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Brazed-plate heat exchangers (BPHEs) have been recently introduced in the air-conditioning industry because they could provide higher heat-transfer rate per unit volume and are more compact than conventional tube-and-shell exchangers. This paper presents experimental data of waterside fouling performance of BPHEs used in direct refrigerant- to-water condensers for cooling tower applications. The effects of refrigerant condensation temperature and water quality were experimentally investigated and asymptotic values of the fouling resistance were determined. Two saturation temperatures of 105.5°F and 120°F (~41°C and ~49°C) and two water qualities for high- and medium-fouling potentials were applied in controlled laboratory fouling experiments and BPHEs with soft chevron corrugation angles were significantly affected by these operating parameters. For hard chevron corrugation angles, the fouling resistance was still dependent on the refrigerant saturation temperature, but the degradation of the heat flux in fouled condition was only of few percents. The fouling of the plates affected the waterside pressure drop significantly, which was from 10% higher up to 11 times higher than the corresponding waterside pressure drop across the BPHE in clean conditions. The effect of the cooling tower water quality was also quantified in the present work and asymptotic values of the fouling resistance were derived for water with moderate to severe mineral scaling conditions. [ABSTRACT FROM AUTHOR]

This study measured airflow static pressure losses through nonmetallic flexible ducts in compliance with ANSI/ASHRAE Standard 120-1999, Method of Testing to Determine Flow Resistance of HVAC Ducts and Fittings. Duct sizes of 6, 8, and 10 in. (15.2, 20.3, and 25.4 cm) were tested in a positive pressure, blow-through configuration. An "as-built" test protocol expands the test configurations specified by Standard 120. Previous work by researchers at Lawrence Berkeley National Laboratories (LBNL) using draw-through configurations showed that the existing data for flexible duct losses exhibit errors greater than 70% from previously published data. Results of the current tests extend the existing ASHRAE/ACCA data for flexible duct, which do not include pressure loss data for flexible ducts that are compressed beyond approximately 4%. This study measured pressure loss at fully stretched, 4% compression, 15% compression, 30% compression, and 45% compression. The data exhibit higher pressure losses than prior ACCA or ASHRAE data. Compression ratios above 15% compression can exceed ten times the pressure loss found in fully stretched flexible duct of the same diameter. [ABSTRACT FROM AUTHOR]

This paper presents a simulation study of the energy impact and cost-effectiveness of improving envelope airtightness in low-rise US commercial buildings. Despite common assumptions, measurements have shown that typical US commercial buildings are not particularly airtight. Past simulation studies have shown that commercial building envelope leakage can result in significant heating and cooling loads. To evaluate the potential energy savings and cost-effectiveness of an air barrier, annual energy simulations and cost estimates were prepared for two nonresidential buildings (a two-story office building and, a one-story retail building) in five US cities. A coupled multizone airflow and building energy simulation tool was used to predict the energy use for the buildings at a target tightness level relative to a baseline level based on measurements in existing buildings. Predicted potential heating and cooling annual energy usage and cost savings ranged from 9% to 36% with the smallest savings occurring in the cooling-dominated climates of Phoenix and Miami. [ABSTRACT FROM AUTHOR]

Packaged HVAC equipment such as rooftop units (RTUs) often use economizers to supply fresh outdoor ventilation air and to exhaust stale building air. The fresh-air intake and the exhaust hoods are typically located very close to one another, often with the exhaust hood directly below the intake hood. In this arrangement, a portion of the exhaust air may be reentrained into the intake air under various operating conditions. This project determined the extent of reentrainment of building exhaust for a variety of wind speeds and directions, RTU designs, and surrounding structures. Experimental data were collected on three packaged rooftop HVAC units at two installation locations. One installation had one 10 ton (35 kW) RTU and an 8 ft (2.44 m) high wall obstruction that could be located either in front of the exhaust/intake hoods or at one side of the unit at distances of 5 ft (1.52 m), 10 ft (3.05 m), or 15 ft (4.57 m). The second installation had two identical 15 ton (53 kW) RTUs located 16.8 ft (5.12 m) apart, and their reentrainments were measured for each unit independently as well as from one unit's exhaust to the other's intake. Sulfur hexafluoride (SF6) was used to spike the exhaust air discharges at a known rate, and monitoring equipment measured the amount of SF6 reentrainment in the air intakes at ten-minute intervals every hour. Data were collected for each different configuration over a period of approximately one month. Computational fluid dynamics modeling was performed on both the single unit and the twin units, and fairly good agreement with the data was achieved. [ABSTRACT FROM AUTHOR]

A new pump speed control method for the primary-secondary system is developed and presented in this paper. The distribution (secondary) pump speed is controlled to maintain the optimized system resistance to make the coil valves open. The system resistance can be obtained by the pump head and the water flow rate, which is calculated by the recently developed pump water flow station (PWS). The PWS measures the water flow rate using the pump head, pump speed, and pump performance curve. This method was proved experimentally in real HVAC systems. A case study is presented in this paper for application of this new method in a continuous commissioning practice. The case study shows that the PWS can control the pump speed to maintain optimized system resistance. It can also measure the water flow rate and monitor energy consumption continuously with minimal installation and maintenance expense. The results show that the new technology can save a significant amount of pump power and increase pump efficiency. [ABSTRACT FROM AUTHOR]

Recognizing that the energy-saving potential of combined heat and power (CHP) systems is underused, the Council of the European Union has issued a Cogeneration Directive. In terms of specific guidelines and rating parameters based on energy efficiency, the objective was to promote "high-energy cogeneration." This paper makes a critical review of the Directive using the rational exergy management model (REMM), which is a common sustainability metric that can better bridge the compound benefits of CHP systems with the environment. REMM is a common rationality metric, which is an indicator of how the supply and demand exergies in the energy sector are balanced. In this respect, the primary energy savings equation of the Directive was modified in order to factor in rational exergy benefits on the environment, which remained hidden so far. Sample calculations made in the Euoropean Union (EU) FP6 Research Project HEGEL show that the rational exergy benefits in conserving primary energy resources are 62% more than what the Directive can indicate. Using parametric analyses, this study draws a new roadmap for better and optimized cogeneration systems. [ABSTRACT FROM AUTHOR]

Mass, energy, entropy, and exergy balances and exergy efficiency relations are developed for common air-conditioning processes that include simple heating and cooling, heating with humidification, cooling with dehumidification, evaporative cooling, and adiabatic mixing of airstreams. An illustrative example of a heating process with humidification is considered and the effects of air temperature and relative humidity at the inlet and exit, the temperature of steam used for humidification, and the dead state properties of exergy efficiency and exergy destruction are investigated. The results indicate that processes with low exergy efficiency and high exergy destruction have significant potential for improving performance. A parametric investigation shows that exergy efficiency and exergy destruction are very sensitive to air properties and dead state conditions. It is seen that the use of exergy in assessing HVAC&R systems can be highly advantageous, leading to technical advantages such as improved efficiency as well as environmental improvements through reduced emissions and economic benefits. Many of the benefits of applying exergy analysis are not necessarily attainable via energy methods. [ABSTRACT FROM AUTHOR]

Quantification of natural ventilation rates is an important issue in HVAC system design. Natural ventilation in buildings depends on many parameters whose uncertainty varies significantly; hence, the results from a standard deterministic simulation approach could be unreliable. This study involved performing uncertainty analyses to predict natural airflow rates. The paper presents relevant uncertainty in model parameters such as meteorological data, building properties (leakage areas of windows, doors, etc.), etc. Uncertainties of the aforementioned parameters were quantified based on data available from literature and on-site visits. The Latin Hypercube Sampling (LHS) method was used for uncertainty propagation. LHS is one of the Monte Carlo simulation techniques that is suited for our needs. CONTAMW was chosen to simulate natural ventilation phenomena in a high-rise apartment building that is typical of residential buildings in Korea. It is shown that the uncertainty propagated through this process is not negligible and may significantly influence the prediction of the airflow rates. [ABSTRACT FROM AUTHOR]

This paper presents a practical method for characterizing the static nonlinearity or gain variation in HVAC plants. The proposed method involves calculating the plant gain at different points of its input range and using the gain information to characterize the nonlinearities. Characterization of the static nonlinearity helps identify problems such as equipment oversizing, which can help in commissioning the system. A methodology is presented for cancelling the nonlinearity in software without replacing the device. This approach reduces the occurrence of oscillations caused by poor equipment sizing and provides consistent control performance across the range of the controlled device. Simulation and field results are presented to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Frank J. Dean, Jr., was a pioneer in the use of variable-air-volume systems, which are used today in nearly 70% of large commercial air-conditioning systems. He also was one of the first to utilize computer technology in air-conditioning design. His efforts in the development of low-frequency sound attenuation accelerated the growth of large central air-conditioning systems. [ABSTRACT FROM AUTHOR]

The main issues facing the supermarket refrigeration industry are the phaseout of ozone-depleting refrigerants and the improvement of refrigeration waste heat recovery. The system presented in this paper involves secondary fluid loops on both condensing and refrigerating sides, with water-to-air heat recovery heat pumps. This improved concept has demonstrated its ability to reduce by at least 82% the quantity of primary refrigerant required. It has also a considerable potential to reduce combined refrigeration and HVAC energy use in stores located in northern climates compared to multiplex refrigeration systems with more conventional heat recovery approaches. [ABSTRACT FROM AUTHOR]

Human responses and safe work time limits for persons wearing the US Army's Self-Contained Toxic Environment Protective Outfit (STEPO) with personal CO2 scrubber, O2 supply, and upper body cooling system were determined from human tests and human simulation modeling. STEPO is the Army's highest-level protective system. A rational thermal physiological model was assembled to simulate the responses and extend the human test results to other conditions. Comparisons between human and simulated responses include core and skin temperature, heart rate, thermal sensation, and water loss. Safe work time limits were until core temperature and heart rate exceeded 38.3°C (101°F) and 150 bpm. [ABSTRACT FROM AUTHOR]

This paper summarizes the results of field measurements that were conducted in four operating diesel locomotive shops. The physical geometry and ventilation system design are documented for each shop, and their usage is described. Measurements taken over a four-day period at each location are discussed, and typical data are presented. When possible, average contaminant concentrations for similar operating events are also analyzed together to provide a more complete assessment of ventilation system operation. Finally, qualitative observations gathered during the field study that may be useful to designers are discussed. These include insights on locomotive position within the shop, control issues, and the importance of temperature in certain types of design. [ABSTRACT FROM AUTHOR]

When ASHRAE Standard 52.2-1999 was written. Standard Project Committee 52.2 recognized that the first dust hading step, also called the conditioning step, was not fully adequate for revealing the drop in efficiency that electret filters undergo during actual use. This is pointed out in the standard's foreword: "The initial conditioning step of the dust-loading procedure described in this standard may affect the efficiency of the filter but not as much as would be observed in actual service." To address this issue, and a related issue with high voltage electronic air cleaners, an ASHRAE research project was undertaken. 1190-RP. "Develop a New Loading Dust and Dust Loading Procedures for the ASRHAE Filter Test Standards 52.1. and 52.2.'' An aerosol-based laboratory method was developed to reproduce the drop in efficiency that electret filters can undergo with use. The method exposes the filter to a high concentration of solid-phase (i.e., dry) submicrometer salt aerosol particles. The approach successfully reveals the drop in efficiency for both low- and high-efficiency electret filters. To address differences seen in an interlaboratory comparison, additional qualification criteria were added to the conditioning procedure; however, the adequacy of these additional criteria was not evaluated on the project. The conditioning procedure may also reduce the measured weight gain of some filters relative to the current 52.2 procedures. A draft addendum to ASHRAE Standard 52.2 was prepared. Incorporating this new conditioning procedure into the 52.2 test standard would allow the standard test to better reflect the minimum efficiency performance of electret filters that may be experienced during actual use. [ABSTRACT FROM AUTHOR]

Extensive research in the field of fault detection and diagnosis has produced useful tools and techniques that have been applied to continuously operating building HVAC systems. A few researchers have applied some of these to commissioning of new buildings. This paper reports on a project that adapted or developed models of air-handling unit components and controls and combined them into an automated functional testing tool. Operation of the tool is demonstrated in testing a real air-handling unit. [ABSTRACT FROM AUTHOR]

Fan energy use in variable-air-volume (VAV) systems can be reduced by resetting the supply duct pressure. The standard way to reset duct pressure is by controlling the most open terminal damper to a nearly open position. This strategy is rarely used because of a variety of issues including sensing limitations, network bandwidth, and stability. This paper describes the development of a new method of determining the critical supply duct pressure for VAV systems. The method relies on a short, simple functional test and a data processing technique that is based on a simple model of the system behavior The method can be implemented during normal system operation, and it could be automated. The system model includes the effect of duct leakage, which offers the potential for dual use as a duct leakage diagnostic. Results from experiments on a laboratory-scale system demonstrate good accuracy for determining critical pressure and moderate accuracy for determining duct leakage. Results from experiments on two commercial air-handling units demonstrate that the method is practical and that it offers the potential for large energy saving. [ABSTRACT FROM AUTHOR]

A metric that is paramount in today's datacom (data processing and telecommunications) facilities is reliability. It is a requirement that is often quantified by the facility decision makers. As load densities increase, the challenges to plan, implement, and operate reliable cooling systems to satisfy the associated high density loads also increase and the performance of the cooling systems is required to he much more reliable. Therefore, the need to understand the approach to developing reliable cooling systems also increases. The reliability of a cooling system for a datacom facility is not simply a quantitative .statistical calculation but also involves many qualitative practical aspects involving the design, construction, implementation, and commissioning. The purpose of this paper is to discuss some of the practical aspects of cooling system reliability and the approach that can be used to maximize it. [ABSTRACT FROM AUTHOR]

A two-dimensional steady-state mathematical model is developed from physical principles to study heat transport of a run-around heat recovery system for air-to-air heat recovery in HVAC applications. A finite difference method is employed to solve the governing equations of the cross-flow flat-plate heat exchanger, giving the outlet air properties for any inlet operating conditions. The accuracy of the model is verified by comparisons with known theoretical solutions for individual cross-flow exchangers and run-around systems. The effectiveness of each exchanger and the overall run-around heat recovery system is shown to be dependent on the dimensionless area to the thermal capacity rate. N. and the thermal capacity ratio, Cr, of the heat exchanger Designers are presented with a method to select the best operating flow rate of the coupling fluid and the dimensionless design parameters of the exchangers that will maximize the overall effectiveness and heat rate of the run-around system and allow for its part-load control. [ABSTRACT FROM AUTHOR]

The ventilation airstream required to maintain acceptable indoor air quality is typically a .significant contributor to the total heating and cooling load in commercial buildings. Demand-controlled ventilation (DCV) and enthalpy exchangers are two technologies that can be used to reduce ventilation loads and overall operating costs. This paper evaluates the operating cost savings and overall economics associated with these two different ventilation load reduction technologies for a variety of small commercial building types and climates. A specialized simulation tool was developed and utilized to perform the evaluations. Both demand-controlled ventilation and enthalpy exchangers were shown to result in significant operational cost savings as compared with fixed ventilation and no energy recovery in a number of small commercial buildings and locations. For both technologies, the savings potential and economic payback are better in more extreme climates. The opportunities are particularly great in cold climates because the ventilation load is a larger portion of the overall toad. For retrofit applications, demand-controlled ventilation (DCV) with an economizer was found to give the greatest savings in utility costs for all the buildings and climates considered. Air-conditioning utility cost savings for DCV of up to 52% were found for offices and restaurants. Payback ranged from about one to six years for most locations. Although utility cost savings were found to be less for enthalpy exchangers, they have the advantages of allowing smaller primary cooling and heating equipment for new applications and providing better indoor air quality. The operating cost savings for both DCV and enthalpy exchangers are dependent on assumptions concerning occupancy. The impact of occupancy schedules on cost savings for DCV and enthalpy exchanger systems should be considered in more detail in future studies. [ABSTRACT FROM AUTHOR]

This paper shows how a combined air-to-air heat and energy recovery system design problem can be formulated for HVAC cabinet units and solved for the least life-cycle cost system while still retaining a small time period payback. Mathematical expressions are presented to address the complicating interaction between the components of the unit to facilitate the design process. The design process is illustrated for the city of Chicago where both large heating and cooling loads occur in HVAC applications. The example design problem presented shows that payback periods of a little over a year are often achieved for retrofitted units, and the life-cycle cost savings for auxiliary heating and cooling ventilation air far exceeds the capital cost even when only a 10-year life cycle is considered. [ABSTRACT FROM AUTHOR]

The humidity of rooms and the moisture conditions of materials in the enclosure of buildings depend much on each other because of the moisture exchange that takes place over the interior surfaces. These moisture influences also depend strongly on the thermal conditions of indoor spaces and enclosure elements of buildings. In turn, the moisture and humidity conditions have significant impact on how buildings are operated. In hot, humid climates, it may be desirable to keep the ventilation rates low in order to avoid too high indoor humidity, while in cold climates, ventilation can be used to keep the humidity low enough to ensure only a small risk of moisture damage in the building enclosure. In either case, the indoor humidity has a direct or indirect impact on the energy performance of the HVAC system of a building. To analyze this situation, it is today possible to benefit from some recent developments in integrated computational analysis of the hygrothermal performance of whole buildings. Such developments have led to models for whole buildings (the indoor climate, the enclosure, and the systems), which not only predict the thermal performance, such as in contemporary building energy simulation. A growing number of building energy simulation tools have added models for transient moisture migration. The paper gives examples of two such recent developments and will highlight some calculation results that can be obtained. Finally, the paper will mention some further developments and international collaboration for the near future, introducing a proposal recommendation for a common numerical test case. [ABSTRACT FROM AUTHOR]

This paper presents an innovative oil circulation observer to estimate oil concentration and oil amount in refrigerant compressors. This model-based dynamic observer is based on oil models for the components of an air-conditioning or refrigeration system. Oil models for HVAC&R components are developed in this paper to estimate oil mass and refrigerant mass in each component. Using all of the component oil models and both heat exchanger dynamic observers, which provide the estimation of inner geometric lengths of two-phase-flow heat exchangers, a system-level dynamic observer is established by integrating all of the component models. Experimental testing has been conducted to verify the performance of this dynamic observer for steady-state operation and dynamic processes. This research on the oil circulation observer has direct applications for safe and reliable operation of residential and commercial air-conditioning and refrigeration systems. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the benefits of plenum fans and a detailed discussion of some of the pitfalls. After covering some of the benefits leading to extensive use of plenum fans, included is a brief discussion of the major complaint expressed about plenum fans, which is that plenum fans are less efficient than housed fans. Finally, the bulk of the paper covers problems that can result from poor design practices, sloppy construction, and careless handling. [ABSTRACT FROM AUTHOR]

The HVAC plenum is commonly applied as a means to reduce problematic low-frequency noise produced by mechanical equipment in ducted systems. The predicted acoustical performance has been derived from an earlier investigation (Wells 1958). This early work did not focus on low-frequency performance, the effects of wall linings, or typical geometric variables. Through the ASHRAE-sponsored research project RP-1026, conducted by Vibro-Acoustics®, rigorous testing enabled the identification of comprehensive attenuation properties for common HVAC plena. A two-stage prediction approach resulted, which applies an improved version of the Wells equation for mid- to high-frequency attenuation (5000 Hz upper frequency limit), quantified as a transmission loss (TL), and a surface area and wall characteristic model for the critical low-frequency TL (50 Hz lower frequency limit). This method has improved the prediction accuracy of flow-through type HVAC plena with a volume range of 20-1100 ft³ (0.5-30 m³). In addition, this work has identified acoustical effects for seven different wall-lining systems and typical geometric variables, such as opening offsets, opening ratio variables, and multiple openings. [ABSTRACT FROM AUTHOR]

This paper describes the validation and performance of an optimal neural network-based controller for an ice thermal storage system. The controller self-learns equipment responses to the environment and then determines the control settings that should be used. As such, there is minimal need to calibrate the controller to installed equipment. Results are verified using computer simulation as well as with the operation of a full-scale HVAC laboratory. These results demonstrate the robustness of a neural network-based controller and its ability to develop an optimal solution with minimal human interaction. [ABSTRACT FROM AUTHOR]