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Carbon dioxide as a refrigerant is becoming increasingly more popular globally. With thousands of commercial transcritical systems running worldwide, much knowledge and experience have been gained on this topic. Indeed, these systems can be employed in many larger applications. However, large commercial systems have increased complexities; not just larger capacities, but also longer pipe runs and/or more dramatic load shifts. These factors should drive a transcritical CO2 system designer to consider additional measures. In this paper, we first discuss oil management considerations for commercial systems and then explain some of the unique challenges that large commercial systems might find and offer potential solutions as to how to solve them. In addition, the selection and sizing of the components discussed here is paramount to ensure proper compressor lubrication and maintain high levels of heat transfer and efficiency while removing as much oil as possible from the refrigerant. [ABSTRACT FROM AUTHOR]

There is a compelling body of evidence calling for a reduction in the amount of carbon dioxide (CO2) that mankind is emitting into the atmosphere. A segment of climate science community contends that we will be required to actively “reduce” the magnitude of our atmospheric CO2 content, not merely reduce mankind’s contribution to the increase. Five methods of CO2 mitigation are briefly mentioned, followed by the description of a sixth, innovative method of using chemical or adsorption scrubbing techniques to remove indoor air CO2 from building HVAC systems for the purpose of reducing the required outdoor air (OA) ventilation to provide energy and CO2 reductions. The reduced OA ventilation will correspond to a reduced source energy consumption while simultaneously scrubbing other indoor air contaminants, improving indoor air quality (IAQ). A building HVAC energy model is presented in which an indoor air CO2 scrubbing technology is incorporated. Although the scrubbed indoor CO2 is merely vented and released into outdoor air, the resulting reduction in source fossil fuel energy related CO2 emissions is calculated for the analysis of the net CO2 reduction potential. An eQuest building model is utilized for three different locations in the USA (Atlanta, Detroit, and Los Angeles) and the 2016 USEPA eGrid database is used to calculate the local electric powerplant source CO2 emissions. The results indicate that regions in the United States with both high HVAC loads for heating and/or cooling coupled to a carbon intense local electric supply will benefit the most by utilizing the proposed HVAC / CO2 mitigation system. Of the three sample areas, Detroit had the highest CO2 source emissions saving potential from this application at 66,560 lb/yr (30,255 kg/yr) followed by Atlanta with 46,149 lb/yr (20,977 kg/yr). The mild southern California weather coupled with the less carbon intense electric grid only produced 2,340 lb/yr (1,064 kg/yr) source CO2 reductions. The addition of other energy conservation measures or site renewable energy generation would obviously increase these source carbon reductions. If the human occupant respiration CO2 were captured and permanently sequestered from this same office building’s indoor air, 55,600 lb/yr (25,300 kg/yr) would be sequestered. Ultimately, the hypothesis of this paper is that a more lucrative market for these emerging CO2 scrubbing techniques may first find a beneficial use in the HVAC product and/or energy efficiency space. This application may create a viable business model in which these technologies are deployed, tested and refined as profitable HVAC products, and then hopefully deployed in future years for direct atmospheric CO2 mitigation. Further study of this concept seems warranted, and the author invites future discussion and critical review of this papers concepts and conclusions. [ABSTRACT FROM AUTHOR]

Demand-controlled ventilation (DCV) systems have some advantages over other building ventilation strategies, as they can maintain acceptable indoor air quality (IAQ) of a space while reducing the overall energy consumption of building ventilation. When selecting sensors for DCV, it is important to consider their performance and cost. Over the past several years, there has been an increase in the availability of low-cost sensors. However, the feasibility of using the currently available low-cost sensors within DCV is an area that requires further investigation. The focus of the work presented in this paper is to evaluate the feasibility of current low-cost carbon dioxide (CO2) sensors for use in DCV using a controlled environment. The performance of three low-cost CO2 sensor models was verified to determine their suitability in the control of DCV. Preliminary testing revealed unacceptable inaccuracy in one of the three sensors. This sensor uses micro-hotplate technology for gas sensing and was excluded from detailed testing. The two sensors tested in detail use nondispersive infrared (NDIR) technology. The accuracy of the first NDIR sensor (model A) was satisfactory; some of the sensor measurements deviated from the dosed concentration by more than 100 ppm, but remained within 150 ppm. The nonlinearity of sensor model A was greater than model B but was acceptable—the maximum deviation from the linear line of best fit ranged between 55 and 92 ppm. The repeatability of sensor model A was acceptable; sensor measurements during the three days of testing were always within 100 ppm when measuring the same CO2 concentration. In fact, the maximum recorded nonrepeatability was 73 ppm. The hysteresis of sensor model A was satisfactory; most sensor measurements were within 100 ppm and all were within 150 ppm when measuring the same CO2 concentration when approached from varying directions. However, sensor model A had a tendency to underreport CO2 concentrations, which could reduce IAQ if the sensors were not calibrated or if the tendency to underreport was not considered in the control algorithm. Sensor model A consistently underreported decreasing CO2 at a larger magnitude, which would likely cause the DCV system to turn off sooner than desired, potentially negatively impacting IAQ. The accuracy of the second NDIR sensor (model B) was found to be better than model A and was deemed acceptable. The sensor measurements were always within 100 ppm of the dosed concentration. Sensor model B did have a tendency to overreport CO2 concentrations, which could result in more energy consumption than ideal; however, the impact is expected to be low due to the better accuracy of the sensor. The nonlinearity of sensor model B was satisfactory; the maximum deviation from the linear line of best fit ranged between 30 and 55 ppm. The repeatability of sensor model B was satisfactory; all but one of the sensor measurements during the three days of testing were within 100 ppm when measuring the same CO2 concentration. The hysteresis of sensor model B was exceptional; sensor measurements were typically within 20 ppm when measuring the same CO2 concentration when approached from either high or low concentrations and were always within 60 ppm. Sensor model B was found to be suitable for use in DCV. This work shows that ultra low-cost CO2 sensors in the area of $27 CAD ($20 USD) each may not be suitable for DCV, but that low-cost CO2 sensors in the area of $80 CAD ($60 USD) could be suitable for developing a low-cost controller and sensor package for managing indoor CO2 concentrations. [ABSTRACT FROM AUTHOR]

As environmental concerns and accompanying regulations grow around the world, the Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC&R) industry is working to develop technologies that utilize low-global warming potential (GWP) refrigerants and remain within competitive coefficient of performance (COP) values of previous hydrofluorocarbon (HFC) systems. Carbon Dioxide (CO2) has been investigated extensively in the past 25 years as a potential substitute for HFCs in refrigeration application in mild ambient climates. In efforts to increase the efficiency of CO2 systems, researchers and industry have identified cycle modifications that are particularly beneficial in transcritical CO2 cycle application, such as expansion work recovery and economization. This paper presents an overview of the design and operation of a multi-stage transcritical CO2 cycle with two independentlycontrolled evaporators. The cycle utilizes three stages of compression with intercooling between the second and third stages, as well as flash tank economization at each evaporator, including evaporator bypass lines for vapor from the flash tank. Furthermore, the cycle was designed to allow transition between methods of expansion work recovery without the need to stop the compressors. The cycle can switch between electronic expansion valve (EXV) mode, ejector mode, and a turbomachine expander mode with the actuation of several ball valves mid-operation. The purpose of this work is to describe the theory and rationale behind system design, discuss how the test stand will be controlled, and provide instruction on the transition between expansion methods without shutting down the compressors. [ABSTRACT FROM AUTHOR]

Indoor environment in an institutional building, including ventilation, indoor air quality (IAQ), acoustic and thermal conditions, as well as lighting, directly influence the students' study and health performance. In this paper, all five aspects were studied to evaluate the indoor environmental quality (IEQ) in an institutional building. This study examines IEQ parameters, including pressure, illuminance level, acoustics, carbon dioxide (CO2) levels, temperature, and humidity, with appropriate monitors allocated during a lecture duration (50min or 80 min) in four lecture classrooms (59187 ± 1554 ft3, 1676 ± 44 m3) repeatedly from October 2018 to March 2019 with the objectives of providing a comprehensive analysis and updating the literature. Outdoor temperature was -13°F to 54°F (-25°C to 12°C) during two-season measurements, while the classroom environment was maintained at 73 ± 2°F (23 ± 1°C) and 33% ± 3% RH. Indoor CO2 had mean concentrations of 550-1055 ppm and a mean sound level of 58 ± 3 dBA. Using the one-zone steady-state box model, the air change rates were configured at 1.3-6.5 per hour based on continuous CO2 measurements and occupant loads in the lectures. Results were compared to ventilation guideline for lecture classrooms by ASHRAE. Building features and mechanical operation details were discussed to analyze the relationships between building design/operation and IEQ performance. [ABSTRACT FROM AUTHOR]

Heating, ventilation, and air-conditioning (HVAC) systems consume more than 40% of a building's total energy use. Several strategies have been developed to decrease the energy consumption of HVAC systems. But few energy reduction strategies also impact indoor air quality (IAQ). Providing a risk-free indoor environment is crucial for the occupant's comfort and safety, especially in the post-pandemic scenario. The CO2 concentration significantly impacts indoor air quality (IAQ) complaints and health symptoms in buildings, while ventilation levels are below the recommended rates. In a typical all-air HVAC system, a fraction of return air is recirculated into the space to reduce the system load. The recirculated air containing metabolic carbon dioxide (CO2) generated by the occupants is mixed with the outdoor air to dilute the CO2 concentration before being supplied into the conditioned space. This return air ratio plays a vital role in balancing the energy demand and providing acceptable IAQ. For spaces fitted with individual split AC systems without a fresh air duct option, 100% of the return air is recirculated into the conditioned space. The IAQ is highly affected in such space as it relies entirely on infiltration. There is a need to study methods to reduce energy demands while maintaining indoor air quality (IAQ) requirements. Computational Fluid Dynamics (CFD) simulation of indoor environments can help analyze different CO2 concentration reduction strategies, thus improving the HVAC design to provide a healthy, code-compliant indoor air quality. In this study, a CFD model is developed to compute the CO2 concentration at the supply considering the recirculation ratio of return air. The developed model estimates the optimum return air ratio that minimizes the energy cost of the system while maintaining acceptable IAQ. [ABSTRACT FROM AUTHOR]

In recent years, interest in heat pump water heaters as energy- and cost-saving devices has increased, corresponding with a recent surge in available heat pump water heater products. While a traditional electric resistance tank heater can offer a theoretical maximum COP of 1, heat pump water heaters can deliver several units of heat energy to water for every unit of electrical energy used by the system. Heat pump water heaters have, in particular, sparked the interest of electric utility companies, who see them as a potential energy-saving and peak load-reducing asset. However, modern heat pump water heaters have limitations. They generally rely on electric resistance heat to provide backup during large loads and when ambient temperatures are low. Water heaters using CO2 as a refrigerant have addressed some of these issues, but have yet to emerge in the United States for a variety of reasons. This paper describes modeling of heat pump water heater systems, including a potential next generation of systems using variable speed compressors to eliminate the electric resistance element in R134a systems. A high level of detail is required in order to evaluate the performance of different systems and control strategies, thus the heat pump cycles were modeled at the component level using a commercially available equation solving tool. In this work, a vapor compression cycle using R134a and fixed-speed compressor was modeled as well as an R134a heat pump with a variable-speed compressor and a CO2-transcritical variable-speed heat pump. The heat exchanger geometries, heat transfer and pressure drop correlations, and compressor and fan efficiencies were all considered based on available manufacturer data. A transient simulation software tool is used to simulate the weather, building, and water tank and is coupled with the vapor compression cycle model in order to simulate system performance over time. This paper details the modeling approach and simulation results for several heat pump water heater designs which use a variety of control algorithms and operate in several climatic conditions. Initial results show good agreement between the model's predictions and actual field test data recorded by the project's sponsors. The paper identifies numerous control algorithms and system configurations which offer potential energy savings and also quantify the potential advantages of using a variable-speed compressor and CO2 as a refrigerant. [ABSTRACT FROM AUTHOR]

This paper proposes a methodology to calibrate multi-zone airflow models in existing buildings. The methodology has been demonstrated with the widely used multi-zone model CONTAM and applied to two buildings, one synthetic and one actual. The methodology builds on previous work with the calibration process enhanced by the use of carbon dioxide tracer gas test data. A key concept highlighted in this paper is that calibration of airflow models is a highly over-parameterized problem and that some form of model reduction is imperative. This is achieved by performing an airflow-based sensitivity analysis to identify influential system drivers, a tracer gas-based sensitivity analysis to identify macro-zones (i.e. groups of rooms that can be combined into one zone for the purposes of predicting or studying dynamic airflow behavior under different types of stimuli), and finally, a process of tuning the model parameters. It is found that for mechanically ventilated commercial buildings, calibrating multi-zone models by reconciling differences between measured and predicted tracer gas behavior is more strongly impacted by those factors which significantly influence room air change rates than by airflow path leakage parameter tuning. [ABSTRACT FROM AUTHOR]

This paper provides a methodology to evaluate end use options to reduce primary energy consumption and CO2 emissions associated with buildings. First, the paper discusses alternative energy efficiency metrics, their uses, and limitations. In particular, limitations of site energy and cost as meaningful societal metrics are reviewed, along with the challenges associated with alternative metrics such as full fuel cycle energy efficiency and CO2 emissions. In addition, the paper provides a methodology and example calculations for evaluating the site energy, full fuel cycle energy, and CO2 emissions of targeted direct use options. Results of the sample calculations show that natural gas water heaters can reduce primary energy consumption and CO2 emissions significantly compared to equivalent electric resistance water heaters. Variationsin calculated reductions occur depending on the fuels used to generate electricity and region selected for analysis. [ABSTRACT FROM AUTHOR]

This is the third paper in a four-part series reporting on the test and evaluation of typical carbon-dioxide sensors used in building HVAC applications. Fifteen models of NDIR HVAC-grade CO2 sensors were tested and evaluated to determine the humidity, temperature, and pressure sensitivity of the sensors. This paper reports the performance of the sensors at various relative humidity, temperature, and pressure levels common to building HVAC applications and provides a comparison with manufacturer specifications. Among the 15 models tested, eight models have a singlelamp, single-wavelength configuration, four models have a dual-lamp, single-wavelength configuration, and three models have a single-lamp, dual-wavelength configuration. The sensors were tested in a chamber specifically fabricated for this research. A description of the apparatus and the method of test are described in Part 1 (Shrestha and Maxwell 2009). The test result showed a wide variation in humidity, temperature, and pressure sensitivity of CO2 sensors among manufacturers. In some cases, significant variations in sensor performance exist between sensors of the same model. Even the natural variation in relative humidity could significantly vary readings of some CO2 sensor readings. The effects of temperature and pressure variation on NDIR CO2 sensors are unavoidable without an algorithm to compensate for the changes. For the range of temperature and pressure variation in an airconditioned space, the effect of pressure variation is more significant compared to the effect of temperature variation. [ABSTRACT FROM AUTHOR]

This is the second paper in a four-part series reporting on the test and evaluation of typical carbon-dioxide sensors used in building HVAC applications. Fifteen models of NDIR HVAC-grade CO2 sensors were tested and evaluated to determine the accuracy, linearity, repeatability, and hysteresis of each sensor. This paper describes the performance of the sensors and provides a comparison with the manufacturers' specifications. The sensors were tested at 40% relative humidity, 73°F (22.8°C) temperature, 14.70 psia (101.35 kPa) pressure, and at five different CO2 concentrations (400, 750, 1100, 1450, and 1800 ppm). The test results showed a wide variation in sensor performance among the various manufacturers and in some cases a wide variation among sensors of the same model. In all, 45 sensors were evaluated: three from each of the 15 models. Among the 15 models tested, eight models have a single-lamp, single-wavelength configuration, four models have a dual-lamp, single-wavelength configuration, and three models have a single-lamp, dual-wavelength configuration. [ABSTRACT FROM AUTHOR]

Carbon-dioxide sensors are widely used as part of a demand controlled ventilation (DCV) system for buildings requiring mechanical ventilation, and their performance can significantly impact energy use in these systems. Therefore, a study was undertaken to test and evaluate the most commonly used CO2 sensors in HVAC systems, namely the non-dispersive infrared (NDIR) type. The procedures presented here provide a methodology to test and evaluate NDIR CO2 sensors for accuracy, linearity, repeatability, hysteresis, humidity sensitivity, temperature sensitivity, and pressure sensitivity. The test and evaluation procedures presented in this paper are all inclusive in that they range from procuring the CO2 sensor to comparing the performance of the sensors. Specifically, a procedure is presented to both procure CO2 sensors from the manufacturers and to maintain quality control by controlling the storage and handling of the sensors. Further, it describes the apparatus and instrumentation, along with test conditions, used to test the sensors. Additionally, it outlines a detailed experimental procedure to evaluate the accuracy of the sensors. Finally, a discussion is presented on analyzing and comparing the performance of CO2 sensors by using the test data. Partial results of the accuracy test and evaluation of the CO2 sensors and the results of the linearity, repeatability, hysteresis, humidity sensitivity, temperature sensitivity, and pressure sensitivity evaluation are included in this paper. The full test results will be presented in a later publication. [ABSTRACT FROM AUTHOR]

This paper presents a critical review of cascade refrigeration systems for low-temperature refrigeration. The recent interest and issues in the development of two-circuit cascade systems are highlighted. A survey of successful installations was carried out to judge the state of the art of the technology. A thermodynamic analysis of these systems was carried out using natural refrigerants with carbon dioxide as a low-temperature fluid and propane, propylene, and ammonia as high-temperature fluids. The results are compared with a system using R-404A and CO2 as high- and low-temperature refrigerants, respectively. The emerging trends and research directions for these systems are discussed in the paper. [ABSTRACT FROM AUTHOR]

The paper discusses the applications of CO2-based demand-controlled ventilation DCV strategy integrated with the economizer for air source heat pumps in schools, investigates their impact on the annual energy consumption, and determines the potential savings achieved in different USA locations. The study includes detailed energy analysis on an existing middle school through whole building simulation energy software. The simulation model is first calibrated and checked for accuracy using actual monthly utility data. This model is then used for savings calculations resulted from a combination of air-side economizer and CO2-Based DCV and with various occupancy profiles and locations. The results show that a significant saving could be obtained as compared to the actual operating strategy implemented in the existing system and this saving depends mainly on the actual occupancy profile and building locations. [ABSTRACT FROM AUTHOR]

Refrigeration systems using carbon dioxide (CO2) as a refrigerant, either in subcritical or transcritical cycles, or as secondary coolant systems, have recently received considerable attention due to carbon dioxide's low Global Warming Potential (GWP). This paper presents a comparative analysis of various CO2 transcritical refrigeration systems to optimize the operating parameters of these systems. In addition, the performance of selected CO2-based refrigeration systems is compared to the baseline R-404A multiplex direct expansion system using bin analyses in sixteen cities from eight climate zones of the United States. The operating parameters considered in this study include ambient temperature, suction line heat exchanger (SLHX) effectiveness and evaporator superheat. [ABSTRACT FROM AUTHOR]

A mechanical ventilation system should be designed to provide a minimum amount of outdoor air to each space, based on occupancy number and building area, according to ANSI/ ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality (ASHRAE 2010c).Demand-controlled ventilation (DCV) can be used to reduce unnecessary ventilation and save energy when a space is occupied at less than its design level. Carbon dioxide sensing could be used to estimate the number of people in a space or the strength of occupant-related contaminant sources. This control approach is called CO2-based DCV. CO2-based DCV is based on several assumptions, which should be validated for the application of CO2-based DCV. This paper describes the results of a literature search performed to review these assumptions. The study concludes that the assumptions are valid and that CO2-based DCV can meet the objectives of ANSI/ ASHRAE Standard 62.1-2010. [ABSTRACT FROM AUTHOR]

Recently, building energy retrofits are performed for existing buildings to minimize CO2 emission of building sector in Korea. When energy retrofit is applied, the effect of the energy conservation measures (ECMs) should be evaluated with standardized method. Energy saving effect cannot be measured directly at the planning stage in building retrofit, the savings can be determined by simulation methods in this stage. In this study, the measurement and verification (M&V) methods to reliably determine actual savings created within an individual measure or integrated measures by a building energy retrofit project were reviewed. In this paper, especially, the calibrated simulation method as an M&V method was accomplished for the small-sized office building in Korea. The considerations to set up the baseline simulation model for target building were described and the validity of the baseline model was analyzed with field measurement results based on ASHRAE Guideline 14-2002. [ABSTRACT FROM AUTHOR]

Heat pump water heaters using CO2 as a refrigerant have been available in Japan and elsewhere in the world since the early 1990s, with many devices already installed. However, they have yet to emerge in the United States. One major reason is cost: heat pump systems will cost more than an equivalent electric resistance water heater, and CO2 systems tend to be have premium features and costs. Another reason for the lack of CO2 water heaters in the US is that existing models have differed strongly from the conventional water heating equipment seen in the US marketplace. Models developed under the EcoCute label often have an indoor tank with an outdoor heat pump, and features such as remote controls, bath water recirculation loops and others. This study examines a new, integrated CO2 heat pump water heater developed by a Japanese manufacturer and marketed in Europe, which removes many of the features common to CO2 systems and is meant for indoor, single-location installation. The integrated CO2 system was tested in the laboratory at a variety of conditions to map performance. It was tested in climate-controlled environmental chambers for a variety of ambient air conditions and also in an approximated Energy Factor test. The system tested has two modes: a comfort mode in which compressor power is high, and the system always charges to full capacity; and an economy mode in which the compressor power is low, and the system charges to full capacity during pre-set (generally overnight) hours and reheats only partially during another pre-set time period. It was tested in both modes. The system was also installed in a test home in Tennessee which features simulated occupancy and detailed data monitoring. The system was installed in the garage and allowed to run in each of the operating modes at different times. The water draw was controlled in the home to a typical load profile. This paper will outline the testing and monitoring approach. Results for both the completed laboratory testing and ongoing field testing will be shown. [ABSTRACT FROM AUTHOR]

This paper presents energy and life cycle climate performance (LCCP) analyses of a variety of supermarket refrigeration systems to identify designs that exhibit low environmental impact and high energy efficiency. EnergyPlus was used to model refrigeration systems in a variety of climate zones across the United States. The refrigeration systems that were modeled include the traditional multiplex DX system, cascade systems with secondary loops and the transcritical CO2 system. Furthermore, a variety of refrigerants were investigated, including R-32, R-134a, R-404A, R-1234yf, R-717, and R-744. LCCP analysis was used to determine the direct and indirect carbon dioxide emissions resulting from the operation of the various refrigeration systems over their lifetimes. Our analysis revealed that high-efficiency supermarket refrigeration systems may result in up to 44% less energy consumption and 78% reduced carbon dioxide emissions compared to the baseline multiplex DX system. This is an encouraging result for legislators, policy makers and supermarket owners to select low emission, high-efficiency commercial refrigeration system designs for future retrofit and new projects. [ABSTRACT FROM AUTHOR]

The paper discusses a new ventilation control strategy based on supply air CO2 concentration for multi-zone HVAC systems. The strategy offers a great opportunity to reduce energy consumption in HVAC systems while providing the required ventilation according to ASHRAE standard 62.1 2010. The strategy requires a PI/or PID controller along with a CO2 sensor located in the main supply air duct to control the supply air concentration by adjusting the outdoor air damper. It also includes a control algorithm to dynamically reset the CO2 concentration set point on a proper time interval basis and using the actual zone airflow rates. The strategy is evaluated by simulations on multi-zone office building conditioned by a typical VAV system and under various USA locations. The results show that a significant saving could be obtained by implementing the proposed strategy as compared to the design-occupancy ASHRAE Standard 62.1 2010 procedure and this saving depends mainly on actual occupancy profile and building locations. [ABSTRACT FROM AUTHOR]

A strong emphasis is currently being placed on the use of natural ventilation as a means for providing a safe and healthful indoor environment as part of green building programs. There has been an increasing interest in developing natural ventilation design strategies that can furnish adequate fresh air to the building interior and simultaneously control the indoor air quality effectively, while providing significant energy savings. In naturally ventilated spaces, furnishing a suitable air exchange rate between the building exterior and interior can create a thermally comfortable and healthy indoor environment. However, the air exchange must occur such that the indoor air quality of the building is not compromised and thermally comfortable conditions for the occupants can be maintained. Architecture Hall is a recently renovated, naturally ventilated building located on the University of Washington campus in Seattle. The natural ventilation in this building was evaluated using a variety of experimental techniques, which included measurement of carbon dioxide (CO2) levels, air exchange rates and air velocities. High CO2 concentrations are a good indicator of inadequate ventilation rates and poor air movement in a space. Hence, a number of standards and certification programs specify the use of outdoor air monitoring based on CO2 concentrations in an occupied space. Occupant surveys, based on a U.S. EPA study, were also administered to understand and analyse occupant perceptions about the indoor thermal environment and to identify the prevalence of any building related illness symptoms. The discussion in this paper will focus on the findings of the occupant surveys and how they relate to the measured CO2 levels, air exchange rates and air velocities in the naturally ventilated spaces. The natural ventilation function in Architecture Hall is largely climate driven. For the period of November through March particularly, outside temperatures are quite low and windows are seldom opened by the occupants, in spite of a large number of occupants being dissatisfied with the indoor environmental quality. Consequently, CO2 concentrations consistently exceed acceptable levels and very little air movement is recorded. [ABSTRACT FROM AUTHOR]

ASHRAE Standard 62.1 is the basis for most commercial ventilation system designs in the United States. Comparisons between the actual performance of these buildings and their designs are often difficult to find in the open literature. This paper reports carbon dioxide tracer gas measurements of ventilation rates in bars and restaurants in Minnesota prior to implementation of a statewide smoking ban. Seventy-five percent of the estimated ventilation rates were less than those required for the default occupancies of the 65 bars and restaurants sampled. On the other hand, 80% of these venues had acceptable ventilation rates based on the actual occupancies observed during the measurements. This suggests that high pollutant concentrations in the bars and restaurants were driven by large pollutant sources, not by low ventilation rates. [ABSTRACT FROM AUTHOR]

In this paper a comparative study of different configurations of refrigeration systems is presented. The main focus of the study is the comparison of energy efficiency and TEWI. The study was done by means of simulation software. According to the study a suitable system configuration with natural refrigerants not only reduces the direct global warming impact, but also improves energy efficiency. The study indicates that in comparison to two independent R404A systems for supermarket applications, an NH3/CO2 cascade system will always have superior performance, while a CO2 booster system provides best efficiency in moderate and cold climates. A R290/CO2 cascade has similar performance to the reference system (heat reclaimed not considered). Even though real system data are scarce, available studies confirm the theoretical simulations. [ABSTRACT FROM AUTHOR]

This paper aims to study the impact of introducing the return air concept into rooms conditioned by chilled ceiling displacement ventilation (CC/DV) system to save energy while limiting a time-dependent return fraction based on room load in order to maintain an acceptable air quality in the breathing zone. A transient coupled thermal and contaminant transport model is needed to assess the indoor air quality based on predicted levels of carbon dioxide concentrations in the radiant-cooled space under varying load conditions. For that reason, the Kanaan et al. (2010) contaminant transport model in CC/DV conditioned spaces is extended to transient applications that have substantial wall plumes induced by external loads. Experiments are performed to validate the extended model predictions of air quality expressed in the level of CO2 concentration in spaces conditioned by CC /DV system. Experiments are conducted in a chamber with two external walls in Kuwait Climate. Measurements are recorded in time of the air temperature and carbon dioxide concentration at selected location in the room and are compared with values predicted by the model. The experimental results agreed well with extended contaminant transport model predictions. The maximum errors in predicted CO2 concentrations are less than ± 25ppm in presence of external load. It was also found that the mixing fraction reaching up to 60% resulted in 37% less energy consumption of the system when compared with 100% fresh air CC/DV system. [ABSTRACT FROM AUTHOR]

According to the Carbon Trust of the United Kingdom, "CHP for industrial, commercial and domestic applications has the potential to make a significant contribution to energy efficiency improvements and to reducing CO2 emissions. It is a key technology needed to help meet the UK's greenhouse gas emission reduction targets and begin the transition to a low carbon economy" (CTUK 2002). CHP has the potential to reduce a facility's CO2 emissions provided there is good power and thermal load matching and a credible means to calculate these potential CO2 emissions savings. The Regional Greenhouse Gas Initiative (RGGI) is the first mandatory, market-based effort in the United States to reduce greenhouse gas emissions. Ten Northeastern and Mid-Atlantic states will cap and then reduce CO2 emissions from the power sector by 10% by 2018. Midwestern and West Coast states have created similar organizations and are expected to monetize carbon emissions. President Obama's intentions are for sweeping changes in how Americans use energy, and he has made it clear that the United States will participate in talks on the successor to the United Nations' Kyoto Protocol. The engineering community is increasingly called upon to calculate the carbon emissions impact of applying a CHP system at the design stage. This paper explores important dataset choices when comparing fuel use and CO2, SO2, and NOx emissions at the design stage for CHP systems with the electric grid in various locations throughout the United States. [ABSTRACT FROM AUTHOR]

Combined heat and power (CHP) is an efficient and clean method of providing energy services at the point of use. Instead of purchasing electricity from the local utility and burning fuel in an on-site furnace or boiler to produce needed thermal energy, an industrial or commercial user can use CHP to provide both energy services in one energy-efficient step. Consequently, CHP can provide significant energy efficiency and environmental advantages over separate heat and power. It is becoming increasingly critical that a common approach be established to estimate the fuel and CO2 emissions savings of CHP. This approach will need to recognize both outputs of the CHP system, and be able to compare the fuel use and emissions of the CHP system to the fuel use and emissions that would have normally occurred in providing energy services to the site through separate heat and power. A key factor in estimating the energy and CO2 emissions savings for CHP is determining the nature of the avoided central station generation. Should the calculation of the displaced energy and CO2 emissions be based on the all-generation average of the region the facility is located in, the all-fossil average, the average for some specific fuel type, an estimate of marginal generation, or a projection of future installed generation? This paper provides a suggested methodology for calculating fuel and CO2 emissions savings from CHP, and develops recommendations on the appropriate nature of avoided central station generation and the level of regional aggregation for accurate estimates of energy and emissions savings. The methodology for calculating fuel savings is consistent with and equivalent to the calculation of primary energy savings (PES) included in the European Union Cogeneration Directive (EU 2004). [ABSTRACT FROM AUTHOR]

Demand control ventilation (DCV) has the potential to save energy by reducing ventilation rates in accordance with occupancy levels provided by the surrogate indication of CO2 levels. However, improperly installed, designed, or operated systems may save energy at the expense of Indoor Air Quality (IAQ) or enhance IAQ at the expense of energy. These outcomes may have the potential to foul the image of an otherwise viable energy efficiency measure. This paper reports what the authors believe to be common problems in the design, installation and operation of DCV systems which use CO2 as a surrogate for occupancy levels. Six HVAC systems were investigated: two commercial offices, two medical offices, and two school environments. The design drawings, air balance reports, and current equipment set up were investigated. Four systems were controlled locally through roof top unit control logic and two systems were controlled by central building energy management systems. Functional testing of equipment was carried out and system parameters were logged including CO2 levels, fans states, and air stream temperatures. Functional testing was broken up into three system aspects. First, CO2 control signal functional testing was conducted to confirm that the control link between CO2 sensors and outside air damper positioning was in place. Second, sensor placement functional testing was conducted to confirm that the sensors placement could accurately report the CO2 levels of the controlled zone. Third, the Outside Air (OSA) level test was conducted by inspecting the air balance reports to determine the OSA rates and to confirm that the system was balanced in accordance with DCV standards. The study found that no systems were functioning properly for a number of reasons, some of which were overlapping. Reasons for non-functionality included poor sensor placement, improper information provided in mechanical schedules or design documents, fan cycling issues, and poor installation. Details on failure modes will be presented. Proper engineering documentation requirements will be explained. Test, Adjust, Balance (TAB) specifications and DCV specific requirements for TAB along with information that building operators need to know about system operation will be presented. [ABSTRACT FROM AUTHOR]

The use of CO2 in cascade refrigeration systems is increasing to achieve low temperatures, particularly in food and refrigeration industries, where understanding of the flow boiling heat transfer mechanisms is essential for heat exchanger design. This paper presents preliminary experimental results of the flow boiling heat transfer of CO2 -- lubricant mixture at low saturation temperatures varying between -30°C to -40°C, oil concentration varying between 0 - 4%, along with the effects of refrigerant vapour quality. The addition of low oil quantities to the flow (<3%) show an increase in local heat transfer coefficients at low vapour qualities (<60%), followed by a drop as the oil concentration is further increased, particularly at high vapour qualities (>80%). [ABSTRACT FROM AUTHOR]

This paper presents the experimental as well as the simulated performance studies on the transcritical CO2 heat pumps for simultaneous water cooling and heating; effects of water mass flow rates and water inlet temperatures of both evaporator and gas cooler on the cooling and heating capacities, system COP and water outlets temperatures are investigated. Study shows that both the water mass flow rate and inlet temperature have significant effect on system performances. Test results show that the effect of evaporator water mass flow rate on the system performances and water outlet temperatures is more pronounced (COP increases 0.6 for 1 kg/min) compared to the gas cooler water mass flow rate (COP increases 0.4 for 1 kg/min) and the effect of gas cooler water inlet temperature is more significant (COP decreases 0.48 for given ranges) compared to the evaporator water inlet temperature (COP increases 0.43 for given ranges). Comparisons of experimental values with simulated results show the maximum deviation of 5% for cooling capacity, 10% for heating capacity, 16% for system COP. This study offers useful guidelines for selecting appropriate water mass flow rate to obtain required system performance. [ABSTRACT FROM AUTHOR]

Carbon Dioxide (CO2), which is generally associated with green house effect and damage to the environment, can be used in the fight against ozone depletion. CO2 (R744) is a practical replacement to existing fluoro-carbon based refrigerants. Although R744 has a global warming potential (GWP) of 1, it is about 1000-3000 times lower than the GWP of most other commonly used refrigerants. This paper follows a theoretic approach to compare the performance of R744 with other natural refrigerants, employing the first law of thermodynamics, i.e., using coefficient of performance (COP). It shows the optimized pressure plots of a R744 compressor and sketches the effect of compressor performance on the COP of the refrigeration system. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive, yet easily expandable, friendly to use building appliance taxonomy. The suggested classification is part of the major four year research project Carbon Reduction in Buildings, (CaRB), involving a consortium of 5 UK. universities, to investigate the associated carbon dioxide emissions from UK. domestic and non-domestic building stock. The classification main aim is to assist understanding energy use as it facilitates the production of equipment inventories, the allocation of energy to end uses, and it supports statistical analysis. The appliance taxonomy is being used for surveying and modelling in the CaRB project, and can be applied to energy end-use surveying fieldwork and analysis of all building types. [ABSTRACT FROM AUTHOR]

Clear associations are being established between ventilation rates, indoor air quality (IAQ), and the productivity of the workforce in various types of buildings, most significant of which is the commercial and office building sector. While source control is commonly advocated as the fundamental approach to eliminating or containing the contaminant levels inside the building, a more practical and often necessary approach is likely to be exposure control. Thus, ventilation plays an important role in providing a good quality built environment. However climatic conditions pose considerable challenges in the design of air-conditioning systems, and, in a hot and humid climate, this can translate to significant energy penalty. Two considerations are highlighted in order to achieve ‘good’ IAQ and energy efficiency—the enhanced dehumidifying performance of cooling coils and the effectiveness of air distribution strategies. This paper reviews some of the current and future technologies for air conditioning and air distribution that can collectively contribute to the design of energy-efficient healthy buildings. The air-conditioning technologies reviewed include outside air pretreatment systems, single-coil twin-fan (SCTF) systems employing a compartmented cooling coil, desiccant dehumidification systems, and heat pipes. The air distribution systems reviewed include an SCTF system with independent ‘ventilation’ and ‘thermal cooling’ on zone-based demand, a personalized ventilation system coupled with secondary ambient air distribution system, a displacement ventilation system, an underfloor air distribution system, and a dedicated outdoor air system coupled with radiant chilled ceiling. Applications of some of these technologies, such as the SCTF air-conditioning and air distribution systems and personalized ventilation systems, in Singapore are presented. [ABSTRACT FROM AUTHOR]

This paper reports a study on the airborne transmission of the infectious disease(s) in the mock-up of a Boeing 767-300 aircraft cabin, using a tracer gas method with a high temporal resolution. Carbon dioxide was used as the tracer gas to simulate the pulse emitting such as coughing or sneezing of a sick passenger in a commercial aircraft. The net tracer concentration and a self-defined factor called the normalized cumulative factor (CFN) were analyzed. A detailed description of the transient airborne transmission was obtained based on the contour maps of tracer gas propagation from its release source to other locations. The distance between the release source and the receptors, the location of the release source and the total air supply rates were varied, to investigate the dependence of airborne transmission on these factors. The results showed that the close proximity between the occupants increased the exposure risk, and that the location of the release source was an important factor affecting the airborne transmission. In real aircraft, one possible way to decrease the exposure risk of the infectious diseases would be to move the release source from the center to the sides or from the back seats to the front seats. This would facilitate discharging a larger portion of the airborne pollutants directly to the return air duct before they were spread to other locations in the aircraft cabin. Increasing the total air supply rate could also lower the exposure risk. [ABSTRACT FROM AUTHOR]

Despite the higher operating pressure, carbon dioxide has attracted many researchers' attention because of its higher density, favorable heat transfer characteristics, and environmental friendliness. In order to design components and systems for carbon dioxide, a performance database should be established. As part of the efforts for developing such a performance database, a set of tests were conducted for a fin-and-tube type heat exchanger serving as a gas cooler in the transcritical cycle by using a specially designed test facility. Furthermore, to provide a better understanding of the performance ofa carbon dioxide gas cooler a set of parametric measurements at various inlet air temperatures and velocities, refrigerant mass flow rates, and operating pressures were conducted. The test results of one CO2 gas cooler are reported in the current paper. In the second phase of the study, fin-and-tube type heat exchangers (as a condenser and an evaporator) and micro channel heat exchangers (as a gas cooler a condenser, and an evaporator) will be constructed and tested. Then experimental results of those studies will serve as our design database for the CO² heat exchangers. [ABSTRACT FROM AUTHOR]

This paper presents an integrated IAQ/HVAC simulation environment that can model the impact of contaminant-based demand-controlled ventilation (DCV) strategies on both indoor air quality and HVAC system energy use for multizone buildings. The predictions of the integrated IAQ/HVAC simulation environment are first validated against experimental data obtained from laboratory testing. Then the simulation environment is used to investigate the performance of three ventilation control strategies, namely: one conventional control using fixed-position for outside air damper and two DCV strategies, including on/off control and proportional- integral-derivative (PID) control. In particular a series of parametric analyses is conducted to determine the impact of selected design and operational features of DCV strategies on both indoor air quality and HVAC system energy use. The sensitivity analysis revealed that leakage from outside air dampers, use of a temperature economizers, selection of CO2 sensors, tuning of PID controllers, and selection of CO2 set points can have a significant impaction both indoor air quality and energy consumption of HVAC systems. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the heat transfer characteristics of supercritical CO2 gas cooling down in a microchannel gas cooler over a range of operating conditions encountered in typical residential heat pumps. The microchannels used in the present study had a hydraulic diameter of approximately 1 mm. The experiments were conducted to evaluate the heat transfer performance of the microchannel gas cooler at different test conditions by varying airflow rates, air temperatures, refrigerant inlet temperatures, and mass flow rates. All experimental results are tabulated in the present paper It was found that the refrigerant mass flow rate is the dominant factor for the capacity of a CO2 gas cooler, and a significant portion of the heat transfer in a CO2 gas cooler was carried out in the heat exchanger module on the refrigerant inlet side. The temperature and pressure of CO2 significantly affect the heat transfer and fluid flow characteristics due to the fact that some important thermal physical properties of CO2 (such as specific heat, density, viscosity) are strongly dependent on its temperature and pressure. All experiments were successfully conducted with an energy balance of ± 3%. [ABSTRACT FROM AUTHOR]

Maintaining adequate indoor air quality (IAQ) in occupied spaces is important for human health and wellbeing, and it is strongly related to energy consumption. In terms of IAQ, it is usually recommended that concentrations of carbon dioxide (CO2) should not exceed 1000 ppm, total volatile organic compounds (TVOCs) not exceed 300-400 μg/m³, and PM2.5 not exceed 10 - 25 μg/m³. In practice, relatively little is known about how IAQ varies over a long timeperiod (several months to years); and economic as well as climatic challenges may limit possibilities to always maintain optimal, steady indoor conditions. Nevertheless, understanding the temporal variations that each individual building exhibit due to its location, design, condition, or use, could lead to more effective operation strategies. This study utilizes continuous time series data on CO2, TVOCs, and PM2.5 collected using IoT sensors located in the breathing zone of over 2400 spaces in about 260 buildings. About 90% of the buildings are located in Finland, and the majority of them are mechanically ventilated offices. About 45% of the spaces have been monitored for over a year, and 15% over three years. In this study, we analyzed the time series data in order to detect seasonal patterns and trends. Our results indicate these time series were stationary for 75%, 85% and 90% of the spaces regarding daily maximum CO2, TVOCs and PM2.5, respectively. We will present results from both stationary and non-stationary cases and discuss about observed differences; further analyses leading to forecasting concentrations of the IAQ parameters monitored. [ABSTRACT FROM AUTHOR]

Indoor temperature, relative humidity, particulate matter, volatile organic compounds, and carbon dioxide (CO2) concentrations were monitored continuously in the breathing zone of some 150 Finnish office buildings (average five rooms per building). For this study focusing on ventilation, we selected those 35 buildings that had data from at least six months in both 2016 and 2017. Daily outdoor air ventilation rates in each room were estimated based on the steady state / peak CO2 approach for each day when the difference between maximum and minimum CO2 concentration was > 100 ppm. In addition, we modelled relative work performance based on the daily ventilation rates. On the building level, estimated mean ventilation rates (SD) ranged from 18.4 (20.3) to 65.8 (21.6) l/s person. Temporal variations were seen by year, month and weekday, which could be partially explained by occupancy patterns and outdoor temperatures. Estimated work performance was high as compared to 6.5 l/s·person, which exceeds the minimum required ventilation rate in Finland. Thus, improving performance by increasing ventilation rates would be limited in this sample. Building owners/operators can access the monitoring results, including CO2 concentrations, almost real-time using a web-based platform, which provides them an opportunity to use these data to improve environments cost-effectively. Platforms processing raw data into estimates and, moreover, suggestions or action plans, could be beneficial. [ABSTRACT FROM AUTHOR]

A series of field studies on the performance of displacement ventilation (DV) were carried out in schools across Canada during the heating season over the last three years. Indoor air quality was evaluated using the IAQ index Contaminant Removal Effectiveness (CRE) based on carbon dioxide concentrations for three schools equipped with DV systems. Results from the three field studies have shown values of CRE to be higher than 0.7 (ventilation effectiveness specified in ASHRAE 62.1-2007 when DV systems are used for heating, with ceiling return). The measured CRE in the three schools was often greater than 1.0 even in the middle of the heating season. The results show that as long as the supply air is cooler than the room air, DV system works well in achieving good contaminant stratification and ventilation effectiveness in the space when combined with a perimeter heating system. [ABSTRACT FROM AUTHOR]

HFC refrigerants such as R-404A have come under scrutiny due to high global warming potential and relatively high leak rates in supermarket systems. In Europe, several design modifications such as cascade systems and new refrigerant choices are being investigated. One of the leading options is to employ a cascade or hybrid system using carbon dioxide (CO2) on the low temperature refrigeration side and R-134a in medium temperature. R-134a has higher efficiency than R-404A and about one third the GWP. To make even greater gains in GWP reduction, a new lower GWP refrigerant XP10 has been developed that has the potential to be retrofitted into the medium temp R-134a circuit with minimal to no system changes. This refrigerant has less than half the GWP of R-134a, has no ozone depletion potential (ODP), and is also non-flammable. It can therefore be used in existing supermarket systems with large charge sizes without concern for flammability. Toxicity has also been fully characterized and it is anticipated it will be an ASHRAE class A1 refrigerant. This report will show results of experimental performance testing compared to an R-134a baseline in a supermarket system. [ABSTRACT FROM AUTHOR]

Rooftop packaged HVAC units (RTUs) serve over 40% of commercial building space with relatively reliable air conditioner and furnace operation; however, improper settings and failed controls--especially economizers--negatively impact indoor air quality and energy use. A field survey of over 300 packaged units found 91% with at least one problem and 64% with two or more problems. To date, utility HVAC programs, codes, and green standards have focused on higher efficiency units or unit tune-ups to the exclusion of ventilation and control upgrade opportunities. Hourly simulation over a range of U.S. climates shows that a comprehensive package of RTU control retrofits produced HVAC savings between 30% and 48%--ten times the savings from incrementally higher efficiency unit replacement. The proposed RTU control retrofits make economizers more reliable, improve ventilation control, and reduce energy use. The retrofits include stand-alone direct digital controls, demand controlled ventilation with integrated fan cycling or fan speed control, premium economizer control, and ventilation lockout during warm up. Field testing showed that for RTUs, a single return air carbon dioxide sensor was as effective as multiple-room sensors in allowing demand controlled ventilation to improve indoor air quality. Field testing of four RTUs with variable speed fans and solid-state DCV controllers was extended to include six additional units that are using DDC controls with fan cycling rather than fan speed reduction. The fan cycling control algorithms are demonstrated to comply with ASHRAE Standard 62.1. [ABSTRACT FROM AUTHOR]

Experimental study of condensation of carbon dioxide in brazed plate heat exchangers is the main objective of this research project. However, it is essential to characterize the single-phase flow through these minichannel heat exchangers in order to analyze and formulate the two-phase flow. In this manuscript, the open literature on the subject is reviewed first, the facility for testing the entire system is then described, and the initial results on the single-phase flow are presented at the end. Three brazed plate heat exchangers with different interior configurations, each consisting of three channels, are considered and tested in this study. For the two-phase analysis, carbon dioxide is the working fluid, flowing through the middle channel, while dynalene is the cooling fluid, flowing through the side channels. For the single-phase analysis, data was taken using hot and cold water flow through the middle and side channels, respectively. Data was also taken using hot water in the middle and chilled dynalene in the surrounding channels. The modified Wilson plot technique was applied to obtain single-phase heat transfer coefficients, and Fanning friction factor was estimated for the pressure drop. The resulted correlations were within reasonable range of standard deviation and uncertainty, and compared well with other relevant studies. [ABSTRACT FROM AUTHOR]

For reduction of Green house Gas emissions, Polymer Electrolyte Membrane Fuel Cells (PEFC) is promoted by the government in Japan as more efficient co-generation system (CGS). On this study for the purpose of finding the efficient energy supply system with PEFC in the apartment house, first the author proposed "PEFC Apartment House" as more efficient system than the current one (boiler and electric power), which consists of PEFC-CGS, thermal storage tanks, power network and management system. Second, in order to develop the planning method of facilities with PEFC, the author has built up a database of PEFC performance by carrying out measurements at a residential house, and has developed an environmental and economical evaluation system. Third, for prediction of energy conservation and environmental effect of "PEFC Apartment House", with the evaluation system the author has predicted annual primary energy consumption and carbon dioxide emissions at a 30-unit apartment house in Tokyo. As a result, the author estimated about 14% reduction of annual primary energy consumption and about 28% reduction of carbon dioxide emissions. At last, in order to confirm an economical condition to compose this system, the relation between the price of the city gas and the profit of the energy supplier was examined. As a result, it was found that if the city gas unit price falls up to about 2.4 [yen/MJ], the profit is added and if the city gas unit price falls up to about 1.4 [yen/MJ], the investment collection years would become ten years or less. [ABSTRACT FROM AUTHOR]

Dynamic and static performance of a VAV system under different ventilation control strategies is investigated. The effect of many factors on the performance of ventilation control strategy, such as occupancy and thermal load distributions between zones, locations and number of zones served, outdoor air CO2 concentration, and PI control, is discussed. A new ventilation control strategy based on supply air CO2 concentration is proposed for multizone VAV systems. Results are compared with those of existing ventilation control strategies, such as C02-based demand-controlled ventilation and the multi-space equation strategy proposed by ASHRAE Standard 62. Simulation results made on a typical multizone VAV system show that the studied factors play an important role in selecting ventilation control strategies for better performance. [ABSTRACT FROM AUTHOR]

In low-energy building design; energy consumption due to space conditioning is responsible for over 30% of total energy consumed in commercial buildings. In an effort to evaluate low-energy building designs, two commercial office buildings were each monitored for 16 months. A comparison of the two buildings, with different ventilation strategies but located in the same climate, is presented. One is naturally ventilated without mechanical chillers, and the other uses a raised floor system combined with a chilled ceiling for space conditioning. The data were evaluated for thermal comfort, ventilation effectiveness, and energy efficiency. The buildings were of similar configuration: three stories, with a central atrium and an open floor plan, located in office parks outside of London, UK. The energy consumption for the mechanically ventilated building was significantly higher on a kWh per floor area basis (318 kWh/m2 [29.6 kwh/ft2] for the mechanically ventilated building and 216 kWh/m2 [20.1 kWh/ft2]for the naturally ventilated building), primarily due to the energy required for cooling and fan energy. The temperature of the office space also varied depending on the ventilation used. Mechanically ventilated buildings had much tighter control of the interior temperature when compared with the naturally ventilated building. Both buildings had areas for improvement to further reduce energy consumption. [ABSTRACT FROM AUTHOR]

Dedicated outdoor air systems (DOAS,) are first defined. Then the single-space operating system, whose performance is presented here, is shown to conform to that definition. The controlled components are identified, along with the minimal instrumentation needed/or control. Control of each component individually, and in the context of the whole, is presented. Supplemental controls to reduce terminal reheat energy consumption in multi-space applications are developed. Issues surrounding the use of CO2-based demand-controlled ventilation, in light of ASHRAE Standard 62.1-2004 (former addendum 62n), are presented. Finally, experimental data are presented in the overall success of the DOAS design and control to provide air distribution and thermal comfort. [ABSTRACT FROM AUTHOR]

The results of a literature survey and an engineering analysis are presented that evaluate the process, technical, and sizing considerations of photocatalytic oxidation (PCO,) as a commercial technology to treat (i.e., remove) low-level contaminants in feed streams of air PCO uses the energy of photons from light sources to activate a catalyst. Upon activation, adsorbed gases, particularly molecular oxygen (O2,), water vapor (H2O), and contaminant species, can participate in surface-mediated reactions that, under appropriate operating conditions, can produce and desorb product species, notably carbon dioxide (CO2) and H2O. Approximately 60 organic compounds have been studied in heterogeneous gas-phase PCO, while only a few inorganic compounds have been studied. With regard to commercial-scale applications, the present challenge is to design photocatalytic treatment devices that have low pressure drop, make efficient use of light, and employ a stable catalyst that can be readily regenerated if it becomes poisoned or deactivated. Presently, gas-phase heterogeneous photocatalysis will likely find application wherein (1) the gas-phase contaminants have been identified in a feed stream and demonstrated to be removed when the feed is passed through the PCO device and (2) reaction by-products have been studied and not found to be of concern. [ABSTRACT FROM AUTHOR]