In a study reported in Meyer (2000), in which the interviewees were asked which functions they would expect and require to be performed by a home automation system, the temperature reduction during the occupants' absence was requested in the first place. This request implies the reduction of heating energy consumption and the associated reduction of heating costs.
As mentioned earlier, an installed bus system provides the option of single room control. The target room temperature can be (pre) determined for each room for a given time. Furthermore, the flow temperature can be adjusted depending on the heat output demanded by the individual spaces. These control options can reduce heating energy consumption, provided that they are properly programmed. However, the amount of energy to be actually saved strongly depends on the structural conditions of a specified building. The smaller the thermal mass of the building and the poorer the thermal insulation of the building skin, the greater the achievable savings will be. Accordingly, poorly insulated, lightweight constructions have the greatest energy saving potentials. It is therefore not possible to state a general rate of energy conservation.
A study is reported in Bitter (2000) that was conducted to investigate the control performance of radiator controllers in a test facility. The tests comprised three electronic continuous controllers and one conventional thermostatic valve. The test results suggested that about 15 per cent less heating energy was required when electronic control valves were used (compared to thermostatic valves).
To determine the amount of energy saved due to intelligent control systems under actual conditions, a field test was performed including both property and dwellings (Balzer, 1999). Here, 1161 dwellings were provided with time programme single-room temperature control systems and integrated energy consumption metering. In the 950 dwellings that were used for comparison purposes, the room temperature was controlled by means of conventional thermostatic valves. In addition to the time programmable single-room temperature control, the control system also comprised window status monitoring, which will stop the heating water flow as soon as the window is opened. However, if the duration of window venting exceeds 30 minutes, the water flow will be reactivated for reasons of comfort. This function also contributes to reducing the demand of heating energy. Compared to the dwellings controlled by conventional thermostatic valves, heating energy savings of about 15 per cent were determined in the field test.
These values were measured in existing houses with a heating energy consumption of approximately 110 kWh/m2a. According to experience, energy savings are not that substantial in new buildings, their energy demands being significantly lower. Following German standard DIN 4101 (DIN 4701-part 10, 2003), a loss per unit area of 3.3 kWh/m2a has to be assumed concerning the heat transfer to the space in buildings equipped with thermostatic valves (design proportional margin: 2 Kelvin); on the other hand, only 0.4 kWh/m2a are assumed for buildings provided with an electronic control system and window state monitoring. This means that one assumes energy savings of 2.9 kWh/m2a compared to customary thermostatic valves.
It must still be mentioned that the functions of single room control and window state monitoring can be implemented either with the EIB system or with other manufacturer-specific solutions.
The amount of lighting energy saved due to a bus system significantly depends on the occupants' behaviour and cannot be quantified. On the basis of experience, a lighting system that is coupled to a bus system will not save more energy than a conventional lighting system that is operated by energy responsible users.
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