Atila Novoselac

Dynamic Demand Response Controller Based on Real-Time Retail Price for Residential Buildings

Demand response and dynamic retail pricing of electricity are key factors in a smart grid to reduce peak loads and to increase the efficiency of the power grid. Air-conditioning and heating loads in residential buildings are major contributors to total electricity consumption. In hot climates, such as Austin, Texas, the electricity cooling load of buildings results in critical peak load during the on-peak period. Demand response (DR) is valuable to reduce both electricity loads and energy costs for end users in a residential building. This paper focuses on developing a control strategy for the HVACs to respond to real-time prices for peak load reduction. A proposed dynamic demand response controller (DDRC) changes the set-point temperature to control HVAC loads depending on electricity retail price published each 15 minutes and partially shifts some of this load away from the peak. The advantages of the proposed control strategy are that DDRC has a detailed scheduling function and compares the real-time retail price of electricity with a threshold price that customers set by their preference in order to control HVAC loads considering energy cost. In addition, a detailed single family house model is developed using OpenStudio and Energyplus considering the geometry of a residential building and geographical environment. This HVAC modeling provides simulation of a house. Comfort level is, moreover, reflected into the DDRC to minimize discomfort when DDRC changes the set-point temperature. Our proposed DDRC is implemented in MATLAB/SIMULINK and connected to the EnergyPlus model via building controls virtual test bed (BCVTB). The real-time retail price is based on the real-time wholesale price in the ERCOT market in Texas. The study shows that DDRC applied in residential HVAC systems could significantly reduce peak loads and electricity bills with a modest variation in thermal comfort.

A critical review on the performance and design of combined cooled ceiling and displacement ventilation systems

This paper reviews the studies and design of cooled ceiling and displacement ventilation (CC/DV) systems in buildings. If properly designed, the combined CC/DV systems can provide better indoor air quality and thermal comfort level compared to the widely used variable air volume (VAV) mixing systems. The cooling load removed by DV is a key design parameter. A low DV load has a positive effect on thermal comfort due to a small vertical temperature gradient, yet also has a negative effect on indoor air quality due to the increased mixing of room air. The impact of the room height on the temperature and contaminant concentration profiles is negligible in the occupied zone. The CC/DV systems are more effective in removing active contaminants (as indicated by CO2) than passive contaminants (e.g. VOCs). The condensation risk on the chilled ceiling panel is high because of the high humidity ratio in the region close to the panel. To prevent condensation on the panel, it is important to properly control the system for transient regimes, such as startup and shutdown periods, and to minimize infiltration of humid outdoor air. Whether a CC/DV system may or may not reduce energy consumption depends on the supply air temperature, outdoor airflow rate, and cooling load. Therefore, it is necessary to develop design guidelines for CC/DV systems for US buildings because the climate, building layout, and cooling load can be different from those studied elsewhere.

Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment

Particle deposits on indoor surfaces can be as complex and diverse as the indoor environments in which they exist. Dust loading can range over several orders of magnitude, suggesting the existence of different types of particle deposits. These deposits can be broadly classified as either a monolayer, in which particles are sparsely deposited on a surface, or a multilayer, in which particles are deposited on top of one another and there is particle-to-particle adhesion and interaction. Particles within these diverse structures of settled indoor dust can become airborne through a process known as resuspension, which can occur due to airflow in ventilation ducts or human activity indoors. The dust loading and deposit structure on an indoor surface may have important implications for resuspension in the indoor environment. This literature review provides a summary of dust loads found on indoor surfaces in field studies and classifies each dust load as either a monolayer or multilayer particle deposit. The article highlights the unique attributes associated with resuspension from both types of particle deposits by summarizing key findings of the experimental resuspension literature. The fundamental differences in the resuspension process between monolayer and multilayer deposits suggest that resuspension may vary considerably among the broad spectrum of dust loads found on indoor surfaces. Copyright 2013 American Association for Aerosol Research

The Effects of Filtration on Pressure Drop and Energy Consumption in Residential HVAC Systems (RP-1299)

The use of high-efficiency HVAC filters is a common strategy to control exposure to airborne particulate matter in residential buildings. However, high-efficiency filters generally have a higher pressure drop and are widely assumed to have large energy penalties. In this paper, we explore the underlying theoretical energy implications of high-pressure-drop filters and we present the results of a four-month-long period of detailed energy monitoring of two air-conditioning systems in a test home in Austin, Texas. A theoretical analysis shows that the magnitude of potential energy impacts associated with high-efficiency filters are overall likely to be small and can result in either a net savings or additional expenditure, depending on the system. The measured results in the test systems confirm these findings, and energy consumption generally did not differ with high-efficiency filters compared to low-efficiency filters. These results suggest caution when assuming that high-efficiency filters require more energy than low-pressure-drop filters in residential HVAC systems.

Impact of Airflow Characteristics on Particle Resuspension from Indoor Surfaces

Resuspension is an important source of indoor particles. We measured the resuspension of 1 to 20 μm particles on common indoor materials and explored the importance of turbulence to the resuspension process. Experimental variables included materials (linoleum, carpet, and galvanized sheet metal) and bulk air velocity (5, 10, 15, 20, and 25 m/s). At each of these conditions the turbulence intensity in the boundary layer was varied between a low, medium, and high state and ranged from 9 to 34% at the surface. For comparison of resuspension from the considered surfaces and at different flow conditions, we use the relative resuspension, which quantifies resuspension without requiring knowledge of the number of particles initially seeded on the surface. The relative resuspension compares the fraction of particles resuspended at the experimental conditions to the maximum achieved with a controlled impinging jet. In general, the results show that for the ranges considered, increasing velocity caused the largest increase in resuspension, followed by increasing turbulence intensity and then increasing particle diameter. All three material types showed consistent patterns with carpet having the largest resuspension for a given set of conditions, followed by linoleum and then by galvanized sheet metal. High turbulence and high velocity conditions minimized the differences between materials. An understanding of the relative magnitudes of these effects allows for better analysis and mitigation of indoor resuspension.

Walls talk: Microbial biogeography of homes spanning urbanization.

Home microbes track space-use and reflect a decreasing exposure to environmental microbes due to urbanization. Westernization has propelled changes in urbanization and architecture, altering our exposure to the outdoor environment from that experienced during most of human evolution. These changes might affect the developmental exposure of infants to bacteria, immune development, and human microbiome diversity. Contemporary urban humans spend most of their time indoors, and little is known about the microbes associated with different designs of the built environment and their interaction with the human immune system. This study addresses the associations between architectural design and the microbial biogeography of households across a gradient of urbanization in South America. Urbanization was associated with households’ increased isolation from outdoor environments, with additional indoor space isolation by walls. Microbes from house walls and floors segregate by location, and urban indoor walls contain human bacterial markers of space use. Urbanized spaces uniquely increase the content of human-associated microbes—which could increase transmission of potential pathogens—and decrease exposure to the environmental microbes with which humans have coevolved.

Use of model predictive control to enhance the flexibility of thermal energy storage cooling systems

This paper investigates the application of a model predictive controller (MPC) to both a traditional and a novel chilled water thermal energy storage system over for an Austin, Texas, climate. In the novel system, the thermal storage discharges during peak electricity times to meet building cooling load and to supply reduced temperature water for heat rejection in the chillers condenser. Chiller efficiency improves as the condenser water temperature decreases, shifting more electrical usage to off-peak hours, but may increase overall electrical usage. The MPC is designed to optimize the discharge and recharge of the thermal storage in order to minimize operation costs or energy consumption over a 24-hour prediction horizon. The ability of MPC to level the electrical load profile is also considered. The way in which demand charges are considered in the objective function can greatly influence the systems electrical load profile.

Characterizing particle resuspension from mattresses: chamber study

UNLABELLED People spend approximately one-third of their lives sleeping, where they can be exposed to a myriad of particle-bound biological agents and chemical pollutants that originate within mattresses and bedding, including allergens, fungal spores, bacteria, and particle-phase semi-volatile organic compounds. Full-scale particle resuspension experiments were conducted in an environmental chamber, where volunteers performed a prescribed movement routine on an artificially seeded mattress. Human movements in bed, such as rolling from the prone to supine position, were found to resuspend settled particles, leading to elevations in airborne particle concentrations. Resuspension rates were estimated for the size fractions of 1-2 μm, 2-3 μm, 3-5 μm, 5-10 μm, and 10-20 μm, and were in the range of 10(-3) to 10(1) h(-1). Particle size had the most significant impact on the resuspension rate, whereas dust loading, volunteer body mass, and ventilation rate had a much smaller impact. Resuspension increased with the intensity of a movement, as characterized by surface vibrations, and decreased with repeated movement routines. Inhalation exposure was characterized with the intake fraction metric. Intake fractions increased as the particle size and ventilation rate decreased and ranged from 10(2) to 10(4) inhaled particles per million resuspended, demonstrating that a significant fraction of released particles can be inhaled by sleeping occupants. PRACTICAL IMPLICATIONS Full-scale chamber experiments with human volunteers demonstrate that body movements in bed can resuspend settled particles from mattresses, leading to elevated airborne particle concentrations in both the breathing zone and bulk air of the chamber. Numerous variables influence resuspension, including particle size and intensity of a specific body movement. The results suggest that human-induced resuspension in the sleep microenvironment may play an important role in contributing to our inhalation exposure to mattress dust pollutants.

Occupational Exposure to Hazardous Airborne Pollutants: Effects of Air Mixing and Source Location

The presence of airborne pollutants in indoor environments has been associated with occupants’ discomfort and/or adverse health effects. This study investigates occupational exposure in relation to indoor air mixing and source location relative to a human body. Experimental and computational methods were used to provide information about the pollutant distribution in the vicinity of the human body for different levels of room air mixing. Study results show that the often used assumption of uniform pollutant distribution in an occupied space is not always appropriate for estimation of inhalation exposure. Results also indicate that an occupant may experience very high acute exposure to airborne pollutants when little air mixing exists in a space and the pollutant source is in the vicinity of the occupant. The buoyancy-driven flow induced by the convective heat transfer from an occupants body can transport pollutants in the occupants vicinity to the breathing zone. Specific study results reveal that a source located in the occupants front chest region makes a relatively large contribution to the breathing zone concentration compared with the other sources in the vicinity of the human body. With the source position in this region, exposure can be nine times greater than that calculated with the uniform mixing assumption. The buoyancy-driven convective plume around a body seems to have a significant influence on pollutant transport and human exposure, especially in the absence of room air mixing.

Infant exposure to emissions of volatile organic compounds from crib mattresses

Infants spend most of their time sleeping and are likely to be exposed to elevated concentrations of chemicals released from their crib mattresses. Small-scale chamber experiments were conducted to determine the area-specific emission rates (SERs) of volatile organic compounds (VOCs) in a collection of twenty new and used crib mattresses. All mattress samples were found to emit VOCs and the mean values of total VOC (TVOC) SERs were 56 μg/m(2)h at 23 °C and 139 μg/m(2)h at 36 °C. TVOC SERs were greater for new mattresses compared to used ones and were influenced by the type of foam material and the presence of mattress cover layer. A variety of VOCs were identified, with polyurethane foam releasing a greater diversity of VOCs compared to polyester foam. Large-scale chamber experiments were conducted with an infant thermal manikin. TVOC concentrations sampled in the breathing zone and interior pore air of the crib mattress foam were found to be greater than the bulk room air by factors in the range of 1.8 to 2.4 and 7.5 to 21, respectively. The results suggest that crib mattresses are an important source of VOCs and infant exposure to VOCs are possibly elevated in their sleep microenvironments.