Optimal thermal insulation thicknesses

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Optimum thermal insulation thicknesses: CTE Plus study.

When analyzing a home energetically, the thermal insulation thickness It is one of the basic issues that will lead us to an improvement of the habitability conditions of the dwelling to be treated, for which it is essential to know all the pertinent characteristics related to the house insulation.

Following the publication of a technical report of a new study called CTE Plus, prepared by CENER (National Center for Renewable Energies) for ROCKWOOL, which focuses on quantify what is the potential for energy savings in homes by improving thermal insulation in their envelope. It proposes to increase the insulation thickness above those that are limited to meeting the requirements of the Technical Code, depending on the climatic zone where the building is located.

To carry out the study and identify the potential for the calculation of thermal insulation, three different models of buildings were used, two of a residential type, and a third of offices. These were simulated in three different climatic zones (Seville-B4, Madrid-D3 and Burgos-E1). The mean potential savings was calculated by applying a population distribution (63% in climatic zone B4, 34% in D3 and the remaining 3% in zone E1).

It raises the effect of a possible future scenario, by comparing the scenario of the CTE (Version April 2005) with a scenario named CTE-Plus whatwhich is based on the mathematically optimal thickness, further demonstrating that the necessary cost of investment on thebuilding insulation it can be amortized in a short time. As models, they are considered single-family homes and apartment blocks, as shown in detail in Annex 1.

In the parameters used for the study, the energy price, the price of the insulation, the durability of the insulation, the CO2 price penalty and the CO2 conversion values are considered.

Calculation model for optimal insulation:

In order to get the optimal insulation thickness, a calculation model similar to that used in the ECOFYS report is used: "Cost-Effective Climate Protection in the EU Building Stock", by creating the economic benefit function defined as the difference between income (Total annual costs derived from savings when insulation is increased) and expenses (Annual investment cost when insulation is increased).

Figure showing the difference between optimal and ideal thermal insulation:


The number of years in which the costs of the energy saved equal the initial investment made is considered as amortization. An insulation amortization period of 40 years is considered for this study, estimating that it is the time it takes for a building to be fully rehabilitated and the moment in which the insulation of the envelope is possibly improved or changed despite the fact that it could be in good condition.

Angles resulting from the study:

The following table shows the insulation thicknesses used in the “CTE scenario”:

While the following table shows the values corresponding to the “CTE-PLUS” scenario, being the insulation thicknesses used in the simulations for each climatic zone.

Energy savings between both scenarios:

For individual homes, the savings in each of the climatic zones corresponds to that indicated in the following table:

For blocks of flats, the savings in each of the climatic zones correspond to that indicated in the following table:

Most relevant conclusions of the CTE Plus study:

The simulations show that by increasing the insulation thickness by 5, 9 and 13 cm over what is required in the CTE, and depending on the climatic zone, the accumulated energy savings is ~ 10 TWh (9873 GWh) for new homes built in Spain in the period 2006 - 2012.

The huge market represented by the rehabilitation of the existing housing stock, nor the tertiary sector buildings, was not taken into account in the study. The study shows that the greatest potential for energy savings by increasing the thicknesses above those indicated in the CTE. The greatest savings are obtained in heating periods while in cooling periods the savings are less.

The energy savings obtained per m2 in the isolated houses are higher than those obtained in blocks of flats. One of the reasons that justify this result is that single-family homes have a greater exposed area per m2 than the housing block and, therefore, the influence of changes in the thermal characteristics of the enclosures is very important.

You can access all the documentation of the study or CTE Plus report from… HERE.

As a complement you can access the post… «Thermal transmittance tools«With different sheets in Excel to perform calculations.

Note: I add a Linkedin link to the debate that we believe is of general interest and to complement this post….HERE.

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