appln assignment #2

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Course Instructor: Dr. Adel Abdou Student ID: g201004120

King Fahd University of

Petroleum & MineralsCollege of Environmental Design

Architectural Engineering Department ARE 510 Computer Utilization in Architectural Engineering

Syed Ashraf Tashrifullahi

Application Assignment #2



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Course Instructor: Dr. Adel Abdou 1 Student ID: g201004120

Contents

1. Introduction ..................................................................................................................................... 3

1.1 Building Envelope........................................................................................................................... 3

1.2 Importance of Assessing Building Envelope .................................................................................... 3

1.3 Software Tool................................................................................................................................. 4

2. Modeling & Simulation of the Best Overall Wall System ................................................................. 5

2.1 Simulation Results of Previous Assessments .................................................................................. 5

2.2 Modeling of the Best Wall System .................................................................................................. 6

2.3 Simulation of the Modeled Wall System......................................................................................... 7

2.4 Assessing the Results ..................................................................................................................... 9

2.4.1 Temperature and Moisture Content ........................................................................................ 9

2.4.2 Total Moisture Content ......................................................................................................... 11

2.4.1 Transfer Rate of Heat ............................................................................................................ 12

3. Comparison with Previous Assessments......................................................................................... 13

4. Conclusion ..................................................................................................................................... 14

References............................................................................................................................................. 15



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List of Figures

Figure 1: Wall Systems #2 & #3 respectively. .................................................................................................................... 5

Figure 2: (a) Exterior Option Selection, (b) Interior Data Setting ........................................................................... 7

Figure 3: Simulation of Wall Assembly .................................................................................................................................. 8

Figure 4: (a) Simulation of Wall Assembly (January), (b) Simulation of Wall Assembly (June) ........... 10Figure 5: Total Moisture Content ........................................................................................................................................... 11

Figure 6: Heat Transfer ............................................................................................................................................................... 13

List of Tables

Table 1: Materials selection of Wall #2 ................................................................................................................................. 6

Table 2: Moisture Content by Layer ..................................................................................................................................... 12



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1. Introduction

1.1 Building Envelope

For the design, construction and operation of a facility, there is an especially important

interface between the indoor and outdoor environments which is known as building envelope. Itis one of the most important elements in ensuring comfort and is comprised of the outer elements

of a building such as foundations, walls, roof, windows, doors and floors [1]. The main function

of the building envelope is to manage the flow of air, moisture and heat between different

environments, typically exterior and interior. This helps prevent material deterioration, corrosion,

mold growth and heat loss [2]. Besides this, the building envelope serves many prime functions

of which the functions of interest for the present study are thermal control and moisture control.

1.2 Importance of Assessing Building Envelope

Sustainability now-a-days is an increasing priority for facilities [1]. Building construction

and operation have an enormous direct and indirect impact on the environment in terms of many

factors of which one that I feel the most important for the current study is energy use. The impact

of both thermal and moisture transfer could be accountable for this. The fact, increase in the heat

gain increases the cooling load and results in higher use of energy, does not support the issues

pertaining to sustainability. Similarly, moisture transfer within a wall assembly could result in

concealed condensation and is accountable for increased rate of heat transfer, mold growth and

air quality.

Heat is conducted most easily through solid materials. The goal for any wall should be to

minimize the amount of conductivity through the materials in the wall, including the framing

materials and the insulating materials. Also, the potential for condensation occurring in walls is

one of the most important considerations when deciding on the building envelope system. This

decision for the selection of the best envelope system, for example a wall system, requires an in

depth assessment and can be accomplished by state of art tools.

Recent trends in North America towards green buildings resulted in the development and

increased popularity of several green building assessment tools. These tools were primarily

developed to assess, or measure specific aspects of a building, pertaining to sustainability goals

[3]. The tools emphasize on early design phase of the building. The initial design ideas are



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conceptualized with the formulation of building project requirements. Most tools focus on three

main areas; energy, water and material use in buildings. The conceptual approaches adopted and

technical implementation of these tools varies significantly [4]. The former area of study

(energy) is of primary interest to this report.

1.3 Software Tool

For the present study of hygrothermal (moisture and thermal) analysis, one of the tools

available to assess the flow of heat and moisture through the wall section is hygIRC. It is a 1-D

state-of-the-art hygrothermal model developed to help building design professionals in

simulating the response of each element to environmental conditions on either side of the

envelope on an hourly basis by allowing them to choose optimal building envelope components

and systems. It produces information on the temperature and relative humidity distributions

within the wall assembly. The program is targeted to engineers, architects, building scientists,

contractors, and students in investigating the transfer of heat, air, and moisture through common

construction materials [5].



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2. Modeling & Simulation of the Best Overall Wall System

2.1 Simulation Results of Previous Assessments

Previous assessments constituted the analysis of wall systems #2 and #3, as shown in

figure 1, from the point of view of thermal and moisture transfer using the state of art

CONDENSE.

Figure 1: Wall Systems #2 & #3 respectively.

Both wall systems were analyzed for the given conditions of Dhahran city taking into

consideration the heat gain, thermal resistance, cost aspect and most importantly the purpose for

which the software tool ³CONDENSE´ was built, i.e., the risk of condensation. The assessmentdid not reveal any sort of condensation in any part of the wall assembly for the given conditions

and resulted in the selection of wall #2 based on the heat gain, thermal resistance and cost

aspects. A sensitivity analysis was also carried out to assess the behavior of wall #2 by varying

the thickness of insulation while keeping relative humidity constant and vice-versa.



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Condensation was observed on the exterior surface of wall #2 where changes to relative humidity

were found accountable [6].

For the present study/assessment, the best wall system, i.e., wall #2, as per the assessment

results of CONDENSE, the same wall system was modeled using hygIRC. This was

accomplished by considering either same or similar materials while constructing the wall

assembly depending upon the material database of hygIRC compared to the material database of

CONDENSE. The thickness of various layers in this analysis was considered the same as it was

in the previous assessment. Same boundary conditions were imposed and the assessments were

carried out from the point of view of thermal and moisture transfer only.

2.2 Modeling of the Best Wall System

As mentioned earlier, the best wall was considered for the purpose of thermal andmoisture analysis. The wall #2, as shown in figure 1, is composed of a brick with an air gap,

rigid insulation and concrete block in between followed by interior finish from outside to inside

along its cross-section. This type of wall system is known as ³Cavity Wall Insulated in Cavity´

meaning that the insulation is installed within the cavity in between the wall. Table 1 shows the

selection of materials for various components of wall #2 depending upon the material database of

hygIRC compared to CONDENSE.

Table 1: Materials selection of Wall #2S. No. Component Material Thickness (mm)

1 Brick (Outer Wythe) Concrete brick 100

2 Rigid Insulation Extruded Polystyrene 50

3Concrete Block

(Inner Wythe)Aerated Concrete 75

4 Interior Finish Gypsum 13

The materials selection for inner wythe and interior finish in this analysis had to be different

compared to the previous assessment because of their unavailability in hygIRC materials

database. The properties of the selected materials for hygIRC were first observed and compared

by using the ³value´ command in CONDENSE. The materials very close to the materials in

CONDENSE were selected based on their density. The thickness of all components of the wall

assembly was kept the same.



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2.3 Simulation of the Modeled Wall System

The modeled wall system was simulated for the simultaneous thermal and moisture

transfer under the weather conditions of Dhahran city, (2002). The simulation variables were set

to temperature and total moisture content. The exterior conditions were set and analyzed using

the Dhahran weather file of the year 2002. Preference to time selection, as shown in figure 2 (a),

was given to ³years´ and the input type selected was ³system input´ as it was instructed to assess

the wall assembly using Dhahran 2002 weather file. The selection of system input option in

hygIRC constructs the weather file from the database and does not require inputting constant

environmental conditions by the user. This helps in the analysis of the wall assembly taking into

consideration the real life environmental conditions of the year 2002 for Dhahran city.

(a) (b)

Figure 2: (a) Exterior Option Selection, (b) Interior Data Setting

With respect to the data pertaining to the interior space, constant values were given as

input to the software tool. This was purposely done in relation to the assessment carried out in

application assignment #1 [6]. The indoor data settings there were as shown in figure 2 (b). This

helped in the preparation of a base for the comparison of the two wall assemblies using the two

software tools which is discussed later in this report.

Over to the structure of the wall assembly, its orientation and inclination are east oriented

and 90o

respectively. The layers of the wall assembly were selected as described in the modeling

part of this report. The indoor ventilation pressure in the air diffusion tab was provided with a

value of 5 Pa. The internal pressure need only be slightly higher than ambient on average to

achieve the goal of excluding humid outdoor air from building cavities. In any case, internal

pressure shall not be greater than 10 Pa [7]. There are some suggestions of recommended

pressurization levels of the order 5 Pa to perhaps 10 Pa. Each building¶s pressurization strategy



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should be designed based on the climate, the building height and the envelope leakage [8].

Because the pressurization varies from 0 to 10 Pa, average value of 5 Pa was selected for the

current study. The initial conditions were set based on temperature and RH. Constant conditions

were set for the whole structure of the wall keeping in mind the time constraints for the report.

The simulation parameters were set for the complete year of 2002 for Dhahran city. The

simulation was then started and observations were made.

Figure 3: Simulation of Wall Assembly

Figure 3 shows the temperature and total moisture content within the wall assembly for the

complete year. The temperature is found to be at its peak during the summer months with themoisture content being at its minimum values. This implies that at the verge of completion of

winter season, the total moisture content gradually decreases and reaches its minimum value

during the summer season. The location of Dhahran city being very close to the coast results in

increased humidity levels even reaching up to around 95% during the summer period. The

decreased levels of moisture content within the wall during this period are an appreciation of the



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wall system to be suitable for the climatic conditions of Dhahran city from the perspective of

moisture transfer. This is an indication of reduced risk of concealed condensation.

Figure 4 (b) shows the variations in temperature and moisture content during the month of June.

It can be seen that the exterior temperature is high compared to interior. There was gradual

decrease in the temperature in the air gap. The presence of insulation resulted in an increase in

the slope of the curve depicting in much more decrease in the temperature. Decrease in the

moisture content was observed. This was as a result of the insulation material.

2.4 Assessing the Results

The results were assessed considering the following indicators:

y Temperature and Moisture Content

y Total Moisture Content

y Transfer Rate of Heat

2.4.1Temperature and Moisture Content

Shown in figure 4 are animation stills of the simulation carried out on the wall assembly.

In order to report on the performance of the assembly during the simulation period, two stills

were captured and analyzed. The first one, as shown in figure 4 (a), was for the month of

January. Gradual increase in the temperature from outside to inside can be seen. A sudden

increase in the temperature was observed in the thermal insulation layer. Because the indoor

environment is at a higher temperature compared to outside during the winter season, the

insulation reduces the amount of heat to pass through to the outer environment. Higher value of

moisture content was observed in aerated concrete layer as it has high moisture absorbing

capacity. The sudden increase in the curve in that layer may be due to the presence of moisture

(45%, as given as input for the interior space) in the interior space.

Figure 4 (b) shows the variations in temperature and moisture content during the month

of June. It can be seen that the exterior temperature is high compared to interior. There was

gradual decrease in the temperature in the air gap. The presence of insulation resulted in an

increase in the slope of the curve depicting in much more decrease in the temperature. Decrease

in the moisture content was observed. This was as a result of the insulation material.



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Figure 4: (a) Simulation of Wall Assembly (January)

Figure 4: (b) Simulation of Wall Assembly (June)



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2.4.2Total Moisture Content

Data pertaining to total moisture content within the wall assembly was first exported to a

specialized application ³Surfer´ in the form of a ³.dat´ file. This data contained information

about moisture content for various layers of the wall on an hourly basis for the complete year.

Average values were derived for every 30 or 31 days respectively using basic application ³MS

Excel´ in order to summarize the data for a monthly basis as shown in table 2. This was then

used to assess the performance of the layers of the wall assembly. Besides this, total moisture

content was analyzed and is shown in figure 5.

Figure 5: Total Moisture Content

It was observed that initially the moisture content was higher during the winter months and

decreased to its minimum during August. This is an indication that the wall selected based on the

previous assessments and selected materials is not absorbing the moisture during the summer

conditions when the temperature outside is high. This could also be seen in figures 4 (a) and 4



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(b) in which the moisture content is high and low respectively. It could be said that, for the

combination of wall assembly and the materials selected, the moisture is being accumulated on

the higher temperature side (either interior or exterior) based on winter or summer conditions

respectively. The use of insulation in between the wall assembly holds good for the summer

conditions of the region selected.

Table 2: Moisture Content by Layer

Time

(Months)

Concrete

brick

(Layer 1)

Air Space

(Layer 2)

Extruded

Polystyrene

(Layer 3)

Aerated

Concrete

(Layer 4)

Gypsum

(Layer 5)

January 6.849242 0.079336 2.138081 0.84875 0.000344

February 7.157829 0.075673 0.734786 0.83105 0.000367

March 6.819879 0.064564 0.217681 0.819391 0.000518

April 6.31128 0.063175 0.19747 0.816866 0.00062

May 5.484105 0.064691 0.192752 0.813914 0.00089

June 4.704008 0.062631 0.190473 0.812935 0.000869

July 4.226199 0.056615 0.183783 0.811556 0.000734

August 4.036284 0.054081 0.181963 0.81181 0.000612

September 4.255493 0.052847 0.182756 0.812843 0.000501

October 4.838691 0.052588 0.184202 0.813775 0.000441

November 5.144714 0.054014 0.193228 0.817678 0.000298

December 6.408029 0.056783 0.200802 0.820065 0.000264

The moisture content in the concrete brick was observed to be maximum compared to all other

layers. This could be due to the fact that the concrete has higher tendency to absorb moisture.

The air gap/space provided after the brick does not allow the moisture to pass through and

reduces its level to negligible values throughout the year. The insulation layer on the other hand

initially absorbs moisture and as time passes allows limited amount of moisture to pass through

compared to the first layer. The fourth layer being aerated concrete has a tendency to absorb

moisture and has higher values of moisture content compared to layer 3. Moisture transfer is

almost zero in layer 5.

2.4.1Transfer Rate of Heat

The heat transfer through the wall is shown in figure 6. It can be seen that the majority of

heat transfer occurs from outside to inside along the wall assembly during the summer season

and is depicted by positive readings. Less amount of heat transfer is observed from inside to

outside. Maximum heat gain was observed during the end of February and during October. This



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means that the wall system designed does not allow the flow of heat along its cross-section

throughout the summer season. Less heat gain results in decreased cooling loads.

Figure 6: Heat Transfer

3. Comparison with Previous Assessments

The capabilities of the software tool CONDENSE are limited to the thermal transfer and

identification of condensation in any part of the wall assembly at a particular instant of time.

CONDENSE does not deal with the dynamic aspects of weather conditions. On the other hand,

hygIRC is capable of simulating the modeled wall assembly throughout a complete year (or even

more than a year) taking into consideration the dynamic aspects of the surrounding atmosphere.

The assessments carried out by the two tools had one similarity. The assessments using

the state of art tool CONDENSE didn¶t reveal any sort of condensation in the selected wall for

the given conditions. Sensitivity analysis carried out resulted in the identification of



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condensation on the exterior surface. In the case of hygIRC, maximum amount of moisture

content was observed in layer 1 (Concrete Brick). Both these assessments revealed the

accumulation of moisture and maximum accumulation of moisture in the first layer, i.e., either

on exterior surface or within layer 1 using the software tools CONDENSE and hygIRC

respectively.

4. Conclusion

Based on the analysis of the selected wall system, it could be concluded that the wall is

suitable for the summer conditions of Dhahran city. While assessing the results it was found that

the moisture accumulation in layer 1 was high. The concrete brick acting as the first layer needs

to be replaced by some other material which is cheap and absorbs less moisture. The air space

and thermal insulation suit well in restricting the flow of moisture and heat respectively, or both.

The simulations done by hygIRC have many results compared to CONDENSE.

Limitation in hygIRC is that it assesses the thermal and moisture transfer in only one dimension

based on certain assumptions. Use of much more advanced software tool such as WUFI 2D is an

appreciation as it is capable of executing hygrothermal analysis in two dimensions.



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References

[1] Rob Bolin, ³Sustainability of the Building Envelope´, National Institute of Building

Sciences. Last updated: December 14, 2009.

[2] The Challenger Series, Canada. Information available at: http://www.thechallengeseries.ca/chapter-04/building-envelope/#importanceofenvelopes.

[3] Jamie McKay, ³Green Assessment Tools: The Integration of Building Envelope

Durability´, 11th

Canadian Conference on Building Science and Technology, Banff,Alberta, 2007.

[4] Khee Poh Lam, Yi Chun Huang and Chaoqin Zhai, ³Energy Modeling Tools

Assessment for Early Design Phase´, Center for Building Performance and Diagnostics,Pittsburgh, December 31, 2004.

[5] hyg IRC 1-D User¶s Guide.

[6] Syed Ashraf Tashrifullahi, ³Building Envelope Preliminary Design & Assessment´,

Evaluation Based on Introduction of CONDENSE Software Tool, K FUPM, October 16,2011.

[7] US General Services Administration. Information available at:

http://www.gsa.gov/portal/content/101291.

[8] Andy Persily, ³Building Ventilation and Pressurization as a Security Tool´,ASHRAE Journal, September 2004.

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