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Low-cost optical particle counters (OPC) have gained increasing attention in recent years in exposure studies. Previous studies reported that the OPCs’ performance varies considerably with type of particles being measured; however, little information on their performance in monitoring common indoor aerosols is available. Given the significance of exposure to indoor aerosols and their associated adverse health effects, this experimental study investigates the performance of low-cost OPCs in monitoring individual aerosols that are commonly found indoors in a controlled chamber environment. Performances of four low-cost OPCs were examined under exposure to varying concentrations of biological (dust mite, pollen, cat, and dog fur) and non-biological (monodisperse silica and melamine resin) aerosols. Each particle sample was dispersed into the chamber using a computer-controlled syringe injection system, while size-resolved particle number concentrations were simultaneously measured by four low-cost OPCs (OPC N2, IC Sentinel, Speck, and Dylos) as well as a lab-grade reference sensor (AeroTrak). The study results showed measurable effects of particle size, particle type, and concentration on the low-cost OPC responses. Particle concentration had the most dominant effect on the linearity of low-cost sensors. Results also revealed that the sensor responses to four biological particles follow a similar pattern and converge to a linear line as the number concentration increases above 5 cm−3. As for non-biological particles, the OPC responses were more varied depending on the particle type and size, especially in the concentration range −3. Calibration equations developed in this study provide baseline information for correcting low-cost OPC readings when utilized to measure concentrations of individual indoor aerosol sources. Copyright © 2019 American Association for Aerosol Research

This study examines economic viability of combined cooling, heating, and power (CCHP) systems when applied to the Department of Energy (DOE) reference large office building in three locales in the U.S.: San Francisco, Boston, and Miami. For realistic power generation unit (PGU) sizes, annual, monthly, and hourly operation costs are estimated using local utility tariffs and compared to those of conventional separate heat and power systems. The results show that compared to conventional systems, CCHP systems reduce operation cost by 0.11–0.42 million $/y in San Francisco and Boston, whereas they increase the cost by 0.16–0.29 million $/y in Miami. The cost savings are mainly attributed to electricity savings; therefore, be maintained unless electricity costs drastically decrease. Considerable cost savings are attributed to both energy and demand charges if tariff structures estimate demand charges as much as energy charges (e.g., San Francisco). Under time-of-use rates, the largest cost saving occurs during peak periods because of high utilization of PGUs that significantly reduces energy and demand charges. Although a larger PGU capacity yields a greater cost saving, an over-sized PGU decrease profitability. The results suggest that for regions with relatively expensive natural gas and low electricity cost, CCHP systems would not be profitable.

Convenience stores are known to have higher Energy Use Intensities (EUIs) than most other commercial building types. However, convenience store energy performance analyses have not been systematically investigated. Moreover, current national convenience store benchmarks are inconsistent from one data base to another due to lack of relevant energy data. This paper assesses the energy performance of more than five hundred convenience stores in the same fleet in Eastern United States. The investigation aims to establish benchmarks for convenience stores with and without gasoline pumping stations. The main factors influencing the actual convenience store building energy use were determined. Multiple regression models were developed to find relationships between annual energy consumption per unit area and gross floor area, customer transaction count, building operating year, etc. The statistically characterized results are meant to serve as a reference data set in comparing the whole-building energy performance index for buildings of similar functionality. The statistical correlation analyses can strengthen the robust prediction of energy performance in convenience stores, enabling proper assessment of energy conservation measurements (ECMs) for convenience store operations, as well as guiding additional such energy performance studies.

Hybrid chiller systems that combine electric and absorption chillers can play critical roles in performances of a combined cooling, heating, and power (CCHP) or trigeneration system. The objective of the present study is to investigate a new strategy for hybrid chiller-based CCHP systems that can optimize electric power production while achieving zero-excess electricity generation for a given building. Using this operation strategy, energy and environmental performances were examined for two U.S. Department of Energy reference buildings (large office and hospital) located in two climates (San Francisco, CA and Long Island, NY). The results show that the hybrid chiller-based CCHP systems can save the primary energy consumption up to 5.8 GWh/y for the large office building and 13.6 GWh/y for the hospital compared to the conventional reference system that utilizes a central grid. More significant energy savings are realized for the hospital than the large office mainly due to high electric and thermal loads throughout the year. Carbon dioxide emission associated with a CCHP system highly varies with the emission factor of a local grid. In case of using the hybrid chiller system in Long Island, NY, the carbon dioxide emission is 0.2–1.5 kton/y lower than the reference system, whereas it is 1.1–1.5 kton/y higher in San Francisco. However, compared to traditional CCHP systems that utilize only absorption chillers, the hybrid chiller-based CCHP systems can reduce carbon dioxide emission by 0.7 kton/y for the large office and 3.5 kton/y for the hospital. When comparing the effects of building types and local climates, building types have more significant effects on the energy performance, while local grid conditions have larger impacts on carbon dioxide emission of a hybrid chiller-based CCHP system. Overall, the study results suggest that the hybrid chiller-based CCHP systems can reduce more energy and carbon dioxide emission for commercial buildings or districts with high thermal and electric loads during the cooling season.

In the US, building sector consumes approximately 41% of all U.S. primary energy and 70% of all generated electricity. Office building uses the largest percentage of primary and derived energy in the commercial buildings sector. Therefore, energy saving is the primary target of building renovation and equipment retrofit. To estimate energy savings after a renovation or equipment retrofit, measurement and verification (M&V) must be conducted based on energy use models or benchmark tools to track and assess savings. Although some methods and modeling tools are applied more often, there is no well-accepted model formulation methodology and some methods have high uncertainty. This paper discusses a method to formulate the energy use model as an inverse regression model via an advanced and robust high-dimensional data analysis method. According to the inverse regression model, independent variables determined to be most influential to the energy consumption should be metered prior to building retrofit or audit. To select the most influential variables, this research considers a comprehensive set of potential key variables to avoid underspecified model issue. The models established by this method are observed to have great power in predicting the building energy consumption. More importantly, through the variable selection procedure, the method identifies key variables that should be monitored to continuously improve the building energy performance. A simulation study and a case study are presented to show the effectiveness of the new approach.

Human exposure to airborne particles can lead to adverse health outcomes such as respiratory and allergic symptoms. Understanding the transport mechanism of respirable particles in occupied spaces is a first step towards assessing inhalation exposure. Several studies have contributed to the current knowledge of particle resuspension from indoor surfaces; however, few published studies are available on resuspension of biological particles from indoor surfaces. The objective of this study is to investigate the impacts of humidity and air swirl on resuspension of biological particles from floor and duct surfaces. Controlled laboratory experiments were conducted under varying degrees of humidity and airflow conditions. Resuspension rates of five types of particles (quartz, dust mite, cat fur, dog fur, and bacterial spore-Bacillus thuringiensis as an anthrax simulant) were determined for two types of floor surface (carpet and linoleum) and a duct surface (galvanized sheet metal). The results show that the particle property of being hydrophilic or hydrophobic plays an important role in particle resuspension rate. Resuspension rates of hydrophilic dust mite particles increase up to two orders of magnitude as relative humidity (RH) decreased from 80% to 10% at 25°C. However, resuspension rates of cat fur and dog fur particles that are hydrophobic are within the measurement error range (±15%) over 10-80% RH. With regard to resuspension of bacterial spores (Bacillus thuringiensis) from a duct surface, the resuspension rates are substantially affected by air swirl velocity and particle size. However, no discernible increase in particle resuspension was observed with duct vibration.

Building-scale microgrids are a type of behind-the-meter microgrids where the building operator has control of the distributed energy resources, including, in this case, a natural gas-fired microturbine in addition to solar PV and battery energy storage systems. There is a growing trend in deploying behind-the-meter microgrids due to their benefits including the resiliency of serving critical loads, especially in regions with abundant natural gas. In order to ensure distributed energy resources are dispatched optimally for the desired mode of operation, a hierarchical control platform including a centralized controller was developed and installed. The platform includes communication and control infrastructure that interface with controllers for distributed energy resources and the building automation system of a recently built energy efficient commercial building. Based on desirable outcomes under different grid and building conditions, operational modes were defined for the microgrid controller. The controller is programmed to map each mode to respective operational modes for distributed energy resources controllers. Experimental data for test runs corresponding to two operational modes confirm the communication and control infrastructure can execute hierarchical control commands. Finally, dispatch optimization for a year-long simulation of system operation is presented and the benefits of the hybrid solar PV-natural gas setup are evaluated.

We developed, characterized, and tested a new dual-collimation aqueous UV reactor to improve the accuracy and consistency of aqueous k-value determinations. This new system is unique because it collimates UV energy from a single lamp in two opposite directions. The design provides two distinct advantages over traditional single-collimation systems: 1) real-time UV dose (fluence) determination; and 2) simple actinometric determination of a reactor factor that relates measured irradiance levels to actual irradiance levels experienced by the microbial suspension. This reactor factor replaces three of the four typical correction factors required for single-collimation reactors. Using this dual-collimation reactor, Bacillus subtilis spores demonstrated inactivation following the classic multi-hit model with k = 0.1471 cm 2 /mJ (with 95% confidence bounds of 0.1426 to 0.1516).

Deregulation of the electricity sector, the rise of distributed generation, and a growing interest in local resilience have led to increasing attention on microgrids. In this paper, we present an approach for sizing the microgrid components that accounts for the load flexibility available in buildings with model predictive control. As buildings are becoming smarter, the use of building control systems to regulate building load for different strategies, such as peak demand limiting or load shifting, is becoming increasingly prevalent. When sizing microgrid components under islanded operation, it becomes critical to consider the dynamic nature of the building load, since the intelligent control systems can use the building response to help balance energy flows. An optimal sizing and dispatch model of the microgrid with model predictive control is developed. Simulations are carried out for representative days for a building-level microgrid serving a medium-sized commercial building. Results show that savings in first costs and operational costs can be realized if advanced controls are considered during design and component selection.

This study examines the impacts of uncertainties in energy demands and solar resources on the energy and economic performances of hybrid solar photovoltaic and combined cooling, heating and power (CCHP + PV) systems with variations in PV penetration levels. This study investigates two models: a deterministic and stochastic model. The deterministic model uses hourly demands of the U.S. Department of Energy (DOE) reference large office building in San Francisco, CA and solar irradiance profiles in the Typical Meteorological Year (TMY) data as the independent variables. The stochastic model accounts for uncertainties in these independent variables using a Monte-Carlo method. The results show that regardless of PV penetration levels, the uncertainties in building energy demands and solar irradiance marginally influence the energy performance of CCHP + PV systems; however, they can notably increase annual operating costs up to $75,000 per year (13%). The annual cost increase is mainly attributed to a significant increase in demand charges (up to $79,000 per year). The demand charges tend to increase with higher uncertainties in the peak demand. The results suggest that in cases of the demand charge being responsible for a large portion in electricity bills (i.e., demand tariffs), a deterministic model tends to underestimate operating costs of CCHP + PV systems or other analogous distributed energy systems compared to a stochastic model. The errors with the deterministic model can become more extreme when demand charges outweigh energy charges.

Literature on aerosol behavior in conventional heating ventilating and air conditioning duct systems that is directly applicable to modeling and simulation of deposition and resuspension of particulate matter is reviewed. Open literature discussing particle resuspension from duct surfaces is rare and most studies investigating particle deposition consider only clean duct surfaces. There is a similar lack of studies on particle deposition and resuspension in mechanical components found in air distribution systems (e.g., heat exchangers, fans, dampers, etc.) and in duct flows where the turbulent velocity profile is not fully developed. An example calculation of penetration through a simple duct system illustrates the characteristics of results produced by the identified modeling methods.

Ultraviolet germicidal irradiation (UVGI) uses UVC radiation produced by low pressure mercury vapor lamps to control biological air contaminants. Ambient air velocity and temperature have a strong effect on lamp output by influencing the lamp surface cold spot temperature. In-duct UVGI systems are particularly susceptible to ambient effects due to the range of velocity and temperature conditions they may experience. An analytical model of the effect of ambient conditions on lamp surface temperature was developed for three common lamp types in cross flow from a convective–radiative energy balance assuming constant surface temperature. For one lamp type, a single tube standard output lamp, UVC output and cold spot temperature data were obtained under typical in-duct operating conditions. Over an ambient temperature range of 10–32.2 °C and an air velocity range of 0–3.25 m/s, measured cold spot temperature varied from 12.7 to 41.9 °C and measured lamp output varied by 68% of maximum. Surface temperatures predicted by the heat transfer model were 6–17 °C higher than corresponding measured cold spot temperatures, but were found to correlate well with cold spot temperature via a two-variable linear regression. When corrected using this relationship, the simple model predicted the cold spot temperature within 1 °C and lamp UVC output within ±5%. To illustrate its practical use, the calibrated lamp model was employed in a simulation of the control of a contaminant in a single-zone ventilation system by an in-duct UVGI device. In this example, failure to account for the impact of ambient condition effects resulted in under-prediction of average space concentration by approximately 20% relative to a constant output system operating at maximum UVC output.

The feasibility of wireless measurements for rapid tuning of a multizone airflow model was extensively investigated using a small-scale residential building as a test site. The main objective of the research was to provide fundamental information, such as measurement time and cost for various measurement techniques, needed for selecting an appropriate field measurement strategy. Potential advantages of the wireless measurement approach were evaluated. These include: portability and flexibility, fast equipment setup, time synchronized data collection, negligible interruption to the occupants’ activity during the measurement, and installation time and cost savings. Currently, the high equipment cost of the wireless approach, relative to more conventional techniques, may offset the noted advantages and be the highest barrier to the wide use of wireless sensors in field measurements. Consequently, conventional hand-held measurements can be more economical, but the stability of the building HVAC system operating status should be considered before selecting the hand-held measurement approach. System stability and the ambient and internal building load status to which it is responding have significant impact on the model tuning usefulness of this approach

Airborne concentration of micron-sized particulate matter (PM) is an important index of indoor air quality. While human activity is considered the main reason causing indoor particle resuspension, theoretical particle adhesion force models give predictions of adhesion force much larger than the disturbance forces introduced by human activity. This work suggests that the imperfect contact between particles and surfaces can greatly reduce the adhesion bond. Electrostatic detachment method is used to measure the actual adhesion force distribution of micron-sized particles to such common indoor flooring materials as vinyl and rubber. Comparisons are made between the theoretical predictions and experimental measurements. Factorial experiments are also designed to study the influence of particle type, flooring type and contact time on particle adhesion force.

The air-handler fan pressurisation method can be a practical way to estimate envelope leakage in large scale or tall buildings where a conventional blower door test is not practical. Standards such as CGSB 149.15 describe desirable test conditions and protocols for such tests. However, because of the variety of building air handling system constructions and site conditions, and limited time and budget available for testing, one may not be able to perform the test under the recommended standard conditions, especially when the system configuration and operation at the site are unfavourable. This study describes air-handler fan pressurisation tests performed for two existing buildings having problematic site conditions affected the ability to perform standard test protocols. Envelope leakage was measured with and without sealing of elevator shafts. Both buildings were found to have standard leakage flow rates that exceed typical levels, with or without elevator shaft leakage. This paper provides some insight into what should be done to ensure a successful air-handler fan pressurisation test by describing what was done to deal with undesirable site conditions which could occur in many buildings. Practical applications: This study shows that air-handler fan pressurisation tests can be performed even in problematic buildings by improving test conditions at the site by adjusting the system operation and by utilising site specific measurement techniques and instrumentation. The applicability of recently developed fan airflow and outdoor intake flow measuring sensors to the air-handler fan pressurisation test is also discussed. However, it also shows that perfect implementation of standard air-handler fan pressurisation test procedure may be difficult in real buildings for a reasonable cost. Published case studies providing methods for solving various practical problems at the test site are very rare. This paper is useful for engineers who are seeking practical information about the air-handler fan pressurisation.

This study presents and develops a controlled and characterized method to explore the influence of specific occupant activity on the aerosolization of allergen-containing particles. Indoor allergen-related diseases are primarily inhalation sensitized and developed, suggesting an aerobiological pathway of allergen-containing carrier particles from dust reservoir to occupant respiration. But the pathways are not well understood or quantified. The influence of occupant walking on particle aerosolization is simulated by a system in which complex floor disturbances are deconvoluted into aerodynamic and mechanical components. Time resolved particle size distributions are measured for particles resuspended from representative samples of flooring materials and different types of floor disturbances in an environmentally controlled experimental chamber. Results indicate aerodynamic disturbances, relative to mechanical, dominate the particle resuspension behavior. Dust type, dust load and floor type showed marginal influences on a normalized surface loading basis. Humidity effects were not clear since during experiments the floor samples may not have reached moisture partitioning equilibrium with the controlled air humidity. Average resuspension rates ranged from 10 −7 to 10 −3 min −1 , having phenomenological consistency with previous, large room or chamber investigations, suggesting the method can be utilized to develop a database for particle resuspension rates.

This paper presents results from the simulation of localized, short-duration bioaerosol releases in a hypothetical building similar to a dormitory or barracks using public domain multizone air flow and contaminant dispersion modeling software. The primary purpose of the modeling was to generate example exposure data to be used in the development of a comprehensive microbial risk assessment methodology. However, these results are also of intrinsic interest for what they reveal about the contribution of various building characteristics to risk from airborne contaminants. A variety of parameters were varied, including building construction, heating, ventilating, and air-conditioning (HVAC) system design, and release characteristics, among others. Results of these simulations demonstrate the variability of exposure possible under different scenarios and, more particularly, the impact that HVAC design decisions can have on risk. Although a single building and restricted set of scenarios was investigated, several general conclusions could be drawn regarding factors, such as HVAC zoning and filter maintenance, that intrinsically contribute to vulnerability reduction.

Nanoscale TiO2 catalysts prepared using a sol–gel method exhibit higher initial activity than commercially available P-25 TiO2 for the photocatalytic oxidation of toluene. Unlike P-25 TiO2, nonporous, nanoscale TiO2 catalysts are composed mainly of mesopores with pore sizes in the range of 35–44 nm. Calcination at 420°C leads to agglomeration of nanoscale TiO2 particles, formation of rutile, a decrease in pore capacity, and an enlargement of the mesopores. Catalysts treated at such a temperature display relatively low activity. Results of competitive adsorption of water and toluene on TiO2 samples confirm that TiO2 has a highly hydrophilic surface, which intrinsically suppresses the oxidation rate of toluene at high water content in the feed stream. Severe deactivation of TiO2 catalysts is due to the accumulation of partially oxidized intermediates, such as benzaldehyde and benzoic acid, on active sites. Complete recovery of catalytic activity requires a regeneration temperature above 420°C. Using platinum loaded on TiO2 results in lower oxidation rates of toluene, but facilitates the removal of poisonous intermediates from the deactivated TiO2 surface. Kinetic studies of the deactivation process indicate that the adsorption of poisonous intermediates in the initial stage of the photocatalytic reaction is almost irreversible. The initial oxidation rates on the catalysts are proportional to their surface areas. The surface concentration of illuminated active sites on TiO2 catalysts is estimated to be 0.85–0.96 μmol/m2.

Photooxidation of triethylamine (TEA) in the presence of O2, N2, and H2O over titanium oxide (TiO2) was investigated using a flat plate reactor. TEA was photocatalytically oxidized to CO2 and some by-products on TiO2 thin film catalysts. The intrinsic oxidation rate of the reaction was determined and was dependent on TEA concentration, humidity level, and light intensity. Photocatalytic deactivation was observed in these reactions. Fourier transform infrared (FTIR) and temperature-programmed desorption with a mass spectrometer as a detector (TPD-MS) were used to characterize the surface of the catalyst and study the deactivation mechanism. FTIR and TPD-MS results suggest that accumulation of carboxylic acid species, –N–N=O, and some other carbonaceous species occurred during the reaction. These by-product species or intermediates were chemisorbed on the catalyst surface. They were stable under reaction conditions and might be responsible for deactivation of TiO2 by either poisoning the active sites directly or blocking the adsorption of TEA on the catalyst surface.

Three types of films were prepared by a dip-coating process for the photocatalyzed decomposition of 1-butene in a gas-solid reaction. Under UV illumination ({lambda} > 300 nm, 352 nm peak intensity), ultrasmall SnO{sub 2} with a diameter of 5 nm exhibited initial photoactivity as high as 3 times that of P-25 TiO{sub 2} (30 nm) in the absence of water vapor whereas SnO{sub 2}-l (22 nm) did not show photoactivity. Quantum size effects were mainly responsible for the high photoactivity achieved by SnO{sub 2}. Inactivity of SnO{sub 2}-l film was due to the absence of active hydroxyl groups on the catalyst surface and low surface areas. By investigation of the effects of humidity, water has two different functions: maintaining constant oxidation rates at low water levels by replenishing hydroxyl groups and decreasing the photoactivity at high water levels by competitive adsorption with butene on active sites. Compared with TiO{sub 2}, SnO{sub 2} cannot withstand high humidity since it is very sensitive to water concentration. Hydroxyl groups on catalyst surfaces are the active centers for the reaction. The occurrence of obvious deactivation on SnO{sub 2} films was due to the depletion of hydroxyl groups and the accumulation of carbonate species onmore » particle surfaces, i.e., M-OCOOR species in place of M-OH. The kinetic data correlate with a Langmuir-Hinshelwood single-site model. XRD, UV-vis spectroscopy, and FTIR techniques were employed to characterize the particle size, band gaps, and surface properties of the catalysts.« less

To determine the end use energy utilization profiles of major building subsystems ‐ heating, ventilation, cooling, lighting, plug loads and/or servers ‐ and accurately target potential energy efficiency improvement measures as well as establishing a building’s performance relative to peer facilities, it is necessary to establish dynamic plug load energy use associated with occupant activity. As building facade, HVAC, and lighting component technologies improve and optimally employed in the context of the integrated design of a building, plug load related energy use becomes a more dominant component of the overall building energy utilization index. To clearly identify potential building subsystem energy efficiency improvements and develop strategies for ameliorating increases in plug load energy use via dynamic control and occupant awareness and involvement, rapid plug load measurement and assessment techniques are necessary. The current lack of measured plug load data that could be used as input for energy modelling has represented a significant gap in associating energy models with real building energy consumption. In this investigation, the circuits of multiple distribution panels were monitored to create hourly energy use plug load profiles associated with different end users within a tenant space of a medium-sized office building. The main use within the monitored space was associated with specialty conference rooms (ICON Lab and Telepresence Room), servers, workstations, copier/printer, kitchen amenities, and vacuum cleaning. Furthermore, the energy use data was further characterized according to day type (weekday and weekend). As a result of this work, hourly plug load profiles were generated based on actual measured data which will be used as input to energy models.

Before a dynamic, whole-building energy model (BEM) can be used to evaluate proposed energy conservation measures (ECMs) with reasonable certainty, it must be constructed and calibrated with metered site data to a predetermined level of fidelity using the existing building’s actual operation conditions. In practice, ASHRAE level I or II energy audits are used to initiate a building retrofit project. Recorded variables and building operation measurements, particularly energy use associated with specific end use functionalities that are subsequently used as BEM inputs, can significantly impact the model’s accuracy. Therefore, to efficiently establish a precise model, it is necessary to identify the minimum instrumentation and measurements needed to calibrate the BEM to the level of fidelity required for significant ECM to be specified, prioritized and implemented. This paper describes case studies of constructing and well-tuning EnergyPlus BEMs to “as-operated” conditions for two medium size office buildings located in Mid-Atlantic region (Climate Zone 4A). Guided by a prioritized, key parameter list generated through an EnergyPlus BEM sensitivity study, information collected from the buildings “as-built” drawings, the building automation system (BAS) sequence of operation documents, screenshots of the BAS interfaces, together with hourly sub-metering data and a short two-hour site visit are used to develop the “as-operated” BEMs. The actual meteorological year (AMY) weather file is used to perform real-time simulations and the simulated building energy use is then compared to the actual building monthly utility bills and sub-metered hourly energy data.

Amorphous MnOx(AMO) has been prepared by the reaction of potassium permanganate and oxalic acid. Surface area measurements and pore size distribution analyses show that AMO has high surface (200 m2/g) area and a microporus structure. Kinetic results indicate that methyl bromide degradation using AMO photocatalysts is due to a combination of thermocatalytic and photocatalytic reactions; however, the photocatalytic reaction is predominant. Detailed studies show that both molecular oxygen and bulk lattice oxygen of AMO can be involved in the oxidation of methyl bromide to carbon dioxide. Kinetic data, Auger analyses, and FTIR spectra suggest that both oxidation state changes of Mn and the presence of bromide adsorbed on the surface might lead to deactivation of the catalyst. According to mass balance calculations and analyses with potassium iodide solutions with starch, the final products are bromine, carbon dioxide, and water. The overall reaction for methyl bromide degradation under illumination using AMO photocatalyst can be expressed as CH3Br(g) + 7/4O2(g) → CO2(g) + 3/2H2O(g) + 1/2Br2(g).

Sponge type deposits composed of nanometer sized Si whiskers were formed on Davisil (porous SiO2) gel substrates by chemical vapor deposition (CVD) using methyltrichlorosilane (MTS) as a precursor and H2 as carrier gas. The diameters of the fine whiskers are estimated to be 100 nm or smaller from SEM observations. XRD analyses revealed that the coatings formed at 800 and 900°C contained microcrystalline Si and the Auger analysis indicated the existence of free carbon. The surface area of the coated Davisil was approximately 189 ± 5 m2/g, as obtained from BET measurements. The coatings were also applied on several other substrates, such as AIN and low surface area (< 224 m2/g) silica gel, with the same coating conditions. On these substrates, highly porous Si has also been observed on AIN substrates, and nonporous, half sphere shaped coatings were observed on low surface area silica gel substrates.