Ventilative Cooling in a School Building: Evaluation of the Measured Performances

Home , Room temperature, Ventilative cooling

fluids

Article Ventilative Cooling in a School Building: Evaluation of the Measured Performances

Hilde Breesch * , Bart Merema and Alexis Versele

Department of Civil Engineering, Katholieke Universiteit Leuven, Construction Technology Cluster, Sustainable Building, Technology Campus Ghent, 9000 Ghent, Belgium; [email protected] (B.M.); [email protected] (A.V.) * Correspondence: [email protected]; Tel.: +32-9-331-6592

Received: 26 August 2018; Accepted: 18 September 2018; Published: 23 September 2018

Abstract: The test lecture rooms on Katholieke Universiteit Leuven (KU Leuven) Ghent Technology Campus (Belgium) are a demonstration case of Annex 62: Ventilative Cooling of the International Energy Agency’s Energy in Buildings and Communities programme (IEA EBC). The building is cooled by natural night ventilation and indirect evaporative cooling (IEC). Thermal comfort and the performances of ventilative cooling are evaluated. Long-term measurements of internal temperatures, occupancy, opening of windows and IEC were carried out in the cooling season of 2017. The airflow rates through the windows in cross- and single-sided ventilation mode were measured by both tracer gas concentration decay and air velocity measurements. In addition, the air flow pattern is visualized by measuring air temperatures in the room. The results show that good thermal summer comfort was measured except during heat waves and/or periods with high occupancy. Both nighttime ventilation and IEC operate very well. IEC can lower the supply temperature by day significantly compared to the outdoor temperature. The Air Changes Rates (ACR) of the night ventilation greatly depends on wind direction and velocity. The air temperature profile showed that the air is cooled down in the whole lecture but more in the upper zone. The extensive data monitoring system was important to detect malfunctions and to optimize the whole building performance.

Keywords: ventilative cooling; nearly zero-energy buildings (nZEB); school building; measurements; thermal comfort

1. Introduction In the recently approved second recast of the Energy Performance of Buildings Directive (EPBD) [1], the member states of the European Union committed themselves to develop a sustainable, competitive, secure, and decarbonized energy system by 2050. An important aspect to achieve this goal is to find a cost-efficient equilibrium between decarbonizing energy supplies and reducing final energy consumption of the building stock. While the first recast of the EPBD [2] required that from 2020, all new buildings in the European Union have to be nearly zero-energy buildings (nZEB), this second recast focusses on renovation strategies. An average renovation rate of 3% annually towards nZEB, where nearly means cost effective, is needed [1]. One of the major new challenges in these highly insulated and airtight buildings is the increased need for cooling and the risk on overheating not only during summer but all year round. In addition, this cooling demand depends less on the outdoor temperature and more on the internal and solar heat gains [3]. A shift is noticed from reduction in heating to reduction in cooling demand. As a consequence, conceptual and building technical measures as well as energy efficient cooling systems are needed in these nZEB buildings to guarantee good thermal comfort all year round. Ventilative cooling is an example of an energy efficient cooling method that can contribute to achieve the goal

Fluids 2018, 3, 68; doi:10.3390/fluids3040068 www.mdpi.com/journal/fluids Fluids 2018, 3, 68 2 of 14 of the 2nd recast of the EPBD and was extensively studied within IEA EBC Annex 62 [4]. Ventilative cooling is defined as “the application of the cooling capacity of the outdoor air flow by ventilation to reduce or even eliminate the cooling loads and/or the energy use by mechanical cooling in buildings, while guaranteeing a comfortable thermal environment” [3]. Ventilative cooling strategies depend on the indoor-outdoor temperature difference. For temperate outdoor conditions, i.e., mean outdoor 2 to 10 ◦C lower than indoor temperature, an increased airflow rate by day and night is recommended. For hot and dry, i.e., indoor–outdoor temperature difference between −2 ◦C and +2 ◦C, only the airflow rate during nighttime, i.e., night ventilation, is maximized. Extra natural cooling, like evaporative cooling and earth-to-air-heat-exchanger, or mechanical cooling can be provided to reduce the air intake temperature during daytime [3]. Santamouris and Kolokotska [5] reviewed the state of the art technologies for passive cooling including ventilative cooling and concluded that “the efficiency of the proposed passive cooling systems is found to be high while their environmental quality is excellent. Expected energy savings may reach 70% compared to a conventional air conditioned building”. Night ventilation was found to be very effective to reduce the cooling demand in office buildings and improve thermal summer comfort regardless the climatic conditions [5]. In free floating buildings, amongst others [6–10] monitored that night ventilation can decrease the next day peak internal temperature up to 3 ◦C. In addition, the climatic cooling potential of buildings with night ventilation in Europe was evaluated by Artmann et al. [11]. A very significant climatic cooling potential was found in Northern Europe; a significant in central and Eastern Europe but series of warmer nights can occur. As a consequence, night ventilation may not be sufficient to guarantee good thermal comfort during these periods [11]. Santamouris and Kolokotska [5] also concluded, based on amongst others [12–14], that “indirect evaporative cooling techniques can be low energy solutions for medium and large buildings where passive cooling techniques cannot reach the required comfort conditions”. However, these systems require fan energy, which can be up to 20% less due to lower air velocities [5]. Kolokotroni and Heiselberg [15] give amongst other things, insight in the limitations and barriers to ventilative cooling. The most important are the impact of global warming and heat island effect [6,16,17] noise and pollution [18]. It is expected that the average cooling potential of night ventilation will decrease significantly with regionally varying implications. In Northern Europe, the risk of thermal discomfort in buildings that use exclusively night ventilation is increased while in Central Europe the periods with low night cooling potential are becoming more frequent [19]. Appropriate control is also a requirement to guarantee good thermal comfort. To ensure that the required window opening on a regular basis, the night ventilation strategy should be integrated to the office buildings energy management system [5]. The test lecture rooms of KU Leuven Ghent Technology Campus, which are studied in this paper, were one the demonstration cases of IEA EBC Annex 62: Ventilative Cooling [20]. Natural night ventilation and indirect evaporative cooling techniques are applied. This paper aims to evaluate thermal comfort in this nZEB school building and to discuss the performances of its ventilative cooling systems. First, a description of the building, its systems, and more specifically the ventilative cooling and control strategies are presented. Afterwards, the measurement setup for the evaluation of air flow rates, operation of ventilative cooling and thermal comfort is shown. Section3 presents the results of the measurements and finally the conclusions and lessons learned are presented.

2. Materials and Methods This paragraph describes the building, its systems and the ventilative cooling as well as the measurement setup. Fluids 2018, 3, 68 3 of 14

2.1. Building Description

2.1.1. Building and Use The nZEB school building is realized at the technology campus Ghent of KU Leuven (Belgium) on top of an existing university building. The building contains four zones (see Figure1): two large lecture roomsFluids 2018 (1), 3, andx FOR (2),PEER a REVIEW staircase (3) and a technical room (4). The lecture rooms have a3 floor of 14 area of about 140 m2, a volume of 380 m3. The lecture rooms are designed as identical zones with a different thermal mass.The nZEB The lowerschool building room has is realized a brick at externalthe technology wall camp withus exterior Ghent of insulation KU Leuven while(Belgium) the upper room hason atop lightweight of an existing timber university frame building. external The wall building with contains the same fourU zones-value. (see Both Figure lecture 1): two rooms large have a lecture rooms (1) and (2), a staircase (3) and a technical room (4). The lecture rooms have a floor area concrete slab floor. This results in a light (2nd floor) and a medium (1st floor) thermal mass according of about 140 m2, a volume of 380 m3. The lecture rooms are designed as identical zones with a different to EN ISOthermal 13790 mass. [21 The]. lower room has a brick external wall with exterior insulation while the upper room Tablehas1 a shows lightweight the building timber frame properties. external The wall school with the building same U is-value. designed Both andlecture constructed rooms have according a −1 to the Passiveconcrete slab House floor. standard.This results Thisin a light means (2nd floor) that and the a air medium tightness (1st floor)n50 thermalis lower mass than according 0.6 h and the U-valuesto EN ISO of 13790 the envelope[21]. parts are maximum 0.15 W/m2 K. The windows are constructed Table 1 shows the building properties. The school building is designed and constructed with triple glazing and have a g-value of 0.52. The window-to-wall ratio is 26.5% on both façades. according to the Passive House standard. This means that the air tightness n50 is lower than 0.6 h−1 The window-to-floorand the U-values ratio of the is 13%.envelope The parts windows are maximum are equipped 0.15 W/ withm2 K.internal The windows and externalare constructed solar shading. The externalwith triple solar glazing shading and have are a moveable g-value of 0.52. screens The window on the-to southwest-wall ratio is façade 26.5% on which both façades. are controlled automaticallyThe window and- providedto-floor ratio of manual is 13%. The overrule. windows are equipped with internal and external solar Theshading. occupancy The external level in solar the building shading are is dependent moveable screens on the on academic the southwest year, façade which which counts are 124 days with coursescontrolled and automatically 63 days with and examsprovided (in of January,manual overrule. June and August–September). Holiday periods The occupancy level in the building is dependent on the academic year, which counts 124 days are in April (2 weeks), July and the first half of August (6 weeks) and December–January (2 weeks). with courses and 63 days with exams (in January, June and August–September). Holiday periods are The lecturein April rooms (2 weeks), are July in use and fromthe first Monday half of August to Friday (6 weeks) between and December 8 h15– andJanuary 18 h(2 withweeks). a The maximum 2 occupancylecture of rooms 80 persons are in use or 1.78from mMonday/pers. to FigureFriday between2 shows 8 detailsh15 and of18 1h with typical a maximum week of occupancy occupancy. Theof net80 persons energy or demand 1.78 m2/pers. for Figure heating 2 shows in this details school of 1building typical week is calculatedof occupancy. in [22]. The annual net heating demandThe net is energy 11 kWh/(m demand2 for·a), heating fulfilling in this the school requirements building is ofcalculated Passive in House [22]. The standard annual net in school 2 buildingsheating [23]. demand In addition, is 11 kWh large/(m heat·a), fulfilling gains duringthe requirements the whole of Passive year and House a short standard heating in school season, i.e., buildings [23]. In addition, large heat gains during the whole year and a short heating season, i.e., from Novemberfrom November till March, till March, are are noticed. noticed.

TableTable 1. 1.Building Building properties. properties.

PropertyProperty ValueValue Unit Unit 2 U-valueU- Wallvalue Wall 0.150.15 W/m W/m K 2 K U-valueU- Roofvalue Roof 0.140.14 W/m2W/m K 2 K U-valueU- Floorvalue Floor 0.150.15 W/m2W/m K 2 K U-valueU- Windowvalue Window 0.650.65 W/m2W/m K 2 K g-valueg- Windowvalue Window 0.520.52 (-) (-) n 1st ﬂoor 0.41 1/h 50 n50 1st floor 0.41 1/h n50 2nd ﬂoor 0.29 1/h n50 2nd floor 0.29 1/h

FigureFigure 1. Section 1. Section (left ()left and) and ﬂoor floor plan plan ( right (right)) of of the the test test lecture lecture rooms rooms on Katholieke on Katholieke Universiteit Universiteit LeuvenLeuven (KU Leuven) (KU Leuven Technology) Technology campus campus Ghent. Ghent. Fluids 2018, 3, x FOR PEER REVIEW 4 of 14

Fluids 2018, 3, 68 4 of 14

Fluids 2018, 3, x FOR PEER REVIEW 4 of 14

Figure 2. Typical occupancy profile in the lecture rooms during one course week (Monday to Friday). Figure 2. Typical occupancy profile in the lecture rooms during one course week (Monday to Friday). Figure 2. Typical occupancy proﬁle in the lecture rooms during one course week (Monday to Friday). 2.1.2. Systems 2.1.2.2.1.2. Systems Systems The buildingThe building is equipped is equipped with with an an all all air air systemsystem withwith balanced balanced mechanical mechanical venti ventilationlation with witha a The building is equipped with3 an all air system with balanced mechanical ventilation with a total total supply airflow of 4400 m /h3 (see Figure 3). Demand controlled ventilation with 4 Variable Air supplytotal airﬂow supply of airflow 4400 m of3/h 4400 (see m Figure/h (see3 Figure). Demand 3). Demand controlled controlled ventilation ventilation with with 4 Variable 4 Variable Air VolumeAir VolumeVolume (VAV (VAV) boxes) boxes control control the the airflow airflow based based on CO22--concentrationsconcentrations in in the the rooms. rooms. For Forheating heating (VAV) boxes control the airflow based on CO -concentrations in the rooms. For heating purposes, the air purposes,purposes, the airthe isair preheated is preheated by by air air-to-to-air-air 2heat heat recovery,recovery, i.e. i.e., ,two two cross cross flow flow plate plate heat heat exchangers exchangers is preheated by air-to-air heat recovery, i.e., two cross flow plate heat exchangers connected in series, connectedconnected in series, in series, with with an an efficiency efficiency of of 78%. 78%. Additionally, heating heating coils coils of 7.9of 7.9 kW kW each each are are with an efficiency of 78%. Additionally, heating coils of 7.9 kW each are integrated in the supply ducts in integratedintegrated in the in thesupply supply ducts ducts in in each each lecture lecture room.room. TheThe heatingheating production production system system consists consists of a of a each lecture room. The heating production system consists of a condensing wood pellet boiler with an condensingcondensing wood wood pellet pellet boiler boiler with with an an internal internal storagestorage ofof 600 600 L L. The. The maximum maximum heating heating power power is 8 is 8 internalkW storageand the ofmaximum 600 L. The efficiency maximum is 95%. heating power is 8 kW and the maximum efficiency is 95%. kW and the maximum efficiency is 95%.

Figure 3. Ventilation system (supply in green, return in brown) of the test lecture rooms on KU

Leuven Technology campus Ghent. Figure 3. 3. VentilationVentilation system system (supply (supply in green,in green, return return in brown) in brown) of the of test the lecture test lecture rooms onrooms KU Leuven on KU TechnologyLeuven2.1.3. Ventilative Technology campus Cooling Ghent.campus System Ghent . 2.1.3. VentilativeTwo different Cooling principles System of ventilative cooling are implemented in this building: (1) natural night 2.1.3. ventilationVentilative (2) Cooling an air handling System unit (AHU) that cools the supply air by controlling the modular bypass Twoand by different using indirect principlesprinciples evaporative ofof ventilative cooling cooling(IEC). are implemented in this building: (1) natural night ventilationDesign (2) an of air the handling building unit and its(AHU) ventilative that cools cooling the systems supply is air described by controlling controlling in [22]. Thermal the modular summer bypass comfort and net cooling demand in both lecture rooms are evaluated using building energy and by using indirect evaporative cooling (IEC). simulations (BES). Without ventilative cooling, none of the lecture rooms meet the requirement of EN Design of the building and its ventilative cooling systems is described in [[22]22].. Thermal summer comfort15251 and [24] net of cooling overheating demand hours in less both than lecture 5% of rooms the time are in evaluated use. Night using ventilation building (with energy an airflow simulations of comfort5 h −1) and significantly net cooling lowered demand the predicted in both overheating lecture roomshours. However, are evaluated it was concluded using buildi fromng these energy (BES).simulations Without (BES). ventilative Without cooling, ventilative none cooling, of the none lecture of roomsthe lecture meet rooms the requirement meet the requirement of EN 15251 of [EN24] BES simulations that thermal summer comfort was reasonable but not excellent in these densely −1 of15251 overheating [24] of overheating hours less hours than 5%less ofthan the 5% time of the in use.time Night in use. ventilation Night ventilation (with an (with airflow an airflow of 5 h of) significantly5 h−1) significantly lowered lowered the predicted the predicted overheating overheating hours. hours. However, However, it was it concludedwas concluded from from these these BES simulationsBES simulations that thermal that thermal summer summer comfort comfort was reasonable was reasonable but not butexcellent not excellent in these densely in these occupied densely lecture rooms. As a result, it was decided to add indirect evaporative cooling. Moreover, the annual Fluids 2018, 3, 68x FOR PEER REVIEW 5 of 14 occupied lecture rooms. As a result, it was decided to add indirect evaporative cooling. Moreover, 2 thenet coolingannual netdemand cooling of the demand building of the with building night ventilation with night is ventilation equal to 6 kWh/(m is equal to·a), 6 fulfilling kWh/(m2 the·a), 2 fulfillingPassive House the Passive requirement House ofrequirement 15 kWh/( mof 15·a) kWh/( in school m2· buildingsa) in school [23 buildings]. [23]. Night ventilation relies on cross ventilation through openable windows at both sides of the room 2 (see Figure4 4).). TheThe systemsystem includesincludes 10 10 motorized motorized bottom bottom hung hung windows windows (1.29 (1.29 ×× 1.38 m2,, maximum ◦ opening angle angle of of 8.8°) 8.8 )with with a achain chain actuator. actuator. There There are are 6 windows 6 windows on onthe the southwestern southwestern side side and and 4 on 4 theon thenortheastern northeastern side side of ofthe the lecture lecture room room located located at at1m 1m h heighteight from from the the bottom. bottom. The The depth depth of of the lecture room isis 3.963.96 timestimes thethe heightheight ofof thethe room,room, i.e., i.e., smaller smaller than than the the maximum maximum depth-to-height depth-to-height of of 5 5according according to theto the rule rule of thumb of thumb as described as described in [25 ]. in The [25] total. The effective total effective opening opening area of these area windows of these windowsis 4.0% of is the 4.0% floor of area. the floor area. 3 The modular modular bypass bypass and and IEC IEC are are part part of ofthe the AHU. AHU. The The maximum maximum airflow airflow rate rate is 4400 is 4400 m3/h. m The/h. maximumThe maximum capacity capacity of IEC of IECat maximum at maximum airflow airflow is 13.1 is 13.1kW. kW.

2 Figure 4. Principle of natural night ventilation (leftleft)) andand detaildetail ofof motorizedmotorized windowwindow (1.29(1.29 ×× 1.38 m², m , ◦ maximum opening angle of 8.8°) 8.8 )( (right)).. 2.1.4. Control Strategy 2.1.4. Control Strategy Control strategy of the systems consists of two parts. First, the control strategy of the mechanical Control strategy of the systems consists of two parts. First, the control strategy of the mechanical ventilation system (operation of bypass and IEC) during occupancy is based on internal and external ventilation system (operation of bypass and IEC) during occupancy is based on internal and external temperatures (see Figure5 left). This strategy actuates the supply air temperature and the air flow temperatures (see Figure 5 left). This strategy actuates the supply air temperature and the air flow rate. The internal room temperature set point is 22 ◦C. When the room temperature exceeds the set rate. The internal room temperature set point is 22 °C. When the room temperature exceeds the set point +4 ◦C, the evaporative cooling is activated on maximum airflow rate. IEC is active until the room point +4 °C, the evaporative cooling is activated on maximum airflow rate. IEC is active until the temperature is lower or equal to the set point −0.5 ◦C. When the external temperature is higher than room temperature is lower or equal to the set point −0.5 °C. When the external temperature is higher 22 ◦C, indirect evaporative cooling is activated. If the external temperature is between 16 ◦C and 22 ◦C, than 22 °C, indirect evaporative cooling is activated. If the external temperature is between 16 °C and the bypass on the heat exchanger is active. When the external temperature is between 14 ◦C and 16 ◦C, 22 °C, the bypass on the heat exchanger is active. When the external temperature is between 14 °C 50% of the fresh air is sent through the heat exchanger and 50% is bypassed. When the outside air is and 16 °C, 50% of the fresh air is sent through the heat exchanger and 50% is bypassed. When the colder than 14 ◦C, the bypass is switched off. outside air is colder than 14 °C, the bypass is switched off. Second, the control strategy at night that actuates the opening of the windows is based on internal Second, the control strategy at night that actuates the opening of the windows is based on temperature and relative humidity and external weather conditions (temperature, rain) measured on internal temperature and relative humidity and external weather conditions (temperature, rain) site (see Figure5 right). This strategy is inspired by the recommendations of [ 26]. The windows remain measured on site (see Figure 5 right). This strategy is inspired by the recommendations of [26]. The open/closed for at least 15 min. Windows are opened between 10:00 p.m. and 6:00 a.m. from April 1st windows remain open/closed for at least 15 min. Windows are opened between 10:00 p.m. and 6:00 to October 31st when the following criteria are fulfilled: a.m. from April 1st to October 31st when the following criteria are fulfilled: ◦ ◦ • Room temperature exceeds exceeds both both the the heating heating set set point point (=22 (=22 °C)C) and and the the external external temperat temperatureure +2 +2 °C C • Maximum room temperature of the previous day exceeds 2323 ◦°CC • External temperature is higher than 12 ◦°CC • Internal relative humidity is smaller than 70% • There is no rainfall and the wind velocity on site is smaller than 10 m/s Fluids 2018, 3, 68 6 of 14 Fluids 2018, 3, x FOR PEER REVIEW 6 of 14

FigureFigure 5. Control5. Control strategy strategy flowchart flowchart of AHUof AHU during during occupancy occupancy (left ()left and) naturaland natural night night ventilation ventilation (right ). (right). 2.2. Measurement Setup 2.2. Measurement Setup 2.2.1. Airflow Rate and Room Air Temperature Profile 2.2.1.Air Airflow Changes Rate Ratesand Room (ACR) Air as Temperature result of the Profile opening of the windows in the lecture rooms was measuredAir Changes using a tracer Rates gas (ACR) concentration as result of decay the test opening method of inthe March windows and Aprilin the 2017. lecture The roo usedms gas was is measuredN2O also knownusing a astracer laughing gas concentration gas. Tests were decay completed test method in accordance in March and with April the procedures2017. The used set gas out in EN 12569 [27]. The measurements were carried out in a representative zone with two opposing is N2O also known as laughing gas. Tests were completed in accordance with the procedures set out windowsin EN 12569 with [27] a. widthThe measurements of 3.04 m (see were Figure carried6, left). out Tracer in a representative gas was injected zone and with sampled two opp inosing the windowsmiddle of with this smalla width room. of 3.04 A m fan (see was Figure used 6, to left). spread Tracer the tracergas was gas injected over the and entire sampled zone in at the to middle reach a ofhomogenous this small concentration. room. A fan was This used concentration to spread was the increased tracer gas in overthis sealed the entire room zone to a constant at to reach value a homogenousof 200 ppm. Afterconcentration. reaching This this goal,concentration one or two was opposing increased windows in this sealed (depending room to on a constant the test) value were ofopened. 200 ppm. The After accuracy reaching of the this tracer goal, gas one equipment or two opposing is 10% of thewindows measured (depending value. on the test) were opened.ACR The was accuracy also estimated of the tracer from thegas airequipment velocity measurements.is 10% of the measured Figure6 (right) value. shows the test setup: the airACR velocity was also is measured estimated every from 10 the s during air velocity 30 min measurements. with omnidirectional Figure sensors.6 (right) The shows following the test 4 setup:locations the are air selected: velocity V1 is and measured V4 are positioned every 10 s in during the side 30 triangles min with of the omnidirectional window opening sensors. at 0.28 The m followingbelow the 4 top locations of the window. are selected: In addition, V1 and V4V2 andare positioned V3 are positioned in the side in the triangles top opening of the at window 0.43 m openingfrom the at left 0.28 and m right below end the of thetop windowof the w (i.e.,indow. at 1/3 In addition, and 2/3 of V2 the and width). V3 are The positioned effective areain the of top the 2 windowopening at is calculated0.43 m from at the 0.109 left m and. The right airflow end of is the determined window as(i.e. the, at effective 1/3 and area2/3 of multiplied the width). by The the effectivemedian of area the of air the velocity. window is calculated at 0.109 m². The airflow is determined as the effective area multipliedMoreover, by the the median air flow of pattern the air isvelocity. visualized by measuring air temperatures in the room. Figure7 showsMoreover, the grid ofthe sensors: air flow positions pattern is with visualized horizontal by distancesmeasuring and air heights.temperatures The measuring in the room. 5 different Figure 7heights shows for the each grid position of sensors: were determined positions with as follows horizontal (see reference distances [28 and]). On heights. each position, The measuring 15 sensors 5 weredifferent located height froms for 0.3 each m toposition 2.4 m withwere adetermined height difference as follows of 0.1 (see m. reference Air temperatures [28]). On each are measured position, 15 sensors were located from 0.3 m to 2.4 m with a height difference of 0.1 m. Air temperatures are measured during 20 min after opening of the window. Heights are eliminated whenever the Fluids 2018, 3, 68 7 of 14

Fluids 2018, 3, x FOR PEER REVIEW 7 of 14 duringFluids 20 2018 min, 3, x after FOR PEER opening REVIEW of the window. Heights are eliminated whenever the temperature7 of 14 differencetemperature between difference two consecutive between two heights consecutive smaller heights is than smaller 0.1 ◦C, is i.e.,than the 0.1 accuracy°C, i.e., the of accuracy the sensors. of temperature difference between two consecutive heights smaller is than 0.1 °C, i.e., the accuracy of Moreover,the sensorssensors. Moreover, are distributed sensors over are distributed the height over of the the room, height representing of the room, representing the different the stratiﬁcation different the sensors. Moreover, sensors are distributed over the height of the room, representing the different stratification zones at the different positions. Table 2 shows the resulting measurement heights in zonesstratification at the different zones positions.at the different Table positions.2 shows Table the resulting 2 shows the measurement resulting measurement heights in heights plane 2,in i.e., plane 2, i.e., the central plane perpendicular to the window opening. the centralplane 2, plane i.e., the perpendicular central plane toperpendicular the window to opening. the window opening.

Figure 6. Test setup tracer gas measurement (left) and air velocity measurement (position of the Figure 6. Test setup tracer gas measurement (left) and air velocity measurement (position of the Figure 6.sensors)Test setup(right).tracer gas measurement (left) and air velocity measurement (position of the sensors)sensors) (right (right). ).

Window Window

Plane 3 Plane 3

Plane 2 Plane 2

Plane 1 Plane 1

Figure 7. FigureTest setup 7. Test air setup temperature air temperature measurements: measurements: horizontal horizontal distances distances (left)) and and heights heights (right) (right) [28].[ 28]. Figure 7. Test setup air temperature measurements: horizontal distances (left) and heights (right) [28]. TableTable 2. Measurements 2. Measurements heights heights (plane (plane 2) of2) of test test set set up up air air temperatures.temperatures. Table 2. Measurements heights (plane 2) of test set up air temperatures. Position A2Position Position A2 Position B2 B2Position Position C2 C2 Position Position D2 D2 Position Position E2 E2 Position A2 Position B2 Position C2 Position D2 Position E2 0.8 m 0.8 m 0.5 m 0.4 m 0.4 m 0.8 m0.8 m 0.8 m0.8 m 0.50.5 mm 0.4 m 0.4 m0.4 m 0.4 m 1.9 m1.9 m 1.9 m1.9 m 0.80.8 m m 0.5 0.5 m m 0.6 m 0.6 m 1.9 m 1.9 m 0.8 m 0.5 m 0.6 m 2.1 m2.1 m 2.1 m2.1 m 1.31.3 m m 0.7 0.7 m m 0.7 m 0.7 m 2.1 m 2.1 m 1.3 m 0.7 m 0.7 m 2.2 m2.2 m 2.2 m2.2 m 1.91.9 m m 1.3 1.3 m m 1.9 m 1.9 m 2.2 m 2.2 m 1.9 m 1.3 m 1.9 m 2.3 m2.3 m 2.3 m2.3 m 2.32.3 m m 2.3 2.3 m m 2.3 m 2.3 m 2.3 m 2.3 m 2.3 m 2.3 m 2.3 m 2.2.2. Indoor Climate and Operation of Ventilative Cooling 2.2.2.2.2.2. Indoor Indoor Climate Climate and and Operation Operation of of Ventilative Ventilative CoolingCooling A set of sensors has been installed to monitor continuously indoor and outdoor conditions and A setA of set sensors of sensors has has been been installed installed to to monitor monitor continuously continuously indoorindoor and and outdoor outdoor conditions conditions and and is is described in [29]. The lecture rooms have their own weather station that monitors the main outdoor describedis described in [29]. in The [29]. lecture The lecture rooms rooms have have their their own own weather weather station that that monitors monitors the the main main outdoor outdoor parameters: global horizontal solar radiation, outdoor temperature, relative humidity, wind speed parameters:parameters: global global horizontal horizontal solar solar radiation, radiation, outdooroutdoor temperature, temperature, relative relative humidity, humidity, wind wind speed speed and direction. For the indoor conditions, the temperature, CO2 concentration and the humidity are continuously monitored. The occupancy of the lecture room is measured by using counting cameras Fluids 2018, 3, 68 8 of 14 which were installed in the lecture room. The operational data of the AHU, night ventilation, IEC, heating systems, etc. is also continuously monitored. The data from these sensors are displayed in real time and recorded within a computer based monitoring and control system. The time step is 1 minute. Table3 shows type and accuracy of the sensors used in this study.

Table 3. Properties of the sensors.

Parameter Type Sensor Accuracy Air temperature Omega PT100 ±0.10 ◦C Air velocity TSI 8475 3% of reading and 1% measurement range (0.05–2.50 m/s) Room temperature SE CSTHR PT1000 ±0.1 ◦C Supply temperature SE CSTHK HX ±0.4 ◦C Occupancy Acurity Crosscan Camera ±5% Outdoor temperature Vaisala HMS82 ±0.3 ◦C at 20 ◦C Wind velocity Ultrasonic 2D Anemometer ±0.1 m/s (0–5 m/s) Wind direction Ultrasonic 2D Anemometer ±1◦

In this study, internal temperatures and operation of ventilative cooling are studied during the cooling season in 2017 in the lecture room on the first floor, i.e., from 22 May to 30 September 2017. As there was no occupancy in July and only limited in August, these months are excluded from the analysis. Belgium has a temperate climate without dry season with warm summer, i.e., climate zone Cfb according to the Köppen–Geiger classification [30]. A typical year includes 28 days with a maximum outdoor temperature above 25 ◦C. 2017 had 33 and 7 days with a maximum outdoor temperature exceeding 25 ◦C and 30 ◦C, respectively [31].

3. Results and Discussion

3.1. Airflow Rate Table3 presents the results of the tracer gas decay tests for single sided and cross ventilation including the local weather conditions (wind velocity and direction) and the average indoor-outdoor temperature difference during the test. For single-sided and cross ventilation, the 95% confidence interval for ACR is respectively 1.21 to 2.12 and 2.17 to 4.64 h−1. Figure8 shows the results of the air velocity measurements for cross ventilation executed at the same moment as the first tracer gas test in Table3. The median value on the different positions equals 1.21 m/s, 1.25 m/s, 1.05 m/s, and 0.65 m/s. Only the velocity at position V4 (see set up in Figure6) has a deviating value. This air velocity results in an ACR of 4.21 ± 0.13 h−1. A good agreement with the result from the tracer gas decay method was found (see line 1 in Table4). It can be concluded that these ACR are rather low caused by the large installation depth of the windows in the façade. In the cross ventilation case, the ACR depends, as expected, greatly on wind direction and velocity. The ACR in these lecture rooms can be increased and made more reliable and stable by adding mechanical exhaust. However, this measure will also increase the fan energy.

Table 4. Measured air changes rates (ACR) with tracer gas decay during spring 2017.

-1 ◦ Ventilation Mode ACR (h ) Wind Velocity (m/s) Wind Direction Ti − Te ( C) Cross ventilation 4.18 ± 0.42 1.9 WNW 4.3 Cross ventilation 3.76 ± 0.38 2.1 ESE 1.6 Cross ventilation 3.04 ± 0.30 2.2 ESE 2.4 Single sided 2.05 ± 0.21 2.3 SSW No data Single sided 2.00 ± 0.20 2.68 S No data Single sided 1.17 ± 0.12 1.45 SSW 5.1 Single sided 1.56 ± 0.16 1.78 S 8.6 Fluids 2018, 3, 68 9 of 14 Fluids 2018, 3, x FOR PEER REVIEW 9 of 14 Fluids 2018, 3, x FOR PEER REVIEW 9 of 14

FigureFigure 8. Boxplots 8. Boxplots of air of air velocity velocity for for cross cross ventilation ventilation (wind velocity velocity = =1.9 1.9 m/s, m/s, wind wind direction direction = WNW = WNW and temperatureFigureand temperature 8. Boxplots difference difference of air velocity = 4.3= 4.3◦ C).for °C) cross. ventilation (wind velocity = 1.9 m/s, wind direction = WNW and temperature difference = 4.3 °C). 3.2. Room3.2. Room Air TemperatureAir Temperature Proﬁle Profile 3.2. Room Air Temperature Profile FigureFigure9 shows 9 shows the the air air temperatures temperatures measured measured inin the cent centerer plane plane (i.e. (i.e.,, plane plane 2 on 2 onFigure Figure 7) at7 ) at the startthe start andFigure and 10, 9 20, 10,shows and20, and the 60 60 minair min temperatures after after opening opening measured thethe window in the in incent case caseer ofplane of cross cross (i.e. ventilation., ventilation. plane 2 onThe Figure Thehorizontal horizontal 7) at the start and 10, 20, and 60 min after opening the window in case of cross ventilation. The horizontal axis showsaxis shows the distancethe distance to theto the window window (starting (starting atat 0.5 m), m), the the vertical vertical axis axis shows shows the theheight height from from the the axisfloor shows (starting the atdistance 0.4 m) .to The the local window weather (starting conditions at 0.5 m),(wind the velocity vertical andaxis direction)shows the andheight the from average the ﬂoor (starting at 0.4 m). The local weather conditions (wind velocity and direction) and the average floorindoor (starting–outdoor at temperature0.4 m). The local difference weather during conditions the test (wind are summarized velocity and in direction) Table 5. and the average indoor–outdoorindoor–outdoor temperature temperature difference difference during during thethe test are are summarized summarized in inTable Table 5. 5.

Figure 9. Air temperature profile in the room at the start, after 10, 20, and 60 min for cross ventilation. FigureFigure 9. Air 9. temperature Air temperature profile profile in in the the room room atat thethe start, start, after after 10, 10, 20,20, and and 60 min 60 minfor cross for crossventilation ventilation.. The stratification at the start changes to a more uniform air distribution after 60 min. The air in Thethe wholeThe stratification stratification lecture room at at the is the cooled start start changesdown:changes in to tothe a a moreupper more uniform zone uniform by airalmost airdistribution distribution 5 °C, in afterthe lower 60 after min. zone 60 The min. by air only Thein air in thethe whole whole lecturelecture room room is iscooled cooled down: down: in the in upper the upperzone by zone almost by 5 almost°C, in the 5 lower◦C, in zone the by lower only zone by only 1 ◦C. This conclusion is in line with the conclusions of [32] who noticed in a full scale test room with a transition flow with a limited ceiling attachment length during most of the time with Fluids 2018, 3, x FOR PEER REVIEW 10 of 14 Fluids 2018, 3, 68 10 of 14 1 °C. This conclusion is in line with the conclusions of [32] who noticed in a full scale test room with a transition flow with a limited ceiling attachment length during most of the time with a long-term a long-term unstable behavior. However, due to the stratified initial conditions, it is hard to derive generalunstable conclusions behavior. However, from the results. due to the stratified initial conditions, it is hard to derive general conclusions from the results. Table 5. Local weather conditions during test of room air temperature profile (plane 2). Table 5. Local weather conditions during test of room air temperature profile (plane 2). Ventilation Mode Wind Velocity (m/s) Wind Direction ∆T(◦C) Ventilation Mode Wind Velocity (m/s) Wind Direction T (°C) Cross ventilation 0.78 SW 8.0 Cross ventilation 0.78 SW 8.0

3.3. Operation of Ventilative Cooling Figure 10 presents the ratio of operation time of the windows to the possible total opening hours by night (22(22 hh tottot 66 h) h) and and the the ratio ratio of of the the operation operation of of the the IEC IEC to theto the operation operation hours hours of the of AHUthe AHU by day. by IECday. andIEC nighttime and nighttime ventilation ventilation are in useare duringin use during 66% respectively 66% respectively 45% of the 45% time. of the This time. finding This confirms finding theconfirms conclusions the conclusions of the prediction of the simulationsprediction simulations of thermal summer of thermal comfort summer in [ 22 comfort]. High in internal [22]. High heat gainsinternal cause heat the gains need cause of ventilative the need of cooling ventilative during cooling more thanduring half more of the than occupied half of hoursthe occupied in the cooling hours season.in the cooling In addition, season. this In observationaddition, this has observation the effect that has thethe faneffect energy that isthe increased fan energy due is toincreased (1) the AHU due runningto (1) the at AHU maximum running airflow at maximum when IEC airflow is in operation when IEC and is in (1) operation a higher pressureand (1) aloss higher caused pressure by the loss air flowingcaused by through the air theflowing heat exchanger.through the heat exchanger.

Figure 10. Percentage of hours of operation of windows by night and indirect evaporativeevaporative cooling (IEC)(IEC) by day from May to September 2017.2017.

In addition, Figure 11 shows the operation of the windows for night ventilation respectively indirect evaporative cooling during extremely warm days in June 2017. In that period, IEC operates the whole day during operation and can lower the supply temperature significantly significantly compared to the outdoor temperature. Natural Natural night night ventilation ventilation only only operated operated very very short short time time the second night in between two hot summer days because the requirement that the outdoor temperature has to more ◦ than 2 °CC lower than the room temperature was not fulfilled.fulfilled. This finding finding confirms confirms the findings findings of other studies (e.g.,(e.g., [1111,,3333]])) that night ventilation cannot guarantee good thermal comfort during the whole year and especially not during heat waves.waves. Fluids 2018, 3, 68 11 of 14 Fluids 2018, 3, x FOR PEER REVIEW 11 of 14

Figure 11. Operation of windows ( above) and IEC ( below) during an extremely warm period (21 (21–23–23 June 2017) 2017)..

3.4. Thermal Comfort Figure 12 presents hourly indoor operative temperature in this lecture room. The percentage of ◦ ◦ ◦ hours of exceedanceexceedance perper monthmonth aboveabove 23 23 C,°C, 25 25 C,°C and, and 28 28 C°C are are shown. shown. Furthermore, Furthermore, the the number number of ofoccupied occupied hours hours of exceedance of exceedance of a particular of a particular indoor indoortemperature temperature above a threshold above a threshold value is commonly value is commonlytaken as an taken overheating as an overheating performance performance indicator. Inindicator. this lecture In this room, lecture during room, operation during operation of the AHU, of ◦ ◦ the5.1% AHU, and 0.3%5.1% ofand the 0.3% hours of the in 2017hours exceeded in 2017 exceeded 25 C respectively 25 °C respectively 28 C. This 28 means°C. This good means thermal good thermalcomfort comfort according according to EN 15251 to EN [24 15251]. [24]. Thermal comfort in this lecture rooms is also evaluated as a function of the running mean outdoor temperaturetemperature asas deﬁneddefined by by the the Dutch Dutch adaptive adaptive temperature temperature limits limits indicator indicator [34 ][34] (see (see Figure Figure 13). The13). maximumThe maximum indoor indoor temperatures temperatures during during extremely extreme warmly warm days in days June in 2017, June as 2017, discussed as discussed before, before,are indicated are indicated in Figure in Figure13. This 13. graph This graph shows shows that summer that summer comfort comfort is generally is generally good. good. Only Only in hot in hotsummer summer and/or and/or periods periods with withhigh occupancy, high occupancy, high indoor high temperaturesindoor temperatures are monitored. are monitored. In addition, In veryaddition, low temperaturesvery low temperatures are noticed are in noticed September in September in the morning. in the morning. Fluids 2018, 3, 68 12 of 14 Fluids 2018, 3, x FOR PEER REVIEW 12 of 14

Fluids 2018, 3, x FOR PEER REVIEW 12 of 14

Figure 12. Percentage of hours above threshold values for internal temperatures in the lecture room FigureFigure 12. Percentage 12. Percentage of hoursof hours above above threshold threshold values values for for internal internal temperaturestemperatures in in the the lecture lecture room room on onthe the ﬁrston first the ﬂoor firstfloor (May–September floor (May (May–September–September 2017). 2017) 2017). .

FigureFigure 13. Thermal 13. Thermal comfort comfort evaluation evaluation according according to the the adaptive adaptive temperature temperature limits limits method method [34]. [34].

4. Conclusions and Lessons Learned 4. ConclusionsFigure 13. andThermal Lessons comfort Learned evaluation according to the adaptive temperature limits method [34]. TheThe test test lecture lecture rooms rooms of of KU KU Leuven Leuven Ghent Ghent Technology Campus Campus are are one one the thedemonstration demonstration cases of IEA EBC Annex 62: Ventilative Cooling. Two different principles of ventilative cooling are cases4. Conclusions of IEA EBC and Annex Lessons 62: Learned Ventilative Cooling. Two different principles of ventilative cooling are implemented in this building: (1) natural night ventilation, (2) AHU with indirect evaporative cooling implemented in this building: (1) natural night ventilation, (2) AHU with indirect evaporative cooling The(IEC). test Thermal lecture comfort rooms in ofthis KU nZEB Leuven school Ghent building Technology and the performances Campus areof its one ventilative the demonstration cooling (IEC).casessystems of Thermal IEA wereEBC comfort evaluated.Annex in 62: this Ventilative nZEB school Cooling. building Two and different the performances principles of of ventilative its ventilative cooling cooling are systemsimplemented wereGood in evaluated. thermal this building: summer (1) comfort natural was night measured ventilation, in the (2) test AHU lecture with roomsindirect at evaporative the Technology cooling (IEC).Goodcampus Thermal thermal Ghent comfort of summer KU inLeuven this comfort nZEB(Belgium). was school measured Only building during in heat theand testwaves the lectureperformances and/or rooms periods at of with the itsTechnology highventilative occupancy campuscooling Ghentsystemsrates, of were KU high Leuvenevaluated. indoor temperatures (Belgium). Only were duringmonitored. heat Both waves nighttime and/or ventilation periods and with indirect high occupancy evaporative rates, highG indoorcoolingood thermal temperaturesoperate very summer well. were IEC comfort monitored. can lower was Boththe measured supply nighttime temperature in theventilation test by lecture day and significantly indirect rooms evaporative at compared the Technology coolingto the outdoor temperature. IEC is in use during more than half of the occupied hours in the cooling operatecampus veryGhent well. of KU IEC Leuven can lower (Belgium). the supply Only temperature during heat by waves day signiﬁcantly and/or periods compared with high to the occupancy outdoor season due to high internal heat gains in the lecture rooms. temperature.rates, high indoor IEC istemperatures in use during were more monitored. than half Both of the nighttime occupied ventilation hours in the and cooling indirect season evaporative due to highcooling internal operate heat very gains well. in theIEC lecture can lower rooms. the supply temperature by day significantly compared to the outdoor temperature. IEC is in use during more than half of the occupied hours in the cooling season due to high internal heat gains in the lecture rooms. Fluids 2018, 3, 68 13 of 14

The ACR of the nighttime ventilation is rather low and, in case of cross ventilation, depends a lot on wind direction and velocity. The ACR in these lecture rooms can be increased and made more reliable and stable by adding mechanical exhaust. However, this measure will also increase the fan energy. The room air temperature profile showed that the air in the whole lecture room is cooled down by opening of the windows. The extensive data monitoring system was of great value to detect malfunctions, to improve the control of the building systems and optimize the whole building performance. Monitoring showed e.g., that the windows for night ventilation opened and closed a lot at night during the first weeks. This was due to (1) poor translation of the signal of the rain sensor and (2) peaks in the wind velocity. These parameters are part of the control of the windows. This malfunctioning was discovered and solved by analyzing the monitoring results. Furthermore, attention has to be paid to the users. Many different teachers give classes in these lecture rooms. Most of them are not used to automate blinds, ventilation and ventilative cooling. It is important to educate and inform the users about the operation of the automated system to come to a comfortable and energy efficient building.

Author Contributions: H.B. and A.V. designed the experiments; B.M. performed the experiments; B.M. and H.B. analyzed the data; H.B. and A.V. wrote the paper. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂicts of interest.

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