3.2.2. Numerical Analysis

This study addresses a number of design parameters to focus on prominent geometric variables regarding building form, i.e., the envelope characteristics of case buildings. It discusses total seven design parameters:


Bivariate Pearson correlation coefficient analysis was selected to understand empirically the relation between the design parameters and annual energy consumption of the case buildings. It is a statistical analysis method used to determine whether there is a linear relationship between two numerical variables, and, if any, the degree of the relationship. The Pearson correlation coefficient is expressed in 'r'. It can take a range of values from +1 to −1, depending on whether the relationship is positive or negative, respectively [42] (Table 2):



**Table 2.** Range of values and relation of Pearson correlation coefficient.

#### *3.3. Determination of Energy-E*ffi*cient Solutions*

In order to determine energy-efficient solutions for historic urban fabric and find the most appropriate solutions for building envelope, a set of actions were organized, starting with a preliminary analysis of possible retrofit solutions by taking into account a literature survey, including guidelines, standards and publications. This section continues with the categorization step. A total of 22 buildings were classified and characterized by number of qualitative and quantitative data. Afterwards, a pre-assessment was conducted to find the best retrofit solutions by excluding inappropriate ones and identify a series of acceptable measures. After this process, retrofit solutions were grouped under retrofit packages by combining the best solutions. This step served the purpose of revealing which packages were most appropriate toward the targets of the study by evaluating and comparing different retrofit scenarios with each other and the base case. The final step was composed of the decision and presentation of retrofit packages (Figure 5). *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 8 of 33

**Figure 5.** Determination process of energy-efficient solutions of the study. **Figure 5.** Determination process of energy-efficient solutions of the study.

#### 3.3.1. Retrofit Impact Assessment for Historic Buildings 3.3.1. Retrofit Impact Assessment for Historic Buildings

prolongs the life of historic buildings.

interdisciplinary approach [44].

potential and fabric compatibility [35,46] (Table 3).

Historic buildings differentiate in two major ways that can affect energy retrofits in comparison with other building categories. The first one is physical characteristics, such as the complexity of geometry, method of construction, used materials and existence of inherently passive climatic strategies. The second one is conservation principles, since historic buildings are held to account for established conservation principles to preserve their historic fabric and distinguishing characters [43]. Historic buildings differentiate in two major ways that can affect energy retrofits in comparison with other building categories. The first one is physical characteristics, such as the complexity of geometry, method of construction, used materials and existence of inherently passive climatic strategies. The second one is conservation principles, since historic buildings are held to account for established conservation principles to preserve their historic fabric and distinguishing characters [43].

It is essential to point out the need for providing a convenient balance between building conservation principles and energy-efficient improvements. Implication of a well-understood energy-efficient retrofit approach protects architectural, aesthetic and heritage values, reduces energy It is essential to point out the need for providing a convenient balance between building conservation principles and energy-efficient improvements. Implication of a well-understood energy-efficient retrofit approach protects architectural, aesthetic and heritage values, reduces energy

bills and improves comfort conditions and health of occupants, as well as increases the value and

standardized retrofit process cannot be conducted, and accordingly, a method for retrofit impact assessment becomes inevitable in determining the best retrofit solutions that can be implemented to historic buildings. Therefore, energy-efficient retrofitting of historic buildings requires an

The retrofit impact assessment has an approach based on certain criteria for each type of existing building. These criteria can be grouped under different topics, such as energy aspect, i.e., energy saving, embodied and operational energy, and economic aspect, indoor and outdoor environment and hygrothermal performance, i.e., durability, moisture risk and thermal transmittance. However, the criteria and process of retrofit differ by conservation principles for historic buildings [42]. Thus, heritage value protection commonly plays a leading role in the assessment of historic buildings [26,35,43,45]. The criteria for retrofit impact assessment specific to historic buildings can be scrutinized under specific subtopics: retrofit effects on building envelope, i.e., visual and spatial effects from the interior and exterior, and properties of retrofit materials, i.e., reversibility, damage bills and improves comfort conditions and health of occupants, as well as increases the value and prolongs the life of historic buildings.

As such, in existing non-historic and contemporary buildings, it is possible to develop energy-efficient strategies for historic building envelope and system and equipment. However, a standardized retrofit process cannot be conducted, and accordingly, a method for retrofit impact assessment becomes inevitable in determining the best retrofit solutions that can be implemented to historic buildings. Therefore, energy-efficient retrofitting of historic buildings requires an interdisciplinary approach [44]. *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 9 of 33 **Table 3.** Criteria for retrofit impact assessment.

The retrofit impact assessment has an approach based on certain criteria for each type of existing building. These criteria can be grouped under different topics, such as energy aspect, i.e., energy saving, embodied and operational energy, and economic aspect, indoor and outdoor environment and hygrothermal performance, i.e., durability, moisture risk and thermal transmittance. However, the criteria and process of retrofit differ by conservation principles for historic buildings [42]. Thus, heritage value protection commonly plays a leading role in the assessment of historic buildings [26,35,43,45]. The criteria for retrofit impact assessment specific to historic buildings can be scrutinized under specific subtopics: retrofit effects on building envelope, i.e., visual and spatial effects from the interior and exterior, and properties of retrofit materials, i.e., reversibility, damage potential and fabric compatibility [35,46] (Table 3). **Criteria for Retrofit Impact Assessment Şahin et al., 2015 [46] Eriksson et al., 2014 [35] Broström et al.,2014 [26] Webb, 2017 [43] Criteria for Heritage Value Impact Assessment Grytli et al., 2012 [46] Eriksson et al., 2014 [35]**  Energy saving Indoor environment Energy savings Global environment Reversibility Visual Cultural heritage values Fabric compatibility Economic aspect Building fabric Visibility Physical Durability Heritage Heritage Indoor Effects on the



interior or the exterior

Spatial

An overview about the retrofit impact assessment of various scientific studies and guidelines are presented based on two major criteria, including heritage value protection and energy saving. The assessment was conducted for all building components covering walls, floors, roofs, oriels, openings and shutters and a range of retrofit solutions in accordance with these building components. Moreover, the retrofit assessment of sources was interpreted by utilizing the five-level assessment criteria introduced by EN 16883:2017 (Figure 6 and Table 4). insulation of walls, basement floor insulation, attic floor insulation, flat roof insulation and adding a secondary glazing on existing windows have less risk on the heritage value, while they provide low benefit for energy efficiency. Implementation of weather stripping and roof insulation at rafter level have no risk on the heritage value and building appearance, as well as presenting moderate energy savings. Finally, shading control, night-time ventilation and use of oriels as sun space can be considered as the retrofit solutions without risk for the heritage value, because they do not cause any change on buildings' envelopes.


**Figure 6.** Five-level assessment scale for retrofit impact assessment [21]. **Figure 6.** Five-level assessment scale for retrofit impact assessment [21].

**Table 4.** Retrofit solutions for the building envelope based on retrofit impact assessment (red: high risk; yellow: low risk; white: neutral; light green: low benefit; dark green: high benefit) (Sources: 1, [46]; 2, [47]; 3, [48]; 4, [49]; 5, [50]; 6, [46]; 7, [26]; 8, [51]; 9, [10]; 10, [52]). *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 10 of 33 **Table 4.** Retrofit solutions for the building envelope based on retrofit impact assessment (red: high risk; yellow: low risk; white: neutral; light green: low benefit; dark green: high benefit) (Sources: 1,

[46]; 2, [47]; 3, [48]; 4, [49]; 5, [50]; 6, [46]; 7, [26]; 8, [51]; 9, [10]; 10, [52]).


A list of possible energy-efficient solutions was addressed to develop the retrofit strategies for case buildings, including both historic and contemporary ones. Among a wide range of possible energy efficient retrofit solutions based on the literature survey, only 17 envelope-related retrofit solutions were selected (Table 5): **Table 5.** Possible retrofit solutions for building envelope based on the literature survey. **For All Heated Zones Draught Proofing / Weather Stripping Walls Roofs** External insulation of walls Insulation of flat roof Internal insulation of walls Insulation of pitched roof **Floors Windows and doors** Insulation of basement floor Changing windows Insulation of ground floor Adding a secondary glazing According to the retrofit assessment, external insulation of walls, ground floor insulation, changing/improving windows, doors and shutters predominantly result in high risk on the heritage value and historic building character, while they provide substantial energy savings. Internal insulation of walls, basement floor insulation, attic floor insulation, flat roof insulation and adding a secondary glazing on existing windows have less risk on the heritage value, while they provide low benefit for energy efficiency. Implementation of weather stripping and roof insulation at rafter level have no risk on the heritage value and building appearance, as well as presenting moderate energy savings. Finally, shading control, night-time ventilation and use of oriels as sun space can be considered as the retrofit solutions without risk for the heritage value, because they do not cause any change on buildings' envelopes.

#### Insulation of external floors Changing doors Insulation of oriels' ground floor Use of oriels as a sunspace 3.3.2. Possible Retrofit Solutions for Building Envelope

building category.

3.3.2. Possible Retrofit Solutions for Building Envelope

Insulation of oriels' attic floor *3.4. Categorization of Buildings* In this study, a categorization process was conducted for the case buildings by characterizing according to their heritage values and architectural characteristics. This process aims at ensuring the most appropriate energy-efficient solutions by properly matching the retrofit packages with each A list of possible energy-efficient solutions was addressed to develop the retrofit strategies for case buildings, including both historic and contemporary ones. Among a wide range of possible energy efficient retrofit solutions based on the literature survey, only 17 envelope-related retrofit solutions were selected (Table 5):

Insulation of attic floor to existing windows


Categorization starts with the heritage significance level, which is of top priority because of the **Table 5.** Possible retrofit solutions for building envelope based on the literature survey.

#### *3.4. Categorization of Buildings*

In this study, a categorization process was conducted for the case buildings by characterizing according to their heritage values and architectural characteristics. This process aims at ensuring the most appropriate energy-efficient solutions by properly matching the retrofit packages with each building category.

Categorization starts with the heritage significance level, which is of top priority because of the most decisive and distinctive criteria at the first stage of categorization. It continues with characterizing the architectural components of building envelopes, i.e., walls, floors, roofs and oriels affecting the number and type of retrofit solutions produced for each building and how they work and are applied to building structure. The availability of basement floors and oriels in the case buildings were initially selected as criteria after the selection of the heritage significance level. *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 11 of 33 and are applied to building structure. The availability of basement floors and oriels in the case

In accordance with the categorization process, the case buildings were gathered under three main groups based on the heritage significance level of buildings. These groups are officially registered historic buildings named Group 1 buildings, with non-registered historic buildings named Group 2 buildings and contemporary (non-historic) buildings named Group 3 buildings (Figure 7) buildings were initially selected as criteria after the selection of the heritage significance level. In accordance with the categorization process, the case buildings were gathered under three main groups based on the heritage significance level of buildings. These groups are officially registered historic buildings named Group 1 buildings, with non-registered historic buildings named Group 2

buildings and contemporary (non-historic) buildings named Group 3 buildings (Figure 7).

**Figure 7.** Categorization of buildings. **Figure 7.** Categorization of buildings.

Group 1 buildings were solely composed of 11 officially registered buildings, encoded as "historic registered (HR)". Two buildings, representing Group 2 "historic non-registered (HNR)" were not officially registered buildings but they were in harmony with the officially registered ones in terms of the physical, visual and material characteristics of the historic buildings' envelopes. Group 3 buildings were non-historic ones, consisting of nine buildings and characterized as "contemporary (C)" buildings. Group 1 buildings were solely composed of 11 officially registered buildings, encoded as "historic registered (HR)". Two buildings, representing Group 2 "historic non-registered (HNR)"—were not officially registered buildings but they were in harmony with the officially registered ones in terms of the physical, visual and material characteristics of the historic buildings' envelopes. Group 3 buildings were non-historic ones, consisting of nine buildings and characterized as "contemporary (C)" buildings.

#### *3.5. Impact Assessment of Possible Retrofit Solutions for Building Groups 3.5. Impact Assessment of Possible Retrofit Solutions for Building Groups*

Regulation on Buildings of Turkey [18].

#### 3.5.1. Impact Assessment of Possible Retrofit Solutions for Group 1 buildings 3.5.1. Impact Assessment of Possible Retrofit Solutions for Group 1 Buildings

First, defining the retrofit targets is of importance to properly assess the energy-efficient retrofit solutions and decide the appropriate ones for buildings. Several targets are specified for Group 1 buildings: First, defining the retrofit targets is of importance to properly assess the energy-efficient retrofit solutions and decide the appropriate ones for buildings. Several targets are specified for Group 1 buildings:


there is no description about officially registered historic buildings in the Energy Performance

• to select the insulation materials to meet TS 825 Thermal Insulation Requirements, although there is no description about officially registered historic buildings in the Energy Performance Regulation on Buildings of Turkey [18].

After the definition of retrofit targets, 18 possible energy-efficient retrofit solutions for Group 1 buildings were evaluated based on the retrofit impact assessment through utilizing the five-level assessment criteria introduced by EN 16883:2017 (see Figure 6 in Section 3.3.1). As a result of the assessment, all retrofit solutions were gathered under three risk groups, based on the heritage value: high-risk solutions (red), low-risk solutions (yellow) and neutral solutions (white). Additionally, grey colored boxes show that there is no solution defined for the case buildings (Table 6).

Initially, three retrofit solutions, including the external insulation of external walls, changing windows and doors, were specified the high-risk solutions for the heritage value after the assessment. Therefore, they were excluded from the scope of the solutions for Group 1 buildings.

Six retrofit solutions were determined as the low-risk solutions after the heritage value impact assessment. These solutions are considered to have less impact on the heritage value and the buildings' appearances while causing changes on the buildings' constructions. The retrofit solutions with low risk were:


Considering the heritage value impact assessment, six retrofit solutions were determined as the neutral solutions causing physical change on buildings' envelope. These solutions improve the energy efficiency of Group 1 buildings without damaging the heritage value. The neutral retrofit solutions were:


The remaining three retrofit solutions were the passive solutions related to building operation. They were also entitled as the neutral solutions which do not cause any physical change on the buildings' envelopes (white color shown in building operation section of Table 6. These retrofit solutions were the following:


After the determination of appropriate retrofit solutions based on the heritage value impact assessment for Group 1 buildings, some of the retrofit solutions were grouped under the retrofit packages while some of were individually assessed. The neutral retrofit solutions causing physical changes on buildings' envelopes were included in a package named Package 1, separately simulated for Group 1 Buildings. Low-risk solutions for Group 1 buildings were not being separately evaluated, since they are not a foremost option in terms of preference and application priority. Therefore, Package 2 is generated by adding the low-risk retrofit solutions to Package 1 solutions and then evaluated. Moreover, operational solutions were not grouped, in order to observe their individual effects on the buildings' envelopes. Table 7 presents all retrofit solutions and packages determined for Group 1 buildings. *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 13 of 33

**Table 6.** Heritage value impact assessment for 18 energy-efficient retrofit solutions of Group 1 buildings (red: high risk; yellow: low risk; white: neutral; gray: no solution). **Table 6.** Heritage value impact assessment for 18 energy-efficient retrofit solutions of Group 1 buildings (red: high risk; yellow: low risk; white: neutral; gray: no solution).


**Table 7.** Determined retrofit solutions and packages for Group 1 buildings. **Table 7.** Determined retrofit solutions and packages for Group 1 buildings.


Insulation of ground floor Insulation of attic floor Specifications about Package 1 for Group 1 buildings: Package 1 aspired to enhance the energy efficiency of Group 1 buildings without damaging the heritage value. The package contained an implementation of weather stripping to improve air-tightness of the building envelope, insulation of attic floor, insulation of flat roof, insulation of oriels' roof, insulation of pitched roof and insulation of ground floor. Considering air-tightness improvements, the air exchange rate (ACH) was assumed to have improved from 0.7 h−<sup>1</sup> to 0.4 h−<sup>1</sup> in heated zones and from 0.9 h−<sup>1</sup> to 0.7 h−<sup>1</sup> in unheated zones to repair the cracks and holes on the building envelope. For floors, ground floor and attic floor insulation existed in Package 1. On the other hand, regarding the ground floors of some buildings, it was decided that they should not undergo a change during the retrofit interventions due to their Specifications about Package 1 for Group 1 buildings: Package 1 aspired to enhance the energy efficiency of Group 1 buildings without damaging the heritage value. The package contained an implementation of weather stripping to improve air-tightness of the building envelope, insulation of attic floor, insulation of flat roof, insulation of oriels' roof, insulation of pitched roof and insulation of ground floor. Considering air-tightness improvements, the air exchange rate (ACH) was assumed to have improved from 0.7 h−<sup>1</sup> to 0.4 h−<sup>1</sup> in heated zones and from 0.9 h−<sup>1</sup> to 0.7 h−<sup>1</sup> in unheated zones to repair the cracks and holes on the building envelope. For floors, ground floor and attic floor insulation existed in Package 1. On the other hand, regarding the ground floors of some buildings, it was decided that they should not undergo a change during the retrofit interventions due to their structural composition and historic material properties.

Weather stripping

structural composition and historic material properties.

Specifications about Package 2 for Group 1 buildings: Package 2 was intended to reveal the effects of both neutral and low risk retrofit solutions by providing as much as energy saving for Group 1 buildings as possible. Package 2 presented the combination of the low-risk and neutral solutions named (Package 1). The content of the low-risk solutions was composed of six retrofit solutions, including internal insulation of external wall, insulation of oriel wall, insulation of oriels' attic floor and oriel ground floor and roof, insulation of the external floors (floor of protrusion and floor above entrance) and adding secondary glazing to existing windows.

Considering the walls, internal insulation of external wall and oriel wall were implemented for heated spaces. If there was a case building with a gable roof, the gable walls were also insulated from inside. Moreover, external wall surfaces, as an adiabatic, were not insulated.

Specifications about Insulation Materials for Group 1 buildings: Determination of insulation material carries importance to protect the heritage value and fabric of historic buildings. Therefore, the use of natural, breathable and reversible materials was beneficial for minimizing the risks, i.e., moisture generation, on historic building construction and components. Wood fiber board and sheep wool were selected as the internal insulation material for Group 1 buildings.

Installation of secondary glazing was selected to provide an effective insulation for historic windows and limit draughts without changing any components of windows and damaging their character and heritage values. However, changing windows (glazing and frame) was envisaged on the façades of some Group 1 buildings. As for floors, the ground and attic floor of the oriels and external floors such as ground floor of protrusions and floors above the buildings' entrances were also included in low-risk solutions. Overall heat transfer coefficient targets to meet TS 825 Thermal Insulation Requirements for Buildings were achieved after the retrofits.

3.5.2. Impact Assessment of Possible Retrofit Solutions for Group 2 Buildings

Identified retrofit targets for Group 2 buildings:


A total of 17 possible energy-efficient retrofit solutions were evaluated considering the five-level assessment criteria introduced by EN 16883: 2017. All retrofit solutions were divided into three risk groups, including high-risk solutions, low-risk solutions and neutral solutions (Table 8).

First, external insulation of external walls and changing doors were eliminated, since they carry a risk for Group 2 buildings according to the heritage value impact assessment. Thus, these solutions were left out of the scope of appropriate solutions for Group 2 buildings.

Five retrofit solutions, the yellow colored boxes shown in Table 8, were specified as low-risk solutions which cause less impact on the buildings' façade characters and appearance while causing change on the buildings' components. The retrofit solutions with low risk were:


Seven retrofit solutions were specified as the neutral solutions causing physical change on the buildings' envelopes, but without damaging the historic character of buildings according to the heritage value impact assessment. The neutral retrofit solutions for Group 2 buildings were:


**Table 8.** Heritage value impact assessment for 17 energy-efficient retrofit solutions of Group 2 buildings (red: high risk; yellow: low risk; white: neutral; gray: no solution). **Table 8.** Heritage value impact assessment for 17 energy-efficient retrofit solutions of Group 2 buildings (red: high risk; yellow: low risk; white: neutral; gray: no solution).


Some of the retrofit solutions were grouped under the retrofit packages while some were individually evaluated. The neutral solutions which cause the physical changes on buildings' envelope were included in a package named as Package 1 and separately simulated for Group 2 buildings. Low-risk solutions for Group 2 buildings were not individually performed because of similar reasons to the Group 1 buildings. Unchanged or less changed façades for this group of buildings are principally desired due to their façade characteristics. Low-risk solutions were combined and simulated with the Package 1 for Group 2 buildings. Thus, Package 2 originated from the combination of solutions with low risk and a neutral effect on the heritage value of Group 2 buildings. Furthermore, operational solutions were not grouped in order to observe their individual effects on the buildings' envelopes (Table 9). Some of the retrofit solutions were grouped under the retrofit packages while some were individually evaluated. The neutral solutions which cause the physical changes on buildings' envelope were included in a package named as Package 1 and separately simulated for Group 2 buildings. Low-risk solutions for Group 2 buildings were not individually performed because of similar reasons to the Group 1 buildings. Unchanged or less changed façades for this group of buildings are principally desired due to their façade characteristics. Low-risk solutions were combined and simulated with the Package 1 for Group 2 buildings. Thus, Package 2 originated from the combination of solutions with low risk and a neutral effect on the heritage value of Group 2 buildings. Furthermore, operational solutions were not grouped in order to observe their individual effects on the buildings' envelopes (Table 9).

> **Table 9.** Determined retrofit solutions and packages for Group 2 Buildings. **Group 2 Buildings.**

> > **Package 2 (Combination of Neutral and Low-Risk)**

Internal insulation of

Insulation of basement floor Insulation of oriel wall Shutter control Insulation of attic floor Insulation of oriel ground floor Nightime ventilation

Insulation of oriel roof Insulation of external floor Insulation of pitched roof Changing windows Insulation of ground floor Insulation of oriel attic floor

**Individual Operational Solutions (Neutral Related to Building Operation)**

external wall Use of oriel as sunspace

**Package 1 (Neutral Related to Building Envelope)**

> Insulation of oriel attic floor


**Table 9.** Determined retrofit solutions and packages for Group 2 Buildings.

3.5.3. Assessment of Possible Retrofit Solutions for Group 3 Buildings

The retrofit targets determined for Group 3 buildings were:


The heritage value impact assessment for Group 3 buildings was not performed, because they consisted of contemporary buildings which did not present any historic character and heritage value. Therefore, a list of 11 possible retrofit solutions was prepared. Then, the retrofit solutions were grouped according to their vertical and horizontal building components. The solutions applied for the vertical building components, i.e., walls, windows and doors, were determined as Package 1. Package 2 consisted of the combination of retrofit solutions applied for both the vertical and horizontal building components. Then, the operational solutions were individually assessed for Group 3 buildings (Table 10). Package 1 included the retrofit solutions which were thought to be preferable in terms of priority and ease of implementation.


**Table 10.** Determined 11 retrofit solutions and packages for Group 3 buildings.

Package 2 aimed to observe the effect of the combined solutions produced for both vertical and horizontal components of Group 3 buildings, except for the operational solutions. Therefore, following specifications on the solutions for horizontal building, components were presented in addition to the above-mentioned specifications about the vertical components within Package 1. When insulating all the floor types for Group 3 buildings, it was considered whether to directly implement insulation materials to the upper level of the existing floor without excavating and then place floor covering material on it.

## **4. Results**

The results of the determined retrofit packages and individual retrofit solutions for each building category, i.e., Group 1, Group 2, and Group 3, are presented in separate subsections. All retrofit proposals were simulated by using DesignBuilder BPS software version 5.2.003 and 5.5.0.012. The comparison among retrofit packages and base case conditions of the buildings are illustrated in the next sections.

#### *4.1. Results of Retrofit Solutions Belonging to Group 1 Buildings (HR)*

#### 4.1.1. Results of Retrofit Packages for Group 1 Buildings (HR)

Regarding total energy consumption for heating, the amount of energy saving for Group 1 buildings ranged from 9.0% (Building 15) to 17.89% (Building 19) with Package 1. This rate changed from 34.64% (Building 12) to 60.6% (Building 22) through Package 2 (Table 11). For the total energy consumption for cooling, Package 1 significantly enabled reductions on energy consumption of almost all the buildings. However, there exists an increase in cooling consumption of 25.92% and 41.7% in Building 15 and 21, respectively. The minimum energy saving achieved by Package 1 was 2.45% in Building 12, while the maximum energy saving was 85.87% for Building 22. Package 2 provided a minimum energy saving of 28.11% in Building 15 and a maximum of 91.15% in Building 22, in comparison to the base case of buildings (Table 11).



The results of annual energy consumption indicated that the minimum energy saving obtained from Package 1 was 8.12% (Building 15) and the maximum was 31.43% (Building 22). Through Package 2, the energy saving rate increased by a minimum of 34.67% (Building 12) and a maximum of 65.8% (Building 22) in proportion to base case (Table 11).

#### 4.1.2. Results of Operational Solutions for Group 1 Buildings (HR)

According to the results of individual operational solutions, it could be remarked that the night-time ventilation slightly differed from other operational solutions, in terms of providing more energy saving specifically for the cooling season and applicability to all existing windows of Group 1 buildings. The use of oriels as a sunspace and shading control did not completely perform for all case buildings because of the use of the existing shutters and the fact that not all buildings had an oriel. These solutions implemented to the existing building components had close results as compared with the night-time ventilation strategy (Table 12).


**Table 12.** Change rates in annual energy consumption compared to base case of Group 1 buildings through operational solutions.

#### *4.2. Results of Retrofit Solutions Belonging to Group 2 Buildings (HNR)*

4.2.1. Results of Retrofit Packages for Group 2 Buildings (HNR)

The energy consumption results for heating season indicates that there is a remarkable difference between Package 1 and Package 2. Through Package 2, the highest reduction occurred in Building 8, by 47.34%, and Building 1, by 42.63%. Package 1 provides less energy saving, by 17.56% in Building 1 and 10.06% in Building 8, compared to the base case (Table 13).

**Table 13.** Change rates in annual energy consumption compared to base case of Group 2 buildings through Package 1 and Package 2.


The results of energy consumption for cooling show that Package 1 and Package 2 unexpectedly increased the energy consumption of two buildings while only Package 2 provided a reduction of 23.98% for Building 8. The increase rate was 34.99% for Building 1 and reached 13% for Building 8 through Package 1 (Table 13).

Considering the total annual energy saving rates, there was a significant difference varying from 30% to 35% between Package 1 and Package 2. The maximum saving obtained from Package 2 was 44.65% for Building 1 and 42.36% for Building 8. The minimum energy saving rate was 9.41% for Building 8 and 17.56% for Building 1 through Package 1 (Table 13).

#### 4.2.2. Results of Operational Solutions for Group 2 Buildings (HNR)

Individual operational solutions provided minor energy savings for Group 2 buildings. Nevertheless, these solutions can be considered as favorable since they did not damage on historic buildings' envelopes and appearances, although Group 2 Buildings were not officially registered. Among the individual solutions, the strategy of the use of oriels as a sunspace was conducted for only Building 1. All operational solutions indicated the same amount of saving, i.e., 1.7%, for the heating season, compared with energy consumption for cooling. It can be concluded that the night-time ventilation strategy is more effective for reducing energy for cooling (Table 14).


**Table 14.** Change rates in annual energy consumption compared to base case of Group 2 buildings through operational Solutions.

#### *4.3. Results of Retrofit Solutions Belonging to Group 3 Buildings (C)*

#### 4.3.1. Results of Retrofit Packages for Group 3 Buildings (C)

Regarding the total energy consumption for heating, both packages revealed significant reductions for most of Group 3 buildings. The highest energy reduction for heating occurred in Building 11, with 67.43%, through Package 2, while the lowest result was in Building 16, with 9.3%, through Package 1 (Table 15).

**Table 15.** Change rates in annual energy consumption compared to base case of Group 3 buildings through Package 1 and Package 2.


The energy consumption for cooling also decreased with both packages, yet Package 2 provided higher energy saving rates. The highest reduction occurred in Building 16 (83.59%), through Package 2, while Package 1 resulted in the lowest reduction rate of 8.77%, in Building 16 (Table 15).

Regarding annual energy consumption, although Package 2 enables more energy saving, both retrofit packages provide significant energy conservation. The maximum rate was 67.05% for Building 11, through Package 2, while the minimum was 9.26% in Building 16, through Package 1 (Table 15).

#### 4.3.2. Results of Operational Solutions for Group 3 Buildings (C)

Individual operational solutions create more energy savings compared to other building groups. Both strategies including night-time ventilation and shading control with shutters providing close results for energy consumption for heating and cooling. The use of shutters resulted in higher energy saving rates for Building 2 and 3 with a marked difference. The operation of the night-time ventilation strategy was effective on Building 11 and 13, compared to shading control for cooling season (Table 16).


**Table 16.** Change rates in annual energy consumption compared to base case of Group 3 buildings through operational solutions.

#### **5. Discussion**

#### *5.1. Evaluation among Building Categorizations*

For Group 1 buildings, Package 1 (the neutral solutions) provided an average of 15.11% of energy saving, while the highest energy savings was 50.90% obtained from Package 2 (the combination of low risk and neutral solutions). Considering the Group 2 buildings, 11.93% of energy saving was achieved by implementing Package 1 (the neutral solutions) while Package 2 (the combination of low risk and neutral solutions) provided an energy saving of 43.33%. Regarding Group 3 buildings, Package 1 (the retrofit solutions for vertical building components) provided a 30.11% energy saving for Group 3 buildings. Package 2 (the combination of solutions for both vertical and horizontal building components) resulted in 50.90% of the energy saving rate (Table 17).



Among all the building categories, Package 2 achieved the maximum energy saving of 50.90%, while the minimum energy saving rate of 11.93% was obtained from Package 1. It was deduced that for all building groups, Package 2 enabled the saving of considerably more energy than Package 1. Only for Group 3 buildings, there occurred a close energy saving result between Package 1 and Package 2, compared to the other building groups (Table 17).

Individual operational solutions provided minor energy savings, in comparison to the solution included in packages for case building groups. Although these individual solutions did not provide as effective energy savings as the packages, they did not cause any changes on buildings' envelopes; therefore, these solutions have an importance in terms of protecting the heritage values and the characteristics of the Group 1 and Group 2 buildings. The night-time ventilation strategy saved the highest energy of 6.81% for the Group 3 buildings. A minimum energy saving rate of 1.45% was obtained from the strategy of the use of oriels as sunspace for Group 1 buildings. Night-time ventilation was the most effective solution in terms of energy saving among individual operational solutions (Table 17).

## *5.2. Evaluation of All Case Buildings*

Out of all case buildings, the maximum energy saving was provided by Package 2, with 48.57%, while the minimum energy saving was obtained from Package 1, with 19.8% (Table 18). Among the individual operational solutions, night-time ventilation and shading control provided similar energy savings. The energy saving rates were 5.2% and 5.4%, for night-time ventilation and shading control, respectively. The use of oriels as sunspace resulted in a minor energy saving rate of 1.5% for all case buildings (Table 19).

**Table 18.** Evaluation of annual energy consumption results for retrofit packages in all case buildings.


**Table 19.** Evaluation of annual energy consumption results for individual operational solutions in all case buildings.


#### *5.3. Evaluation of Building Groups Based on Energy Classes*

In this section, all the building groups were evaluated according to the energy classes for energy consumption. The energy class of the buildings was determined by calculating the annual primary energy consumption per unit occupied floor area. For new and existing buildings, the Energy Performance Regulation on Buildings of Turkey stipulates the preparing of a Building Energy Certificate that includes a classification of energy performance varying between A (the best) and G (the worst). According to the regulation, new buildings are required to have a rating of class C or higher [37]. Although there is no restriction about the energy class of historic buildings, all building groups were included in this evaluation.

Among Group 1 buildings (HR), two base case buildings (Building 14 and 20), three buildings with Package 1 (Building 14, 20 and 21) and seven buildings with Package 2 (Building 4, 7, 14, 17–18, 20, 21, and 22) met the minimum energy class of C and above, according to the regulation. Building 12, 15 and 19 did not meet the minimum energy class of C and above in any cases, before or after retrofit. Package 1 provided the highest change rate on energy class for Building 22 (from F to C), compared to base case. There was no change in energy class for Building 4, 12 and 15 by implementing Package 1. Through Package 2, the highest change rate on energy class occurred in Building 17–18 and 22 (from F to B) compared to the base cases (Table 20).

Among Group 2 buildings (HNR), the energy class results for the base case and all the packages were the same as energy class B for Building 1. For Building 8, the energy classes of both base case and Package 1 were found to be energy class F, which is not acceptable, according to the Energy Performance Regulation on Buildings of Turkey. Through Package 2, it achieves minimum energy class (C) (Table 20).


**Table 20.** Primary energy consumption and energy classes of the base and retrofitted cases for all case buildings (light green: minimum energy class C; green; energy class B; dark green: energy class A).

Among Group 3 buildings (C), the highest change rate in energy class (from G to C) was provided in Building 2 through Package 1. There was no change in the energy class of Building 16 with Package 1. Through Package 2, energy classes of most buildings were class B. The highest change rate occurred in Building 2 (from G to C), followed by Building 3 (from E to B), Building 5 (from F to C), Building 11 (from D to A), Building 16 (from G to D), Building 6 (from B to A), Building 13 (from C to B) and Building 9 (from E to D) (Table 20).

For all building groups, Package 2 provided the highest improvements on energy classes compared to Package 1. Moreover, Group 3 buildings indicated better performance in energy classes in comparison to the other building groups.

#### *5.4. Evaluation of Relationship between Design Parameters and Building Energy Consumption*

The numerical analysis was conducted by using Pearson correlation analysis. Seven design parameters, based on the geometric variables of building form, mentioned in the Section 3.2.2, were investigated for each case building to find the most influential parameters on building energy consumption.

The calculated values of parameters belonging to each case building are presented in (Table 21), while the results of Pearson correlation analysis (R values) are presented in Table 22. The outcomes convey that DP1 (total surface area to conditioned volume ratio (S/V)) and DP5 (usable ground floor area (m<sup>2</sup> ) to conditioned volume (m<sup>3</sup> )) are negatively and significantly related to the annual energy consumption of buildings. In other words, buildings that have lower levels of S/V and usable ground floor area (m<sup>2</sup> ) to conditioned volume (m<sup>3</sup> ) are likely to have higher annual energy consumption per m<sup>2</sup> . P4 (length to depth), DP6 (total usable floor area to conditioned volume) and building DP7 (height to depth), on the other hand, are the variables are positively related to energy consumption, although the correlation is statistically insignificant (Table 22).


**Table 21.** Numerical analysis results for design parameters.

**Table 22.** Results of Pearson coefficient analysis.


Note: \* r values closest to −1.

#### *5.5. Integrated Approach to Identify Case-Specific Energy-E*ffi*cient Solutions for Retrofit Strategy of Larger Scale Historic District*

The need for developing retrofit strategy for larger scale case studies was confronted while deciding which buildings could provide the most energy saving within the given time limitations of the project. In cases with insufficient building data, it was required to focus on accessible data derived from building envelope with a quick field survey. This study introduced an integrated approach to identify case-specific energy efficient solutions for a retrofit strategy of a larger scale historic district.

This approach was composed of eight main steps, the approach starting with determination of the most effective design parameters on annual energy consumption of buildings (Table 23). Then, identified parameters were sorted within themselves and 50% of buildings with more energy consumption were chosen. The same building(s) in each identified design parameter were selected. Then, BPS model of the selected buildings was created, and their annual energy consumption was calculated. Energy classes of the buildings, considering primary energy consumption, were defined. Afterwards, the buildings meeting the minimum energy class (C) and above (B and A) were eliminated. The retrofit solutions/packages were applied to the rest of the BPS model of the building(s). Finally, it was decided whether the buildings met the minimum energy class (C).


**Table 23.** Integrated approach of this study for retrofit strategy of larger scale historic district.

In this research, P1 (total surface area to conditioned volume ratio (S/V)) and P5 (usable ground floor area (m<sup>2</sup> ) to conditioned volume (m<sup>3</sup> )) were determined as the two most influential parameters. The calculated values of these parameters were sorted from minimum to maximum value. Of the buildings with more annual energy consumption per each design parameter, 50% corresponded to the first 11 case buildings, colored grey in Table 24 (a) and (b). Then, the same buildings in both parameters were determined, as shown in blue in Table 24 (a) and (b). This means that the number of case buildings to work on decreased to eight.

**Table 24.** Sorted and determined case buildings based on (a) DP1 (total surface area to conditioned volume ratio (S/V)) and (b) DP5 (usable ground floor area (m<sup>2</sup> ) to conditioned volume (m<sup>3</sup> ) ratio) (grey: 50% of case buildings; blue: same buildings in both parameters).


The energy classes of the identified eight buildings, based on primary energy consumption, are presented. The buildings with minimum energy class (C) and above, i.e., Building 1 (HNR), 6 (C)

**6. Conclusion**

was the primary concern.

and 14 (HR), in base cases were eliminated since they already met the requirements of the Energy Performance Regulation on Buildings of Turkey.

Finally, the remaining four buildings, including Building 8 (HNR), 11 (C), 15 (HR) and 21 (HR), were evaluated according to the energy class change of the retrofit packages. Building 15 (HR) was disregarded in the evaluation process, because both Package 1 and Package 2 did not cause any change in the energy class of this building. Consequently, three buildings (Building 8 (HNR), 11 (C) and 21 (HR)), that did not meet minimum energy class (C) were determined as the buildings which could be initially retrofitted (Table 25). *Atmosphere* **2020**, *11*, x FOR PEER REVIEW 24 of 33 Building 2 1.36 Building 20 0.22 Building 5 1.40 Building 10 0.24

**Table 25.** Energy classes of identified eight buildings based on primary energy consumption (blue: buildings which do not meet minimum class (C)). Building 9 1.56 Building 5 0.29 Building 12 1.58 Building 3 0.34

Building 4 1.51 Building 7 0.25


Package 1 solutions provided an improvement for only Building 11 (C), from D to B. Package 2 solutions provided an improvement for Building 8 (HNR) from F to C and for Building 21 (HR) from E to B and for Building 11 (C) from D to A (Table 25). **Building 8** F F C **Building 15** F F D **Building 11** D B A

**Building 1** B B B

Three buildings, which can initially be retrofitted, represent each building group: Building 21 (HR) belonged to officially registered historic buildings (Group 1), Building 8 (HNR) belonged to non-registered but historic buildings (Group 2) and Building 11 (C) belonged to contemporary buildings (Group 3) (Figure 8). Building 8 (HNR) and 21 (HR) were the second most energy saving buildings in their own groups, through Package 2. Package 1 did not provide effective energy saving results for Building 8 (HNR) and 21 (HR). Building 11 (C) had the second most energy saving potential, through Package 1, and the most energy saving potential by Package 2 among Group 3 Buildings. **Building 21** E D B Three buildings, which can initially be retrofitted, represent each building group: Building 21 (HR) belonged to officially registered historic buildings (Group 1), Building 8 (HNR) belonged to non-registered but historic buildings (Group 2) and Building 11 (C) belonged to contemporary buildings (Group 3) (Figure 8). Building 8 (HNR) and 21 (HR) were the second most energy saving buildings in their own groups, through Package 2. Package 1 did not provide effective energy saving results for Building 8 (HNR) and 21 (HR). Building 11 (C) had the second most energy saving

**Figure 8.** (**a**) Building 21(HR) (9% energy saving by Package 1; 60% energy saving by Package 2), (**b**) Building 8 (HNR) (9% energy saving by Package 1; 42% energy saving by Package 2) and (**c**) Building 11 (C) (44% energy saving by Package 1; 67% energy saving by Package 2) where retrofit solutions can be applied initially. **Figure 8.** (**a**) Building 21(HR) (9% energy saving by Package 1; 60% energy saving by Package 2), (**b**) Building 8 (HNR) (9% energy saving by Package 1; 42% energy saving by Package 2) and (**c**) Building11 (C) (44% energy saving by Package 1; 67% energy saving by Package 2) where retrofit solutions canbe applied initially.

while protecting and maintaining the heritage value and architectural character of historic buildings,

As a consequence, following conclusions can be derived:

This paper presents the study at the urban neighborhood, consisting of a total of 22 historic and

## **6. Conclusions**

This paper presents the study at the urban neighborhood, consisting of a total of 22 historic and contemporary buildings with residential and commercial use. It introduces an integrated approach to retrofit buildings in the larger scale historic urban fabric. Improving the energy performance of the buildings' envelopes by proposing energy-efficient retrofit solutions in different impact categories, while protecting and maintaining the heritage value and architectural character of historic buildings, was the primary concern.

As a consequence, following conclusions can be derived:


This study provides information regarding different retrofit approaches, i.e., the energy-efficient retrofitting of buildings from different categorizations in the same neighborhood. Overall consideration in determining the possible energy-efficient retrofit solutions for urban building stock, hosting both historic and contemporary buildings, enables its usability, in terms of bringing different retrofit approaches together. This contributes to the current literature by developing an integrated approach about how to decide retrofit solutions at a neighborhood scale, consisting of both historic and contemporary buildings, via quick survey analysis without extensive data collection. It points out the retrofit strategies are characterized for the representative neighborhood so that they may be extrapolated to wider scale urban historic fabric of that particular city.

On the other hand, this research indicates the significance of determining case-specific retrofit packages. The findings related to the retrofit solutions and their interpretation cannot be generalized for other studies. However, the approach of the study can serve as a model for historic building stock in the Mediterranean climate, i.e., the determination process of energy-efficient retrofit solutions and packages within several retrofit strategies. Nevertheless, the number and type of retrofit solutions and packages differ in other studies, since historic buildings have different historic and architectural characteristics depending on cultural, social and geographical facts.

**Author Contributions:** Conceptualization, M.U. and Z.D.A.; methodology, M.U. and Z.D.A.; software, M.U.; formal analysis, M.U. and Z.D.A.; investigation, M.U. and Z.D.A.; data curation, M.U.; writing—original draft preparation, M.U. and Z.D.A.; writing—review and editing, M.U. and Z.D.A.; visualization, M.U.; supervision, Z.D.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank Izmir Metropolitan Municipality Directorate of Historic Environment and Cultural Properties and Konak Municipality for documents and information shared. The authors wish to express special thanks to H. Engin Duran from the Department of City and Regional Planning at Izmir Institute of Technology for his supervision on statistical analysis of this study. Lastly, many thanks should be given to Geothermal Energy Research and Application Centre of Izmir Institute of Technology (IZTECH JEOMER) for the support on measurement of thermal properties of local building materials.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **Abbreviations**


#### **References**

1. *World Energy Perspective, Energy E*ffi*ciency Policies: What Works and What Does Not*; World Energy Council: London, UK, 2013.


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*Article*
