Experimental simulation of wind driven cross-ventilation in a naturally ventilated building

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 29).A device was designed and constructed to simulate cross-ventilation through a building due to natural wind. The wind driver device was designed for use with a one tenth scale model of an open floor plan office building in Luton, England. The air flow patterns produced by the wind driver were observed, and the uniformity of the velocity of the flows into the model windows was measured for the three settings of the wind driver fans. The temperatures and velocities of flows on the interior of the building and at the exhaust windows were also examined. The wind driver device was capable of producing uniform velocities across the face of the model to within 20 to 27%, depending on the fan setting. The consistency of certain features of the velocity distributions produced by the wind driver operating at different speeds suggest that improvements made to the design of the wind driver could lower this variation to about 15%. The velocities measured on the interior of the model seem consistent with interior velocities in the Luton building, although further experimentation is needed to confirm this trend. Cross-ventilation was effective in reducing interior model temperatures by up to 10⁰C from the natural convection case.by Erin L. Hult.S.B

Energy Management in Small Commercial Buildings: A Look at How HVAC Contractors Can Deliver Energy Efficiency to this Segment

While buildings smaller than 50,000 sq ft account for nearly half of the energy used in US commercial buildings, energy efficiency programs to-date have primarily focused on larger buildings. Interviews with stakeholders and a review of the literature indicate interest in energy efficiency from the small commercial building sector, provided solutions are simple and low-cost. An approach to deliver energy management to small commercial buildings via HVAC contractors and preliminary demonstration findings are presented. The energy management package (EMP) developed includes five technical elements: benchmarking and analysis of monthly energy use; analysis of interval electricity data (if available), a one-hour onsite walkthrough, communication with the building owner, and checking of results. This data-driven approach tracks performance and identifies low-cost opportunities, using guidelines and worksheets for each element to streamline the delivery process and minimize the formal training required. This energy management approach is unique from, but often complementary to conventional quality maintenance or retrofit-focused programs targeting the small commercial segment. Because HVAC contractors already serve these clients, the transaction cost to market and deliver energy management services can be reduced to the order of hundreds of dollars per year. This business model, outlined briefly in this report, enables the offering to benefit the contractor and client even at the modest expected energy savings in small buildings. Results from a small-scale pilot of this approach validated that the EMP could be delivered by contractors in 4-8 hours per building per year, and that energy savings of 3-5percent are feasible through this approach

Blower-door techniques for measuring interzonal leakage

AbstractThe standard blower door test methods, such as ASTM E779, describe how to use a single blower door to determine the total leakage of a single-zone structure such as a detached single-family home. There are no standard test methods for measuring interzonal leakage in a two-zone or multi-zone building envelope such as might be encountered in with an attached garage or in a multifamily building. Some practitioners have been using techniques that involve making multiple measurements with a single blower door as well as combined measurements using multiple blower doors. Even for just two zones there are dozens of combinations of one-door and two-door test protocols that could conceivably be used to determine the interzonal air tightness. We examined many of these two-zone configurations using both simulation and measured data to estimate the accuracy and precision of each technique for realistic measurement scenarios. We also considered the impact of taking measurements at a single pressure versus over multiple pressures. We compared the various techniques and evaluated them for specific uses. Some techniques work better in one leakage regime; some are more sensitive to wind and other noise; some are more suited to determining only a subset of the leakage values. This paper makes recommendations on which techniques to use or not use for various cases and provides data that could be used to develop future test methods

Timescales of hydrothermal scavenging in the South Pacific Ocean from 234 Th, 230 Th, and 228 Th

International audienceHydrothermal activity in the deep ocean generates plumes of metal-rich particles capable of removing certain trace elements from seawater by adsorption and sedimentation. This removal process, known as scavenging, can be probed using the insoluble radiogenic isotopes of thorium (Th), which are produced at a known rate in the water column via the decay of soluble uranium (234 Th, 230 Th) and radium (228 Th) isotopes. We present dissolved and particulate measurements of these three thorium isotopes in a hydrothermal plume observed in the southeast Pacific Ocean on the GEOTRACES GP16 section. Since their half-lives vary from days (234 Th) to years (228 Th) to tens of thousands of years (230 Th), the combination of their signals can be used to understand scavenging processes occurring on a wide range of timescales. Scavenging is a multi-step process involving adsorption and desorption onto particles, followed by particle aggregation, sinking, and eventual sedimentation. We use thorium isotopes to study how hydrothermal activity affects these steps. The rate constants for net adsorption of 234 Th determined here are comparable to previous estimates from hydrothermal plumes in the Atlantic and North Pacific Oceans. The partitioning of 234 Th and 230 Th between large and small particles is more similar in the hydrothermal plume than above it, indicating faster aggregation of particles within the hydrothermal plume at stations nearby the East Pacific Rise than in waters outside the plume. In addition to rapid scavenging and aggregation near the ridge axis, we also infer continuous off-axis scavenging from observations and modeling of 228 Th/ 228 Ra activity ratios. The degree of depletion of the three thorium isotopes increases in order of half-life, with total 234 Th activity close to that of its parent 238 U, but 230 Th showing nearly 70% depletion compared to expected values from reversible scavenging. By modeling the variations in depletion for the different isotopes, we show that much of the 230 Th removal is inherited from scavenging events happening long before the most recent hydrothermal inputs

Timescales of hydrothermal scavenging in the South Pacific Ocean from 234Th, 230Th, and 228Th

Hydrothermal activity in the deep ocean generates plumes capable of removing trace elements from seawater by adsorption and subsequent sinking of particles. This removal process, known as scavenging, can be probed using the insoluble radiogenic isotopes of thorium (Th), which are produced at a known rate in the water column via the decay of soluble uranium (234Th, 230Th) and radium (228Th) isotopes. We present dissolved and particulate measurements of these three isotopes in a hydrothermal plume observed during the GEOTRACES GP16 section in the southeast Pacific Ocean. Since their half-lives vary from days (234Th) to years (228Th) to tens of thousands of years (230Th), the combination of their signals can be used to understand scavenging processes occurring on a wide range of timescales. Scavenging is a multi-step process involving adsorption and desorption onto particles, followed by particle aggregation, sinking, and eventual sedimentation. We use thorium isotopes to study how hydrothermal activity affects these steps. The rate constants for net adsorption of 234Th determined here are comparable to previous estimates from hydrothermal plumes in the Atlantic and North Pacific Oceans. The partitioning of 234Th and 230Th between large and small particles is more similar in the hydrothermal plume than above it, indicating faster aggregation of particles within the hydrothermal plume at stations nearby the East Pacific Rise than in waters outside the plume. In addition to rapid scavenging and aggregation near the ridge axis, we also infer continuous off-axis scavenging from observations and modeling of 228Th/228Ra activity ratios. The degree of depletion of the three thorium isotopes increases in order of half-life, with total 234Th activity close to that of its parent 238U, but 230Th showing nearly 70% depletion compared to expected values from reversible scavenging. By modeling the variations in depletion for the different isotopes, we show that much of the 230Th removal is inherited from scavenging events happening long before the most recent hydrothermal inputs.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard