![]() ![]() There are clear relationships between the infiltration rates calculated by CONTAM and weather, which are not exhibited in the EnergyPlus results. Annual airflow simulations were performed in CONTAM for six of the sixteen reference buildings. A number of additional inputs had to be defined for the CONTAM models to realistically account for airflow, including the addition of several building zones. These models employed an oversimplified approach to infiltration in which infiltration rates were input as constant values. The EnergyPlus models were created for assessing new technologies and supporting the development of energy codes in pursuing building energy efficiency improvements. In future columns, we will address how a smart ventilation system keeps air quality excellent throughout a home.Sixteen reference building models were created in the multizone airflow and contaminant transport program CONTAM in order to support physically based airflow calculations, as well as indoor air quality analyses, that are not possible using the existing EnergyPlus input files of these buildings. We use the same relation to determine the change of CO 2 concentration when we know the airflow into a space.Īdding 400ppm for atmospheric CO 2 = Total CO 2 = 3400ppmĬlearly, with constant, low flow ventilation systems, occupied rooms have the potential to become very polluted while air flowing to unoccupied rooms waste fresh air. If the home in Example 1 has a constant ventilation airflow of 60cfm evenly divided evenly among 6 rooms, how high can the living room CO 2 concentration reach if everyone is in the living room? But, during the home’s occupancy, each home requires the same fresh air flow. A home with continuous occupation requires more ventilation than a home with less than continuous occupation. Note that the fraction of the day (ratio of hours occupied to 24 hours in a day) is used in the calculation. You are much smarter in an atmosphere of 700ppm of CO 2 than 1000ppm. Note that our chosen target of 700ppm of average CO 2 concentration requires twice the airflow needed for an indoor air CO 2 concentration of 1000ppm. What is the average daily ventilation rate required in order to keep indoor CO 2 concentration below 700ppm (300ppm above an atmospheric level of 400ppm)?Īverage Daily Airflow = 29liters/sec = 60cfm That is, 10l/s is 20cfm with reasonable engineering accuracy, and certainly, with more accuracy that anyone can measure airflow in the field.Ī home has two adults and a half grown child (note: respiration, metabolism, and CO 2 exhalation rates are related strongly to body mass….you can use this on your pets, including chickens….yes, we have chicken respiration data). To those who are used to working with “cfm” (cubic feet per minute) airflow units, multiply by 2. For 1 person in a room with an increase of 600ppm-CO 2 above outdoor conditions, the above relation shows us that an airflow of 10liters per second will keep indoor air at an average of 1000ppm (400ppm + 600ppm). With a bit of analyses and unit conversions, we find the following result:Īirflow(liters/second) X CO 2(ppm) Concentration Change = #People X 6000 Ĭurrent building ventilation standards, which are based on odor rather than pollution, result in an average CO 2 concentration change of 600ppm to 700ppm above atmospheric CO 2 concentration. Assuming a home’s adult occupants to be sedentary “plus” (somewhere between watching television and washing the dishes), means that they are exhaling approximately 0.04kg per hour of CO 2. For all-electric homes without internal combustion sources, humans generate the carbon dioxide. ![]() Let’s break it down into terms that you can use to determine ventilation airflow.įresh airflow and the change of carbon dioxide (CO 2) concentration in a building space are related to the generation rate of CO 2. Ventilation doesn’t need to be a mysterious chart or a set of intractable, IRS-like, tax code calculations. What does this reading mean in terms of the amount of ventilation airflow? How does one calculate the airflow required to meet a desired level of air quality in your home? Of course, some homes are higher and some are lower, but when you visit our site, you will most likely find the CERV Community to average 600 to 700ppm. At that time, CERV homes spread across the country had a collective carbon dioxide concentration of 612ppm. The screen copy from our Build Equinox site was taken on a Saturday morning. Airflow Calculation for Ventilation SystemsĬERV homes are fresh air homes! This screen shot shows the average carbon dioxide concentration in CERV homes spread throughout the all climatic zones in the US. ![]()
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