With the aim of achieving an optimum indoor environment and lowering operating costs in the long term, the performance of a so-called “operational optimisation with weather forecast control” system has been tested in three administrative buildings in the German state of North Rhine-Westphalia since 2007. The operation of the heating systems is optimised based on a thermodynamic computer model and local weather forecast data. The result: A tangible increase in comfort with simultaneous heat energy savings.

Monolithically constructed buildings store heat in the walls, floor ceilings and fixtures. Depending on the insulation standard, type of heat exchangers (radiators, concrete core activation, HVAC system) and ventilation habits of the users, a change in the external temperature often only makes itself noticeable in the interior spaces after several hours or even days. A time delay therefore occurs between changes in the weather and the resulting heating requirement in the building interior. This can lead to increased energy consumption and reduced comfort caused by overheating.

Conventional control technology works with fixed time settings (e.g. day-night reductions) and rigid heating characteristic curves coupled with external temperature sensors. This is technically simple but has the disadvantage that adjustments have to be made by hand when changes in the weather occur. Many people will be familiar with this problem when it comes to underfloor heating. During the transitional periods, users helplessly play around with the heating settings to no avail. Sometimes it is too warm, sometimes too cold. In order to avoid complaints, the problem is often “solved” by setting the operating times and characteristic lines so generously that the heating technology safely copes with even the coldest day of the year. As a consequence, during most days with mild weather the heating “stubbornly” switches on too early at a fixed time and, despite the exterior temperature measurement, runs with an excessive supply temperature. And solar gain, which can have an enormous impact on the indoor environment in accordance with the building’s orientation and the amount of glazing, is not taken into account at all.

Radiators are mostly mounted beneath windows. Permanent ventilation caused by users keeping windows open causes cold air to fall on the legally required thermostatic heads on the radiator valves, which as a result open and demand the maximum output from the heating boiler. Above the radiators, warm air considerably above the room temperature level rises upwards and escapes directly through the open windows to the outside. The radiators therefore give off considerably more heat than would be required if the room were correctly ventilated (intermittent ventilation instead of permanent ventilation). A solution is therefore being sought for supplying heat that does not provide heat on demand in the traditional manner but instead heats the rooms in accordance with precise structural and user requirements.