This is a repository for TC 4.3 related publications.
Compression Effects on Pressure Loss in Flexible HVAC Ducts
Authors: Bass Abushakra, Ph.D., Member ASHRAE; Iain S. Walker, Ph.D., Member ASHRAE; Max H. Sherman, Ph.D., Fellow ASHRAE
Abstract: A study was conducted to evaluate the effect of compression on pressure drop in flexible, spiral wire helix core ducts used in residential and light commercial applications. Ducts of 6, 8, and 10 in. (150, 200, and 250 mm) nominal diameters were tested under different compression configurations following ANSI/ASHRAE Standard 120-1999, Methods of Testing to Determine Flow Resistance of HVAC Air Ducts and Fittings. The results showed that the available published references tend to underestimate the effects of compression. The study demonstrated that moderate compression in flexible ducts, typical of that often seen in field installations, could increase the pressure drop by a factor of four, while further compression could increase the pressure drop by factors close to ten. The results proved that the pressure drop correction factor for compressed ducts cannot be independent of the duct size, as suggested by ASHRAE Fundamentals; therefore, a new relationship was developed for better quantification of the pressure drop in flexible ducts. This study also suggests potential improvements to ASHRAE Standard 120-1999 and provides new data for duct design.
Exhaust Contamination of Hidden vs. Visible Air Intakes
Authors: Ronald L. Petersen, Ph.D., John J. Carter; John W. LeCompte
Abstract: A wind tunnel dispersion modeling study was conducted to investigate exhaust contamination of hidden versus visible air intakes. A “hidden” intake is typically on a building sidewall or on the sidewall of a roof obstruction opposite the exhaust source. A “visible” intake is at roof level or on top of an obstruction, directly above the hidden intake. Overall, the study has shown what designers suspected: placing air intakes on building sidewalls is beneficial when the stacks are on the roof. Significant concentration reductions were found when air intakes are placed right below the building roof edge on the building sidewall. The farther down the building sidewall the air intake is placed, the larger the reduction. However, the largest relative reduction between a visible and hidden intake is achieved by just moving the intake a few feet from the edge of the building roof to a point just around the corner on the building sidewall.
Air Leakage Through Automatic Doors Authors: Grenville K. Yuill, Ph.D., P.E.,
Fellow ASHRAE Rebecca Upham Chen Hui, Member ASHRAE
Abstract: A method has been developed to estimate the air leakage through high-use automatic doors. This air leakage is specified as a function of the rate of use of the door, the door geometry, and the pressure difference across the door. Two studies were carried out to obtain these results. One was a laboratory study of the discharge coefficients of doors of various geometries. The other was a field study of the times when automatic doors are open as a function of use. The results of the field study were analyzed and combined with the discharge coefficients that were measured in the laboratory study. The result was an air flow coefficient that is a function of the number of people using a door each hour. The designer can use this coefficient with the pressure difference across the door to estimate the rate of air leakage through the door.
Placement of Ventilation Air Intakes for Improved IAQ
Authors: Brian A. Rock, Ph.D., P.E., Kelly A. Moylan
Abstract: ASHRAE Research Project 806, Design Criteria for Building Ventilation Inlets, reviews existing knowledge of the placement of ventilation air louvers, produces a design guide, and suggests additional research, all with the intention of improving indoor air quality in commercial and institutional buildings. Decisions about intake and exhaust placements made early in the architectural and HVAC system design processes will impact occupants over the life of a building. Such placement decisions, therefore, require proper consideration. There is little guidance currently available to designers, but research efforts in this area are expanding.
Previous research efforts and standards relating to ventilation air intake placement are described in this paper. However, more extensive coverage and a lengthy bibliography are provided in the project's "Literature Report." In "A Designer's Guide to Placement of Ventilation Air Intake Louvers" for the project, the phenomena, standards, and design experiences that affect the placement of intake air louvers are reviewed using less technical text, many graphics, and example calculations.
More research is needed on ventilation intake placement for common commercial HVAC systems with rooftop, through-the-wall, and at-grade louvers. Most existing knowledge is derived from the many studies on industrial stack exhaust-gas reentrainment and not common HVAC geometries. The find-ings of such future research and a summary of this project's "Designer's Guide" need to be included in future revisions of ASHRAE Handbook chapters.
