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 methods. Heat sinks are used to help regulate the internal temperature of the greenhouse, the main benefits of building a heat-sink is growing season extension and frost protection.
The heat sink we aim to build will be based around capturing 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 has ideal thermal conductivity properties, offering a good surface area for the air to pass over and also a good thermal mass. The air will then pass through the chamber and across the material, as the air passes through the material the heat energy will be passed from the air to the material, thus storing the heat. Depending on the heat-sink size this system should help to regulate and keep the greenhouse temperature at a mean value compared to the ambient temperature.
The image below was created to visualise what a finished system could look like.
Our aim is to make the entire system Open Source, we also have smaller key goals:
- Extended growing season and frost protection
- Keep the cost as low as possible
- Easy installation and accessibility of parts
- All plans, work instructions, technical documents, electronic design and software will be freely available
- Low power system running from Solar and battery back-up
- Eco-Friendly by using recyclable materials when ever possible
Our aim is to validate a heat-sink concept through material testing, as well as using 2 similar sized greenhouses: the 1st will act as a control providing base-line readings with no heat sink and the 2nd will have a heat-sink system in operation.
We will build data loggers to monitor temperatures at various points in the greenhouse, heat-sink and externally. These will give a detailed dataset that can then be analysed, it can then be compared against different materials to find the most effective system. All the metrics of the system will be recorded so the system can potentially be scaled upon these findings.
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 microcontroller system to control the speed of the fan, will allow temperature differential measurements to control the fan speed, this will allow the stored heat energy to be used more effectively.
We are in the process of constructing some prototypes for testing, the image below shows our progress so far.