Development of a CO2 based air-to-air heatpump for Food drying System

The idea is to develop an energy efficient, portable/ mobile and green drying system that can be easily installed at any place and used by anyone. The given drying system will utilize a CO2 based heat pump system having a low GWP and ODP as well as a high COP and produce higher temperatures needed for drying process. A CO2 based heat pump system was designed and developed at DTU. The prototype developed was tested for the design temperature of 60 degrees Celsius. The results demonstrated the feasibility of CO2 as a heat pump for drying.

However, further improvements can be done. The modular portable drying unit developed, using
heatpump, has demonstrated its applicability to efficiently process the surplus food and is approved
by fødevarestyrelsen to process both organic and conventional fresh fruits.

UpFood aim was to develop a mobile/portable drying system that can be transported to any surplus food or by- product source like a farm or a food industry etc. and save the food by drying right there. Imagine a drying system that can be easily transported and parked at a farm, catering or food production company and outside a supermarket.

Based on field experiences and requirement of the dried fruit value chain, it was decided to design a complete miniature portable drying factory instead of just a drying system. The design was based on utilizing the shipping containers which will provide easy deployment on a global scale considering food waste/loss is a global challenge. The container based modular was supposed to have both pre and post processing facility providing a complete solution where raw fruits/vegetables come and go out packed and ready for the market.

The results herein have demonstrated the feasibility of CO2 as a heat pump for drying. More investigations are planned targeting the effect of the speed of the compressor, as well as the effect of the heat recovery heat exchanger. Furthermore, real dryer operation including significant dehumidification is pending. The development of the prototype and experimental results has also outlined that further investigations and evaluations are necessary to understand in more detail the losses and implications in the system especially as the gas cooler pressure as well as the return air is varied. The critical challenge here is to exploit the return air, but at the same time cool the gas cooler outlet gas as much as possible.

The modular drying unit, has demonstrated its applicability to impact the challenge of food loss at farms. The integration of CO2 heat pump will not only improve its capability to efficiently process the surplus food but will also make it a more sustainable to the environment in terms of technology.