A growing population and need for energy in all forms is a fact, and with the justification for making a large amount of energy-related products more effective, the directive Eco-design was developed. Section 6 in the directive covers ventilation units, and specific requirements are set for different components within the unit. Eco-design oversees the entire European Union and the requirements that come with the directive create special problems, frost formation and freezing, for climates that, by comparison with the rest of Europe, are naturally colder. The purpose of this study is to investigate and evaluate whether the Ecodesign directive is suitable as a design method for the Swedish climate with regard to recycled energy, for liquid-coupled heat recovery systems. In collaboration with the company Aircoil, which specializes in various cooling systems, goal formulation was set, and the objective of this study was to focus on recovering as much energy as possible, by regulating the liquid flow in a liquid-coupled recycling system according to the current outdoor temperature and investigating what effects this flow control may have on temperature efficiency, total pressure drop and specific fan power (SFP). To reach the objective, the group got access to the software AC MasterSelection, which is the software used by Aircoil to make dimensioning calculations for liquid-coupled heat recovery systems. The software is certified and approved by Svensk Ventilation, which is the organization that represents the Swedish ventilation industry vis-à-vis authorities, government and the European Union - in terms of legislation and regulations. The software was used to obtain a large amount of data which was then compiled in Microsoft Excel to take flow variation profiles that generate higher recycling effect for the locations Malmö, Stockholm and Kiruna. The same profiles were then simulated in Matlab SimuLink to investigate the effect that a varying fluid flow has over the period of one year. Five different airflows for the heat recovery system were tested, 1 to 5 m3/s. According to the results, an estimated annual heat energy saving potential could be derived by utilizing a varying liquid flow for Malmö to be between 0.9 to 8.7%, for Stockholm between 1.1 to 4.4% and for Kiruna 3.3 to 15.8%. The results indicate that Eco-design and the regulations and requirements that come with the directive are not the most efficient design-wise from an energy recovery aspect for the Swedish climate, especially for the coldest locations, and that the electrical energy supplied to the system for the extra pump work is recovered in thermal energy to a much greater extent.