Indoor Air Quality and Building Diagnostics

The post originally appeared on the Green Building Advisor website.

I recently purchased the CPS IAQ PRO SmartAir professional indoor air quality meter to use during energy audits and building diagnostics/investigations.  My intent with the purchase was two-fold, first to learn more about indoor air quality metrics by testing homes in my market, and second, to have a more accurate temperature/humidity/dew point estimation inside these homes.  I recently had the opportunity to use the tool on a building investigation, I’ll outline this case study later in this post.  First let’s talk about the features of the CPS IAQ PRO SmartAir.

The SmartAir has a similar size and looks almost identical to one of the larger Alexa smart speakers.  It comes in a handy carrying case with a USB power cord and separate wall plug.  The meter is not equipped with a battery, it requires a 120V power supply to function.  There is no screen on the unit, it ties to a phone, tablet or computer by Bluetooth.  The SmartAir requires an initial calibration that takes about 24 hours to complete before it can be used.

According to the manufacturer, there are four different sensors in the meter.  A true NDIR (non-dispersive infrared) carbon dioxide sensor, true particulate matter sensor that determines volume of PM2.5 and PM10.0 particles, a volatile organic compound (VOC) sensor and a temperature, relative humidity , pressure and dew point sensor.  The eight metrics that the sensor monitors are CO2, PM2.5, PM10.0, VOC’s, temperature, relative humidity, pressure and dew point (simply a calculation using the information from RH and temperature).  I have yet to figure out the use for the pressure (inWC) metric.  There is no way to reference indoor pressures with relationship to the pressure outside.  I believe it is simply supplying me with the barometric pressure.

The first time I used the SmartAir meter was at the Barndominium project.  The screenshot of the CPS app used to control the meter with my smartphone is shown.  There is still some construction work ongoing at this project and an ERV has yet to be installed.  Not horrible indoor air quality, but the installation of the balanced mechanical ventilation system plus the completion of work should help to improve air quality.

The Case Study

I was asked to investigate a home that has water dripping out of the tongue and groove ceiling during the winter months.  The home is located in climate zone 7.  I was fairly certain before arriving at the home why there was moisture accumulating in the attic but wanted to confirm through the use of a blower door and a discussion with the homeowner as to how the home was constructed and if there were any habits of the homeowner that may lead to an elevated humidity level.  I also thought this might be a good opportunity to try out the SmartAir meter.

I started the air monitoring test when I first arrived at the home.  This gave the meter about 25 minutes to collect data before I started the blower door.  As you can see, the PM2.5 and PM10.0 along with the VOC numbers are good, but the CO2 and RH numbers are high.  This may indicate that the home is fairly tight, not a lot of natural air exchange.

The outdoor air temperature at the time of the investigation was around 10°F and there was a substantial buildup of moisture on the double pane windows.  The temperature of the glass was probably in the 30’s with the dew point temperature at 53°F.  Thermal imaging conducted before starting the blower door did not show much for cold temperatures on either the upper walls or ceiling, though there were some indications of it being cooler near the floor.

Talking with the homeowner, I learned there is a vented crawlspace with a dirt floor under the home without any type of vapor retarder either on the ground or at the subfloor/floor framing.  There is also no insulation in the floor.  The crawlspace is the source of the humidity inside the building.

The ceiling was recently replaced by a tongue and groove paneled ceiling which was air sealed using 2 inches of closed cell spray foam applied in the attic directly to the tongue and groove boards, and then more than a foot of blown in fiberglass insulation was added to the vented attic to meet the R-value requirements.

The blower door test did reveal some air leaks in the ceiling, but for the most part the ceiling was fairly tight.  The blower door test result was 570 CFM50/3.43 ACH50, not bad for a home constructed in the 1980’s.  My thought is the air leaks contributed to some of the attic moisture, but there may also be a vapor diffusion component to this ceiling.  2 inches of closed cell spray foam is considered a vapor retarder in most climates.  In structures located in areas with more than 10,000 heating degree days (the location of this home) with indoor relative humidity levels around 50%, two inches may not be enough.  RR-0912: Spray Polyurethane Foam: The Need for Vapor Retarders in Above-Grade Residential Walls | Building Science Corporation

What are my recommendations?  Turn the vented crawlspace into a conditioned crawlspace and encapsulate the dirt floor using a 6 mil or thicker polyethylene sheet sealed to the foundation walls.  Add balanced mechanical ventilation in the form of either an HRV or ERV.  This will help to further reduce indoor humidity levels during the heating season if needed plus provide the homeowners with a better indoor air quality by lowering the CO2 levels.  (Operating the blower door for 15 minutes dropped the CO2 levels to around 800ppm and indoor humidity to just above 30%.)  Lastly, try to air seal the ceiling in the areas with the higher air infiltration indicated during the blower door test (shown in the thermal imaging above.

I would have determined many of the issues with this home without the SmartAir meter, but I would never have known there was an elevated level of CO2 present.  Had there been some other air quality issues in the home, these would have also gone undiscovered.  The Smart Air meter is not inexpensive (around $600), but it has already shown value in the additional information I can provide to homeowners during energy audits and building diagnostic investigations.

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