Building Thermal Mass Research Articles

Mitigating energy poverty: Potential contributions of combining PV and building thermal mass storage in low-income households

The issue of energy poverty has devastating implications for the society, and it has been aggravated in the past years due to the economic crisis and the increase of energy prices. Among the most affected are those with low incomes and living in inefficient buildings. Unfortunately, the bitter reality is that sometimes this part of the population are facing the next question: Heating, or eating? The declining prices of distributed energy technologies such as photovoltaics provides an opportunity for positive social change. Although their use does not address energy poverty directly, substantial contributions may be made.Measurements of indoor temperatures in a social housing district of southern Spain in 2017 have revealed the unbearable temperatures that the occupants have to endure, both in summer and winter. Using this district as a case study, the present work aims to evaluate the benefits of exploiting its rooftop PV potential to cover part of the electricity consumption of the district (reducing the energy bills), and use the surplus electricity to supply power for the heat pumps in the district. Optimal alternatives regarding maximum PV production, maximum self-sufficiency ratio and minimum investment costs have been found, considering as well different options when sharing the available electricity surplus to improve the thermal comfort of the occupants. As far as the authors know, no previous study has followed an approach aimed at energy poverty alleviation such as the one presented in this work. The results show that using the surplus electricity to heat or cool the whole dwellings would improve the thermal comfort of the occupants in average up to 11% in winter and 26% in summer. If all the PV generation was used or more buildings in the area were employed to install PV modules, improvements up to 33% in winter and 67% in summer could be obtained, reducing at the same time the thermal comfort differences among the dwellings of the district.

Single and combined phase change materials: Their effect on seasonal transition period

Phase change materials (PCMs) are being used as thermal mass in buildings to conserve energy. In this research, the application of appropriate PCMs to reduce building energy consumption and operating time of mechanical equipment during spring and autumn transition period in hot arid climate is studied. The study was conducted in buildings with diurnal occupation pattern. The simulation results were compared against measurements obtained from a calorimeter that was constructed for this purpose. The results show that PCM 29 °C and 5 air change natural ventilation rate reduce annual energy consumption by 15%. This means that while for 38 days in spring and 29 days in autumn, the mechanical equipment can be turned off. The thermal performance of PCM 25 °C is very well in spring. The appropriate PCM is the one with combined phase change melting point of 29 °C and 21 °C PCMs, which reduces energy consumption and increases the seasonal transition period 8% more than that of the single PCM 29 °C.

Model reduction and model predictive control of energy-efficient buildings for electrical heating load shifting

In France, buildings account for a significant portion of the electricity consumption (around 68%), due to an important use of electrical heating systems. This results in high peak load in winter and causes tensions on the production-consumption balance. In view of reducing such fluctuations, advanced control systems (including the Model Predictive Control framework) have been developed to shift heating load while maintaining indoor comfort and taking advantage of the building thermal mass. In this paper, a framework for developing optimisation-based control strategies to shift the heating load in buildings is introduced. The balanced truncation method and a time-continuous optimisation method were used to develop a real-time control of the heating power. These two methods are well suited for control problems and yield precise results. The novelty of the approach is to use reduced models derived from advanced building simulation software. A simulation case study demonstrates the controller performance in the synthesis of a predictive model-based optimal energy management strategy for a single-zone test building of the “INCAS” platform built in Le Bourget-du-Lac, France, by the National Solar Energy Institute (INES). The controller exhibits excellent performance, reaching between 6 and 13% cost reduction, and can easily be applied in real-time.

Model Predictive Control (MPC) for Enhancing Building and HVAC System Energy Efficiency: Problem Formulation, Applications and Opportunities

In the last few years, the application of Model Predictive Control (MPC) for energy management in buildings has received significant attention from the research community. MPC is becoming more and more viable because of the increase in computational power of building automation systems and the availability of a significant amount of monitored building data. MPC has found successful implementation in building thermal regulation, fully exploiting the potential of building thermal mass. Moreover, MPC has been positively applied to active energy storage systems, as well as to the optimal management of on-site renewable energy sources. MPC also opens up several opportunities for enhancing energy efficiency in the operation of Heating Ventilation and Air Conditioning (HVAC) systems because of its ability to consider constraints, prediction of disturbances and multiple conflicting objectives, such as indoor thermal comfort and building energy demand. Despite the application of MPC algorithms in building control has been thoroughly investigated in various works, a unified framework that fully describes and formulates the implementation is still lacking. Firstly, this work introduces a common dictionary and taxonomy that gives a common ground to all the engineering disciplines involved in building design and control. Secondly the main scope of this paper is to define the MPC formulation framework and critically discuss the outcomes of different existing MPC algorithms for building and HVAC system management. The potential benefits of the application of MPC in improving energy efficiency in buildings were highlighted.

WITHDRAWN: Assessment of an algorithm involving building thermal mass, indoor and outdoor mean running temperatures to enhance the control of night ventilation

Abstract The aim of the present work is to improve night ventilation control strategy, especially for the mid-season periods where an unadapted control scheme can result in significantly undesirable heat loads or either in a lack of thermal comfort that may be due to high variations in climate conditions. It concerns mainly buildings where the indoor air is conditioned all the year like commercial buildings or offices. An algorithm is developed and handled to control night ventilation for different kinds of buildings presenting different thermal masses. Two variables are calculated at every time step: the sliding average of outdoor and indoor temperatures. Also three features are required to be set to adapt the algorithm to the building and its environmental conditions: a coefficient related to the building time constant and two selected set-point temperatures that are respectively compared to the outdoor and indoor sliding average temperatures for every time step. The two selected set-point temperatures are specified with a parametric study realized on the building such that they minimizes the discomfort period, the heating load and the fan electric power. The confrontation of the adaptive night ventilation and the classic night ventilation was achieved showing that besides feasible energy savings (up to 30%) and about 57% less discomfort hours, the algorithm was effectively able to identify with accuracy the periods where the night ventilation should be activated in the building and the periods where it shouldn't, thus limiting drastically concomitant night ventilation and diurnal heating load hours. The effectiveness of the algorithm was also shown in its capacity of reducing the electric power demand of the fan by a factor of 2. Results show that the adaptive algorithm was able to adapt to the mid-season period thus preventing unwanted heat and fan electric loads while preserving very good thermal comfort conditions.

Buildings with environmental quality management, part 2: Integration of hydronic heating/cooling with thermal mass

The quest for a sustainable built environment brought dramatic changes to architectural design because of the integrated design process. The integrated design process is the modern way to realize “performance architecture,” that is, design with a view to field performance. Integrated design process permits merging of concepts from passive-house designs, solar engineering, and an integration of the building enclosure with mechanical services. In part 1 of this series, the emergence of many new multi-functional materials was discussed. Yet, current innovation is guided by lessons from history. Thermal mass in heavy masonry buildings allowed periodic heating. The authors postulate integration of a hydronic heating system with the walls and the use of smart temperature control of the heating system to modify and optimize the thermal mass contribution. To use the mass of a building, one must accept transient temperature conditions where the indoor temperature varies but is confined by comfort requirements for both summer and winter conditions. On the other side, resiliency requirements dictate that in the absence of electricity the air temperature does not fall below about 12°C over a period of several hours. This requirement implies that summer cooling will likely be separated from the heating systems and that operation of a low-energy building is heavily dependent on the design of smart control systems. Analysis of control systems provided in this article for earth-to-air heat exchangers and cooling of houses with lightweight walls lead us to the requirements of separation between heating and ventilation and needs for different sources of fresh air. Finally, a new concept emerges.

Occupant-behavior driven appliance scheduling for residential buildings

Building-to-grid integration is one important step in having a smart grid. This integration will support energy efficiency, load balancing, and the incorporation of renewables. This study introduces a residential building energy management solution to control connected devices based on economic signals from the grid and occupant behavior. An air-conditioning unit, a water heater, and an electric vehicle (EV) were modeled and controlled using a traditional on/off controller and model predictive controller (MPC). The MPC is designed to minimize the total building electricity costs while maintaining occupant comfort. The MPC utilizes the building thermal mass, the EV battery storage, and the water heater’s hot water tank to shift electricity use to a period when the price is lower. This controller considers occupant behavior as a constraint in controlling these devices to maintain users’ comfort. The simulation results show a 10%–30% reduction in the electricity bill by applying the MPC in a dynamic electricity price scenario, as compared to the traditional methods of control. The proposed method of control makes buildings responsive to grid signals that provide the potential of peak shaving and ancillary services.

Reducing the Cooling Energy of Existing Commercial Buildings with Passive Thermal Mass

A major part of sustainability theory and practice is to reuse existing building stock wherever possible and to refrain from demolition and rebuilding minimising the resources and associated energy used. Many buildings therefore have internal refurbishments during their lives, the scale of which can range from minor fit outs through major interior refurbishments to finally those which see the central services replaced also. The ability to greatly improve the efficiency of a building during only minor refurbishment is an attractive proposal which would provide an intermediate opportunity to building owners to reduce cooling energy and its associated cost and more importantly avoid disruption to the base building services. This study investigates the effect of exploiting inherent building thermal mass in a standard commercial building in the Australian cities of Adelaide and Brisbane, and demonstrates the energy savings that can be made in the order of 30%.

Derivation of simplified control rules from an optimal strategy for electric heating in a residential building

In France, 40% of buildings are heated with electrical devices causing high peak load in winter. In this context, advanced control systems could improve buildings energy management. More specifically, optimal strategies have been developed using a dynamic programming method in order to shift heating load, taking advantage of the building thermal mass. However, this optimization method is computationally intensive and can hardly be applied to real-time control. Statistical techniques can be used to derive near-optimal laws from the optimal control results. These rule extraction techniques model the relationship between explanatory variables and a response variable. This paper investigates the use of Beta regression model. This regression-based strategy was able to mimic the general characteristics of the optimization results with a small mean bias error (−6%) and greatly reduce computational effort (150 times faster). Given its simple mathematical formulation, it could be implemented in real-time building systems control.

Reducing the Cooling Energy of Existing Commercial Buildings with Passive Thermal Mass

A major part of sustainability theory and practice is to reuse existing building stock wherever possible and to refrain from demolition and rebuilding minimising the resources and associated energy used. Many buildings therefore have internal refurbishments during their lives, the scale of which can range from minor fit outs through major interior refurbishments to finally those which see the central services replaced also. The ability to greatly improve the efficiency of a building during only minor refurbishment is an attractive proposal which would provide an intermediate opportunity to building owners to reduce cooling energy and its associated cost and more importantly avoid disruption to the base building services. This study investigates the effect of exploiting inherent building thermal mass in a standard commercial building in the Australian cities of Adelaide and Brisbane, and demonstrates the energy savings that can be made in the order of 30%.

Development of mathematical correlations for indoor temperature from field observations of the performance of high thermal mass buildings in India

Use of stone and brick wall as high thermal mass is a common strategy in residential and commercial buildings in a hot tropical country like India for thermal comfort and energy savings. In this paper, thermal monitoring of high thermal mass residential buildings is performed in the composite climate of India for the summer and winter season. Separate mathematical correlations are developed to predict the indoor temperatures, as the functionality of high mass buildings is different for the summer and winter season. Statistical significance of developed correlations is further analyzed and found good correlation coefficient with field measurement. Finally, based on the thermal performance of these high thermal mass monitored buildings to produce thermal comfort indoors, the bio-climatic boundary of ambient conditions for the use of high thermal mass in buildings is developed for one climatic zone of India. The new bio-climatic boundary extends up to an average monthly maximum ambient temperature of about 38.4 °C at 2 g/kg specific humidity and follows a tilted line up to 35 °C at 20 g/kg specific humidity for indoor thermal comfort in the composite climate of India. Also, the high mass comfort zone extends to a limit of 40.9 °C when the airspeed is up to 1 m/s using a ceiling fan.

Metrics of urban morphology and their impact on energy consumption: A case study in the United Kingdom

Energy policies implemented by local authorities and targeted at the domestic sector have focussed on interventions, which are usually selected after an optimisation procedure. This paper identifies differences and similarities between three Medium Layer Super Output Area (MLSOA) districts in the United Kingdom (UK) and draws conclusions which prove to be useful to interpret other districts in the city and provide general rules for energy efficiency measures and distributed supply interventions in Newcastle upon Tyne, UK, and potentially beyond. The core argument aims at provide an important link between the energy-reducing and energy-increasing effects of four urban morphology characteristics in ‘place-specific’ neighbourhoods. Our methodology explores the potential application of the close relation between four urban morphological characteristics and the spatial aggregated building energy end-use in the roll-out strategy of interventions. Our findings first indicate that the combination of shape and size of continuous building classes (in a building class the main residential buildings are grouped by their age and building type) and their extent using patch areas potentially simplify retrofit campaigns. We argue that the whole continuous building class influences the building's thermal mass (the building massing) and their extent (the patch area or patch in short) and these are better descriptors for the energy use in the occupational phase of a building. Second, the building massing and the plot ratio (the ratio of the building floor area to the land area in a given territory) are a better descriptors of building density/mixing of land use and built form leading to the potential use of adequate distributed energy supply. Third, the way in which social and economic factors interact to shape area-based of household energy consumption leads to a possible better spatially-enabled policies for low income families; and fourth, the layout and orientation design of the neighbourhood may identify municipal sites for potential renewable energy projects. The use of the building massing and patch areas as spatial cluster operators simplify the complexity of aggregated building energy consumption by representing its spatial incidence through a smooth continuous surface. Additionally, building classes and its patch area extent show notable differences across different sub-city areas. Furthermore, the greater the number of building classes, the more diverse is the socio-economic make-up of a sub-city area.

INVESTIGATING THE INTEGRATION OF AIR-BASED THERMO-ACTIVE BUILDING STRUCTURE (A-TABS) INTO SCHOOL BUILDINGS IN EGYPT

Passive use of thermal mass in buildings has been widely studied and proved its efficiency in increasing thermal comfort and decreasing cooling load. Whereas active utilization of building’s thermal mass can enhance the indoor thermal performance and decrease the cooling loads with low energy consumption. This study investigates the integration of active thermal mass strategies into educational buildings. As a case study, a classroom in a governmental school has been referenced and modeled throughout this paper. In this paper, the main focus is drained to numerical simulation which investigates the thermal performance of the classroom case study when its structure is integrated to the proposed Air-based Thermo Active Building Structure (A-TABS) System. Herewith, a set of different simulation scenarios with different simulation parameters are conducted. In this case, every A-TABS system scenario is modeled separately in order to investigate its performance separately and easily compare the results. Results indicate that, by integrating the A-TABS system into the classroom model and under typical summer day conditions; it is observed that the indoor air temperature can be decreased by a range from 0.8°K to 3.2°K. Additionally, the thermal comfort is also monitored to be increased with less energy consumptions and less running costs compared to conventional air conditionings.

Evaluation of energy savings potential of variable reflective roofing systems for US buildings

This paper explores the potential energy savings of using dynamic cool roofs (DCRs) with seasonally variable reflective surface for various building prototypes when compared to static cool roofs. The analysis conducted demonstrates that the additional energy savings from DCRs depend largely on the climate, insulation level, and reflectance of the roof, as well as but to a lesser extent on the building thermal mass. This study shows that older buildings, with low insulation levels, in colder climates are the best target for retrofit using DCRs. Specifically, the results show that when a variable reflective costing is applied to low insulation buildings, source energy savings can be achieved and range from 4.33 to 19.44MJ/m2 (i.e., 1.6–4.9%) for residential units and from 1.17 to 18.00MJ/m2 (i.e., 0.3–3.9%) for offices. Based on an economic analysis, it is found that the break-even cost for a variable reflectance coating system with a 22-year life span ranges from 0.80 to 4.84$/m2 for residential buildings, and from 0.86 to 4.92$/m2 for commercial buildings.

The Diurnal Cycle of Urban Thermal Environment in Scale-model Street Canyons by Outdoor Field Measurement

Building thermal mass is significant to influence urban climate. We performed scale-model field measurement of thermal environment and turbulence in summer of 2015 in Guangzhou, China. Two types of scale-model were used to arrange north-south street canyons ▪ (the ‘empty’ model with wall thickness of 1.5cm and the ‘sand model’ in which all buildings are filled with sand producing bigger heat capacity) to conduct measurement over three days.The urban roughness layer turbulence and temperature characteristics in such idealized street canyons were investigated by using several instruments such as ultrasonic anemometer, temperature and humidity sensors, four component radiometers, infrared camera. We study velocity distribution, air temperature and basic characteristics of radiation in the idealized city. Especially focus on the different building heat storage impact on the thermal environment.The thermal mass in the empty model is much smaller than the sand model. Therefore, the measurements show that, during daytime wall temperature (Twall) and air temperature (Tair) of empty model reached its peak earlier and this peak value is much higher than those of the sand model. After sunset, result is quite contrary. Twall in the sand model are higher than those in the empty model because the thermal storage of the former is much greater than the latter, but Tair in these two models are similar because the measured location of Tair is at the centre of street canyon and far from building walls ▪.The street canyons were subjected to differential wall heating and overlying wind. As overlying wind is relatively weak, the heating of building walls may induce thermally driven circulation. A buoyancy parameter, ▪, was used to demarcate thermal and inertial circulation regimes. When the street canyon was dominant by the wind, and the canyon velocities scaled by u0 are approximately constant. When the thermal circulation becomes important, velocity in canyon and buoyancy parameter shows a relationship: ▪.

The effect of window opening ventilation control on residential building energy consumption

Occupant behavior in terms of the operation of natural ventilation is a significant parameter that affects the thermal performance of residential buildings. The objective of this study was to evaluate the influence of the occupant behavior regarding the window opening ventilation control and the building thermal mass on the energy consumption related to HVAC system in residential buildings in Brazil. The focus of the study was on analysing different natural ventilation operation scenarios: morning to night ventilation, automated ventilation control, and night ventilation. The combined use of a HVAC system and natural ventilation was applied using an Energy Management System that enables advanced controls during simulation in the EnergyPlus program. The results indicate that buildings with medium thermal capacity have a greater potential to provide thermal comfort for users, since using an appropriate building ventilation control. Also, appropriate building ventilation achieved through automated ventilation control combined with medium thermal inertia provided a reduction in the energy consumption for HVAC system.

Multi-objective optimization for thermal mass model predictive control in small and medium size commercial buildings under summer weather conditions

Building thermal mass control has great potentials in saving energy consumption and cost. Optimal control schemes are able to utilize passive thermal mass storage to shift the cooling load from peak hours to off-peak hours to reduce energy costs. As such, this paper explores the idea of model predictive control for building thermal mass control. Specifically, this paper presents a study of developing and evaluating a multi-objective optimization based model predictive control framework for demand response oriented building thermal mass control. This multi-objective optimization framework takes both energy cost and thermal comfort into consideration simultaneously. In this study, the developed model predictive control framework has been applied in six commercial buildings at Boston, Chicago, and Miami, under typical summer weather conditions. Time-of-use electricity prices from these three locations are used to calculate the cooling and reheating energy costs. Pareto curves for optimal temperature setpoints under different thermal comfort requirements are calculated to show the trade-off between the cost saving and thermal comfort maintaining. Comparing with a typical “night setback” operation scheme, this model predictive control schemes are able to save energy costs from 20% to 60% at these three locations under different weather and energy pricing conditions. In addition, the Pareto curves also show that the energy cost saving potentials are highly dependent on the thermal comfort requirements, weather conditions, utility rate structures, and the building constructions.

Development and validation of grey-box models for forecasting the thermal response of occupied buildings

Building thermal wall mass provides a flexible heat capacity which can be effectively used for load shifting, thus enabling demand side management (DSM). The most crucial barrier for a practical application of buildings as short term heat storage is the lack of knowledge about the building physical properties. This study presents a model identification approach for forecasting the building thermal response based on grey-box models. The model parameters are estimated by optimizing the model output to historical data under the consideration of plausible physical constraints. The thermal flexibility of a building and therewith its demand side management potential can be determined based on the assessed model parameters. This study uses measurements from buildings in normal operation to evaluate the thermal prediction of grey-box models despite the stochastic events within the training data. In order to find the best level of model complexity, four grey-box models were compared in their ability to forecast the building indoor temperature behaviour. The analysis revealed that a two-capacity model structure with an additional consideration of the indoor air as a mass-less node (4R2C-model) enables the most accurate qualitative prediction of the indoor temperature. Further, the general validity of the model structure allows for its application on different buildings types.

Using phase change materials for residential air conditioning peak demand reduction and energy conservation in coastal and transitional climates in the State of California

The recent rapid economic and population growth in the State of California have led to a significant increase in air conditioning use, especially in areas of the State with coastal and transitional climates. This fact makes the electric peak demand to be dominated by air conditioning use in buildings during the summer time. However, this extra peak demand caused by the use of air conditioning equipment lasts only a few days out of the year. As a result, avoidable power outages occur when power utilities do not keep up with such demand. This paper proposes a possible solution to this problem by using building thermal mass via phase change materials to reduce peak air conditioning demand loads. This proposed solution was tested using a wall herein referred to as phase change frame wall (PCFW). The PCFW is a typical residential frame wall in which Phase Change Materials (PCMs) were integrated to add thermal mass. The thermal performance of PCFWs using a hydrated salt PCM was evaluated via computer simulations of residential buildings located in coastal and transitional climates in California. Simulated results indicated that the PCFWs would reduce the space cooling load by an average of 10.4%.

Case-study of Thermo Active Building Systems in Japanese Climate

Thermo active building systems (TABS) have been applied in office buildings as a promising energy efficient solution in many European countries. The utilization of building thermal mass helps to provide high quality thermal environments with less energy consumption. However, the concept of TABS is entirely new in Japan. This paper introduces and evaluates TABS under Tokyo weather conditions to clarify the potential of use TABS in Japan. Cooling capacity of thermo active building systems used in an office building was evaluated by means of dynamic simulations. Two central rooms of the office were selected for the analysis. Six water control strategies were studied and two of those were found reasonable and suitable for TABS use in Tokyo. These two strategies are: free-cooling using underground heat exchanger combined with TABS and free-cooling with desiccant dehumidification system. For these two cases, the operative temperature was between 22-27°C during 97∼99% of the occupation time. The operative temperature drift was less than 4°C per day. The pump running time was 7hours per day and the cooling power of the TABS was 36W/m2 floor area. For those free-cooling cases, the average supply water temperature was 20°C, which shows that free-cooling is achievable using underground heat exchangers even considering the temperature increase of the ground during cooling season.