Greenhouse Heating Basics From The National Greenhouse Manufacturers Association

NGMAHow did your heating systems perform this winter? Could they use a little boost? Here’s a Q&A from the National Greenhouse Manufacturers Association that might help you improve your greenhouse. For more, including the differences between benchtop heating and infrared radiant heating, visit the NGMA Helpful Hints site on heating.

How does heat loss occur?

Heat loss occurs from a greenhouse structure whenever the interior temperature exceeds the exterior temperature. The rate at which it occurs is affected primarily by the efficiency of the covering materials (glazings) installed on each surface (roof, side walls and end walls). The most commonly used covering materials all have published heat transfer factors called “U” factors that provide a means of calculating their impact on heat loss in different scenarios.

What is the “U” factor?

“U” factors are the inverse of the commonly used “R” factors, where “U” = 1 / “R”. The lower the “U” factor, the less ability your glazing material has to transfer heat, therefore, the lower the heat loss.

What is a British Thermal Unit?

In North America, heat loss is typically expressed in terms of total British Thermal Units per Hour (BTUH) loss. British Thermal Unit (BTU) is the amount of energy it takes to warm one pound of water 1°F.

Are there any special considerations for calculating heat loss?

Yes, there are unique crop considerations. Many growers do not use the total volume of their structures to grow crops. Consequently, they may not need to have the total conductive heat load available in their heating system. While the standard means of calculating heat loss are well accepted and documented, considerations should be made as to whether your crop requirements justify installing the total number of BTUH indicated by this calculation.

What is zone heating?

A zone heating system is one that places the BTUs in a specific portion of the structure.

How is air circulation affected by cold weather?

During cold weather, when greenhouses are virtually closed in, there is often insufficient air circulation to maintain desired conditions. The appropriate type of air circulation equipment will help obtain a more uniform relative humidity and provide the proper air movement. Continuous circulation produces gentle air movement and has been reported to maintain better leaf surface microclimates and prevent pockets of disease‐producing high humidity. This gentle air circulation may result in slightly higher heating demand, yet many regard it as advantageous from a plant production and quality standpoint.

Does a thermal blanket save on heating bills?

Installation of a thermal blanket system can impact the total heating requirement of your greenhouse by reducing the heat loss. These systems are typically designed to automatically retract in the daytime and close in the nighttime to trap energy.

What is convection heat?

Convection heat utilizes the forces of natural air circulation currents to transfer heat. Convection involves two basic principles: First, cold air displaces warm air and second, warm air rises in the presence of cold air. With convection, heat is transferred by air currents, which transport energy throughout the structure. When these air currents pass by plant material, energy is transferred to the plant. Because of this, it is very important that some means of air circulation is used (HAF fans, perforated polyethylene duct tubes or ceiling fans) to assure the maximum amount of warm air is transferred to the plant environment to evenly distribute heat throughout the structure.

What is conduction heat?

Conduction heat utilizes direct application to transfer heat energy to the plant. Physically touching any warm object demonstrates the principle of conductive heating. In greenhouses, this type of heating is most commonly distributed with hot water tubes, and occasionally electric resistance strips, which are placed directly on the growing surface or in the growing media. The soil, containers and growing surface in direct contact with the warm tubes or strips are heated and subsequently transfer that heat energy to adjacent material.

What is radiant heat?

Radiant heat utilizes electro‐magnetic infrared waves to transfer heat energy. Since this is a little
understood form of heating, it bears detailed explanation. Anyone who has warmed themselves by a hot wood stove or warmed their hands at a campfire has experienced radiant heat. It is also demonstrated by standing in the sun on a winter’s day or walking near a brick wall that has been exposed to the sun during the day. In both examples, although the air may not be warm, you are able to feel the heat energy radiating from these surfaces.

For more, visit the NGMA Helpful Hints site on heating.

Leave a Reply

More From Greenhouses...
Aquaponics At Brogue Hydroponics

March 30, 2015

10 Things You Need To Know About Aquaponics

Are you curious about expanding into aquaponics? From pest control to equipment, Bob and Jesse Kilgore of Brogue Hydroponics offer 10 factors you need to consider.

Read More
Aquaponics At Brogue Hydroponics

March 30, 2015

Aquaponics Is Making A Splash At Brogue Hydroponics

The owners of Brogue Hydroponics explain why they expanded into aquaponics, and how the shift has helped them uncover a new market opportunity.

Read More
Hendriks-Half-Open-Roof_GGS

March 26, 2015

10 Greenhouse Products For First-Rate Growing Environments

From coverings to fork-lifts, greenhouse suppliers offer a variety of products to make growing easier. Check out the slideshow to learn more about these, plus several other products that can offer you value, versatility and durability.

Read More
Latest Stories
Hendriks-Half-Open-Roof_GGS

March 26, 2015

10 Greenhouse Products For First-Rate Growing Environme…

From coverings to fork-lifts, greenhouse suppliers offer a variety of products to make growing easier. Check out the slideshow to learn more about these, plus several other products that can offer you value, versatility and durability.

Read More

March 16, 2015

Cozy Acres Greenhouses: Operating With Zero Emissions

With the help of federal funding, Cozy Acres Greenhouses was able to take a greener approach to its latest expansion, building a zero emissions greenhouse that operates year round.

Read More
interior view EDDG vent_energy efficiency codes

March 16, 2015

Stricter Energy Codes May Impact Your Ability To Expan…

Energy efficiency building codes that greenhouses are required to meet could soon be much more stringent, unless the National Greenhouse Manufacturers Association is successful in its bid to gain exceptions on greenhouse owners’ behalf.

Read More
NorthCreekGreenhouse_midmarch15

March 13, 2015

GGS Helps North Creek Nurseries Take Efficiency To A Ne…

North Creek Nurseries recently built a new GGS gutter connected poly greenhouse range with the intent of saving energy and implementing Lean Flow Practices. The aim was to help North Creek improve the quality of products and meet increased customer demand, while at the same time saving money on labor.

Read More
Retail Greenhouse

March 12, 2015

The Right Greenhouse For Any Grower

Selecting the right structure for your operation can be difficult. With so many options, it’s easy to feel overwhelmed. The good news is that greenhouse manufacturers are experienced in the art of matching customers with the ideal product. Here’s their advice for how to pick your next structure.

Read More
Fall Creek Farm and Nursery Expansion

March 12, 2015

Conley’s Helps Fall Creek Farm And Nursery Increase Blu…

In order to meet its customer’s increasing demands for domestic blueberry production in the United States, Fall Creek Farm and Nursery needed much more indoor growing space. The company selected Conley’s for a recent expansion of Conley’s Gable Series 7500 in a two-phase project. The first 14-greenhouse range sold by distributor Horticulture Services, measures 170,000 square feet in size and finished construction in 2013.

Read More
Emerald Coast Grower's Atlas Greenhouse

March 12, 2015

Emerald Coast Growers Steps-Up Production Efficiency An…

Emerald Coast Growers, a supplier of perennial starter plants and ornamental grass liners, is not averse to expansion projects. In 2010, it celebrated its 20th anniversary with an expansion of its perennial production space. More recently, the company has been in a nearly continuous phase of construction and improvement projects.

Read More
ArmstrongGrowers Hanging Basket Area

March 12, 2015

Armstrong Growers And Pike Farms Grow With Sustainable …

Rebuilding and retrofitting greenhouses has been key to Armstrong Growers’ expansion on the West Coast, and Pike Farms will follow the same business model on the East Coast. The four-acre wholesale operation that is currently Pike Farms produces only about 5 percent at the most of Pike Nurseries’ retail garden center needs; however, that’s going to change in the next couple of years.

Read More
Metrolina Greenhouses Loading-Dock

March 12, 2015

Metrolina Greenhouses Expands With High- And Low-Tech …

Heralded as one of the most automated greenhouse operations in the U.S., Metrolina Greenhouses continues to build in Huntersville, N.C., and York, S.C. Art Van Wingerden, chief operating officer and co-owner of Metrolina Greenhouses, estimates that as his big box customers continue to grow at a 3 to 5 percent rate, so will Metrolina Greenhouses’ growing facilities to keep up with demand.

Read More
GrowCo_greenhouses

March 10, 2015

Greenhouses Are More Efficient For Marijuana Production

At least 30 percent more efficient and productive than warehouse growing, greenhouses are the way of the future for commercial cannabis production, experts say. Cannabis growers and advisors are starting to move production out of the warehouse and into the greenhouse, to benefit from the efficiencies that the sun’s natural light and environmental controls provide.

Read More
Pleasant View Gardens New Expansion

March 10, 2015

Pleasant View Gardens Transitions Old-School Hoop Hous…

A new production expansion optimizes labor efficiency and adds growing space, while optimizing energy use.

Read More
Rough Brothers aeroponic greenhouse project

February 24, 2015

Rough Brothers Takes A Hands-On Approach To Several Pro…

Two projects Rough Brothers worked on for Altman plants in Giddings, Texas, and Scissortail Farms in Tulsa County, Okla., show that pre-planning on the grower's part opens the way for a smooth-running expansion project.

Read More
Stuppy Greenhouse Manufacturing's Rainbow Super Structure

February 23, 2015

Stuppy Greenhouse Manufacturing Says Every Customer’s G…

Well-suited greenhouses that function efficiently for customers arise from involving them in the design process from start to finish. Stuppy Greenhouse Manufacturing put this philosophy on a greenhouse design for a wholesale grower looking to expand his annuals operation. The grower's needs were simple, yet daunting: design a greenhouse that delivers the perfect growing environment, but keep maintenance and operating costs low.

Read More
National Greenhouse Manufacturers Association

January 27, 2015

Stricter Energy Codes May Impact Your Ability To Expand

Are you aware stricter energy codes may be on the horizon that will certainly impact your business in a big way? Here's a Q & A from the National Greenhouse Manufacturers Association that helps explain the dangers of the coming energy codes and what we as an industry can do to prevent them.

Read More

January 27, 2015

10 Questions To Ask Before Purchasing A Greenhouse Cove…

Whether you’re replacing an existing greenhouse covering or building a new greenhouse, it’s a significant investment, so you need to make sure you have the right type of covering to suit your needs and budget. What’s more, with production costs on the rise, you can’t afford to have anything less than a durable, high-quality covering that is energy efficient. To make a smart purchase, do your homework before you buy. A good place to start is by answering the following questions, which will help you separate the good products from the mediocre ones.

Read More

January 26, 2015

Greenhouse Growers Look To Build And Retrofit In 2015

You’re likely to see more construction work going on in the greenhouse industry in 2015, according to Greenhouse Grower’s 2015 State of the Industry survey. Responses show growers have high hopes for the future, which may be one reason why more of them are looking to spruce up their facilities.

Read More
Griffin Logo

November 10, 2014

Griffin Announces Dates For 2015 Grower And Retailer Ex…

Griffin Grower and Retailer Expo 2015 dates set for Massachusetts and Pennsylvania.

Read More

September 30, 2014

Emerald Coast Growers Adds Greenhouse Space To Increase…

Emerald Coast Growers has expanded with the addition of 25,344 square feet at their Milton, Fla., facility. The construction is in response to increased demand for their products, and will primarily be used for ornamental grass production.

Read More