannot change going forward. Usually, an increase in strength costs but a small premium on the total project.
Nothing else done in the greenhouse matters until a photon strikes a leaf, so select the best affordable glazing.
The glazing type will also help define the type of structure.
Double poly is popular because it and the structures are inexpensive to build. Their frames cast much less shadow than equivalent glass houses. Multi-wall structured sheets are a good semi-permanent choice for harsh weather environments. They also lower your risk, but increase installation costs.
Glass is less common but produces a premium bright environment. Similar to corrugated single layer polycarbonate, it is permanent, but a poor insulator so must be accompanied by heat retention curtains.
Greenhouses need heat, and natural gas is usually the least expensive source. Waste heat from HID lighting can help to offset some heating costs, but should not be counted on as a primary heat source.
Local fuel costs should be compared by cost-per-therm delivered to the greenhouse. For example, if gas is $1 per therm and burned at 80 percent efficiency, then electricity needs to be $0.042 per kilowatt-hour to match the heat value. High-efficiency gas heaters and boilers give many options for delivering the heat to the crop with mid-90 percent efficiencies. Propane is a clean fuel, but usually considerably more expensive per therm of heat.
Using shading to reduce high sunlight increases crop quality. Automated “energy shade curtains” manage light intensity and double as energy-blankets during the night, reducing heat loss by upwards of 40 percent. A second layer system with a “black-out” curtain can manage day-length response. Be sure to specify the maximum allowable foot-candles of light under the blackout.
Cooling systems using vents, fans and evaporative pads are a proven design standard and can also be outfitted with black-out accessories. Cooling efficacy will be close to the wet-bulb temperature, often dropping temperatures 15-20 degrees below outdoors. The cool and bright conditions are favorable.
Internal air circulation fans are needed to prevent stagnant air, and also distribute heat and cooling. A good rule of thumb is to size numerous small fans to produce 2 cfm (cubic feet per minute) per square foot of floor.
A happy plant is one that is transpiring heavily, which results in humid air that has to be managed. Ventilation systems have to be designed to bring in sometimes very cold outside air without shocking the plants.
Your preferred rooting media will define whether tables (benching) are necessary. Benching holds plants off the cold floor and then defines the best heating scheme. Study the advantages of “rolling benches” and “pallet tray systems” for increased space utilization, but beware that labor is usually the first or second highest operation cost, and your work-flow benching design can significantly affect labor efficiency.
Choose a commercial quality environmental control system, which is purpose-built for greenhouses and which will manage all of the complex equipment interactions such as cooling, shading, light intensity and CO2. Avoid systems designed for people comfort — we are warm-blooded; plants are not. Electronic sensor packages with aspirated covers react rapidly to changes and prevent equipment cycling and “hunting” in a way that thermostats cannot. Integrated controls are proven to save energy and increase plant quality. With built-in alarms and Web access, they also reduce risk from equipment failures.
As you transition from indoor growing to greenhouse growing, be aware that things get easier and harder. Facility construction can be out in the open, but will necessitate land-use and building permits, code compliance, large utility connections and the high cost of electrical installation.
Electrical installation is always under-budgeted. A smart design and most importantly, professionally designed and drawn schematics will balance all the loads and lower electrician bids. Don’t expect to use the plug-and-cord approach to large facilities. Many states mandate U.L. (Underwriters Laboratories, Inc.) or CSA (Canadian Standards Association) listings.
The cost of lighting infrastructure for indoor growing can be huge — and the electric rate can vary with demand charges. Check the demand rate add-on costs, and the off-peak rates with your utility. Emerging LED lighting technologies will continue to improve. They can be very energy efficient, but not always capital efficient. It all depends on the local power rates.
Return on invested capital is important, but also important is risk management. Especially when financing is involved. Risks can be simple and insurable such as fire or theft. Self insure by designing redundancy and having spare parts on hand for critical systems. More complex are “side effect” risks such as those associated with power outages – can an emergency generator cover the power demand? Not likely for HID lighting.
Other aspects to consider are employee safety and pest/disease exclusion or control. Smart designs take these into account to prevent small oversights from becoming catastrophic events.
Be aware of the “rule of unintended consequences” which warns that sometimes a good idea can backfire unless the effect on the entire system is considered.
Plant growth curves are somewhat like compound interest.
A small percentage difference over a long period of time can add up to a significant factor.
Greenhouse growing is a proven and long-term competitive way to go. Best wishes with your personal endeavors.
Chris Guntermann is a 44-year veteran of the greenhouse industry with a horticultural degree and engineering training. He has teamed with Horticultural Services and its additional 130 years of combined horticultural experience to serve the Northwest from three offices.