Presentation on theme: "1 Schedule of classes in PRC I need your availability on - Wednesday - Thursday - Friday afternoon."— Presentation transcript:
1 Schedule of classes in PRC I need your availability on - Wednesday - Thursday - Friday afternoon
Objectives Compare lab and field work Examples Introduce measurement terminology Discus quality control
Lab Measurement Strictly design experiments Focus on maintaining one group of parameter in a controlled environment to measure other Often the only way to document the real world Often conducted in conjunction with laboratory measurements Many phenomena can not be meaningfully modeled or reproduced in the laboratory 3 Field Measurements
Lab vs. Field measurements 4 Field results Lab results
5 Las class Example Lab work Convection Correlation Development
6 Example of Field Work: Energy Implications of Filters Does using a better filter increase energy use? Conventional wisdom: Yes For smaller buildings: Maybe not Flow, fan energy, system energy, SHR, AC capacity All DECREASE 15
7 Experimental Design Why can’t this study be done in a laboratory? Monthly measurements in 17 buildings over the course of a year with different filters installed Additional measurements in test house 16
8 Instrumentation Power draw Fan and compressor Pressure drop Filter and coil Temp. and RH Capacity Fan flow Duct leakage Major issue?
11 Summary Fieldwork is very messy Confounding variables and outliers Need large sample sizes Expensive and time consuming
Terminology What is the difference between accuracy and precision? Note that these terms are often confused and conflated with other terms Accuracy – “Capability of an instrument to indicate the true value of a measured quantity.” Precision – “Repeatability of measurements of the same quantity under the same conditions; not a measure of absolute accuracy” Precision not often reported Reference ASHRAE Guideline 2
Terminology Example of accuracy and precision: High accuracy, low precision Low accuracy, High precision Good measurement result is both: accurate and precise
Some Comments about Instrument Accuracy Manufacturers are almost always optimistic Make the difference between accuracy defined for full scale and reading Instrument 1: Accuracy: ±1.5% of full scale Repeatability: ±0.5% of full scale Instrument 2: Accuracy: ±1.5 % of reading (limited in certain range) Repeatability: ±0.5% What is Repeatability ?
Some Comments about Instrument Accuracy Accuracy is rarely constant over Range Assume frequent calibration Requires standard Calibrate over range of interest Don’t use complicated calibration curves Anything other than linear requires justification Consider arrangement with multiple sensors
Example of built-in calibration system Automatic Tracer Gas Monitor 16 signal Measured variable Linear relation 0
17 Other things that you should care about Sensitivity Sensitivity of the sensor is defined as the slope of the output characteristic curve Thermistors Resistor Temperature range Which one is more sensitive? (1/Voltage)
Other things that you should care about Response time Can be defined for other % values Standard definition Examples
Other things that you should care about Response time Hobo U12 internal temperature sensor Response time in airflow of 1m/s (2.2mph) 6 minutes, typical to 90% Telaire 7001 CO 2 sensor <60 seconds to 90% of step change How do you use these values?
20 Other things that you should care about Hysteresis Sensor should follow the changes of the mesured parameter regardless of which direction the change is made; hysteresis is the measure of this property How this affects the instrument accuracy?
Other things that you should care about Resolution the smallest detectable incremental change of input parameter that can be detected in the output signal Hobo U12 internal relative humidity sensor 0.03% RH Telaire 7001 CO 2 sensor ±1 ppm How do you use these values? Note that resolution can be limited by data logger
Other things that you should care about Range and detection limit How do you use these values? Note that you are often trading off range and resolution and/or accuracy Example: Measuring CO 2 with Telaire 7001 CO 2 sensor
23 Other things that you should care about Example: In our test house we use CO 2 as tracer gas We use Telaire 7001 CO 2 sensor for concentration measurement What is the range accuracy and detection limit? http://www.microdaq.com/telaire/index.php
(Some) Real World Concerns First and operating cost Ease of use Safety Durability Flexibility Reliability Power requirements Environmental requirements/conditions
25 Quality Assurance (QA) Quality Control (QC) How to incorporated QA/QC into your experimental study? Experiment Design Phase: Define objective - What question are you trying to answer? - How will you know you are finished? Choose -Factors of interest - Parameters to measure -Experiments control method(s) -The data analysis techniques
26 How to incorporated QA/QC into your experimental study? Experiment Design Phase: For measured parameters consider: - Range - Number of points - Number of repetitions Create an experimental matrix
27 How to incorporated QA/QC into your experimental study? Experimental matrix Be real: - Consider available time and funding - Predict potential for failure - predict more experiments than minimum - predict extra time for repetition - Preliminary experiments help
28 How to incorporated QA/QC into your experimental study? Measuring Phase: - Use measuring techniques that will meet the needs of your experiment - Collect sufficient data (including repetition) to adequately characterize the measured parameter - Record all available conditions/parameters (even those that are not in your matrix) - Use experiment control methods
29 How to incorporated QA/QC into your experimental study? Data Analysis Phase: Graphs & descriptive statistics first Hypothesis testing Regression next Interpret the results Draw conclusions
30 How to incorporated QA/QC into your experimental study? Be ready to modify and/or go back and forth between phases Example…..