Near zero, zero and plus energy buildings: revised definitions

Here a survey of current definitions is the starting point to underline inconsistencies and critical issues, and to identify weak points. From these, distinguishing between energy and primary energy, with all its attributes, and between energy sources and energy carriers, a proposal of revised definitions of near zero, zero and plus energy buildings is formulated. This analysis is based on the use of the classic energy balance, but taking into consideration that a building is always a net energy consumer (it always produce entropy or destroy exergy). Special attention is then paid in clearly defining primary energy factors for energy carriers produced from renewable energy sources on site, nearby or far. Although the primary energy factors values have been fixed sometime by political reasons, a clear scientific definition is limiting them to a reasonable range these values, which at least do not violate the basic principles of thermodynamics. Finally, to clarify that a “plus” building cannot create energy but can just contribute to the local or regional electrical energy production by feeding the grid, a complementary energy index is then proposed beyond than required by the EPBD. This can overcome the questioning on the “negative” primary energy index that can be achieved by such building using some of current net ZEB definition. In this way is possible to spit the main function (and its quality) of a building from the secondary function (and quality) of being a distributed electric generator for the grid without losing any values and complying with the nearly Zero Energy Building definition of EPBD

The Dual Air Vented Thermal Box: A Laboratory Apparatus to Test Air Permeable Building Envelope Technologies

Dynamic insulation technology has been investigated in detail in the context of a research program conducted by the Building Physic group of the Department of Energy in the Politecnico di Milano. In order to assess the energy performance of this kind of building envelope, either in steady-state or in dynamic conditions, a specific test apparatus has been designed and built. It consists of two thermally controlled chambers, separated by a metal frame hosting the air-permeable wall sample, one fed by a temperature controlled air flow, and the other discharged of the air flowing through the sample. The air flow is realized through a close air loop between the two chambers. The temperature control is achieved with three parallel water circuits (two for the boxes, one for the air loop) mixing cold (~11°C) and hot (~60°C) water. This work deals with the description of the whole apparatus and its measurement and control system, along with the procedure of characterization and calibration of the temperature control system in steady-state conditions

On time-alignment of weather data in Building Performance Simulation

While simulating complex systems, information exchange among components is one of the most important aspects. A specific kind of information is that related to weather data. The format of the climatic data diffusely used in Building Performance Simulation tools (BPSts) contains information about weather variables which are different from each other as far as concern their nature and timing. They have a statistical origin and, in the majority of the cases, are provided on an hourly basis. Given this inhomogeneity and hourly time base, care had been taken to manage their timing and different approaches are today’s in use by BPSts. Furthermore, when the building involves complex components and control strategies, sub-hourly simulation are needed to understand the efficiency of the enquired system. This necessity has led to the implementation of even more different interpolation routines. The capability of these interpolation routines to represent weather conditions that change much more frequently than shown on an hourly basis is here investigated. Besides, BPSts are today used also at operational time, as predictive tools for control strategies and/or Fault Detection and Diagnosis. In this scenario, the statistical validity of climatic data is not anymore sufficient, while their variability profile, recorded with high frequency, and their correct interpretation/synchronization (integral values vs instantaneous values), might became relevant. In this article will be presented a review of the choices implemented by two well-known software, such as TRNSYS 17 and EnergyPlus 8.4.0, to handle weather data and further considerations will be made upon possibilities offered or denied by this choices when different components are involved in the simulation

Advancement in the development of an Open Source Object Oriented BPSt: development methodology

In order to promote its readability, modularity and maintainability, a new Object Oriented (OO) tool for the simulation of buildings performance, has been developed in the last years. The first results of a comparative validation done on our tool, following the BESTEST standard, have been published in the 2013 IBPSA International Conference. The chosen development methodology aims to achieve efficient and high quality software’s development in the field of Building Performance Simulation tools (BPSts) and is based on an Open Source (OS) development approach. Given the selected approach, the contribution of volunteer developers should be encouraged and supported. To effectively support the work of an OS community, key aspects are tasks automation, traceability and communication in the developing phase. The implemented development methodology is then based on: 1) the use of a Software Forge (SF) to promote communication between community members and to help in the management of the software development life-cycle, 2) the use of UML diagrams to describe community-agreed architectural decisions and enforce their implementation into the project, in a way that their implementation can be automatically checked, 3) the ability to group single tests of different modules in one automatic test session of validation, which also simplify final reporting, 4) the use of inheritance, offered by Object Oriented Programming (OOP), to specialize existing classes which, avoiding rewriting, partially automate code writing. As far as concern the quality of the tool, the definition of specific standards for programming, documenting and validating is also important. In particular, the validation phase has to be carried out in pool of verifiers, well documented and provided as an integral part of the documentation available to the user

CTF vs FD Based Numerical Methods: Accuracy, Stability and Computational Time's Comparison

AbstractConduction Transfer Function (CTF) and Finite Difference (FD) based numerical methods, are widely used to calculate transient heat conduction in Building Performance Simulation tools (BPSts). The first method is still preferred, when linear system are modelled, to the second one, thanks to the small computational time required during the simulation. However, current BPSts have not yet implemented effective warning messages to stop their “costumers” when these methods are misused. In this article, those methods are compared in terms of computational time and accuracy, with the aim of identifying selection criteria based on the specific addressed problem

Characterization of Fibrous Insulating Materials in their Application in Dynamic Insulation Technology

AbstractPrevious studies dealing with dynamic insulation technology neglect the microscopic interaction between the solid matrix of the porous material and the air flowing through the pore structure. The main goal of this work is to investigate this interaction, and its effects on the heat transfer phenomena at macroscopic scale using the Volume Average Method. At first, the microscopic geometry of two samples of rock wool is investigated through image analysis, leading to the evaluation of porosity and granulometry. Then, the volume averaging technique is applied to the microstructure of fibrous materials. Thermal dispersion and thermal tortuosity are introduced and evaluated through numerical simulations of simplified geometry in laminar and low-Pe conditions, and two regression equations are defined

Analytical modelling of Breathing Walls: experimental verification by means of the Dual Air Vented Thermal Box lab facility

Breathing Walls are air permeable envelope components based on porous materials. In contra-flux operation air flows opposite to conductive flux, while in pro-flux they have the same direction. The Breathing Wall behaves either as a ventilation heat exchanger or as an active insulation. In literature an analytical model describing steady state heat transfer across a Breathing Wall can be found. Since it lacks an exhaustive experimental validation, a facility developed at the Energy Department of Politecnico of Milano was used to investigate the thermo-physical behavior of a no-fines concrete based Breathing Wall in steady state Dirichlet conditions and contra-flux operation

Integration time step issue in Mediterranean Historic Building energy simulation

The European target towards Zero Energy buildings is focusing on the energy retrofit of existing buildings. Often, in Mediterranean countries, existing buildings have historical relevancies, involving constraints, when dealing with their energy renovation, due to conservation reasons. To analyze possible energy retrofit actions, building energy performance simulation tools (BEPSt) are valuable. However, old buildings are often made of large stone walls whose resolution through conduction transfer function (CTF) used for sub-hourly time step simulation might be critical. This paper analyses how EnergyPlus and TRNSYS address such problem, explaining the differences between them and the reasons for low quality results

The Continuous Commissioning in the European Context: The Project Building EQ

The Commissioning of both existent and new not residential buildings is a common practice in USA or Japan, whereas in Europe can offer new market and technological developments. When an optimization and a continuous evaluation of the performance of building/plant system is in place, the ongoing commissioning of the building and his system is operating. This is seen as a prerequisite for the persistence of high energy performance of buildings. Its practical implementation is constrained by a lack of data and cost, whereas the effects have been proofed to allow energy savings in ranges between 5 -30%. The actual legal and economical framework in Europe (Directive 2002/91/CE and his recasting, 2006/32/CE, 20/20/20 plan etc.) offer the possibility to a synergy between the energy certification of buildings and the aim to reduce the final consumption of energy through the ongoing commissioning of building/plant systems, that represent about the 40% of the EU energy consumption. The aim of project Building EQ is to develop tools and instruments for link the energy certification and the ongoing commissioning of not residential buildings. Objective of the project is to apply “light” monitoring of equipment performance in order to identify saving potential through the set-points optimization and the fault detection and diagnosis. Expected payback is under 3 years. The article aim to show the actual results of the project, like the procedure developed, the minimal data set that is measured on 13 demonstration buildings in Europe by the six participants and highlight result expected by the short coming end of the project

Calibrating the Dynamic Energy Simulation Model for an Existing Building: Lessons Learned from a Collective Exercise

Calibration of the existing building simulation model is key to correctly evaluating the energy savings that are achievable through retrofit. However, calibration is a non-standard phase where different approaches can possibly lead to different models. In this study, an existing residential building is simulated in parallel by four research groups with different dynamic simulation tools. Manual/automatic methodologies and basic/detailed measurement data sets are used. The calibration is followed by a validation on two evaluation periods. Monitoring data concerning the windows opening by the occupants are used to analyze the calibration outcomes. It is found that for a good calibration of a model of a well-insulated building, the absence of data regarding the users’ behavior is more critical than uncertainty on the envelope properties. The automatic approach is more effective in managing the model complexity and reaching a better performing calibration, as the RMSE relative to indoor temperature reaches 0.3 C compared to 0.4–0.5 C. Yet, a calibrated model’s performance is often poor outside the calibration period (RMSE increases up to 10.8 times), and thus, the validation is crucial to discriminate among multiple solutions and to refine them, by improving the users’ behavior modeling