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

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

WKK or CHP stops innovation in Horticulture Holland

In the Netherlands in the last years greenhouses are heated and powered by WKK (warmte kracht koppeling) in English CHP which means Combined Heat and Power also known as co-generation. By installing a CHP system designed to meet the thermal and electrical base loads of a greenhouse, CHP greatly increases the greenhouse operational efficiency and decrease energy costs. How does a CHP work in a greenhouse, a plant in a greenhouse in the northern  hemisphere  need most of the time heat, light and CO2 to grow optimal.  A CHP is providing this by burning natural gas and giving electricity, heat and CO2 in return.

CHP Cogeration

If you look at today’s power plants which burns natural gas still 45% is turned into heat and not into electricity this is a waste of energy because most of the time the heat is unused and therefore dumped. A greenhouse grower is burning natural gas to make electricity, one part of the electricity he is using for his grow light another part he is using to heat his greenhouse with. The CO2 which the grower is producing he feeds to his plants so they are more productive. A greenhouse has an efficiency of 90% compared to a gas powered electricity plant of around 45%

In Holland the co-generation became very popular of the current 10,000 hectare of greenhouses 6,000 hectare is using the thermal and electricity power of an CHP. Those greenhouses are producing now around 2000 Mwe and in 2011 this will be around 3000 Mwe. Currently around 20% of the total electricity demand in the Netherlands is produced by greenhouse growers and this will further grow in the coming years.


The dutch government and some NGOs like LTO Glaskracht and the  Association Nature and Environment have the ambition for 2020, to have a climate neutral Dutch Greenhouse sector which is independent on high energy prices.

Down site to the success of the CHP in the Dutch horticultural sector is that it slows down  innovation which is so badly further needed. The CHP is still using environmental unfriendly fossil fuel and it’s giving the greenhouses grower an income for producing electricity which inflates the price of the horticultural product they are growing such as tomato, chrysanthemum, bell peppers or cucumbers (decrease cost price). So CHP is an economical solution to keep on competing with countries which have a better climate to grow vegetables or flowers.

At this moment of the 10.000 hectares of greenhouses, 6.000 is heated with a CHP installation, so what to do with the other 4.000 hectares. Geothermal heating? At this moment it’s very popular but according to calculations of the Product Board of Horticulture Geothermal heating will only be able to heat 1.000 hectares in Holland. Another option is to burn bio fuels in stead of natural gas. Or maybe we have shouldn’t think of conventional greenhouses but look at new greenhouse concepts? We still have some time before it’s 2020.

Please comment any Greenhouse concepts or Energy solutions you think are worth investigating.

ELKAS Electricity Producing Greenhouse

Elkas (the electricity supplying greenhouse) shows how to convert solar energy into electricity. In designing energy generating greenhouses the emphasis still lies in systems that supply low-grade forms of energy (i.e. warmth). The electricity generating greenhouse is aimed at catching the radiation that is not being used for crop growth and converting it in high grade power.

ELKAS Energy producing greenhouseThe inteligent solution for this greenhouse is an integrated filter for rejecting near infrared radiation (NIR) and a solar energy delivery system. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated.

The special spectral selective properties of these materials have to block up to 50% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity.

The second measure is the integration of a solar energy system. When the NIR reflecting coating is designed as a parabolic or circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PV cell in the focus point delivers electric energy. With a ray tracing computer program the geometry of the reflector was optimally designed with respect to the maximum power level. The PV or TPV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (concentration factor of 40-120).

Or to say it simple PAR light (growth light) enters the greenhouse and the NIR light is reflected via the special foil to produce electricity. The foil to produce the electricity contains a few hundreds very thin layers, during tests the cheap silicium cells where found the most efficient solar cells. Because the sun is moving during the day and during the season the solar pannels are moveable and will move with the sun.

So far the results are promising and there was decided to built a research greenhouse which has been finished construction by the end of June 2008. This is the first electricity producing greenhouse in the world but so far it’s a small greenhouse of only 10m2 by 10m2. According to researcher Piet Sonneveld the concept has a lot of potential and it will be economically profitable within the next 5 years. In potential the ELKAS only needs 10% of a conventional Greenhouse. The electricity production of the ELKAS should be around 0.4 MW / Ha. Because the smart foil is keeping the excessive heating outside the climate inside the greenhouse for the plants is much better.

Policy of the Dutch governments is aimed at sustainable glasshouse horticulture in terms of economy, environment and labour conditions. In the Covenant Glasshouse Horticulture and Environment, government and glasshouse industry have set ambitious goals for energy, crop protection and fertilization for glasshouse industry in 2010.
The goals for energy saving are linked to the Kyoto protocol on the reduction of CO2 emission by setting a maximum for the glasshouse industry CO2 emission to 6.5 Mton at the actual area of 10.500 ha, which will be increased to 7.1 Mton if the area increases to 11.500 ha.

The ambition is that greenhouse systems built from 2020 on will compensate equally energy consumption by energy production. Assimilation lighting has proven to be a powerful tool to increase production and quality, especially in winter.

Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhosue
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse
Elkas Greenhouse

Partners in development of ELKAS

  • Wageningen UR
  • Plant Research International B.V. WUR
  • Bosman kassenbouw
  • EOS regulation center/Novem (financing)
  • Dutch ministry of Agriculture (financing)
  • Product Board of Horticulture (financing)
  • Stichting Energy Leverende kas (financing)