night ventilation

Urban heat island, with the associated urban overheating, is a well-documented phenomenon, which demonstrates the hazard related to local climate change and the related negative impacts at environment, economic, social and public health level, with heavier consequences on the low income and more fragile segment of the population. The phenomenon takes origin by the positive thermal balance in the urban built environment mainly, depending on the synergic effect of different causes.

Global and local climate changes affect the energy performance of buildings, especially during the warm season, with relevant increase of cooling uses in mechanically cooled buildings and discomfort hours in naturally ventilated ones. The ventilative cooling is proved to be a promising strategy to tackle this threat, however installing new ventilation systems in existing buildings is challenging in technical and economic terms. The strategy can be also pursued by motorized windows duly operated.

The interest in phase change materials (PCMs) as a solution for thermal energy storage has been growing for the last decades. It is clear that PCMs are promising for reducing the summer heat peaks without increasing the energy demand for cooling. A new modular, reversible, lightweight retrofitting system was developed and integrated in a real size experimental test cell.

The current type of construction preferred for new high energy efficient buildings in Germany, featuring highly insulated building components and an almost completely airtight building shell, raises several new challenges with regard to design, construction and use of these buildings. Cooling, in particular, is an issue that gains importance also in the residential sector, in connection with rising temperatures induced by the climate change.

With the combination of two fans and a heat exchanger in one single component there is the possibility to design a compact and highly efficient ventilation system especially for use in building modernization. One crossflow fan generates both airflows (outdoor/supply and extract/exhaust air) and simultaneously acts as counterflow heat exchanger. The space between the fan blades is filled with elements which operate as regenerative heat exchanger. The modified laboratory prototype of the so called Counterflow Heat Recovery Fan was optimized for the use as single/double room unit.

Night ventilation is used extensively as a low energy strategy to cool buildings in climates where night temperatures are suitable. It can be used for spaces utilising natural or mechanical ventilation systems as well as active refrigerant cooling. Most published work focuses on domestic and relatively simple in operation commercial buildings such as offices. This paper presents a study of the cooling benefits of night ventilation for frozen food supermarkets with high cooling demand.

An experimental analysis of the night ventilation technique for cooling in buildings, was performed in a test cell with the aim of establish the potential of this technique in two scenarios: a) when the air-stream is in poor contact with the thermal mass and b) when the air-stream is in close contact with the thermal mass of the test cell. The test cell is a small one-room building equipped with instrumentation for measurement and control the night ventilation following a strategy based in the values of indoor and outdoor temperatures.

Supermarkets are a category of non-domestic buildings with high energy use because of their operation. Recent work indicates that by improvements to the energy delivery systems through which internal environmental conditions are maintained such as thermal properties of external envelope including airtightness, HVAC systems and lighting, substantial energy savings can be achieved. Work to date has focused on typical supermarkets while the present paper examines frozen food supermarkets which include more refrigeration cabinets and therefore result in higher energy use per sales floor area.

Passive cooling by night ventilation is one of the most promising approaches to reduce cooling energy demand of office buildings in moderate climates. However, the effectiveness of this system depends on many parameters.

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper analyses the thermal comfort achievable in office buildings in Spain according to European standard EN 15251:2007. Furthermore, the comfort level is evaluated using the Degree Hours (DH) criteria and the maximum indoor temperature.