Guideline for evaluating energy saving potential, environmental impact and life cycle cost

The main goal of this guideline is to provide support to the building owner or the building owner’s consultant to assess the energy saving potential, the environmental impact and the life cycle cost of internal insulation solutions.

This guideline presents a set of practical procedures on how to select an optimal internal insulation solution in a renovation scenario based on a number of decision criteria. First, the guideline shortly introduces three different methods for estimating the energy saving potential based on heat loss calculations. Second, it illustrates how to quantify the environmental impact caused by the application of internal insulation using Life Cycle Assessment (LCA). Finally, it details the calculation of Life Cycle Cost (LCC) of internal insulation solutions.

Figure 6.1 presents the link between a probabilistic hygrothermal assessment and a subsequent calculation of heat loss, environmental impact and life cycle cost, all being part of tools prepared within RIBuild. The calculations of heat loss, environmental impact and life cycle cost has been implemented in the WP5 software tool (RIBuild Deliverable D5.1, 2017) and in a simplified way in the WP6 web tool for hygrothermal assessment (RIBuild Deliverable D6.1),both accessible through the RIBuild project webpage. These tools enable the probabilistic assessment for both hygrothermal performance and environmental impact/life cycle cost of an internal insulation solution, to support risk management and decision-making.

Energy saving potential

The energy saving potential is found by comparing the heat loss through the existing external wall before and after applying an internal insulation system. Heat transmission loss exists as soon as there is a temperature difference between indoor (e.g. set at 20°C) and outdoor. Calculating the heat loss requires values for the U-value of the wall, monthly outdoor temperature at the location, average indoor temperature and the number of heating hours. The U-value represents the ability of the external wall to resist to the heat transfer through the wall. Energy saving potentials are expressed for instance as kWh/m2 per year.

The RIBuild web tool provides energy saving potential for different internal insulation systems, external wall types, climate and location. The energy saving potential of different systems are only comparable if there is a common basis for the comparison (e.g. the same U-value for each alternative). In the case of comparing insulation systems with the same thickness, it is important to keep in mind that systems with a better thermal performance will be favored, as they require less thickness to provide the same savings. The more the wall is insulated, the higher the savings will be. However, the thickness is in general limited from a hygrothermal point of view, as the risk of moisture related damage described in ’Damage risks in historic buildings’ and ‘Assessment of state of the building envelope’ otherwise might be too high.

It is important to recall that heat losses through the opaque or non-transparent part of the facade do not cover the entire heat demand of a building. More aspects have to be included such as solar gains, ventilation losses, thermal bridges etc. Those aspects are not investigated in the RIBuild web tool and guidelines.

Different calculation methods can be used to perform the annual calculations of heat loss through the facade during the heating season. Three different approaches (or ”options”) can be considered:

1. coupled heat and mass (HAM) transfer numerical model based on hourly climate data;

2. monthly calculation between the internal temperature and the average monthly temperature;

3. annual calculation based on annual Heating Degree Days (HDD).

Option 1 allows having an accurate and consistent assessment on hygrothermal aspects prior to the LCA. However, option 1 is highly demanding in terms of accurate climatic data and indoor conditions, material properties of the historic facade and of the chosen internal insulation systems. The details of the heat loss calculations using a coupled heat and moisture transfer simulation are not presented in this guideline. Nevertheless, the software tool for probabilistic LCA of internal insulations developed as WP5 software Tool (RIBuild Deliverable D5.1, 2017) allows using HAM tools results (even provided as PDFs) for the LCA assessment.

The other two calculation procedures can be used when a HAM simulation is either not feasible or not possible (i.e. calculation cost or time issue, missing material properties leading to irrelevant HAM simulations etc.). The procedures can be used, as stand-alone calculation methods, to estimate the heat losses through the facade using simplified but standardised approaches, as described in ‘Environmental impact using life cycle assessment’ and ‘Life cycle cost assessment’. Option 3 has been implemented into the WP5 software tool (RIBuild Deliverable D5.1, 2017) to easily obtain transmission losses through the wall in a probabilistic or deterministic way.

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Environmental impact using Life Cycle Assessment

The environmental impact associated to the implementation of internal insulation should be quantified by a consolidated, comprehensive and systematic method. Life Cycle Assessment (LCA) is a standardized and internationally recognized method to quantify resource consumption, environmental impact, and emissions linked to a product or service through its whole life cycle. The probabilistic LCA methodology developed in RIBuild, as implemented in the WP5 tool and WP6 web tool, can calculate possible ranges of the environmental impact of several internal insulation solutions, thus to investigate and compare different design options upon their optimized hygrothermal performance.

To do so, both induced and avoided impacts of the insulation systems should be quantified (Figure 6.2). The former is related to the added internal insulation system, and the latter is due to the heat losses reduction (i.e., the energy saving potential) for a specific heat source in the building (heat pump, oil-fired boiler, natural gas, wood pellet boiler, district heating, etc.).

For the internal insulation of 1 m2 opaque facade, the environmental impact is mainly dominated by the operational energy use, rather than the induced impact from the applied internal insulation systems. Here, the most influencing factor is whether the heat production system has been replaced during the renovation as the environmental impact is mainly driven by the operational energy use.

LCA can calculate a number of indicators to evaluate the environmental performance among different insulation solutions. RIBuild focuses on the indicator of Global Warming Potential (GWP) by quantifying the greenhouse gas emissions (GHG) caused by the construction materials (induced impact) and the transmission heat loss (avoided impact). The defined system boundaries of the insulation systems in RIBuild are in accordance with  (EN 15804, 2012), as shown in Figure 6.3. The analysis covers the production stage (modules A1-A3), the use stage (module B2 (maintenance), B4 (replacement) and B6 (operational energy use)), and the end-of-life stage (EoL) (modules C1-C4), making this a 'cradle-to-grave' simplified LCA. Modules A1-A3, B2, B4 and C1-C4 are the induced impact, whereas module B6 is the avoided impact from saved energy consumption via space heating. Due to the assumed low influence of impact from construction materials in the scope of RIBuild (where most of the impacts are linked to the operational energy use), module A4 (the transportation to building site), module A5 (construction process), module B1 (use), B3 (repair) and B5 (refurbishment) are excluded in the RIBuild LCA modeling. More information is available in (RIBuild Deliverable D5.1, 2017). Practitioners should be aware that the defined system boundary in RIBuild WP6 web tool can be different from the WP5 tool.

The LCA calculation requires input data on transmission heat loss before and after the renovation (i.e. data from the energy saving potential calculation, see section 6.1) to determine the operational energy use and the environment impact savings caused by the added insulation thickness. To do that, heat loss savings are converted into environmental impact savings using LCA data, expressed as 1 kWh (or MJ) of heat provided by the building’s heating system (e.g., heat pump, oil boiler, naturel gas, wood pellet boiler, district heating etc.).

Figure 6.4 presents an example of a typical probabilistic LCA result, where uncertainty ranges of environmental impact are calculated for five insulation solutions and different heat producer replacement scenarios. The calculation takes account of parameter uncertainties in the heat loss and LCA input. As shown in Figure 6.4 (left), there are no significant differences in terms of the GHG emissions among the internal insulation systems. While in comparison, a clear ranking with a relatively high confidence (robust choice) is shown for the GHG emissions in the scenario of heat producer replacement, see Figure 6.4 (right). This result suggests that, the LCA results are highly influenced by the choice of a new heating system, rather than the material of insulation systems.

More information, case studies and interpretation are available in (RIBuild Deliverable D5.1, 2017). Further, in the WP6 web tool, heat loss and environmental impact are computed based on user input about a specific building (RIBuild Deliverable D6.1).

Other tools exist as well to calculate energy saving potential and LCA for a 1 m2 of an opaque facade insulation as well as for a whole building, including tools developed and used in RIBuild partner countries, such as the Swiss tools Eco-sai (Ecosai) and Lesosai (Lesosai, 2017), the Danish tool Be18 (Aggerholm, 2018), and the Italian software Termo Namirial (Termo Namirial, version 3.3). However, they do not cover a full probabilistic LCA approach as the one developed in RIBuild.

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Life Cycle Cost assessment

Life Cycle Cost assessment (LCC) is a useful decision support method to investigate benefits and risks of the investments in the building renovation sector. LCC can be practically used to select the most profitable design option, providing estimates of total expected costs and savings (due to lower energy consumption), during an established time period and adjusted for the time value of money.

Concerning LCC of internal insulation solutions, it is important to consider the initial investment costs (to install the insulation system) and the future costs over a certain time period, i.e. the costs related to the possible maintenance and replacement needs and the costs related to the building (reduced) heating energy consumptions due to the renovation measure (Figure 6.5).

In practice, the initial investment cost represents the cost for the purchase and construction/installation of the insulation system. It depends on the cost of each material and on the installation procedure and time. When installing internal insulation there might be additional investment costs depending on the intervention complexity that should be considered (Figure 6–4), such as: removing everything fixed to the walls to be insulated, cleaning and preparing the wall surface, eventually reinstalling the previously removed items (see ‘Insulation Systems’). Furthermore, in certain Countries and for certain building typologies with high architectural and cultural value, additional costs could be due to the administrative process to get the intervention permissions.

When the internal insulation is applied to a wall, during the building life cycle, possible maintenance or replacement operations could occur for preserving and restoring the desired quality of the building element (e.g. in case of mould growth on the new internal surface).

The energy cost is the cost related to heating/cooling the building. It is obtained by multiplying the energy consumption with the tariff for the energy carrier considered.

The importance of using LCC in the building sector has been attested at regulatory level in Europe by Directive 2010/31/EU (European Parliament, 2010), which establishes that Member States shall calculate “cost-optimal levels” of their building energy performance requirements using a comparative methodology framework (EU No244/2012, 2012), (European Parliament, 2012). “Cost-optimal level” means the building energy performance level which leads to the lowest cost during the estimated economic lifecycle, where the lowest cost is determined by taking into account energy-related investment costs, maintenance and operating costs including energy costs and savings.

The main reference standard in the field is EN 15459-1:2017 “Energy performance of buildings – Economic evaluation procedure for energy systems in buildings. Part 1: Calculation procedures, Module M1-14” (EN 15459-1, 2017). It provides a calculation method for the economic assessment of the building components and equipments named “Global Cost”, used for aggregation of the past, present and future costs over a calculation period. Indeed, as costs are accumulated during a time period, the assessor needs to keep in mind that the monetary flows can occur at quite different times, and costs that occur at different times are not directly comparable.

In the long run there is a general increase in the overall prices of goods, which at the same time may affect the purchasing power of currency—known as “inflation”. A solution facilitating the comparison among future and present costs in LCC is “discounting”, which assigns a lower “weight” to costs in the future than present costs. The discount rate allows to figure the performance of the money placed on the market during time. It depends on inflation and interest rates and may be different for different types of costs, due to different price development rates for energy, human operation, components, etc.

The outputs of the LCC method included in the standard EN 15459-1:2017 are: global cost and payback period.

The global cost is determined by summing up the costs of all categories and subtracting the cost of the final (residual) value.

The payback period illustrates the potential of different options compared to a reference situation, by the time when the initial investment is expected to be recovered. For internal insulation, the reference could be the actual state (uninsulated wall). Since an investment with future expenditure is considered, a “discounted” payback period is used to reflect the time value of money.

A considerable amount of research refers to standardized LCC methods (EN 15459-1, 2017) to assess the economic impacts of energy efficiency measures for building design and renovation. In compliance with European and national legislations across Europe, LCC of building design options is usually performed based to these methods, with notable simplifications related to the cost items selection and quantification and to the forecast of macro-economic variables.

Unfortunately, LCC procedures applied to energy renovation measures on historic buildings most often suffer from several intrinsic uncertainties especially related to the long-term perspective of the building intervention. Taking into account uncertainty and variability in LCC is an important challenge to improve the reliability of LCC based decision making. RIBuild Work-Package 5 addressed this issue and proposed a “probabilistic” approach and a software tool for LCC of internal insulation. Further information can be found in  (RIBuild Deliverable D5.2, 2018) and (Baldoni, Coderoni, D’Orazio, Giuseppe, & Esposti, 2019).

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