Greenhouse Heating systems

Heating in Greenhouses is one of the first and oldest horticultural revolutions that took place. In the Netherlands wide use of heating systems started in the sixties. In the eighties the second horticultural revolution took place which was the wide use of computerized control systems, in the mid nineties grow lights were added to the equation. At the moment we are in the middle of the closed greenhouse revolution. In this article we will talk about the various heating systems we have in greenhouses and the benefits and disadvantages. For heating your produce or flowers in the greenhouse for crops like roses, chrysanthemum, carnation, tomatoes, cucumbers and bell pepper you have a choice, between a central heating system or a localized heating system or no heating at all.

Central heating: hot water or steam boiler with pipe system

  • large investment, large capacity
  • less expensive fuels can be used
  • breakdown or failure could be critical if no backup
  • inefficient if not run near capacity
  • bottom heating is more practical

Localized heaters often called Forced Air heaters: gas-fired unit heaters or furnaces, possibly with convection tube; infrared heaters

  • lower first investment
  • versatile
  • can be for any area, easily expanded or contracted
  • if the unit fails, others can carry the load
  • more difficult to efficiently distribute the heat

If we take a closer look at central heating there are two options:

Hot Water A central boiler is used to heat water between about 120 F and 180 F. The water is distributed through pipes in the greenhouse. Pumps and mixing valves are used to uniformly distribute the heat and to control how much heat goes out to the greenhouse. Gives good control of temperature, more gradual changes in temperature, may be slow to respond to sudden drops in temperature. Large volumes of water are used.

Steam A steam system uses a smaller boiler, less plumbing and no circulating pumps. It is more difficult to control the flow of steam or heat into the greenhouse. High heat input and quicker changes in temperature are possible. Generally low pressure systems are used in greenhouses (5 to 15 pounds). Water expands as it is converted to steam which causes pressure and forces the steam from the boiler, through the pipes in the greenhouses. As it condenses, volume is lost and the condensate drains back to the boiler by gravity flow. One cubic foot of water will expand to 58.8 cubic feet of steam. Steam pipe is generally smaller than hot water pipe since there is less resistance to flow and a high heat loss per foot of pipe.

The boiler has to distribute the steam or hot water into the greenhouse there are various ways of doing this:

Pipe/Rail Heating distribution

Pipe Rail Heating System

Pipe rail heating systems are widely used and important to get the humidity out of the greenhouse. In the morning they turn on the pipe rail system which is mostly called “minimum pipe” temperature, in this way they get the access humidity out so a better climate is achieved. So apart from temperature control this is one of the most important tools in humidity control. In the picture below you so a similar system for chrysanthemums these growers use a special system which is called a hoist heating system because they need to improve the soil by steaming, plowing and adding organic material. In this system the grower is able to lift the system and do the work properly

Hoisting Heat system Chrysanthemums

Under bench Heating distribution

When you grow the pot plants on table you need a heating system very similar to the pipe rail system but in this system it’s located under the table.

Under bench Heating

In-Floor Heating distribution

in floor heating

In the picture you see the tubes of an in-floor heating system, this system hasn’t been finished yet since concrete needs to be poured on top of it. This photo gives a good overview of how the system works. Sometimes this heating distribution system is called a radiant heating system. This is system is mostly used for pot plants grown directly onto the floor. The floor heats up, this causes air movement which has a positive effect on the humidity around the plant since that can be moved away. Since the system is in the floor it gives a lot of freedom to work it won’t disturb any worker.

Overhead Heating distribution

Overhead Heating Systems

Overhead heating is very important in areas were they have a cold winter, since it provides additional heating. The systems are very nice compatible with hanging baskets. A disadvantage of this heating system is that is takes a lot of light away from the plants.

Perimeter Heating distribution

perimeter heating tubes and star fin pipes

In the very cold winter months when the normal heating system can’t cope on the north faced wall of the Greenhouse additional perimeter heating distribution will help. In the picture above you can see top fin heating pipes.

Types of steam valves

  • pneumatic: air pressure controlled by the thermostat opens and closes the valve
  • modulating valve: electric motor opens or closes the valve

In localized heater you have the forced air heaters:
  • approximately 80% efficiency
  • power vented
  • direct Spark Ignition
  • Big disadvantage of these heaters are that they bring a lot of humidity in the greenhouse, which makes them unsuitable to use in many climates for bell peppers and tomatoes the biggest vegetable greenhouse crops in the world.


Thermostatics  Units of heat quantity

  • British thermal unit (Btu): amount of heat energy required to raise the temperature of 1 pound of water 1 °F
    1 Btu = 252 cal
  • Horsepower (hp): another measure of energy; boiler heat output is reported as hp
    1 hp = 33,475 Btu

Japanese rebuilding horticulture after tsunami

Who doesn’t remember the horrible pictures and videos of the earthquakes and the follow up tsunami in Tohoku Japan in March 2011? The Tohoku earthquake, as the Japanese call it and tsunami that followed left around 16,000 people dead and many more displaced without housing or job-site to go to. The Japanese started immediately making plans for rebuilding the region there is still a lot to do, but they are going strong.


Clean up teams are still working in the area collecting rubbish and garbage. The total area that has to be cleaned up is around 23,600 Ha which is a little less than 20% of total area of the Netherlands. This is going in quite an efficient way. It’s not only the visible things that needed to be cleaned up also the soil is quite contaminated with the salty water from the sea. Just a friendly reminder the EC level of sea water is around 54. It’s not possible to grow rice or strawberries on these soils before they are cleaned up.

2012-07-24 03.32.49 30%

As there is quite some strawberry production in Yamamoto-cho in Miyagi, the Japanese government decided to build a new research station called High-tech Professional Research Facility. Advanced researches for tomato and strawberry are taking place in this modern greenhouse of 7,200 m2. Several national and public research institutes, universities and private companies form a consortium to conduct researches together. Research goals by 2017 are to improve production and quality of the products, reduce production costs and improve profit of farm management. The first phase of the greenhouse construction was done by one of the Japanese leading greenhouse builders Ishiguro Nozai who not only built the greenhouse but also supplied the irrigation, cooling and heating systems. The computer controls for this project were delivered by Hoogendoorn which installed an iSii computer for complete control of the greenhouse.

2012-07-24 01.22.08 30%

The Japanese users are very happy with the system as it is easy to operate and Ishiguro has developed some very handy visualizations so a good understanding of all the processes going on in the greenhouse is easily achieved.


Prime Minister Noda 45%

The projected was inaugurated by the Japanese Prime Minister Yoshihiko Noda, see picture.

Next photos give you an impression of the greenhouse constructed by Ishiguro

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2012-07-24 01.17.59 30%

At the moment the construction for the second phase has started.

2012-07-24 01.19.05 30%


Horticulture one liners

Tomato production per m2

Over the last 50 years, the greenhouse industry has grown from small family based operation to large enterprises, from low-tech glasshouse with little environmental control to high-tech modern greenhouse with complex climate control systems, from soil to soiless production, and from short production cycle to year-round production of high quality produce.

Some important facts to know:

  1. Light is the most important growth factor in plants production 1% more light in a greenhouse gives 1% more production.
  2. Adding CO2 to your greenhouse production will increase your tomato production by 30% to 40%.
  3. By the year 2020 The Netherlands will have an energy neutral greenhouse production
  4. Labor and shipping costs in North America can be at least five times more costly than heating so mechanize where possible.

The most productive tomato farm in the world at this moment produces 104 Kg tomatoes per m2. Numbers tell the tale: Without adequate water tomato yields around Leamington Ontario in Canada run about 75.000 – 86.000 kg tomatoes per hectare. If the growers has a good irrigation system it will achieve almost double, 124.000 to 148.000 kg tomatoes per hectare. If these tomato plants are put in Greenhouses, you can achieve a 500.000 in an average middle tech greenhouse up till over 1.000.0000 kilos per hectare in a high tech greenhouse such as Village Farms

The computer age has been with us for 30-plus years and many operations still don’t take advantage of its potential. Computers are tools that can enhance steps and procedures in our business when we know what the outcomes are. The can definitely solve problems. By using the computer to take care of routine tasks of record keeping, planning and retrieving information, we will have more time to solve problems and improve our operations.

Greenhouse concept of electrical combination panels

A Typical Greenhouse installation has many separate electrical control panels.

Typical American Greenhouses Electrical Pannel Installation
Typical American Greenhouses Electrical Panel Installation

You can make your installation simple and less costly by having:

[checklist icon=”fa-chevron-circle-right” iconcolor=”” circle=”” circlecolor=”” size=”small” class=”” id=””]
[li_item icon=””]No separate 575V or 480V Circuit Breaker Panel[/li_item]
[li_item icon=””]No separate 208V Circuit Breaker Panel[/li_item]
[li_item icon=””]No cables and conduit between Circuit Breaker Panels and Motor Control Panel[/li_item]
[li_item icon=””]No separate Computer Panel[/li_item]
[li_item icon=””]No separate Computer Override Switch Panel[/li_item]
[li_item icon=””]No separate Motor Control Panel[/li_item]
[li_item icon=””]No cables and conduits between Computer Panel and Override Switch Panel[/li_item]
[li_item icon=””]No cables and conduits between Computer Panel and Motor Control boxes[/li_item]
[li_item icon=””]No cables and conduits between Override SwitchPanel and Motor Control Boxes[/li_item]

Scratch from your installation

What you can take out to make it simple
What you can take out to make it simple

Save money

[checklist icon=”fa-chevron-circle-right” iconcolor=”” circle=”” circlecolor=”” size=”small” class=”” id=””]
[li_item icon=””]By not installing separate Circuit Breaker panels, Computer panels and motor starter boxes[/li_item]
[li_item icon=””]By not installing all interconnecting cables for all these enclosures[/li_item]
[li_item icon=””]By not terminating all these external cables (both sides)[/li_item]
[li_item icon=””]By installing less conduit[/li_item]
[li_item icon=””]By not having to “trouble shoot” all external wire connections[/li_item]
[li_item icon=””]By not servicing and maintaining all separate boxes[/li_item]

Do not only look at purchasing cost of individual equipment when you start

But look at the total cost of the final installation

The end result can be …..

Electrical Combination Panel
Electrical Combination Panel

Everything in just one panel

[checklist icon=”fa-chevron-circle-right” iconcolor=”” circle=”” circlecolor=”” size=”small” class=”” id=””]
[li_item icon=””]Drawings of all circuitry provided with the panel[/li_item]
[li_item icon=””]Installation can be done by any electrician even if they are untrained in greenhouse automation systems[/li_item]
[li_item icon=””]Less clutter of all separate boxes with interconnections and conduit in the greenhouse[/li_item]
[li_item icon=””]Lower maintenance and troubleshooting costs[/li_item]
[li_item icon=””]A clean installation in your greenhouse at a lower total installed cost[/li_item]

Final Scheme

Be wise invest in Electrical Combination panels for the long term.

Thanks to Al van den Ende Ispecs

también está disponible en español

El Concepto de Panels de Control

Un invernadero tiene muchas cajas de control e interruptores.

Panels son menos costoso y mas fácil instalación
La combinación de los requisitos de los controles eléctricos y los cortacircuitos en unos pocos paneles fácil de instalar, simplifica la instalación complete y ahorrar dinero en todo el proyecto.

Estos paneles personalizados contienen y combinan todos los puntos de datos Hoogendoorn, los módulos de interfaz los arrancadores de motor y tambien los paneles de cortacircuitos norteamericanos.

Los puntos de datos son el hardware de la computadora, tambien conocidos como los módulos o terminales de entrada y salida.

Quitar de su instalación

What you can take out to make it simple
What you can take out to make it simple

Ahorra dinero

Módulos de interfase han sido agregados para vincular el hardware de la computadora con los circuitos de controles eléctricos.

Reveladores de control de alto voltaje han sido agregados para vincular los módulos de interfaz a los circuitos eléctricos de control de alto voltaje.

Arrancadores de moteres han sido agregados para encender y proteger los circuitos de suministro del motor.

El resultado final …..

Panel eléctrico de combinación Panel
Panel eléctrico de combinación Panel
Proyecto Final
Final Scheme

Sé prudente invertir en paneles eléctricos de combinación para el largo plazo

Gracias Al van den Ende Ispecs

Also available in English