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Abstract
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This manuscript explores the effectiveness of determining a building’s air changes per hour by monitoring indoor CO2 concentrations. 
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Specifically, experiments involving the measure of infiltration and exfiltration were conducted using a NetAtmo indoor Weather-Station. 
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The results of these experiments were then compared to the traditional method of blower-door tests. 
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Through this comparison, the effectiveness of this new and easier method was determined. 
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Using decay rates of tracer gases can significantly impact the cost, time, and frequency of measuring and quantifying a building’s efficiency. 
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All measurements and data collected were on site at Sonoma State University’s Environmental Technology Center (ETC)
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Introduction
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Energy efficiency is at the forefront of building science. Buildings make up -- percent of the total energy use in America. 
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A building envelope, whether effective or ineffective, is the physical separator between the inside and outside environment. 
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A building’s ability to passively control the indoor climate is fundamentally linked to the temperature, energy efficiency, and air quality of the building. 
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A successful building envelope is one that can generally maintain comfortable temperatures and high air quality. 
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Ventilation rates serve as quantitative measure of a building’s envelope. 
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Air-tightness can have positive and adverse effects. 
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The blower door test is the current standard for measuring a building’s air changes per hour (ACH). 
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This test requires specific equipment that requires some level of training. 
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In addition to tetious equipment, the blower-door test requires a completely controlled system. Typically, it requires the building to be out of use.  
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*Air Exchange rates.
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As an alternative to the blower door test, cheap and easy data loggers can incorporate simple calculations to determine ACH. 
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By measuring the concentrations and decay rate of tracer gases, data loggers have the potential to measure ACH. 
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Data loggers provide a significantly less intrusive, cheaper, and more reliable alternative to measuring ACH. 
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This method allows for repeated measurements, which add to the precision of the determined ACH calculations.
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offer a less labor-intensive approach to analyzing a building’s envelope.
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This manuscript aims at determining the legitimacy of measuring CO2 decay rates in order to receive the same quality of measurements from blower-door tests. 
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By exploring the associated mathematics and unit analysis of both the blower-door test and the extrapolated ventilation rates from CO2 decay, relations can be drawn. 
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The relationship of these measurement methods should, in theory, allow for a modified tracer-gas decay equation. This equation can be used to determine various ventilation measurements (air changes per hour). 
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Research question: Can the implementation of simple calculations provide considerably more reliable measurements of a building’s ventilation rates?
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When beginning, we expected a generally easy comparison. 
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Limitations
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Our blind spot → only measuring ETC. what we are unsure able: is the ETC even “useful”. This is a clear weakness. 
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The ETC is a well-used building with occupancies that are nearly impossible to model. 
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Materials
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How, what, when, where, why.
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NetAtmo Weather Station (indoor), used to record CO2 concentrations (ppm). 
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Data every ,x, minutes. From this data..(Methods). What are we looking at? Measuring directly, and then what are we inferring. 
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Blower Door: measures pressure delta, flow rate, and exchange rate. 
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Sagemath Cloud/ Jupyter Notebook / python softwares
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Data/Methods (methods here for now)
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CO2 concentration is measured approximately every 3 minutes.
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We use linear interpolation to get X minute samples
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We observe an increase in CO2 concentration while students are present in the lecture hall
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We observe a decrease in CO2 concentration after students leave and the room is ventilated by passive infiltration.
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By measuring the rate of decrease in the CO2 concentration, we can infer the rate of fresh air entering the building stale CO2-rich air leaving the building.
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We select periods of CO2 decrease that are “amenable to analysis” 
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Assumptions: I have many.. Need to pin-point what’s most important. Listed below are just a few. 
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gas concentrations are the same for entire building
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Gases are stable and inert(doesn’t react/change)
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Exchange rates are assumed to be constant over time interval
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Preliminary data: Using simple proportions to look at exchange rates from CO2. 
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I’ll need standard deviation from various days of NetAtmo CO2 decay
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Linear least squares regression, to find air exchange rate.. (R kernel in SMC?)
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For CO2 decay, I will need to go from ppm to total volume of CO2 inside ETC. Then from decay rate/NetAtmo slope I’ll determine the CO2 CFM. Next, CFM to ACH (times 60 mins divided by total volume of ETC).  (I want to take a look at pressure delta, from before and after decay, to further analyze). Then from ACH of CO2, ACH of all gases needs to be extrapolated. 
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I’ll need all pertinent measurements from Blower-Door Tests. Outside/inside pressures, CFM. 
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From blower door test, I’ll need all data. With measured CFM at controlled pressure, I need extrapolated CFM at 1 atm (or whatever pressure it was outside) in pascals. (system of extrapolation needs to be flushed out). Once at CFM at non-controlled pressures, it will be easy to determine ACH of building. 
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Results
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Need a comparison. (Just how easy can I make the comparison)
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Will need to boil-down ppm-->ACH into hopefully 1 or two algebraic equations. 
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Need to test equation(s) with data from blower-door test day(s). 
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Conclusion/Discussion
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Measuring CO2 concentrations in a building can be easily transformed into monitoring a building’s ventilation rates. With only a monitoring device, architects, carpenters, and energy-saving building owners can analyze a building’s envelope more often and with greater ease.  
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References
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Have 4+ articles in pdf form. (ask Soto if he’d like to see/ How to best share these here without links)
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Brainstorming: 
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-What are the current Ventilation standards? (Email from Beeler).
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A large part any building envelope is, 
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-infiltration rate: the volumetric flow-rate of air INTO the building. 
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-exfiltration rate: the flow-rate of air OUT of the building
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-Stack effect: The flow-rate of air INTO and OUT of the building. 
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“ETC’s Green Design”
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(intro or abstract) 
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...can be the deciding factor of whether comfortable temperatures, suitable air quality, and energy efficiency.
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In regions with climate extremes, the measurement and effectiveness of a building’s envelope can become increasing important. 
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Questions for data (to be determined):
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-For every m^3 of CO2, how many m^3 of other gases are leaving?(least squares application seems like best approach) 
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Go to graphing for R : GG plot
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Notes from Soto:
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“Outlining is 80% of your time.” - on the topic of 
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Find simple proportions of CO2 exchange and room exchange. 
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It seems comparing the Blower-Door ACH and decay-rate-determined ACH is my main focus. The units check out. 
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Nomenclature 
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CO2 decay: 
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CFM = ft^3 per min.
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ACH = Air Changes per Hour 
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ppm= parts per million (volumetric) 
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m^3 = volume in meters cubed
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Pa = pascals (Newton per square meter) 
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V_dc = volumetric decay (exfiltration)
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Converting from ppm to CFM then to total air exchange rate
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Blower Door 
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CFM 
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ACH
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Pa
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V_T = total volume of building
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V_in = volume into building (infiltration) 
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Ideal gas law
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PV = nRt = NkT
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n = number of moles
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R = universal gas constant (8.3145 J/mol K)
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k = Boltzmann constant = 1.38066E-23 J/K; k= R/N_A
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N_A - Avogadro’s number (6.0221E23 per mol) 
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