Lecture Objectives: Accuracy of the Modeling Software

Accuracy of Building Energy Simulation Tool Large number of: –Analytical –Numerical –Empirical models for energy and mass transfer calculation in building envelope and building systems

Modeling steps Define the domain Analyze the most important phenomena and define the most important elements Discretize the elements and define the connection Write the energy and mass balance equations Solve the equations (use numeric methods or solver) Present the result

Accuracy of energy simulation There are many different factors for inaccuracy of energy simulation results …..... …….

Accuracy of energy simulation Depends on 2 Assumptions - simplification which you introduced to solve the problem - level of details in your analytical and numerical models 1 Input data –geometry –material properties –weather data –operation schedule 3 Numerical methods - used to solve equations from analytical and numerical models Find the balance ! Always think what you want to achieve (what kind of analysis you want to provide)

How to check the validity of the larger simulation models? Building room: large number of analytical and Numerical equations (sub-models) Energy balance

How to evaluate the whole building simulation tools Two options: 1)Comparison with the experimental data - monitoring - very expensive - feasible only for smaller buildings 2) Comparison with other energy simulation programs - for the same input data - system of numerical experiments - BESTEST

Comparison with measured data Cranfield test rooms (from Lomas et al 1994a)

BESTEST Building Energy Simulation TEST System of tests (~ 40 cases) - Each test emphasizes certain phenomena like external (internal) convection, radiation, ground contact -Simple geometry -Mountain climate COMPARE THE RESULTS

Example of best test comparison

What are the reasons for the energy simulation Design (sizing of different systems) Economic benefits Impact on environed Budget planning

Example Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - variable frequency drive in the school building in NYC

Natural ventilation

Combined 1) Air flow and 2) Energy flow modeling Example: Night Cooling/Hybrid Ventilation: The IONICA Office Building, Cambridge, UK

Night Cooling/Hybrid Ventilation: The IONICA Office Building, Cambridge, UK

Energy and Airflow simulation domain Coupling surfaces

Coupling Energy Simulation Program Air Flow Program IAQ Data: geometry weather materials T wall, CFM, T supply T near surface, h surface V,T,… Energy cons.

Airflow simulation can be based on: 1) CFD (computational fluid dynamics) 2) Multizone modeling

Coupling

Coupled Airflow and Energy Simulation Software Components and Data flow

Thermal comfort - Temperature & gradient Ventilating Systems Evaluation DV/CC DV

Energy Modeling for LEED Projects The methodology described in ASHRAE 90.1–2004 (Appendix G), California Title 24–2005, and Oregon Energy Code 2005 involves the generation of two energy models: –one representing a baseline minimum-standard building and the –other representing the proposed building with all its designed energy enhancements. ASHRAE Standard 90.1 “Energy Standard for Buildings Except Low-Rise Residential Buildings” –posted in the course handouts, also UT library has all ASHRAE and ANSI standards Relevant LEED Documentation –ttp:// –Software List

DOE reference building that satisfy ASHRAE 90.1 Sixteen climate zones Sixteen building types al_initiative/reference_buildings.htmlhttp://www1.eere.energy.gov/buildings/commerci al_initiative/reference_buildings.html Models already built for use in EnergyPlus

How to get more info about software (any software) Software documentation – –….. Forums – –…. Call developers –works primarily for non-free software

1. Identify basic building elements which affect building energy consumption and analyze the performance of these elements using energy conservation models. 2. Analyze the physics behind various numerical tools used for solving different heat transfer problems in building elements. 3. Use basic numerical methods for solving systems of linear and nonlinear equations. 4. Conduct building energy analysis using comprehensive computer simulation tools. 5. Evaluate the performance of building envelope and environmental systems considering energy consumption. 6. Perform parametric analysis to evaluate the effects of design choices and operational strategies of building systems on building energy use. 7. Use building simulations in life-cycle cost analyses for selection of energy- efficient building components. Review Course Objectives