Choose the Right Dry Cooler System for Your Greenhouse

dry cooler system

A greenhouse owner knows how important it is to maintain the right temperature and humidity levels. A dry cooler system is a key component of achieving this. You will learn about the factors for choosing a dry cooler system in this guide.

Understand Dry Cooler Systems

Let us understand how they work before choosing a right dry cooler system for your greenhouse.

Working Theory of Dry Cooler System

Dry cooler systems use air to accomplish process cooling, heat is transferred from the working fluid to the ambient air through a surface, such as a tube to air, which is then circulated through your greenhouse to regulate temperature.

There are two main types of dry cooler systems: air-cooled type and water-cooled type.  

Type of Dry Cooler System


Air-cooled system

  • More energy-efficient and easier to maintain.
  • Use fans to draw hot air out of the greenhouse, and cool air is then circulated back into the space.
  • Suitable for small to medium-sized greenhouses. 
  • Ideal for areas with low humidity.

Water-cooled system

  • Better suited for larger greenhouses with higher cooling demands.
  • Use water to transfer heat from the greenhouse to a cooling tower, where the heat is dissipated into the atmosphere.
  • More complex and require more maintenance than air-cooled systems.
  • But more efficient at cooling larger spaces and maintaining consistent temperatures.

Evaporative Cooling

Greenhouses can get extremely hot, which can be detrimental to plant growth. To combat this, many greenhouse owners use a dry cooler system. This system works by using evaporative cooling to reduce the air temperature.

As water evaporates, energy is lost air, causing its temperature to drop. Two temperatures are essential when dealing with evaporative cooling systems—dry and wet bulb temperatures.

Dry Bulb Temperature: Use with a regular thermometer exposed to the airstream.

Wet Bulb Temperature: The lowest temperature can be reached by the water evaporation.

Importance: Greenhouse owners can get plants the right temperature by monitoring both temperatures.


Wet Bulb Temperature - A Precision Tool for a Thriving Greenhouse

Several tools are available to determine the wet bulb temperature, which measures the moisture in the air, such as an aspiration psychrometer, a sling psychrometer, or an electronic humidity meter.

A damp bulb psychrometer consists of two thermometers, one with a wetted wick that evaporates water and cools the thermometer to the wet bulb temperature, while the other measures the dry bulb temperature.

The difference between sling psychrometer and aspiration psychrometer is the method of providing air movement, with the former being whirled rapidly and the latter using a small fan. 

Humidity Control: Ensuring Plant Success with Accurate Measurements

In a greenhouse, controlling the humidity levels is crucial for the growth of plants. While handheld electronic humidity meters are more convenient, wet bulb psychrometers are more useful for evaporative cooling systems. This is because damp bulb temperature directly determines the temperature at which air can be cooled by evaporative cooling alone. However, even if a humidity meter does not display wet bulb temperature, psychrometric charts and software packages are available to calculate it based on the dry bulb temperature and relative humidity.

Remind: electronic humidity meters may drift out of calibration and should be regularly checked against standards.

Optimal Greenhouse Temperatures

For the best plant growth, greenhouses need a controlled environment with a dry cooling system. This system can lower the air temperature by up to 13.5°F and is efficient up to 85%, even in hot, humid conditions. It's a practical and energy-saving choice for cooling greenhouses. The cooling efficiency affects the air temperature:

  • With 85% efficiency, air cools from a 95°F dry bulb and 80°F wet bulb temperature to 82°F.
  • At 70% efficiency, air cools to 84.5°F.
  • With 50% efficiency, air cools to 87.5°F.

Efficiency for Challenging Climates

A dry cooler system circulates air through a heat exchanger, which cools the air without adding moisture. This can be beneficial in areas with high humidity or where water is scarce.

However, users should note that the effectiveness of a dry cooler system also depends on outside temperature, humidity, and airflow. Therefore, it is recommended to monitor the wet bulb temperature in the afternoon, when the dry bulb temperature is at its peak, to determine the potential cooling performance of the system.

Superior Cooling for Optimal Plant Growth

Greenhouses require a cooling system to maintain a suitable temperature for growing plants, which uses a fan to circulate air through a water-filled pad. As the air passes through the wet place, the water evaporates, cooling the air before it enters the greenhouse. This process helps to regulate the temperature and humidity levels, creating a comfortable environment for plants to thrive.

Greenhouses also require cooling systems to maintain optimal humidity levels for plant growth. One such system is the dry cooler system, which uses high-pressure fog to cool the air. This method is more effective than traditional fan and pad systems, as it can maintain more uniform temperatures and humidities. While it may be more expensive, it is often the best option for achieving the necessary conditions for plant growth.

Factors to Consider a Right Dry Cooler System

Determining your cooling needs is the first step. The factors include greenhouse size, the type of plants you are growing, and the climate in your area, the desired temperature range, and the heat load from your plants and equipment.

Consider the Size and Location of Your Greenhouse

When choosing a dry cooler system for your greenhouse, it's essential to consider the size and location of your greenhouse. A giant greenhouse will require a more extensive dry cooling system to maintain optimal growing conditions.

Consider the size and location of your greenhouse. A giant greenhouse will require a more extensive dry cooling system to maintain optimal growing conditions. Additionally, the location of your conservatory can impact the effectiveness of your dry cooling system. A greenhouse located in a high-temperature or humid area may require a more assertive approach to keep the plants healthy and cool.

Location and Orientation

The efficiency of a dry cooler system in a greenhouse is greatly influenced by the orientation of the greenhouse concerning other buildings or structures, as well as the direction of prevailing summer winds.

Therefore, it is essential to consider these factors when selecting the placement and arrangement of fans and pads to ensure optimal operation. Proper greenhouse location and orientation can significantly enhance the effectiveness of a dry cooling system.

Evaluate the Energy Efficiency 

  • High COP (Coefficient of Performance) ratings or energy-efficient systems can help you save money on energy costs and reduce carbon footprint.
  • Systems with variable-speed fans and pumps, which can adjust to the specific needs of your conservatory and reduce energy waste.
  • Consider each system's maintenance requirements, as a well-maintained system will operate more efficiently and last longer.

Calculating Cooled Air Temperature: Precision in Greenhouse Climate Control

A dry cooler system is prevalent in greenhouses to regulate temperature. It uses the outside air, known as "tout," to cool down the greenhouse. A heat exchanger transfers the heat from the inside of the greenhouse to the outside by passing hot air through it. The cooled air is then circulated back into the greenhouse.

The formula used to calculate the cooled air temperature is:

Tcool=Tout - (% efficiency) (Tout - Twb)

This formula considers the outside temperature (Tout), the efficiency of the cooling system, and the wet bulb temperature (Twb) to determine the cooled air temperature. Greenhouse owners can use a dry cooling system to maintain a consistent and comfortable plant temperature.

Water Flow Rate

A dry cooling system is a common, energy-saving choice for greenhouse cooling. For best results, it needs enough pad surface area and a well-planned water supply system. The water needed varies, but generally, 1/3 gallon per foot of pad length is suggested for thorough wetting.

This is because you avoid excessive water flow, which can impede airflow and cause water transfer into the greenhouse. Instead, the pad surfaces should be covered with a thin film of water. Water collected by the bottom gutter is returned to a sump and pumped back to the upper distribution pipe or channel. For longer water distribution pipes, the sump should be located near the center of the line and have a capacity of 1 to 1¼ gallons per linear foot of pad to hold the water that drains back to the sump when the system stops.

Choose a System with the Right Features for Your Greenhouse

Selecting the right dry cooler system for your greenhouse is crucial. Keep these factors in mind:

  1. Greenhouse size, crop type, and local climate - a hot, humid environment may need a higher cooling capacity and dehumidification.
  2. Plant sensitivity - delicate plants may require precise temperature and humidity control, needing advanced controls and sensors.
  3. By considering these factors, you can maintain optimal growing conditions and maximize crop yields in your greenhouse.


Selecting the appropriate dry cooler system is essential for maintaining an ideal greenhouse environment with optimal temperature and humidity levels. Understand dry cooler basics, evaluate energy efficiency, and choose a system that meets your specific needs. Factors to consider include your greenhouse's size, location, the type of crops you're growing, and the local climate.

By making a well-informed choice, you'll enhance greenhouse performance, maximize crop yields, and support a successful, sustainable operation.


1. What is a dry cooler system?

A dry cooler is a type of cooling system used in various industries including HVAC. It works by using a fan to blow ambient air over a heat exchanger, which cools the process fluid flowing inside it. This happens in a closed loop, meaning the process fluid never comes into contact with the air and stays "dry".

2. What is the difference between air cooled chiller and dry cooler?

While both air-cooled chillers and dry coolers are used to remove heat, their operation differs. Air-cooled chillers use a refrigerant to absorb heat and then air to remove heat from the refrigerant. Dry coolers, on the other hand, use a heat exchanger and ambient air to directly cool the process fluid.

3. Why is it called a dry cooler?

The term "dry cooler" stems from the fact that the process fluid being cooled (like water or a glycol mix) doesn't evaporate. Unlike evaporative coolers, where water evaporates into the air to achieve cooling, the fluid in a dry cooler remains in a liquid state, hence it stays "dry".

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