Building Thermal Mass Research Articles

A generalized control heuristic and simplified model predictive control strategy for direct-expansion air-conditioning systems

This article presents a generalized control heuristic to reset supply air temperature set-points for direct-expansion units with capacity modulation and variable airflow and integrates the heuristic into a simplified model predictive control framework that precools building thermal mass through zone temperature set-point adjustments. The resulting control methodology is appropriate for control of medium-sized commercial buildings that employ variable air volume air distribution with direct-expansion units for primary cooling. The heuristic is shown to work well for different direct-expansion systems with different compressor types and fan–duct combinations. To assess the integrated energy savings potential of the heuristic strategy and simplified model predictive control, a simulation platform was developed for a medium-sized commercial building. Simulations were carried out for a 100-day cooling season in different U.S. locations and under different control strategies. The heuristic control provided energy savings of between 5% and 10% relative to conventional control, depending on the system type and location. Approximately 4% additional energy savings was achieved when the heuristic was integrated into a simplified model predictive control having only moderate computational requirements. The cost savings could be significantly greater if time-of-use and demand charges were considered.

Load Management in District Heating Operation

Smooth operation of district heating system will avoid installation of expensive peak heat boilers, improve plant partial load performance, increase the system redundancy for further network expansion and improve its resilience to ensure security of supply during severe heating seasons. The peak heating load can be reduced through building demand side management. The building thermal mass can be used to shift the heating supply under the circumstance without jeopardizing the consumer thermal comfort. In this paper, the multi-agent framework is applied to a simplified building dynamic model to regulate the heating supply to a cluster of buildings. The aim is to level out the total heating supply under a reference temperature and meanwhile maintain the consumer thermal comfort.

Influence of occupant’s behavior on heating needs and energy system performance: A case of well-insulated detached houses in cold climates

Modeling simplification related to occupant’s behavior is a major cause of gap between actual and model’s predicted energy use of buildings. This paper aims to identify those parameters of realistic occupants-related heat gains that actually cause this gap. The investigation therefore, systematically distinguishes the occupant behavior using three behavior parameters, namely: the occupancy behavior, the appliance use behavior and the family size. The effect of these parameters is investigated on a building for two different insulation standards using heat pump as energy supply system. The results identifies the occupancy patterns and the household size as two major parameters that explains a large portion of the gap between actual and model’s predicted energy use of the building. Results further show that variation in household sizes is an important parameter to understand the variation in the actual energy use for similar buildings. The study also shows a clear influence of occupant’s behavior on the performance of heat pumps and pinpoints the variations in share of space heating needs compared to domestic hot water needs as a major cause for this influence. Sensitivity of findings is tested against building thermal mass and condensing gas boiler. Analysis shows no significant variations in the conclusions. The study therefore concludes that using identified parameters in modeling practices can contribute to improve the prediction of actual energy use of buildings.

Evaluating synergistic effect of optimally controlling commercial building thermal mass portfolios

In order to achieve a sustainable energy future, advanced control paradigms will be critical at both building and grid levels to achieve harmonious integration of energy resources. This research explores the potential for synergistic effects that may exist through communal coordination of commercial building operations. A framework is presented for diurnal planning of multi-building thermal mass and HVAC system operational strategies in consideration of real-time energy prices, peak demand charges, and ancillary service revenues. Optimizing buildings as a portfolio achieved up to seven additional percentage points of cost savings over individually optimized cases, depending on the simulation case study. The magnitude and nature of synergistic effect was ultimately dependent upon the portfolio construction, grid market design, and the conditions faced by buildings when optimized individually. Enhanced energy and cost savings opportunities were observed by taking the novel perspective of optimizing building portfolios in multiple grid markets, motivating the pursuit of future smart grid advancements that take a holistic and communal vantage point.

Peak load reductions: Electric load shifting with mechanical pre-cooling of residential buildings with low thermal mass

This study uses an advanced airflow, energy and humidity modelling tool to evaluate the potential for residential mechanical pre-cooling of building thermal mass to shift electricity loads away from the peak electricity demand period. The focus of this study is residential buildings with low thermal mass, such as timber-frame houses typical to the US. Simulations were performed for homes in 12 US DOE climate zones. The results show that the effectiveness of mechanical pre-cooling is highly dependent on climate zone and the selected pre-cooling strategy. The expected energy trade-off between cooling peak energy savings and increased off-peak energy use is also shown. The best pre-cooling results (more than 75% energy use shifted away from peak while minimising the total energy penalty) for most climates were obtained using a medium (5 h) pre-cooling time window with a shallow (23.3 °C) pre-cooling set point temperature. All of the pre-cooling strategies investigated caused the annual cooling energy demand of the simulated buildings to increase. Additionally, all of the pre-cooling strategies shifted at least 50% of the on-peak cooling loads away from a peak period window of 4pm–8pm in all climate zones.

Analysis and experiments on the periodically fluctuating air temperature in a building with earth-air tube ventilation

A more thermally comfortable indoor environment with cooler indoor air in summers but warmer air in winters could be achieved by the use of earth-air tube ventilation. The periodically fluctuating behavior of indoor air temperature, which characterizes the indoor thermal environment, is not determined from the earth-air tube system alone but by the coupling of earth-air tube ventilation and the thermal mass contained in a building. A model for the coupling effects of earth-air tube ventilation and building thermal mass on periodically fluctuating air temperature has been previously developed (Yang et al., Energy and Buildings 81: 182–199, 2014). This paper integrates both the yearly and daily fluctuations of air temperature into unified equations. A method for determining the penetration depth of the oscillating tube-air temperature wave in the surrounding soil is proposed to enhance the model accuracy. An experiment was conducted to test the model, and the model predictions show good agreement with the measured data. The roles played by the key engineering parameters with respect to the overall efficiency of the combined system were analyzed. The findings suggest that the effectiveness of an earth-air tube ventilation system cannot be quantified in isolation from the building characteristics. This model is helpful to the optimization of the coupled system.

Application of economic MPC to the energy and demand minimization of a commercial building

This paper presents an application case study of an economic model predictive control (EMPC) method for optimizing the building demand and energy cost under the time-of-use price policy. The control strategy is comprised of an economic objective function that accounts for the combination of energy and demand costs with a time-of-use rate structure, a dynamic thermal process and power model of the building thermal mass dynamics, and a set of constraints to ensure the building is operated properly. The optimization is a min–max optimization problem and is converted to a linear program. The EMPC method is implemented in a commercial office building located in Milwaukee, Wisconsin, USA. An internet-based control architecture is developed to carry out tests with the EMPC controller at a remote location. The test results show that the EMPC strategy is capable of shifting the peak demand to off-peak hours and reducing energy costs compared to a baseline case for the building.

Theoretical assessment of the combined effects of building thermal mass and earth–air-tube ventilation on the indoor thermal environment

Both earth-tube systems and building thermal mass have the potential to provide desired performance levels for both indoor thermal comfort and energy saving; however, their coupling effects need to be further investigated. A model for evaluation of the combined effects of earth-tube ventilation systems and building thermal mass is proposed. Both the time-averaged indoor air temperatures and periodic temperature fluctuations are given as explicit formulas. Unlike the time lag induced by the separate use of building thermal mass, which is no longer than 6h, the combination with an earth-tube system could extend the time lag of indoor air temperature in an annual fluctuation period by tens of days and that of a daily period by a couple of hours. It is noticeable that the building thermal mass has significant impact on the effectiveness of earth-tube systems; therefore, a small heat transfer coefficient of external envelopes helps increase the annual time lag of indoor air temperature. Using a proper combination of building thermal mass and earth tubes, indoor thermal comfort can be achieved for a building located in a region with both hot summers and cold winters without any additional cooling or heating load.

A study of building envelope and thermal mass requirements for achieving thermal autonomy in an office building

It is common knowledge that buildings should be constructed with good envelopes and sufficient masses. However, U.S. building codes make no provision for a building's thermal mass. This may result from that the conventional heat balance design—which assumes constant indoor air temperature, any heat imbalance resulting from corresponding envelope heat loss or gain and internal heat gain is accounted for by HVAC equipment—aims for HVAC selection, not for determining required building thermal qualities. We propose the concept of building thermal autonomy and a two-step process assumption-based design method. Thermal autonomy is a building's capability of keeping its indoor temperature sans HVAC equipment within a prescribed temperature range. The first step of the process assumption-based design method aims for the determination of building thermal qualities for a thermally autonomous building. Our finding shows that optimum slab thickness for a building's ceilings and floors is 25-cm and recommends 10-cm thick concrete slabs for its envelope walls. More interesting is the finding that climate-specific factor of diurnal temperature amplitude should be taken into consideration in the envelope design: a maximum WWR (Window-to-Wall Ratio) is given as a function of diurnal temperature amplitude.

An evaluation of robust controls for passive building thermal mass and mechanical thermal energy storage under uncertainty

Passive building thermal mass and mechanical thermal energy storage (TES) are known as one of state-of-the-art demand-side control instruments. Specifically, Model-based Predictive Control (MPC) for this operation has the potential to significantly increase performance and bring economic advantages. However, due to the uncertainty in certain operating conditions in the field, its control effectiveness could be diminished and/or seriously damaged, which results in poor performance.This study pursues improvements of the control performance of both thermal inventories under uncertainty by proposing a robust MPC in which relevant uncertainty sources are compiled; therefore, it is designed to perform more stable than traditional MPCs under uncertain conditions.Uniqueness and superiority of the proposed robust demand-side controls include:(i)Controls are developed based on the a priori uncertainty assessment, such that a systematic modeling approach for uncertainty was taken according to characteristics and classifications of uncertainty.(ii)The robust MPC reduces the variability of performance under varied and non-indigenous conditions compared to the deterministic MPC, and thus can avoid the worst case situation.

Peak load shifting control using different cold thermal energy storage facilities in commercial buildings: A review

For decades, load shifting control, one of most effective peak demand management methods, has attracted increasing attentions from both researchers and engineers. Different load shifting control strategies have been developed when diverse cold thermal energy storage facilities are used in commercial buildings. The facilities include building thermal mass (BTM), thermal energy storage system (TES) and phase change material (PCM). Little study has systematically reviewed these load shifting control strategies and therefore this study presents a comprehensive review of peak load shifting control strategies using these thermal energy storage facilities in commercial buildings. The research and applications of the load shifting control strategies are presented and discussed. The further efforts needed for developing more applicable load shifting control strategies using the facilities are also addressed.

On the proper integration of wood stoves in passive houses: Investigation using detailed dynamic simulations

Wood stoves are attractive for the space-heating (SH) of passive houses. Nevertheless, there are still questions about their integration. Firstly, the power oversizing of the current stoves and their long operating time may lead to unacceptable overheating. Secondly, it is also unclear how one stove can ensure the thermal comfort in the entire building. The paper investigates these aspects using detailed dynamic simulations (TRNSYS) applied to a detached house in Belgium. An 8kW stove is assumed to be representative of the lowest available powers in the market. Results confirm that a large power modulation is important to prevent overheating. Opening the internal doors, a high building thermal mass and a heat emission dominated by radiation also reduce the overheating risk, but to a smaller extent. Besides, a single stove cannot enforce the thermal comfort during design weather conditions: a peak-load system is then needed. Using more standard conditions, a Typical Meteorological Year (TMY), the stove can mainly perform the SH but it then requires the internal doors inside the building to be opened. The temperature distribution between rooms is in fact dominated by the architectonic properties. Finally, the emission and distribution efficiency of the stove is also investigated.

Integrating renewable energy using a smart distribution system: Potential of self-regulating demand response

A self-regulating distribution system simulation platform is presented for a smart-grid with Distributed Energy Resource (DER) wind power injection in which load flow fluctuations are controlled via self-regulating air-source heat pump (HP) cycling. The grid power injection fluctuations are mitigated by bus-level HP control, while ensuring compliance to both consumer comfort constraints and distribution grid load flow requirements.The effects of applying a number of different bus-level HP control algorithms are evaluated. The results show that using building thermal mass in conjunction with simple control strategies can effectively accommodate large fluctuations associated with high penetration of wind energy. The number of HPs in each distribution phase significantly affects the load flow characteristics and the ability of the bus-level control to smooth the distribution grid regulator power.The bus-level control improves power and voltage ramping rates, reduces wind power injection fluctuations, and also reduces the energy reserve requirements.

Optimal controls of building storage systems using both ice storage and thermal mass – Part II: Parametric analysis

This paper presents the results of a series of parametric analysis to investigate the factors that affect the effectiveness of using simultaneously building thermal capacitance and ice storage system to reduce total operating costs (including energy and demand costs) while maintaining adequate occupant comfort conditions in buildings. The analysis is based on a validated model-based simulation environment and includes several parameters including the optimization cost function, base chiller size, and ice storage tank capacity, and weather conditions. It found that the combined use of building thermal mass and active thermal energy storage system can save up to 40% of the total energy costs when integrated optimal control are considered to operate commercial buildings.

A Virtual Model for Civil Building Electric Control Based on Matlab Controller

The purpose of this study is correct and effective model predictive control (MPC), in reduce energy demand and cost of buildings in power network and use pricing -- a demand and charges. A virtual model, for a single floor, the article commercial buildings equipped with variable air volume (VAV) based on Energyplus cooling system. Real-time data between the realization of the switch Energyplus and Matlab into building control virtual test bed (BCVTB) as a middleware. System identification technology is to realize get zone temperature and the power function model, which is used in the MPC framework. With economic target, target function is formulated as a linear programming problem and solves the problem. In the rush hour pre-cooling effect and independent cooling unloaded from building thermal mass in supply and demand can be observed during a consecutive weekly simulation. The MPC brings the cost comparison, the control strategy and other are preprogrammed baseline.

Demand reduction in building energy systems based on economic model predictive control

This paper proposes and demonstrates the effectiveness of an economic model predictive control (MPC) technique in reducing energy and demand costs for building heating, ventilating, and air conditioning (HVAC) systems. A simulated multi-zone commercial building equipped with of variable air volume (VAV) cooling system is built in Energyplus. With the introduced Building Controls Virtual Test Bed (BCVTB) as middleware, real-time data exchange between Energyplus and a Matlab controller is realized by sending and receiving sockets. System identification is performed to obtain zone temperature and power models, which are used in the MPC framework. The economic objective function in MPC accounts for the daily electricity costs, which include time-of-use (TOU) energy charge and demand charge. In each time step, a min–max optimization is formulated and converted into a linear programming problem and solved. In a weekly simulation, a pre-cooling effect during off-peak period and a cooling discharge from the building thermal mass during on-peak period can be observed. Cost savings by MPC are estimated by comparing with the baseline and other open-loop control strategies. The effect of several experimental factors in the MPC configuration is investigated and the best scenario is selected for future practical tests.

An investigation of optimal control of passive building thermal storage with real time pricing

The cost savings potential of optimal passive thermal storage control were examined for day-ahead real time electricity rate structures. The operational strategies of three office building models were optimized in four US cities (Chicago, New York, Houston and Los Angeles) using price and weather data for the summer of 2008. Optimization of building thermal mass was conducted using a predictive optimal controller to define supervisory strategies in terms of building global cooling temperature setpoints. A global minimization algorithm determined optimal setpoint trajectories for each day divided into four distinct time periods. Cost savings were found to range from 0 to 14% depending on the building, climate, and characteristics of the rate signal. The best cost savings occurred for price spikes or cool nighttime temperatures. Moreover, it was found that low internal gains favoured a more flexible precooling strategy, while high internal gains coupled with low thermal mass resulted in poor precooling performance.

Advances in Near-Optimal Control of Passive Building Thermal Storage

Using a simulation and optimization environment, this paper presents advances toward near-optimal building thermal mass control derived from full factorial analyses of the important parameters influencing the passive thermal storage process for a range of buildings and climate/utility rate structure combinations. Guidelines for the application of, and expected savings from, building thermal mass control strategies that can be easily implemented and result in a significant reduction in building operating costs and peak electrical demand are sought. In response to the actual utility rates imposed in the investigated cities, fundamental insights and control simplifications are derived from those buildings deemed suitable candidates. The near-optimal strategies are derived from the optimal control trajectory, consisting of four variables, and then tested for effectiveness and validated with respect to uncertainty regarding building parameters and climate variations. Due to the overriding impact of the utility rate structure on both savings and control strategy, combined with the overwhelming diversity of utility rates offered to commercial building customers, this study cannot offer universally valid control guidelines. Nevertheless, a significant number of cases, i.e., combinations of buildings, weather, and utility rate structure, have been investigated, which offer both insights and recommendations for simplified control strategies. These guidelines represent a good starting point for experimentation with building thermal mass control for a substantial range of building types, equipments, climates, and utility rates.

A STUDY ON THE ENERGY EVALUATION OF THE BUILDING THERMAL MASS STORAGE SYSTEM WITH THE CHILLED WATER STORAGE SYSTEM

In this paper the energy characteristics of the building thermal mass storage system with the chilled water storage system is evaluated. A typical commercial building model is simulated by a computer and the influence of the regions, the daily weather and the heat load in the room is examined. The results show that the increase rate of the cooling load and the electricity consumption is high in the months of the low cooling load comparing with the non-storage case. And the building thermal mass storage system with the water storage reduces the primal energy consumption by 2.7% and the exhaust carbon dioxide by 10.4% in the optimized case in Tokyo.

B-64 粒状潜熱蓄熱材を用いた躯体蓄熱空調システムに関する研究 : その2 PCM敷設量の違いによる性能評価に関する検討

B-64 粒状潜熱蓄熱材を用いた躯体蓄熱空調システムに関する研究 : その2 PCM敷設量の違いによる性能評価に関する検討