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Energy Modeling Applications for Existing Buildings Presented by: Clark Denson PE, CEM, BEMP, LEED ® AP BD+C 4/27/12
Energy Modeling Applications for Existing Buildings
Presented by:
Clark DensonPE, CEM, BEMP, LEED®
AP BD+C
4/27/12
Learning Objectives1.
List available methods and tools for energy modeling
2.
Explain how energy modeling can be used at different times during the life of a building
3.
Identify appropriate steps for using energy models to explore energy use in existing buildings
4.
Understand how energy models can be used to estimate savings of ECMs/FIMs
5.
Identify how energy models can be used as a part of an M&V plan to measure actual savings of ECMs/FIMs and ensure those measures are persisting.
What is an Energy Model?
•
Energy Model▫
A mathematical representation of how building energy systems react to external or internal loads.
•
Whole-building simulation▫
“An energy model that represents the operations of all building systems simultaneously as opposed to a specific system or area of a building.”
Presenter
Presentation Notes
An energy model could be a simple as a single equation, a single spreadsheet, or as complicated as computer program requiring 3D rendering capabilities and fast processing speeds.
Why Do We Use Energy Modeling?•
Comparative Analysis -
Decision-making tool
•
Find areas of highest potential impact/savings
•
Identify synergies to reduce equipment size
•
Identify counter-intuitive building performance relationships
“Determining the most appropriate calculation methodology and energy analysis tool is perhaps one of the most challenging and important steps in the energy audit process.”▫
ASHRAE Procedures for Commercial Building Energy Audits, 2nd
Edition
•
2009 ASHRAE Fundamentals says to consider the following factors:▫
Accuracy▫
Sensitivity▫
Versatility▫
Speed and cost▫
Reproducibility▫
Ease of use•
More critical decisions require more accurate tools
Presenter
Presentation Notes
PCBEAv2 Same thing could be said for any existing building commissioning scope. While an ASHRAE Level 1 audit doesn’t require an energy model, an investment-grade Level 3 audit definitely would.
Spreadsheet-based Calculators
Presenter
Presentation Notes
Some utility incentive programs provide savings calculators (usually based on calibrated models and weather bin data) that allow for savings to be estimated for a pre-programmed set of potential energy conservation measures.
Spreadsheets vs. Whole-building Simulation•
Spreadsheets▫
Simpler to understand and review
▫
Encouraged by several utility incentive programs▫
Limited in their applicability
•
Whole-building simulation▫
More comprehensive measures
▫
Accounts for interactive effects▫
More training to master
Presenter
Presentation Notes
Some utility rebate programs offer spreadsheet-based savings calculators to their EBCx service providers, such as Xcel Energy and several California utility companies. Be aware, however, that many of these are based on bin weather data that is localized to the service areas of those utility companies (e.g. Colorado, Wisconsin, California)
Energy Simulation Approaches and Tools
•
Steady-state calculations▫
Degree-day method▫
Balance-point Temperature▫
Limited to thermal performance & plant efficiency
•
Bin Method▫
Provides reasonable savings for preliminary assessments
▫
Using a more detailed tool will not always result in more accurate results if based on estimated operation
▫
Limited in its application
•
Whole-building modeling/simulation▫
Captures the dynamic nature of commercial buildings
▫
Complexity of an hourly simulation model may be required for projects where deeper level of analysis is required, such as:
Building Envelope measures
Comprehensive projects with interactive measures
Documenting tax incentives or green ratings
Effect of building massing on cooling load
Capability of program to model specific features and technologies such as VRF, daylighting, thermal ice storage, etc.
Presenter
Presentation Notes
PCBEAv2 Bin Method - Generally, audits are not detailed enough to understand the hourly variations in building loads or equipment operation.
When translating real building geometry into an energy model, simplifications will need to occur. The trick is understanding the right simplifications to make, that won’t compromise the integrity of the model. Thermodynamically, only surface area, orientation, and tilt matter when modeling heat transfer surfaces. This one fact allows for many simplifications. * Please note that total volume of enclosed spaces matters IF infiltration is specified in terms of air changes per hour (ACH). With regards to the Performance Rating Method of ASHRAE 90.1-2007, simplifications are allowed for uninsulated assemblies and exterior surfaces with similar orientation and tilt. There are many interfaces that exist to streamline the creation of building geometry and we will cover a few of more important ones here. SketchUp Plugins: A few plug-ins exist to Google Sketch including… Open Studio for EnergyPlus: Allows users to create and edit EnergyPlus zones and surfaces, define surface adjacencies, and define constructions. The Integrated Environmental Solutions Virtual Environment: allows you to assign a location, building type, room type, construction types and HVAC systems to a SketchUp model and then import it directly into an IES tool for analysis, without having to re-build any geometry. CAD (dwg files) 2-D CAD plans may be imported into energy modeling programs as a background image. This often occurs in the wizard. The user then traces over the image for Shell and Zone geometry gbXML – green building XML schema: facilitates the transfer of information stored in CAD building information models, enables integrated interoperability between these design models and a myriad of analysis tools. Can be exported from BIM models and other 3D modeling tools and be used in Green Building Studio to read geometry and to perform an energy analysis.
Weather Data - Annual Weather Files
•
Necessary for annual energy and economic analysis
•
Useful for developing HVAC design strategies
•
Must include 8760 hours•
Generally from sets of averaged data (TMY)
•
Actual weather data may be preferred in EBCx
*RMI Building Energy Modeling Workshop
Presenter
Presentation Notes
Annual weather data is necessary for annual energy and economic analysis. Luckily, there are hundreds of weather stations around the country with hourly weather data to use. It is also useful for developing HVAC design strategies. Annual weather data should include 8760 hours and is generally developed from sets of averaged data. TMY, or “Typical Meteorological Year ” data, for instance, was produced using 30 years of data for the available sites. TMY data includes temperature, solar radiation, and wind. TMY data was originally developed for designing solar thermal and PV systems so “typical” weather conditions are weighted towards the solar radiation data. While TMY data is generally used for predicting future savings, it does not include extreme conditions that may not be seen from year to year. For this reason, actual weather data may be preferred when calibrating a model of an existing building to actual utility bills.
Lighting, Occupancy, & Plug Loads
• Daily/Weekly/Annual Occupancy Schedules• Hourly fractional multiplier for peak values• Daylight Dimming or Occupancy Sensors
• Total watts of all connected power• Peak number of occupants• Can be input with density values
• Assign proportional amounts of heat to space vs. plenum
Peak Power and Occupancy
Fractional Schedules
Fraction of Heat Gain to space
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 3 5 7 9 11 13 15 17 19 21 23
Lighting
Wk
Sat
Sun
Presenter
Presentation Notes
Modeling lighting, plug loads, and occupants requires the specification of three things; installed peak power and peak occupancy, operation schedules, and fraction of heat gain to the conditioned space. This section will cover each of these topics in detail, and also touch on how daylight simulation can impact electric lighting energy consumption. Finally, we discuss the estimation of peak plug load power, and how this value is often overestimated. Installed Peak Power and Occupancy: Includes the total watts of all connected lighting , including ballasts and the estimated misc. equipment. Occupant values should represent the peak number of people that could occupy these spaces. These values can also be input as area density values, such as W/sf, or sf/person. Importance of Schedules: Peak lighting, occupancy and equipment values are modeled as a fraction of estimated use with daily, weekly, and annual schedules. These schedules can be modified to account for things like daylight dimming sensors or occupancy sensors. Fraction of Heat Gain to Space: Some portion of the internal gains from people, lights and equipment can go directly into the plenum and this should be specified within your energy model. In displacement ventilation systems, a larger portion of the internal gains should be assigned to the plenum space because of a stratified air layers. Schedules control how the peak values are used as a percentage of the full load assigned in hourly increments for the whole year. Schedules are unregulated by ASHRAE 90.1, but must be identical in the baseline and proposed models. Actual schedules are best to use if known, but typical schedules for many building and program types are available from ASHRAE 90.1 User’s Manual, Title 24 ACM Manual, COMNET, and The ASHRAE Handbook of Fundamentals
Mechanical Equipment
Presenter
Presentation Notes
This shows common central plant system technologies for cooling and heating systems. Central plants typically serve multiple zones or very large singe-zone loads. The most common type of central plant cooling system consists of chillers providing chilled water to either central or distributed HVAC systems. Chillers can be air, water (via cooling towers), or evaporatively-cooled. Central plant heating systems usually have boilers, which can either provide hot water or steam to heat the zones. Many distribution systems exist to provide cooling and/or heating to individual zones. Air handlers with cooling and heating coils, fan coils (essentially simplified, smaller air handlers), steam and hot water radiators, and radiant systems like floor piping or chilled beams are all options for heating or cooling zones. (Click) Energy Modeling Tip: When modeling central plants, pay particular attention to pump power and part load curves, which can have a huge impact on annual energy consumption.
Source: DOE2.2 Volume 2 Dictionary
Mechanical Systems Part-load Performance Curves
•
Fan power = f(airflow) for VAV systems
•
“Canned”
& custom curves
•
Similar curves for pumps, chillers, boilers
Fan Curve Issues:•“Canned”
VSD fan curves are often optimistic•If creating a custom curve, plot it and check it, set appropriate minimum value
Presenter
Presentation Notes
In most programs, fan power in a VAV system varies as a function of airflow. We usually call these equations “fan curves”. These fan curves are not the same thing as the fan curves that mechanical engineers use to select fans, so that’s a potential point of confusion. These simulation fan curves are typically a quadratic or cubic curve, with the X-value being part-load ratio varying from 0 to 1 (or a little more), and the Y value also ranging from 0 to 1 representing fan power as a fraction of full load power. That full load power value is typically a separate input. If, for example, a fan motor draws 100 kW at full flow, then the power required at partial flow would be 100 kW multiplied by the value of one of these curves. Different fan control methods differ in their part-load efficiency characteristics. This chart shows the canned fan curves in DOE2.2. Most programs also allow you to create your own custom fan curves by either entering coefficients or points along the curve. In the latter case, the program will calculate the coefficients for you in a curve fit calculation. I find that I prefer to calculate the coefficients myself in a spreadsheet, and then plot the resulting curve to make sure it looks reasonable.
Utility rates Types of Charges and Rate Structures
0–350 kWh $0.06 per kWh
350–700 kWh $0.04 per kWh
700+ kWh $0.02 per kWh
$0.40 per KVAR
$0.06 per kWh
$35 per month
$7.53 per kW
Peak Time $0.24 per kWh
Off Peak Time $0.06 per kWh
Presenter
Presentation Notes
The importance of utility rate structures within an energy model is often overlooked. In today’s LEED driven world, most energy models are gauged according to percent utility cost savings. It is essential that energy modelers are well versed in the various components of complex utility rate structures, and the impacts of these parameters within an energy model. This section reviews the most important components of utility tariffs and how they impact hourly energy simulations. Types of energy charges Monthly charge: a fixed, recurring charge which reflects the average cost to the utility for services associated with providing energy such as billing, metering, meter reading, and maintenance. This is also frequently called a customer charge or service charge. Energy charge: a variable charge that is based on the amount of energy used by the customer during the billing period. The charge is generally billed using a uniform rate per unit of energy, such as $0.06 per kWh. For simple utility rate structures, the energy charge has the most direct relationship to energy cost savings in an energy model. As utility rate structures become more complex, other charges or factors may have a bigger impact on energy costs. Demand charge: an additional charge that is based on the maximum or peak amount of energy used at any one time. The charge can be based on the maximum amount of energy used during the billing period (usually one month), or on the highest demand recorded in the previous 11-12 months. Demand is measured using specialized meters that record the highest average usage during 15 or 30 minute intervals throughout the billing period. Demand charges are often associated with peak periods, and some utilities only measure demand during their peak hour periods. When this is the case, energy cost savings can be realized not only from reducing the total amount of energy used, but also potentially from load-leveling and peak-shifting strategies. Power factor charges: an additional charge for having a low or less than optimum power factor. Power factor is the ratio of real power (kW) to apparent power (kilovolt-ampere) for any given load and time. A low power factor affects the utilization of the installed capacity of the electric system. Power factor charges are often structured as an additional Demand charge or can be a per kilovolt-ampere reactive (KVAR) charge. Other charges: utilities often charge additional taxes and surcharges based on local regulations and/or programs, such as energy conservation and low-income assistance programs. Additionally, there can also be fuel adjustment charges, which are related to the cost of resource energy to the utility. Often this charge is an additional multiplier that is applied to the Energy charge and will vary monthly based on fuel cost fluctuations. Block charges: rate structure where a certain unit cost is charged based on different blocks of energy demand. Energy use within the first block is charged at one rate and then usage above that block is charged at a different rate. Blocks can be either increasing or decreasing. In increasing blocks, the unit price of each succeeding block of usage is higher than the previous block(s). Decreasing blocks have the opposite cost structure, with the unit price of each succeeding block of usage lower than the previous block(s). Energy cost savings within utility rates with block charges will largely depend on whether it is an increasing or decreasing block, since decreasing blocks do not encourage energy conservation. Time of Use rates: rate structure where the unit cost for energy changes during different times, which are typically associated with peak and off-peak periods. Prices can vary based on the time of day, week, season, or year and are higher during peak load periods and lower during off-peak periods. Since Time of Use rates are designed to encourage energy conservation during peak periods, peak-shifting strategies used in the energy model can result in significant energy cost savings. Other rates: when utilities use an unbundled rate structure, the costs of each major component of providing energy is separated out. For example, an electric utility may bill different charges for generation, transmission, and distribution of electricity.
Life-Cycle of a Building
New Construction Existing Buildings
Presenter
Presentation Notes
New Construction How is energy modeling used during the design of a new building? Existing Buildings How does energy modeling relate to existing building commissioning? Energy Modeling can be used in Energy Assessments and Retro-Commissioning Energy Modeling is used in Measurement & Verification as a part of IPMVP Option D – Whole Building Calibrated Simulation Let me talk for about 5 minutes on how energy modeling can be used during the design of new buildings.
Typical energy modeling timeframePerformance
Impact
TimeProject Start
Project Finish
HIGH
LOWLevel of Effort
Leve
l of
Effo
rtNew Construction: When Do We Use Energy Modeling?
Presenter
Presentation Notes
Let’s start with New Construction . In these projects, (click) we often stress that decisions made early in the design levels have a much higher potential for performance impact than those made late in the game. The opportunities for cost-effective, energy saving design solutions have decreased tremendously by the time the design team has traditionally met for the first time. Similarly, (click) making important decisions and design changes is much easier at the start of the project timeline. In the later design phases, there is a risk of potentially impactful changes being set aside due to the level of effort required to realize such a change when the design has progressed so far already. (Click) With that in mind, its clear that the timeframe in which energy modeling is typically performed is far too late in the design process to maximize impact. Preferably, energy modeling should begin during pre-design or conceptual design phase to maximize the potential for superior energy performance.
New Construction: Setting Energy Target/Goals
•
“If you aim at nothing, you’ll hit it every time.”
–
Zig Ziglar
•
An OPR, written during the pre-design phase, is essential to establishing energy targets for the design team to strive for.
•
Energy modeling facilitates setting your target
Applicable to Existing Building Commissioning, too!
New Construction: Energy Modeling Process
Existing Buildings: AABC Energy Management Guidelines1.
Project Assessment▫
Goal Setting2.
Energy Use Exploration▫
Annual Energy Balance▫
Model Development3.
Site Investigation▫
Data Collection and Calibration
4.
ECM/FIM and EBCx Analysis
5.
Implementation6.
Final Acceptance▫
Measurement and Verification
7.
Continuous Energy Management
▫
Update model as a part of Ongoing Commissioning
Presenter
Presentation Notes
I may not use the exact same terminology as the Energy Management Guidelines, but the concepts are compatible.
Project Assessment: Setting Energy Efficiency Goals
Use Energy Modeling to Quantify Targets
Goal Setting CharretteGoal Setting Charrette
*RMI Building Energy Modeling Workshop
Presenter
Presentation Notes
At the beginning of a project, it is important to identify project goals. In the concept phase, an energy modeler can help influence energy-related goals. These may include a target for annual energy use per unit area (e.g. kBtu/sf/yr), a percent reduction below a certain baseline (e.g. 40% below an ASHRAE 90.1 2007 baseline), or specific strategies (e.g. no mechanical cooling). Because there will be a limited number of known variables at this early stage, the energy modeler has free reign to create the lowest energy use building possible to show what targets are possible. In general, goals can be classified into broad categories as shown here. Overall target values are very concrete, and often specify a required energy use intensity (EUI) or other metric such as net zero operating carbon. Comparative goals are used in relation to energy codes and baselines, and also to compare against similar building types or current consumption rates. Sometimes a specific type or level of certification is very important to the stakeholders, and this is set as an overall project goal. Finally, end use specific goals are very useful in terms of guaranteeing a concrete result and assigning responsibility amongst the design team. And, of course, many other performance goals should also be addressed in an integrated design process, including things like indoor air quality, thermal comfort, and visual comfort.
Project Assessment: Observation of Potential Measures
•
Similar to ASHRAE Level 1 (Walk-through) Audit
•
Estimate rough energy cost savings and payback
•
No energy modeling necessary
Energy Use Exploration: Annual Energy Balance•
Based on available energy data•
May not require energy model•
Created by estimating, measuring, or modeling each energy end-use
•
Energy Model Development▫
Helpful in verifying results of the utility consumption analysis
▫
Outputs are only as good as the inputs
▫
Useful for analysis of potential ECMs/FIMs
▫
Should be calibrated to utility bills
Presenter
Presentation Notes
An energy balance may not require the use of an energy model. Spreadsheets and Bin data may be sufficient. A very important early step in an Energy Management Project is to develop an Energy Balance for the building to estimate the amount of energy consumed by various building systems such as: lighting, HVAC, domestic hot water, “plug” load, etc. By establishing an estimate of consumption attributable to each energy using system a baseline (or in some cases a boundary) is set for calculating potential savings of Energy Conservation Measures (ECM) which affect those systems. Calibration should be performed to ensure that the model more accurately behaves like the actual building, providing a more reasonable baseline for calculating savings.
Site Investigation: Data Collection•
On-site data collection serves two purposes:
▫
Identify actual building operation for use in model calibration
▫
Identify potential Energy Conservation Measures
•
Areas of Interest
▫
Building Geometry/Envelope
▫
Internal Loads
▫
Airside Systems
▫
Waterside Systems
▫
Controls and Operation
Presenter
Presentation Notes
Since the value of energy model outputs is dependent on the quality of the inputs, significant effort should be made in adequately collection data from the site. A thorough site investigation is critical for a successful energy model.
Site Investigation: Data Collection•
Building Geometry/Envelope
▫
Building Orientation
▫
Window-to-Wall Ratio
▫
Effective R-value
▫
Mass Effects
▫
Building Infiltration
2D drawings
Satellite images
Google Earth
Presenter
Presentation Notes
ModelCalibrationData_Hanson-Morales_PECI.pdf Use Google Earth to quickly estimate WWR and elevations
Site Investigation: Data CollectionInternal Loads Do schedules match occupancy?
•
Concentrated Process Loads▫
Kitchens▫
Servers▫
Elevators▫
DHW•
Unoccupied Loads▫
Lighting▫
Equipment▫
Process•
Frequency of Use
*Gathering Data for Building Simulation Model Calibration
Presenter
Presentation Notes
ModelCalibrationData_Hanson-Morales_PECI.pdf Simulation programs typically include default utilization profiles, but these are poor substitutes for actual data. Work with facility personnel to develop more accurate usage profiles and schedules.
Site Investigation: Data CollectionAirside & Waterside Systems Data Most Relevant to Calibration
•
Many moving parts•
Integrated Control Strategies•
Check visible conditions of equipment
•
Analyze trend data for proper operation of controls
•
Schedules▫
On/Off Status▫
Unoccupied setpoints▫
Fan cycling?
Presenter
Presentation Notes
I recommend reviewing plans and control sequences as much as possible before the site investigation, and once on site, setting up trends in order to verify proper operation of control sequences.
Site Investigation: Data CollectionAirside & Waterside Systems Data Most Relevant to Calibration
•
Air-side▫
Outside Air Settings▫
Economizer Function▫
VAV box Airflow Reset▫
Supply Air Temperature Reset
•
Equipment Efficiency▫
Fans▫
Pumps▫
RTUs▫
Boilers▫
ChillersOutside Air, Anyone?
Presenter
Presentation Notes
Is there sufficient trend data of fan airflow and power to create custom fan part-load curves?
Site Investigation: Data CollectionAirside & Waterside Systems Data Most Relevant to Calibration
•
Water-side▫
Hydronic Loop Flow & Pressure & Reset Controls
▫
Chilled Water Temperature & Reset Controls
▫
Condenser Water Temperature & Reset Controls
•
Boiler & Chiller loading/ cycling
ECM/FIM and EBCx Analysis
•
Energy Model Calibration•
Estimate Energy Savings of ECMs/FIMs
•
Validate savings estimates•
Bundle measures to maximize payback
Presenter
Presentation Notes
Up till now, all energy savings estimates have been “rough order of magnitude” numbers. Once we have accurate data from the site investigation, we are ready to provide investment-grade energy savings.
ECM/FIM and EBCx Analysis: What is Model Calibration?
•
A process where model inputs are adjusted so that the model outputs correlate better to actual performance
•
Goals:▫
Enhanced model accuracy
▫
Increased level of confidence in simulation results
Adjust unknown load schedules, infiltration, efficiencies, and part-load performance for fine tuning
ECM/FIM and EBCx Analysis: Model Accuracy Criteria•
ASHRAE Guideline 14, IPMVP, and FEMP all provide various accuracy criteria
•
Mean Bias Error (ERR)▫
A measure of the model accuracy relative to the mean of the data set
•
Coefficient of variation of the Root Mean Squared Error [CV(RSME)]▫
A measure of the residuals of the data set not accounted for by the model
Model Calibration
Uncalibrated
ModelCalibrated
Model CV(RMSE) 16.2% 3.3%NMBE 12.6% 2.6%
Presenter
Presentation Notes
So what? Why should I calibrate my model? Answer: Savings can be overestimated or underestimated with an uncalibrated model, leading to inaccurate payback periods. Model calibration is more of an art than a science.
ECM/FIM and EBCx Analysis: Calculating and Validating Savings•
Using the calibrated energy model as a baseline, apply ECMs/FIMs and calculate savings.
•
Validate estimated savings against previous experience of actual savings or case studies
•
Based on project financing, group/bundle measures to meet project energy goals.
*A Study on Energy Savings and Measure Cost Effectiveness of Existing Building Commissioning
Presenter
Presentation Notes
The study analyzed about 30 of the most common ECMs used in dozens of projects to calculate the anticipated range of annual savings for each measure in terms of kBtu/sf.
Final Acceptance: Measurement & Verification
??????????????? Possible Causes
•
Differing Weather•
Differing Building Usage•
Differing Control•
Equipment Installation and O&M
•
Sub-optimal System Operations
Predicted Actual
Final Acceptance: Measurement & Verification
“Savings Meter”•
To measure the actual savings of each ECM, consider sub-metering and data trending.
•
IPMVP, ASHRAE 14, and FEMP provide multiple ways to develop and implement an M&V plan
•
More energy model calibration may be needed▫
Calibrate Pre-retrofit and Post-
retrofit models to actual weather and operational data
•
M&V can help to identify systems that are not operating as intended
Presenter
Presentation Notes
Most buildings don’t come with a meter in the mechanical room that shows how much energy is being saved. That’s because energy savings is the absence of energy use. In order to measure savings, you have to compare the actual energy usage after improvements have been made to a calibrated baseline model that represents what the energy usage would have been had the improvements not been made.
Continuous Energy Management: Measure Persistence
•
Use the energy model to estimate impact on savings for ECMs/FIMs found not to be persisting
•
Coupling sub-metered data with updating the model can help to ensure that the savings from previously installed measures are persisting
Continuous Energy Management: Measure Persistence
55
56
57
58
59
60
61
62
63
64
65
55 56 57 58 59 60 61 62 63 64 65
Supply Air Temperature (F)
Supply Air Temperature Setpoint (F)
AHU‐1 Supply Air Temperature AHU‐1 Supply Air Temperature Setpoint
Presenter
Presentation Notes
Fig 1 - SAT setpoint controlled to reset from 55F to 65F based on outside air temperature. The chart compares the SAT sensor readings to SAT setpoint. Post-implementation verification shows the AHU CHW valve is controlling to maintain SAT setpoint.
Continuous Energy Management: Measure Persistence
55
56
57
58
59
60
61
62
63
64
65
55 56 57 58 59 60 61 62 63 64 65
Supp
ly Air Tempe
rature (F)
Supply Air Temperature Setpoint (F)
AHU‐1 Supply Air Temperature AHU‐1 Supply Air Temperature Setpoint
Presenter
Presentation Notes
Fig 2 - 1 year after post-implementation verification shows the operations of the SAT reset has severely degraded. After investigation, electronic-to-pneumatic (E-to-P) transducer controlling the CHW valve needed to be calibrated. Also, investigation showed that the parameters for the PID loop controlling the CHW valve were different than those recorded during the post-implementation verification testing. Interviews with the operations staff indicated that the E-to-P transducer was replaced 6 months after post-implementation verification. However, the operations staff was not aware that the PID loop parameters had changed, and could not provide a explanation. As a result the measure was not persisting for 6 months, resulting in a loss in energy savings.
Continuous Energy Management: Energy Model Maintenance•
The energy model is an investment for ongoing commissioning and continuous improvement
•
In the hands of a skilled modeler, the model can be used to simulate specific conditions, operating schedules, different utility rates.
•
A calibrated energy model can be valuable decision-making tool, both for new and existing buildings.
Resources•
DOE Building Energy Software Tools Directory
•
Rocky Mountain Institute BEM Workshop•
ASHRAE Procedures for Commercial Building Energy Audits, 2nd
Edition
•
AABC Energy Management Guideline•
Calibrating Simulation Models for Existing Buildings
•
A Study on Energy Savings and Measure Cost Effectiveness of Existing Building Commissioning
