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Pipe-embedded concrete radiant floor system has gained much popularity due to its higher energy efficiency and better thermal comfort. Simplified yet accurate heat transfer models are essential for energy simulation of this system. This study presents the development and validation of a simplified RC-network model for the pipe-embedded concrete radiant floors. A concrete radiant floor mainly consists of three parts which are the cover layer, the pipe-embedded concrete slab and the insulation layer. The cover layer and the insulation layer are simplified as one-dimensional and represented by RC models with two resistances and one capacitance (2R1C). Within the pipe-embedded concrete slab, the complex heat transfer is represented by a coupled RC model which includes two parts describing the heat transfers of the concrete slab and the water loop respectively. In the case studies, the coupled RC model for the pipe-embedded concrete slab has been validated in both numerical and experimental ways. The experimental validation results show that the average relative errors of the coupled RC model in predicting the upper and bottom surface heat fluxes are all less than 5.5%. Validation has also been conducted to demonstrate the accuracy and effectiveness of this developed simplified RC-network model in predicting the dynamic thermal performance of a multi-layer pipe-embedded concrete radiant floor. The developed simplified RC-network model can be beneficial for design and optimal control of the pipe-embedded concrete radiant floor system. [ABSTRACT FROM AUTHOR]

The study proposes a new low-grade energy utilization system, i.e. a pipe-embedded wall integrated with ground source-coupled heat exchanger, and investigates its energy saving potentials in five typical climate regions of China. The cool/hot water produced by the ground source-coupled heat exchanger is supplied to the pipe-embedded wall to intercept the heat gain/loss through the wall. A real-scale building energy simulation platform has been developed for estimating the energy saving potentials. The study results show that the energy saving potential of the proposed system varies with the climate regions. With the same sized pipe-embedded wall system, the building in warm climate regions achieves the largest energy saving percentage. It is followed by the buildings in the hot summer and cold winter climate region, the severe cold climate region, the cold climate region, and the hot summer and warm winter climate region in the declining sequence of energy saving. Meanwhile, a multi-criteria performance evaluation has been conducted to search for the optimal size of the low-grade-energy system in each climate region. The proposed system can be utilized in practice for energy saving, and the study results are helpful in guiding the practical applications of the pipe-embedded wall system in different climate regions. [ABSTRACT FROM AUTHOR]

Hollow blocks or bricks are widely used due to the good thermal insulation, lightweight, acoustic insulation, etc. This paper presents the development of a simplified heat transfer model of hollow block for simple and efficient heat flow calculation. This model is developed based on parameter identification in frequency domain by using finite element method in frequency domain. Firstly, the frequency domain finite element model (FDFEM) of the hollow block is developed by using finite element method in frequency domain to obtain the theoretical frequency characteristics of this structure. Then, the heat transfer function model in the form of s -polynomial (i.e., the s -polynomial heat transfer function model) is identified by using a parameter identification procedure based on the calculated theoretical frequency thermal characteristics. Finally, the simplified heat transfer model, i.e., the Conduction Transfer Function (CTF) coefficients, of this hollow block are derived from the identified s -polynomial heat transfer function model. A case study is presented for the prediction of the dynamic heat transfer of this hollow block by using the simplified heat transfer model. The predicted dynamic heat transfer of this block is validated by experimental data. [ABSTRACT FROM AUTHOR]

Active pipe-embedded building envelope is a new kind of external building wall or roof which usually has pipes embedded in it to let water circulate in these pipes for heat transfer. This structure may effectively intercept the heat/coolth from the ambient environment to indoor space and provide extra space conditioning for the indoor space. Frequency-domain finite-difference (FDFD) model can predict the frequency thermal response of active pipe-embedded building envelope directly and provide some important guidelines for system control and system sizing. This paper presents the experimental validation of this model in time domain by using Fourier series analysis. An experiment test rig was developed for the thermal response measurements of the pipe-embedded building envelope under pre-defined conditions. First, the measured time series of surface temperatures are transformed into complex Fourier series by using Discrete Fourier Transform and applied into the FDFD model as the boundary condition for calculation. Then, the calculated frequency thermal responses by FDFD model can be easily transformed into time series by using Inverse Discrete Fourier Transform. Finally, the time-domain thermal responses of FDFD model are obtained. The results show that the calculated time-domain thermal responses of the active pipe-embedded building envelope by using FDFD model agree well with the experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: Low-grade energy sources such as geothermal energy, favorable ambient air and industrial waste heat etc. exist widely. Sufficient utilization of these low-grade energy sources may reduce our daily dependence on high-grade energy sources such as electricity resulting in reduced emission of green house gas for environmental conservation. Active pipe-embedded structure as floor/ceiling usually with water as the medium to carry heat or coolth may utilize these low-grade energy sources for providing space air-conditioning. Compact arrangement of pipes in the structure may significantly enlarge heat transfer surface between the slab mass and water in the pipe allowing substantial heat flows even for relatively small temperature differences. Application of the heat or coolth storage capacity of this structure for preheating or pre-cooling is also one among the advantages of this structure for shifting load and exploiting the nighttime cheap electricity tariff in some regions. This paper presents the technology of the active pipe-embedded structure for utilizing widely existing low-grade energy sources following by a comprehensive review on the heat transfer calculation models of this structure and its practical applications in real building systems for space air-conditioning. This review shows that more works on the active structure, especially simple and transient models for dynamic and accurate performance prediction and easy integration with existing building energy simulation packages, are worthwhile for further promoting the practical application wherever the low-grade energy sources are favorable. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a simple time domain calculation method to derive thermal response factors and conduction transfer conduction (CTF) coefficients of finite differential models for estimating transient heat transfer through building structures. It is developed on the basis of converting the matrix exponential function, which is a part of the solution of the state equation established from the finite differential equations of building finite differential models, to matrix polynomial. The thermal response factors and CTF coefficients can be easily derived from the matrix polynomial with simple arithmetic and integral in time domain. This method avoids the time-consuming root-finding process of conventional methods and the computation of all the internal temperature of the finite differential model, while utilizing the advantage of the thermal response factors/CTF coefficients which relate the desired outputs at a moment to the previous inputs through a set of coefficients. Various case studies were conducted to validate the performance of this time domain calculation method in calculating the thermal response factors and CTF coefficients of various order finite differential models. [Copyright &y& Elsevier]

Abstract: Simple and effective building energy models are essentially needed for many applications, such as building performance diagnosis and optimal control, etc. The energy model involves two important parts of building components, i.e., building envelopes and building internal mass. This paper presents a methodology for parameter optimization of 3R2C thermal network model of building envelopes (composed of three resistances and two capacitances) based on frequency domain regression using genetic algorithm (GA). First, the theoretical frequency characteristics of heat transfer through building envelope are calculated using detailed physical description within the frequency range of concern. Second, the frequency characteristics of the simplified 3R2C model are calculated with random values of individual resistances and capacitances which constrain to total thermal resistance and capacitance. Then, the errors between the theoretical frequency characteristics and the frequency characteristics of the simplified model are calculated. Finally, GA estimator is developed to optimize the parameters of the simplified model, allowing the frequency responses of the simplified model match the actual heat transfer through building envelope the best. Various case studies are conducted also to validate the parameter optimization method of the simplified 3R2C model. The accuracy of simplified models for constructions of different weights is studied. [Copyright &y& Elsevier]

The hollow block ventilated wall is a new kind of ventilated wall, the exhaust air of HVAC system is used as the supply air to flow through the cavity of this wall in this paper. The heat or cool storage in the wall is reduced by using the heat recovery technology; the temperature of internal surface is lowered in summer and increased in winter, and the human thermal comfort is enhanced. A semi-dynamic heat transfer model of the ventilated wall is presented for thermal performance prediction. The dynamic optimized resistance-capacitance (ORC) model and the number of transfer units (NTU) model are joined together to develop the semi-dynamic heat transfer model of this ventilated wall. The experimental study is carried out for validating the semi-dynamic heat transfer model. The maximum relative error is 4.3% for mean internal and external surface temperatures, and it is 2.6% for the outlet air temperature of the cavity. The heat transfer model established for hollow block ventilated wall is fairly reasonable and possesses high accuracy. This model can be used to predict the surface temperature of the hollow block ventilated wall and the heat flux removed by the airflow in the cavity for performance evaluation. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on a bilinear temperature control of a ground source heat pump (GSHP) integrated variable air volume (VAV) air-conditioning system, which may experience significant variations in the supply air temperature due to the frequent on/off switch of the ground source heat pump and the low thermal capacity at the air side. The bilinear control was realized in a building automation system (BAS) and applied to a test rig. The experimental results show that with an online estimation of the cooling load the bilinear control was able to maintain the space temperature at its set-point well and the control performance was superior to that of a conventional PI control. Therefore, the bilinear control has the potential to be used in GSHP integrated air-conditioning systems to improve the robustness and accuracy of the space temperature control. [ABSTRACT FROM AUTHOR]

This paper presents a method which combines the bilinear control technique with a set-point reset technique to control the space temperature when its cooling is provided by a GSHP equipped with an on/off capacity control, aiming to (i) improve the robustness of the space temperature control by taking account of load uncertainty; and (ii) to reduce the frequency of the GSHP on/off cycling by using the indoor space temperature set-point reset. When the GSHP is on, a smaller space temperature set point is used; while the GSHP is off, a larger set point is used. The proposed control was tested on a simulation platform, which consists of a ground source heat exchanger, a GSHP, an air-handling unit (AHU) and a middle-sized room. The test results show that the proposed control method is able to achieve a good control performance and has the potential to be applied to a real GSHP integrated air conditioning system to improve the robustness of space temperature control and simultaneously reduce the on/off frequency of the GSHP. [ABSTRACT FROM AUTHOR]

• Energy performance of HVACs in super high-rise buildings were field-tested and analyzed. • The representative issues leading to large energy consumption of HVACs were summarized. • Commissioning of VAV system and multistage chilled water systems were conducted. • The setting values of HVACs should be adjusted in time according to practical cooling demand. The HVACs in super high-rise buildings commonly consists of variable air volume (VAV) systems, multistage chilled and cooling water systems, primary-secondary chilled water system in chiller plant, and the chillers combination is much more complex, leading to the significantly higher energy consumption than that of normal buildings. This paper contains field tests and comparative studies on the operation performance of HVACs in two super high-rise buildings and summarized representative issues accounting for the high energy consumption. Field test results showed that the annual energy efficiency of the whole HVAC system, before being commissioned, was only 1.79 and 2.15 in two projects. The HVACs, typically VAV systems, chilled and cooling water systems, all suffered from over-supplying and energy wasting. Besides, the chillers commonly operated with a low partial load ratio (PLR), whose energy performance was much lower than expected. Aiming to dig out the typical issues, analyses were carried out from external, internal factors, and their interconnection. Furthermore, optimization methods were put forward with corrected vital indexes. Results showed that proper control strategies should maintain the VAV system, multistage chilled and cooling water system operating with significant distribution temperature differences, tiny distribution pressure drops, and high energy efficiency, thus achieving energy saving and ensuring space cooling effects. Besides, the control strategies, especially the number control of chillers, were influential during the whole cooling season to ensure the chillers operate with optimal PLR and thus achieve better energy performance. [ABSTRACT FROM AUTHOR]

Effective evaluation on the thermal performance of envelope plays an important role towards the reduction of energy consumption for space cooling and heating. In order to calculate the energy consumption for cooling and heating and assess the whole energy efficiency of envelop designs, a new evaluation index on energy and thermal performance for office building envelop (EETPO) is put forward. Three cities of Shenyang, Wuhan and Guangzhou in China are selected for EETPO analysis, which represent the cold zone, hot summer cold winter zone and hot summer warm winter zone, respectively. The regression equations between EETPO and energy use for cooling/heating are studied in three cities, illustrations indicate that the regression lines fit extremely well and the algorithm is accurate and simple. According to the compulsory indices stipulated by standard (GB50189-2005), the maximum allowable values of EETPO are determined in three cities, the maximum EETPO c in cooling period is 1.750 W/m 3 K in Wuhan and 1.733 W/m 3 K in Guangzhou, the maximum EETPO h in heating period is 0.200 W/m 3 K in Shenyang and 0.414 W/m 3 K in Wuhan. This index and energy use calculation method can help designers to evaluate the whole energy and thermal performance of the proposed envelopes and analyze energy saving effects for different energy conservation measures. [ABSTRACT FROM AUTHOR]

Abstract: Heat pumps could be used to produce hot water for hybrid cooling towers for preventing the occurrence of plume in subtropical regions. The evaporative side of the heat pump system could be arranged either at the inlet side or at the outlet side of these cooling towers for cooling down the cooling water temperature. Alternatively, the evaporative side of the heat pump system could also be arranged at the evaporative side of chillers to reduce return chilled water temperature and therefore to reduce the cooling load of chillers. This study presents the evaluation of the impacts of these three arrangements of the heat pump system on the plume control performance and the energy performance in a large-scale chiller plant in Hong Kong. The performance prediction and evaluation of the chiller plant and the plume abatement system were conducted on a dynamic simulation platform. The results show that these three arrangements have almost the same plume control performance with sufficient plume control capability. The results also show that the arrangement of the evaporative side of the heat pump system for cooling down return chilled water temperature has much better performance that the other two arrangements for improving the overall energy efficiency. [Copyright &y& Elsevier]

[Display omitted] Energy efficiency in residential buildings can be improved considerably by optimizing the allocation of thermal resistance (R) and capacitance (C) of external walls. However, it is difficult to identify which RC allocation yields the minimum heat loss or heat gain for a given climate region, due to a lack of understanding of how regional climate affects optimal RC allocation. In this study, we determine the effect of the climate characteristics on the development of optimal RC allocation by combining the RC network model and the particle swarm optimization algorithm, taking five representative climates in different Chinese cities as examples. The energy efficiency potential and the ratio of heating to cooling load are introduced to comparatively analyse the energy savings after optimization for the five cities. The results indicate that the energy efficiency potential of residential buildings in Harbin is the largest, ranging from 6.2% to almost 20.6% for different total building capacitance. In Harbin, Beijing and Kunming, the energy efficiency potential is larger than those in Guangzhou and Shanghai, which is attributed to the larger heating to cooling load ratio of the former than that of the latter. An approximately linear relationship between the energy efficiency potential and the ratio of heating to cooling load is also built to fast predict the maximum energy savings for any given climate regions. This study could serve as useful references for the optimal design of thermal resistance and capacitance in different climate regions to save energy of residential buildings. [ABSTRACT FROM AUTHOR]

A concept of exhaust air insulation (EAI) is proposed for application in cooling dominated buildings. The EAI wall in basic form is composed mainly of an air-permeable porous material layer, a ventilated cavity, and an external protection structure. The excessive indoor air pressure or mechanical ventilation forces the exhaust air from the conditioned space to flow through the porous layer firstly, and eventually to ambient through the ventilated cavity. The outflowing exhaust air makes the temperature of the inner surface of the porous layer very close to that of the indoor air. And consequently, the heat gain through the building envelope wall can be dramatically reduced in the cooling season. In this paper, an unsteady-state heat transfer model is developed to predict the temperature distribution of the EAI wall. Experimental measurements are carried out for validating the heat transfer model. Numerical simulations are performed to simulate the transient heat transfer of the EAI wall in cooling season. The exfiltration heat recovery efficiency of the EAI wall is quantitatively investigated. Effects of the airflow velocity, the thickness of porous layer, and the thermal conductivity of porous material on the thermal performance of EAI wall are analyzed. Performances of a conventional brick wall and an external insulation wall are also calculated and compared with that of the EAI wall. Results show that the EAI wall can reduce 84.7% and 67% of the daily total heat gains in cooling season compared with the brick wall and the external insulation wall, respectively. Excellent thermal performance can be achieved by employing thicker porous layer or higher airflow velocity. At a velocity of 0.003 m/s with porous layer thickness of 50 mm, the heat flux entering indoor spare can be decreased to practically zero. [ABSTRACT FROM AUTHOR]

Radiant cooling is an energy-efficient space cooling technology in built environments to achieve high thermal comfort. However, there are technical bottlenecks of condensation risk and insufficient cooling capacity in hot and humid climates. The use of double-skin infrared-transparent membranes (DIMs) to separate the radiant cooling surface from the air-contact surface can improve the cooling capacity while preventing condensation. Current research focuses on theoretical analysis and reduced scale experiments, and the lack of measured operational and performance data creates a key limitation on DIMs use. Therefore, the verification of radiant cooling system with DIMs in a full-scale experimental space and its radiant cooling performance need to be further studied. In this study, two full-scale radiant cooling chambers (one with DIMs and one without DIMs) were constructed. The effect of DIMs on radiant cooling performance was studied by monitoring surface temperature, condensation risk and cooling capacity. The results indicated that the air-contact surface temperature in radiant cooling with DIMs was always maintained above the dew point temperature for condensation-free safety at a low water supply temperature of 8 °C. In contrast, the conventional radiant cooling without DIMs had severe condensation. Moreover, the cooling capacity of radiant cooling panel with DIMs was 105.5 W/m2 at water supply temperature of 8 °C, 24.4 % improved compared to radiant cooling panel without DIMs at water supply temperature of 14 °C. This study provides prototype experimental verification for new technology with DIMs to improve radiant cooling performance and provides experimental data as a reference for related theoretical and model studies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sensitivity analysis of energy performance is performed for residential envelope. [•] EETP method is introduced to calculate cooling and heating energy use. [•] Shading coefficient and window to wall ratio are the most vital factors in summer. [•] Wall heat transfer coefficient and shape coefficient have crucial effect in winter. [•] Wall heat transfer coefficient and window to wall ratio weight the most in a year. [ABSTRACT FROM AUTHOR]

Abstract: Thermal protection of building envelope is one of the most effective ways for building energy conservation. In this study, the determination of optimum insulation thickness for residential roof with different surface colors is studied based on life cycle cost analysis and solar-air degree-hours in four typical cities of hot summer and cold winter zone of China. Four insulation materials including expanded polystyrene, extruded polystyrene, foamed polyurethane and foamed polyvinyl chloride are analyzed. The solar-air degree-hours are calculated considering night time operation and 24-h operation of the cooling and heating equipments. Life cycle total costs (LCT), life cycle savings (LCS) and payback period resulting from the use of optimum insulation thickness are calculated. Depending on different cities, insulation materials and roof surface colors, optimum insulation thicknesses of a typical roof vary from 0.065 to 0.187m and payback periods vary from 0.9 to 2.3 years for 24-h operation of cooling and heating equipments; optimum insulation thicknesses are between 0.051 and 0.149m and the payback periods are between 1.1 and 2.8 years for night time operation. At last, the effects of present worth factor, thermal resistance and climate on the optimum thicknesses are studied which is very useful for practical use to estimate the optimum thickness of insulation material. [Copyright &y& Elsevier]

The coupled pipe-encapsulated PCM wall system with a nocturnal sky radiator is a novel type of building envelope structure for low energy buildings. It absorbs outdoor heat and stored it by using the pipe-encapsulated PCM inside the wall in the daytime, and the stored heat is automatically discharged into space through the sky radiator by the effect of the gravity heat pipe at nighttime. It makes full use of the natural cooling source, which can effectively reduce indoor heat gain through the envelope and improve the utilization efficiency of PCM. In this paper, an experiment platform integrating the pipe-encapsulated PCM wall module, the nocturnal radiator module, the heat pipe circulation module and measurement system together is established. The heat transfer characteristics of the wall system in four cases under the dynamic boundaries are tested, and the performances are contrastively discussed. Comparing to the wall without nocturnal radiation, the coupled wall system can well reduce the indoor cooling load and the wall internal surface temperature. The wall internal surface average heat flux can reduce 10.2 W/m2, and the cumulative indoor heat gains can reduce 29.7%. The results show the good thermal performance and energy-saving potential of this coupled pipe-encapsulated PCM wall system with a nocturnal sky radiator. With the development of new materials for enhancing the capability of radiative cooling such as the glass-polymer hybrid metamaterial, the performance of the coupled wall system may be significantly improved when these materials are used in the sky radiators. [ABSTRACT FROM AUTHOR]