The idea of a greenhouse heat sink is not new and many examples can be found on the internet, using various technologies and different novel approaches. The heat sink is used to help regulate the internal temperature of the greenhouse, the main benefits of building a heat sink is to extend growing season and provide frost protection.
The principle relies on the sun to generate warm air in side the greenhouse, the warmest air then collects at the greenhouse apex.
The heat sink we aim to build will be based around transporting the warm air from the upper parts of the greenhouse, then transporting this air down into an underground chamber. The chamber will be filled with a material that possess good thermal conductivity properties, offers a good surface area for the air to pass over and also a large enough thermal mass to ensure sufficient energy is stored.
The warm air will be drawn into a pipe or pipes using a fan and forced down into the heat sink, where it will passed into the chamber with the heat sink storage material. As the air passes through the material the warm air is cooled by the material as the heat is transferred from the air into the material, thus storing the heat.
Depending on the heat-sink size this system should help to regulate and keep the greenhouse temperature with an improved yearly mean value compared to the ambient temperature. A larger heat sink will allow a larger amount of energy to be stored, but the key factor here is the sun as any stored energy will be constantly bleeding from the system, so a long period of no sun will allow the system to cool significantly.
The image below was created to visualise what a finished system could look like.
The aim is to make the entire system as accessible as possible and share it as Open Source:
Growing Season Extension: allow plants to be sown earlier and grown later due to improved frost protection and higher mean average temperatures.
Heat Sink Volume: provide some data based on a heat sink to greenhouse size ratio of 1:10, this should give other users a potential benchmark to follow.
The system should also be fairly easy to install, use recyclable materials where possible, use easily accessible parts and run off a solar panel and battery ideally.
Our aim is to validate a heat-sink concept through material testing, as well as using two similar sized greenhouses: the first will act as a control providing base-line readings with no heat sink and the second will have a heat sink system in operation.
A simple data logger built from an Arduino will monitor and log temperatures at various points. The logged values will then provide a data set to be analysed and the heat sink performance evaluated.
As well as testing the systems performance and efficiency, all current air heat-sink systems lack a control element, the fan driving the air is kept at a constant speed. Implementing a more intelligent system based on a microcontroller will allow a simple algorithm to be used that controls the speed of the fan depending on the various temperature measurements. The fan speed control will allow the heat sink stored energy release to be throttle depending on the ambient temperatures so the stored heat energy is used more effectively.
Andrei, Daniel, Jens, Ant and Christian (not in the image)