STUDY OF THE INFLUENCE OF HYSTERESIS LEVEL ON INDOOR THERMAL COMFORT AND ENERGY CONSUMPTION OF AN AUTOMATED MICROCLIMATE CONTROL SYSTEM

Abstract

This article presents the results of the development, implementation, and in-depth investigation of a mathematical model for an automated room temperature control system that utilizes a Hydronic Underfloor Heating (HUH) unit operating under a hysteresis-based control principle. The model was implemented within the Python environment, employing numerical methods to ensure high accuracy in dynamic simulation. Key physical factors rigorously accounted for in the model include: detailed thermophysical properties of the room structure and air mass; heat losses through enclosing structures (walls, windows); the significant thermal inertia of the massive concrete heating floor slab; and the time-varying influence of outdoor temperature as the primary disturbance factor.

The central objective of the investigation was to quantify the impact of the hysteresis bandwidth on key system performance indicators: energy consumption, frequency of actuator cycling, and the resulting level of thermal comfort.

The simulation experiment was conducted over a continuous period of 30 calendar days for each scenario, encompassing typical and distinct seasonal conditions: winter, spring, summer, and autumn. The hysteresis width was systematically varied from a minimal, narrow band of $0.1 \text{ °C}$ up to $5.0 \text{ °C}$ in precise increments of $0.1 \text{ °C}$. This comprehensive sweep allowed for the construction of complete relationships between the control parameter and the system's dynamic response.

The obtained simulation results clearly demonstrated a critical trade-off: increasing the hysteresis width significantly reduces the number of heater activations, thereby potentially extending the lifespan of the actuator mechanisms. However, this action concurrently leads to an increase in the total operational time of the system and, consequently, a higher overall energy consumption due to less precise regulation. It was established that excessively wide hysteresis bands (e.g., beyond $1.0 \text{ °C}$ for most seasons) cause significant indoor temperature fluctuations that exceed acceptable limits, leading to a sharp reduction in occupant thermal comfort.

Based on the detailed analysis, optimal hysteresis ranges were empirically determined for varying climatic conditions, providing the best achievable balance between energy conservation and the maintenance of a stable microclimate:

For winter conditions (high heat loss): $0.6–0.8 \text{ °C}$. This value effectively compensates for the high thermal inertia of the floor while limiting temperature drift.

For spring and autumn (shoulder season) conditions (moderate heat loss): $0.4–0.5 \text{ °C}$. A narrower band is required here for faster response to external disturbances and reduced energy overshoot.

The developed mathematical model is a powerful and flexible tool. It can be utilized not only for tuning and optimizing control parameters (such as hysteresis width) of automated microclimate systems but also for predicting and evaluating their energy efficiency under various climatic scenarios during the preliminary design phase.