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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.