Energy performance of a ventilation system for an apartment according to the Italian regulation

P. Valdiserri 0 C. Biserni 0 M. Garai 0 0 P. Valdiserri C. Biserni (&) M. Garai Department of Industrial Engineering (DIN), School of Engineering and Architecture, Alma Mater Studiorum, University of Bologna , Viale Risorgimento 2, 40136 Bologna , Italy According to recent regulations on energy saving in buildings, all new structures should guarantee high-energy performance. To this aim, the building envelope should be equipped with insulated walls and high-efficiency windows. This approach leads to considerable thermal insulation, but at the same time, in the absence of a suitable ventilation system, it results in a worsening of indoor air quality. A healthy quality of life requires good indoor air quality; especially in places where people spend most of their time, adequate air exchanges should be guaranteed and indoor pollution reduced to ''acceptable'' levels. In the present work, we performed a dynamic simulation of a ventilation system for an apartment using a mathematical model, i.e., the Trnsys commercial code. The model has been applied to an apartment of 66 m2 inside a condominium located in Bologna (Italy), but can also be used for other types of buildings as well. The variation of energy request due to different measurements of volume flow rate was evaluated. - European residential and tertiary buildings are responsible for 40 % of final energy consumption. Energy consumption for domestic use in Europe is estimated around 35 % of the total primary energy used [1, 2]. Therefore, the building sector has a very high potential in terms of reducing consumption and lowering emissions. To reduce this consumption, the European Community issued Directive 2002/91 on Building Energy Certification, [3] which came into effect in Italy through the Legislative Decree no. 192/2005 [4] and no. 311/2006 [5]. Unfortunately, it should be noted that on the Italian territory (301,336 km2), existing dwellings have a very high density (about 27 million units). Also, statistic studies confirmed that between 1971 and 2001, these were augmented approximately by 36 %, because of the growth in population by 55 % and the number of families by 26 % [1]. Therefore, even though a certain percentage of the new buildings are energetically more efficient, the energy consumption is still globally increasing. The above-mentioned need to reduce energy consumption in new buildings implied the use of considerable thermal insulation, but at the same time in the absence of a suitable ventilation system it could result in a worsening of indoor air quality. A healthy quality of life requires good indoor air quality; especially in places where people spend most of their time, adequate air exchanges should be guaranteed to reduce indoor pollution to acceptable levels. Due to the increasing indoor air quality standard, the ventilation loads constitute a growing part of the heating demand between 20 and 50 % for new and retrofitted buildings [6, 7], depending on building insulation, compactness, air change rate, indoor heat sources, indoor set points and outdoor climate. Heat recovery ventilation (HRV) principle is to recover heat from the exhaust air and to transfer it to the supply air through a heat exchanger. With the growing share of ventilation heating loads, heat recovery over the mechanical ventilation systems appears as one of the key solutions to reduce heat losses and generate consequent energy savings [8]. With rapid economic growth, the need for better indoor built environment has become more pronounced. Both thermal comfort and indoor air quality issues have gained increasing attention. Adequate ventilation is necessary to maintain a desired indoor air quality [911]. In the present work, we performed a dynamic simulation of a ventilation system for an apartment using a mathematical model, i.e., the Trnsys commercial code [12]. Trnsys is an extensible simulation environment for the transient simulation of energy systems including multizone buildings. It is used to validate new energy concepts, design and simulation of buildings and their equipment, including control strategies, occupant behavior and alternative energy systems (wind, solar, photovoltaic, hydrogen systems, etc.). The variation of the energy request due to different measurements of volume flow rate has been contemplated in this study, according to the Italian regulation on residential buildings. Description of the cases under investigation The numerical model has been applied to an apartment of 66 m2 inside a condominium located in Bologna (Italy), but can also be used for other types of buildings, as well. The apartment, highlighted in Fig. 1, is a six-roomed flat. Table 1 Surface of each room of the apartment and acronyms adopted in the simulations Surface (m2) Table 1 illustrates the surface of each room and the acronyms used in the calculations. Table 2 highlights the thermal characteristics of the apartment envelope. To simulate the ventilation system working, four people are supposed to live in the apartment, according to the timetable shown in Table 3.: It is worth noting from Table 3 that between 7 a.m. to midday nobody is at home. We performed a dynamic simulation of a ventilation system for the above-described apartment by means of the Trnsys commercial code. We studied the performance of the ventilation system in four different conditions. All the cases under investigation are referred to the period when the heating system is switched on (winter period), for Bologna from October 15 to April 15. The heating system is supposed to operate 14 h a day according to the following timetable: Fig. 1 Plan of the studied apartment from 5 a.m. to 10 a.m; from 12 p.m. to 2 p.m; from 4 p.m. to 11 p.m. The heating system is set to maintain the internal temperature of 20 C in all rooms. It is characterized by an air change rate (ventilation and infiltration) of 0.3 h-1 for all the rooms, except the kitchen and the bathroom which have 0.9 air changes per hour. It is characterized by the presence of a heat recovery ventilation system that can save energy from the ejected air, as depicted in Fig. 2. The ventilation system is equipped with two fans that absorb individually the power of 30 W. The model employs a cross flow heat exchanger able to exchange heat, but unable to exchange humidity since the two air fluxes are kept separate by specific sealing in the plates. Any air infiltration, contaminant gases (polluting materials), biological hazards and particulates are completely blocked. Table 2 Values of thermal transmittance with regard to the envelope elements Thermal transmittance U (W m-2 K-1) Table 3 Timetable of people present in each room of the apartment Envelope element Fig. 2 Heat recovery system Number of people The efficiency of the heat recovery system is defined as follows: where TS is the temperature of the supply air; TO is the temperature of the external air (outdoor air); TR represents the temperat (...truncated)