Development of an integrated ventilation, thermal mass, and lighting system for the first Deep Winter Greenhouse (DWG) in North Dakota

Final report for FNC20-1234

Project Type: Farmer/Rancher
Funds awarded in 2020: $8,980.00
Projected End Date: 01/31/2022
Grant Recipient: Folly Hill Farm
Region: North Central
State: North Dakota
Project Coordinator:
Derek Lowstuter
Colorado State University Extension
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Project Information

Description of operation:

Folly Hill Farm is a working demonstration farm that was established in late 2016. The farm is situated on 40 acres of pasture land two miles north of the town of Menoken, ND. It is owned and operated by myself, Derek, and my wife, Claire Lowstuter. We currently live on the property with our daughter, and are looking into additional housing to host interns, seasonal employees, and agritourism guests. I work full time as a Land Management Specialist with the ND Department of Trust Lands. I have a Bachelor’s Degree in Natural Resource Management and a Master’s Degree in Collaborative Forest Management from Colorado State University. I am a
certified arborist, permaculture designer, and agroforester; with experience designing and managing permaculture practices in the western U.S., Ireland, Ethiopia and Thailand. Claire has a Bachelor’s Degree in Human Dimensions of Natural Resources with a minor in Sociology. She is also a certified permaculture designer and shares the same international agricultural experience. We are Returned Peace Corps Volunteers from Ethiopia.

The farm was established as a trial and demonstration farm for the organic soil amendments produced by Black Bison Organics LLC. The primary purpose of the farm is to be a testing ground for these products. The second, but equally important, purpose of the farm is to demonstrate innovative agricultural practices based on permaculture, agroecology, and agroforestry methods. Folly Hill Farm was established as a small, diversified farm that is intended to be self-supporting through the sale of raw and value-added agricultural products, and on-site trainings. The farm is not self-sufficient yet, but we are working towards that goal. Roughly thirty-five acres of the property are grazed by cattle owned by Paul and Gabe Brown of the neighboring Brown’s Ranch. We currently raise 50 laying ducks of various breeds and sell the eggs through local markets. We had plans to add fiber animals in 2021, but that has been delayed until further infrastructure can be built to support them. We grow various fruits and vegetables that we sell at a local market, and also sell to local CSA producers to supplement their share offerings.

There are a number of small fruit and unique trees that have been planted over the past two years. These include haskap, apricot, plum, rose hip, aronia, and many more.

We received grant funding from the ND Deptartment of Agriculture in 2019 to cover some of the cost associated with building the first Deep Winter Greenhouse (DWG) in the state. The building is roughly 90% complete -with the target to have the first planting in February 2022.


The project will monitor and integrate the active and passive environmental control systems of the first Deep Winter Greenhouse (DWG) built in North Dakota. DWGs are passive-solar structures with angles & dimensions that maximize solar heat during winter months, when the sun is low in the sky, and minimize solar heat during summer months, when the sun is high in the sky. The project will help balance the passive components of the greenhouse, such as the innovative use of phase change materials and an underground climate-battery, with the active components of the greenhouse, such as ventilation, heating, lighting, and CO2 supplementation. Funds will be used to professionally monitor and electronically-integrate the systems so they work synergistically, instead of antagonistically; which can easily occur with these multipart, multistage systems.

This work will maximize the efficiency of the greenhouse for growing specialty crops, and  improve its use as a demonstration and educational facility. Although the function of the greenhouse is to grow crops, its primary purpose is to demonstrate the use of innovative production methods for beginning and established producers. This project will improve the utility of the greenhouse as both an educational and agricultural tool.  

Project Objectives:
  1. Develop a monitoring system and integration protocol to maximize efficiency in, and between,  greenhouse heating/cooling, air exchange, humidity, CO2, and lighting systems. This includes improving the way systems work together, but also mitigating system antagonism (e.g. venting air at same time as pulling heat from thermal mass).   
  2. Evaluate the effectiveness of tiles composed of phase change material in regulating the internal temperature of a passive solar greenhouse, reflecting ambient light, and acting as a durable greenhouse wall covering.
  3. Evaluate the effectiveness of a Ground to Air Heat Transfer (GAHT) system in heating, cooling, and dehumidifying a passive solar greenhouse in North Dakota.


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  • Stephanie Blumhagen (Educator)


Materials and methods:

This is the final design used to construct the greenhouse. The brown panels are below grade and the grey panels are above grade.
Greenhouse aerial view showing north wall
View of west and south sides of the greenhouse
View of east and north sides of greenhouse
Installing the polycarbonate panels was difficult due to panel size, wind, and angle of the wall
Anchored columns and below-grade panels being assembled
Building the manifolds for the climate battery system using Wye connections (instead of Tees) to reduce turbulence in the manifold
Lower tier of drain tile for climate battery system being laid out
Climate battery manifolds being staged until drain tile is run

Corrugated polycarbonate panels are installed over phase change tiles

Phase Change tiles are installed in the cavities of the steel-framed prefabricated panels used to construct the greenhouse.
View of north wash/pack room and storage room from back of storage room (during construction)
Inside of growroom while wrapping laminated wood support columns in vinyl, and construction of initial steel raised beds.
The greenhouse can effortlessly handle winds in excess of 90mph. However, wind-driven snow that has blown into the wash/pack room from between the sill plate and slab demonstrates the need to fill gaps both inside and out to create a more stable working and growing environment.

No SARE funds will be used on construction of the greenhouse - only on the monitoring and control systems, and the experimental phase change material.

The greenhouse was designed and built using well-established passive-solar principles. The materials used in the greenhouse and its systems were selected for their appropriateness in this application, including cost. The combination of active and passive environmental control systems with an integrated sensor network will allow us to see how well the systems are working independently and together. The Monnit sensor network and data gateway are designed for greenhouse applications and is composed of a light sensor, humidity sensor, CO2 sensor, and temperature sensors throughout the greenhouse and in the underground thermal/climate battery (GAHT system).  GAHT (Ground-to-Air Heat Transfer) is a trademark of Ceres Greenhouse, which designed the system. The monitoring system will transmit data every 10 minutes, unless condition thresholds are crossed. These data points will allow us to make changes in the environmental control system set-points and draw conclusions regarding the performance of the systems from the resulting sensor data.

The fans, motors, and thermostats used are designed for greenhouses and will improve our ability to manage the environment.

An electrician is needed to effectively, and safely, wire the monitoring and control systems to better control how they operate.

The use of phase change materials as both thermal mass and passive temperature control have tremendous potential in greenhouses; where solar energy must be intercepted, stored, and released. This reduces heating and cooling costs and saves room in the greenhouse that would otherwise be filled with bulkier and less-efficient forms of thermal mass, such as water barrels.


Research results and discussion:

The greenhouse is a solar-collecting building shell at this point. Construction delays and material shortages have pushed back full operation of the greenhouse environmental control systems into 2022. However, this has given us an opportunity to evaluate just the building itself without any electronically controlled environmental controls (i.e. exhaust fan/ intake louvres, geothermal (climate battery) circulation fans, supplemental heating, etc.).

To date, the main benefit of the building for growing plants has not been temperature moderation, but rather protection from damaging wind and hail. Hundreds of transplants were set outside in spring 2021 to harden-off but were destroyed in a wind storm before they could even be planted into outdoor beds. The few plants in the greenhouse were completely unimpacted. The greenhouse has withstood wind gusts up to, and potentially exceeding, 85mph. The louvres on the exhaust fan were blown out and destroyed during this storm, but it was ultimately determined that these were unnecessary for fan operation, complicated sealing the exhaust fan opening in winter, and rattled loudly at even a slight breeze. However, some surrounding producers had high tunnels destroyed or severely damaged from these winds, which significantly impacted their operations. Protection from damaging weather is an important consideration for growers contemplating construction of a solid-walled greenhouse structure. 

It may seem obvious, but the role of relative sunlight levels in heating the greenhouse cannot be overstated. The amount of sunlight entering (and heat retained) can have a greater impact on interior temperatures than exterior temperatures alone. For example, the greenhouse temperature can be higher on a clear, calm day with a 20 degree F exterior temperature than on an overcast, windy day with a 50 degree exterior temperature. The greenhouse design is so effective in capturing solar energy that changes in cloud cover can significantly impact the interior temperature. It would be extremely difficult to manually maintain ideal growing conditions in the greenhouse unless a person was working in there all day - opening and closing windows/ vents and turning on fans as needed. Our experience with the greenhouse has emphasized the need for automation in temperature control.          

Participation Summary
2 Farmers participating in research

Educational & Outreach Activities

5 Consultations
3 Webinars / talks / presentations

Participation Summary:

79 Farmers participated
Education/outreach description:

Corrugated polycarbonate panels are installed over phase change tiles
Phase Change tiles are installed in the cavities of the steel-framed prefabricated panels used to construct the greenhouse.

I have received several calls/ Facebook messages regarding the greenhouse project. I have helped these people answer one-off questions or had lengthy discussions on how the practices could be applied to their own operations. Some of the lessons learned on this project are applicable to high tunnels or significantly smaller "hobby" greenhouses.

I have presented during FARRMS Farm Beginnings and Farm Dreams workshops on the greenhouse and other on-farm activities. 

I joined other agricultural professionals and producers to participate in a Facebook Live webinar on SARE Farmer Rancher Grant project development and application. We shared our projects and experiences with the Farmer Rancher Grant Program. The webinar can be viewed on the FARRMS Facebook page:

I was named the 2021 Makewell - Maker of the Year for my efforts to educate new growers on unique techniques and horticultural practices that can be used at various scales. This provided opportunities for conversations with an audience I might not been able to interact with otherwise.  


Learning Outcomes

3 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Lessons Learned:

We broke ground on the greenhouse in November 2019, just months before the seriousness of COVID-19 was recognized. The coronavirus pandemic and its associated impacts adversely affected nearly every aspect of the project. This primarily came from life-threatening health concerns for the main manufacturer/contractor in 2020 and again in 2021, and then increased material costs and supply availability in 2021. The specialized, pre-fabricated panels and laminated wood columns used in the greenhouse construction, and previous agreements with the manufacturer, did not allow us to find cost-effective replacement labor for aspects of the greenhouse. 

This project was designed and implemented as an application of a unique steel-framed construction system. That is, not completely DIY and not completely a kit, but having aspects of both. This system was high quality and efficient to build with. However, the system reduced our options, or complicated work, when it came to some aspects of the project (e.g. pre-drilling holes to allow wall panels to be screwed to the steel studs, trying to insulate between the highly thermally-conductive steel studs and wall panels).  I recommend that other producers interested in a building a Deep Winter (or at least late fall and early spring) greenhouse build one as EITHER a well-designed DIY project with materials readily available from local stores or go with a complete turn-key kit, which can then be built independently or with contracted labor. Much of this project required "making things work" instead of having a complete, holistic design and materials list from a kit or having the flexibility of a DIY structure that does not rely on specialized components. The impacts of COVID-19 on this project could not have been predicted, but many problems could have been resolved if the project was conducted in either of these ways. 

VENTILATION: It was understood that proper ventilation is absolutely necessary in all but the coldest months of the year, and experience in early winter 2021 demonstrated why. The intake louvres were blocked using a piece of extruded foam board and the exhaust fan was blocked using a piece of leftover twin-wall to reduce heat loss in winter months. This was done in early November 2021, but the weather stayed unseasonably warm and sunny in November. This caused extreme diurnal temperature changes in the greenhouse. On one sunny day  the exterior temperature reached 65 degrees F. However, due to the ventilation being blocked in anticipation of colder weather, the interior temperature reached 128 degrees F! The weather shifted and the next day was cold, windy, and overcast. The interior temperature of the greenhouse dropped to 19 degrees F on the night following this cold day because the stored heat was quickly depleted. Without proper ventilation on the first day and without supplemental heating on the second day (geothermal system fans not connected yet) the greenhouse experienced a roughly 100 degree temperature change in a 36 hour period! This killed some perennial plants that would have been able to survive that cold temperature if they had been able to properly harden off . 

These dynamic temperature changes should be reduced once the exhaust fan and louvres are powered, and once the ground to air heat transfer fans are able to tap into the stabilizing subsoil temperature.

AIR GAPS: The south wall of the greenhouse is covered in triple-wall polycarbonate panels. The ceiling and all other walls are spray foamed to insulate and seal the structure. However, there were still some air gaps (i.e. cold air leaks) around doors and windows, where prefabricated panels joined, and in wall corners. The impact of these air gaps on the interior temperature was deceptively large - especially on windy days.  During a windstorm with 60mph gusts, a barely noticeable air gap in the corner of the growroom appeared to lower the air temperature by roughly 12 degrees to about 8ft away and created a noticeable draft. These gaps are sealed as they are noticed, but efforts should be made to proactively scout out air gaps and seal them with expanding spray foam or other appropriate sealant. This should be done before exterior finishes are added to the greenhouse to ensure that these gaps are sealed and not just covered up. Covering the gaps will still reduce heat loss, but may cause issues with condensation. For example, a steel panel installed over an air gap caused condensation to form and drip down the steel panel. This may become a significant issue if it is against untreated wood or other building materials not resistant to water.     

PHASE CHANGE MATERIAL INTEGRATION: The phase change tiles used in the greenhouse were designed to freeze/thaw at 72 degrees F, thereby helping to stabilize the temperature of the greenhouse. Phase change material tiles were incorporated into the rear wall of the greenhouse grow room (the wall separating the grow room from the wash/pack room). This required changing the plan for finishing the wall on the wash/pack room side and the grow room side because we had to be careful not to puncture the tiles. The tiles needed to be protected yet still exposed to temperature changes in the grow room so that they could absorb and release as much heat as possible. 

Many passive solar greenhouses use the thermal mass in water barrels or other containers to help stabilize greenhouse temperatures. These are relatively inexpensive, but take up a lot of valuable greenhouse space. The freezing point (phase change temperature) of water at 32 degrees F is also below what would be useful for most plants to benefit from. The main advantage of engineered phase change materials is that the phase change temperature can be adjusted to better store and release heat at a temperature range that plants can benefit from. The phase change tiles allowed us to increase the overall thermal mass of the greenhouse without taking up any additional greenhouse space because they were recessed into the steel-framed wall cavity. However, several of the tiles have begun leaking despite following manufacture instructions for attaching them. The steel in the greenhouse is corrosion resistance and the wood used is critical ground-contact treated wood. The salt solution in the tiles should not harm these building materials and will not come into contact with any growing media because any slow leak is in the wall assembly itself. Ways to protect the tiles from punctures and ways to minimize damage from potential leaks should be considered when using phase change materials in a greenhouse environment. Data is not available to conclude how much the tiles assisted in stabilizing the greenhouse temperature, although I question their practicality and cost-effectiveness. The installation of the tiles and the translucent polycarbonate paneling over them increased construction costs and added several full work days to accomplish. These additional expenses may not be feasible to many small to mid-sized producers. Managing thermal mass is one of the most effective ways to stabilize greenhouse temperatures and adding thermal mass can be worth the investment. Although, I would recommend adding thermal mass that provides secondary benefits to the greenhouse operation, such as water barrels or IBC totes with workspace on top, water reservoirs for hydroponics/aquaponics, and water holding tanks for backup irrigation or dechlorination.   

SUPPLEMENTAL HEATING: The wash/pack room of the greenhouse is plumbed so the temperature must be maintained above freezing to prevent damage. The grow room of the greenhouse is able to heat itself and the back room reasonably well on sunny and still days. But the temperature can drop very quickly on an overcast or windy day. The large surface area of the south wall allows in abundant solar energy, but it also has the lowest R-value of any part of the greenhouse and bleeds out heat quickly. The structure is able to maintain an internal temperature about 15 degrees F above the exterior temperature on severely overcast days, but this would still be insufficient to prevent freezing for much of the winter. The inside temperature after several overcast days and outside temperatures around -20 degrees F fell to around 6 degrees above zero. Supplemental heating will be required in the wash/pack room, which will provide some additional heat in the grow room as well. Infrared cove heaters will be added to the north wall of the wash/pack room and direct infrared energy towards the interior dividing wall and floor of the wash/pack room. The wall of the wash/pack room is finished in thermally-conductive galvanized steel panels. These will release heat back into the wash/pack room, but will also help transfer some heat through the phase change tiles in the wall and then into the grow room.

The geothermal (ground to air heat transfer) system is not in operation yet, but it will help stabilize the temperature in the greenhouse above freezing. Nevertheless, supplemental heating will still be needed once it is operational to prevent depleting the heat stored in the insulated soil column under the greenhouse. Ceres Greenhouse Solutions, the company that developed the geothermal system, recommends turning it off when the exterior temperature drops below 10 degrees F and to instead rely solely on a secondary heat source.           

Project Outcomes

2 Farmers changed or adopted a practice
1 Grant received that built upon this project

I would like to see additional work done to compare the construction and operation of various passive solar greenhouse designs. The University of Minnesota has done great work with the Deep Winter Greenhouse project, but additional work would be beneficial to synthesize information on different operations so that producers considering a passive solar greenhouse could access information on a range of growers so that they can get ideas and make a better informed decision about what may work best for their operation. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.