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/EC31/2010/EC

NZEB by 2018 and later for NewNew public financed buildings.

27/2012/EC27/2012/EC

Existing public buildingsExisting public buildings

Acceleration of public-buildings renovation: 3% of the total usable surface area 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.

• “NZEB means a building of very high energy performancevery high energy performance. The low amount of energy required should be covered in a significant extent by energy from RES, including RESin a significant extent by energy from RES, including RES on-site or nearby”

• “BEP should be expressed through numeric indicator of primary energy usenumeric indicator of primary energy use…”• “The calculation methodology should take into account European Standards 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 annual energy

consumed 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 requirementsthey 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 minimum requirements for energy performance in order to achieve cost-optimal levels.to achieve cost-optimal levels.”

EPBD definitions

• 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?

Issues raised

NZEB definitionNZEB definitionIn 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 definitionNeed: Formulation of a sustainable, effective and practical NZEB definition

RecommendationsRecommendations*:-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.

Topics of Analysis [1/4]

* Evaluating and Modelling Near-Zero Energy Buildings; Are we ready for 2018?, JRC Technical Reports, Expert meeting 30-31 Jan 2012, Glaskow.

Topics of Analysis [2/4]State of the art of building simulation softwareState 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 Need: Bridge the two simulation concepts towards recommendations for simulation tools revision

RecommendationsRecommendations*:-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.



Occupancy related issuesOccupancy related issuesBEP should be evaluated taking into account occupancy profiles patterns impacttaking into account occupancy profiles patterns impact.

Need: Account for realistic occupancy behaviour patterns effects in the design stageNeed: Account for realistic occupancy behaviour patterns effects in the design stage

RecommendationsRecommendations*:-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.



Input data and optimizationInput data and optimizationImportant 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 Need: Account for physical and technology “uncertainties” as well as for coupled optimization methodsoptimization methods

RecommendationsRecommendations*:-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.


Design for reliable

predictions

Design for compliance

Methods that respond to new requirements for directives

implementation

Methods that respond to new requirements for directives

implementation

Buildings-Indoor-outdoor interactions-Energy behaviour-Retrofit technologies

Buildings-Indoor-outdoor interactions-Energy behaviour-Retrofit technologies

Open spaces-UHI assessment-New insights on urban environmental planning

Open spaces-UHI assessment-New insights on urban environmental planning

OptimizationOptimizationPilot applicationsPilot applications

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

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

Plans to introduce approach to policy makers

Training seminars

Plans to introduce approach to policy makers

Training seminars

Physical models-BuildingsBuilding Thermal Behaviour ModellingBuilding 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.

The US Department of Energy has developed a directory of building energy software tools which reports 402 building software tools 402 building software tools for evaluating energy efficiency, renewable energy and sustainability in buildings. http://apps1.eere.energy.gov/buildings/tools_directory/

Tools often used for whole building energy performance assessment

Multi-zonal approach/BES tools

Autodesk Green Building Studio

DeST ENER-WIN

ESP-r

SUNREL

BEAVER DOE-2

Energy plus

IDA-ICE TAS

BSim ECOTECT

eQUEST IESVE TRNSYS

http://apps1.eere.energy.gov/buildings/tools_directory/



Most popular BES toolsTRNSYS: 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.

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.

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.

Tool Strengths Weaknesses

Special features

Most common applicatio

ns

Availabilit

y

Handling of climate

conditions

Handling of building systems

operating schedules and

occupancy Building systemsAutodesk 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 buildingsystems 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)

> User-defined schedules

> 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

Strengths and weaknesses of BES tools [1/5]

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)

“The Urban Heat Island is the most obvious climatic manifestation of urbanization”Landsberg, 1981

Causes:

Physical models- Open spaces [1/3]

Trapping of short and long-wave radiation in areas between buildings Decreased long-wave radiative heat loss due to reduced sky-view factors Increased storage of sensible heat in the construction materials Anthropogenic heat released from fuel combustion Reduced potential for evapotranspiration Reduced convective heat removal due to the reduction of wind speed

Urban Heat Island EffectUrban Heat Island Effect

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- Fairly accurate- Main use: UHI effects on global

climate change

- Comfort and air quality indicators- 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- Turbulence modelling is required

Maximum size of city-scape domain

Whole City Whole City Building block

Spatial resolution for grid meshing

1-10 m 1-10 km 0.2-10 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 [2/3]

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

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).

Open spaces-Tools [1/5]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.

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.

Open spaces-Tools [2/5]

Tool Method Strengths Weaknesses

Special modelling features

Accuracy CPU time AvailabilityEvaporation and evapotranspirati

onRadiation

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

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 performanceUHI affects building energy performance

CFD/BES coupling for building energy assessment

Findings of past studyFindings of past study*

CFD/BES coupling for building energy assessment

*J. Bouyer et al., Microclimatic coupling as a solution to improve building energy simulation in an urban context, Energy and Buildings 43 (2011) 1549-1559.

Classic method (far-field climate data)

Novel method (Local climate data via

CFD/BES)20% difference!!!

Problem statementProblem 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 [1/5]


Recognition of targeted parametersRecognition 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


Determination of desired values of targeted parametersDetermination of desired values of targeted parameters

Which is the desired value of targeted parameter (GOAL)???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


Recognition of design parameters (Retrofit options)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 goalsthe 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.


Means to solve the problemMeans to solve the problem

Parametric analysisParametric analysis

OROR

Algorithm Algorithm

Level of use of novel methods-BES

0

20

40

60

80

100

120

Italy France Greece Spain Croatia

France 4%

Greece2%

Italy7% Spain

1%

Elsewhere86%

EnergyPlusLevel of use in partner Countries and Worldwide

France 13%

Greece4%

Italy9%

Spain3%

Elsewhere71%

TRNSYSLevel of use in partner Countries and Worldwide

Level of use of novel methods-Field models

0

10

20

30

40

50

60

Italy France Greece Spain Croatia

France 5%

Greece2%

Italy7% Spain

3%

Elsewhere83%

ANSYS-FluentLevel of use in partner Countries and

Worldwide

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.

Reasons of limited use

• 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

ConclusionsThe 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 YOUDr. George M. StavrakakisChemical Engineer, PhD, MSc

Division of Development Programmes

Centre for Renewable Energy Sources and Saving (CRES)

Email address: [email protected] Postal address: 19th km, Marathonos Av., GR-19009, Pikermi, Attiki, GreeceTel.: +30 210 6603372Fax: +30 210 6603303

mailto:[email protected]

Documents

Dr. George M. Stavrakakis