Greenhouse thermostats versus environmental ventilation controller

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The energy savings are significant when a thermostat with a 4 - 6°F difference between on and off is replaced with an electronic controller with a 2°F difference. The heater turns off quicker, resulting in less heat loss from the greenhouse surface and energy savings.
For example, in a 30' x 100' double-covered greenhouse heated to a night temperature of 60°F in a northern climate (Hartford, CT) during the winter, replacing the mechanical thermostat with a 6°F differential with a controller with a 2°F differential will result in a savings of approximately 750 gallons of fuel oil. Instead of heating the greenhouse air to 66°F before turning off the heater, the controller will turn it off at 62°F. Each degree less temperature in the greenhouse saves around 3% in fuel. The payback period for installing the controller is less than a year at today's energy pricing. It is the reason mechanical thermostats are becoming increasingly obsolete.
A programmable controller is a logic-capable control device that is not powerful enough to be considered a computer. The most basic ones replace numerous thermostats and often include 5 to 6 control stages (two heat stages, 3 or 4 cooling stages, and a setpoint).
Controllers monitor environmental data in the greenhouse and generate output signals that activate equipment based on a set of internal programmed instructions. They use basic low cost microprocessors that are reliable and accurate in a greenhouse setting. Basic step controllers typically cost between $600 and $1500, depending on the number of steps, relays, or contactors required to regulate the equipment.

Environmental Ventilation  Controller benefits:

The greenhouse's heating and cooling operations are divided into stages. The controller switches between them as the circumstances in the greenhouse change. Each stage can have multiple pieces of equipment, such as two heaters, HAF fans, and an energy screen. The farmer programs the sequence of equipment operation and the temperature at each stage.
All components are contained under a single weatherproof enclosure, which reduces moisture, dust, and maintenance.
Relays, switches, and controllers can be purchased  prewired  to decrease installation time.
The temperature sensor is usually on the end of a long cord and can be placed within the plants.
Energy consumption is lowered as a result of more precise sensing and control.
Controllers work using a setpoint, the desired air temperature in the greenhouse. If the temperature falls below the set point, the heating system fires up. If the temperature rises beyond the set point, the vents will open, or the fans will turn on, bringing cold air in. With various cooling stages, vents open or extra fans activate. The activation of an evaporative cooling system could be the last stage. For manual operation, an override is offered at each level.
Depending on the manufacturer and model, the following features or functions may be standard or optional:
LED or touchscreen display - Shows the current temperature, time, date, and other data.
Battery backup - Saves the settings in the event of a power outage.
Alarm activation - This feature can be linked to a trouble alarm.
Ramping - Controls the rate at which day and night settings change.
Temperature sensitivity - For best control, the accuracy should be between 1/2° and 1°F.
The temperature difference between stages can be fixed or variable.
Temperature settings for day and night: This is called temperature diffs and is good method of improving your growing conditions
Aspirated sensor box - A small blower sweeps air over the sensors to calculate the average temperature in the greenhouse.
Tracking entails storing high/low-temperature data for each setpoint. This is normally done online. AutoVent's Farmshield tracks it for two weeks and allows downloads of the temperature data.
Advanced environmental controllers usually have extra control stages, weather station options, and the ability to operate numerous zones.
Ventilation controllers are typically meant to manage roof vents, side vents, roll-up walls, and retractable roofs. It can operate in a variety of stages or settings.
Irrigation and misting controllers control solenoid valves that automate the irrigation system. Soil moisture, a vapor pressure deficit, and the time of day can trigger activation. Controlling many zones is possible.
Energy/shade screen system controllers open and close screens automatically using a light sensor. Safety safeguards that protect the motor and screen from overload are typically included.
When the controller detects that the motor amps are approaching a critical level, it turns off the motor.
Boiler controllers detect carbon dioxide and oxygen levels in flue gases and adjust the combustion air intake to achieve maximum combustion efficiency.
Controllers are the next level of control after thermostats and time clocks. They save electric and improve environmental control at the same time.

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