Building Thermal Systems Research Articles

An optimization study into thermally activated wall system with latent heat thermal energy storage

Thermally activated building structures with latent heat thermal energy storage (LHTES) are relatively new elements of building thermal energy systems. The system considered in the present study involved lightweight wall panels with a plaster containing a microencapsulated phase change material (PCM). The polyethylene tubes of small diameter for heat transfer fluid were embedded in the plaster. The wall panel system could be used for both heating and cooling. The PCM provided short-term thermal energy storage in case of intermittent supply of heat and cold (e.g. in case of a PV powered heat pump). A 1D computer model of the wall system was developed and implemented as a TRNSYS type. Consequently, an optimization model based on the 1D model of the system was developed. The optimization model employed a metaheuristic particle swarm optimization method. The aim of the optimization was to determine the position of the tubes for HTF, relative to the surface of the panel, that would provide fast thermal response and, at the same time, high amount of stored heat. The optimization was performed for heating operation.

Incentive-Based Mechanism for Truthful Occupant Comfort Feedback in Human-in-the-Loop Building Thermal Management

Energy inefficiency and underlying occupant discomfort associated with building thermal management systems have led to the development of a human-in-the-loop control system. Minimizing total energy use and maximizing comfort of all the occupants present is the major objective of such system based on human comfort feedback. However, the approaches proposed so far lack a built-in mechanism to elicit truthful comfort feedback from the occupants. In this paper, we utilize an incentive-based mechanism design framework to elicit true thermal comfort feedback (function) from the occupants present. This requires the building occupants to “purchase” or spend credits to achieve their personalized comfort levels within their zone of occupancy. The comfort pricing policy has been derived as an extension of the Vickrey–Clarke–Groves pricing. It ensures incentive compatibility of the mechanism, which implies that an occupant acting in self-interest cannot stand to benefit by declaring their comfort function untruthfully. This would hold irrespective of the thermal comfort choices made by the other occupants present in the building. We further propose as to how this mechanism could be implemented in practice with limited comfort feedback complexity, where the building operator would iteratively learn and refine the occupants comfort function based on simple 2-D comfort feedback (preferred temperature setting, and willingness-to-pay value) by the occupant. Simulations using parameters based on our Watervliet experimental facility demonstrates the effectiveness of the proposed mechanism.

Energy consumption reduction proposals for thermal systems in residential buildings

The energy efficiency in the building sector, a widely accepted point inside world energy sustainability, can be pursued in a variety of complementary ways, being energy consumption reduction one of them. Specifically, the residential buildings are responsible for more than 40% of the total energy consumption of the European Union. Therefore, this residential sector is an important target for optimizing the use of energy. This paper examines the energy saving measures for multi-family residential building thermal systems in the city of Granada. The state and usage patterns of such systems in a middle-size city are surveyed and analysed in order to propose sounded saving measures. The proposed measures were quantified according to two parameters: energy saved and CO2 emissions reduction. This quantification enables the identification of best measures either cost or energy effective, concluding that the biggest benefits are obtained adopting solar/biomass energy, while other zero-cost measures like the information campaign have more impact than, for instance, boiler replacement. Finally, it is concluded that an extension of mandatory installation of solar systems to existing buildings should be considered.

Contract Design for Aggregating, Trading, and Distributing Reserves in Demand-Side Frequency Regulation

With the integration of renewable energy sources to the power grid, the volatility of supply in the system will increase. Consequently, the mismatch between the power supply and demand may happen frequently and, thus, lead to frequency deviation from its nominal value. To avoid this scenario, demand-side flexibility has been widely considered to provide frequency regulation services. In this paper, we focus on the flexibility of thermal systems in buildings and propose a hierarchical demand-response market with a three-step algorithm to model the interactions among three entities: the independent system operators (ISOs), aggregators, and end users. The flexibility from the end users is aggregated in step 1, which is based on the incentive and electricity prices broadcasted by the aggregator. A robust optimization approach is adopted to improve the user's decision under the electricity price uncertainty. To model the interaction between the ISO and aggregators in step 2, a bilevel optimization problem is solved, in which the ISO seeks to minimize its cost, while the aggregators maximize their benefits in the day-ahead market. In step 3, each aggregator allocates its successful trading reserve among end users based on their performance scores.

Energy Renovation of Cultural Heritage Buildings “by the Book”

A draft of Slovenian national technical guidelines for energy efficient renovation of cultural heritage buildings has been prepared in January 2016 in order to increase exploitation of the energy saving potential in a field of cultural heritage buildings. The guidelines include measures to improve the building thermal envelope, energy systems and installations as well as ways to increase the use of renewable energy and organizational aspects with respect to their influence upon protected features, along with warnings and recommendations. The paper presents the mentioned concept and its application on a practical case.

Assessment of the Impact of a Centralized Heating System Equipped with Programmable Thermostatic Valves on Building Energy Demand

Abstract The aim of the work presented in this paper concerns the assessment of actual energy savings achieved adopting a common tool of building thermal automation systems such as thermostatic valves. The idea comes from the study of the European Standard CEN EN15232 “Energy performance of buildings - Impact of Automation, Controls and Building Management” which highlights how the inclusion in buildings of automation systems leads to a reduction of energy consumption for the whole building. Starting from here, the actual advantages for the single user in adopting programmable thermostatic valves was evaluated taking into account the possible differences in heating energy demands due to an on/off timetable customization. The case study is a reference building sited in three different locations in Italy with two different values of envelope insulation. By means of Trnsys17 tool the reference building was divided into six thermal zones each one modelling an apartment. The possibility to customize the on/off timetable, through the use of programmable thermostatic valves, may introduce thermal dispersions. As a matter of facts when a user switch off his heating terminals his apartment tends to be a heat sink for the adjacent ones. The purpose of this study is to evaluate if the switching inhomogeneity due to the customization may constitute sensible energy penalties to other users. The results of this study may provide a contribution to the definition of the correct management policies of the terminals customization in order to optimize the use of the building automation systems.

A thermo-activated wall for load reduction and supplementary cooling with free to low-cost thermal water

A building envelope serves as a thermal barrier and plays an important role in determining the amount of energy used to achieve a comfortable indoor environment. Conventionally, it is constructed and treated as a passive component in a building thermal energy system. In this article, a novel, mini-tube capillary-network embedded and thermal-water activated building envelope is proposed to turn the passive component into active, therefore broaden the direct utilization of low-grade thermal energy in buildings. With this proposed approach, low-grade thermal water at a medium temperature close to the ambient environment can be potentially utilized to either counterbalance the thermal load or indirectly heat and cool the space. With the revealing of the idea, effects of water temperature and flow rate on the envelope's thermal performance are investigated using a transient model. The results indicate that the thermo-activated wall can be effective in stabilizing the internal surface temperature, offsetting the heat gain, and supplying cooling energy to the space in summer. Utilization of the innovation should take the cost of total energy, energy benefit and efficiency into consideration. This article illustrates how low-grade energy can be actively used as a means for achieving net-zero energy buildings.

Parametric study of ice thermal storage system with thin layer ring by Taguchi method

A numerical study of material, thickness and arrangement of thin layer ring has been comparatively conducted to achieve heat transfer enhancement in the building thermal storage system. The parameters of thin layer ring from three perspectives have been numerically investigated and optimized by the Taguchi method to find the optimal combination. Nine combinations of model are carried out by combining different levels of each factor, and ice generated area of each combination has been statistically analysed. The results show that material and arrangement of thin layer ring have the most significant impact on the ice formation, but the thickness of thin layer ring has trifling effects on the ice formation. From this study, the optimal combination (A3B2C1) is acquired, and the reproducibility of the results is verified by two analytical results.

Numerical study of thin layer ring on improving the ice formation of building thermal storage system

Ice thermal storage systems have been widely used in HVAC&R systems for improving energy efficiency and reducing energy costs around the world. In this paper, a numerical model is developed to simulate the ice formation in a typical ice thermal storage system. The first study is to investigate the effect of a cooled cylinder placed in a rectangular space filled with water on the ice formation process. The validated numerical model can predict temperature distribution associated with liquid fraction during the process. Based on the result obtained from the first study, further research is focused on the novel structure of thin layer ring. The computational solutions can demonstrate that the thin layer ring structure can successfully increase an ice generated area and shorten the ice formation period in a typical ice thermal storage system. Finally, a parametric study was carried out to investigate the effect of material, thickness, and arrangement of thin layer ring. It predicted that the heat transfer performance of the thin layer ring is dependent on its material, thickness, and arrangement. Ice formation with novel thin layer ring can be improved by increasing the thermal conductivity of a material. A copper ring has the best performance among aluminum, stainless steel, magnesium alloy. The results show that the ice formation rate can be increased by increasing the thickness of the ring from 0.25 mm to 1 mm, while slowed by increasing from 1 mm to 2 mm and has the best performance with 3 mm ring in this study. Finally, the staggered arrangement of ring shows the best results of the ice formation compared to one parallel and two parallel cases.

Solar thermal systems for high rise buildings with high consumption demand: Case study for a 5 star hotel in Sao Paulo, Brazil

Solar thermal has been consolidated as a renewable energy solution for new buildings during recent years. Although this system has been easily integrated in low-rise buildings, a continuous challenge is the integration of solar thermal into the demanding architectural solutions for high-rise buildings. This article presents solutions for solar water installations in high rise buildings. It describes the integration of solar collectors into the building, hot water distribution installation and proposes a solution to minimise the risk of exposure to Legionella. As an example of the requirements of solar thermal in developing countries, the article analyses the development of the solar hot water standards in Brazil, where although there is a draft document for a federal standard, cities like Sao Paulo have already in place solar thermal requirements for any new building in the city. In order to promote the development of renewable integration, initiatives like PROCEL certify buildings energy performance if they meet the improved target, compared to regulatory requirements, of generating a minimum of 60% of hot water using solar thermal. The presented case study for a 5 star hotel clearly justifies the installation of solar thermal systems in buildings with a high demand for hot water.

Hybrid Predictive Control for Building Climate Control and Energy Optimization

The growing world's energy use and energy prices have raised a concern about the efficiency of energy management systems, energy resources and environmental impacts. In developed countries, buildings are accredited for 40% of the global energy consumption, being the heating and cooling system one of the main causes of it; as the growth of population, comfort levels and services are directly related to thermal systems. For this reason we present a Hybrid Model Predictive Control (HMPC) strategy to control all rooms of a building apartment in a centralized manner. This approach decreases energy consumption, maintaining comfort levels in an acceptable range, and showing that MPC control solutions can be substituted by more complex controls (as HMPC) to manage building thermal systems.

친환경 건축물 단열재 최근 연구 동향

The pros and cons of green building thermal insulation materials and systems have been reviewed from traditional thermal insulation materials such as mineral wool and polyurethane to new thermal insulation materials like VIP and aerogel and future insulating VIM and DIM. VIPs and aerogels with very low thermal conductivity can use for green buildings to significantly increase residential area by reducing energy consumption. Aerogels can be produced as not only opaque and but also translucent forms, thus enabling a wide range of possible building application. For building applications, there are many properties to consider like building site adaptability and mechanical strength, fire protection, cost and environmental impact.

System parameter identification theory and uncertainty analysis methods for multi-zone building heat transfer and infiltration

Methods for on-site measurement of building thermal performance system parameters such as coefficient of heat loss, solar heat gain, effective thermal capacity, infiltration rate, and effective mixing volume are very important, yet a nontrivial task. Although these are steady-state parameters, on-site measurements are exposed to changing meteorological conditions and are affected by the thermal capacity of the building. In addition, these parameters should generally be estimated by using a multi-zone model such as inter-zone flow rates. In this regard, a state space equation model, referred to as a “thermal network model,” has been devised to generalize such multi-zone heat transfer system and tracer gas diffusion system measurements. This model is composed of three parameter types, and we have developed a system parameter identification theory and uncertainty analysis method using least squares, as well as actual measurement systems. In the present paper, we improve the least-squares regression equation, the uncertainty analysis method, and the reliability evaluation method. We investigate appropriate excitation waveforms and frequencies for heating and tracer gas release, as well as a low-pass filter for pre-processing measurement data. We verify these theories and methods using computer-simulated measurement.

District Heating: Results of a Monitoring Campaign in Lombardy Region

Urban neighborhoods could represent an optimal scale for the implementation of innovative energy strategies. However, barriers at the economic, regulatory and administrative level are still present. In this framework, it is important to operate on three levels of the energy system: by reducing energy demand; by optimizing generation and management system, and by integrating local renewable energy sources. In recent years, as a result of an important agreement with the Italian Ministry of Environment, Lombardy Region has supported numerous measures for energy efficiency and renewable resources integration among its territory. The funding supported different actions such as improvements of the buildings envelope, substitution of old gas boilers for heat generation with more efficient components, integration of solar thermal systems in buildings, hydrogen and more sustainable mobility, and district heating plants, which present contribution concerns. About district heating the incentives were provided within two different calls: one aimed at the creation of plants and district heating networks and another for the extension of existing systems. Main aim of the research is to evaluate effects, effectiveness, pros and cons of the several calls for funding; to that end a methodology was developed in order to collect the data and elaborate representative energy, environmental and economic indicators. The most important characteristics, conditions and technical features of the considered plants are described in the present paper trying to provide information on the effectiveness of the supporting measures taken in order to orient future choices and to identify the most promising strategies and technologies for improving energy and environmental performances of communities. In particular present paper is related to 10 district heating plants: 6 are based on biomass and located in mountain areas, 3 are based on natural gas and located in urban areas, while the last is connected to the urban waste to energy plant.One of the important lesson is learned is that district heating (fuelled by biomass, fossil, waste and CHP or not) represents an innovative field of knowledge far from standard: in general each plant has to be evaluated on the basis of specify characteristics and it is very hard to find out average performances from the environmental and economic point of view.The results obtained during the monitoring campaign could help in providing information on the effectiveness of the supporting measures adopted and also to orient future choices by Lombardy Region and, in particular, to identify the most promising technologies for improving energy and environmental performances of communities and to develop a model for the optimization of energy use in the built environment.

Prediction of Hourly Solar Radiation on Horizontal and Inclined Surfaces for Muscat/Oman

In this paper, hourly terrestrial radiation: direct beam, diffuse and global solar radiation are modelled and calculated based on daily measured data for a horizontal surface. In addition, the same parameters were modelled for inclined surfaces. Most of the parameters modelled in this work represent a part of the input data required by building thermal simulation and solar energy systems software. Important trends of the solar radiation on tilted surfaces as a function of time and direction are being presented and discussed. The comparison of some of the results with measured data from other sources shows good agreement. The effect of tilt angle and orientation on the incident solar radiation fluxes arepresented along with optimum surface tilt angles and directions for maximum solar radiation collection in Muscat area. The results presented in this paper are quite useful for quick estimation of solar radiation for calculations of cooling load and solar collector performance. Also, the models and the computer code developed in this work form the backbone of any computer-aided building thermal design and solar systems design calculations.

A comparison of the accuracy of building energy analysis in Bahrain using data from different weather periods

Weather data are important in building design and energy analysis. In Bahrain, the weather data currently used are based on far past climatic information. Climate variability during the last few decades has raised concern over the ability of these data to provide accurate results when analysing the energy performance of buildings. This study discusses issues related to climate variability and evaluates its impact on the performance of weather data used in building simulation. An evaluation was performed using two methods: firstly, a comparison of measured climatic elements and secondly, a comparison of the thermal performance of two statistically based weather data files. With respect to their impact on typical Bahraini building thermal systems, the comparison was carried out between simulation results and the actual energy consumption of two case studies. This paper shows a 14.5% difference between simulation results based on far past data and present electricity consumption and concludes that the prediction of present and future performance based on recent updated data gives better results.

Comparison of methodologies for TMY generation using 10 years data for Damascus, Syria

Abstract The generation of a typical meteorological year (TMY) is of great importance for calculations concerning many applications in the field of thermal engineering. The need of an accurate TMY for simulations has been well recognized over the years. Various methods for deriving TMYs have been developed, but their final results can be significantly different. In this paper, the major methodologies reported in the literature were applied to 10 year hourly measurements of weather data from Damascus, Syria. The TMYs obtained were evaluated according to their impact on the typical Syrian building’s thermal system in order to decide which method should be recommended for generating typical meteorological years and for predicting the performance of thermal systems in buildings. Based on simulation results for seasonally, monthly and daily building thermal loads, three widely used statistical estimators, namely, root mean square difference RMSD, total standard error SEE and chi square χ 2 were calculated to assess the performance of each TMY. The findings showed that the TMY giving the closest performance to the average performance of the building’s thermal system as predicted using the 10 year weather data is the one generated by using the modified Sandia method. This method gives sufficiently accurate results compared with the other methods reported in the literature.

Public energy performance policy and the effect on diffusion of solar thermal systems in buildings: A Dutch experience

Energy performance policy is an important element in the European Energy Performance of Buildings Directive (Directive 2002/91/EC—in short: EPBD, published 4 January 2003), which the European Commission is now urging all European member states to introduce for the building sector by 2006. One of the expected benefits of energy performance policy is that it can help to introduce innovations such as solar thermal systems. However, few studies have analysed this so far. This paper describes the extent to which the penetration of solar thermal systems in the residential building sector is directly related to energy performance policy in the Netherlands. The concept of energy performance policy is explained and the effects of using energy performance policy for several years in the Netherlands are described, through the results of an empirical study. Statistical analysis appears to show no association between Dutch energy performance policy and the application of solar thermal systems in the domestic sector.

Study of Dynamic Thermal Response and Implementation of Proportional Integral Derivative (PID) Controllers in Buildings Using Spreadsheet Models

Difficulties arise in the teaching of control concepts applicable to thermal systems in buildings because these systems are large and respond slowly. Also, traditional control system analysis does not easily accommodate the examination of real scenarios. In this paper, spreadsheet-based techniques are described that allow students to simulate thermal responses using real and hypothetical data. Controller tuning can be simulated and alternative designs can be simultaneously examined and compared. The spreadsheet models are routinely used by distance-learning students, but have proved useful also in teaching full-time students on campus.

Investigation of practical issues in building thermal parameter estimation

Practical issues in implementation of recursive least-squares techniques are investigated through experiments for the robust parameter estimation of a building's thermal processes. A set of supervisory rules is derived from the basic physical laws and the necessary conditions for stable systems. An approach to robust parameter estimation of a building's thermal systems is developed and implemented for the real-time identification of an outdoor test-room with high solar gains and radiant heating. Experimental results show that the room temperatures computed by the identified models agree well with the measured data.