Analysis of a variable auxiliary volume predictive-controller for an auxiliary-energy producer with a stratified solar thermal combistorage

Abstract

Status quo controllers of auxiliary-energy system in a hybrid thermal energy system use a simple dual-auxiliary-zone method where the maximum temperature and maximum volume of the space heating (SH) and domestic hot water (DHW) loads on highest consumption day in a year are utilized. Due to this simple control, there are high storage losses in the winter period an also less storage space available for the renewable production. In this paper, the authors propose a novel predictive control strategy with the use of stratified thermal storage. The control strategy is further, in terms of as ideal simulation study, investigated for a decentral thermal energy system in southern Germany with solar thermal collectors and a gas boiler auxiliary energy system for a stratified combistorage with DHW and SH loads. The obtained results in a Sonnenhaus standard single-family house show that the auxiliary energy input is reduced by 650 kWh (6%) annually with a maximum of 190 kWh reduction in March. Moreover, in the month of March, a 5% increment in terms of solar thermal fraction and a 5.5% decrement in terms of the gas boiler fraction is achieved. And by better use of the storage, especially during the winter months (November to March), a 16–20% reduction in storage losses is achieved. Annually, 2.2% reduction of gas boiler fraction, 4.6% reduction of storage loss and 1.8% increase of solar fraction are attained.