A common component of many building heating systems is a thermostat that controls the power on the radiators by changing the mass flow and/or temperature of the feed water. In some cases, these old thermostats malfunction or do not work quite as they should. This can contribute to large indoor-temperature fluctuations, which in turn can lead to unnecessary energy use and poor thermal indoor climate.

The goal of this paper is to develop a thermal dynamic model of hydronic radiators as well as a thermal dynamic building model to build Simulink models and investigate different control strategies to control the indoor temperature. By adapting better control strategies, one can reduce indoor-temperature fluctuations and reduce energy use.

The results of simulations in this paper suggest new ways of thinking concerning building a model of hydronic radiators and controlling them and that the temperature control of the studied building will be improved by using a well-functioning thermostatic radiator valve (TRV) instead of a poor-functioning TRV. The smaller fluctuation of the indoor temperature when using a well-functioning TRV compared to a poor-functioning TRV results in better indoor climate. Different types of TRV failures might give rise to large indoor-temperature oscillations, very high/very low indoor temperature and/or high energy use. In some cases, a poor-functioning TRV results in unreasonably high indoor temperatures and high energy use, and in other cases it might result in very low indoor temperatures, whereas the difference in performance when using well- functioning controllers (P and PI) is marginal. © 2015 juniper publishers,