The objective of this one year research project is to test and measure the energy impact of
capturing excess daytime heat within a greenhouse and transferring it through an air-to-water
exchanger to then store the thermal energy in water. Solar collectors will also be implemented to
boost the heat that is stored. This same system will provide cooling during the day and heating at
night for the greenhouse. The stored heat will be used to help reduce costly energy consumption
that negatively impacts the environment and decreases farm profitability. The design for this
system will be open sourced and the monthly data will be graphed out over the year and shared
on our website and social media. We will also present the findings as an article through the
National Young Farmers Coalition, an organization with over 130,000 young farmers and
1. To research the process of capturing daytime air heat of a greenhouse and exchanging and
storing it into water.
2. To research the effects of solar hot water collectors in combination with the heat
exchanger to increase the temperature of water storage.
3. To research the effectiveness of using the stored heat in water as a heat source during the
4. To visualize the system with sensors and data logging technology.
5. To publish findings of this research and encourage its adoption.
To start this project, we installed a 3×3 ft. air-to-water heat exchanger and a 12 in. centrifugal fan rated at 2,050 CFM within our 20×28 ft. greenhouse. A custom duct was built from sheet metal in order to house the air-to-water heat exchanger and the centrifugal fan. A 12 in. round duct was attached to the inlet side of the fan to pull hot air from the top of the greenhouse.
A 1/25HP circulation pump was installed to cycle the water between the storage tanks and the exchanger.The next step was to setup four IBC totes full of water and plumb them in serial so that water would cycle through the heat exchanger and all the tanks.
An off-the-shelf weather station was setup outside the greenhouse which allowed for additional wireless thermometers to monitor the system for both air and water temperatures. The wireless sensors had difficulty communicating to the weather station because of interference created by the sheet metal of the ducting and the metal (copper tubing & aluminum fins) of the heat exchanger. The entire weather station’s receiver later failed so no data has been able to be captured.
After dealing with these issues, it was determined that it would be best approach would be to use wired sensors. The cost of many of the available commercial sensors and data loggers were cost prohibitive to the project so it was determined that it would be best build our own with the help of an electronic specialist who we met at the local hackerspace.
During the setup process for the new sensors the greenhouse was inadvertently left without power which allowed the heat exchanger to freeze overnight. The damage to the copper tubing was too extensive to repair and the entire unit will be replaced.
Once the new heat exchanger arrives, the system should be ready to take back online and with the new sensors we should be able to actively monitor the system and make necessary adjustments as we go. We expect the system to be fully operational by February when the primary production work begins in the greenhouse for the 2019 season.
Our future steps will be to add on the solar hot-water panels to the system this winter and then sometime in the Spring we will experiment with insulating the tanks within the greenhouse to reduce heat loss.
We setup an initial test of the system in June 2018 which provided a 40F temperature reduction from the air at the top of the greenhouse (115F) to the air released after the heat exchanger (75F). A single 275 gallon IBC tote was filled with 58F well water and cycled through the 3×3 ft. heat exchanger for 2 hours with the cooling effect during the day. It increased the temperature of the water to 80F.
The 2 hours of operation allowed for a 1.2 kilowatt reduction of energy to operate the centrifugal fan (500 watts) and 1/25 HP circulation pump (82 watts). This is compared with the normal energy consumption to cool by powering two exhaust fans (500 watts/ea.) and a water pump (190 watts) for the evaporative cooler. This is a 51% reduction in energy consumption over the conventional cooling system for the greenhouse.
Educational & Outreach Activities
The data from the custom built logger and sensor array will be shared online and we will be working towards publishing the designs of the system. As we have a better understanding of how the system is operating and have the data to back up our claims we will then seek to publish an article about what we’ve learned.
Without data monitoring it's very difficult to understand energy consumption within a greenhouse.
So far in our progress, we have discovered that a heat transfer system can reduce energy consumption over a traditional cooling system if adequate storage is available. Lower energy consumption means lower utility costs which increases profit margins. We have also learned that a centrifugal fan can operate at a lower noise level than the exhaust fans. This makes the working condition within the greenhouse better for staff.