An overview of heat recovery from ventilation

The energy crisis that is occurring nowadays requires that new smart energy solutions be found. The range of solutions varies, from finding new sources of energy to reducing energy consumption. The former solution mainly relies on renewable energy sources such as solar and wind energy, whilst the latter solution emphasises proposing smart energy systems capable of lowering energy consumption. One of these solutions is the use of heat recovery which can be applied to any engineering system dissipating waste heat, and ventilation is a typical source of waste heat. Investigating different available systems in terms of characteristics, available amount of waste heat in addition to its operational mode, provides guidance for understanding a heat recovery system according to the ventilation system specifications, space availability, cost, and climate. For this purpose, a review of available ventilation heat recovery systems was performed to investigate the optimal configurations of ventilation heat recovery. The systems were categorised according to three techniques: heat pump ventilation heat recovery system, wall-type ventilation heat recovery systems and earth-to-air ventilation heat recovery system. In this paper, the operational mode, type of heat exchanger, type of ventilation, advantages and disadvantages are discussed for each system. The analysis method followed in each system available is also provided. The efficiencies provided by the techniques reached, in some cases, 80%, with an average energy consumption reduction that varied largely between 60 and 80%. The inlet fresh air temperature increased between a range of 2 and 15°C. The COP value increased between 0.7-6.7 depending on investigated technique and season of operation. Another important parameter highlighted was the ability to defrost in extreme cold conditions below -5°C.