1 Schedule of classes in PRC I need your availability on - Wednesday - Thursday - Friday afternoon.

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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

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Field Measurements

Lab vs. Field measurements

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Field results

Lab results

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Las class Example Lab work Convection Correlation Development

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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

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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

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Instrumentation• Power draw

• Fan and compressor

• Pressure drop• Filter and coil

• Temp. and RH• Capacity

• Fan flow• Duct leakage

• Major issue?

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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 calibrationsystem

• Automatic Tracer Gas Monitor

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signal

Measured variable

Linea

r rela

tion

0

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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 CO2 sensor• <60 seconds to 90% of step change

• How do you use these values?

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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 CO2 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 CO2 with

Telaire 7001 CO2 sensor

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Other things that you should care about

Example:In our test house we use CO2 as tracer gas

We use Telaire 7001 CO2 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

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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

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How to incorporated QA/QC intoyour experimental study?

Experiment Design Phase:

For measured parametersconsider:- Range- Number of points- Number of repetitions

Create an experimental matrix

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How to incorporated QA/QC intoyour 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

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How to incorporated QA/QC intoyour 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

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How to incorporated QA/QC intoyour experimental study?

Data Analysis Phase:

• Graphs & descriptive statistics first• Hypothesis testing • Regression next• Interpret the results• Draw conclusions

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How to incorporated QA/QC intoyour experimental study?

Be ready to modify and/or go back and forth between phases

Example…..