Ingenieurbüro Arbeitsgestaltung und Baubiologie <a href=Peter Rauch">
(This page was automatically translated from German. Wärmespeicher)

Does a heat insulation bring a saving of energy?

If one runs barefoot with summery temperature over the beach or over one fast ones, then, one notices the high temperatures at the soles even if only 25 or 30ºC amount to the air-temperature. The cause is the radiation-heat from the sun, that heats up the solids. However, the same takes place also at a house-wall if the sun shines on the day. The heat becomes in the massive wall stored and in the night again affected. If the more outer wall-section has a higher temperature in the average through the stored solar-energy, so also the temperature-difference of indoors outside decreases, that him/it Heat flux influence. (See the contribution to the examination here "Stored solar-energy at an outside-wall"). According to wall-setup, the stored solar heat quantity lies approximately so highly at a South-page that itself the temperature-difference about about. 4 K reduced.

In a small case in point, this should be clarified. The ambient air should amount to 20ºC and the outside-air -5ºC.

Outside-wall unit of heat-transfer 0,5 W/m2K
21 K x 0,5 W/m2K = 10,5 W/m2 per h.

Retroactive heat insulation of this wall with a heat insulation (6 cm) U=Value 0,3 W/m2K
Corresponds to 25 K x 0,3 W/m2K 7,5 W/m2 per h.

It is saved 3 W heat circa with the additional heat insulation per m2 outside-wall per hour. On the day is the 72 W.

Exactly the average-temperatures over several years would have to be grasped for an exact economic viability-contemplation. The Gradtagzahl for example for Leipzig lies with 3350 Kds / a. This gets together from medium number of the Heiztage and the medium air-temperature of all Heiztage.
A saving of energy emerges through this retroactive heat insulation between 5 to 10 KW/m2 outside-walls. (Heizwert of fuel oil 10 KILOWATTS / l for circa 0,55 Euro, this corresponds to a cost for heating-restriction of approximately 0,27 to 0,55 Euro / year per m2 outside-wall. The square meter heat insulation costs between 50-85 Euro. Is still remarked here that a Wärmedämmverbundsystem a stand-time of about. 20 maybe also 30 years has. The facade must be restored after it.

The diminution of the unit of heat-transfer of 0,5 W/m2K on 0,3 W/m2K corresponds 40 per cent. This diminution becomes 100 years of erkauft with an investment-time limit of bigger.

The Swiss energy-specialist Dipl.-Ing. Paul Bossert makes big single-family home at the case in point of a 135 qm with about. 165 qm outside-wall-plain following balance sheet:
1. Outside-wall with 40 cm massive brickwork (unit of heat-transfer 1,5 W / m2K), after former construction-sages, with a computational share at the energy consumption per Heizperiode 1.920 liter fuel oil.
2. Outside-wall after present-day well dammed construction-sages (unit of heat-transfer 0,5 W / m2K) and a computational share of the energy consumption per time limit 640 liter fuel oil.

During this theoretical comparison, a saving of energy of 66 per cent is performed in favor of the dammed facade. Everywhere, the positive energy-profit margins are accentuated by solar-collectors, who correspond approximately 40 liters of fuel oil per square meter. If one takes only one quarter of the "profit" and transfers this outside-wall massive on the above named, so this corresponds a cost-free sun-heat-profit margin of 1.600 liters of fuel oil per year with this case in point opposite a dammed facade. At a brick-building, only 320 liters would be required fuel oil consequently. That however, this is not so few, still is because of other elements, how for example the necessary ventilation, sees ventilation the contributions to this and Humidity) and the respective utilization-performance. But these elements effect also the very strongly dammed building so that the "promised" low energy consumption never is kept to here. A builder (even small trade-masters) told me a few years ago, the fuel oil-consumption is exactly in duplicate so high as he/it was declared (calculate) in the specifications. Other builders didn't do so concrete statements, was very much (negative) surprised over the essentially higher energy consumption after the collection, however.

In the following graphics, the relationship between improvement of the unit of heat-transfer and the heat insulation-strength is shown. If one is performed respectively damming brickwork with a heat insulation badly insulating 11er or 24er wall later, for example, so considerable saving of energy can be achieved. If however, the outside-wall has already an unit of heat-transfer of 0,5 W/m2K, so this expenditure brings only a low improvement (see this above named case in point). As well one cannot achieve as well as any additional restriction with a very thick heat insulation since a part of the heat-energy is exchanged by the ventilation. The exact Erläutung of the construction-physical connections takes place atmospheric humidity in the contribution in the apartment.
Kurve Transmissionswärmeverlust
U-value-curve detailed.

The politics use relationship-statements very gladly, for example it is 30 per cent to save. An efficiency can be expressed only by absolute numbers in principle. Case in point: On an in stock outside-wall with u=1's ,55 W/m2K, a heat insulation is found (see graphics) by 4 cm. Become about theoretical with a temperature-difference of 20 K (indoors to outside) and the maintenance of the constant space-temperature. Saved 20 W/m2 outside-wall-expanses per hour. With very firm heats insulation, hardly another additional saving of energy takes place on the other hand. So, it becomes a 11 cm of heat insulation with a 17 cm opposite heat insulation about theoretical. 1 W/m2 outside-wall-plains on hour saved.

Tap to the yielding a return energy-utilization, a radiation-heater and massive heat storing walls (above all inner-walls), covers and floors.

Online-calculation of the effective one - and transmission-heat loss at an outside-wall and comparison with a measures for a heat insulation and practical attempt this Heat-storage of an outside-wall.

A retroactive heat insulation is not in every case meaningful. Here, different considerations should be employed previously. Also following two contributions could help with the decisionMistakes and errors, deceits and cover-ups and Redevelopment-giddiness

Ingenieurbuero Peter Rauch

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