Steven J. Emmerich

State-of-the-Art Review of CO2 Demand Controlled Ventilation Technology and Application | NIST

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Modeled infiltration rate distributions for U.S. housing.

UNLABELLED A set of 209 dwellings that represent 80% of U.S. housing stock is used to generate frequency distributions of residential infiltration rates. The set of homes is based on an analysis of the 1997 U.S. Department of Energys Residential Energy Consumption Survey, which documents numerous housing characteristics including type, floor area, number of rooms, type of heating system, foundation type, and year of construction. The infiltration rate distributions are developed using the multizone network airflow model, CONTAM (CONTAMW 2.4 User Guide and Program Documentation, NISTIR 7251. National Institute of Standards and Technology.). In this work, 19 cities are selected to represent U.S. climatic conditions, and CONTAM simulations are performed for each of the 209 houses in these cities to calculate building air change rates for each hour over a year. Frequency distributions are then developed and presented nationally as well as based on house type and region. PRACTICAL IMPLICATIONS These distributions will support indoor air quality, exposure, and energy analyses based on a truly representative collection of U.S. homes, which has previously not been possible. In addition, the methodology employed can be extended to other countries and other collections of buildings. For U.S.-specific analyses, these homes and their models, can be extended to include occupants, contaminant sources, and other building features to allow a wide range of studies to address other ventilation and indoor air quality issues.

Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use.

This report presents a simulation study of the energy impact of improving envelope airtightness in U.S. commercial buildings. Despite common assumptions, measurements have shown that typical U.S. commercial buildings are not particularly airtight. Past simulation studies have shown that commercial building envelope leakage can result in significant heating and cooling loads. To evaluate the potential energy savings of an effective air barrier requirement, annual energy simulations were prepared for three nonresidential buildings (a two-story office building, a one-story retail building, and a four-story apartment building) in 5 U.S. cities. A coupled multizone airflow and building energy simulation tool was used to predict the energy use for the buildings at a target tightness level relative to a baseline level based on measurements in existing buildings. Based on assumed blended national average heating and cooling energy prices, predicted potential annual heating and cooling energy cost savings ranged from 3 % to 36 % with the smallest savings occurring in the cooling-dominated climates of Phoenix and Miami. In order to put these estimated energy savings in context, a cost effectiveness calculation was performed using the scalar ratio methodology employed by ASHRAE SSPC 90.1.

Simulated Performance of Natural and Hybrid Ventilation Systems in an Office Building

Past research on natural ventilation has revealed that the application of pure natural ventilation systems may be limited in the United States by issues such as climate suitability, humidity control, and reliability. However, hybrid (or mixed-mode) ventilation systems offer the possibility of attaining energy savings in a greater number of buildings and climates through the combination of natural ventilation systems with mechanical equipment. The objective of this study is to investigate the potential energy and indoor environmental performance of natural and hybrid ventilation alternatives in low- to mid-rise US commercial buildings in a variety of US climates. In this effort, the National Institute of Standards and Technology (NIST) reviewed hybrid ventilation approaches and conducted simulations to predict and compare the indoor environmental and energy performance of natural, hybrid, and mechanical systems in an otherwise similar building. Due to the strong interaction of airflow and heat transfer in naturally ventilated buildings, a coupled multi-zone airflow and thermal simulation tool was used to model the systems in a five-story office building in five US cities. Overall, the natural ventilation system performed adequately in San Francisco and Los Angeles, although some tolerance for imperfect thermal and indoor air quality (IAQ) control is required. Natural ventilation system performance was poor in the more challenging climates of Boston, Minneapolis, and Miami due to poor thermal control, unreliable ventilation, or high heating loads. The hybrid ventilation system improved on the performance of the natural ventilation system in all climates, with dramatic improvements in some. Compared to the mechanical system, the hybrid system saved significant amounts of fan energy, reduced cooling loads, or reduced both fan and cooling loads in all climates but often resulted in higher heating loads. Although the hybrid system provided acceptable thermal control, the mechanical system provided more consistent control, as expected. The hybrid ventilation system provided better IAQ control, as indicated by CO2 concentrations, in most but not all cases.

Measurement and Simulation of the IAQ Impact of Particle Air Cleaners in a Single-Zone Building

This article describes the first phase of an effort to evaluate the ability of multizone airflow and pollutant transport models to predict the impact of residential IAQ control technologies. Measurements of the performance of several particulate air cleaning devices and related particle transport parameters were performed in a one-room test house. These measurements were used to calculate building air change rates, particle deposition rates and penetration factors, and air cleaner removal efficiencies. Two separate 24 h tests were performed with two of the tested air cleaners, and the measured air change rates and particle concentrations were compared to predicted values obtained with the CONTAM model. For both tests, simulated 24 h average air change rates were within 5% of measured air change rates and simulated 24 h average particle concentrations were within 30% of measurements for all particle sizes.

Air and Pollutant Transport from Attached Garages to Residential Living Spaces – Literature Review and Field Tests

Abstract The National Institute of Standards and Technology (NIST) is conducting a study on the indoor air quality (IAQ) impacts and engineering solutions related to the transport of pollutants from attached garages to residential living spaces. Natural or fan-induced pressure differences across air leakage paths in house-garage (HG) interfaces can result in the transport of the contaminants generated in garages into adjacent living spaces. This paper summarises a literature review on the transport of pollutants from garages to residential living spaces and describes a field study to estimate the range of airtightness of attached garages and of HG interfaces in the United States. Although the body of literature on pollutant transport from attached garages to residential buildings is limited, the studies reviewed provide substantial evidence that transport of contaminants from garages has the potential to negatively impact residential IAQ in either an acute (e.g., carbon monoxide from automobiles) or chronic manner (e.g., storage of chemical products). However, the literature contains few answers on issues such as the airtightness and geometry of the HG interface, the impact of heating and cooling equipment in the garage, and the effectiveness of potential engineering solutions. To address one gap in understanding these issues, the airtightness of garages and HG interfaces was measured in five residences using fan pressurisation. While the small sample of houses limits generalisation of the results, a range of house ages, styles, and sizes was included. For all homes tested, the garage was found to be at least twice as leaky as the house, based on air change per hour at 50 Pa. The leakiness of the garage envelope, based on surface area normalised effective leakage area at 4 Pa (ELA4/SA), ranges from a high of nearly eleven times to a low of two and a half times that of the house exterior envelope leakage. On average, the HG interface was almost two and a half times as leaky as the rest of the house envelope, when based on ELA4/SA. However, this average is somewhat skewed due to one HG interface measured in this study that is almost eleven times as leaky as the rest of the house envelope. Conversely, a larger Canadian study found HG interfaces to be comparable to house envelopes but found the average garage to be about ten times as leaky as houses – possibly because Canadian houses are consistently tighter than U.S. houses (Fugler et al. 2002). The knowledge gained from this review and the field study will be used in a simulation study of the potential occupant exposure to pollutants from attached garages and to explore potential engineering solutions to this IAQ problem.

Indoor air quality in sustainable, energy efficient buildings

Building designers, contractors, owners, and managers have long been challenged with providing quality indoor environments at a reasonable energy cost. Current efforts to improve building energy efficiency, including goals of sustainability and net-zero energy use, are bringing more focus on how to simultaneously achieve energy efficiency and good indoor air quality (IAQ). While energy efficiency and IAQ are sometimes viewed as incompatible, there are many strategies than support both ends. This article discusses the relationship between IAQ and energy efficiency, with outdoor air ventilation being the primary connection. A number of strategies that are currently being used or proposed to provide both improved IAQ and energy efficiency are highlighted, including increased envelope airtightness, heat recovery ventilation, demand controlled ventilation, and improved system maintenance. In addition, the manner in which various green and sustainable building programs, standards, and guidance documents address IAQ is reviewed. These programs and documents are driving the trend towards sustainable buildings, and the manner in which they consider IAQ is critical to achieving energy efficient buildings with good indoor environments.

Validation of multizone IAQ model predictions for tracer gas in a townhouse

To provide additional validation data for the multizone airflow and contaminant model, CONTAMW, experiments were performed in an occupied three-storey townhouse in Reston, VA. A tracer gas, sulfur hexafluoride (SF6), was manually injected within one room of the house and the concentration of SF6 was then measured in nine rooms. This same process was then recreated in CONTAMW and the resulting predictions were statistically compared to the measured values. A total of 10 experiments were conducted and simulated between May 2000 and June 2001. In four cases, the heating and air-conditioning system fan was operating. SF6 was injected in the recreation room (basement level), the kitchen= dining room (main level) and the master bedroom (upstairs level). A statistical comparison of measurements and predictions was performed per ASTM D5157 (ASTM 1997) for all cases. Comparisons were made for overall zone average concentrations and individual zone transient concentrations. The results for zone average concentrations were very good with many cases meeting most or all of the D5157 criteria. Several cases showed a poor to fair correlation between average measurements and predictions due to discrepancies with a single zonemdashthe main floor bathroommdashbut excluding that zone resulted in these cases meeting or nearly meeting the D5157 criteria. Comparisons of individual zone transient concentrations were mixed with many good to excellent cases but also numerous fair to poor. Zones other than the bathroom had occasional poor comparisons between predictions and measurements but no consistent discrepancies. The predicted SF6 concentration averaged over all zones and cases was within 10% of the average measured concentration.

Analysis of U.S. Commercial Building Envelope Air Leakage Database to Support Sustainable Building Design

Abstract In 1998, NIST published a review of commercial and institutional building airtightness data that found significant levels of air leakage and debunked the “myth” of the airtight commercial building (Persily, 1998). Since then, NIST has expanded and maintained a database of whole building envelope leakage measurements of U.S. commercial and institutional buildings. In addition to building leakage values collected from research publications, low-energy building programs and private pressurization testing firms, the database includes basic building characteristics such as year built, building type, floor area, number of storeys, location, and wall construction type for many of the buildings. The purposes of the database are to support the design and construction of low-energy buildings, to establish default values for building simulation, to estimate the energy savings potential of airtightness requirements in standards and codes, and to identify opportunities for additional improvements in building airtightness performance. The U.S. commercial building envelope leakage database contains data for almost 400 buildings including about 70 constructed in the past decade. The average air leakage for the buildings is 20% tighter than the average for the 228 buildings included in a similar 2011 analysis. The data were analysed to determine the factors that impact airtightness such as building type and height. Recent additions to the database include numerous buildings constructed to meet the specifications of sustainable building programs such as the U.S. Green Building Council’s LEED rating system, as well as buildings designed and constructed with air barriers. The analysis found that the 79 buildings with an air barrier had an average air leakage almost 70% less than the average for the 290 buildings not specified as having an air barrier thus demonstrating the critical need to design and construct commercial buildings with an air barrier to support sustainable building design.

Simultaneous solutions of coupled thermal airflow problem for natural ventilation in buildings

Natural and hybrid ventilation can be sustainable building ventilation strategies, where airflow is driven naturally by thermal buoyancy and/or wind forces other than pure mechanical means. The simulation and design of these systems need to consider the combined impact of thermal and airflow transport behaviors. The numerical solution of such combined thermal airflow problems often employs a segregate and iterative approach. Either the air temperatures in the thermal problem or the air pressures in the airflow problem are solved separately with the other parameter known from a previous iteration. The newly solved parameters are then substituted successively into the other calculation. For highly coupled thermal airflow problems, the segregate method can cause solution fluctuation or even divergence when relaxation factors are not carefully selected to avoid abrupt changes of air parameters in the successive substitution procedure. This article investigated two nonsegregate methods to solve thermal and airflow problems simultaneously. In the fully simultaneous method, air temperatures and pressures for all rooms of a building are solved simultaneously using a single Jacobian matrix. In the semi-simultaneous method, a Jacobian matrix for the air temperature and pressure of one room is solved when air temperatures and pressures of other rooms are kept as constants. The same procedure is then repeated for each room of a building. In both cases, relaxation factors are not required. The simultaneous solution methods are demonstrated for a two-zone building with thermal buoyancy-driven flows and validated for an experimental study of combined wind and buoyancy forces in a light well. It was shown that the simultaneous solvers provide stable solutions without using any relaxation in both cases. The predicted results also agree reasonably well with the experimental data.