Udvikling af klimaskærmskonstruktioner

Henrik Monefeldt Tommerup, Jørgen Munch-Andersen, Peter Kjær Esbensen

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Abstract

The present report concludes the work concerning the development of building envelope constructions, which can form the basis of new buildings with considerably less heat demand than in the present building regulations.

It has been made probable that it is technically possible to build exterior walls with less heat loss than those just complying with the requirements of the current building regulations with no considerably added use of material apart from insulation. In their structure many of the shown constructions resemble types that are used today, while others pre-suppose that one part of the wall is attached to the other part or possibly to the rafters.

It has been pointed out that line loss at the foundation is still considerable when the foundation, in the form of two lightweight aggregate concrete (LWAC) blocks (the upper 40 cm of the foundation), penetrates the insulation. Development of new components for the upper part of the foundation will therefore be desirable. One possible solution might be bigger elements of LWAC with suitable recesses filled with insulation material.

The contribution of the window rabbets to the heat loss is fairly small for the shown solutions since the insulation thickness of the window rabbet is relatively large. The comparatively large line losses that are calculated are mainly due to the two-dimensional heat flow caused by the joining between window and wall. The line loss can be reduced by development of window types that cause less two-dimensional heat flows and by aiming at a window placement around the middle of the window-rabbet-insulation – in other words, relatively far back in the façade compared to traditional Danish architectural tradition. However, the last-mentioned proposal has great architectural and aesthetical consequences. In addition, the solar energy transmission through the window will be reduced whereby the heat loss saving to some extent will be counterbalanced by a smaller solar heat contribution.

Calculations concerning the importance of heat capacity for a 100 m2 single-family house have been made which confirm that by using heavy rather than light envelope constructions the reduction of the heating requirements is relatively small. Therefore optimisation of the insulation level can be carried out separately on the building components.

A method has been developed for the evaluation of the optimum insulation level for the individual building components of the building envelope based on life cycle cost analysis. The method is based on making up the changes in the operational energy costs / heating-costs and the cost of construction due to a change in the insulation thickness over a 30-year period. The life span of the primary parts of the building envelope is estimated at 100 years. It is assumed that the gross energy consumption that covers the heating requirements and the heat loss (determined by a simple calculation of degree days) changes concurrently with the change in the insulation thickness, which has been proved to be a reasonable approximation.

The life cycle cost analysis has been carried out for a test-house of about 100 m2 and with two different energy price scenarios: 0.60 dkk/kWh (including taxes and VAT) which roughly corresponds to the present energy price level, and 1.20 dkk/kWh. Calculations show that based on the present energy price level the economically optimum insulation thicknesses are 25 to 100 % larger than those which just comply with the requirements of the building regulations. The increase is largest for exterior walls and smallest for the ceiling construction. The high energy price of 1,20 ddk/kWh results in an increase of 100 to 150 %. In this connexion it should be pointed out that the insulation thickness that corresponds to the same life cycle cost (neutral investment or a net present value of zero) as the level of the building regulations is even larger.

The energy consumption for heating concerning the two optimum scenario solutions for the test-house is reduced yearly by about 15 and 22 kWh per m2 heated floor space in the case of the traditional cavity wall with aerated lightweight-concrete back-wall. The incremental cost of construction for these optimum scenario solutions amounts to 20,000 and 50,000 ddk, which corresponds to 2 and 5 % of the total construction cost. Consequently, it is possible to insure a house in the future as far as energy consumption is concerned. All in all there are many aspects which point to the fact that it would be appropriate to tighten the requirements concerning the level of insulation in the new building regulations.
Original languageDanish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark, Department of Civil Engineering
Number of pages93
ISBN (Print)87-7877-044-0
Publication statusPublished - 2000

Bibliographical note

R-042

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