Surface temperature of the wall or slab refers to thermal conditions inside the room. Surface temperature, together with the inner temperature of the slab are indicators of the forthcoming indoor conditions. This can be benefitted for instance in floor heating, optimum start time control or thermally active building systems (TAB). However, direct surface measurement is difficult and sometimes even impossible. The new method makes possible to measure (actually estimate) the inaccessible and unknown surface temperature or heat flux of a slab using temperature measurements at an interior point of the slab (Fig. 1). Thus, both the inner and surface temperature can be measured and estimated using one sensor. The basic idea is to record data from inner point of the slab as a response to changes in surface temperature. Mathematically, this is called an inverse problem. This is also an ill-posed problem, where the noise corrupted measurements inside the slab are used as input data of the system. That is why, the data needs regularization, which is completed with digital filters. The test runs give promising results. However, due to the time derivative approximation and disturbances, abrupt changes in the estimated signal cannot be perfectly reproduced. This is shown in Fig. 2, which presents estimation of the square wave surface temperature when the measurements contain disturbances. The figure illustrates results in a two-layer slab. The first layer consists of insulation and the second of concrete. The sensor is installed in the middle of the second layer.
The presented solution to the surface temperature measurement problem represents a theoretical procedure, not yet applied in practice. However, the method has several good properties compared to other methods, which support its further development and productizing.
The solution can be derived mathematically in an explicit, recursive form, which is easy to transform into a computer program. The next step is to demonstrate its use in real environment. The method could be applied in heating or cooling control of floor heating, optimum start time or thermally active building systems.