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...

January 19, 2016

Tips For Cherry-Picking The Right LED Lighting Solution For Your Greenhouse

If you want to find the right LED lighting solution for your greenhouse, start with these tips from top lighting manufacturers.

Read More
Philips Lighting, Colorado State

January 14, 2016

Philips Lighting, Colorado State University Partner On New LED Lighting Research And Training Center

The partnership will allow the two entities to perform collaborative research and focused cultivation studies to validate and innovate around the application of advanced LED lighting for horticultural activity.

Read More

December 21, 2015

More Than 40% Of Growers Will Add Or Retrofit Structures In 2016

An early look at 2016 State of the Industry results shows why some growers are looking to add or retrofit structures in the coming year.

Read More
Latest Stories
Philips Lighting, Colorado State

January 14, 2016

Philips Lighting, Colorado State University Partner On …

The partnership will allow the two entities to perform collaborative research and focused cultivation studies to validate and innovate around the application of advanced LED lighting for horticultural activity.

Read More

December 21, 2015

More Than 40% Of Growers Will Add Or Retrofit Structure…

An early look at 2016 State of the Industry results shows why some growers are looking to add or retrofit structures in the coming year.

Read More
Stuppy Greenhouse Manufacturing's Rainbow Super Structure

December 21, 2015

Three Strategies For Overcoming Greenhouse Heating Conc…

Lost heat, maintaining an ideal greenhouse temperature, and inefficiency in heating systems are three of the most common problems growers face when it comes to heating. Here’s a look at some ways to overcome these challenges.

Read More
Europes Largest Rooftop Farm

December 7, 2015

Europe’s Largest Rooftop Farm Underway, Scheduled To Op…

The Netherlands-based facility, a collaboration between Urban Farmers and Van der Valk•Kleijn, will comprise 14,000 square feet of vegetable production in an aquaponics system.

Read More
Battlefield Farms in Virginia noticed an improvement in the quality of heuchera propagation plugs after using Philips’ LED production modules

November 23, 2015

LED Lighting May Be The Next Frontier For Plant Nutriti…

Philips Lighting’s senior plant specialist, Dr. Abhay Thosar, shares how the company is working with growers to help create custom plant recipes for streamlined production of better quality crops.

Read More

June 21, 2015

Greenhouse Project Moves Pavlodar (Kazakhstan) Closer T…

Despite regional challenges, greenhouse specialists Dalsem and automation supplier Hoogendoorn have collaborated on a greenhouse complex with the PTK company to bring Pavlodar (Kazakhstan) closer to self-sufficient, local food production.

Read More
Greenhouse Electrical System

May 26, 2015

Don’t Let Your Greenhouse Electrical System Come …

Ensuring your greenhouse has enough electricity to operate all the equipment that is installed takes planning and consideration of an operation's needs. Part one of two articles on greenhouse electrical systems covers choosing an electrician, meeting immediate and future needs and planning for back-up power.

Read More

May 22, 2015

Nexus Greenhouses Is Optimistic For Expansion Into New …

Cheryl Longtin and Mike Porter, who own Nexus Corporation, say they were excited to attend the grand opening of Gotham Greens’ new structure atop the new Whole Foods grocery store in the Gowanus neighborhood in Brooklyn, N.Y., when it opened in December 2013. The project is just one example of some of the new and expanding markets that Nexus Corporation has expanded into over the past few years. Jeff Warschauer, vice president of sales for Nexus, says the company has enjoyed getting to know and working with the founders of Gotham Greens, Viraj Puri and Eric Haley, and Jennifer Nelkin Frymark, the chief agriculture officer, on their innovative approach to business. “They are very excited and work hard internally – just great people,” he says. “From our perspective, it’s great to see that excitement and vision. The employees there are happy and there’s no turnover; they’re only adding new people […]

Read More
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
[gravityform id="35" title="false" description="false"]