Greenhouse Energy Conservation and Efficiency

How can you save energy and reduce greenhouse costs?

Saving energy is good for the planet and good for your wallet! All plants develop at a rate determined by temperature and tend to grow most optimally within specific temperature ranges. There's a sweet spot between managing energy costs and maintaining ideal temperatures to produce the most abundant and profitable harvests. Taking time to consider all of the variables that go into greenhouse heating will put you on the path to success.

Greenhouse Climate Variables and Cost Calculations

Depending on your greenhouse setup, calculating your costs can involve ideal temperature, time of year, expected weather, energy (gas/electric) price, insulation, and ventilation methods. You can adjust these variables to estimate your costs and stay on schedule. Calculating and tracking your average climate settings and energy costs is very helpful when it comes to budgeting and tracking energy savings. The information you will get from keeping these records is especially helpful if you have multiple harvests planned per year and limited time between harvests.

Quick Tips for Tracking Greenhouse Energy Use

• Keep track of energy prices
• Consider seasonal weather variation
• Seal air leaks
• Use greenhouse insulation
• Optimize greenhouse ventilation
• Thermostat type, settings, and climate control systems increase efficiency
• Greenhouse design should suit the needs of the climate and location

Once you have this data gathered and calculate your costs per crop cycle, you can have more predictability in your energy costs and greenhouse climate settings. Next, you can consider places that might be areas to improve. Adding insulation, upgrading ventilation, and performing regular greenhouse maintenance can all help improve energy efficiency.

Benefits of Sealing Greenhouse Air Leaks

There's no shortage of stories about the surprising amount of energy a grower lost to air leaks. Being detail-oriented and sealing your greenhouse pays off in a number of ways. Thinking about air leak prevention while you're building your greenhouse will help you guide your construction and make sure attention is directed to potential air leaks. The tighter the seal, the less warm air you lose, the less propane (or other fuel sources) you'll need. Sealing greenhouse air leaks also improves your ability to control your environment in terms of pests, pathogens, and weeds.

To avoid serious air leaks, pay attention to the following details:

• Seal the perimeter of your foundation
• Make sure your doors, shutters, and exhaust fan housing fit properly
• Make sure your doors, shutters, and exhaust fan housing are weather-stripped
• Check for holes in your plastic (greenhouse glazing/greenhouse poly) and repair holes in greenhouse plastic
• Eliminate any gaps that open to the outside
• Make sure your wire lock is properly installed with greenhouse poly firmly in place

Greenhouse Insulation for Energy Conservation and Efficiency

There's an obvious balance to be had in terms of insulation between upfront costs and effectiveness. Better insulation will increase up-front costs but pay off in the long run in energy savings. Depending on your climate and how frequently you grow greenhouse crops, you may or may not want to insulate your greenhouse. If the greenhouse will be used year-round, and if seasonal temperatures reach below 28°F for at least five hours per day, you run the risk of plants freezing. When these conditions are possible, you will most definitely want to consider greenhouse heating options and greenhouse insulation,

Greenhouse End Wall Insulation Options

Here are just some of the materials that you can use to insulate the end walls of a greenhouse:

• Twin wall polycarbonate (8mm)
  • The most cost-effective way to insulate greenhouse end walls
  • Twin wall polycarbonate insulation has an R-value of 1.6 (insulation measurement)
  • Costs more than film but performs significantly better  
• 1/2" Plywood (R-value of .62)
• Double 6mil poly end walls (can be messy)
• Single wall corrugated polycarbonate is not an effective insulator

Greenhouse Sidewall Insulation Options

The most cost-effective way to insulate your sidewalls is to install two layers of "6mil" polyethylene plastic. This creates an air barrier between the outside elements and your greenhouse. At night and during colder months double 6mil or "double bubble" does a remarkably good job at trapping heat in to lower your heating costs.

R-Values Explained

The R-value of a material tells how well it insulates. Higher R-values have better insulation properties. Here are some examples of greenhouse plastics and their insulation values. You can see, as mentioned above, twin wall polycarbonate is a great option because it has good insulation ability and a long lifespan.

Energy Conservation and Efficiency for Greenhouse Ventilation

Greenhouse cooling is a topic we talk about more in our Greenhouse Ventilation Guide, but it is worth noting that activities like sealing air leaks will also improve the efficiency of cooling and greenhouse ventilation systems. Greenhouse ventilation comes in many forms such as exhaust fans, circulatory fans, and passive ventilation options like roll-up sidewalls. Even during times that you are heating your greenhouse, you will want to pay attention to ventilation. Air circulation is important when heating because it helps keep temperatures and humidity even.

Thermostats and Climate Control Systems

Thermostats can play a very important role in energy conservation and greenhouse energy efficiency. Some greenhouse thermostats are very simple and inexpensive, these should be used (at a minimum) in any greenhouse with climate control systems. Manually operating greenhouse heating and ventilation is very inefficient. In addition to basic thermostats, there are many newer greenhouse climate control systems that can use advanced sensors and WiFi connected software to provide detailed environmental monitoring and control. These systems can be more expensive upfront but will pay for themselves in the energy and labor savings they provide, and the superior growing conditions that they offer.

Energy Conservation in Greenhouse Design

It is very important to think about energy conservation and efficiency when designing your greenhouse. Retrofitting to improve efficiency can be more costly down the road and making these initial considerations will help set your greenhouse business up for success. Any efficiency you can muster will help you get an edge in the marketplace.

One of the biggest considerations to make when it comes to greenhouse design efficiency is which way to orient your greenhouse and what shape of greenhouse to purchase. Greenhouses come in a variety of shapes and sizes. Greenhouse shape and orientation are important features that influence crop success and operational efficiency. If the shape of the greenhouse follows the slope of the surrounding area, it will have reduced heating needs. Asymmetric and pitched roof greenhouse shapes are some options that allow for greenhouses to simulate surrounding geography.

When it comes to greenhouse orientation, less heating is required for east-west facing greenhouses than for north-south facing ones. Latitude also has an effect on how much energy reduction is realized. High latitudes show less effect from orientation than lower latitudes. Light exposure and distribution can also be influenced by latitude and orientation so it is important to research a greenhouse site thoroughly.

Taking advantage of the sun's day-arc maximizes available light for plants. For light deprivation greenhouses, this is especially important due to how much light blackout endwalls can block if not positioned optimally to the day-arc. In addition, inconsistencies in light availability to plants create variation in growth between plants. Having to deal with a greenhouse full of plants with differing needs is more work and leads to less predictable results. This can include having to adapt watering, nutrients, care procedures, and more. Your geographic location and climate should determine what greenhouse structure and equipment is optimal.

Closing Thoughts on Greenhouse Energy Conservation and Efficiency

Not all greenhouses in all locations will need active heating and ventilation, many greenhouses are very successful with passive ventilation alone. However, when it comes to growing high-value crops and artisanal crops, more climate control will ensure those crops grow to their fullest potential. Simultaneously there is a great need to control energy costs and prevent energy waste. Paying attention to energy-efficient greenhouse design features will help start you off on the right foot. Continuing to monitor and track greenhouse climate data, climate control settings, and energy costs and savings will help your business stay competitive and save money. You can use this energy efficiency checklist to help assess your personal situation.