Integrating Startup and Defrosting Factors in Building Energy Simulations

By Srikanth
6 Min Read
Integrating Startup and Defrosting Factors in Building Energy Simulations

The global imperative to achieve decarbonization targets within the building sector is a driving force behind innovation in heating technologies. Among these, the integration of hybrid systems stands out as a promising solution. By combining the strengths of air-source heat pumps (HPs) and gas-fired boilers, these hybrid systems address the limitations of standalone HP systems, particularly in retrofitting existing buildings. The key advantage lies in their ability to ensure efficient and reliable heating solutions while optimizing energy consumption.


Dynamics of Hybrid Systems

Hybrid systems, characterized by the fusion of air-source heat pumps and gas-fired boilers, have garnered substantial attention due to their potential for revolutionizing heating solutions. However, their performance hinges on a nuanced understanding of two crucial but often neglected factors: startup performance and defrosting cycles.

The startup phase of hybrid systems plays a pivotal role in determining their overall efficiency. During this period, the heat generators’ performance can experience notable degradation, impacting the system’s energy consumption and overall effectiveness. Furthermore, defrosting cycles, a necessity in colder climates, contribute to performance losses in HPs. These cycles introduce complexities due to the interplay between temperature, humidity, and system control strategies.

Bridging the Knowledge Gap

The realm of hybrid systems holds significant potential; however, their optimal application demands precise models capable of factoring in startup and defrosting dynamics. To address this need, an innovative approach has come to light. Utilizing an array of meticulously conducted laboratory tests and experiments, correlations have been formulated that delve into the nuanced intricacies of startup losses and defrosting cycle impacts.

Diverging from previous studies that relied on general assumptions, these fresh correlations establish a strong connection with operational circumstances and the duration of startup phases. By accommodating the fluctuations in startup behavior across various operational contexts, this model elevates the accuracy of energy simulations, enabling a more comprehensive grasp of system performance dynamics.

Decarbonization Goals and the Role of Hybrid Systems

In the quest for decarbonization, heat pumps have emerged as a steadfast contender in the realm of sustainable heating solutions. These systems tap into the potential of renewable energy sources like air, water, and ground heat. Among the spectrum of choices, air-source heat pumps have taken the spotlight due to their accessible installation process and affordability. Yet, a persistent challenge remains: the disconnect between heating capacity and energy demand, particularly in the context of pre-existing buildings.

Enter hybrid systems, a pragmatic remedy to this conundrum. Through the strategic fusion of air-source heat pumps and gas boilers, these systems bridge the chasm between heating capacity and load demand. This seamless integration not only optimizes energy consumption but also ensures effective heating performance. Such hybrid solutions serve as a valuable interim strategy, guiding the transition towards comprehensive renovation and the broader objective of decarbonization within existing building stocks.

Expanding the Scope of Dynamic Simulation Algorithms

The adoption of hybrid systems necessitates a comprehensive understanding of their behavior across diverse operating conditions. While some previous findings touched on various aspects, there’s a clear gap in the dynamic simulation algorithms and subroutines required to capture startup and defrosting effects. New studies fills that gap by introducing a model that not only considers these factors but also offers correlations based on empirical data and experimentation.

Dynamic simulation models, often based on steady-state experimental data, are limited in their applicability to real-world scenarios. By integrating experimentally derived correlations, this approach enhances the accuracy of predictions and offers a practical tool for researchers, practitioners, and policymakers.

In the wake of escalating decarbonization imperatives, the pivotal role of hybrid systems within the realm of existing building stocks is becoming undeniably pronounced. These systems, adept at harmonizing efficiency, sustainability, and reliability, hold the key to a more sustainable future in the battle against climate change. As the world pivots toward a low-carbon trajectory, the trajectory of hybrid systems within the domain of building solutions demands thorough exploration and development.

To chart a promising course forward, it is imperative for future research to assume the mantle of refinement and validation of simulation models. As these models act as the compass for predicting hybrid system behaviors, they must be honed to greater precision. The incorporation of a diverse spectrum of data and real-world conditions will be instrumental in yielding more comprehensive and accurate outcomes. The pursuit of these objectives not only amplifies the credibility of hybrid system simulations but also facilitates their seamless integration into practical applications. By illuminating unexplored dimensions and refining existing paradigms, this research direction underpins the evolution of hybrid systems as a cornerstone in our journey towards a greener, more sustainable future.


The integration of startup and defrosting factors into building energy simulations represents a significant stride in the optimization of hybrid systems. By addressing these often neglected dynamics, this approach ensures a more accurate representation of real-world performance. As the world strives to meet ambitious decarbonization goals, innovations like these will play a pivotal role in reshaping the building sector’s energy landscape.

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