WHOLE-BUILDING PERFORMANCE SIMULATION OF A LOW ...

Proceedings of Building Simulation 2011: 12th Conference of International Building Performance Simulation Association, Sydney, 14-16 November.

WHOLE-BUILDING PERFORMANCE SIMULATION OF A LOW-ENERGY RESIDENCE WITH AN UNCONVENTIONAL HVAC SYSTEM Omer Tugrul Karaguzel*, Khee Poh Lam Center for Building Performance and Diagnostics, School of Architecture, Carnegie Mellon University, Pittsburgh, U.S.A. *Corresponding author. E-mail address: [email protected]

ABSTRACT This paper presents an analysis of whole-building performance modelling and simulation process of a low-energy single-family detached residence located in Northeast U.S. A total of six design alternatives are modelled with EnergyPlus to predict relative performance improvements associated with a diverse set of energy efficiency measures of both building envelope assemblies and unconventional HVAC systems with inclusion of on-site renewable energy technologies. Simulation results indicate 29.3% energy cost savings (with respect to ASHRAE 90.1 2004 Standard Model) achieved through envelope efficiency measures only and 49.1% savings through coupling with a complex HVAC configuration and renewable energy systems.

INTRODUCTION According to current statistics (U.S. DOE, 2010), residential buildings in the U.S. are responsible for 22% (6.2x1012 kWh) of primary energy demand per year. 68.8% of this demand is to generate electricity for space cooling, ventilation, lighting and household appliances, which accounts for about 36% of national electricity demand. Residential sector uses 20.8% of annual natural gas production (23.4 Quads) for space heating and domestic hot water generation. Reduction of energy intensity of residential buildings started with passive solar homes movement of 1960s. It then evolved to super-insulated, highly airtight envelope designs. Technological advancements in residential HVAC systems and small-scale renewable energy technologies further led to potentially netzero energy homes of today. Contemporary low energy residential buildings combine passive and active solar features with highly insulated and weatherized envelopes coupled with high efficiency domestic appliances, and lighting systems to minimize space heating, cooling and household electrical loads (demand side efficiency measures) (Parker, 2009 and Malhotra et al., 2010). Overall building load minimization paves the way to significant reductions of energy use intensities when such loads are managed by optimally controlled, high-performance and mixed mode HVAC systems coupled with air-based heat recovery equipments and ground source heat exchangers (supply side efficiency

measures). Moreover, utilization of grid-tied building integrated photovoltaic systems together with hot water systems backed up with solar thermal collectors can shift net energy balance to potentially zero level on an annual basis (on-site renewable energy measures). The complex and highly integrated nature of the above mentioned efficiency strategies and related technologies pose considerable challenges for analysing and evaluating the building energy performance with simulation-based assessment techniques. For instance, Brahme et al., 2009 discussed capabilities of three whole-building energy simulation tools (eQUEST, EnergyPlus, TRNSYS) to simulate a number of zero energy building technologies common to single-family residences in Southeast U.S. It was claimed that current simulation tools are not effectively supporting passive design strategies and unconventional HVAC configurations. Literature indicates the necessity of using dynamic, and integrated whole-building energy simulation methods, which require coupling multiple modelling tools for majority of the cases. For instance, Brahme et al., 2008 conducted a study on performance-based design process of a low-energy single-family residence in Northeast U.S. involving programs of RetScreen for electricity and solar thermal energy production analysis, eQUEST for envelope, internal load and system analyses, and Trane Trace 700 for equipment sizing. This paper presents whole-building performance simulation of a low-energy residence with an unconventional HVAC system. Emphasis is given to full exploitation of integrative simulation capabilities offered by EnergyPlus program without recourse to other simulation tools. Comparative evaluations of simulation results are also presented.

METHODOLOGY In order to form a basis for energy performance comparison of possible design alternatives, a baseline model (referred as ASHRAE Baseline Model) is first established. Since the residential building project under consideration was already registered as a lowrise commercial building type for Leadership in Energy and Environmental Design-New Construction (LEED-NC) rating calculations, the baseline model development is in accordance with Performance

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Rating M Method desccribed in AP PPENDIX G of ASHRAE E Standard 90.1-2004 9 (A ASHRAE, 20004). Proposedd Design Model is determined by comparisons of annuaal energy use intensities (E EUI) as well as a calculations of percentaage improvem ments over the ASHRAE Baseline B in terms of an nnual energy ccost and corrresponding LEED-NC L crredit points. Thhe Proposed Design D Model is disaggreggated into fourr sub-models for analysinng the effects of demand side s and suppply side efficieency measurees on the oveerall energy performancce as well as contributiions from ren newable energgy systems (T Table 1). An eenergy effectiiveness scale is introducedd to compare relative efficiency gains from each submodel wiith respect to total efficienccy gains from m the Proposedd Design Modeel. Taable 1 EnergyyPlus model allternatives MO ODEL ASHRAE Baseline Model Demand S Side Efficiency Model (DS SEM)

Supply Sidde Efficiency Model (SSEM)

Renewablee Energy Model (RE EM) DSEM + S SSEM Proposed D Design Model (DSEM+S SSEM +REM)

DEF FINITION ASHRAE 900.1 2004 complliant model (for Climate C Zone 4A) 4 Thermally reesistant and air-tight enveloppe (external waalls and roof) + Insulated I Glazin ng Units + Reduuced Lighting Power Densiities (LPD) Water-to-waater geothermal heat pumps with ground source heat exchangers + Energy recovvery ventilators (E ERVs) + Demaand Controlled V Ventilation (DC CV) + Whole hoouse ventilation fan + Radiant flooor heating systtem + Efficient hot h water system m Solar thermaal collectors + Solar S power generration (PV) systtem Sub-model excluding e renewable ennergy features Final design model combinning all efficiencyy sub-models

Thee thermal enveelope enclosess all conditionned spaces whiich include the t attic spaace and the basement. Loccation is Neew Jersey, U.S. with a heating dom minated climaate (HDD-18 oC and CDD--18 oC are 50660 and 1037) classified as Zone 4A acccording to ASH HRAE 90.1 2004 standard.

SIM MULATION N MODEL DEVELOP PMENT Buiilding Envelo ope Thee baseline model repreesents a liightweight connstruction (steeel joist extern nal walls and floors, f and a metal m deck rooff). Envelope assemblies a of ASHRAE Basseline model are a developed d based on reqquirements provvided in ASH HRAE 90.1 staandard with U-values U in accordance withh minimum allowances a foor Climate Zonne 4A. Insulaation levels arre R-2.3 and R-2.6 for wallls and roof (where insulaation is entireely above decck), respectively. Insteaad of layeer-by-layer defi finitions, baseement walls are developeed by an alteernative metho od in EnergyP Plus, which reequires Cfacttor and heigh ht of the undeerground wall to define an entire consstruction asseembly. Winddows are ntations with WWR of equually distributeed to all orien 21.66%, which iss the same ass the Proposeed Design Moodel. Overhan ngs and othher forms off shading med to be devvices are omittted and winddows are assum flusshed with thee external waall surface. Thhe DSEM Moodel and its coombinations are a equipped with w R-35 CF) (above and a below insuulated concreete frame (IC gradde) external walls compoosed of minneral fibre inseert and concreete filled coree between twoo layers of perm manent therm mal wall form ms. Roof coonstruction com mprises woodeen joists and deck with upp to 20.32 cm of R-28 icynene i spraay insulationn. Heated basement concreete slab is insu ulated with 7.62 cm of R-113 expanded polystyrene p inssulation (Tablle 2). Taable 2 Comparrison of opaqu ue envelope asssemblies DS ASHRAE E SEM BASELIN NE ALTER RNATIVE U U-value (W/m2K) K Exteernal Walls 0.703 0.216 ( Basement Walls C-6.473 (1) 0.216 Rooof (Exposed) 0.360 0.182 Basement Floor 0.372 0.372 Note: (1) C-Facto or (steady-statee heat flow thhrough unit baseement wall areea excluding heat h resistance of soil/air film m) is used as a siimulation modeel input. ENVELOPE E A ASSEMBLY

Case of this t study is an unusually large (753.6 m2) two-storeey single-famiily residence (for a househhold of 6 peoople) with a conditioned c b basement flooor, 5 bedroomss and 5 bathrrooms togethher with a lib brary and a ddouble-volumee lounge area for meettings (Figure 11). The short axis a of the buuilding is orieented 27o east of North. Tootal window to t wall area ratio r (WWR) iis 21.6%.

Envvelope infiltraation rate is upgraded u from m 0.30 to 0.255 ACH for th he DSEM Moddel having doouble-pane low w-E with Argo on gas (6-12-66 mm) window ws instead of ASHRAE A com mpliant window ws (Table 3). Table 3 Comparisonn of windows WIINDOW TYPE E

D Modell Figurre 1 3D View of Proposed Design

ASH HRAE Baselinee DSE EM Alternativee

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UE U-VALU (W/m2K) K 3.224 1.793

C SHGC

VT

0.39 0.27

0.495 0.220


Internal Gains and Exterior Lightts LPD) Reductionns of interior lighting poweer densities (L are refleccted on all models m alternnatives exceptt for ASHRAE E Baseline moodel, and SSE EM model (T Table 4). Howeever, equipmeent power dennsities (EPD) and exterior lighting levels (2.2 W/m2 for 961 m2 of illuminateed wall surfaace) are kept constant betw ween models w with respect too Performancee Rating Metthod. An astroonomical cloock control is assigned for automaticcally switchin ng off exteriorr lights after sunrise and vvise versa. Forr all model altternatives, rad diant fraction of o heat gain from f equipmeents is set to 0.5. Lighting fixture type is assumed to be suspennded ble fractions oof 0.42 and 0.18, 0 with radiiant and visib respectiveely. Total nu umber people occupying the building is not more than t 6 whichh is also the peak p c spaaces, occupanccy for living, dining, and circulation and reducced to its one third for bedrooom spaces.

Equuipment and lighting den nsities are sett to their maxximums durin ng occupied periods p and reduced r to 5% of maximum m power (to o account forr parasitic lossses) for the resst of the timess.

Taable 4 Compa arison of Interrnal Gains ASH HRAE BASE ELINE LPD EPD

DESIGN AL LTERNATIVE ES LP PD EPD D W/m m2 3.1//1.6/ Living Room (1) 12.0 8.07 2.44/1.8 Same as Dining Rooom 12.0 8.07 4 4.5 AE ASHRA (1) Circulationn 6.0 5.0 3.88/2.3 Baseliine ((1) Bedroom 12.0 8.07 1.88/2.0 Mechanicaal 3.0 5.0 3 3.1 Note: (1) Has multiple rooms r under thhe same space use with varying LPD Ds. type but w SPACE USE U TYPE E

Environm mental Contrrols and Scheedules All buildding models have h the sam me thermal zonning layout iincluding 133 different thermal zoones. Basemennt and 1st floorr has living rooom spaces and d 2nd floor hass bedroom spaces s linkedd with respecctive occupanccy profiles givven in Figure 2. Environmeental control vvariables at thhermal zone leevel are set-ppoint and set-bback temperaatures for sppace heating and cooling, aand minimum m outside air veentilation ratees all of which are kept constant throughoout all simulaation P R Rating Methood of models (aaccording to Performance ASHRAE E 90.1 2004 4). Temperatuure-based conntrol variables (dual-band thhermostat setttings) are derrived from desiign specificatiions as 20 oC,, and 23.33 oC for heating aand cooling seet-points with setbacks of 16.67 o C and 226.67 oC forr heating andd cooling moodes, respectiveely. Minimum m outdoor airr ventilation rates r are aggreegated from diiscrete inputs (sum method) for 2 minimum m flow per flooor area (0.3 L/sec-m L ) and d per person (22.5 L/sec-person) in compliiance with rellated ventilatioon standardds (ASHR RAE 62.1-2 2004 Ventilatioon for Acceptable Indoor Air A Quality). Operationnal schedules for HVAC syystem, equipm ment and lightting are couupled to occuupancy sched dules (Figure 22). HVAC systtem control iss based on thee setpoint tem mperatures durring occupiedd periods and setback teemperatures during unnoccupied ones. o

Figgure 2 Occupa ancy scheduless for living roooms (top) an nd bedrooms (bottom) ( Dom mestic Hot Water W (DHW)) System DH HW system forr model alternnatives (excludding REM andd Proposed Design D Model)) includes a 20500 W proppane fired gas g storage water w heater (detached from m the plant looop) with 0.2284 m3 (75 gallons) g of storrage tank. Ennergy factor (EF) of this heater is calcculated as 0.4477 for ASH HRAE Baselinne Model, an EF of wheereas for SSE EM and its combinations c 0.5880 is assu umed (accorrding to mechanical m specifications). Each E water use equipmeent (sinks, tubss, showers, dishwasher d a and clothes w washer) is indiividually modelled in EnnergyPlus witth a total watter flow rate of 0.50448x10-4 m3/sec (corrresponding to t 84 gallonss/day typical hot water usage of a U.S. family of sixx). Peak flow w rates are h fractionnal scheduless of water moddified with hourly use equipmentts. Deliveryy water temperature assuumptions are 43.3 oC,, and 50.0 oC for sinkks/showers an nd washing machines, m resspectively. Waater mains tem mperature is prredicted by E EnergyPlus based on a corrrelation metho od taking into account aveerage outdoor dry-bulb tem mperature (122.2 oC) of the building’s loocation and thhe maximum difference betw ween averagee monthly ouutdoor air tem mperatures (22.9 oC). Ren newable Enerrgy Systems Botth REM and Proposed P Dessign Model allternatives incoorporate a solar therm mal collectorr system com mposed of three flat plate solar s collectorrs (3x2.96

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m2 with a tilt and azim muth angles off 34o and 1399o), a 3 0.45 m (119 ( gal) storrage tank, a 0.284 0 m3 (75 gal) gas storagge water heateer, a collector loop pump, and a a temperingg valve (to avoid a scaldingg temperaturees at the fauceets) (Figure 3)). Solar collecctors’ perfomaance data is deerived from U.S. U Solar Raating Certificaation Corporatiion’s (SRCC) database alreeady included into EnergyPllus input dataa sets. Solar thermal t system m is utilized aas a backup to o gas storage water heater and its operattion is contollled by a diffeerential thermoostat (by sensing temperaturres at Node A and B in Figure 3). Uppeer and lower thresholds of o the differenntial thermostaat is assumed as 10 oC and 2 oC, respectiveely. System overheating o is avoided by a cutoff (Nodee D) temperatture control (60 ( oC maxim mum) at the tannk outlet, whereas freezingg is prevented d by re-circulaation of hot water w (generaated by gas water w heater) in i the collecctor loop annd controlled d by temperatuure of one of the t collector’ss outlet (Nodee C).

Figure 3 Schematic diaagram of solar collector sysstem Solar elecctrical power generation syystem of REM M and Proposedd Design Moddel includes tw wo different roofr mounted,, grid-tied PV arrays comprrising a total of o 44 modules (specific pow wer of 225 W at maxim mum power pooint - MPP) with w a total DC D rating of 9.90 kWp (at STC). Solaar cell technnology is moonoSi). Tilt angle of all modulees is crystallinne silicon (c-S 34o, wherreas azimuth angle of 30 modules m is at 178o o and the rremaining is at a 212 . Total active PV areea is calculatedd as 54.6 m2 based onn single module performaance data impoorted from ceertified Sandiaa PV dataset off EnergyPlus data library. A simple DC-AC inverter m model with an n efficiency of 0.89 is assu umed for the enntire PV system. PV modulles are assumeed to be decouupled (heat transfer integration modee is “Decouplled NOCT Conditions”) C f from the building envelope where theree exist no thhermal interacction b tem mperatures. Duue to affecting solar cells’ back-face current limitations of EnergyyPlus, ancilllary equipmennts of the PV system otherr than inverterr are not modeeled and it is assumed that system is alw ways operatingg at MPP without mismatchh losses. HVAC Systems S As the buuilding case iss less than 3 floors f with a total t floor areaa smaller thann 7000 m2, HVAC H system m for

ASH HRAE Baseliine Model, SS SEM and REM M models is assumed a to be packaged single s zone roooftop air connditioner withh an electric heat pump (ASHRAE ( 90.1 2004 Appen ndix G System 4, PSZ-HP P). HVAC systtem model is imported and adapted from m a sample buillding model developed d byy the use of web-based w EneergyPlus Exaample File Generator G (U U.S. DOE, 20111) program considering c thhe same climatte zone as welll as Appendixx G HVAC ty ype. System fans f (with effiiciency of 0.60) are constan nt volume conntinuously opeerated during occupied hou urs and cyclinng to meet heaating or coo oling loads imposed by set-back tem mperatures duuring unoccuppied periods. A night cyccle availabiliity managerr is establlished in EneergyPlus forccing individu ual zone fanss to start opeeration to meeet setback loadds with a tolerrance of 1 o C. With respeect to ASHR RAE requirem ments, no ecoonomizer is modelled for Climate Zone 4A. 4 Direct exppansion (DX) cooling coil’ss COP is set to t 3.0, and heaating efficienccy of electricc heat pumpss to 0.80. HV VAC system componentss are auto--sized by EneergyPlus with h sizing factorrs of 1.25 andd 1.15 for heaating and coo oling, respecctively. An all-electric a HV VAC system (P PSZ-HP) is asssumed for thhe baseline moddel considerin ng the fact thaat HVAC systtem of the Proposed Design n Model is also a relying on o an allelecctric system without w gas booilers on the plant p side. Theerefore, reducctions due to o variations of o site-tosouurce conversio on factors of utilized u energgy sources (refflected on ennergy cost and a savings) between baseline and Propposed Design Models are avvoided. HV VAC system modelled m for SSEM, DSEM M+SSEM, andd Proposed Design D Modeel includes a ground souurce heat pum mp (GSHP) and a a heat exchangere (GS SHX), three air handling g units (AHU Us), three eneergy recovery ventilators (ERVs), a whhole-house venntilation fan (WHVF), a demand controlled venntilation system m (DCV), and d a radiant floor heating systtem (RFHS).

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Figure 4 Scchematic diaggram of plant loop l


HVAC ssystem includ des a water--to-water gro ound source heeat pump connnected to chillled water andd hot water looops serving cooling and heating coilss of AHUs as well as radiaant floor heatinng system (Figure 4). GSHPs are circulating R22 refrigerant r in the condenseer loop, whicch includes a vertical gro ound source hheat exchangeer on the suupply side. Since S EnergyPllus has no fu unctionality foor auto-sizingg the GSHX, iit is assumed d that a single bore hole with w 0.1524 m diameter andd 45.72 m lennght is capablle of satisfyingg 1 ton (3517 W) of heatingg and cooling load of the buuilding (Rafferrty 2008). Therefore, GSH HX is sized so as to handle pre-calculatedd GSHP capaacity l pumps for f hot water and (Table 5)). The plant loop chilled w water are auto--sized by EnerrgyPlus with flow f rates of 00.0024 and 0.00014 m3/s, resppectively. HVAC topology is the sam me for SSEM, DSEM+S SSEM, and Proposed Design Moodel. Howeverr, HVAC inp put parameters given here are representting only Prop posed Design Model attribuutes. Assumptiions for such h input param meters are derrived from maanually calcullated values based on deesign principless, values from fr EnergyyPlus auto-sizing routines aand from sampple EnergyPluus models inpuuts. Table 5 G GSHX and GSH SHP system deesign parameteers PARAMETE ER ATTRIBUT TE Maximum Flow w Rate (1) 0.0035 m3/s Number of Borre Holes (2) 12 GSHX Bore Hole Length (2) 45.72 m Bore Hole Raddius (3) 0.0762 m Pipe Thicknesss (3) 0.0024 m Heating - Cooling 41 kW and 288 kW GSHP Capacity(2) Heating – Coolling COP (3) 2.36 and 4.100 Notes: (1) Autozised valuues (2) Manuallly calculated vaalues (3) Sample model values

unooccupied hours. Minimum supply air tem mperatures of 20 oC and 12 1 oC for heeating and coooling are assuumed with maximums m o 30 oC and 18 oC, of resppectively. Syystem set-pooint temperattures are sensed by AHU U heating coiil outlet (heaating) and AH HU supply fann outlet or mixed air node (cooling). Eneergy recovery ventilators (E ERVs) are connnected in seriies to each outdoor air mixing box off the three AH HUs. 300 W ERVs E are flat--plate type annd recover bothh sensible andd latent energyy in the returnn air loops withh sensible an nd latent effeectiveness of 0.76 and 0.688 at maximum m heating air flow. Capacitty of each ERV V equipment is optimized so s that averagge air flow ratee of each AHU U can stay beetween 50% and a 130% of nominal n supplly air flow ratte of an integrrated ERV equuipment for maximum heat recoveery. ERV opeerations are in tandem with w AHU aavailability schedules and frost controll is deployedd with a y outdoor air inlets for threeshold of 1.7 oC on supply exhhaust recirculaation. In EnerggyPlus there iss no direct wayy of modellinng a single whole w house ventilation v fan (WHVF) (forr the Proposed d Design Moddel) which o of HVAC H system m air loop assuumes hybrid operation undder certain acceptable condditions for inddoors and outsside environm ment. Therefo ore, proposedd 1118 W WH HVF with maaximum flow w rate of 1.89 m3/s is disccretized into 6 individual zone z ventilatioon objects (of exhaust type)) which have varying v flow rates r (with a constant pressure rise of 414 4 Pa) and fan f power ratinngs. Linear correlations c arre establishedd between venntilated zone volume v and co orresponding flow f rates. Zonne ventilation objects (1st and a 2nd floorss) are then couupled with a hybrid ventilation v a availability mannager controlling the altternating opeeration of resppective AHUss with WHVF F. The controol logic is based on indooor and outdoor ambient conditions c (Figgure 5).

Main air loop componnents are threee AHUs servving each flooor of the buildiing. AHU 1 annd 2 are operaating under daytime schedules for liiving spacess of basementt and 1st flooor, respectivvely. AHU 3 is serving nnight time zonnes of 2nd floor (bedrooms).. All AHU coils are auto-sizzed by EnergyyPlus (Table 6). 6 Tablee 6 Air handling units desiggn parameterss PARAMETER Max Air Flow F Rate (m3/ss) Min Air Flow Rate (m3/s)) Supply Faan Power (W) Heating Coil Hot Water m Flow Rate (l/s) Maximum Cooling C Coil Chilled Watter Maximum m Flow Rate (l/s)

AH HU 1 0.770 0.009 938

AHU 2 0.93 0.12 1352

AHU A 3 0 0.77 0 0.07 1 1275

0.554

0.60

0 0.47

0.339

0.64

0 0.38

System ffans are variab ble volume draw-through d type with tottal fan efficciencies of 0.7. Night-ccycle availabiliity managers are a defined for each AHU so s as to avoidd unnecessarry system operation o du uring

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Figuree 5 Control log gic of WHVF


Outdoor air controlllers of eacch AHU (uusing determiniistic operatioonal schedulees for minim mum flow ratees per unit areea and per perrson) are cou upled with a deemand contro olled ventilatioon (DCV) sysstem performinng first order evaluations of o carbon dio oxide concentraations (CO2) in pre-defineed control zoones. DCV oobjects of the mechannical ventilaation controllerrs assume Inndoor Air Quality Q Procedure (IAQP) for minim mum outdoor airflow rate determinaation. At each e simulaation time step EnergyPllus evaluates the indoor CO C 2 concentraation levels geenerated by occupancy (with a ratee of 3.82x10-88 m3/s-W of o metabolicc activity) and modulatees outdoor airfflow rate to keep k concentraation levels beelow 900 pppm with the assumption that outside eenvironment has h a constannt CO2 source of 400 ppm. A CO2 contrroller object is i developed for f a representtative zone of o each AH HU under “Z Zone Control: Contaminaant Controlller” class in f and WH HVF, EnergyPllus. In additioon to system fans, the building models (oof all alternatives) include five w maximum m exhaust ratees of 132 W eexhaust fans with 0.059 m3/s. Exhaust fan f operationn is coupled with w hourly ooccupancy scchedules of bathrooms and restroomss to model lighht-switch conntrol system. Radiant floor f heating system s is the water-side w HV VAC component and classified as zone type low temperatuure variablee flow raddiant object in EnergyPllus. This systeem consists of o 7 radiant zoones with embbedded hydroonic tubing (oof 0.012 m in nside diameter)). EnergyPluss auto-sized tuube spacing, total t hydronic tubing lengthh (in the rangge of 522 to 1127 1 r m per zonne) as well as maximum hoot water flow rates (varying between 0.0076 to 0.2144 l/s per zoone). Radiant system heatiing set pointt control type is n air temperaature and assuumed specified as zone mean to be 4-55 oC (derived from manual generate andd test routines ffor each zonee) lower than room r heating setpoint wiith a throttliing range off 2 oC. Speecial constructtion objects arre created for radiant slabs with w the positiional indicatioon of internal heat source in n the ordered list of materiaal assemblies. Specific building surfaces of radiant slaabs are also iddentified and area r weightedd fractions are applied to hoot water flow rates of radiant slabs consissting of multipple floor surfaaces. RFHS iss connected to plant sidee HVAC sysstem through hot water demand d splittter connectedd to GSHP onn the supply siide. Energy S Sources and Rates R Electricitty and propanee are the enerrgy sources foor all building models. Energy E rates for residenntial buildingss in New Jerseey are used too calculate energy costs andd associated saavings. (Table 7).

SIM MULATION N RESULT T ANALYSIS Ann nual Energy Consumption n and Cost Analysis A A comparison c o annual site energy use intensities of (EU UI) (cumulativ ve energy coonsumption normalized n by floor f area of 753.6 7 m2) withhout the contrribution of PV--generated eleectricity is givven in Figuree 6 below. Thee largest EUII reduction (336.8%) with respect r to ASH HRAE Baseline Model is observedd for the Proposed Modell including all a possible efficiency meaasures discusssed in this study. Deplooyment of dem mand side efficiency measuures focused onn building envvelope alone can providde about 28.2% EUI reduuction as oppposed to 7.8% % reduction achievable a throough incorporation of a complex c (suppply side) HV VAC system without reco ourse to dem mand side meaasures.

Figure 6 Annalysis of enerrgy use intenssities Couupling supplyy side and demand d side measures (DS SEM+SSEM) yields considerable reduuctions in space heating ennergy (48.4%)) due to grouund source heaat exchange an nd ERVs. Hoowever, total efficiency gainn (6.3%) is diminished d duue to increaseed fan and pum mp energy usaage of the centtralized HVAC C system.

Table 7 Enerrgy sources annd rates ENERGY Y SOURCE E Electricityy Propane

ENERGY UNIT 1 kWh 1 Gallon

KWH CONVERSIION 1 kWh 27 kWhh

ENER RGY RAT TE 0.11 $/k kWh 1.4 $/gaallon

F Figure 7 Analyysis of energy consumption and a cost Unllike DSEM, SSEM alternaative cannot provide a signnificant reduction in space cooling energgy (26.9%

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comparedd to ASHRAE E 90.1) due to high internal heat gains from m unchanged LPDs. EPDs are kept consstant between altenatives annd result in 32.07 3 kWh/m m2 of annual E EUI with increasing percenntages in endd-use energy breakdowns ass total EUI teends to decreease. Auxiliaryy system compponents (AHU U fans, pumpss and ERVs) oof models equuipped with advanced HV VAC system arre responsiblee for about 13 to 15.5% of total t energy consumption. Baseline HVAC sysstem (without pumps on the plant side and ERV E equipmennt) includees auxiliarry compon nents contributiing not more than 4% to tootal consumpttion. Majority of the energyy is coming froom electricity fuel where prropane is useed for water heating purposes (Figure 77). Energy cosst for propane consumptionn can be decreaased from $3 334 to $71 with w solar therrmal collectorss coupled withh high-efficienncy water heaaters. DSEM oonly has the potential p of decreasing d an nnual total eleectricity cosst by a faactor of 0.697. Furtherm more, the Proposed Design Model M achiev ves a reductionn of 33.6% onn annual electtricity cost wiith a saving of $3292 per year. DSEM M also provides a consideraable amount of annual electricity cost reductionn (30.2%) with h a saving of 2967$. 2 Renewab ble Energy Syystems Contrribution 9.90 kW Wp solar PV syystem assumed for REM and Proposedd Design Model yields apprroximately 12,912 kWh (17..1 kWh/m2) of electricity onn an annual basis. Such genneration capacity is enough to cover 15% % and 22% of total electricity demandd of REM and Proposedd Design modeel, respectivelyy.

Figuure 8 Proposeed Design Moddel- Monthly electricity deemand and genneration Increasedd PV generration (Figuure 8) prov vides increasedd demand covverage in the range of 36% % to 27% betw ween May too September for the Propoosed Design Model. M Highhest electricitty generationn is predictedd for May (with relativvely clear skies s coincidinng with milderr ambient tem mperatures) wiith a peak of 1452.9 kWh h covering 36% 3 of monnthly electricityy demand off 3999 kWhh. 8.88 m2 solar s thermal collector c systeem generates 1388.6 kWh heat

eneergy per year.. When used as a backup to a high effiiciency water heater, this onn-site renewabble energy systtem provides 78.6% reduction in wateer heating eneergy requirem ments. Annuaal air to airr thermal eneergy recovery is about 701.3 and 6344.99 kWh for coooling and heatting, respectiv vely. Three 3000W ERV equuipments conssume 3088.8 kWh k electriciity energy for such a recoveery rate (annu ual overall resuulting in a totaal system efficciency of 43.8%). Eneergy Cost Savvings and LE EED-NC Cred dit Points Com mparisons of relative r energyy cost savingss achieved withh the Propossed Design Model M with respect r to ASH HRAE 90.1 Baseline B form the basis of crredit point calcculations for LEED NC EA E Credit 1-Optimize Eneergy Perform mance sectionn. Similarly, for EA Creedit 2-On-Siite Renewab ble section, positive conntribution off renewable energy syystems is calcculated as sho own in Table 8. 8 T Table 8 Energyy cost savingss and PV contrribution E LEED EA % CREDIT 1 M MODEL PV AND 2 (%) TS POINT DSE EM 29.3 6/0 0.0 SSE EM 7.2 0/0 0.0 REM M 16.6 2/3 14.4 DSE EM +SSEM 33.2 7/0 0.0 PRO OPOSED 49.1 10/3 21.6 Perccent saving = 10 00x(1-Alternatiive Cost/ASHR RAE 90.1) Perccent PV = PV generation/(Alte g ernative + PV Generation) G ENERGY CO OST SAVINGS %) WITH PV (%

Witth the contribuution of PV generated electtricity, the Proposed Designn Model achiieves 49.1% of energy orresponding to 50.2% of o energy costt saving (co saving) and receeives all posssible LEED EA E Credit M+SSEM poinnts. Comparred to basseline, DSEM alteernative witho out renewable energy sysstems can achhieve 33.2% total energy cost savings. DSEM alonne can achieeve 29.3% saavings before coupling withh supply sidee efficiency measures. m SSE EM cannot pass the thresholld of significaant energy perrformance f achieving LEED EA Credit 1 impprovements for poinnts. On-site reenewables alo one has the pootential of colllecting a totaal of 5 LEED D EA pointss for both eneergy performannce and on-siite renewabless. In order to facilitate com mparisons off relative energy cost perfformance off alternative models bassed on a norm malized effecctiveness conncept, an effe fectiveness scalle (from 0.0 to o 1.0) is deveeloped (Figuree 9) where eneergy cost sav ving of each model is diivided by maxximum achievvable savingss percentage among a all posssible model alternatives. Maximum M ennergy cost saving percentagge is 49.1% with Proposeed Design AE Baseline Model and Proposed Moodel. ASHRA Dessign Model arre found at loower and upper bounds (0 to t 1) of the ennergy cost effeectiveness scaale. SSEM has index point of 0.14, whiich lies closee to lower

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limit, whereas DSEM model (0.59 point) covers almost 60% of all possible efficiency gains. Coupling DSEM with advanced HVAC can only increase index point by 0.08. REM alternative achieves 0.34 point by utilization of solar PV and thermal energy systems only.

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Model Alternative/ Effectiveness Total LEED EA Effectiveness Index Scale Credit Points ASHRAE 90.1/0.0 0.0 0 0.1 SSEM/0.14 0 0.2 0.3 REM/0.34 5 0.4 0.5 DSEM/0.59 6 0.6 DESM+SSEM/0.67 7 0.7 0.8 0.9 PROPOSED DESIGN/1.0 1.0 13



as well as using ground as heat sink provides marginal reductions in overall building energy performance. Combined system configuration and operational strategies of complex HVAC systems for low-energy residential buildings can be handled without recourse to multiple simulation tools by the use of integrated, simulation engines (i.e., EnergyPlus). Current whole-building performance simulation tools are not suited to provide effective support for modelling of hybrid HVAC systems (e.g., whole house ventilation fans alternating with central AHUs for fan-assisted ventilation for space cooling purposes).

ACKNOWLEDGEMENT

Figure 9 Energy cost effectiveness scale

The support of the Stone House Group, PA for this project is gratefully acknowledged.

CONCLUSIONS This paper evaluates whole-building energy performance of a relatively large single-family residence design equipped with state-of-the-art efficiency measures on the demand side and supply side energy flows together with contributions from on-site renewable energy technologies. Through energy simulations and comparative performance assessments of 6 different building models following conclusions are drawn:  Considerable energy performance improvements (29.3% cost reduction) can be gained by giving highest priority to envelope-based demand side energy measures before incorporating unconventional HVAC system components. Coupling high-end HVAC systems with thermally resistive and air-tight envelopes becomes even more significant with 33.2% maximum energy cost reduction.  On-site renewable energy systems (particularly solar electric power generation) can provide significant improvements of netenergy balance (49.1% energy cost reduction) and associated LEED-NC credit points collection from multiple sections of Energy and Atmosphere category (Credit 1 and Credit 2).  Complex HVAC systems with centralized AHUs present inefficiencies and increased energy consumption for auxiliary system components (e.g., fans, pumps, ERVs) for residential buildings having relatively large volumes requiring diversified operational schedules. Under the climatic and geologic conditions of the investigated buildings case, cooling energy recovery through ventilation

REFERENCES ASHRAE Standard 90.1-2004. 2004. Energy Standard for Buildings Except Low-Rise Residential Buildings. ASHRAE Standing Standard Project Committee 90.1, Atlanta, GA. Brahme, R., Dobbs, G., Carriere, T. 2008. Bracketing Residential “Net-Zeroness” During Design Stage; Proceedings of 3rd National Conference of IBPSA-USA, Berkeley, California, USA. Brahme, R., O’Neill Z., Sisson, W., Otto, K. 2009. Using Existing Whole Building Energy Tools for Designing Net-Zero Energy Buildings– Challenges and Workarounds; Proceedings of 11th International IBPSA Conference, Glasgow, Scotland. Malhorta, M., Haberl, J. 2010. Simulated Building Energy Performance of Single-Family Detached Residences Designed for Off-grid, Off-pipe Operation; Proceedings of 4th National Conference of IBPSA-USA, New York, USA. Parker, D.S. 2009. Very Low Energy Homes in the United States: Perspectives on Performance from Measured Data. Energy and Buildings, 41(5): 512-520. Rafferty, K. 2008. An Information Survival Kit for the Prospective Geothermal Heat Pump Owner. Heat Spring Learning Institute. Cambridge, MA, U.SA. U.S. Department of Energy (DOE). 2010. Building Energy Data Book; http://buildingsdatabook. eren.doe.gov/; U.S. Department of Energy (DOE). 2011. EnergyPlus Example File Generator; http://apps1.eere.energy.gov/buildings/energyplu s/cfm/inputs/index.cfm

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