8 research outputs found
Control-oriented modeling of a LiBr/H2O absorption heat pumping device and experimental validation
Absorption heat pumping devices (AHPDs, comprising absorption heat pumps and
chillers) are devices that use thermal energy instead of electricity to
generate heating and cooling, thereby facilitating the use of waste heat and
renewable energy sources such as solar or geothermal energy. Despite this
benefit, widespread use of AHPDs is still limited. One reason for this is
partly unsatisfactory control performance under varying operating conditions,
which can result in poor modulation and part load capability. A promising
approach to tackle this issue is using dynamic, model-based control strategies,
whose effectiveness, however, strongly depend on the model being used. This
paper therefore focuses on the derivation of a viable dynamic model to be used
for such model-based control strategies for AHPDs such as state feedback or
model-predictive control. The derived model is experimentally validated,
showing good modeling accuracy. Its modeling accuracy is also compared to
alternative model versions, that contain other heat transfer correlations, as a
benchmark. Although the derived model is mathematically simple, it does have
the structure of a nonlinear differential-algebraic system of equations. To
obtain an even simpler model structure, linearization at an operating point is
discussed to derive a model in linear state space representation. The
experimental validation shows that the linear model does have slightly worse
steady-state accuracy, but that the dynamic accuracy seems to be almost
unaffected by the linearization. The presented new modeling approach is
considered suitable to be used as a basis for the design of advanced,
model-based control strategies, ultimately aiming to improve the modulation and
part load capability of AHPDs
Optimal operation of residential heating systems with logwood boiler, buffer storage and solar thermal collector
A generally applicable, simple and adaptive forecasting method for the short-term heat load of consumers
Automatic thermal model identification and distributed optimisation for load shifting in city quarters
Buildings with floor heating or thermally activated building structures offer significant potential for shifting the thermal load and thus reduce peak demand for heating or cooling. This potential can be realised with the help of model predictive control (MPC) methods, provided that sufficiently descriptive mathematical models of the thermal characteristics of the individual thermal zones exist. Creating these by hand is infeasible for larger numbers of zones; instead, they must be identified automatically based on measurement data. In this paper an approach is presented that allows automatically identifying thermal models usable in MPC. The results show that the identified zone models are sufficiently accurate for the use in an MPC, with a mean average error below for the prediction of the zone temperatures. The identified zone models are then used in a distributed optimisation scheme that coordinates the individual zones and buildings of a city quarter to best support an energy hub by flattening the overall load profile. In a preliminary simulation study carried out for buildings with floor heating, the operating costs for heating in a winter month were reduced by approximately 9%. Therefore, it can be concluded that the proposed approach has a clear economic benefit