Control strategies of solar heating systems coupled with seasonal thermal energy storage in self-sufficient buildings

Abstract

A numerical analysis is carried out to investigate the influence of different solar collector control strategies on the performance of a solar heating system coupled with seasonal thermal energy storage. The system is used for space heating and domestic hot water production in a low-energy residential building. The performance of the controller is measured in terms of the minimum storage volume required to achieve an annual solar fraction of 100%. Three controllers were numerically investigated: (1) a high-flow controller (HFC) with a constant nominal flow rate of 40 l/h⋅m2, (2) a low-flow controller (LFC) with a constant nominal flow rate of 12.5 l/h⋅m2, and (3) a variable-flow controller (VFC) with a flow rate in the range 4 – 40 l/h⋅m2 whose objective function is given by a predefined temperature at the outlet of the collector. The performance of the investigated controllers is assessed by conducting full year simulations using an in-house, experimentally validated model. A detailed comparative analysis reveals that the reasons behind the specific performance characteristics of each controller are closely related to the thermal stratification effected in the storage and to the capability of the controller to preserve the stratification throughout the year.