simulation-based parametric analysis part i: one - andrew cmu
TRANSCRIPT
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Task 2.2.11 – CMU Report 02:
Simulation-Based Parametric Analysis Part I:
One-Factor-at-a-Time (OAT) Evaluation of Enclosure
Measures for Building 661
Department of Energy Award # EE0004261
Omer T. Karaguzel, PhD Candidate
Khee Poh Lam, PhD, RIBA, Professor Of Architecture
Center for Building Performance and Diagnostics
Carnegie Mellon University
February 2012
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TABLE OF CONTENTS
List of Figures 2
List of Tables 2
Introduction/Executive Summary 3
1. External Wall Insulation Measures 4
2. Roof Insulation Measures 10
3. Infiltration Rates 12
4. Glazing Types 13
5. Schematic Depiction of OAT Approach with Simulation Results 15
6. Conclusions 17
References 18
APPENDIX A – A Detailed Interpretation of Simulation Results for OAT Analysis 19
LIST OF FIGURES
Figure 1 Comparison of external wall thermal insulation levels 6
Figure 2 Varying thickness of PUR and effects on space heating and cooling energy 7
Figure 3 Varying thickness of PUR and effects on total building energy 7
Figure 4 Varying PUR thickness with different internal loads 8
Figure 5 Varying PUR thickness with different infiltration rates 9
Figure 6 Comparison of different thermal insulation materials with varying thicknesses 9
Figure 7 Schematic depiction of different roof alternatives developed for simulation analyses 11
Figure 8 Effects of roof thermal insulation thickness on space heating energy consumption 12
Figure 9 Variations of envelope infiltration rates and effects on space heating energy 13
Figure 10 Variations of glazing types and effects of space heating, cooling and fan energy 14
Figure 11 Parametric tree for external wall thermal insulation alternatives 15
Figure 12 Parametric tree for roof thermal insulation alternatives 16
Figure 13 Parametric tree for glazing alternatives 16
Figure 14 Parametric tree for infiltration rate alternatives 17
LIST OF TABLES
Table 1 A simple tool for R-value, and λ conversions 4
Table 2 Comparison of external wall thermal insulation alternatives 5
Table 3 Comparison of roof thermal insulation alternatives 11
Table 4 Comparison of glazing alternatives 13
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Introduction/Executive Summary
This study is focused on simulation-based parametric evaluation of building enclosure measures that can
be taken during the retrofit of Building 661 case. The main objective is to exemplify a simulation based
building analysis approach that includes iterative performance assessments on key design features so as to
construct a framework that can be utilized as an effective mean of design decision support during initial
phases of a comprehensive energy retrofit project. With proposed analysis methodology decision makers
responsible for selecting key components of energy retrofit projects can be supported with quantitatively
founded and highly structured (that can be repeatable for alternative design measures as well as building
cases) decision-making systems.
At this phases of the study focus is given to key components of external enclosure systems, namely
external walls, roofs, infiltration rates, and glazing types as described in the following sections. Current
study is connected to its former (Whole-building energy performance modeling as benchmarks for retrofit
projects) so that necessary parametric variations are deployed on ASHRAE 90.1 with Existing Envelope
baseline model option developed within the scope of this study. Therefore, the above mentioned baseline
model option forms a point of reference or energy performance benchmark to gauge relative effectiveness
of various enclosure design options investigated at this phase.
Parametric analysis approach followed throughout in current phase of the study can be simply defined as
one-factor-at-a-time (OAT) method in which all other input variables are kept constant at their initial
values (which are the ones assumed for the selected benchmark model) during perturbation of a specific
independent variable. Below is a list of main enclosure measures investigated in this study:
External Walls – Thickness of thermal insulation layer (m)
Roofs – Thickness of thermal insulation layer (m)
Infiltration Rate – Uncontrolled air flow rate per unit area of external surfaces (m3/s-m
2)
Glazing Type – Varying configurations of glazing units identified with overall performance
indicators of U-factors (W/m2K), Solar Heat Gain Coefficient (SHGC), and Visible
Transmittance
Please note that enclosure measures mentioned above are distinct categories of analysis due to the fact
that this phase of simulation-based parametric study does not include combinatorial effects where more
than one independent variable is perturbed during an individual simulation run. Relative energy
performance of alternative enclosure measures are compared based annual site energy use intensities
(kWh/m2) with relevant disaggregation (e.g., total of space heating, cooling, fans), and assembly
thicknesses (in the case of walls and roofs) together with the indication of percentage variations from the
reference model.
This report includes four successive sections for 4 building enclosure measure categories. Summary of
simulation input parameters (as independent variables) and simulation results (as dependent variables)
together with necessary interpretations of the findings are given at each section. A schematic depiction of
OAT method (with simulation results) is also provided in this report.
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1. External Wall Insulation Measures
The objective of external wall analysis is to cover a wide range of thermal insulation alternatives from
ASHRAE 90.1 compliant types up to super insulation level. A preliminary study is conducted on possible
types of insulation materials that can be incorporated into the simulation models. A total of four
types/categories of wall thermal insulation materials were analyzed; foam boards/rigid boards, batt
insulation, loose fill/powder insulation, and spray-filled insulation represented by varying thicknesses of
XPS (Extruded Polystyrene), Polyurethane, fiber glass, cellulosic insulation and Icynene insulation [1].
Such an analysis revealed that polyurethane foam board (PUR) (in the form of foam boards or rigid
panels) has the largest R-value per inch of thickness (around R-7 with a conductivity of λ=0.0206
W/mK). Therefore, simulation models from which main conclusions drawn are developed with varying
thickness of this particular type of insulation material. However, comparison of XPS, PUR, and cellulosic
loose fill insulation material types is also conducted separately. A simple MS Excel based calculation tool
is developed during insulation material analysis studies. This tool accepts two inputs from the user (λ-
thermal conductivity in SI units), and R-value per inch (in IP units) and provides not only unit
conversions between the two but also calculates the required amount of insulation thickness for various
total R-value targets (e.g., R-30, R-40, etc.) assumed for wall measures.
Table 1 A simple tool for R-value, and λ conversions
R-VALUE CALCULATOR
Parameter Value Unit
Lamda 0.020604 W/mK
Lamda/inch 0.811181 W/m2K
R-value 1.23277 m2K/W
R-IP per inch 6.99967 IP Units
R-60 thickness 8.571833 inch
R-60 thickness 21.77246 cm
R-40 thickness 5.714555 inch
R-40 thickness 14.51497 cm
R-30 thickness 4.285916 inch
R-30 thickness 10.88623 cm
R-ASHRAE thickness 0.514286 inch
R-ASHRAE thickness 1.306286 cm
R-value per inch 7 ft2-hr/Btu
R-value per inch 1.23277 m2K/W
U-value per inch 0.811181 W/m2K
Lamda 0.020604 W/mK
Insulation thermal resistive categories are R-60 super insulation (best case), R-40 and R-30 super
insulation (mid-range), R-3.6 ASHRAE 90.1 compliant insulation (for Climate Zone 4A), and R-0 non-
existent thermal insulation (actual situation).
User Input 1
User Input 2
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Table 2 Comparison of external wall thermal insulation alternatives
Insulation
Category
Insulation
Layer
Thermal
Resistance
Entire Wall
Thermal
Resistance
Thermal Insulation
Technology
Insulation Thermal
Properties
IP: R-value per inch SI: Conductivity
(W/mK)
Insulation
Thickness
Entire
Wall
Thickness
Percent
Change in
Wall
Thickness
Annual Energy
Use Intensity –
EUI
(Heating/Cooling/
Fans/Building
Total)
[kWh/m2]
Percent Change
in Annual EUI
(Heating/Coolin
g/Fans/Building
Total
[%]
Super Insulation
(Best Case)
R-60
R-value
10.5 m2K/W
R-64.5
U-factor
0.088 W/m2K
XPS Extruded Polystyrene (Foam Boards/Rigid
Panels)
IP: R-4.4 SI: 0.0327
34.5cm (13.5”)
70.06cm (27.5”)
97%
H: 77.8
C: 15.7
F: 5.6 ∑: 179.0
H: -19.8%
C: +4.1%
F: -6.7% ∑: -12.5%
Polyurethane Foam Board (Foam Boards/Rigid
Panels)
IP: R-7.0
SI: 0.0206
21.7cm
(8.5”)
57.1cm
(22.5”) 60%
Fiber Glass
(Batt Insulation) IP: R-4.3
SI: 0.0335 35.3cm (14”)
71.1cm (28”)
100%
Cellulosic Insulation
(Loose Fill/Powder)
IP: R-3.7
SI: 0.0389
41cm
(16”)
76.2cm
(30”) 114%
Icynene Insulation (Spray-applied)
IP: R-3.6 SI: 0.0400
42.2cm (16.5”)
77.4cm (30.5”)
117%
Super
Insulation
(Mid 01)
R-40
R-value 7.04 m2K/W
R-42.3 U-factor
0.127
W/m2K
XPS
Same as Related R-60
Values
23cm
(9”)
58.4cm
(23”) 64.2%
H: 78.4 C: 15.8
F: 5.6
∑: 179.8
H: -19.1% C: +4.1 %
F: -6.1%
∑: -12.2%
Polyurethane 14.5cm (5.7”)
50cm (19.7”)
40.6%
Fiber Glass 23.5cm
(9.3”)
59.1
(23.3”) 66.2%
Icynene 28.2cm
(11”)
63.5cm
(25”) 78.5%
Super
Insulation
(Mid 02)
R-30
R-value 5.28 m2K/W
R-34.6 U-factor
0.164 W/m2K
XPS
Same as Related R-60
Values
17.2cm
(6.8”)
52.8cm
(20.8”) 48.4%
H: 79.0 C: 15.7
F: 5.6
∑: 180.3
H:-18.5 % C: +4.1%
F: -6.0%
∑: -11.9%
Polyurethane 10.8cm (4.3”)
46.4cm (18.3”)
30.4%
Fiber Glass 17.7cm
(7”)
53.3cm
(21”) 49.8%
Icynene 21cm (8.3”)
56.6cm (22.3”)
59.1%
ASHRAE
2007 Baseline
(Standard)
R-3.6
R-value
0.45 W/m2K
R-10.9 U-factor
0.520
W/m2K
Nonres_Wall_Insulation
(Theoretical Wall
Insulation)
IP: R-2.94 SI: 0.049
5.4cm (2.1”)
40.8cm (16.1”)
14.7%
H: 84.17
C: 15.6 F:5.8
∑: 185.5
H: -13.2%
C: +3.6% F: -3.0%
∑: -9.3%
Existing
Envelope
(As-built)
R-0.0
R-value
0.00 W/m2K
R-3.6 U-factor
1.553 W/m2K
NONE N/A N/A 35.56cm
(14”) 0%
H: 97.0
C: 15.1
F: 6.0
∑: 204.7
H: 0%
C: 0%
F: 0%
∑: 0%
Note: H- Heating, C- Cooling, F- Fans energy. Sigma - ∑ indicates total building energy consumption (including heating, cooling, fans, interior lights, exterior
lights, interior equipment, water heating) excluding the exterior lights (which was originally assumed 19.6 kWh/m2 for the baseline). Negative (-) sign in front of
a percentage indicates an energy reduction/saving, whereas positive (+) is the reverse.
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Since all 5 different thermal insulation layers reached the same R-value but with different thicknesses
(due to their individual conductivities) only polyurethane material was used to obtain energy consumption
results for each different thermal resistance categories (e.g., R-60, R-40, and R-30) for super insulation
class. ASHRAE Baseline (R-3.6) was modeled with a theoretical thermal insulation material thermo-
physical attributes of which was directly taken from DOE Reference Medium Office (for Climate 4A).
All of the insulation layers (including ASHRAE 2007 baseline insulation) were assumed to be applied to
the inner face of the existing external walls and finished with double-layer gypsum wall board (GWB).
Therefore, the entire wall assembly with thermal insulation had the following material layers from outside
to inside: (1) Brickwork 4” + (2) Air Gap 1” + (3) Concrete Blocks 8” + (4) Thermal Insulation (Varies) +
(5) GWB 2”. Table 2 given above indicates both single thermal layer R-value and entire wall assembly R-
value. All simulation models are assumed to have 1.0 ACH (1/h) of air-infiltration (for occupied and
conditioned thermal zones) decreased to 25% of maximum during HVAC day-time operation (based on
DOE Reference Models).
As can be seen from Table 2, largest possible reduction is space heating energy (the most dominant end-
use energy category) as well as total building energy is observed for R-60 thermal insulation option. Such
a reduction is at the expense of using around 35cm (13.5”) of insulation layer with 97% increase in
overall wall thickness. On the other hand, even with the inclusion of R-3.6 insulation (ASHRAE
compliance) level around 13.2% energy reduction can be obtained for heating energy. It can be concluded
that insulation levels of R-30, R-40, and R-60 varies only marginally from each other in terms of energy
performance.
Figure 1 Comparison of external wall thermal insulation levels
Simulation results reveal that the first couple of inches of thermal insulation provide the largest deviation
from no-insulation case. From that point onwards, only marginal energy saving gains can be obtained
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(maximum change of 6.6% heating energy from R-3.6 to R-60 insulation). Results also indicate that
focusing solely on external wall thermal insulation thickness is not enough to provide optimized energy
savings where biggest effect is obtained by incorporating minimal resources (e.g., material thickness).
Evaluation of the simulation model’s sensitivities with respect to other enclosure measures should be
realized. To do this, a series of parametric studies are conducted on varying thicknesses of individual
insulation materials with a higher resolution (per inch simulation analysis). Below are given the results of
such a study focused on polyurethane foam board (PUR) insulation material.
Analysis of PUR Thickness
In this analysis, thickness of PUR material is varied from 1” (0.0254m) up to 9” (0.2286m) with intervals
of 1” while all other simulation inputs are kept constant at their benchmark values. Thicknesses
corresponding to R-30 (T 4.3”), R-40 (T 5.7”) and, R-60 (8.5”) are also indicated among all alternatives.
Figure 2 Varying thickness of PUR and effects on space heating and cooling energy
As shown in Figure 2, space heating energy gains after T-4” is marginal with relative change between T-
1” and T-4” about 11.4%.
Figure 3 Varying thickness of PUR and effects on total building energy
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Effect of different PUR insulation is almost negligible under the climate of Philadelphia, Pa and for B-
661 case (Figure 2). As space heating is the dominant end-use energy category, a similar insulation
thickness effect is observed for total building energy consumption. Model response to PUR thickness falls
to a plateau after T-4”, and only marginal gains are found up to the upper thickness boundary of T-9”
which is even higher than T-8.5” super insulation case.
Analysis of PUR Thickness with Internal Load Modifications
Possible effects of internal heat gains (internal loads) due to lights and equipment on the model response
with varying PUR thickness are examined in this analysis. Two distinct internal load characteristics are
analyzed which are high loads (where LPD and EPD values are 10.76 W/m2 for all thermal zones – equal
to benchmark levels) and low loads (where LPD and EPD are reduced by half, 5.00 W/m2 with respect to
benchmark levels).
Figure 4 Varying PUR thickness with different internal loads
As can be seen from Figure 4, decreasing internal gain characteristics has profound effect on space
heating energy (with an increase of 30% at T-1” level) since less heat is generated from internal sources
which should be complemented by the HVAC system. However, model behavior with respect to PUR
thickness seems to be unchanged and although at different consumption levels, space heating energy falls
into a plateau after T-4” PUR thickness.
Note that envelope infiltration rate for PUR thickness and PUR thickness with different load analyses is
assumed to be 0.000302 m3/s-m
2 (from 0.24 to 0.44 ac/h for different thermal zones) of external envelope
surface as obtained from DOE reference models.
Analysis of PUR Thickness with Infiltration Rate Modifications
This analysis reveals PUR insulation characteristics under different envelope infiltration rates. Three
different categories of infiltration rate are simulated, 0.10 ac/h (super-tight envelope), 0.60 ac/h
(moderately tight envelope), and 0.24-0.44 ach/h (DOE reference model-compliant envelope). It can be
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concluded from Figure 5 (below) that envelope infiltration rates have significant effects on space heating
energy (inversely proportional) without any effect on the model behavior to varying PUR thicknesses.
Figure 5 Varying PUR thickness with different infiltration rates
Analysis of Varying Thicknesses of Different Thermal Insulation Materials
A range material thickness from T-1” to T-16” is analyzed for three different thermal insulation material
types which are XPS, PUR, and cellulosic loose fill insulation. The three types differ from each other by
their thermal resistance per inch characteristics (XPS R-4.4, PUR R-7.0, and Cellulosic R-3.7 per inch of
thickness). Among all alternatives, PUR gives the highest insulation capacity per thickness, whereas
cellulosic insulation type requires around 1.89 times more thickness to provide the same thermal
resistance.
Figure 6 Comparison of different thermal insulation materials with varying thicknesses
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PUR does not provide considerable space heating energy gains after T-4”, this critical point is reached at
T-8” for XPS and at T-10” for cellulosic type. Such a behavior clearly reveals the importance of using
high-grade thermal insulation materials so as to keep overall wall thicknesses (and related construction
interventions at reasonable levels). Even with relatively low performance insulation materials thicknesses
above T-10” provide negligible variations in space heating energy consumption.
2. Roof Insulation Measures
Roof insulation measures consist of 6 alternatives including the benchmark model. They have varying
thermal insulation levels starting from R-5 (benchmark) up to R-90 (super insulation) including R-14.7
(ASHERAE 90.1 compliant), R-30, R-40 and R-70 insulation cases. Building 661case has two different
roof configurations as given below (for gym section on the west side, and front office section on the east
side). Increasing thicknesses of roof thermal insulation are applied as two distinct layers assumed to be
applied above and below of precast concrete structure existing for both roof configurations.
ROOF ASSEMBLY of Building 661 GYM SECTION
R-5 (Existing) : Outside >> Single ply EPDM Roof membrane (1/2”) + PUR Foam Board (1”) + Precast
Concrete (4”) >> Inside
Other Roof Alternatives: Outside >> Single ply EPDM Roof Membrane (1/2”) + Insulation Layer 2 +
Precast Concrete (4”) + Insulation Layer 1 + Gypsum Board (1/2”) >> Inside
ROOF ASSEMBLY of Building 661 FRONT OFFICE SECITON
R-5 (Existing): Outside >> Roof Slate Tiles (1/2”) + Nailing concrete (2”) + Precast Concrete (3/2”) +
Fiberboard Ceiling (1/2”)
Other Roof Alternatives: Outside >> Roof Slate Tiles (1/2”) + Nailing Concrete (2”) + Insulation Layer
2 + Precast Concrete (3/2”) + Insulation Layer 1 + Gypsum Board (1/2”) >> Inside
In Table 3 given below is listed roof insulation R-values of different alternatives, entire roof R-value,
entire roof U-factor in SI units, insulation thicknesses for the two separate layers, total roof thickness
together with percent deviation from the benchmark thickness. Table 3 also reveals simulation results of
heating, cooling, fan and total building energy in a comparative approach.
Roof insulation attribute listed in Table 3 below are for the roof of GYM Section only. Thermal insulation
material for alternative roof assemblies of R-90, R-70, R-40, and R-30 is assumed as high performance
polyurethane foam boards with R-7 per inch (0.0206 W/mK thermal conductivity). However, insulation
layer for R-14.7 (ASHRAE) case is imported from DOE Reference Models in compliant with maximum
U-factor requirements for roof assemblies in Climate Zone 4A (Philadelphia). Such an insulation layer
has R-2.94 per inch resistance capacity (0.049 W/mK). On the other hand, R-5 (Existing) case represents
as-built conditions where polyurethane (PUR) foam boards have R-5.1 per inch resistance to heat flows
(0.028 W/mK). It should be noted that parametric variations are only applied to roof assemblies and all
other design parameters are left unchanged (as-built conditions). Therefore, simulation model alternatives
represent building cases with increasing levels of thermal insulation for the roof assembly while having
low-resistance, low-performance external walls and window assemblies. Air infiltration rate is assumed as
ACH 1.00 (1/h) for all thermal zones of the model. Building 661 front office section roof does not include
a thermal insulation layer and not shown in Figure 7 given below. This roof assembly has a total roof R-
value of 3.26 (U-factor 1.739 W/m2K).
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Table 3 Comparison of roof thermal insulation alternatives
Roof
Insulation
R-value IP
[ft2 oF h/Btu]
Entire
Roof
R-value
IP
[ft2 oF
h/Btu]
Entire
Roof
U-factor
SI
[W/m2K]
Insulation
Layer 1
Thickness
[Inch/cm]
Insulation
Layer 2
Thickness
[Inch/cm]
Total
Roof
Thickness
[Inch/cm]
Percent
Change
in Roof
Thickness
[%]
Annual Energy Use Intensity –
EUI
(Heating/Cooling/Fans/Building
Total)
[kWh/m2] [kBtu/ft2]
Percent Change in Annual EUI
(Heating/Cooling/Fans/Building Total
[%]
R-90 R-93 0.061 6”/15.24 7”/17.78 18”/45.72 227% H: 74.7 C: 14.5 F: 5.2 ∑: 174.3
H: 23.6 C: 4.6 F: 1.6 ∑: 55.2 H:-23% C: -3.8% F: -13.8% ∑: -14.8%
R-70 R-71.8 0.079 4”/10.16 6”/15.24 15”/38.1 172% H: 75.2 C: 14.6 F: 5.2 ∑: 174.8
H: 23.8 C: 4.6 F: 1.6 ∑: 55.4 H: -22.5% C: -3.6% F: -13.5% ∑: -14.6%
R-40 R-44.3 0.128 3”/7.62 3”/7.62 11”/27.94 100% H: 76.6 C: 14.6 F: 5.2 ∑: 176.4
H: 24.2 C: 4.6 F: 1.6 ∑: 55.9 H: -21.0% C: -3.6% F: -12.5% ∑: -13.8%
R-30 R-33.8 0.168 3”/7.62 1.5”/3.81 9.5”/24.13 72% H: 77.8 C: 14.7 F: 5.3 ∑: 177.8
H: 24.6 C: 4.6 F: 1.6 ∑: 56.3 H: -19.8% C: -2.6% F: -11.6% ∑:-13.1 %
R-14.7
(ASHRAE)
R-17 0.334 3”/7.62 2”/5.08 10”/25.4 81% H: 82.4 C: 14.9 F: 5.5 ∑: 182.7
H: 26.1 C: 4.7 F: 1.7 ∑: 57.9 H: -15.1% C: -1.6% F: -8.6% ∑: -10.7 %
R-5
(EXISTING)
R-7 0.814 - 1”/2.54 5.5”13.97 0% H: 97.0 C: 15.1 F: 6.0 ∑: 204.7
H: 30.7 C: 4.8 F: 1.9 ∑: 62.8 H: 0.0% C: 0.0% F: 0.0% ∑: 0.0%
Building 661 GYM Section R-5 (Existing)
Building 661 FRONT OFFICE Section No Insulation (R-3.26 entire roof)
Building 661 Roof Alternatives GYM Section
R-70 High Performance Roof
Building 661 Roof Alternatives FRONT OFFICE
R-70 High Performance Roof
Figure 7 Schematic depiction of different roof alternatives developed for simulation analyses
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Table 3 above shows that about 65% of maximum possible energy gains can be achieved only by
implementing ASHRAE 90.1 2004 compliant roof assembly. Increasing roof insulation level up to super-
insulated category of R-90 can provide23% reduction in space heating energy, and the combined total
energy gain is 14.8% with this alternative. Only marginal variations are observed for R-40, R-70 and R-
90 insulation alternatives.
Figure 8 Effects of roof thermal insulation thickness on space heating energy consumption
R-30 roof insulation is found to be a critical point in the observation of model response. From this point
onward only marginal variations/decreases are seen with increasing levels of insulation. Maximum
reduction between any two points is observed between R-5 existing and R-14.7 ASHRAE 90.1 2004
compliant cases.
3. Infiltration Rates
Infiltration rates of the external envelope are varied between 0.10 ac/h and 0.60 ac/h with 0.05 ac/h
increments and the model response is analyzed at each interval point. Changes of infiltration rates are
applied only to occupied and conditioned thermal zones of the simulation models. Other zones are
assumed to have 0.000302 m3/s-m
2 of infiltration rates which corresponds to varying levels of ac/h based
on each zones volume and exposed surface area. As mentioned before, air-infiltration rates are decreased
(by the use hourly, fractional schedules) to 25% of their maximum assumptions during HVAC day-time
operation (based on DOE Reference Models inputs).
Figure 9 indicates an almost linear (with R2= 0.9966) positive relationship between envelope infiltration
rate and space heating energy consumption. Decreasing infiltration rate down to 0.1 ac/h level
(representing a super-tight/ Passive House standard infiltration) yields annual space heating EUI below 28
kWh/m2, on the other hand a moderate/average rate of 0.6 ac/h can result in an increase of around 100%.
The steepness of the correlation indicates the high sensitivity of model response to envelope infiltration
rate from space heating point which is the most dominant end-use energy category for B-661 case.
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Figure 9 Variations of envelope infiltration rates and effects on space heating energy
4. Glazing Types
Effects of various glazing types with different thermal resistance and solar and visible transmittance are
analyzed in this section. A total 10 different glazing alternatives are considered and key properties are
listed in Table 4 below, however 6 out 10 alternatives are incorporated into the simulation models and
analyzed in detail. These types are single clear glazing (reflecting the existing case – benchmark model),
double and triple alternatives with low-E coating and filled with either air or argon gas and a super-
insulated case which is a quadruple glazing with krypton mid-pane gas type. All glass panes are 6mm
thickness (except single clear type – 3mm) and mid-pane gas has a thickness of 13mm. No change was
applied to window frames which are assumed as 400mm wooden for existing case and 400mm UPVC for
other alternatives. Glazing options are applied evenly to all window surfaces facing all orientations as
well as to skylight components.
Table 4 Comparison of glazing alternatives
Window Alternative
Assembly Explanation U-factor (W/m
2K)
R-Value (hft
2
oF/Btu)
SHGC Visible
Transmittance Frame Type
Frame U-factor (W/m
2K)
Single Glazing 3mm clear glazing 5.89 0.97
0.86 0.89 4cm
wooden 3.633
Double Glazing (Air) – low-E
6/13/6mm low-E with air gas 1.91 2.9
0.59 0.74 4cm UPVC
3.476
Double Glazing (Air) - clear
6/13/6mm clear with air gas 2.66 2.1
0.70 0.78
Double Glazing (Argon) – low-E
6/13/6mm low-E with argon gas
1.81 3.1
0.59 0.74
Double Glazing (Argon) – clear
6/13/6mm clear with argon gas
2.51 2.3
0.70 0.78
Triple Glazing (Air) – low-E
6/13/6/12/6mm low-E with air gas
1.01 5.6
0.46 0.63
Triple Glazing (Air) - clear
6/13/6/12/6mm clear with air gas
1.72 3.3
0.61 0.69
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Table 4 - continued
4cm UPVC
3.476
Triple Glazing (Argon) – low-E
6/13/6/12/6mm low-E with argon gas
0.87 6.5
0.46 0.63
Triple Glazing (Argon) – clear
6/13/6/12/6mm clear with argon gas
1.59 3.5
0.61 0.69
Quadruple Glazing (Krypton)
5.7mm clear glass + 9.7mm krypton + Heat Mirror suspended film 1 + 9.7mm krypton + HM Suspended film 2 + 9.7mm krypton + 5.7 mm clear glass
0.47 12.19 0.20 0.478
Quadruple glazing with krypton represents the highest overall performance in terms of U-factor (0.47
W/m2K) at the expense of a relatively low SHGC (0.20). The lowest U-factor achieved with double
glazing alternatives is 1.81 W/m2K with the inclusion of a low-e coating and argon mid-pane gas. A triple
glazing alternative with similar characteristics (low-e + argon gas) results in a U-factor of 0.87 W/m2K.
Benchmark model representing existing conditions has a 3mm single clear glass with the largest U-factor
of 5.89 W/m2K and also the highest SHGC of 0.86.
Figure 10 Variations of glazing types and effects of space heating, cooling and fan energy
It is seen that model behavior is not sensitive to changes of glazing types beyond the critical point of
double glazing with air (maximum reduction after this point is only 3.7% for space heating). However,
from single clear to double with air gas option, 10.2% energy reduction is achievable. The super glazing
case of quadruple with krypton gas type results in a slight increase with respect to triple glazing with
argon option due to reduced SHGC. Such an effect is at the opposite for cooling energy consumption.
There exist marginal variations in fan energy by changing glazing types.
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5. Schematic Depiction of OAT Approach with Simulation Results
Below are presented schematic depictions of the one-factor-at-a-time method followed during parametric
simulations performed to evaluate relative effectiveness of a number energy retrofit measures pertaining
to building enclosures. There are 4 different schemas in the form of parametric tree in which each
enclosure alternative is represented with node including key information about the varied component.
Nodes are layered as rows where each row contains all variables within a single enclosure category.
Nodes are connected by lines so as to indicate a model alternative and each connecting line is
differentiated by a color and an end node revealing key simulation results (and necessary interpretations)
of a single model alternative.
External Wall Thermal Insulation
Figure 11 Parametric tree for external wall thermal insulation alternatives
Such a representation technique can be used as a decision support medium during initial phases of a
retrofit project in which the need for relative comparisons of various retrofit alternatives is at its peak. The
schemas given here are developed by the use of Microsoft Visio diagramming program.
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Figure 12 Parametric tree for roof thermal insulation alternatives
Figure 13 Parametric tree for glazing alternatives
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Figure 14 Parametric tree for infiltration rate alternatives
6. Conclusions
Parametric simulations conducted on four key enclosure retrofit measures (external walls, roof,
infiltration rates, and glazing types) are explained and summarized in this study. Parametric modeling
approach followed here is one-factor-at-a-time (OAT) method with which effects due to variation of
individual enclosure measures are investigated on simulation outcomes while keeping all other variables
at their initial values. Some key findings of this study can be listed as (please find a more detailed result
interpretation in APPENDIX A):
Largest jumps between any two alternatives are achieved from existing case to ASHRAE 90.1
2004 compliant envelope measures.
Maximum possible energy saving on space heating is no more than 30.5% (by the incorporation
of a single measure at a time) achieved with decreasing envelope infiltration rate to 0.10 ac/h
level.
Maximum space heating energy (19.8%) saving for external wall is achieved with the super-
insulated case off R-60. However, R-30 wall insulation already provides 15% reduction without
even considering R-40 or R-60 which varies only marginally from the critical point of R-30 for
walls category.
ASHRAE compliant roofs alone can provide 15% reduction on heating energy, R-30 roofs can
only increase possible savings to 17.1%. Whereas super-insulated case of R-90 roofs can
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maximized savings up to 23%. For roofs R-30 appears to the critical point from which onwards
energy savings fall into a plateau effect.
Due to 22.2% of window-to-wall ratio, glazing alternatives can decrease space heating energy to
the level of 13.6% (12.2% at the total energy usage category) with the incorporation of quadruple
glazing with krypton mid-pane gas (which may possibly come with a significantly increased cost
premium). However, Double glazing with low-e coating and argon fill can save 13.8% of heating
energy on an annual basis.
Infiltration rate is strongly correlated with space heating energy with an almost linear, positive
relationship. The sensitivity of model behavior to the alterations of infiltration rate is found to be
significantly high.
In all cases, space cooling energy, and fan energy are not sensitive enough (to envelope
variations) to create considerable changes at overall building performance.
Future work can be enhancing the current parametric approach by taking into account correlations
between different enclosure measures. Since OAT method is not functional to reveal such interactions.
Therefore, this study will proceed with combinatorial parametric analysis in which all possible
combinations of current design parameters are analyzed to reveal interactions.
References
[1] U.S. DOE (Department of Energy). 2011. “Building Energy Data Book - 5.1 Building
Materials/Insulation” Accessed March 28 2011. http://buildingsdatabook.eren.doe.gov/.
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APPENDIX A – A Detailed Interpretation of Simulation Results for OAT Envelope Analysis
Improvements of total building energy use merely based on external wall thermal insulation can
be up to 12.5% achieved with R-60, 8.5” PUR foam board insulation with respect to baseline
model. This same configuration provides a19.8% improvement in space heating energy use.
However, use of an ASHRAE 90.1 2004 compliant external wall assembly already provides 9.3%
improvement (18.5% for space heating energy). Such a wall assembly requires only 2.1” of an
theoretical insulation layer with R-2.94 per inch thermal resistance.
Alternatives of R-30 and R-40 lie between minimum and maximum improvements of 11.9% and
12.2% without a significant variation.
Performance curves generated for varying thicknesses of PUR foam insulation applied to external
walls from inside reveal considerable diminishing returns on space heating (and total building
energy) use starting from first several inches (3.5”-4”). As R-value per inch (resistive capacity)
for an insulation material decreases, layer thickness for which diminishing returns (plateau effect)
is observed increases. For example, for loose fill and powder type insulation materials, the
plateau effect on space heating energy is observed at thicknesses of 9” to 10”.
Cooling energy consumption is marginally affected by thermal resistance of external walls. An
incremental trend is observed with a maximum of 4.1% with respect to baseline.
Change of internal heat gains (indicated by LPD and EPD values) has significant impact on space
heating energy (with a change of 15 kWh/m2 or 34%). However, the general characteristics of
performance curves for varying thickness of insulation remain unchanged.
A similar trend is observed for envelope air-tightness (indicated by infiltration rate – ACH).
A strong linear correlation is found between infiltration rate and space heating energy
requirements. Improvements of total building energy use merely based on external wall thermal
insulation can be up to 12.5% achieved with R-60, 8.5” PUR foam board insulation with respect
to baseline model. This same configuration provides a 19.8% improvement in space heating
energy use.
However, use of an ASHRAE 90.1 2004 compliant external wall assembly already provides 9.3%
improvement (18.5% for space heating energy). Such a wall assembly requires only 2.1” of a
theoretical insulation layer with R-2.94 per inch thermal resistance.
Alternatives of R-30 and R-40 lie between minimum and maximum improvements of 11.9% and
12.2% without a significant variation.
Performance curves generated for varying thicknesses of PUR foam insulation applied to external
walls from inside reveal considerable diminishing returns on space heating (and total building
energy) use starting from first several inches (3.5”-4”). As R-value per inch (resistive capacity)
for an insulation material decreases, layer thickness for which diminishing returns (plateau effect)
is observed increases. For example, for loose fill and powder type insulation materials, the
plateau effect on space heating energy is observed at thicknesses of 9” to 10”.
Cooling energy consumption is marginally affected by thermal resistance of external walls. An
incremental trend is observed with a maximum of 4.1% with respect to baseline.
Change of internal heat gains (indicated by LPD and EPD values) has significant impact on space
heating energy (with a change of 15 kWh/m2 or 34%). However, the general characteristics of
performance curves for varying thickness of insulation remain unchanged.
A similar trend is observed for envelope air-tightness (indicated by infiltration rate – ACH).
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A strong linear correlation is found between infiltration rate and space heating energy
requirements.
Super insulated roofs (with 13” R-90 thermal insulation) can only decrease annual total building
energy use by 14.8% (with 23% reductions of space heating energy) with a trade-off of 227%
increase in overall roof construction thickness (in addition to first-cost increments). ASHRAE
90.1 2004 compliant roof assembly with R-14.7 and 5” of insulation (81% increase of roof
thickness) provides 10.7% reduction in total building energy use (with 15.1% for space heating).
There are insignificant differences in total building use between R-30, R-40, R-70, and R-90 roof
thermal insulation in Building 661.
Similar to external walls, cooling energy use is not sensitive to changes of thermal insulation
layer thicknesses for the climatic location of Building 661.
About 10.6% reduction in space heating energy use can be achieved by upgrading south facing
windows to double clear glazing and all other windows to double low-e glazing (with air as the
infill gas). Changing the infill gas material to argon provides a variation of 0.6% maximum.
Similar marginal variations are observed for alternative models equipped with triple glazing with
air or argon gas and even with high-performance/high-cost quadruple glazing (with krypton gas
and suspended heat mirror films). Space heating energy reduction is not more than 13.7% with
such glazing type.
As an overall conclusion from the first phase of parametric studies, it can be said that energy
performance cannot be significantly improved beyond ASHRAE 90.1 2004 standard envelope
with isolated effects of improvements of independent envelope assemblies. However, this phase
has not investigated the integrated, combined effects of incorporating multiple design parameters
at a time. Second phase of parametric studies (combinatorial parametrics) will focus on
interactive effects of deploying multiple envelope efficiency measures outlined in the first phase
of the project.