Guideline for setting the goal of application of internal insulation
Decision making process
The main goal of this guideline is to provide information for building owners and consultants to set the goal for application of internal insulation and relevant criteria that describe the goal.
Deciding whether and how to implement energy efficiency in historic buildings is a complex process since it involves different technical solutions, heritage value, indoor environment, cost efficiency, interests of stakeholders etc.
Application of internal insulation is a manifold process since it is composed of many variables that can be either independent or interlinked. These are hygrothermal properties of existing and applied building materials, indoor and outdoor climate, energy costs, operation and maintenance costs, human behaviour, occupation loads, mechanical and engineering systems in the building, environmental impact, heritage value, financial resources and their availability, location of the building, building regulations, productivity etc. Decisions about retrofit measures are made based on the goal that has to be reached. The goal can be described by a single criterion or a set of different criteria that are important to the building owner.
The decision making process should be seen as an iterative and circular process, as illustrated in Figure 3–1. The definition of the main goal and decision criteria for process assessment, definition of alternative solutions, estimation of performance, evaluation, and solutions and proposals are strongly interlinked.
Figure 3–1: Decision making process during planning phase (adapted from (Allane, 2004))
A decision making process starts with setting the goal(s). It can be either a single goal like reducing energy consumption or several parallel goals, e.g. reduction of energy costs and reduction of environmental impact. Each goal can be described with one or more criteria.
Work on historic buildings might be challenging in regards to both applicability and unacceptable hygrothermal risks as a consequence of applying internal insulation. Application of internal insulation in historic buildings can be carried out based on several goals: energy consumption reduction or energy savings, purely economic goals, indoor climate improvement, loss of floor space and reduction of environmental impact as illustrated in Figure 3–2 and further described in ‘Reduction of energy consumption’ and ‘Reduction of environmental impact’.
These goals have to be reached without compromising hygrothermal behaviour of existing wall (for more details, see ‘Know Your Building’) and heritage value.
Figure 3–2: Classification of goals for internal insulation in historic buildings used in the RIBuild guidelines and webtool.
European standard EN 16883:2017 Conservation of cultural heritage. Guidelines for improving the energy performance of historic buildings (EN 16683, 2017) provides a holistic approach to energy efficieny in historic buildings. The standard is a guideline on how to sustainably improve the energy performance of historic buildings, and it presents a normative working procedure for selecting measures to improve energy performance, based on investigations, analysis and documentation of the building, including its heritage significance. EN 16883:2017 has a much broader scope than RIBuild as it is not limited to specific measures targeted at specific building components but looks into all kind of renovation of historic buildings, aimed at improving the energy performance. EN 16883 includes a list of assessment categories that are relevant when downsizing the number of potential measures:
Technical compatibility
Heritage significance of the building and its settings
Economic viability
Energy performance
Indoor environmental quality
Impact on the outdoor environment
Aspects of use.
Reduction of energy consumption
This goal is to minimize building’s operational energy consumption, expressed as energy spent for either heating, ventilating or cooling the building regardless the energy source. RIBuild web tool uses energy savings (kWh/m2 year) as the criteria for energy consumption reduction goal.
Example:
The owner of a historic building has collected data about specific heating energy consumption during the last three years and the average consumption is 150 kWh/m2/year. This number is very high compared to requirements for new buildings. The owner sets the goal to reduce energy consumption by at least 25% without risks caused by changes in hygrothermal behaviour of the wall and without impact on the heritage value of the building.
Other energy use criteria can be (not used in the RIBuild web tool)
heating and cooling load for conditioned buildings (kWh/year; MWh/year)
normalized specific energy consumption for heating and cooling (kWh/m2/year; MWh/m2/year)
energy savings reached by internal insulation expressed as fraction from baseline energy consumption (%)
U-value of wall (W/(m2K)).
Example:
The building owner would like to carry out major renovation of his historic building. National building regulations demand to reduce energy consumption of buildings if major renovation is carried out. U-values of external walls are defined in national or local building regulations and based on this the building owner sets the goal for internal insulation to reduce U-value of external walls from 1.9 W/(m2K) to 0.2 W/(m2K).
Reduction of environmental impact
This goal is to reduce possible environmental impact when applying internal insulation. It can be either reduction of CO2 emissions to lower the impact on climate change during operation phase of the building or reduction of environmental impact considering cradle-to-grave approach (incl. the construction phase, the operation and maintenance phase, and the end of life phase). In the RIBuild web tool the goal to reduce CO2 emissions from energy consumed during building operation phase (kg CO2/m2/year) is provided. Results obtained from the web tool can be used further to assess cradle-to-grave life cycle impact for 1 m2 of surface with LCA tool available in the web tool.
Example:
A state owned university has signed a voluntary agreement with the government to reduce CO2 emissions by 2000 t CO2/year. University campus comprises several historic buildings with heritage value and external insulation is not applicable. The university management decides to reach the goal by implementing different measures, including reduction of CO2 emissions by applying internal insulation.
CO2 emissions is used as climate change impact criterion while a set of different indicators is used for the environmental impact for assessment of life cycle impact from cradle to grave. Environmental impact criteria are
annual CO2 emissions (t/year)
for life cycle impact assessment for the functional unit:
o climate change
o biodiversity
o use of nonrenwable natural resources
o human health.
Detailed information about life cycle assessment for 1 m2 of surface using the RIBuild LCA tool is available in (RIBuild Deliverable D5.1, 2017).
Example:
The building owner has decided to apply internal insulation to external walls of his historic building. His aim is to use materials that have the lowest life cycle impact environmental score according to ISO standard 14044 assessed for the proper functional unit (per 1 m2 of insulated surface area).
Reduction of energy and other costs
This goal is set to minimize all costs for application of internal insulation in historic buildings, in particular energy, material and installation costs as well as life cycle costs. It may also consider other costs relevant for a specific case. When preparing the RIBuild web tool, valid data for costs of material and installation (EUR/m2) were not available. Therefore, this goal is not dealt with in the RIBuild web tool.
Example:
A housing company owns rental apartment buildings. Only internal insulation can be applied to external walls due to heritage value. The company has set the goal to reduce annual energy costs with maximum investment budget for material and installation cost of 1.000.000 EUR.
Other costs criteria are encompassing (not included in RIBuild web tool)
reduced energy costs (EUR/year)
investment costs (EUR)
annual maintenance costs (EUR/year)
net present value of the investment (EUR)
internal rate of return of the energy investment (%).
Example:
A municipality owns a vast number of buildings in the historic part of a city and the majority of these buildings contains facades with heritage value. Energy tariffs are increasing every year leading to increasing spendings for energy from the budget. The mayor of the city has set the goal to get a 3 % internal rate of return of an investment to reduce energy consumption.
Improvement of indoor climate
This goal is set to improve the indoor thermal comfort. Unsatisfactory thermal comfort is related to low surface temperature of the wall which causes thermal asymmetry.
Example:
An office is located in a 200 year-old building. Employees with desks close to external walls complain about being cold during the winter season. They are more absent due to illness than other employees. The owner’s goal is to increase inner wall surface temperature to +18°C if the room temperature is +20°C.
Other indoor environment criteria is Predicted Mean Vote (PMV) often used together with Percentage of Person Dissatisfied (PPD) (not included in the RIBuild web tool).
Loss of floor area
This goal is set to have the least possible loss of floor area due to internal insulation. In the RIBuild web tool loss of space area (m2) is used to illustrate the goal.
Example:
An office is located in a very expensive part of the city and loss of any floor area reduces income from the rent to the building owner and might reduce the possibilities to design the office. The building owner therefore has set the goal to apply internal insulation by losing a minimal amount of floor area, limiting the thickness of the possible solution.
Combination of different goals
When multiple goals are set by the building owner they can either complement or oppose each other. For example, reducing energy consumption and reducing CO2 emissions are complementing goals while minimising energy consumption and at the same time maximising the income for renting out the building can be opposite goals. Energy costs are reduced but so is the floor area and considering the price of the floor m2 in some area and the investment costs, insulating a building is often not profitable. Each goal has its weight - some goals can be more important than others. In the RIBuild web tool the user can assign weight to each goal (not important, least important, moderately important, very important). Based on simulation results, insulation systems are ranked, based on multi-criteria decision making analysis.
Multi-criteria decision making (MCDM) is applied if an decision maker, e.g. building owner has several possible alternatives available (e.g. internal insulation systems and materials) and has to select one of them, without any knowledge of which one is the best. Decision is made based on several criteria.
MCDM methods are used to help decision makers making their decision according to their preferences and to help them integrating the information so that they feel confident about making a decision. Mathematical methods provide quantification and prioritization of personal judgments. To use MCDM a complex problem needs to be broken into its smaller components and set importance or priority to rank the alternatives in a comprehensive and general way to look at the problem mathematically.
MCDM methods differ in the nature of the model, in the information needed, and in how the model is used. However, they have in common definition of alternatives, criteria and the relative importance of the different criteria.
In the RIBuild web tool, TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method is used (Yoon & Hwang, 1981). The method is applied in these steps.
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