The refrigerants used in conventional vapor-compression air conditioning systems have detrimental effects on the global environment. Phasing-down hydrofluorocarbon (HFC) refrigerants for HVAC equipment over the next 20 years has been proposed. A thermoelectric air conditioning system that directly converts electrical energy to thermal energy using a simple solid-state semiconductor device, has the advantages of environmentally friendly, no refrigerant, very compact, high reliability, no moving parts (except for small fans), and it can be easily integrated into the building structure. However, the existing thermoelectric air conditioning systems have the problem of low Coefficient of Performance (COP), which limits its applications for domestic air conditioning. With the development of the thermoelectric technologies, the above problem is prospected to be solved. The paper presents an overview of recent advances in thermoelectric materials, thermoelectric module design and thermoelectric heating and cooling system design which would provide the potential to greatly improve the COP of the thermoelectric air conditioner. In addition, utilizing the waste heat of the thermoelectric system for domestic applications to improve the overall COP of the system would be an ideal way to promote public adoption of the TE air conditioner, which is discussed in this paper. The paper also presents an overview of the existing building integrated thermoelectric air conditioning systems and proposes a novel building integrated thermoelectric system that integrates a thermoelectric heat pump unit into a double-skin ventilated facade to provide heating and cooling, heat recovery ventilation and domestic hot water or drying services for buildings, based on the thermoelectric waste heat utilization. Several building integration methods of the proposed system are presented.

Information technology (IT) has brought significant changes in people’s lives. As an important part of the IT industry, data centres (DCs) have been rapidly growing in both the number and size over the past 40 years. Around 30% to 40% of electricity consumption in DCs is used for space cooling, thus leading to very inefficient DC operation. To identify ways to reduce the energy consumption for space cooling and increase the energy efficiency of DCs’ operation, a dedicated investigation into the energy usage in DCs has been undertaken and a novel high performance dew point cooling system was introduced into a DC operational scheme. Based on the cooling load in DCs, a case study was carried out to evaluate the energy consumptions and energy usage effectiveness when using the novel dew point cooling system in different scales of DCs in various climates. It was found that by using the novel dew point cooling system, for 10 typical climates a DC can have a much lower power usage effectiveness (PUE) of 1.10 to 1.22 compared to that of 1.7 to 3.7 by using existing traditional cooling systems, leading to significantly increased energy efficiency of the DC operation. In addition, the energy performance by managing the cooling air supply at the different levels in DCs, i.e., room, row and rack level, was simulated by using a dynamic computer model. It was found that cooling air supply at rack level can provide a higher energy efficiency in DCs. Based on the above work, the energy saving potential in DCs was conducted by comparing DCs using an the novel dew point cooling system and the optimum management scheme for the cooling air supply to that using traditional air cooling systems and the same supply air management. Annual electricity consumptions for the two cases were given. It was found that by using the novel dew point cooling system and optimum management system for the cooling air supply, an 87.7~91.6% electricity consumption saving for space cooling in DCs could be achieved in 10 typical cities at 10 selected climatic conditions.

Vacuum membrane-based air dehumidification (MAD) is potentially more efficient than refrigeration cycles. Air permeance through a membrane is inevitable, especially when there is a large pressure difference between the supply and permeate sides. Given the high specific gas volume under vacuum conditions, removing the permeating air from the dehumidifier is crucial for the stable operation of the vacuum compressor. Energy-efficient air removal techniques are still lacking, thereby hindering the development of MAD technology. This paper proposes a novel MAD approach using a vacuum mixing condenser. The cooling water directly condenses moisture from the vacuum compressor without any heat exchanger. The permeating air and water mixture in the condenser then experiences a quasi-isothermal pressurization process through a multiphase pump, enabling continuous dehumidification and air removal with low power consumption. The fundamentals of the proposed approach are illustrated, and mathematical models are built. Influences of air permeance rate, cooling water flow rate, condenser pressure, membrane area, and gravitational work are investigated. The results show that a COP of 8~12 is achievable to dehumidify air to 50%RH, 25 °C. The vacuum compressor consumes about 80% of the power. A low air permeance rate, low condenser pressure, large membrane area, and high gravitational work positively impact the COP, while the cooling water flow rate has a more complex effect. The proposed dehumidifier can use less selective membranes for higher permeability and cost-effectiveness.