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RED Calc Free Help Advanced Infiltration
Advanced Infiltration with AIM-2 Tool User Guide

Advanced Infiltration with AIM-2
Red Calc Tool User Guide

What this tool can do for you

This tool calculates the hourly infiltration for a selected date range (one day to one year) and the resulting sensible load on a heating and/or cooling system. Daily average infiltration rates (stack, wind, and combined) and daily infiltration load on heating and cooling systems are displayed on separate charts for the selected date range. Additionally, balanced or unbalanced ventilation can be combined with infiltration with the results displayed in a table and on a chart, along with the resulting additional load on the heating and/or cooling system. The tool combines the powerful AIM-2 infiltration model with typical meteorological year data (TMY3 for the US and CWEC for Canada) for over one thousand weather locations in North America. The tool can be used for:

  • Determining the heating and/or sensible cooling infiltration load for the date range selected, annual or otherwise.
  • Disaggregating (separating) the total infiltration for a selected date range into stack-induced and wind-induced infiltration.
  • Determining the energy savings resulting from building air sealing activities (lowering the CFM50 blower door value).
  • Determining the change in infiltration energy load caused by raising or lowering the thermostat setting.
  • Calculating the increase (decrease) in infiltration resulting from clearing trees (planting trees) around a house. This is done by changing the "Building shelter class".
  • Finding the infiltration impact of an open flue or chimney.
  • Investigating the effect leakage distribution has on infiltration.
  • Determining the impact whole-building ventilation (balanced and/or unbalanced) has on heating and/or cooling fuel use.
  • Examining the effects and differences of balanced and unbalanced ventilation on airflow through a building during a selected date range.
  • Examining the effects of infiltration and ventilation to determine when infiltration supplies enough fresh are for acceptable indoor air quality, and when it does not.
EPA pictorial of air leakage locations
Typical air leakage locations, EPA

Calculated values

  • Hourly stack, wind, and total infiltration, and ventilationtotal and infiltration. These values are reported as low, average, and high for the selected date range.
  • Daily average infiltration rates for selected date range (infiltration chart): stack, wind, and combined values.
  • Daily average ventilation, total infiltration, and combined rates for selected date range (ventilation & infiltration chart).
  • Infiltration load on heating system for selected date range.
  • Additional load on heating system due to ventilation, for selected date range.
  • Combined ventilation and infiltration load on heating system for selected date range.
  • Infiltration load on cooling system for selected date range.
  • Additional load on cooling system due to ventilation, for selected date range.
  • Combined ventilation and infiltration load on cooling system for selected date range.
  • Daily ventilation and infiltration load on heating and cooling systems (chart) for selected date range.

Tips

  • Clicking the label for any input or result will cause a popup help box to appear. This help box includes the allowed and normal values (for inputs). Read more.
  • This tool, based on the AIM-2 infiltration method, is not intended for buildings of more than three stories above grade, or for multi-unit buildings.
  • All the results under the date range selectors are calculated for the date range you select.
  • The low (high) values in the table will most likely be lower (higher) than the lows (highs) in the first chart. This is because the chart plots daily average values, while the table reports hourly values.
  • Use the default percentages for leakage distribution unless you have reason to believe you have more accurate vales. The default percentages are dependent on the building height and whether or not the building has a vented crawlspace.
  • Make sure you read the pop-up help for "Terrain category" and "Building shelter class" before making your selection from the drop-downs. Click/touch on the input label to read the pop-up help.
  • Regarding the "Building has open flue/chimney" section inputs:
    • Do not include flues and/or chimneys that are closed, such as fireplaces with tight-fitting dampers.
    • If there are multiple open flues, add their areas and average their heights.
  • Regarding the "Building has a ventilation system" section inputs:
    • This section accomodates balanced and/or unbalanced ventilation. Enter the know flow rates of the whole-building ventilation fans.
    • If the whole-building ventilation fan(s) are automatically controlled to turn on and off, enter the effective ventilation flow rate that results from the intermittent operation.
  • Check "Show infiltration chart" and/or "Show ventilation & infiltration chart" and/or "Show infiltration energy chart" to display the interactive charts. Select the corresponding "Chart units". The chart values change as tool inputs above it are changed. Please refer to the "Interactive chart use" section below for more information.

Interactive chart use

This tool includes three interactive charts that can be used to display results; it may also be used for educational, sales, and marketing purposes. For example, you can save a chart in one of four different file formats, embed it into a customer report, or print it separately.

Tips for using the interactive charts:

  • Click/touch the series labels in the legend of either chart to turn the corresponding chart data on or off. For example, in the first chart, you can turn on or off the data series for "Stack", "Wind", and/or "Total".
  • Click/touch the menu icon in the upper right corner of the chart to show the choices for printing the chart or downloading it as an image file in PNG, JPEG, PDF, or SVG format. You are free to use the downloaded image in any way, including reports, presentations, websites, as long as the attribution for "Residential Energy Dynamics, LLC" is included.
  • If you save the chart as an SVG file, you can change the title or any other chart element with the use of third-party software. Examples of third-party software include Inkscape (a free version is available) and Adobe Illustrator.

Inputs and field measurements

  • Closest weather station - select closest station from three drop downs.
  • Building leakage @ 50Pa - value from standard blower door test at 50 pascals. Ideally, this should be corrected to standard conditions at seal level. This can be done using either the ASHRAE 6.2-2010 or ASHRAE 62.2-2013 ventilation tools.
  • Pressure exponent - use default of 0.65 unless you know the value for the building in question from a multipoint blower door test.
  • Building height - the average distance between (a) the bottom pressure boundary, or grade, whichever is higher, and (b) the top pressure boundary. Generally one story is 8.2 feet (2.5 meters), two stories is 16.4 feet (5 meters), etc. The enclosed volume should correspond to the door positions used during the blower door test as much as possible.
  • Building has a vented crawlspace - check box for indicating that the building sits on top of a vented (or open) crawlspace. This affects the default leakage distribution and the wind infiltration calculation.
  • Building shelter class - five possible selections from a drop down.
  • Terrain category - four possible selections from a drop down.
  • Thermostat setting, (heating) - if a daily setback is used, estimate the average indoor temperature during the heating season.
  • Temperature credit for solar & internal gains (heating) - the number of degrees, on average, that solar and internal gains increase building temperature during the heating season. This input should not include the influence of mechanical ventilation.
  • Thermostat setting, (cooling) - if a daily setback is used, estimate the average indoor temperature during the cooling season.
  • Temperature penalty for solar & internal gains (cooling) - the number of degrees, on average, that solar and internal gains increase building temperature during the cooling season. This input should not include the influence of mechanical ventilation.
  • Specify leakage distribution (optional inputs):
    • Ceiling leakage % - estimated air leakage through, or near, upper ceiling.
    • Floor leakage % - estimated air leakage through lower, or near, floor area.
  • Building has open flue/chimney (optional inputs):
    • Height flue extends above grade - if the grade is uneven, use an average. The default value is the building height plus six feet.
    • Flue cross-section type - three possible selections from a drop down.
    • Flue dimensions - inputs for diameter and rectangular shapes.
  • Building has ventilation system (optional inputs): Check if building has a whole-building ventilation system as defined by ASHRAE Standard 62.2.
    • Balanced ventilation rate - A heat recovery (HRV) or energy recovery ventilation (ERV) system or balanced supply and exhaust fans. If there are supply and exhaust, but they are not completely balanced, enter the portion that is balanced. The remainder should be entered in the "Unbalanced ventilation rate" input.
    • Sensible recovery efficiency (SRE) % - A measurement, that does not include latent heat recovery, used in determining the amount of energy passed between airstreams in a heat or energy recovery ventilator. This value is provided by the manufacturer of the HRV or ERV.
    • Unbalanced ventilation rate - Flow rate from an exhaust-only or supply-only fan, or the unbalanced portion of a combined exhaust-and-supply system (HRV, ERV, or combined exhaust and supply fans operating simultaneously).
    • Method for combining with infiltration - Unbalanced ventilation changes the house pressure, which interferes with natural infiltration so that we can not simply add the two rates together. The reality is that unbalanced ventilation and infiltration combine in a rather complicated way. There are two competing approximate methods in use for combining ventilation and infiltration.
      • Quadrature - This is the method specified in the ASHRAE Handbook of Fundamentals and is our default method. For quadrature, the combination is given by BalVent + UnbalVent 2 + Infil 2
      • 0.5 Rule - This method is preferred by many practitioners. It may give better results in some situations in which the natural infiltration is dominated by the stack effect. For the 0.5 rule, the combination is given by BalVent + max UnbalVent Infil + 0 . 5 × UnbalVent

Background

The Alberta Infiltration Model (AIM-2) applies to low-rise (up to three stories) detached, single-family, residential structures. The development of the empirical model began in the 1980s and was more finely developed over the next decade by David Wilson, Iain Walker, Larry Palmiter, Tami Bond, Max Sherman, and others.

For the mathematical model used for this RED Calc Free tool, "over 3400 hours of measured ventilation rates from the test houses at the Alberta Home Heating Research Facility were used to validate the predictions of infiltration rates and to compare the AIM-2 predictions to those of other infiltration models. The AIM-2 model had bias and scatter errors of less than 15% for wind-dominated ventilation, and less than 7% for buoyancy ("stack-effect") dominated cases." [Please see Walker and Wilson in "References" section below.]

Best practices

Select the weather station closest to the site you are analyzing. If your location is close to a state border, you might find the closest weather station is in another state. The map feature in the Weather Station Data (TMY) tool is helpful for determining this.

References

  • ASHRAE. 2013 ASHRAE Handbook: Fundamentals. Chapter 16, Ventilation and Infiltration, page 16.24. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. This document may be purchased at www.ashrae.org.
    Comment: Here the AIM-2 infiltration model is referred to as the "Enhanced model". Also, equation (51) on page 16.25 shows how ventilation and infiltration are combined.
  • Walker, Iain and Wilson, David. Field Validation of Algebraic Equations for Stack and Wind Driven Air Infiltration Calculations LBNL 42361. 1998. Lawrence Berkeley National Laboratory. http://epb.lbl.gov/publications/pdf/lbnl-42361.pdf
    Comment: This is the paper that explains the AIM-2 infiltration model. From the abstract: "Over 3400 hours of measured ventilation rates from the test houses at the Alberta Home Heating Research Facility were used to validate the predictions of ventilation rates and to compare the AIM-2 predictions to those of other ventilation models. The AIM-2 model had bias and scatter errors of less than 15% for wind-dominated ventilation, and less than 7% for buoyancy ("stack-effect") dominated cases."
  • Users Manual for TMY3 Data Sets: Technical Report NREL/TP-581-43156, revised May 2008. S. Wilcox and W. Marion. www.nrel.gov/docs/fy08osti/43156.pdf
  • Canadian Weather, Energy and Engineering Data Sets and Canadian Weather for Energy Calculations: Updated User's Manual. Revised October 23, 2008. Meteorological Service of Canada (MSC) and The National Research Council of Canada. ftp://arcdm20.tor.ec.gc.ca/pub/dist/climate/CWEEDS_2005/ZIPPED%20FILES /ENGLISH/CWEEDS%20documentation_Release9.txt

Related tools

  • Design Infiltration with AIM-2: This tool calculates the stack-induced, the wind-induced , and the combined infiltration for given indoor/outdoor temperatures and wind speed. The primary use case is determining the design infiltration rate that can be used in a heating or cooling load calculation for system sizing.
  • Weather Station Data (TMY): The embedded Google map feature helps you find the closest (TMY) weather station when your location is close to a state/province or national border and the closest station is actually in a different state/province/country. Additionally, the tool's interactive table and chart help you explore the the Typical Meteorological Year (TMY) data for each of 1,100 weather stations in North America. This hourly data is the foundation for most building energy simulation software.
  • ASHRAE 62.2-2013 Ventilation: Determine whole-building ventilation requirements for new and existing dwellings, with the choice of using advanced blower door options and the alternative compliance path.
    Comment: Use the "Use Advanced Blower Door Inputs" of this related tool for a more accurate "Building leakage @ 50Pa" input.
  • ASHRAE 62.2-2010 Ventilation: Determine whole-building ventilation requirements for new and existing dwellings, with the choice of using advanced blower door options and the alternative compliance path.
    Comment: Use the "Use Advanced Blower Door Inputs" of this related tool for a more accurate "Building leakage @ 50Pa" input.

Related external resources

  • The Energy Conservatory. SeeStack Training Simulator software tool. http://www.energyconservatory.com/software
    Comment: SeeStack is a free graphic training tool that allows the user to experiment with different variables of a house, including the number of floors, type of ventilation, different indoor and outdoor temperatures, and more to visualize stack effect. It includes some of the same variables that the RED Calc Advanced Infiltration tool does and enhances one's understanding of infiltration, neutral pressure planes, and the interreaction of infiltration and ventilation. This tool runs on PC computers only.

Version 2016-07-06_01:30
© 2013 Residential Energy Dynamics, LLC

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