In The Field With Neil: RESNET-Approved Airflow Measurement Techniques

Chapter 8, section 804 of the RESNET Standard provides us with an onsite procedure for measuring the airflow of ventilation systems. These procedures treat the air flows into a grille and out of a register measured separately. There are 3 RESNET-approved test processes used to determine airflow: 1) powered flow hood, 2) air flow resistance and 3) timed bag inflation. Each method, as most things in life, has positives and negatives.

 

Powered Flow Hood

powerflow

The powered flow hood method is the most accurate, but also the most expensive. The powered flow hood differs from a conventional flow hood in that there is a fan which assists air movement through the flow hood to prevent a pressure differential at the register or grill created by the flow hood. The most common is the Energy Conservatory FlowBlaster® which works with your existing Duct Blaster Fan and DG-700 Pressure and Flow Gauge. The fan is powered by a combination fan speed controller and rechargeable Lithium-Ion battery. This method may be used on either exhaust or supply systems.

 

Air Flow Resistance

airflow

The air flow resistance method is probably the most common and can only be used on exhaust systems (air entering grill).  This method determines the air flow by measuring a pressure difference across a known hole size.  The air flow (in cfm) is equal to the hole size (in square inches) times 1.07 times the square root of the pressure difference (in pascals).  (Yes we are mixing units, but the 1.07 factor takes care of the conversions.)  This device will give the best results when the pressure difference is less than 8 pascals – largely because the exhaust fan speed will be reduced with greater pressures.  There is a commercially available “box” or flow meter again from the Energy Conservatory or you can easily create your own.  (If interested in creating your own – drop me a line and I will send you the directions.)

 

bag

Timed Bag Inflation

The timed bag inflation method is the least expensive of all.  It can only be used on supply systems.  As the name implies, a bag (typical a garbage bag) of known volume is inflated by the supply air.  The time required to fully inflate the bag is measured with a stopwatch.  This method takes a bit of practice to get repeatable results, but is rather simple to do.  As the standard indicates, bag volume and thickness play into the accuracy of the results – so a trial and error approach is needed.  Aim for a fill time of 2 to 20 seconds – the longer fill time will be easier to do, but may require a fairly large bag depending on the amount of airflow.  The airflow is easily calculated by multiplying the bag volume (in gallons) by 8 and dividing by the time (in seconds) required to fill it.  The Canada Mortgage and Housing Corporation has a nice write up on the method along with a table to convert to airflow.

 

These three procedures are the only RESNET-approved methods for measuring airflow in either whole house or spot ventilation systems.  (Well, there is one exception – if an ERV/HRV manufacturer has ports installed on their device for the purpose of measuring airflow; that may be used when following their directions.)

So go measure and have fun out there…

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In The Field With Neil: Automatic Fan Control

Most of us use either the Energy Conservatory DG-700 or Retrotec DM-2 digital micromanometers.  These meters have some great, yet under utilized features.  I would like to introduce you to one of the features – automatic fan control.  The Energy Conservatory refers to it as “cruise control” and Retrotec as “set pressure”.  In either case, it allows the digital pressure meter to control the fan speed or flow based on the pressure of “A” channel.

With the Automated Control you can…

  • quickly measure building airtightness using a “one-point” 50 Pa test.
  • quickly measure duct airtightness using a “one-point” 25 Pa total leakage test.
  • simultaneously control both the blower door and duct tester fans during a leakage to outside duct airtightness test. During this test, the meter will maintain a constant 25 Pa building pressure while the gauge connected to the duct tester fan maintains a constant 0 Pa pressure in the duct system.
  • maintain a constant building pressure while pressure pan testing, or locating and sealing building and duct system air leaks.
  • perform series leakage to quantify leakage rates between various zones within a building.  (Check out our class on Advanced Pressure Diagnostics…we will be using the cruise control a lot)

So this sounds great – what do you need in order to use the automated fan control feature?

  • An “automated fan compatible” gauge. Most are, but check that it has either “EC-cruise” or “Retrotec-set pressure” buttons on the front panel of your digital pressure gauge.
  • A blower door or duct tester fan speed controller with proper communication jack.
  • A cable to connect the meter to the fan.

That is it!  And you probably already have everything you need – especially if you recently purchased your equipment.  So next time you are out in the field – give it a try; I know you will ask yourself, ‘how did I ever get along without this?’.

For more information on automated blower door control:

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Tei Explains It: Quality Assurance

It is very important for a builders, superintendents and agents to understand the significance of field quality assurance (QA).  The process on the outside may sound threatening, but it really is a very simple process.  Failure to comply with QA may result in losing your ability to register ratings and ultimately the revocation of your certification.

Question: Is field quality assurance mandatory?

Field quality assurance is not voluntary. It is mandatory requirement by RESNET Standards.

Question: Who must have quality assurance performed?

If you are an Energy Rater and do ratings, then you must have field quality assurance performed on at least one home a year if you perform 1 – 100 ratings.  If you perform ratings on 101 homes in a year, you must have 2 homes quality assured.  RESNET Standards require 1% of your annual total of ratings to have a field quality assurance visit.  Unfortunately, the Standard rounds up to an additional field QA at one not fifty and therefore 202 ratings will result in 3 field reviews.

Your files which come in for registration is also quality assured.  One in ten homes go through a quality assurance process which helps to instill confidence in every rater’s file.  So remember, when you create the file and it has any comments, mistakes or rejections, they reflect on your ability because you are the rater of record.  These are also reported to RESNET on an annual basis.

Question: Who should be informed of these visits?

Everyone! Please inform your builders, clients and your client’s agents that quality assurance is not a voluntary requirement. It is mandatory by RESNET Standards.  In this case, cooperation is essential.  Failure of your builder, client or your client’s agent to cooperate in quality assurance will result in the denial of rating registrations by that particular builder.  The Standard applies to all regardless of what Program, if any, they are participating in.  Also highly recommend upon soliciting a new client you make sure that they understand this process and that all their agents understand so there is less confusion on the field when quality assurance is performed.  You can go as far as having them sign that they acknowledge and understand the process and this may occur at any time with any of their homes.  We strive to make this as painless as possible by soliciting your cooperation so the process is smooth and does not create any undue hardship on the part of your client.  We are able to schedule in the evenings as well as the weekend if necessary.  Again, our aim is to get this done as painless as possible, with as little discomfort as possible.

So remember to make sure your client understands and agrees to quality assurance!

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Tei Explains It: Rater Role & Responsibility

Question: What are my roles and responsibilities as a rater?

You are a rater.  It doesn’t matter what classification. You are considered a third party verifier of energy efficiency of real property.  Decisions made about this property regarding energy efficiency are basically “in your hands”.  Your input to the client, whether it be a builder or homeowner, is important for solid, sound decisions about spending money wisely on replacement or upgrading systems and materials.  Your opinions should be based on solid principles as well as keeping in mind the “law of diminishing returns.”

As a rater, your only responsibility is to your client.  Remember that as a rater you are the person who is certified.  You are the person who passed all of the exams and jumped through all of the hoops.  When you perform a rating, you are putting your reputation on the line as well as the whole energy efficiency industry.  When you perform a rating you are NOT really representing the company you are paid by because companies are not certified.  At this point you are a third party verifier and the client is your only concern.  If you allow any person or circumstance to change your professional judgment you are not being a third party verifier.  You are being a paid “yes” man/woman.  This can cause problems in the future if there is a complaint because defending yourself in a “compromising” situation can be detrimental to you not your employer or client.  You are actually putting your certification in jeopardy, not to mention eroding the integrity of the rating system.

Please make sure you explain to your employer that you represent the rating industry as a third party verifier when you perform a rating, and your job is to verify the features of the home as well as assist with sound, solid advice when asked to do so.  Selling or advising a client to purchase a material or service from your company is fine as long as you can justify its cost through its savings.  If asked to compromise your advice based on what the company sells is a red flag warning. Remember your certification is yours, and will be taken from you, not the company you are employed through.  Trying to “please” your builder because your employer “expects” it also becomes another red flag warning.  Again, remember whose certification is on the line.

So, the next time you hit the road to perform a rating, remember that you are representing yourself as a third party verifier as well as an entire energy efficiency community.  Please take pride in what you do and all of those you represent.

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In The Field With Neil: Digital Meter Calibration

Spring is in the air – so what does that have to do with your manometer calibration?  Probably nothing, except Spring means new beginnings and we need to make sure that our equipment is up to the task ahead.

Question: Why do I need to have my manometer calibrated?

Simply answer – RESNET Standard dictates it and I quote from the standard:

802.9 Equipment Accuracy and Requirements
Blower door fans used for building air leakage testing shall measure airflow (after making any necessary air density corrections) with an accuracy of +/- 5%. Pressure gauges shall measure pressure differences with a resolution of 0.1 Pa and have an accuracy of +/- 1% of reading or 0.5Pa, whichever is greater.

Blower door and associated pressure testing instruments shall be tested annually for calibration by the HERS Rating Provider or Certified Rater. The provider shall use a standard for field testing of calibration provided by the equipment manufacturer. Magnehelic Gauges cannot be field tested and shall be recalibrated by the Blower Door manufacturer annually. Field check the fan and flow measuring systems for defects and maintain them according to manufacturers recommendations. The HERS Rating Provider or Certified Rater shall maintain a written log of the annual calibration check to verify all equipment accuracy for a period of three (3) years. These records shall be made available within 3 business days to the RESNET Quality Assurance Administrator upon request.

Therefore you have 3 options for compliance…

  1. Send your meter(s) to the manufacturer for calibration on a yearly basis.  This is the most expensive method, but has the advantage of having your meter calibrated and brought into factory specifications. (Click on the manufacturer link to go to their site).
    • The Energy Conservatory – TEC recommends that all of it’s digital pressure gauges be recalibrated once per year in order to maintain the instrument’s accuracy specifications of 1% of reading (or 0.15 Pa, whichever is greater). Calibration is performed at our facility in Minneapolis, MN. The cost to calibrate a digital pressure gauge is $75. This price includes return ground shipping within the continental 48 states and Canada (expedited or air shipments will cost more). Turn around time at our facility for calibration is typically 2-3 days following receipt of the instrument (assuming no repairs are necessary). We will provide a NIST traceable calibration certificate which includes “as found” as well as “current condition” pressure data.
    • Retrotec – Our recommendation for manufacturer calibration is: – Every two years for DM-2 pressure gauges – Every five years for the entire flow measurement system.  You will need to send in or call to get a price quote.

     

  2. Send or bring in your meter to us at FSEC.  We will do a field calibration check on your meter(s).  We do not modify, adjust or certify the meter – only verify whether it is within factory specifications.  If your meter is not in spec, we will let you know and it needs to be sent out for repair/factory calibration.  Our cost – FREE to our raters.
    • Make an appointment with Jimmy Williams (jwilliams@fsec.ucf.edu) if you are bringing them by (it takes about 30 minutes to do the check)
    • Send them in to:
      Jimmy Williams, Florida Solar Energy Center, 1679 Clearlake Rd, Cocoa, FL  32922
      • You prepay for the shipping both directions.
      • We are not responsible for any loss or damage done through shipping.

     

  3. Perform a field calibration per the manufacturer as done by a certified RESNET Rater (Class 1 rater in Florida).

     

Now, one more thing – if FSEC is your rating provider, we need a copy of the field calibration for each meter you use.

Send us a copy (pdf format to: Jimmy Williams (jwilliams@fsec.ucf.edu) or by mail  to Jimmy Williams, Florida Solar Energy Center, 1679 Clearlake Rd, Cocoa, FL  32922).  The nice thing about option #2 is that not only is the calibration check free – but all the paperwork we need is done.

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