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1 Pod by TCPDF ( This is an electronic reprt origal article. This reprt may differ origal pagation typographic detail. Taebnia, Mehdi; Toomla, Ser; Leppä, Lauri; Kurnitski, Jarek Air Distribution Air Hlg Unit Configuration Effects on Energy Performance an Air-Heated Ice Rk Arena Published : Energies DOI: /en Published: 20/02/2019 Document Version Publisher's PDF, also known as Version record Please cite origal version: Taebnia, M., Toomla, S., Leppä, L., & Kurnitski, J. (2019). Air Distribution Air Hlg Unit Configuration Effects on Energy Performance an Air-Heated Ice Rk Arena. Energies, 12(4), [693]. This material is protected by copyright or tellectual property rights, duplication or sale all or part any reposiry collections is not permitted, except that material may be duplicated by you for your research use or educational purposes electronic or prt form. You must obta permission for any or use. Electronic or prt copies may not be fered, wher for sale or orwise anyone who is not an authorised user.

2 energies Article Air Distribution Air Hlg Unit Configuration Effects on Energy Performance an Air-Heated Ice Rk Arena Mehdi Taebnia 1, *, Ser Toomla 2, Lauri Leppä 3 Jarek Kurnitski 1,4 1 Aal University, Department Civil Engeerg, P.O. Box 12100, Aal, Fl; jarek.kurnitski@aal.fi or jarek.kurnitski@taltech.ee 2 Granlund Consultg Oy, Malmkaari 21, PL 59, Helski, Fl; ser.omla@granlund.fi 3 Leanheat Oy, Hiomotie 10, FI Helski, Fl; lauri.leppa@leanheat.fi 4 Department Civil Engeerg Architecture, Talln University Technology, Ehitajate tee 5, Talln, Esnia * Correspondence: mehdi.taebnia@aal.fi Received: 14 January 2019; Accepted: 15 February 2019; Published: 21 February 2019 Abstract: Indoor ice rk arenas are among foremost consumers energy buildg secr due ir exclusive door conditions. A sgle ice rk arena may consume energy up 3500 MWh annually, dicatg potential for energy savg. coolg effect ice pad, which is ma source for heat loss, causes a vertical door air temperature gradient. objective present study is twold: (i) study vertical temperature stratification door air, how it impacts on heat load ward ice pad; (ii) vestigate energy performance air hlg units (AHU), as well as effects various AHU layouts on ice rks energy consumption. To this end, six AHU configurations different air-distribution solutions are presented, based on existg arenas Fl. results study verify that coolg energy dem can significantly be reduced by 38 percent if door temperature gradient approaches 1 C/m. This is implemented through air distribution solutions. Moreover, coolg energy dem for dehumidification is decreased 59.5 percent through precisely planng AHU layout, particularly at coolg coil heat recovery sections. study reveals that a more cusmized air distribution results less stratified door air temperature. Keywords: ice rks; air distribution solutions; door air temperature gradient; air hlg unit configuration; buildg energy efficiency; buildg performance simulation; energy HVAC-systems buildgs 1. Introduction reduction energy use buildgs is a strategic research challenge, due significant contribution buildg secr CO 2 emissions. reduction energy use improvement energy efficiency is strongly lked operations performance passive active systems buildgs [1]. potential for reduction energy dem has be evaluated through prioritizg solutions based on ir energy efficiency [2]. Specifically, door ice arenas among buildg secr are an enormous consumer energy, due ir unique door conditions. yearly energy consumption a stard sgle ice rk arena is typically estimated be between MWh [3,4]. However, range dividually measured energy consumptions is even larger, MWh/year, which provides a great potential for energy savgs [5]. ice pad refrigeration hall space heatg are two major contriburs energy use ice rks. By default, mata a steady-state condition, heat removed hall primarily by Energies 2019, 12, 693; doi: /en

3 Energies 2019, 12, refrigeration machery needs be roughly matched heat supplied generated side hall. In case an air-heated arena, vast majority heat balance is mataed through a heated supply air. Generally, ventilation efficiency similar sports halls such as swimmg pools could potentially be improved by various alternative air distribution concepts [6]. However, unique door conditions an ice rk arena proposes challenges energy-efficient heatg ventilation. Due coolg effect ice pad, a vertical temperature gradient side hall space is unavoidably formed. This, accompanied fact that recreational activities practiced on ice pad require a free height approximately five meters, makes space heatg rk difficult. In fact, order mata a set temperature at an occupational height above ice pad, temperature supply air enterg hall at a height below ceilg has exceed occupational set pot temperature by a large amount. Several past studies have focused on reducg heat load wards ice pad, reby reducg refrigeration unit s electricity consumption [7 9]. Simultaneously, numerous efforts have gone modelg air distribution side hall space experimental, zonal model, or Computational Fluid Dynamics (CFD) form [10 14]. As a result, we have a fairly comprehensive understg temperature moisture priles side hall, as well as facrs affectg heat load. vertical distribution temperature various ice rks has been measured current previous studies [12,14 17] ir outcome as temperature gradient curves is used this paper, while similar ice rks as case study arenas have been measured. However, actual role air hlg unit (AHU), along its components control strategies, has only been briefly vestigated two prior publications. Seghouani [8] modeled AHU a simulated ice arena hall space as a two-speed system, eir low or high, which is creased high-speed mode only durg ice pad resurfacg, evacuate combustion gases resurfacg vehicle, no air recirculation or no extract air heat recovery [8]. Piché [18] contued Seghouani s research by addg two possible modifications AHU modeled earlier: an alternative pre-heated fresh air source, or an air--air heat exchanger, both which utilized refrigeration unit s condenser heat. While later study obtaed significant results regardg AHU s energy dem compared prior one, neir implementations represented a typical, modern, real-life door ice rk AHU solution. This means that previous studies about AHUs are outdated, y do not represent a modern AHU layout. Thus, energy performance modern AHUs, equipped full variable-air-volume (VAV) control, a heat exchanger (HX) for extract air heat recovery, possibility for extract air recirculation, context demg door ice rk conditions, should be furr vestigated. objective is determe (quantify) impacts door temperature stratification, as well as AHU layouts, on energy consumption, while two commonly used AHU configurations at different temperature gradients are applied. To study two focus features, AHU design, air stratification tensity, we present six simulation setups, which are based on existg ice rk arenas Fl. AHU for hall space an air-heated ice arena usually has three ma objectives. Firstly, as any ventilation system, it should provide adequate fresh air space, mata satisfacry door air conditions. Secondly, this case, it is solely responsible for supplyg space enough heat. Thirdly, case, no external dehumidification equipment is present, AHU is equipped a condensg dehumidifier, it is thus responsible for matag moisture content under a specific set pot side hall. door air recirculation is implemented by maximum possible rate at any moment, for energy conservation. Each AHU has its own oretical energy dem, dependg on its ma objective. To maximize AHU s energy efficiency, it should be dem-controlled, based on CO 2, temperature, humidity set pot levels, dependg on ir measured values. If eir measured values a particular moment exceeds acceptable

4 exchanger (HX) for extract air heat recovery, an assumed efficiency 85%, two heatg coils (HC). HC1 utilizes condenser heat refrigeration plant, while HC2 is connected district heatg system. HC2 acts as a backup heat device case refrigeration unit is not operatg or is not producg enough condenser heat. In simulation, HC1 is not modeled. Both supply exhaust fans are fully VAV-compatible up 4 m 3 /s, ir speeds are dividually controlled. Energies exhaust 2019, 12, 693 fan is placed outside recirculation loop, makg it possible recirculate air utilizg 3 21 supply fan only. whole unit is dem-controlled based on temperature, humidity or CO2- level measurements ice rk. range, n that parameter s control signal prevails or signals. In case simultaneous AHU2.1, is many aspects very similar AHU1.1, except for one key difference. rotary exceedg set pots, aumation system reacts simultaneously so that each parameter can heat exchanger an assumed efficiency 85% is placed outside recirculation loop, as react presented dependently, by 1b, sendg leavg its it control completely signal unavailable associated for recirculation section mode. AHU that supply parameter. Two extract air-hlg fans are dem-controlled layouts have been used same as fashion simulation as AHU1.1 model rated thisup study. 4 ma section 3 /s. Supply air air-hlg is cooled units dehumidified (AHU1.1) (AHU2.1) a condensg are shown dehumidifier. It 1, is n ir heated specifications two heatg are described coils. followg HC1 utilizes paragraphs. condenser heat HC2 district heat, similar AHU 1. (a) (b) (c) AHU layouts temperature gradient curves. (a) Schematic view AHU1.1; (b) (b) Schematic view view AHU 2.1; 2.1; (c) (c) Estimated presumed models various for temperature gradient gradients. curves. air hlg unit 1.1 (AHU1.1), depicted 1a, is fully aumated, equipped extract air recirculation, a coolg coil (CC) actg as a condensg dehumidifier, a rotary heat exchanger (HX) for extract air heat recovery, an assumed efficiency 85%, two heatg coils (HC). HC1 utilizes condenser heat refrigeration plant, while HC2 is connected district heatg system. HC2 acts as a backup heat device case refrigeration unit is not operatg or is not producg enough condenser heat. In simulation, HC1 is not modeled. Both supply exhaust fans are fully VAV-compatible up 4 m 3 /s, ir speeds are dividually controlled. exhaust fan is placed outside recirculation loop, makg it possible recirculate air utilizg supply fan only. whole unit is dem-controlled based on temperature, humidity or CO 2 -level measurements ice rk. AHU2.1, is many aspects very similar AHU1.1, except for one key difference. rotary heat exchanger an assumed efficiency 85% is placed outside recirculation loop, as presented

5 Energies 2019, 12, b, leavg it completely unavailable for recirculation mode. supply extract fans are dem-controlled same fashion as AHU1.1 rated up 4 m 3 /s. Supply air is cooled dehumidified a condensg dehumidifier. It is n heated two heatg coils. HC1 utilizes condenser heat HC2 district heat, similar AHU 1. In this study, we concentrate first on AHU design its control approach, by presentg two AHU layouts that only differ position ir heat exchangers. Second, we study temperature stratification door air its effects on energy consumption a simplified way. We also study how various air distribution designs relate a temperature gradient. air stratification tensity cases is based on real measured data three ice rk arenas, similar a previous study [14]. Overall, six cases are presented for simulations, two AHU layouts, three temperature gradients. results on-site measurements can only verify three se cases, sce each ice rk is equipped only one AHUs. re are three ice rk arenas, each a dem-controlled AHU equipped a condensg dehumidifier. However, ir fal implementations regardg components control strategies differ each or. In this publication, six simulation models are presented for ice rks, similar real-case study rks, ir measured data have been used verify simulation results. heatg coolg energy dems for each AHU, along door air conditions, as well as ir temperature stratifications, are also presented. 2. Methods 2.1. Buildgs Air Hlg Units three door air distribution models selected for use this study are presented 2. reasons for selectg se particular models is firstly, because y are existg ice arenas Fl, second, because both required measurements for this study (temperature gradient energy consumption measurements) implemented re. This means that each door air distribution models corresponds one measured temperature gradients. refore, se selected air distribution models are case study models. rar simple air distribution system correspondg measured temperature gradient 2.1 is depicted as hall space cross-section 2a. supply air termals this system are located below ceilg level, ir air jets blow horizontally opposite directions. extract air termal is located close one end along space. air distribution system correspondg temperature gradient 1.6 consists multiple supply air termals located above spectar balcony, angled wards ice pad. A cross section hall space is depicted 2b. Supply air jets are located along length hall, while extract air is drawn termals located near end alongside hall. In vertical direction, both supply extract termals are close ceilg level. air distribution system correspondg a temperature gradient 1.5 is unlike or presented systems. Non-heated supply air enters hall space termals connected small holes drilled sideboards rk. idea is ventilate occupational zone above rk out compromisg quality ice pad heated air. Heated supply air is distributed at an angle wards sts, while extract air termal is located wards end hall below ceilg. system is presented 2c. To verify simulation results we used experimental data real ice arenas. It is important present unique features each arena. This generates errors that might favor some outcomes. If results do not make sense out modification, we can n modify simulations based on unique features ice arenas, which have been experimentally measured. We would need show that differences simulations are also seen experimental measurements.

6 air distribution system correspondg a temperature gradient 1.5 is unlike or presented systems. Non-heated supply air enters hall space termals connected small holes drilled sideboards rk. idea is ventilate occupational zone above rk out compromisg quality ice pad heated air. Heated supply air is distributed Energies at an 2019, angle 12, wards 693 sts, while extract air termal is located wards end hall 5 21 below ceilg. system is presented 2c. Energies 2018, 11, x 5 21 (a) (b) (c) Air distributions correspondg measured temperature gradients: (a) (a) A; A; (b) (b) B; (c) B; (c) C. C. InTo order verify compare simulation AHUs results performance we used agast experimental outdoor data door real conditions, ice arenas. ait series is important measurements present performed. unique features A Temperature each arena. This relative generates humidity errors (T/RH)-logger, that might favor shielded some outcomes. direct solation, If results was do not usedmake track sense out temperature modification, relative we can n humidity modify simulations outdoor air based close proximity on unique features studied buildg. ice arenas, Inside which have hallbeen space, experimentally T/RH/CO 2 measured. -loggers measured We would temperature, need show relative that humidity, differences CO 2 simulations level are door also seen air, both experimental skater s measurements. occupational zone above In order ice compare rk, AHUs sts. performance Due agast practical outdoor reasons, door logger conditions, measurga series skatg zone measurements was placed just outside performed. rk A Temperature a height 2 relative 2.5 mhumidity above (T/RH)-logger, rk, dependg shielded on case. direct solation, case study was for used this publication track temperature cluded four relative similar humidity sgle ice rk outdoor door air arenas, close built proximity studied buildg. Inside hall space, T/RH/CO2-loggers measured between , located sourn parts Fl. ir ice pad sizes ranged temperature, relative humidity, CO2 level door air, both skater s occupational 1456 m m 2 ( m 2 ), arena hall volumes fallg between 13,000 m 3 zone above ice rk, sts. Due practical reasons, logger measurg 16,000 m 3. smallest arena had an elevated spectar balcony capacity for 60 stg skatg zone was placed just outside rk at a height m above rk, dependg on spectars, while ors had sts rated for seated spectars. Or spaces case. studied ice rk facilities not considered this publication. descriptions for each measured case study for this publication cluded four similar sgle ice rk door arenas, built AHU between ir 2003 air distribution 2015, located systems sourn are as follows. parts Fl. ir ice pad sizes ranged 1456 m m 2 ( m 2 ), arena hall volumes fallg between 13,000 m 3 16,000 m 3. smallest arena had an elevated spectar balcony capacity for 60 stg spectars, while ors had sts rated for seated spectars. Or spaces studied ice rk facilities not considered this publication. descriptions for each measured AHU ir air distribution systems are as follows. air distribution system correspondg AHU 1.1 is a combation air distribution

7 Energies 2019, 12, air distribution system correspondg AHU 1.1 is a combation air distribution system as shown 2b, AHU1.1 which is depicted followg 3. Energies 2018, 11, x 6 21 Energies 2018, 11, x Schematic view AHU1.1 its its correspondg air air distribution. 3. Schematic view AHU1.1 its correspondg air distribution. AHU1.2, presented 4, 4, is is similar AHU1.1, which is is presented earlier earlier some some modifications. AHU1.2, presented dem control 4, strategy, is similar based based on AHU1.1, on temperature, which is humidity presented humidity or earlier CO2 or level, CO 2 is some level, is same modifications. same as as order order dem components control strategy, supply supply based side on side temperature, unit unit (recirculation humidity or coolg CO2 coolg level, coil, coil, heat is heat exchanger, same as order heatg components coils). core supply differences side are: are: unit (recirculation coolg coil, heat exchanger, Supply air is split heatg heated coils). non-heated core differences flow. are: HC for heated supply air utilizes Supply air is split a heated non-heated flow. HC for heated supply air utilizes condenser Supply air heat is split a refrigeration heated non-heated plant, while flow. only HC form for heatg heated for supply non-heated air utilizes condenser heat refrigeration plant, while only form heatg for non-heated air air condenser is extract heat air heat recovery. refrigeration plant, while only form heatg for non-heated is extract air heat recovery. air extract is extract air air heat heat recovery. unit is a cross-flow air--air plate heat exchanger stead a rotary heat extract exchanger, air heat as recovery AHU1.1 unit is cross-flow air--air plate heat exchanger stead a rotary extract air heat recovery unit is a cross-flow air--air plate heat exchanger stead a rotary heat exchanger, supply as exhaust AHU1.1 heat exchanger, as AHU1.1 fans are rated up 5 m 3 /s correspond 2.5 L/sm 2. supply exhaust/extract supply exhaust exhaust fan is fans fans located are are rated side up recirculation 5 m 3 /s correspond loop; full 2.5 recirculation L/sm 2 3 /s correspond 2.5 L/sm 2.. mode, both fans need exhaust/extract be operated. fan is located side recirculation loop; full full recirculation mode, mode, both both fans be In fans need hall space, be operated. heated supply air is directed wards sts outside rk, while non-heated In In hall hall portion space, serves heated as ventilation supply air is for directed ice wards pad area. sts extract air outside termal rk, is located rk, while while below non-heated ceilg portion level approximately serves as ventilation center for ice pad space. area. A cross-section extract extract air air termal termal space, is located is along located air distribution arrangement, can be examed 4. below below ceilg ceilg level level approximately center space. A Across-section space, space, along along air air distribution distribution arrangement, arrangement, can can be be examed Schematic view AHU1.2 its correspondg air distribution system. 4. Schematic view AHU1.2 its correspondg air distribution system. 4. Schematic view AHU1.2 its correspondg air distribution system. AHU2.2 differs or presented units that it is not fully VAV-compatible. It is AHU2.2 differs or presented units that it is not fully VAV-compatible. It is operated operated AHU2.2 as a differs two-speed unit, or namely presented half- units full-speed, that it is but not both fully speed VAV-compatible. options can It be is as programmed a two-speed unit, any percentage namely half fan s full-speed, maximum but capacity. both speed options supply can fan is be rated programmed up 4 m 3 /s, any operated as a two-speed unit, namely half- full-speed, but both speed options can be percentage exhaust fan fan s up maximum 2 m 3 /s. capacity. Like AHU1.2, supply unit fan is equipped is rated up programmed any percentage fan s maximum capacity. supply 4regenerative m fan 3 /s, is rated up exhaust exhaust 4 mair fan 3 /s, up heat recovery 2 m 3 exhaust /s. Like outside fan AHU1.2, up recirculation 2 m 3 /s. unit Like isloop, equipped AHU1.2, like AHU1.2, unit regenerative is equipped supply exhaust air regenerative is air split heat recovery heated exhaust outside air non-heated recirculation recovery airflows. outside loop, non-heated recirculation like AHU1.2, flow loop, is untreated supply like air AHU1.2, after is split condensg supply heated air dehumidifier, is split non-heated makg heated airflows. its temperature non-heated non-heated airflows. lower than is untreated non-heated AHU2.1. after flow heatg is condensg untreated coil utilizes after dehumidifier, condenser condensg makg heat dehumidifier, its temperature refrigeration makg lower its plant. temperature A schematic lower view than AHU2.2 AHU2.1. is available heatg coil utilizes 5. condenser heat refrigeration plant. A schematic view AHU2.2 is available 5.

8 Energies 2019, 12, than AHU2.1. heatg coil utilizes condenser heat refrigeration plant. A schematic view AHU2.2 is available 5. Energies Energies 2018, 2018, 11, 11, x x Schematic view AHU2.1 its its correspondg air air air distribution system. system. system. air air distribution system correspondg AHU2.2 is is is unlike unlike or or or presented presented systems. systems. systems. Non-heated supply air enters hall hall hall space space space termals termals termals connected connected connected small small small holes holes drilled holes drilled drilled sideboards rk. rk. rk. idea idea idea is is is ventilate ventilate occupational zone zone zone above above above rk rk rk out out out compromisg quality ice pad heated air. air. Heated Heated supply supply air air air is is distributed distributed at at an at an angle angle angle wards sts, while extract air air termal is is located located wards wards end end end hall hall hall below below ceilg. ceilg. system system is is is presented Schematic view AHU2.2 its its correspondg air air distribution system. system. 6. Schematic view AHU2.2 its correspondg air distribution system. It It is is important expla that four models described above above are are used used for for 24 h 24 h measurements, It is important expla that four models described above are used for 24 h measurements, but but re are are temperature gradients measured only three m. refore, those three, which are but re are temperature gradients measured only three m. refore, those three, which similar, are are similar, similar, as shown as as shown shown 2a c, 2a c, 2a c, used used used validate validate simulation simulation results. results Measurements 2.2. Measurements For For each each AHU AHU its its its correspondg correspondg hall hall hall space, space, space, a a series series a series measurements measurements measurements carried carried out. carried out. out. measurement measurement periods periods periods lasted lasted lasted between between between six six sixeight eight days, eight days, days, measurement measurement measurement terval terval terval was was five five was five mutes. mutes. mutes. measurement measurement measurement plan plan plan each each AHU AHU each could could AHU not not be could be perfectly perfectly not be implemented, implemented, perfectly implemented, due due differences differences due differences air air hlg hlg airunits units hlg space space units coverage, coverage, spacecapacity, capacity, coverage, capacity, accessibility accessibility accessibility measurement measurement measurement locations. locations. locations. missg missg measurements missg measurements compensated compensated compensated measurements measurements measurements performed performed performed buildg buildg buildg aumation aumation aumation system, system, when system, when possible. possible. whenall possible. All measurements All measurements measurements carried carried out out carried May May out June June May June door door air air air temperature relative relative humidity humidity measured measured logged logged T/RH-loggers T/RH-loggers (THERMADATA MALLI) before after each AHU component, i.e., before after after heatg (THERMADATA MALLI) before after each AHU component, i.e., before after heatg coils, coolg coils, heat exchangers. door air coils, levels measured coils, coolg coils, heat exchangers. door airco2 2 levels measured T/RH/CO2-loggers T/RH/CO2-loggers at supply extraction extraction air air positions. positions. Meanwhile, Meanwhile, fresh fresh air air was was assumed assumed T/RH/CO 2 at supply air or extracted air positions. Meanwhile, fresh air was have a constant CO2 have a constant level 400 ppm. For airflow rates, pressure difference over fan was CO2 assumed have a constant level CO 400 ppm. For airflow rates, pressure difference over fan was measured measured logged, logged, it it could 2 level 400 ppm. For airflow rates, pressure difference over could n n be be converted converted an an airflow airflow rate rate by by usg usg a a unit-specific unit-specific k- fan was measured logged, it could n be converted an airflow rate by usg k- a facr. facr. An An overview overview conducted conducted measurements measurements for for each each AHU AHU is is presented presented Table Table 1. 1.

9 Energies 2019, 12, unit-specific k-facr. An overview conducted measurements for each AHU is presented Table 1. Table 1. Overview conducted measurements. M = measured, M* = measured short-term, AS = measured by aumation system, E = estimated, C = calculated, - = not valid for said AHU. Measured Parameters Measured at Section Fresh Supply Airflows Maches Total Heated Non-Heated Temperature RH Change over: CO 2 Level Extract Exhaust CC HC1 HC2 HX Fresh Supply Extract AHU 1.1 C M - - E M M M M M E M M AHU 2.1 C M E E M C M M - M E M M AHU 1.2 C E - - E C M M M M E M M AHU 2.2 C M C M* E C M M/AS - M E M M As Table 1 states, a series estimations had be made, especially regardg airflow rates. When extract airflow could not be measured, due fan s location or lack available pressure differential measurg pots, extract airflow rate was estimated match supply airflow rate. For AHU 1.2, airflow measurements could not be performed at all out terferg unit s operation. However, examg temperature RH changes supply air made it clear unit was operated an on f fashion. For example, temperature supply air after coolg coil would periodically lower a constant value for a while, n rise anor value that was constant along whole unit. Based on this behavior, it could be estimated that air side unit was partially movg partially stg still. For when air was movg, it was estimated that unit worked at full capacity, when air was evidently stg still, airflow rate was set 0 m 3 /s. resultg average airflow rate was le measured average rates or AHUs. For AHU 2.1, as ratio between heated non-heated supply airflows could not be experimentally determed, flow rates estimated at 80% 20% tal supply airflow, respectively. estimated ratio resulted a tal supply air average temperature that was le produced rmal conditions side hall space. For AHU2.2, flow rate non-heated supply air was determed short-term measurements, calculated ratio between heated non-heated supply flows was estimated stay constant throughout measurement period. 3. Simulation Setup Buildg Model To highlight core differences between studied AHUs, exclude any external variables affectg ir performance, a version each AHU was modeled, its performance was simulated by usg IDA ICE v Ice Rks Pools add-on, for a period one year, typical meteorological conditions for Helski, Fl. simulated dem-control-strategy, based on temperature, relative humidity, CO 2 -measurements hall space, was unmodified across modeled AHUs. Three built simulation models validated by usg experimental data. For comparison s sake, Seghouani presented, modeled simulated a modified VAV-version AHU study its performance [8] Buildg Specifications We used a rar simplified approach that was common all simulation models. We used a one-zone airspace a size m, one door a size m, which was opened seven times a day for 10 m each time. external walls buildg made Alumum m, light sulation 0.2 m alumum m. Ro was made Alumum m, light sulation 0.3 m, renders 0.01 m. external floor was made floor coatg 0.05 m

10 Energies 2019, 12, m concrete. ma door was made m alumum. re no rmal bridges formed buildg. Infiltration through buildg was constant, 0.03 ACH. coolg pipes submerged 2 cm concrete slab underneath ice pad. rest 0.2 m concrete slab an sulation layer 0.1 m formed base layer underneath ice pad. Heatg pipes are located soil beneath sulation layer. coolg heatg powers 200 W/m 2 40 W/m 2, respectively. ice layer thickness was 3.5 cm, ice temperature set-pot was 5 C Control Strategy zone was ventilated heated by AHU, which was controlled based on measured door extract air conditions. AHU maximizes recirculation air usage for energy conservation. supply exhaust fans controlled by respondg measured temperature, relative humidity CO 2 values zone, boundaries 4 6 C (correspondg output signals eir 1 or 0 respectively), 60 70% RH ppm CO 2 (both correspondg outputs 0 1, respectively). supply air temperature was adjusted accordg zone average temperature simplified set pots 30 C when door air temperature was below 3 C, 3 C when air temperature was above 7 C ( 4). heat recovery unit was always on. coolg coil cooled dehumidified by reducg air temperature +1 C when moisture content air exceeded 3.65 g/kg dry air. fresh air take was controlled by CO 2 concentration extract air, accordg a setpot range ppm, correspondg outputs , respectively. mimum fresh air take was set 3.7%, as reported by Toomla [14]. extract air CO 2 concentration set pots ppm, corresponded signals 0 1, respectively. CO 2 concentration extract air controlled exhaust fan as well. Both fans rated up 4 m 3 /s (2.0 L/s/m 2 ) capacity, accordg ASHRAE 90.1, Specific Fan Power (SFP) set 1.23 (kw/m 3 /s), efficiency Assumptions Parameters for Simulation Models supply fan was operated based on zone signal. Smooth functions ( 0 1) for high-temperature HI 6 low-temperature LO 4, RH HI 0.7 LO 0.6, CO2 HI 1100 LO 1000, MAX signals se three controlled supply fan speed. exhaust fan was controlled by CO 2 content extract air. A smooth function 0 1 was set HI 1100 LO 1050, i.e., refore, exhaust fan only ran when CO 2 level was high. recirculation door air or outdoor air take was controlled by extract air CO 2 content, a smooth function (3.7%) 1 (100%), LO 1000 HI Heat exchangers always function an effectiveness 0.85 an unknown capacity. mimum allowed leavg temperature was +1 C. Dryg coolg coil was controlled so that temperature set pot was mimum eir comg temperature or comg humidity control, so that coolg coil temperature set pots 4 C below 3.15 g/kg, 1 C above 3.65 g/kg. coolg coil effectiveness causes a liquid-side temperature rise 5 C. coolg was simulated as district coolg, show coolg dems dehumidification. heatg coil effectiveness was 1, liquid-side temperature drop was 20 C. heatg coil set-pot temperature for supply air was controlled by zone average air temperature, accordg curve presented 7. door air temperature gradient was set, based on three variants measured values, 1 C/m, 1.5 C/m, 2 C/m. Lightg was carried out W (4.0 W/m 2 ) units a lumous efficacy 12 lm/w, a convective fraction 0.5. lightg was used only when players present. Inside zone, re was an ice pad (60 30 m) Freezium as coolant heatg medium.

11 Energies 2018, 11, x Energies 2019, 12, 693 Energies 2018, 11, x Heatg coil set-pot temperature curve control supply air. air stratification gradient was set, based on three variants measured values, 1 C/m, 1.5 C/m, 2 C/m. Lightg was carried out W (4.0 W/m2) units a lumous efficacy 12 lm/w, 7.7.Heatg curvewhen control control supply supply air. Heatg coil set-pot temperature curve a convective fraction 0.5.coil set-pot lightgtemperature was used only players air. present. Inside zone, re was an ice pad (60 30 m) Freezium as coolant heatg medium. s 9 are a few examples how on system control set-pots C/m, set air8 stratification was set, three variants measured values, 1.5 s 8 9 are agradient few examples based how system control set-pots 1 set simulation stware. All properties system simply set IDA-ICE simulation C/m, 2stware. C/m. All properties system simply set IDA-ICE simulation simulation stware, as shown 8,8,where set pots refrigeration refrigeration plant, ice Lightg was carried W operation (4.0 W/m2)set units a lumous efficacyplant, 12 lm/w, stware, as shown out where operation pots ice pad, heatg, door aircontrol control set-pots flow, subfloor asubfloor convective fraction furr 0.5. details lightg was set. used onlydoor when air players present. Inside pad, heatg, furr details set. set-pots (air(air flow, temperature, relative humidity) also set IDA-ICE (4.7.1, EQUA, Sckholm, Sweden), zone, re was an icehumidity) pad (60 30 m) also set Freezium as coolant heatg medium. temperature, relative IDA-ICE (4.7.1, EQUA, Sckholm, Sweden), as as shown shown s are a few examples how system control set-pots set simulation stware. All properties system simply set IDA-ICE simulation stware, as shown 8, where operation set pots refrigeration plant, ice pad, subfloor heatg, furr details set. door air control set-pots (air flow, temperature, relative humidity) also set IDA-ICE (4.7.1, EQUA, Sckholm, Sweden), as shown Refrigeration Refrigeration plant ice icepad padset setpots. pots. 8. Refrigeration plant ice pad set pots.

12 Energies 2018, 11, x Energies 2019, 12, Energies 2018, 11, x Energies 2018, 11, x Indoor air ventilation quantity quality set pots. ternal gas zone players, spectars, quality lightg. ternal load 9. Indoor air ventilation quantity set pots. 9. Indoor air ventilation quantity quality set pots. players was set based on 20 players air anventilation activity level 5 Metabolic Equivalent 9. Indoor quantity quality set pots. Task (MET), ternal gas zone weekdays, players, spectars, lightg. ternal scheduled as presented 10. On players present 7:00 load 9:00 ternal on zone players, spectars, lightg. ternal load players wasternal setgas based players anplayers, activity level present 5 Metabolic Equivalent Task gas 20 zone lightg. ternal load (MET), a.m., also 3:00 10:00 On weekends, yspectars, 9:00 a.m. 9:00 players was was set based on 20 anfollowg activity level 5 Metabolic Equivalent was Task (MET), players set based onplayers 20 anweekdays, activity level 5 Metabolic Equivalent 7:00 Task (MET), Players accordg schedule. players heat load 20, scheduled aspresent presented players 10. On players present 9:00 a.m., scheduled weekdays, players present 7: :00 scheduled On 10. On weekdays, players 7:00 9:00 an activity levelas3:00 presented 5asMET accordg 10. On schedule below, maximum 100present spectars, also presented 10:00 weekends, y a present 9:00 a.m. 9:00 a.m., also 3:00 10:00 On weekends, y present 9:00 a.m. 9:00 a.m., also 3:00 10:00 On weekends, y present 9:00 a.m. 9: W lamps. Players present accordg schedule. players heaat loadload was was 20, Players present accordg followg followg schedule. players 20, an activity level 5 MET accordg schedule below, a maximum 100 spectars, an activity level 5 MET accordg schedule below, a maximum 100 spectars, 400 W 400lamps. W lamps. 10. Scheduled ternal players. 10. Scheduled ternal loadsloads players. Players present accordg as 25followg schedule. players heat load was 20, spectar attendance was modeled persons 6:00 9:00 on weekdays, an activity level 5 MET accordg schedule below, a maximum 100 spectars, 10. Scheduled ternal loads players. as 50 persons 9:00 a.m. 9: onscheduled weekends, loads a peak 100 persons between 4:00 ternal players W lamps. 7:00 spectar was modeled as as 25set persons 6:006:00 9:00 on weekdays, spectar attendance was modeled persons 9:00 on spectar attendance was modeled as25 25 persons 6:00 9:00 onweekdays, weekdays, as heat load attendance caused by spectars was based on a maximum 100 spectars, an as 50 persons 9:00 a.m. 9:00 on weekends, a peak 100 persons between 4:00 50 persons 9:00 a.m. 9:00 on weekends, a peak 100 persons between 4:00 7:00 as 50rate persons 9:00which on weekends, a spectars peak 100occupancy persons between 4:00 activity 1.5 MET.9:00 a.m. X facr, is percentage different 7:00 heat load caused by simulation spectars accordg was set based a maximum 100 spectars, an 7:00 days/times was implemented on schedule presented followg heat load caused by was was set based on aon maximum 100 an an load caused byxspectars spectars setpercentage based a maximum spectars, 100 spectars, 11: activity rateheat 1.5 MET. facr, which is spectars occupancy different activity rate rate 1.5 X facr, which is spectars occupancy different activity MET. 1.5 MET. X facr, which is percentage percentage schedule spectars occupancy different days/times was implemented simulation accordg presented followg days/times was implemented simulation accordg schedule presented followg days/times was implemented simulation accordg schedule presented followg 11: 11: 11: 11. Scheduled ternal loads spectars. 11. Scheduled ternal loadsloads spectars. spectars. spectars Scheduled Scheduled ternal ternal loads

13 Energies 2019, 12, heat load lightg W lamps a convective fraction 0.5, was similar as player s schedule. Fally, temperature gradient values for simulation models set as 2.0 C/m 1.5 C/m, represent average ice arenas, similar measured air stratification real cases. In addition, stratification value 1 C/m was set describe an arena a lower door air temperature gradient as an ultimate condition, which would be a significant improvement comparison currently measured arenas oretical Heat Exchange Airflow Prciples Ice surface Modelg In order calculate heat that is exchanged between ice surface door air, we needed concentrate on transient model above ice. To do so, it is itially required determe heat transfer coefficients air layer on ice. oretical challenges on how accurate model calculates U_FILM, H Conv, condensation heat transfer through ice surface hall space, are described as: P = 10 5 exp ( T ) (1) P ice = 10 5 exp ( T s ) (2) relative humidity at height h = 0.1 m above ice surface are calculated as follows: RH h = ( ) h (90 RH 1, 5 1,5 ) (3) ( ) RHh dp = (p 100 h p ice ) (4) ( ) dppa dp atm = (5) heat transfer coefficient for condensation is also calculated as: Airflow Balance Equations hd = 1750 h conv P (RH_h/100) (6) T q cond = h d (T T ice ) (7) calculated measured airflow rates, along measured temperature RH changes over components, used calculate component oretical energy output over measurement periods. heatg powers heatg coil heat exchanger calculated as: P heat = q air ρ air c air T air (8) coolg coil s coolg powers as: where enthalpy air can be expressed as: P cool = q air ρ air h air (9) h air = c air T air + x air (c w T air + h we ) (10)

14 Energies 2019, 12, fresh air take AHU was calculated based on CO 2 -level differences between extract, supply, Energies 2018, fresh 11, x air. Any decrease CO 2 level extract supply air meant that a portion supply air was fresh air, sce it is reasonable assume no or CO 2 sources unit exist. Fresh portion air take can supply be calculated air was fresh as: air, sce it is reasonable assume no or CO2 sources unit exist. Fresh air take can be calculated ( as: ) Cext C sup q f resh = q sup (11) q =q C C ext C C f resh (11) C C resultg flow rate for fresh air take serves more as an approximation rar than an resultg flow rate for fresh air take serves more as an approximation rar than an exact exact value, but its accuracy is sufficient determe when unit is operatg full or partial value, but its accuracy is sufficient determe when unit is operatg full or partial recirculation recirculation mode. mode. 4. Experimental Results 4. Experimental Results 4.1. Temperature Gradient Measurements 4.1. Temperature Gradient Measurements vertical temperature priles various ice rks Fl measured previous vertical temperature priles various ice rks Fl measured previous studies studies [10 14], [10 14], its its outcomes outcomes as as temperature temperature gradient gradient curves curves are are used used current current paper, paper, as as energy energy consumption consumption same same ice ice rks rks has has been been measured measured describe describecase casearenas. arenas. set set air air stratification stratification tensity tensity for for simulation is is based on experimental measurements conducted conducted three three ice ice rk rk arenas arenas Fl. procedure measurements is issubsequently described, measurement results results are are presented 12. actual, non-lear temperature stratification was was learized a a gradient facr describg temperature crease as asdegrees Celsius per per meter. meter. cause cause for for this this simplification was limitation simulation stware Air Air stratification measurement results threeice ice arenas Fl. In In order order underst differences between observed energy performances each each AHU, AHU, a perspective a regard ir respective outside air produced doorair air conditions needed be be established. 24-h periods AHUs evaluated based based on on maximum maximum similarity similarity outside air temperature hall hall space space occupational load. load. It is noteworthy It is noteworthy that neir that neir produced door air air conditions nor nor outside air air humidity, whichboth both affected AHU s performance, same across studied arenas. This limitation experimental setup setup will will be be taken taken account when results are discussed h Outdoor Indoor Air Measurements outside air temperature relative humidity measurements implemented for a selected 24-h period close proximity each case study arena, side arena hall space

15 represent temperature (left vertical axis) higher graphs represent relative humidity (right vertical axis). average temperatures between 14.4 C 16.2 C, while average relative humidity has a larger range, 43.5% 83.2%. average door air temperatures 3.5 C 8.8 C, correspondg average relative humidity was 64.5% 82%. Both are presented 13b. It is noteworthy that AHU1.2 produced warmest most humid conditions, even Energies 2019, 12, though temperature relative humidity are versely correlated each or. Hall space CO2 levels are presented 13c. CO2 measurements are required 4.2. underst 24-h Outdoor how door Indoor air CO2 Airlevel Measurements changes agast occupancy variations a 24 h workg period. It is particularly important have a realistic perception about fresh air requirements, order outside air temperature relative humidity measurements implemented for a selected keep door air CO2 levels an acceptable range, which is necessary for control settgs 24-h period close proximity each case study arena, side arena hall space skatg simulation models. zone. AHUs measurement 1.1, 2.1, results 2.2 followed are presented an approximately 13a. similar air lower distribution graphs always system, represent where temperature door air (left vertical axis) higher graphs represent relative humidity (right vertical CO2 level more or less steadily creased wards end day, while for AHU1.2, axis). peak average was reached temperatures midday. between calculated 14.4 fresh C air 16.2 fraction C, while supply averageair relative ranged humidity haseffectively a larger range, 0% for 43.5% AHUs %. 2.2, average 10% for door AHU2.1 air temperatures 19% for AHU C 8.8 fraction C, was correspondg observed stay average relatively relative constant humidity for each was AHU, 64.5% regardless 82%. Both are door presented air CO2 level, leadg 13b. It is noteworthy conclusion that AHU1.2 that each produced AHU operated warmest what most was humid set as conditions, its maximum evenallowed thoughextract temperature air recirculation relative humidity rate. are versely correlated each or. Temperature [ C] AHU 1.1 AHU 2.1 AHU :00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 (a) Relative Humidity [%] Temperature [ C] Relative Humidity [%] 0 0 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 (b) (c) 13. Indoor outdoor air temperature, relative humidity CO 2 measurements (a) Outside air temperature relative humidity measurements; (b) Indoor air temperature relative humidity measurements; (c) Indoor air CO 2 levels. Hall space CO 2 levels are presented 13c. CO 2 measurements are required underst how door air CO 2 level changes agast occupancy variations a 24 h workg period. It is particularly important have a realistic perception about fresh air requirements, order

16 Energies 2019, 12, keep door air CO 2 levels an acceptable range, which is necessary for control settgs simulation models. AHUs 1.1, 2.1, 2.2 followed an approximately similar air distribution system, where door air CO 2 level more or less steadily creased wards end day, while for AHU1.2, peak was reached at midday. calculated fresh air fraction supply air ranged effectively 0% Energies 2018, 11, x for AHUs , 10% for AHU2.1 19% for AHU1.1. fraction was observed stay relatively constant 13. Indoor for each AHU, outdoor regardless air temperature, relative door humidity air CO 2 level, CO2 measurements leadg (a) Outside conclusion that each AHUair operated temperature what relative was set humidity as its maximum measurements; allowed (b) Indoor extract air air temperature recirculation relative rate. humidity measurements; (c) Indoor air CO2 levels Energy Measurements at AHU Sections 4.3. Energy Measurements at AHU Sections tal external heatg coolg powers for each AHU are presented 14. external power tal external is defed heatg as power coolg supplied powers for each supply AHU are air presented by CCs HCs. 14. heat external power is defed as power supplied supply air by CCs HCs. heat exchanger was not considered, as it utilized ternal heatg power removed extract air. exchanger was not considered, as it utilized ternal heatg power removed extract air. Heatg power-wise, AHU operated on a similar scale, averages 33 kw 36 kw, Heatg power-wise, AHU operated on a similar scale, averages 33 kw 36 respectively. kw, respectively. AHU2.2 AHU2.2 had ahad higher a higher average average kw, kw, while while heatg heatgpower power AHU1.2 AHU1.2 was was substantially substantially larger, larger, averagg averagg at at kw. kw. For coolg power, on f on f type type control control CC CC AHU2.2, AHU2.2, as shown as shown 14b, 14b, led led smallest average coolg power kw. kw. averages averages for for AHU1.1, AHU1.1, 2.1, 2.1, kw, kw, kw, 42.5 kw, respectively. (a) AHU 1.1 AHU 2.1 Heatg Power [kw] :00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0: Total 14. Total external external (a) (a) heatg heatg (b) (b) coolg powerused usedby by AHUs AHUs for for supply supply air treatment. air treatment. 15 presents 15 presents tal tal heatg heatg coolg energy consumption by by supply supply air air AHUs durg selected 24 h period, cludg heatg energy supplied by heat exchanger. AHUs durg selected 24 h period, cludg heatg energy supplied by heat exchanger. Where heat exchanger could be utilized despite extract air recirculation, i.e., AHU , Where heat exchanger could be utilized despite extract air recirculation, i.e., AHU , heatg energy supplied by heat exchanger represented approximately 40% tal heatg heatg energy energy supplied dem. Total by amounts heat exchanger heatg represented coolg approximately energy consumed 40% by supply tal air heatg energy treatment dem. ranged Total between amounts 1088 kwh heatg 1951 kwh coolg for heatg, energy consumed between by 182 kwh supply 1021 air treatment kwh ranged for between coolg, as 1088 shown kwh kwh for heatg, between 182 kwh 1021 kwh for coolg, as shown 15.

17 Energies 2018, 11, x Energies 2019, 12, HX HC CC Heatg Coolg Heatg Coolg Heatg Coolg Heatg Coolg AHU Energy [kwh] AHU 1.1 AHU 2.1 AHU 1.2 AHU Total heatg coolg energy consumption each AHU for selected 24 h period. 15. Total heatg coolg energy consumption each AHU for selected 24 h period. 5. Validatg Simulation Models 5. Validatg Simulation Models tal heatg coolg energy dems three different ice rk arenas various AHUs are presented tal heatg Table coolg 2. As shown, energy dems energy dem three different results are ice provided rk arenas twovarious different bases, AHUs oneare presented experimental Table 2. measurements, As shown, energy or dem results runng are provided simulations, two y aredifferent compared. bases, one experimental measurements, or runng simulations, y are compared. Table 2. measurements simulation results three ice rk arenas. Table 2. measurements simulation results three ice rk arenas. Air Hlg Units AHU 2.2 AHU 1.1 AHU 2.1 Temp. Air Hlg gradients 1.5AHU C/m AHU C/m1.1 AHU 2 C/m2.1 Measurements Units T14: T10: T14:50 Temp. date&time gradients T10: C/m T9: C/m T10:20 2 C/m Measurements - Heatg T14: Coolg Heatg T10:50 Coolg T14: Heatg Coolg date&time C: 05-27T10:00 Mäntsälä T9:00 B: Klaukkala 06-21T10:20 A: Tapiola Measurement result Heatg MWh 3755 Coolg MWh Heatg MWh Coolg MWh 10,695.5 Heatg MWh Coolg MWh Simulation result 9485 MWh C: Mäntsälä 3843 MWh 8731 MWh B: Klaukkala 2864 MWh 10,214 MWh A: Tapiola 5179 MWh Measurement Deviation 3.3% % 1.6% % , % % result 3755 MWh MWh MWh MWh MWh MWh , Simulation measurements result performed durg 3843 MWh May June simulations correspondgly ran for MWh MWh MWh MWh MWh similar periods time. simulations carried out while AHU layouts, buildg specification Deviation 3.3% 2.3% 1.6% 1.5% 4.5% 4.8% as well as control strategies similar as measurements, used. simulation results, compared measurement results showed that simulation models nearly always corresponded measurements performed durg May June simulations correspondgly ran real for measurements similar periods time. less than 5% simulations fault, as presented carried Table out while 2. refore, AHU layouts, simulation buildg models specification verified as represent well as control energy strategies dem similar behaviors as measurements, ice rk arenas used. an acceptable simulation range results, accuracy. compared reason for such measurement models isresults because showed it is notthat easy simulation models yearly nearly energyalways dems corresponded ice rks, particularly real measurements variety AHU less layouts than 5% or fault, various as presented temperature Table gradients, 2. refore, which required simulation for models this study. verified refore, represent it is necessary energy validate dem behaviors simulation models ice rk accordg arenas measurements, an acceptable range n accuracy. run simulation reason for models such models for is entire because yearly it is not period, easy measure obta results yearly for various energy combations. dems ice rks, particularly variety AHU layouts or various temperature gradients, which required for this study. refore, it is necessary validate 6. simulation Simulationmodels Results accordg measurements, n run simulation models for entire yearly period, heat exchanger obta results coolg for various coil energy combations. dems dependently studied, order highlight significance AHU configurations. Table 3 16 present heatg 6. Simulation Results coolg energy dems by usg two different AHU layouts, clarify impact AHU layouts on energy consumption. simulation results AHUs dicate that approximately a reduction 60% for coolg energy dems a reduction 21% for heatg energy dems can be achieved by precisely planng AHU layout.

18 can be achieved by precisely planng AHU layout. Table 3. yearly energy consumption results simulation for AHU1.1 AHU2.1. AHU2.1 (Old Layout) AHU1.1 (Energy-Efficient Layout) Reduced kwh Energies 2019, 12, 693 kwh/(m 2 a) kwh/(m 2 a) Energy % Zone % heatg Table 3. yearly energy consumption results simulation for AHU1.1 AHU2.1. Zone coolg AHU2.1 (Old Layout) AHU1.1 (Energy-Efficient kwh kwh/(m 2 a) Layout) kwh/(m 2 Reduced Energy % AHU a) % heatg Zone heatg % AHU Zone coolg % coolg AHU heatg % DHW AHU coolg % DHW heatg heatg Total Total Comparison coolg heatg energy dems between between AHU2.1 AHU2.1 AHU1.1. AHU1.1. simulation results coolg heatg energy dems are are presented Table Table , 17, while various temperature gradientshave havebeen been applied, order order study study impacts impacts temperature gradients on energy consumption. re three temperature gradient values, 2, 1.6, 1.5 C/m, measured on three ice rks, Table 4. Simulation which two results m yearly selected energy consumption be used ice simulation rks as different high (2) temperature medium gradients. (1.5) temperature gradient values. models also simulated an additional temperature gradient value equal one, as Temperature an ultimate ideal Temperature condition. Temperature Temperature Stratification 2 Stratification 1.5 Reduction Stratification 1 Reduction Some Stratifications measured cases ( C/m) cluded two ( supply C/m) air temperatures, warm ( C/m) cool supply. However, this was stead simulated by usg an average supply air temperature. temperature Annual Energy kwh/(m consumption a) kwh/(m 2 a) % kwh/(m 2 a) % Zone heatg AHU heatg Zone coolg AHU coolg Electricity consumption refrigeration plant Condenser heat In case usg 50% condenser heat

19 refrigeration plant Condenser heat In case Energies usg 2019, 50% 12, condenser heat Energy consumption different temperature gradients, AHU1.1. re As presented three temperature Table 4, gradient energy values, dems 2, 1.6, for AHU 1.5 coolg C/m, measured AHU on heatg three ice rks, decreased which by two 24% m 18%, respectively. selected bezone usedcoolg simulation ice-pad, as high as well (2) as medium electricity (1.5) temperature consumption gradient requirements values. models refrigeration also process simulated both reduced an additional by 38%. temperature Fally, overall gradient value results equal demonstrated one, as anclearly ultimate ideal concisely condition. how energy can be significantly saved through replanng Some AHU measured layout cases by reducg cluded two door supply vertical air temperatures, gradient. warm cool supply. However, this was stead simulated by usg an average supply air temperature. temperature 7. Discussion gradient parameter buildg component takes account effects different air distribution solutions that most create crucial various challenge temperature was how gradients implement simulation. air distribution system order form a less As stratified presented door air temperature. Table 4, energy ideal dems condition for is AHU approach coolg a temperature AHUgradient heatg 1 decreased by 24% 18%, respectively. zone coolg ice-pad, as well as electricity consumption requirements refrigeration process both reduced by 38%. Fally, overall results demonstrated clearly concisely how energy can be significantly saved through re-planng AHU layout by reducg door vertical temperature gradient. 7. Discussion most crucial challenge was how implement air distribution system order form a less stratified door air temperature. ideal condition is approach a temperature gradient 1 C/m. To do so, creatg two rmally separated virtual zones should be considered. This means that two different temperatures are mataed two warmer cooler zones. warmer zone is for spectars, cooler zone is for players. refore, it is reasonable supply a more cusmized localized air conditions each zone, n extract m same zone. 18 illustrates air distribution strategies proposed by this study. As shown, warmer air is supplied spectars zone, cooler air players zone. air is extracted same zones similarly. supply air termals have be as close occupants zones as possible. Two virtually separated zones are n created subsequently, two different average temperatures are formed each zone. air distribution solutions reduce risk mixg air zones. virtual zones are dicated via dashed le boxes proposed air distribution models shown 18. As discussed earlier, such air distribution models more likely tend approach ideal temperature gradient 1 C/m on average. This study also verified that lower temperature gradient results lower coolg heatg energy dems, leadg more efficient planng AHU air distribution systems. This is done by planng two separate

20 zones as possible. Two virtually separated zones are n created subsequently, two different average temperatures are formed each zone. air distribution solutions reduce risk mixg air zones. virtual zones are dicated via dashed le boxes proposed air distribution models shown 18. As discussed earlier, such air distribution models more Energies likely 2019, tend 12, 693 approach ideal temperature gradient 1 C/m on average. This study also verified that lower temperature gradient results lower coolg heatg energy dems, leadg more efficient planng AHU air distribution systems. This is done by planng two supply separate supply exhaust ducts, exhaust avoid ducts, avoid mixg mixg warmer warmer cooler air cooler air ma ducts. ma refore, ducts. refore, cooler air may cooler not need air may go not through need go heatg through coil. heat Moreover, recovery, it as justifies well as planng heatg coil. two completely Moreover, separate it justifies AHUs, planng one for two player s completely zone, separate AHUs, or for one for spectar s player s zone. zone, A furr advantage or for this spectar s solution iszone. that A furr spectars advantage AHU does this solution not needis that run contuously. spectars AHU It may run does conditional not need run contuously. spectars presence, It may run conditional speed control spectars beg proportional presence, speed number control spectars. beg proportional number spectars. (a) Energies 2018, 11, x (b) (c) 18. Proposed air ventilation distribution strategies reduce reduce door door temperature gradient. (a) (a) Horizontal supply air; (b) cled supply air; (c) vertical supply air Conclusions This study pots out feasibility reducg heatg energy required for for space space heatg heatg by by approximately 21%, reducg coolg energy dem for for dehumidification by about by about 60%. 60%. se results are achieved by carefully designg AHU layouts. Furrmore, more more significant result study are impacts door air temperature gradients on energy dem. Both simulation measurement results verify that smaller temperature gradient, lower heatg coolg energy dems. results dicate that coolg power required for refrigeration process can be reduced by up 38% by reducg door temperature stratification 2 C/m nearly 1 C/m.

21 Energies 2019, 12, result study are impacts door air temperature gradients on energy dem. Both simulation measurement results verify that smaller temperature gradient, lower heatg coolg energy dems. results dicate that coolg power required for refrigeration process can be reduced by up 38% by reducg door temperature stratification 2 C/m nearly 1 C/m. Considerg aforementioned conclusion necessitates careful design for both AHU configurations air distributions. re are no precise air distribution models for creatg any specific door air temperature gradient. However, as earlier examples proposed 18, more cusmized air distribution models tend be more likely reduce door air temperature gradient this consequently leads a more energy efficient system air distribution. To do so, heights directions airflows have be more carefully planned, so that heated or non-heated air is delivered right occupied zone where it is needed. Fally, for sake energy conservation, it is proposed that common AHUs should not be planned for entire arena. Instead, it is more telligent plan various AHUs for spectar s zone rk zone, so that each AHU circulates air its own rmal zone. supply exhaust air termals have be vertically placed such a position as prevent mixg warmer cooler air zones. If mixg cooler warmer air is avoided, n supplyg additional heatg will subsequently be avoided. additional advantages such a system are control utilization spectar s AHU or its runng speed based on occupancy percentage spectar s zone. Author Contributions: Conceptualization, methodology, data curation, stware, visualization writg-origal draft preparation S.T., L.L. M.T.; Validation, formal analysis writg-review & editg M.T.; Supervision, project admistration fundg acquisition, J.K. Fundg: This study was fanced supported by Fnish Mistry Education Culture, through (OKM) project, by Esnian Centre Excellence Zero Energy Resource Efficient Smart Buildgs Districts, ZEBE, grant funded by European Regional Development Fund. Conflicts Interest: authors declare no conflict terest. References 1. Pisello, A.L.; Bobker, M.; Cotana, F. A buildg energy efficiency optimization method by evaluatg effective rmal zones occupancy. Energies 2012, 5, [CrossRef] 2. Domínguez, S.; Sendra, J.J.; León, A.L.; Esquivias, P.M. Towards energy dem reduction social housg buildgs: Envelope system optimization strategies. Energies 2012, 5, [CrossRef] 3. Laurier Nichols, P. Improvg Efficiency Ice Hockey Arenas. ASHRAE Journal, USA. June Available onle: 20%20Ice%20Hockey%20Arenas.pdf (accessed on 20 February 2019). 4. Rogstam, J.; Dahlberg, M.; Hjert, J. Sppsladd fas 3-Energianvändng i svenska ishallar; En studie av Svenska Ishallar i syfte att Främja Teknikutvecklg och Hållbar Energianvändng; Energy Kylanal. svenska kyltekniska förengen: Älvsjö, Sweden, Rogstam, J.; Dahlberg, M.; Hjert, J. Sppsladd fas 2 Energianvändng i Svenska ishallar; En studie av Svenska Ishallar i syfte att Främja Teknikutvecklg och Hållbar Energianvändng; svenska kyltekniska förengen: Sckholm, Sweden, Rojas, G.; Grove-Smith, J. Improvg Ventilation Efficiency for a Highly Energy Efficient Indoor Swimmg Pool Usg CFD Simulations. Fluids 2018, 3, 92. [CrossRef] 7. Daoud, A.; Galanis, N.; Bellache, O. Calculation refrigeration loads by convection, radiation condensation ice rks usg a transient 3D zonal model. Appl. rm. Eng. 2008, 28, [CrossRef] 8. Seghouani, L.; Daoud, A.; Galanis, N. Prediction yearly energy requirements door ice rks. Energy Build. 2009, 41, [CrossRef] 9. Seghouani, L.; Daoud, A.; Galanis, N. Yearly simulation teraction between an ice rk its refrigeration system: A case study. Int. J. Refrig. 2011, 34, [CrossRef]

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