WHOLE-BUILDING PERFORMANCE SIMULATION OF … · whole-building performance simulation of a...

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 net-zero 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 low-rise 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

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

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0.495 0.220


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lternatives r system rs (3x2.96


- 2485 -

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exchanger-Us), three hole-house controlled or heating

loop


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HVAC ssource hewater looAHUs as 4). GSHcondensesource hEnergyPlGSHX, i0.1524 msatisfyingof the busized so (Table 5)chilled wrates of 0HVAC DSEM+SHoweverrepresentAssumptifrom maprinciplesroutines a

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Notes: (1) (3)

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topology iSSEM, and r, HVAC inpting only Propions for such

anually calculs, values frand from samp

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loop componor of the buildiaytime schet and 1st flonight time zonls are auto-siz

e 6 Air handli

ARAMETER

Flow Rate (m3/slow Rate (m3/s)

an Power (W) oil Hot Water

m Flow Rate (l/sCoil Chilled Watm Flow Rate (l/s

fans are variabtal fan efficity managers ad unnecessar

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re Holes (2)

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Outdoor determiniflow ratewith a deperforminconcentraDCV ocontroller(IAQP) determinaEnergyPllevels ge3.82x10-8

modulatelevels beoutside e400 ppmrepresentControl: EnergyPlthe build132 W e0.059 m3

hourly orestroomsRadiant fcomponetemperatuEnergyPlwith embdiameter)hydronic m per zon(varying Radiant specified to be 4-5routines fpoint wiconstructthe positiordered lsurfaces weightedof radianRFHS isthrough GSHP onEnergy SElectricitbuilding buildingscosts and

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air controlistic operatio

es per unit areemand controng first order ations (CO2) objects of rs assume In

for minimation. At elus evaluates enerated by 8 m3/s-W oes outdoor airfelow 900 ppenvironment h. A CO2 contrtative zone o

Contaminalus. In additioing models (o

exhaust fans w3/s. Exhaust foccupancy scs to model lighfloor heating snt and claure variablelus. This systebedded hydro). EnergyPlustubing length

ne) as well as between 0.0

system heatias zone mean

5 oC (derived for each zoneith a throttlition objects arional indicatioist of materiaof radiant sla

d fractions are t slabs consis

s connected hot water d

n the supply siSources and Rty and propane

models. Es in New Jersed associated sa

Table 7 Ener

Y E

ENERGY UNIT

y 1 kWh 1 Gallon

llers of eaconal scheduleea and per perolled ventilatio

evaluations oin pre-definethe mechan

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each simulathe indoor Coccupancy

of metabolicflow rate to kpm with the has a constanroller object iof each AH

ant Controlon to system fof all alternatwith maximumfan operationchedules of ht-switch consystem is the wssified as

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076 to 0.214ing set pointn air temperafrom manual

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applied to hosting of multipto plant side

demand splittide. Rates e are the ener

Energy rates ey are used toavings. (Table

rgy sources an

KWH CONVERSI

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ch AHU (ues for minimrson) are couon (DCV) sysof carbon dioed control zonical ventila

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HU under “Zller” class fans, and WHives) include

m exhaust raten is coupled w

bathrooms ntrol system. water-side HVzone type

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generate androom heating f 2 oC. Speradiant slabs wheat source inSpecific buil

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Figure 6 An

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Figure 7 Analy

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energy use onsumption nhout the contrven in Figure36.8%) with r

is observedall possible study. Deplo

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and cost

provide a gy (26.9%


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Table 8 Energy

MODEL

EM EM M EM +SSEM OPOSED cent saving = 10cent PV = PV g

th the contribuposed Designt saving (coing) and recents. Compar

ernative withohieve 33.2% ne can achieh supply sides the threshol

provements fnts. On-site relecting a tota

ergy performanfacilitate comformance of malized effecle (from 0.0 to

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odel. ASHRAsign Model arto 1) of the en

index point

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ments. Annuais about 701

ting, respectivsume 3088.8 kery rate (annuciency of 43.8

vings and LErelative energysed Design M

Baseline form LEED NC E

mance sectionite Renewabf renewable own in Table 8

y cost savings

ENERGY COSAVINGS

WITH PV (%

29.3 7.2

16.6 33.2 49.1

00x(1-Alternatigeneration/(Alte

ution of PV gn Model achiorresponding eives all possred to basout renewabltotal energy

eve 29.3% sae efficiency mld of significafor achieving enewables aloal of 5 LEEDnce and on-simparisons off alternative ctiveness cono 1.0) is deve

ving of each vable savingsalternatives. Mge is 49.1%

AE Baseline re found at lonergy cost effe

of 0.14, whi

as a backup n-site renewabction in wateal air to air.3 and 6344.9

vely. Three 30kWh electrici

ual overall resu%).

EED-NC Credy cost savings

Model with rthe basis of crEA Credit 1n. Similarly, ble section,

energy sy8.

s and PV contr

OST

%)

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AND POINT

6/0 0/0 2/3 7/0

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enerated electieves 49.1%

to 50.2% osible LEED Eseline, DSEMe energy sys

cost savingavings beforemeasures. SSEant energy per

LEED EA one has the poD EA pointsite renewablesf relative en

models basncept, an effeeloped (Figure

model is dis percentage aMaximum enwith ProposeModel and

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Proposed er bounds

ale. SSEM e 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.

Figure 9 Energy cost effectiveness scale

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 net-energy 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

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

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/energyplus/cfm/inputs/index.cfm

Effectiveness

Scale

Total LEED EA

Credit Points

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

1.0 13

Model Alternative/

Effectiveness Index

ASHRAE 90.1/0.0

PROPOSED DESIGN/1.0


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