This article explains some of the many different types of heating systems that are available in the Priva Compass.

Hot water heating systems

Hot water heating systems consist of a series of pipes throughout the greenhouse that are filled with water.  A circulation pump continuously moves the water through the pipes.  A water temperature sensor measures the temperature of the water and a mixing valve will bring in hotter water as necessary to maintain the desired water temperature. 

The Priva Compass can control four different hot water heating pipes in a greenhouse zone in various configurations.

Single hot water heating system

This system consists of a single pipe heating system throughout the greenhouse that controls the temperature of the entire greenhouse.  The Priva Compass will control the mixing valve to maintain the desired water temperature.

This type of system uses the following inputs and outputs from the Priva Compass:

• temperature & humidity sensor
• water temperature sensor
• mixing valve control
• circulation pump

Multiple hot water heating systems

The greenhouse can have multiple hot water heating systems in a zone.  Typically there may be one pipe heating system at root level and a second pipe heating system at overhead level.  The root level heating system is used to stimulate air movement by natural heat convection through the plants and to keep the root zone warm.  In order to prevent the roots from getting too warm,  a maximum water temperature is set for the root zone pipe .   The overhead heating system is used when the root zone pipe does not provide enough heat to keep the greenhouse at temperature.

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor
• water temperature sensor for each pipe heating system 
• mixing valve control for each pipe heating system
• circulation pump for each pipe heating system

Divided hot water heating system

There are instances where multiple heating systems are used to control subzones within a greenhouse climate zone. For instance a central concrete walkway may go through the middle of a zone. In this case, two pipe heating systems at ground level in a greenhouse would be separated by the walkway. One pipe heating system would control the left half of the greenhouse and a second pipe heating system would control the right half of the greenhouse.  Each side of the greenhouse has its own temperature and humidity sensor.  The venting is controlled based on the average of the two sensors.

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor for each section of the greenhouse
• water temperature sensor for each section of the greenhouse
• mixing valve control for each section of the greenhouse
• circulation pump for each section of the greenhouse 

Localized hot water heating system

Another type of heating system is a localized heating system.  This is sometimes used as an extra perimeter heating system located along the outside walls of a greenhouse.  The perimeter heating uses a local temperature sensor to monitor the temperature along the perimeter and the control is based on that temperature sensor and the desired heating temperature of the entire heating system.  An offset temperature can be set so the perimeter area can be kept slightly warmer or cooler than the rest of the greenhouse.

This type of system uses the following inputs and outputs from the Priva Compass

• local temperature sensor to measure the air temperature in the perimeter area
• water temperature sensor for the perimeter heating
• mixing valve control for the perimeter heating
• circulation pump for the perimeter heating

Soil hot water heating system

Extra heating systems may be located on or under tables in the greenhouse and is used to keep the soil or growing media warm. The soil heating uses a soil temperature sensor to monitor the temperature of the soil. The soil heating is controlled based on the soil temperature sensor and a desired soil heating temperature set by the customer. 

This type of system uses the following inputs and outputs from the Priva Compass

• soil temperature sensor to measure the soil
• water temperature sensor for the bench heating
• mixing valve control for the bench heating
• circulation pump for the bench heating

 Fixed temperature hot water pipe system 

Mixing valve systems can also be used to maintain a fixed temperature.  This is not typically used as part of the heating system but can be used to heat irrigation water before use.

This type of system uses the following inputs and outputs from the Priva Compass

• water temperature sensor
• mixing valve control

Other types of heating systems

Greenhouses may be heated by something other than hot water.  For all other controls, staged heating systems are available in the Priva Compass.  

Single stage heating systems

These are heating systems that can either be on or off based on whether heat is needed in the greenhouse. When the air temperature goes below the heating temperature, the stage will turn on and when the air temperature goes back above the heating temperature the stage will turn back off

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor
• heat stage output

 Multiple stage heating systems

It is possible to have up to four heating stages to control the temperature in the greenhouse. As more heat is needed, more heating stages will turn on.

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor
• heat stage outputs

 Pulsed heating systems

Pulsed heating can be used if the heat stage produces residual heat even if it is turned off. This is often used for steam heating systems. If heat is needed, the heating output turns on for a short period of time and then turns off again.  If more heat is needed, the heating pulse is longer and the time between pulses is shorter.  At full heating requirement, the heating output is on continuously.

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor
• heat stage digital output

Analog heating systems

The analog output (0-10 VDC) turns on when heat is needed. The voltage level of the analog output goes higher or lower as more or less heat is needed.

This type of system uses the following inputs and outputs from the Priva Compass

• temperature & humidity sensor
• heat stage analog output

 Local on/off heating system 

In addition to the main heating system, an extra heating system can be located in the greenhouse.  This localized heating uses a local temperature sensor to monitor the temperature.  Whenever the temperature is below the desired temperature, the local heating turns on.   The customer can set an offset temperature so the local area can be kept slightly warmer or cooler than the rest of the greenhouse.

This type of system uses the following inputs and outputs from the Priva Compass

• local temperature sensor to measure the air temperature in the local area
• local heating output

Soil on/off heating system

Soil heating stages can also be located under tables. The heating stages use soil temperature sensors to monitor the temperature of the soil. Whenever the temperature is below the desired temperature, the local heating turns on.   The customer can set a desired temperature that they want maintained in the soil. This can be a different temperature than the greenhouse climate.

This type of system uses the following inputs and outputs from the Priva Compass

• soil temperature sensor to measure the air temperature in the perimeter area
• soil heating output