Using heat recovery ventilation systems in high tunnels to increase winter crop production

Using heat recovery ventilation systems in high tunnels to increase winter crop production

Summary

Because humidity control is crucial to the health of leafy greens and other winter high tunnel crops, it is essential for winter growers in the northeast to ventilate during the winter. This can lead to a tradeoff of lower average daily temperatures for humidity control.

The goal of this project is to address this trade off in temperature for humidity control by the use of a heat recovery ventilator to control humidity in winter high tunnel production. The projects tests weather the heat recovery ventilator can achieve adequate humidity control to reduce foliar diseases while maintaining a higher average daily temperature in winter tunnel production in order to increase crop production.

NCAT has partnered with New Morning Farm to install heat recovery ventilation equipment in a high tunnel on the farm and data collectors to monitor a high tunnel crops trial over the winter of 2015-2016.

Objectives/Performance Targets

Two 20X96 foot high tunnels on New Morning Farm were selected for this project. One tunnel is known as the Upper High Tunnel (UHT) and one is called the Lower High Tunnel (LHT). Soil samples were taken in each tunnel in early September and sent to the Penn State Analytical Labs for testing.

Also, in September all ventilation and data logging equipment was purchased. This included a 106 cfm FanTec Heat Recovery ventilator, supply air and exhaust hoods, flexible duct work, and EL-USB 2 data loggers for temperature and humidity recording.

On October 6th NCAT and New Morning Farm teamed up to install the ventilation equipment in the LHT and the data loggers where installed in both high tunnels and outside the tunnels. It took about six labor hours to install all of the equipment and data logging equipment.

Accomplishments/Milestones

• September 2015 – Ventilation equipment, data loggers, and trial plot seeds are purchased. Soil samples are taken in each tunnel and submitted for analysis.
• October 2015 – Heat exchange ventilation equipment and electric meter are installed in the LHT. Data Loggers are installed in both tunnels and outside. This installation was delayed while waiting for 5” flex duct needed for the ventilation system to arrive. Soil was prepared and two beds of transplanted spinach and two beds of direct seeded Asian greens were planted in each tunnel in the last week of October. The tunnels were closed up and the ventilation equipment was turned on in the LHT and all data logging was started.
• November and December 2015 – Crop harvest and disease records were kept and temperature and relative humidity data was collected form data loggers.
• January – April 2016 – Records will continue to be kept on planting, production, harvest and sales for all test plot crops. Ventilation equipment will be maintained consisting of cleaning the air filter and emptying the condensation bucket.
• April – May 2016 – The collected data will be analyzed and NCAT will develop and promote a webinar for the project.
• April 2016 –Project field day event at New Morning Farm and collect participant evaluations. The field day will focus on dissemination of information and lessons learned up to that point and show how the ventilation system was installed.
• May 2016- NCAT will host a webinar on the project and participants will be evaluated.
• July 2016- A final project report will be submitted to NESARE.

Impacts and Contributions/Outcomes

The temperature and humidity data collected from the tunnels on December 18, 2015 has shown a slightly higher average relative humidity in the LHT with the heat recovery ventilation equipment compared to the control tunnel. Also, there has been some foliar disease damage observed in the spinach crop in the UHT.  Niether of these results are conclusive and we will need more information from the rest of the winter growing season to make an assessment of the project.

The unseasonably warm 2015 fall weather has caused the conventional venting system in the tunnels to operate more frequently than they would have under normal fall tempuratures. This may have negated some of the effectiveness of the heat recovery ventilation system that we are testing in this project. 

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