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

Biserni, C.

Garai, M.

Valdiserri, P.

International Journal of Energy and Environmental Engineering

English

P. Valdiserri

C. Biserni

M. Garai

Springer - Publisher Connector

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

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

VALDISERRI, PAOLO

BISERNI, CESARE

GARAI, MASSIMO

Archivio istituzionale della ricerca - Alma Mater Studiorum Università di Bologna

ORIGINAL RESEARCHEnergy performance of a ventilation system for an apartmentaccording to the Italian regulationP. Valdiserri • C. Biserni • M. GaraiReceived: 15 July 2014 / Accepted: 27 December 2014 / Published online: 24 January 2015 The Author(s) 2015. This article is published with open access at Springerlink.comAbstract According to recent regulations on energy savingin buildings, all new structures should guarantee high-energyperformance. To this aim, the building envelope should beequipped with insulated walls and high-efficiency windows.This approach leads to considerable thermal insulation, but atthe same time, in the absence of a suitable ventilation system, itresults in aworsening of indoor air quality. A healthy quality oflife requires good indoor air quality; especially in places wherepeople spendmost of their time, adequate air exchanges shouldbe guaranteed and indoor pollution reduced to ‘‘acceptable’’levels. In the presentwork,weperformedadynamic simulationof a ventilation system for an apartment using a mathematicalmodel, i.e., the Trnsys commercial code. The model has beenapplied to anapartment of 66 m2 inside a condominium locatedin Bologna (Italy), but can also be used for other types ofbuildings as well. The variation of energy request due to dif-ferent measurements of volume flow rate was evaluated.Keywords Heat recovery  Thermal envelope VentilationIntroductionEuropean residential and tertiary buildings are responsiblefor 40 % of final energy consumption. Energy consumptionfor domestic use in Europe is estimated around 35 % of thetotal primary energy used [1, 2]. Therefore, the buildingsector has a very high potential in terms of reducing con-sumption and lowering emissions. To reduce this con-sumption, the European Community issued Directive2002/91 on Building Energy Certification, [3] which cameinto effect in Italy through the Legislative Decree no.192/2005 [4] and no. 311/2006 [5]. Unfortunately, it shouldbe noted that on the Italian territory (301,336 km2), exist-ing dwellings have a very high density (about 27 millionunits). Also, statistic studies confirmed that between 1971and 2001, these were augmented approximately by 36 %,because of the growth in population by 55 % and thenumber of families by 26 % [1]. Therefore, even though acertain percentage of the new buildings are energeticallymore efficient, the energy consumption is still globallyincreasing. The above-mentioned need to reduce energyconsumption in new buildings implied the use of consid-erable thermal insulation, but at the same time in theabsence of a suitable ventilation system it could result in aworsening of indoor air quality. A healthy quality of liferequires good indoor air quality; especially in places wherepeople spend most of their time, adequate air exchangesshould be guaranteed to reduce indoor pollution to‘‘acceptable’’ levels.Due to the increasing indoor air quality standard, theventilation loads constitute a growing part of the heatingdemand between 20 and 50 % for new and retrofittedbuildings [6, 7], depending on building insulation, com-pactness, air change rate, indoor heat sources, indoor setpoints and outdoor climate. Heat recovery ventilation(HRV) principle is to recover heat from the exhaust air andto transfer it to the supply air through a heat exchanger.With the growing share of ventilation heating loads, heatrecovery over the mechanical ventilation systems appearsPublished in the Special Issue ‘‘8th AIGE Conference (ItalianAssociation for Energy Management)’’.P. Valdiserri  C. Biserni (&)  M. GaraiDepartment of Industrial Engineering (DIN), School ofEngineering and Architecture, Alma Mater Studiorum,University of Bologna, Viale Risorgimento 2,40136 Bologna, Italye-mail: cesare.biserni@unibo.it123Int J Energy Environ Eng (2016) 7:353–359DOI 10.1007/s40095-014-0159-4as one of the key solutions to reduce heat losses and gen-erate consequent energy savings [8]. With rapid economicgrowth, the need for better indoor built environment hasbecome more pronounced. Both thermal comfort andindoor air quality issues have gained increasing attention.Adequate ventilation is necessary to maintain a desiredindoor air quality [9–11].In the present work, we performed a dynamic simulationof a ventilation system for an apartment using a mathe-matical model, i.e., the Trnsys commercial code [12].Trnsys is an extensible simulation environment for thetransient simulation of energy systems including multizonebuildings. It is used to validate new energy concepts,design and simulation of buildings and their equipment,including control strategies, occupant behavior and alter-native energy systems (wind, solar, photovoltaic, hydrogensystems, etc.).The variation of the energy request due to differentmeasurements of volume flow rate has been contemplatedin this study, according to the Italian regulation on resi-dential buildings.Description of the cases under investigationThe numerical model has been applied to an apartment of66 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 illustrates the surface of each room and the acro-nyms used in the calculations.Table 2 highlights the thermal characteristics of theapartment envelope.To simulate the ventilation system working, four peopleare supposed to live in the apartment, according to thetimetable shown in Table 3.:It is worth noting from Table 3 that between 7 a.m. tomidday nobody is at home. We performed a dynamicsimulation of a ventilation system for the above-describedapartment by means of the Trnsys commercial code. Westudied the performance of the ventilation system in fourdifferent conditions. All the cases under investigation arereferred to the period when the heating system is switchedon (winter period), for Bologna from October 15 to April15. The heating system is supposed to operate 14 h a dayaccording to the following timetable:Fig. 1 Plan of the studied apartmentTable 1 Surface of each room of the apartment and acronymsadopted in the simulationsRoom Surface (m2) AcronymKitchen 10.07 KLiving room 18.87 LRBedroom 1 12.54 B1Bedroom 2 13.07 B2Access corridor 5.13 ACBathroom 6.18 B354 Int J Energy Environ Eng (2016) 7:353–359123– 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 tem-perature of 20 C in all rooms.Case 1It is characterized by an air change rate (ventilation andinfiltration) of 0.3 h-1 for all the rooms, except the kitchenand the bathroom which have 0.9 air changes per hour.Case 2It is characterized by the presence of a heat recovery venti-lation system that can save energy from the ejected air, asdepicted in Fig. 2. The ventilation system is equipped withtwo fans that absorb individually the power of 30 W. Themodel employs a cross flow heat exchanger able to exchangeheat, but unable to exchange humidity since the two air fluxesare kept separate by specific sealing in the plates. Any airinfiltration, contaminant gases (polluting materials), biolog-ical hazards and particulates are completely blocked.The efficiency of the heat recovery system is defined asfollows:e ¼ TS  T0TR  T0;where TS is the temperature of the supply air; TO is thetemperature of the external air (outdoor air); TR representsthe temperature of the extracted air (return air); the heatrecovery efficiency values adopted in the simulations aree = 0.6 and 0.8.The above-mentioned ventilation system extracts airfrom the bathroom and the kitchen, with the mass flow ratevales of, respectively, 28.3 and 46.0 kg h-1. The fresh airenters the living room and the two bedrooms with thefollowing mass flow rate:– 31.5 kg h-1 of external air in the living room;– 21.0 kg h-1 of external air in bedroom 1;– 21.8 kg h-1 of external air in bedroom 2.Finally, it is important to highlight that 0.1 air changes perhour for infiltration are considered and it is worth under-lining that the total amount of ventilation and infiltration inCase 2 corresponds to the same quantity used in Case 1.Case 3In this case, the ventilation system operates, without heatrecovery, for a total period of 6 h, precisely:– from 7 a.m. to 9 a.m;– from 12 p.m. to 2 p.m;– from 7 p.m. to 9 p.m.The above-mentioned ventilation system extracts airfrom the bathroom and the kitchen, with the mass flow ratevalues of, respectively, 113.0 and 184.2 kg h-1. The freshair coming from outside enters the living room and the twobedrooms with the following mass flow rate:– 126.1 kg h-1 of external air in the living room;– 83.8 kg h-1 of external air in bedroom 1;– 87.3 kg h-1 of external air in bedroom 2.The infiltration of 0.1 air changes per hour remainsunvaried.Table 2 Values of thermal transmittance with regard to the envelopeelementsEnvelope element Thermal transmittance U (W m-2 K-1)Outside walls 0.47Inside walls 0.64Floor and ceiling 0.39Windows 2.83Table 3 Timetable of people present in each room of the apartmentTimetable Room Number of people11 p.m.–7 a.m. B1 211 p.m.–7 a.m. B2 2midday–2 p.m. K 22 p.m.–7 p.m. LR 27 p.m.–9 p.m. K 49 p.m.–11 p.m. LR 4Fig. 2 Heat recovery systemInt J Energy Environ Eng (2016) 7:353–359 355123Case 4It is similar to Case 3, but in the presence of the heatrecovery system. The ventilation system is equipped withtwo fans that absorb individually the power of 60 W. Theexternal air enters the heat recovery and reaches the livingroom, bedroom 1 and bedroom 2 with the same ventilationrates of Case 3 and 6 h per day of total operation. Theexhaust air is extracted from the bathroom and the kitchenand expelled outside after having preheated the inlet air.The heat recovery efficiency values adopted in the simu-lations are still e = 0.6 and 0.8.Results and discussionCase 1The energy need for building heating in the consideredinterval (from 15 October to 15 April) is highlighted inTable 4.:The yearly energy demand for the envelope of 5,312kWh referred to the unit surface becomes 80.7 kWhm-2per year. The part due to ventilation and infiltration is 0.3air changes per hour for all the rooms, except the kitchenand the bathroom which have 0.9, results equal to 1,470kWh per year and per unit surface 22.3 kWhm-2 per year.Case 2Consider the heat recovery working 24 h per day; duringthe winter period (183 days), the energy demand referredto building heating is highlighted in Table 5.From Table 5, the yearly energy demand for the enve-lope, when e = 0.6, is equal to 4,583 kWh and whenreferred to the unit surface becomes 69.6 kWhm-2 peryear. Similarly, the energy demand, when e = 0.8, is equalto 4,353 kWh and when referred to the unit surfacebecomes 66.1 kWhm-2 per year.Case 3The energy demand referred to building heating in thewinter period is highlighted in Table 6.The yearly energy demand for the envelope of 5,486kWh referred to the unit surface becomes 83.3 kWhm-2per year. The part due to ventilation results in augmenta-tion if compared to that of Case 1 because during the 6 h offunctioning the heat generator is permanently switched onin order to maintain the fixed temperature of 20 C in allthe apartment.Case 4Consider the heat recovery working 6 h per day; during thewinter period (183 days), the energy need for buildingheating is highlighted in Table 7.From Table 7, the yearly energy demand for the enve-lope, when e = 0.6, is equal to 4,683 kWh and whenreferred to the unit surface becomes 71.1 kWhm-2 peryear. Similarly, total yearly energy demand, when e = 0.8,is equal to 4,412 kWh and when referred to the unit surfacebecomes 67.0 kWhm-2 per year.Table 5 Monthly and total energy demand with reference to Case 2Month Total energy demand, Q [kWh]e = 0.6 e = 0.8October (15 days) 68 57November 675 641December 1,190 1,141January 1,228 1,171February 950 907March 414 383April (15 days) 58 53Total 4,583 4,353Table 6 Monthly and total energy demand with reference to Case 3Month Total energy demand, Q (kWh)October (15 days) 120November 809December 1,380January 1,447February 1,116March 539April (15 days) 75Total 5,486Table 4 Monthly and total energy demand with reference to Case 1Month Total energy demand, Q [kWh]October (15 days) 104November 785December 1,347January 1,406February 1,086March 513April (15 days) 72Total 5,312356 Int J Energy Environ Eng (2016) 7:353–359123Comparative analysisConsidering a global heating system efficiency equal to0.85, the yearly energy demand can be highlighted in termsof primary energy, as shown in Table 8.With reference to Case 2, the consumption of primaryenergy of the heat recovery system (two fans that absorbindividually the power of 30 W), considering 183 days(24 h per day) and a conversion factor of 0.46, is 573 kWh;when referred to the unit surface it becomes 8.7 kWhm-2per year. According to the considered hypothesis on theheat recovery working period, when the efficiency is 0.8(Case 2B), it is possible to save, in comparison with Case 1,555 kWh per year (that per unit area corresponds to 8.4kWhm-2) and only 285 kWh per year (that per unit areacorresponds to 4.3 kWhm-2) when the efficiency is 0.6(Case 2A).Similarly, with reference to Case 4, the consumption ofprimary energy of the heat recovery system (two fans thatabsorb individually the power of 60 W), considering183 days (6 h per day) and a conversion factor of 0.46, is286 kWh; when referred to the unit surface it becomes 8.7kWhm-2 per year. According to the considered hypothesison the heat recovery working period, when the efficiency is0.8 (Case 4B), it is possible to save, in comparison withCase 3, 978 kWh per year (that per unit area corresponds to14.8 kWhm-2) and 659 kWh per year (that per unit areacorresponds to 10.0 kWhm-2) when the efficiency is 0.6(Case 4A).Analysis of temperature diagramsFigure 3 highlights the temporal trend of temperaturesreferring to a typical winter day, i.e., January 15. Thediagram is directly referred to the simulations performed inCase 2, but can be extended also to Case 4, provided thatthe temporal interval is limited to 6 h. On the ordinate axis,the external temperature scale (right) and the supply airtemperature (left) are shown in case the heat recoveryefficiency is e = 0.6 (bottom) and 0.8 (top). It is worthnoting that in the supply air temperature trend, the maxi-mum temperatures of almost 16 and 12 C, respectively,when e = 0.8 and 0.6, are due to the working of the heatingsystem. Figure 4 highlights the air temperature temporaltrend with reference to Bedroom 2 in a typical winter night(between January 15 and 16). All the investigated caseshave been contemplated: case 2A and 4A correspond toe = 0.6 and, similarly, case 2B and 4B correspond toe = 0.8.Two persons sleeping in Bedroom 2 is expectedaccording to the initial hypothesis. Moreover, it is inter-esting to observe that Bedroom 2 is located at the corner ofthe apartment, so that the building envelope is particularlyexposed to heat losses. Based on pure observation, thetemporal trend referred to Case 3 and 4 is affected by theoccurrence of infiltration with no air ventilation.ConclusionsIn the present work, we performed a dynamic simulation ofa ventilation system for an apartment using a mathematicalmodel, i.e., the Trnsys commercial code, in the context ofthe Italian regulation [13].The model has been applied, with reference to the winterperiod, to an apartment of 66 m2 inside a condominiumlocated in Bologna (Italy), but can also be used for othertypes of buildings as well. The ventilation system treatedhere used both external air supply (Cases 1–3) and fresh airwhich came across a heat recovery unit (Cases 2–4), havingconstant flow rate.Several conclusions and ideas for future researchemerged from this study:– When the system works 24 h, an evident energyconsumption for ventilators occurs.Table 7 Monthly and total energy demand with reference to Case 4Month Total energy demand, Q (kWh)e = 0.6 e = 0.8October (15 days) 74 60November 690 649December 1,211 1,154January 1,253 1,187February 968 918March 427 390April (15 days) 60 54Total 4,683 4,412Table 8 Energy need for building heating in terms of primary energywith reference to all the investigated casesYearly energydemand forheating (kWh)Yearly energydemand for heatrecovery (kWh]Total yearly energydemand per unitsurface (kWhm-2)Case 1 6,249 – 94.7Case 2A 5,392 573 90.4Case 2B 5,121 573 86.3Case 3 6,454 – 97.8Case 4A 5,509 286 87.8Case 4B 5,191 286 83.0Int J Energy Environ Eng (2016) 7:353–359 357123– If the total amount of fans’ energy absorption exceedsthe power of 60 W, the use of the heat recoveryexchanger could be no more advisable. With referenceto the case treated here, a weak energy gain occurs andit is more pronounced when the HR efficiency is equalto 0.6.– If the ventilation system works during a limited timeinterval (Case 4), with the heating system switched on,an incremented air mass flow rate has to be managed sothat fans absorb more power. However, the present casehas highlighted a considerable energy gain, with thehypothesis of total power of the HR equal to 120 W.In future works, these conclusions based on energyperformance comparisons should be balanced by at leasttwo other criteria: indoor air quality and investment costs.Acknowledgments The authors wish to thank the Italian Ministryof Education, University and Research for funding this study.Fig. 3 Temporal trend of theexternal temperature and of thesupply air temperature withreference to Case 2Fig. 4 Temporal trend of airtemperature during a typicalwinter night in Bedroom 2 withreference to all the investigatedcases358 Int J Energy Environ Eng (2016) 7:353–359123Open Access This article is distributed under the terms of theCreative Commons Attribution License which permits any use, dis-tribution, and reproduction in any medium, provided the originalauthor(s) and the source are credited.References1. Aste, N., Adhikari, R.S., Compostella, J., Del Pero, C.: Energyand environmental impact of domestic heating in Italy: evaluationof national NOx emissions. Energy Policy 53, 353–360 (2013)2. Directive 2010/31/EU of the European Parliament and of theCouncil of 19 May 2010 on the energy performance of buildings(recast) (2010)3. Directive 2002/91/CE of the European Parliament, 16 Dec 2002(2002)4. Legislative Decree n 192, 19 Aug 2005 (2005)5. Legislative Decree n 311, 29 Dec 2006 (2006)6. Simonson, C.: Energy consumption and ventilation performanceof naturally ventilated ecological house in a cold climate. EnergyBuild. 37, 23–35 (2005)7. Orme, M.: Estimates of the energy impact of ventilation andfinancial expenditures. Energy Build. 33, 199–205 (2001)8. El Fouih, Y., Stabat, P., Rivière, P., Hoang, P., Archambault, V.:Adequacy of air-to-air heat recovery ventilation system applied inlow energy buildings. Energy Build. 54, 29–39 (2012)9. Calautit, J.K., Hughes, B.R., Chaudhry, H.N., Ghani, S.A.: CFDanalysis of a heat transfer device integrated wind tower systemfor hot and dry climate. Appl. Energy 112, 576–591 (2013)10. Hughes, B.R., Chaudhry, H.N., Calautit, J.K.: Passive energyrecovery from natural ventilation air streams. Appl. Energy 113,127–140 (2014)11. Liu, X.P., Niu, J.L.: An optimal design analysis method for heatrecovery devices in building applications. Appl. Energy 129,364–372 (2014)12. Solar Energy Laboratory, Manual of TRNSYS 16—a TRaNsientSYstem Simulation program (2006)13. UNI TS 11300-1, Determination of the buildings energy demandfor the air-conditioning in summer and winterInt J Energy Environ Eng (2016) 7:353–359 359123

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

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