Uncertainty-based life-cycle analysis of near-zero energy buildings for performance improvements

Near-zero energy buildings( nZEBs) are considered as an effective solution to mitigating CO_2 emissions and reducing the energy usage in the building sector. A proper sizing of the nZEB systems( e. g. HVAC systems,energy supply systems,energy storage systems, etc.) is essential for achieving the desired annual energy balance,thermal comfort,and grid independence. Two significant factors affecting the sizing of nZEB systems are the uncertainties confronted by the building usage condition and weather condition,and the degradation effects in nZEB system components. The former factor has been studied by many researchers; however,the impact of degradation is still neglected in most studies. Degradation is prevalent in energy components of nZEB and inevitably leads to the deterioration of nZEB life-cycle performance. As a result,neglecting the degradation effects may lead to a system design which can only achieve the desired performance at the beginning several years. This paper,therefore,proposes a life-cycle performance analysis( LCPA) method for investigating the impact of degradation on the longitudinal performance of the nZEBs. The method not only integrates the uncertainties in predicting building thermal load and weather condition,but also considers the degradation in the nZEB systems. Based on the proposed LCPA method,a two-stage method is proposed to improve the sizing of the nZEB systems.The study can improve the designers "understanding of the components"degradation impacts and the proposed method is effective in the life-cycle performance analysis and improvements of nZEBs. It is the first time that the impacts of degradation and uncertainties on nZEB LCP are analysed. Case studies showthat an nZEB might not fulfil its definition at all after some years due to component degradation,while the proposed two-stage design method can effectively alleviate this problem.

A modelling method for large-scale open spaces orientated toward coordinated control of multiple air-terminal units

The temperature distribution is always assumed to be homogeneous in a traditional singleinput-single-output(SISO)air conditioning control strategy.However,the airflow inside is more complicated and unpredictable.This study proposes a zonal temperature control strategy with a thermal coupling effect integrated for air-conditioned large-scale open spaces.The target space was split into several subzones based on the minimum controllable air terminal units in the proposed method,and each zone can be controlled to its own set-point while considering the thermal coupling effect from its adjacent zones.A numerical method resorting to computational fluid dynamics was presented to obtain the heat transfer coefficients(HTCs)under different air supply scenarios.The relationship between heat transfer coefficient and zonal temperature difference was linearized.Thus,currently available zonal models in popular software can be used to simulate the dynamic response of temperatures in large-scale indoor open spaces.Case studies showed that the introduction of HTCs across the adjacent zones was capable of enhancing the precision of temperature control of large-scale open spaces.It could satisfy the temperature requirements of different zones,improve thermal comfort and at least 11%of energy saving can be achieved by comparing with the conventional control strategy.

Room temperature and humidity decoupling control of common variable air volume air-conditioning system based on bilinear characteristics

Variable air volume(VAV)air-conditioning(AC)systems are widely employed to achieve a comfortable room thermal and humid environment depending on its better regulation performance and energy efficiency.In the single coil VAV AC system,conventional proportional-integral(PI)control algorithm is usually adopted to track the set-points of the room temperature and humidity by regulating the supply air flow rate and the chilled water flow rate,respectively.However,the control performance is usually not good due to the high coupling of the heat and mass transfer in the air-handling unit(AHU).A model-based control method is developed to realize the decoupling control of the room temperature and humidity according to the bilinear characteristics of the temperature and humidity variation.In this control method,a bilinear room temperature controller is used to track the room temperature set-point based on the real-time cooling load,while a room humidity controller is used to track the room humidity set-point depending on the real-time humidity load.The control performance was validated in a simulated VAV AC system.The test results show that comparing with the conventional PI control,the room temperature and humidity are controlled much more robustly and accurately by using the proposed model-based control method.

Cooling load characteristics of indoor spaces conditioned by decoupled radiant cooling unit with low radiant temperature

Decoupled radiant cooling units(DRCUs)are capable of increasing the cooling capacity without increasing condensation risks even using a much lower cooling temperature than conventional radiant cooling units(CRCUs).However,it is unclear whether DRCUs using low radiant cooling temperature will increase the cooling load of the conditioned indoor spaces.In this study,the cooling load characteristics of a thermal chamber conditioned by a DRCU was investigated through developing a steady-state analysis model suitable for both DRCUs and CRCUs.The total/radiative heat flux,as well as the heat exchange with a thermal manikin and walls were analysed under different surface temperatures of DRCUs.The effect of the emissivity of the thermal chamber’external wall on the cooling load was also investigated.Results indicated that the cooling load under the DRCU was slightly smaller than that under the CRCU when the same operative environment was created.Decreasing the infrared emissivity of the exterior wall’s inner surface could lead to a significant decrease in the cooling load for both the DRCU and CRCU.By decreasing the wall emissivity from 0.9 to 0.1,the total cooling load of the DRCU can be decreased by 8.4%and the heat gain of the exterior wall decreased by 21.6%.This study serves as a reference for developing the analysis model and understanding the load characteristics when DRCUs are used to create the thermal environment for indoor spaces.

Swimming pool heating technology:A state-of-the-art review

A large amount of heat is needed to maintain the thermal comfort of both indoor and outdoor swimming pools in cold seasons.This motivates the development of various heating technologies aiming to reduce energy use,as well as operating and investment costs.Although their development can be traced back to the 1960s,a comprehensive review of these technologies is lacking.Therefore,this paper presents a comprehensive review of the development of heating technologies for swimming pools.This review firstly introduces available heat transfer models that can be used to calculate or predict heat loss and heat gain for swimming pools.Then,different passive and active technologies are summarized.The active heating technologies used for indoor swimming pools include solar collector,heat pump,waste heat recovery,geothermal energy,and congregation technologies.The active heating technologies used for outdoor swimming pools include solar collector,heat pump,PCM storage,geothermal energy,biomass heater,and waste heat recovery technologies.A discussion is presented on the practical and possible heating techniques for swimming pool applications.Finally,through the reviewed literature,future research opportunities are identified,to guide researchers to investigate swimming pool heating systems with suitable and relevant technologies.

Generic load regulation strategy for enhancing energy efficiency of chiller plants

In many chiller plants,high coefficient of performance(COP)is only achieved at a few favorable part load ratios(PLRs),while the COP is low at many other non-favorable PLRs.To address this issue,this study proposes a generic load regulation strategy that aims to maintain chiller plants operating at high COP,particularly under non-favorable PLRs.This is achieved by incorporating thermal energy storage(TES)units and timely optimizing the charging and discharging power of the integrated TES units.The optimal charging and discharging power is determined by solving a dynamic optimization problem,taking into account the performance constraints of the TES units and the chiller plants.To provide an overview of the energy-saving potential of the proposed strategy,a comprehensive analysis was conducted,considering factors such as building load profiles,COP/PLR curves of chillers,and attributes of the TES units.The analysis revealed that the proposed load regulation strategy has the potential to achieve energy savings ranging from 5.7%to 10.8%for chiller plants with poor COPs under unfavorable PLRs,particularly in buildings with significant load variations.