Abstract
In order to satisfy the requirements of Directive 2010/31/EU for Zero Energy Buildings (ZEB), innovative solutions were investigated for building HVAC systems. Horizontal air-ground heat exchangers (HAGHE) offer a significant contribution in reducing energy consumption for ventilation, using the thermal energy stored underground, in order to pre-heat or pre-cool the ventilation air, in winter and summer, respectively. This is particularly interesting in applications for industrial, commercial and education buildings where keeping the indoor air quality under control is extremely important. Experimental measurements show that, throughout the year, the outside air temperature fluctuations are mitigated at sufficient ground depth (about 3 m) because of the high thermal inertia of the soil, the ground temperature is relatively constant and instead higher than that of the outside air in winter and lower in summer. The study aims to numerically investigate the behavior of HAGHE by varying the air flow rate and soil conductivity in unsteady conditions by using annual weather data of South-East Italy. The analysis shows that, in warm climates, the HAGHE brings a real advantage for only a few hours daily in winter, while it shows significant benefits in the summer for the cooling of ventilation air up to several temperature degrees, already by a short pipe.
Highlights
The building sector represents 40% of the European Union’s total energy consumption
The analysis shows that, in warm climates, using the Horizontal air-ground heat exchangers (HAGHE) has its advantages for few hours daily in winter, when the difference between the outdoor air temperature and the soil temperature is small, while it shows significant benefits in the summer for cooling of the ventilation air up to several temperature degrees, when the difference between the ground temperature and the outdoor air temperature is high
As regards the analysis relating to the data of Lecce, the results are represented into four figures: the first three Figures 12–14 show the performances of the air-ground heat exchanger in terms of ground and inlet-outlet air temperatures and air-ground thermal power, by varying air flow rate (150 to 450 m3/h), keeping constant the value of soil conductivity and assuming the temperature of the ground, Tground, with the plant shut down
Summary
The building sector represents 40% of the European Union’s total energy consumption. reducing energy consumption is a priority of the climate and energy package called “20-20-20”.The European Directive 31/2010 [1] upholds the concept of zero or nearly zero-energy constructions (ZEBs or n-ZEBs) which are increasingly becoming more common throughout Europe. The building sector represents 40% of the European Union’s total energy consumption. 2020, all new buildings must be n-ZEBs, and in particular those occupied and owned by public authorities must comply with the same criteria by 31 December 2018. New buildings must fulfill these requirements before construction starts, looking at high efficiency envelopes, the installation of renewable energy systems, heat pumps and cogeneration systems. Many studies have analyzed several types of high energetic efficiency external walls for ZEBs; in particular in the Mediterranean climate, Baglivo et al [2,3] carried out an analysis through the combination of various materials, in terms of steady thermal transmittance, periodic thermal transmittance, decrement factor, time shift, areal heat capacity, thermal admittance, surface mass, thickness
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