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Abstract
The current industry standard method for estimating tall building entryway infiltration rates in cold climates is found in ASHRAE Handbook—Fundamentals (2013). This method was developed in ASHRAE Research Project (RP) 763 (Yuill 1996). In the comparison of an example calculation provided in RP-763 (Yuill 1996) and reproduced in 2013 ASHRAE Handbook Fundamentals (2013) with simulation results for the same example using various building configurations, the multi-node airflow analysis tool simulations consistently calculated significantly lower flow rates than predicted by the RP-763 (Yuill 1996) method (Whitehead and Frisque 2012). Addressing the large over-prediction of infiltration rates resulting from the estimation method currently published in the ASHRAE Handbook—Fundamentals (2013), this article proposes a new method to estimate this infiltration rate. The main difference of this new method (which we refer to as limiting area method [LAM]) is that it takes into account the smallest openings in the flow path limiting airflow. Comparison of results using the LAM to those from the previous simulations show that it is much closer to the more detailed simulation calculations, with estimates ranging from 92% to 134% of simulation results for the building examples considered.
Nomenclature
| A | = | area of opening, ft2 |
| c | = | flow coefficient, cfm/(ft2[in. H2O]n) |
| C1 | = | unit conversion factor = 0.0129 in. H2O/([lbm/ft3][mph2]) |
| C2 | = | unit conversion factor = 0.00598 in. H2O/(lbm/[ft·s2]) |
| C3 | = | unit conversion factor = 776 lbm0.5·ft1.5/(in. H2O0.5·min) |
| CD | = | discharge coefficient, dimensionless |
| CP | = | wind pressure coefficient |
| g | = | gravitational constant, lbm·ft/(lbf·s2) |
| h | = | height of air column, ft |
| n | = | pressure exponent, dimensionless |
| PS | = | stack pressure, in. H2O |
| PW | = | pressure due to wind, in. H2O |
| PW1 | = | wind pressure in ground floor space, in. H2O |
| PW2 | = | wind pressure in shafts, in. H2O |
| Q | = | airflow rate, cfm |
| Qref | = | airflow rate at reference pressure difference, cfm |
| Ti | = | indoor air temperature, °R |
| To | = | outdoor air temperature, °R |
| v | = | air velocity, mph |
| ΔP | = | pressure difference across opening, in. H2O |
| ΔPref | = | reference pressure difference across opening, in. H2O |
| ΔPS | = | stack pressure difference, in. H2O |
| ρ | = | density of air, lbm/ft3 |
| ρref | = | reference density of air, lbm/ft3 |