Stability performance dilemma in hydronic radiators with TRV

Thermostatic Radiator Valves (TRV) have proved their significant contribution in energy savings for several years. However, at low heat demands, an unstable oscillatory behavior is usually observed and well known for these devices. It happens due to the nonlinear dynamics of the radiator itself which results in a high gain and a large time constant for the radiator at low flows. If the TRV is tuned in order to dampen the oscillations at low heat loads, it will suffer from poor performance and lack of comfort, i.e. late settling, when full heating capacity is needed. Based on the newly designed TRVs, which are capable of accurate flow control, this paper investigates achievable control enhancements by incorporating a gain schedulling control scheme applied to TRVs. A suitable linear parameter varying model is derived for the radiator which governs the gain scheduler. The results are verified by computer simulations.