P14419: High Tunnel
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Build, Test, Document

Table of Contents

Test Plans

Test Controlled Environment (constant ambient temp) Outside Environment (varying ambient temp) Supplemental Light Supplemental Heat Procedure Equipment Goals Date Conducted Notes/Results
1 No Yes No No 1)Activate data loggers and attach to thermocouples (see test design for thermocouple placement)

2) Seal high tunnel and place outside for 1 night (or desired test length)

>(3) Soil thermocouples placed in center of soil bed at respected depths of 2, 6, and 10'' below grade >Verify the proper function of thermocouples

>Observe temperature trends/relations between internal air, external air, and soil temperature at different depths

11/2/2014 >Temperatures fluctuated as expected with internal air closely following ambient air, and soil temperatures slower to react.

>Middle of soil slowest to change

>See graphical results from test#1 for more details"

2 Yes (38 F) No No No 1)Activate data loggers and attach to thermocouples (see test design for thermocouple placement)

2) Seal high tunnel and place inside freezer

3) Let temperatures stabilize for 3 days (to ensure steady state has been reached)

>(3) Soil thermocouples placed in center of soil bed at respected depths of 2, 6, and 10'' below grade.

>Walk-in freezer

>Verify the proper function of thermocouples

>Observe temperature trends/relations between internal air, external air, and soil temperature at different depths in controlled cold environment

11/12/14-11/15/14 >Temperatures trended as expected, all converging to freezer internal temperature. Air quickest, soil took about 3 days to reach steady state.

See graphical results from test#2 for more details

3 Yes (38 F) No No Yes 1)Activate data loggers and attach to thermocouples (see test design for thermocouple placement).

2) Set heating cable thermostat to max temperature (70 F)

3) Seal high tunnel and place inside freezer

4) Let temperatures stabilize for 3 days (to ensure steady state has been reached)

>(3) Soil thermocouples placed in center of soil bed at respected depths of 2, 6, and 10'' below grade.

>Walk-in freezer

>HeatSafe Heating Cables (see test design for heating cable details)

>Observe temperature trends/relations between internal air, external air, and soil temperature at different depths in controlled cold environment >Observe function of heating cables

>Prove effectiveness of heating cables to verify thermo model and customer requirement of maintaining adequate soil temperature"

11/20/14-11/24/14

Heating cables may be dysfunctional

4 Yes (38 F) No Yes Yes 1)Activate data loggers and attach to thermocouples (see test design for thermocouple placement).

2) Set heating cable thermostat to max temperature (70 F)

3) Activate light on timer @8 hour/day increments (timer)

4) Seal high tunnel and place inside freezer)

5)Let temperatures stabilize for 3 days (to ensure steady state has been reached)

>(3) Soil thermocouples placed in center of soil bed at respected depths of 2, 6, and 10'' below grade.

>Walk-in freezer

>HeatSafe Heating Cables (see test design for heating cable details)

>Timer for light

>100 Watt incandescent light (see

>Observe temperature trends/relations between internal air, external air, and soil temperature at different depths in controlled cold environment

>Observe function of heating cables

>Prove effectiveness of heating cables to verify thermo model and customer requirement of maintaining adequate soil temperature"

11/20/14-11/24/14

Testing Facility

Testing Facility Breakdown

Testing Facility Breakdown

Before the full scale design is implemented, testing must be done to verify that the design choices made are credible and produce the desired results. To do this, a scale model of the high tunnel was developed to experiment with various features of the full-scale design.

The budget for the test facility comes from the Multidisciplinary Senior Design office and totals $1000. The test facility consists of a simple wooden box that has been screwed to a stand pallet for ease of transportation. A metal frame was cut and welded; it fits snugly inside the wooden box. Different prototype poly-carbonate panels were attached to the two available spaces on the hard panel side. This test facility contains soil heating cables in the middle layer of soil; about a 6” depth from the surface. In order to verify the effectiveness of the soil heating cables, two lengths were installed. The calculated length of 10m and a conservative estimate of 3.5m.

Testing Facility

Testing Facility

Test Results

Test 1 Results: This is the initial test to verify thermocouple function. The test facility was left outdoors over night. All temperature profiles are reasonable and concur with measured outdoor temperature.

Test 1 Results: This is the initial test to verify thermocouple function. The test facility was left outdoors over night. All temperature profiles are reasonable and concur with measured outdoor temperature.

Test 2 Results: This is the temperature vs time curve when the test facility was kept in a temperature controlled freezer. The temperatures converged on the freezer temperature after roughly 36 hours. The transformer connected to the thermostat had tripped at some point and did not heat the soil.

Test 2 Results: This is the temperature vs time curve when the test facility was kept in a temperature controlled freezer. The temperatures converged on the freezer temperature after roughly 36 hours. The transformer connected to the thermostat had tripped at some point and did not heat the soil.

Test 3 Results: This test confirms a severe risk: dysfunctional heating cables. Power was confirmed to the thermostat but the temperatures did not increase. An electronic issue is keeping the heating cables from working at all.

Test 3 Results: This test confirms a severe risk: dysfunctional heating cables. Power was confirmed to the thermostat but the temperatures did not increase. An electronic issue is keeping the heating cables from working at all.

Assembly Instructions

While not optimal, links to a bill of materials are below. This prototype is not meant to be a miniature fully functional high tunnel, though it can function as such, but rather it is designed to best simulate the client's high tunnel environment so that testing, as described in above sections, could be completed and controlled.

Prototype Bill of Materials

There are a few valuable insights that this prototype has provided with regards to building a full scale high tunnel. One of the mistakes of our prototype is the exclusion of a venting system. As a result, moisture was unable to escape the prototype which led to rusting of our frame and other issues. One of the big take aways from building of the prototype is the time it would take to cut and fasten panels to an entire high tunnel. While not a difficult process, it is time consuming. Moving to a full scale high tunnel and implementing irrigation, lighting, and subterranean heating is not as small of a project as it may have originally seemed. The customer, and her class, have a lot of work ahead of them to make this a reality. We have provided the necessary material for the customer to complete this project and have provided useful links and instructions below.

The water system was based off a previous design completed by a team at Iowa State University. A link to their design, complete with general design and assembly guides is below.

Iowa State Water Catchment System

Another useful resource for designing the watering system is http://www.irrigationtutorials.com/. This link provides an outline of the basic of irrigating your crops and provides an in depth process on how to design your own irrigation system.

User or Operator Instructions/Manual

The growing of vegetables is not something that follows a strict user manual as every species of plant has different specific needs and most gardeners (the operator in this case) have different preferences as to what they feel is a best practice for growing. The goal of this project was not to provide a strict instruction on how to grow vegetables, but rather provide the means for the operator to grow vegetables year round in a way that they see fit. There are however, a number of general guidelines that should be followed.

First, we suggest anyone furthering or replicating this project to look into previously written material on high tunnels and winter growing. A resource that we used, and feel provides an adequate introduction to this topic is:

Second, every species of plant has a set of general environmental guidelines that should be adhered to such as proper temperature, watering schedules and seasonality. The final high tunnel allows for these variables to be easily changed to suite the operator's needs. Watering frequency and internal temperature (as set by a compound of lighting, outside temperature, and subterranean heating) can be automated with the use of timers and/or temperature sensors. Sensors exist that will cut power to electrical heating elements when a temperature threshold is reached. An additional element of our design that allows for automation is the use of automated window hinges. These hinges expand or contract based on temperature and help to autonomously keep the high tunnel at a stable temperature. These represent a relatively cheap investment to protect your crop.

Below we have included basic instructions to guide the customer and any other viewers on how best to set up the developed system.

Assembly Instructions


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