Dr. George M. Stavrakakis

Dr. George M. Stavrakakis
The role of building-energy and urban-environment simulation methods in the implementation of the 2010/31/EU directive The REPUBLIC Med project Dr. George M. Stavrakakis

Recent directives 31/2010/EC
NZEB by 2018 and later for New public financed buildings. 27/2012/EC Existing public buildings Acceleration of public-buildings renovation: 3% of the total usable surface area of buildings owned or occupied by the central government should be renovated each year towards the accomplishment of minimum energy performance requirements set in each MS.

EPBD definitions “NZEB means a building of very high energy performance. The low amount of energy required should be covered in a significant extent by energy from RES, including RES on-site or nearby” “BEP should be expressed through numeric indicator of primary energy use…” “The calculation methodology should take into account European Standards and shall be consistent with relevant Union legislation…” “BEP shall be determined on the basis of the calculated or actual annual energy consumed in order to meet the different needs associated with its typical use and shall reflect the heating energy needs and cooling energy needs to maintain the envisaged temperature conditions of the building and DHW needs.” “When undergoing major renovation, existing buildings shall have their energy performance upgraded so that they also satisfy the minimum requirements.” “Member States shall put in place, in compliance with the aforementioned calculation methodology, minimum requirements for energy performance in order to achieve cost-optimal levels.”

Issues raised What is a NZEB? Are any specific thresholds?
How reliable are simulation methods in predicting the primary and final energy consumption? How should input data and modelling uncertainty and the quest for robust designs be integrated into simulation? How should data be acquired and managed? How can output of simulation be used for compliance? How shall we implement cost-optimality conditions for defining minimum requirements?

Topics of Analysis [1/4] NZEB definition
In some MS there is still no specific definition of NZEB in terms of energy indicators’ thresholds, of a specific extent the reduced energy should be covered by RES, and of the “nearby” term interpretation. Need: Formulation of a sustainable, effective and practical NZEB definition Recommendations*: The definition has to be reviewed in relation to the boundaries of the climate and energy resources. Specification of “nearby” term. Specification of thresholds and additional energy and environmental indicators. Improvement of CEN energy calculation models (including occupants’ behaviour). NZEB will require high energy share in the construction phase=> LCA is also required. * Evaluating and Modelling Near-Zero Energy Buildings; Are we ready for 2018?, JRC Technical Reports, Expert meeting Jan 2012, Glaskow.

Topics of Analysis [2/4] State of the art of building simulation software Simulation for compliance: Concluding NZEB based on national tools (in some MS important parameters are neglected, e.g. energy behaviour and external microclimate effects) Simulation for reliable predictions: Concluding NZEB based on novel tools accounting for “uncertainties” Need: Bridge the two simulation concepts towards recommendations for simulation tools revision Recommendations*: Include dynamic terms (max: hourly simulations). Prescribe input fields for innovative technologies. Improving usability=> Creation of skilled modellers. Extension of boundary conditions to account for external microclimate effects and for interactions with the wider energy system. In policy-making terms new CEN standards should ensure design freedom. If CEN produce prescriptive methods (again) then this will restrict novel methods and, consequently, it will restrict the promotion of better-than-compliance performance. * Evaluating and Modelling Near-Zero Energy Buildings; Are we ready for 2018?, JRC Technical Reports, Expert meeting Jan 2012, Glaskow.

Topics of Analysis [3/4] Occupancy related issues
BEP should be evaluated taking into account occupancy profiles patterns impact. Need: Account for realistic occupancy behaviour patterns effects in the design stage Recommendations*: Bottom-up approach: Stochastic models for predicting occupants’ journeys, presence at each destination and presence-dependent activities and related behaviours. Top-down approach: Identification of behaviour profiles effects through smart metering and/or questionnaires. Simulation tools should provide access to systems’ schedules to incorporate energy-related activities. * Evaluating and Modelling Near-Zero Energy Buildings; Are we ready for 2018?, JRC Technical Reports, Expert meeting Jan 2012, Glaskow.

Topics of Analysis [4/4] Input data and optimization
Important input data referring mainly to boundary conditions when setting up the simulation problem should overcome the barrier of being considered as “Uncertainties”, e.g. climate data time series and realistic properties of technologies. In addition, cost-optimal minimum requirements should be concretely defined. Need: Account for physical and technology “uncertainties” as well as for coupled optimization methods Recommendations*: Indoor-outdoor physical interactions should be taken into account in the study phase. Provision of realistic properties of technologies should be boosted by policy makers. Numerous exercises and scenario assessments and in some level optimization approaches are required to conclude cost-optimal minimum requirements. * Evaluating and Modelling Near-Zero Energy Buildings; Are we ready for 2018?, JRC Technical Reports, Expert meeting Jan 2012, Glaskow.

Design for reliable predictions Design for compliance
Methods that respond to new requirements for directives implementation Buildings Indoor-outdoor interactions Energy behaviour Retrofit technologies Open spaces UHI assessment New insights on urban environmental planning Optimization Pilot applications Plans to introduce approach to policy makers Training seminars Enrich design for compliance Impact of accounting for external microclimate effects Impact of accounting for behaviour Reduce uncertainties Optimization=> Possibilities in cost-optimal minimum requirements Train the stakeholders

Physical models-Buildings
Building Thermal Behaviour Modelling Method Technical approach Application field Advantages Drawbacks Field models (CFD) Discretization into control volumes Finite volume method Contaminant distribution Evaluation of Ventilation systems regarding the creation of comfortable and healthy environments. Detailed description of the airflow field within buildings Accounting for physical- parameters non- uniformity Perception of comfort and air quality Accounting for external microclimate effects. High computational time requirements for high computational resources Modelling complexity. Multi-zonal (BES) Discretization into thermal zones Perfect mixing Finite difference method Determination of total energy consumption Indoor average temperature cooling/ heating loads; Time evolution of energy consumption. Whole building energy simulation over long time periods Reasonable computational time within modest computational resources Difficulty to study large building spaces Unable to study local effects as heat or pollutant source Disregard external airflow effects.

Multi-zonal approach/BES tools
The US Department of Energy has developed a directory of building energy software tools which reports 402 building software tools for evaluating energy efficiency, renewable energy and sustainability in buildings. Tools often used for whole building energy performance assessment Autodesk Green Building Studio DeST ENER-WIN ESP-r SUNREL BEAVER DOE-2 Energy plus IDA-ICE TAS BSim ECOTECT eQUEST IESVE TRNSYS

Most popular BES tools DOE-2: Predicts the hourly energy use and energy cost of a building given hourly weather information, a building geometric and HVAC description, and utility rate structure. It has one subprogram for translation of input (BDL processor) and four simulation subprograms. Each of the simulation subprograms also produces printed reports of the results of its calculations. DOE-2 has been used extensively for more than 25 years for both building design studies, analysis of retrofit opportunities, and for developing and testing building energy standards in the US and around the world. EnergyPlus: It is a simulation engine with input and output of text files. Loads are calculated by a heat balance engine at a user-specified time-step and they are passed to the building systems simulation module at the same time-step. EnergyPlus building systems simulation module, with a variable time-step, calculates heating and cooling system and electrical system response. This integrated solution provides more accurate space temperature prediction, which is crucial for system and plant sizing, occupant comfort and occupant health calculations. Integrated simulation also allows users to evaluate realistic system controls, moisture adsorption and desorption in building elements, radiant heating and cooling systems and interzone airflow. TRNSYS: Modular structure that implements a component-based approach. Its components may be as simple as a pump or pipe, or as complex as a multi-zone building model. Building input data is entered through a dedicated visual interface (TRNBuild). TRNSYS library includes components for solar thermal and photovoltaic systems, low energy buildings and HVAC systems, renewable energy systems, cogeneration, fuel cells, etc.

Strengths and weaknesses of BES tools [1/5]
Special features Most common applications Availability Handling of climate conditions Handling of building systems operating schedules and occupancy Building systems Autodesk Green Building Studio > Provision of hourly whole building energy, carbon and water analysis > Reduces design and analysis costs, allowing more design options to be explored > Accelerates analysis for LEED compliance > Resulting DOE-2 and EnergyPlus models can be very detailed > Input available data of specific climate zones > User-defined climate-data time series > User-defined schedules > Common building systems for heating, cooling, Domestic Hot Water (DHW), etc. > Determination of renewable energy potential (Photovoltaic and wind) Whole building thermal performance Subscription web-based service BEAVER > Hourly whole building energy consumption > Estimation of building structure and systems' types to maintain specific environmental conditions > Modelling of a wide range of building services > inputting of data can be very rapid compared to most other similar programs > Some system types are not included and it does not model chilled and condenser water loops > limited range of windows available for selection > It cannot model natural ventilation or daylighting > Input available data of specific climate zones > User-defined climate-data time series (measured or simulated) > Detailed representation of heating and cooling systems > Various extra components or operating strategies can be added including Heat Recovery, Preheating Coils, Exhaust Fan, Temperature reset on heating and cooling coils, etc. Whole building energy performance Commercial In terms of user friendliness, reliability and applicability In terms of Flexibility in input data: External climatic conditions Profiles of systems’ schedules Options of building systems’ representation In terms of common cases the tool is used for and of its availability (commercial or Free)

Special features Most common applications Availability Handling of climate conditions Handling of building systems operating schedules and occupancy Building systems DOE-2 > Detailed hourly whole building energy analysis > multiple zones in buildings of complex design > It facilitates third party interface (Coupled simulation) > Widely recognized as the industry standard > Requires high level of user knowledge > Complexity > Predefined hourly weather files of the climate zone > User-defined climate-data time series > User-defined operating and utility rate schedules > HVAC equipment and controls > Building system input data interfaces > Whole building energy simulation > Widely used for office buildings Commercial

Special features Most common applica-tions Availability Handling of climate conditions Handling of building systems operating schedules and occupancy Building systems EnergyPlus > innovative simulation capabilities including time steps of less than an hour > Simulation modules that are integrated with a heat balance-based zone simulation > It facilitates third party interface (Coupled simulations) > Inclusion of multizone airflow, electric power simulation including fuel cells and other distributed energy systems > Relatively high level of complexity > Energy simulation expertise is required > Library of pre-defined weather of specific locations > User-defined climate-data time series > User-defined systems' schedules > The majority of systems (HVAC, Air handling units and control, DHW, etc.) of various building types can be employed > Systems’ data input fields > Whole building energy analysis for various building types > Coupling with CFD tools Free

Special features Most common applications Availability Handling of climate conditions Handling of building systems operating schedules and occupancy Building systems TRNSYS > Whole building energy analysis > HVAC analysis and sizing, multizone airflow analyses, electric power simulation, solar design, building thermal performance, analysis of control schemes > It interfaces with various other simulation packages such as FLUENT for airflow impact on energy consumption, GenOpt and MATLAB for optimum building control > Energy and building physics expertise is required > Detailed information for building thermo-physical properties and systems is required > User-specified detailed weather data > Default weather files > User defined systems and occupancy schedules > HVAC systems with HVAC manufacturers databases > DHW systems > Daylighting > Renewable energy systems > Systems’ data input fields > Whole building energy analysis > Often used to test PCM performance > Coupling with CFD tools Commercial

Special features Most common applications Availa-bility Handling of climate conditions Handling of building systems operating schedules and occupancy Building systems eQUEST > User friendly building energy analysis tool > It provides interactive graphics, parametric analysis, and rapid execution > Simulation analysis throughout the entire design process, from the earliest conceptual stages to the final stages of design > It offers detailed analysis throughout the construction documents, commissioning, and postoccupancy phases > IP units > Ground-coupling and infiltration/ natural ventilation models are simplified and limited > Approximate representation of geometry and system > Weather data for limited number of regions > Library of pre-defined weather data in US areas > User-defined climate-data time series > User-defined systems' schedules > It contains a relatively large database of HVAC systems > Systems’ data input fields > Whole building energy analysis for various building types > It is particularly useful to assess occupants' behaviour in tertiary buildings Free

Physical models- Open spaces [1/3]
“The Urban Heat Island is the most obvious climatic manifestation of urbanization” Landsberg, 1981 Causes: Anthropogenic heat released from fuel combustion Reduced potential for evapotranspiration Increased storage of sensible heat in the construction materials Decreased long-wave radiative heat loss due to reduced sky-view factors Trapping of short and long-wave radiation in areas between buildings Reduced convective heat removal due to the reduction of wind speed Urban Heat Island Effect

Physical models-Open spaces [2/3]
Approach UCM CFD Macroscale Microscale Advantages Comfort indicators Simulation of heat conservation effects Fairly accurate Main use: UHI effects on comfort indicators of pedestrians and on building energy performance Comfort and air quality indicators Main use: UHI effects on global climate change Accurate Main use: UHI effects on comfort and air quality of pedestrians and on building energy performance Major limitations - Decoupled velocity field - Limited resolution of building geometries - Applied for steady-state simulations mainly - Empirical assumptions for convective latent and sensible heat - Assumption of the urban canopy layer as roughness - Difficult to provide Land-use profiles (user-defined functions are required) - Turbulence modelling is required - Planetary Boundary Layer effects are ignored - Complex setting up - Reliable boundary conditions are required Maximum size of city-scape domain Whole City Building block Spatial resolution for grid meshing 1-10 m 1-10 km m Temporal resolution (time-step) Hour Minute Second Computational cost Medium High Very high (depending on the turbulence model applied and grid size)

Physical models- Open spaces [3/3]
MESOSCALE CFD MODELLING Evaluation of UHI impact on global climate change UCM may be used MICROSCALE CFD MODELLING Evaluation of UHI impact on pedestrian comfort, air quality and building energy consumption UCM may be used for more approximate estimations

Open spaces-Tools [1/5] Rayman: Developed in the Meteorological Institute of Albert-Ludwigs-University of Freiburg, it is a variant of energy balance models, and it is used mainly to compute radiant heat fluxes from the human body. The inputs the user has to provide are the following: temporal data (date and hour); Geographical data (longitude, latitude and elevation); meteorological data (temperature, relative humidity and cloud covering); personal parameters (clothing and activity level); Geological morphology; urban design features (buildings, trees). The results obtained by the model include, among others, the following: Distribution of mean radiant temperature, radiation fluxes and thermal comfort indicators (PMV, SET* and PET). Fluent: It is the one of the most complete platforms existing in the CFD industry including well-known and the latest developments of fluid-flow related models. In addition to phenomena simulated by ENVI-met, it includes: A wide variety of turbulence models; A wide variety of two-phase flow models to capture particles dispersion; A wide variety of radiation models to simulate short and long wave radiation; A pluralism of grid-meshing options including structured and unstructured grids to build grids with the minimum computational cost ensuring adequate resolution of results; Access to input user-defined functions. ENVI-met: It is a micro-scale model for the prediction of UHI effects within the urban canopy with acceptable accuracy for relatively simple geometries. It is a 3D model for simulating microclimate, taking into account the physical interactions among solid surfaces (e.g. ground and building surfaces), vegetation and air. It is based on the theoretical background of CFD. Inputs: properties of the incoming wind (wind speed, direction, temperature, relative humidity); simplified geometry of the urban domain; thermo-physical properties of ground and building materials and of vegetation, personal parameters of pedestrians. outputs: Distribution of temperature, relative humidity, pollutant concentration, turbulence parameters, wind speed and thermal comfort indicators, at different heights throughout the urban area of interest.

Open spaces-Tools [2/5] Tool Method Strengths Weaknesses Special modelling features Accuracy CPU time Availability Evaporation and evapotranspiration Radiation SOLWEIG UCM > Modelling of 3D radiation fluxes > Relatively accurate geometry > Solves for mean radiant temperature (thermal comfort) > Average urban physics expertise is required > Velocity pattern decoupled from heat transfer > Turbulence is not modeled > Limited documentation and tutorials > By-default models for Evaporation > Evapotranspira- tion is ignored Short and long wave radiation models are included Satifying for weak winds only Medium Research-based In terms of the completeness of calculated indicators, prediction accuracy and user friendliness In terms of whether they account for important urban physics phenomena related to UHI Limitations in accuracy and computational time Availa-bility

Special modelling features Evaporation and evapotranspirati on
Open spaces-Tools [3/5] Tool Method Strengths Weaknesses Special modelling features Accuracy CPU time Availability Evaporation and evapotranspirati on Radiation Rayman UCM > 3D radiation fluxes > Relatively accurate geometry > Solves for radiant heat fluxes from solid surfaces and from human body > Solves for thermal comfort indicators > User friendly > Average expertise in urban physics is required > Low accuracy of Velocity pattern > Neglection of Turbulence effects > Limited documentation and tutorials > Evaporation is included > Evapotranspira- tion is ignored Short and long wave radiation models are included Satisfying for weak winds only Medium Free

Special modelling features Evaporation and evapotranspira tion
Open spaces-Tools [4/5] Tool Method Strengths Weaknesses Special modelling features Accuracy CPU time Availability Evaporation and evapotranspira tion Radiation ENVI- met Micro- scale CFD > 3D simulation of airflow pattern > Solution for most important conservation equations > Calculation of thermal comfort and air quality indicators > Relatively accurate geometry > Turbulence modelling > Average expertise in urban physics is required > Coarse grids > No parallel processing potential is available > Only one turbulence model is included > Limited documentation and tutorials > Ready-to-use models for evaporation and evapotranspiration Short and long wave radiation models are included Satisfying for both weak and strong winds Very high Free

Special modelling features Evaporation and evapotranspira tion
Open spaces-Tools [5/5] Tool Method Strengths Weaknesses Special modelling features Accuracy CPU time Availability Evaporation and evapotranspira tion Radiation ANSYS- Fluent Micro- scale CFD > General purpose CFD platform > Many options of turbulence models and radiation models > Flexibility and easiness of grid generation > Parallel processing potential > Accurate geometries > Extensive documentation with tutorials > Since it is a general CFD platform, the user has to develop and incorporate user-defined models, > thus it requires high expertise in urban physics and fluid mechanics > User-defined models for evaporation and evapotranspira tion Short and long wave radiation models are included Satisfying for both weak and strong winds High Commercial

CFD/BES coupling for building energy assessment
Heat exchange between indoor and outdoor space reveals that building surrounding environment influences building energy performance. These influences may be described as follows: The incident solar radiation on building walls, which is affected by the adjacent obstacles such neighbouring buildings, trees and hills. The convective heat flux at the exterior surfaces, which is determined by the Convective Heat Transfer Coefficient (CHTC) and by temperature difference between the outdoor air and exterior surfaces. The intensity of incoming long wave radiation. The heat and moisture transfer through infiltration. UHI affects building energy performance

CFD/BES coupling for building energy assessment
Findings of past study* Novel method (Local climate data via CFD/BES) 20% difference!!! Classic method (far-field climate data) *J. Bouyer et al., Microclimatic coupling as a solution to improve building energy simulation in an urban context, Energy and Buildings 43 (2011)

Decision making [1/5] Problem statement
Determination of the optimal blend(s) of retrofit measures that ensure: acceptable values of living conditions (thermal comfort and air quality indicators) under minimum energy consumption (for buildings) minimum costs and minimum attenuation periods of investments.

Decision making [2/5] Recognition of targeted parameters
Thermal comfort indicators: PMV, PMV(SET*), SET*, PET, etc. Air quality indicators: Pollutant concentration, Displacement efficiency Energy indicators: Energy demand, Energy consumption, etc. Cost indicators: Installation and Operation Time indicators (if applicable): Attenuation period

Decision making [3/5] Determination of desired values of targeted parameters Which is the desired value of targeted parameter (GOAL)??? E.g. Reduction of absolute value of PMV by 15%. Pollutant concentration: Within limits based on the pollutant (thresholds can be found in indoor-health handbooks) Pollution displacement efficiency (Ventilation efficiency): <1 Energy demand: Minimum Energy consumption: According to legislation for major retrofits Costs and attenuation periods: Minimum

Decision making [4/5] Recognition of design parameters (Retrofit options) Once the goals have been specified, the decision maker should focus on the design parameters, i.e. the ways to achieve the specified goals. Buildings: Insulation materials; Windows; Systems for heating, cooling, lighting and hot water production; etc. Open spaces: Ground materials; vegetation species, size and orientation; Water surfaces size and orientation; other measures such as size and orientation of pedestrian roads.

Decision making [5/5] Means to solve the problem Parametric analysis OR Algorithm

Level of use of novel methods-BES

Level of use of novel methods-Field models

Most common BES/CFD coupled tools
ENVI-met/EnergyPlus Fluent/TRNSYS Fluent/Solene It is encouraging that the CFD/BES coupling can be obtained even by using freely available tools such as the ENVI-met and EnergyPlus.

Reasons of limited use Complexity Time consuming
Requirement for advanced urban and building physics expertise Lack of designers’ flexibility and know-how Lack of stimulating mechanisms-Prescriptive design indicated by CEN Standards As regards urban planning, other than empirical guidelines no regulation exists to guide designers towards the use of simulation tools in order to estimate microclimate in open spaces.

Conclusions Current tools used for Compliance are weak as important parameters, such as indoor-outdoor effects and energy behaviour are roughly approximated. Current policies are prescriptive in the use of novel methods that will provide a more realistic NZEBs (No room for design freedom and imagination). Novel methods are not widely used due to prescriptive regulations and to lack of awareness of today’s engineers.

Conclusions The REPUBLIC-MED will:
Propose applicable and cost-effective improvements in the existing design-for-compliance tools Reveal the impact of important effects being considered as uncertainties Suggest ways to account for climatic and behaviour effects Reveal possibilities in cost-optimal requirements through optimization approaches Get engineers familiarized through training seminars and dissemination activities Influence policy makers

THANK YOU Dr. George M. Stavrakakis Chemical Engineer, PhD, MSc
Division of Development Programmes Centre for Renewable Energy Sources and Saving (CRES) address: Postal address: 19th km, Marathonos Av., GR-19009, Pikermi, Attiki, Greece Tel.: Fax:

Dr. George M. Stavrakakis

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