Greenhouse Automation - Overview

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Introduction

The Greenhouse Automation project is comprised of a series of custom automation devices that I designed and built for the purpose of managing of the growing conditions within our residential greenhouse.

Background

In the summer of 2015, my wife and I assembled a Harbor Freight 10 ft. x 12 ft. greenhouse (Item # 93358).

Harbor Freight 10 ft x 12 ft greenhouse product page	Harbor Freight greenhouse illustration

We constructed a concrete footing for the structure and, after assembly, used 3/4" galvanized steel EMT tubing to put horizontal reinforcement midway up the walls, tie the walls together side to side, and place a diagonal brace at the top of each corner. We also doubled the number of clips holding the wall panels in the framing and fastened the panels to structure cross-members with gasketed sheet metal screws. All this was done as a precaution against the high winds we experience at our home (on occasion reaching 40-50 mph and even higher during what seem like microbursts).

Greenhouse, looking northeast	Greenhouse, looking southwest

Ventilation Issues

	Greenhouse manually-operated roof vents

The out-of-the-box greenhouse from Harbor Freight is accessed through a double-section sliding door and comes equipped with four manually-operated roof vents. The vents are positioned using a single arm that is attached to a pivot on the underside of the vent lid (see picture below). The amount that the vent is opened is determined by engaging one of four slots in the arm with a peg that is mounted on the lower edge of the vent sill. The mechanical connection of the slot and the post could fail under sufficient jostling due to wind. Also, the single attachment point on the underside of the vent lid allows the lid to wobble and oscillate with the wind, making the lid more susceptible to wind damage.

Other than the sliding door and the roof vents, there are no other airways provided with the greenhouse. For standard convection-based air circulation, the sliding door would have to be left open to some degree. Since there is no screen on the sliding door, leaving it open would defeat one of the purposes of the greenhouse, namely, protection of the plants from various critters (on our property we have ground squirrels, voles, and field mice that could readily invade the structure if given the chance).

Our Challenges

Our challenges in getting the most out of our greenhouse mainly stem from the kind of weather that we experience where we live. We are situated on the western slopes of Pike's Peak in the mountains of Colorado at an altitude of 9200 feet. As mentioned earlier, we have some considerable winds from time to time. Our growing season is understandably short--the first frost-free date is June 16th! Our air is very clear and we commonly have beautiful scattered clouds in the afternoon, which leads to sudden variations in solar heating for the greenhouse as the clouds roll by. Under these conditions, in order to stay within good growing temperatures in late Spring through early Fall, the venting and air circulation of the greenhouse must be able to respond to these environmental effects within a few minutes. In order to extend our growing season in early Spring and late Fall, heat needs to be captured using some sort of storage strategy to keep temperatures within acceptable bounds during the chilly nights. All of this needs to be accomplished without creating ways for critters to get in and without a need for minute-by-minute attention. Finally, with regard to the structural preservation of the greenhouse, some means of protecting the vent lids against wind damage is very desirable.

Project Goals

In order to address the challenges described above, we determined the following major goals for the project:

• Develop an automated means of opening and closing the vents which includes the following features:
  • Recognizes and responds to temperature changes within a few minutes
  • Adjusts each individual vent opening according to various considerations such as growing bed temperature, time of day, outside temperature, wind conditions, and so forth
  • Attaches to the vent pane by a means that tends to dampen oscillatory motion
  • Provides a continuous range of variation in vent opening
  • Control settings dictated by centralized environmental management system
• Develop an automated active air circulation system which includes the following features:
  • Actively circulates air within the greenhouse and through the vent openings
  • Provides a continuous range of variation in air circulation
  • Control settings dictated by a centralized environmental management system
• Develop a centralized environmental management system to direct the actions of the various controllers in order to achieve the desired growing conditions of the greenhouse

The temperature regulation objectives also lead to developing an automated means of:

• Dermining the aggregate temperature in the growing area
• Determining the relative humidity in the greenhouse enclosure
• Controlling a water circulation system or heating units as part of a heat generation and storage strategy

Project Components

The goals and tasks outlined above lead to the creation of the system components detailed in the subsequent sections:

• Vent Controller - Opens and closes a vent according to commands from the centralized environmental management system.
• Fan Controller - Activates an air circulating fan and variably controls two exhaust vent fans according to commands from the centralized environmental management system.
• Thermal Controller - Gathers temperature readings from an array of digital thermometers positioned throughout the growing area and provides outputs to control a number of valves, relays, and the like that can be used for water circulation, heating, or other purposes. Temperature readings are reported and valve or relay actions are managed via the centralized environmental management system.
• Environment Manager (EM) - Gathers environmental data and directs the actions of greenhouse automation devices to achieve the desired growing conditions.

Continue to System Architecture

This page last revised on 05/05/2018