Sistemas de Calefacción en Invernaderos.

La calefacción en los Invernaderos es una de las primeras y más innovadoras revoluciones que ha tenido la Horticultura. En Holanda el uso extensivo de la calefacción comenzó en los años 60´s. En los 80´s comenzó la segunda revolución con el uso de sistemas computarizados de control, a mediados de los 90´s las luces de crecimiento fueron adheridas a la ecuación. Hasta el momento estamos a la mitad de la Revolución del Invernadero Completamente Cerrado.

En este artículo hablaremos de los diferentes tipos de calefacciones que se usan en los Invernaderos, tanto de sus ventajas como desventajas.

Para calentar tu planta o flor dentro del invernadero, en cosechas como rosas, crisantemos, claveles, tomates, pepinos y pimientos usted tiene la opción entre un sistema de calefacción centralizado o un sistema localizado, o no utilizar ningún sistema (dependiendo de la zona y el clima).

Calefacción Central:

Caldera de Agua caliente o vapor con sistema de tubería metálica.

  • Inversión Grande, Gran capacidad
  • Se pueden usar combustibles más baratos.
  • Una falla o problema puede ser crítica si no se tiene seguridad previa.
  • Ineficiente si no se trabaja cerca de la capacidad necesaria.
  • La calefacción del fondo es más práctica

Calentadores localizados, comúnmente llamados Calentadores de Aire Forzado: Unidades de calentadores de gas o sopletes, pueden ser con un tubo de convección o calentadores infrarrojos.

  • Inversión Inicial Baja
  • Versátiles
  • Pueden ser para cualquier área, fácil de expandir o contraer
  • Si la unidad falla, otras pueden cubrir su trabajo.
  • Mas difícil de distribuir eficientemente el calor

Si vemos a fondo la calefacción central, tenemos dos opciones:

Agua Caliente: Una caldera central se usa para calentar el agua entre 120 F and 180 F. El agua es distribuida mediante tuberías de metal en el invernadero. Bombas y válvulas de mezcla son usadas para distribuir uniformemente el calor y para controlar cuanto calor sale del Invernadero. Da un buen control de la temperatura, cambios más graduales de temperatura, puede ser un poco lento para caídas repentinas de temperatura. Son utilizados grandes volúmenes de agua.

Vapor: Un sistema de vapor utiliza una caldera más pequeña, menos tuberías y no utiliza bombas de circulación. Es más difícil de controlar el flujo de vapor o calor hacia el invernadero. Ingreso rápido de calor y cambios más rápidos en la temperatura, pueden ser posibles. Generalmente sistemas de baja presión son utilizados en los invernaderos (5 a 15 libras). El agua se expande y es convertida en vapor lo que causa presión y fuerza el vapor desde la caldera por las tuberías hacia el invernadero. Mientras se condensa, se pierde volumen y la condensación se drena de regreso a la caldera mediante gravedad. Un pie cubico de agua se expandirá 58.8 pies cúbicos de vapor. El tubo de vapor es generalmente más pequeño que el de agua caliente ya que tiene menor Resistencia al flujo y un alta perdida de calor por pie de tubo.

La caldera tiene que distribuir el vapor o el agua caliente dentro del invernadero, para lo cual hay varias formas de hacerlo:

 

Distribución de calor por Tubo/Riel

Pipe Rail Heating System

 

Los Sistemas de calefacción por tubo/riel son comúnmente usados y son muy importantes para sacar la humedad de los invernaderos. En las mañanas encienden el sistema, que es normalmente llamado temperatura de “tubo mínima”, de esta forma pueden sacar el exceso de humedad del invernadero para obtener un mayor clima dentro. Entonces aparte del control de temperatura, esta es una de las herramientas más importantes en el control de humedad. En la foto debajo, usted podrá ver un sistema similar en crisantemos, en estos cultivos es probable que el agrónomo utilice un sistema especial llamado “sistema de calefacción de alzado” Ya que ellos necesitan mejorar el suelo mediante vaporización, arado y agregando material orgánico. En este sistema el agrónomo tiene la posibilidad de levantar el sistema y hacer el trabajo más fácilmente.

Hoisting Heat system Chrysanthemums

Sistema de calefacción debajo de la mesa.

Cuando se está sembrando en masetas en una mesa, es necesario un sistema de calefacción similar al de tubo/riel pero este sistema está localizado debajo de una mesa.

Under bench Heating

Distribución de calor dentro del piso.

in floor heating

En la fotografía se pueden observar los tubos de un sistema de calefacción dentro del piso, el sistema de la foto no ha sido terminado aún, ya que todavía le falta que le pongan el concreto encima de los tubos. Esta fotografía da una buena mirada a cómo trabaja este sistema. Algunas veces este sistema es llamado “sistema de calefacción de radiador” Este sistema es mayormente usado en plantas en maseta criadas directamente en el piso. El piso se calienta, lo cual causa un movimiento de aire que tiene un efecto positivo en la humedad alrededor de la planta, ya que puede ser removido de ahí. Ya que es un sistema en el piso, el mismo da una mayor libertad para trabajar al obrero, sin que este moleste en sus actividades.

Distribución de calor “sobre la cabeza”

Overhead Heating Systems

Calefacción “sobre la cabeza” es muy importante en aéreas donde se puede tener un invierno muy frio, ya que provee de una calefacción adicional. Este sistema es muy compatible con canastas colgantes. Una desventaja es que el sistema le quita mucha luz a las plantas.

Distribución de calor “Perimetral”

perimeter heating tubes and star fin pipes

E un invierno muy frio, cuando el sistema normal de calefacción no puede detener el frio proveniente del norte, la calefacción adiciona en el perímetro ayudará. En la fotografía superior puede ver un ejemplo.

Tipos de válvulas de vapor:

  • Neumáticas: la válvula se abre y se cierra mediante la presión del aire
  • Válvula moduladora: Un motor eléctrico, abre o cierra la válvula.

Calefacción localizada:

En la calefacción localizada se tienen calefactores de aire forzado:

  • Son aproximadamente 80% eficientes
  • Ventilados eléctricamente
  • Ignición directa por chispa
  • Una gran desventaja es que estos calentadores pueden traer mucha humedad al invernadero, lo que los hace inútiles en muchos climas para pimientos y tomates, las cuales son las más grandes cosechas de vegetales en el mundo.

Cantidades de Unidades termostáticas

  • Unidad británica térmica (Btu): Cantidad de energía calórica requerida para aumentar una libra de agua 1 °F más.
    1 Btu = 252 cal
  • Caballo de fuerza (hp): Otra medida de energía; la salida reportada de una caldera, hablando de caballos de fuerza es:
    1 hp = 33,475 Btu

 

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

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]
[/checklist]

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]
[/checklist]

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]
[/checklist]

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

The white house on Facebook for Energy

facebook logo

I am normally not a supporter of politics on my blog, but today I think we have some interesting news Energy Secretary Steven Chu has joined Facebook to start a conversation about solving today’s energy challenges.

He recently joined Facebook because he wanted to talk with you directly about solving the energy and climate change challenge and ensuring America’s leadership in a clean energy economy. He hopes you will check out his new page at http://www.facebook.com/stevenchu

Steven Chu on Facebook

Steven is excited by the chance to share what the Obama Administration is doing to bring about a revolution in clean energy. They are finding innovative ways to use energy more efficiently, working to deploy clean energy technologies like solar and wind power, and conducting cutting edge research to find the next generation of clean technologies. He will keep you up to date on all the latest developments, as well as share tips that will save you money on your energy bills.

But Steven also want to hear from you about what you’re doing in your communities and the steps you think we should take as a nation. I hope we can have a true dialogue because every American can and must play a role in this effort.

I became a fan of Steven to support his effort to bring politics closer to the people.

fan steven chu