Coil Loads Research Articles

Incorporating novel heat recovery units into an AHU for energy demand reduction-exergy analysis

The building sector is the major energy consumer, accounting for over 40% of global energy demand. Heating and cooling together with domestic hot water energy consumption are estimated to account for 60% of the required energy for buildings’ maintenance and operation. Energy recovery is a suitable technique to tackle high energy consumption in the building. In this study, a new layout of heat recovery units installation (i.e., primary and secondary) is investigated. The main objective of this study is to reduce energy consumption in an air handling unit through the exergy analysis. Owing to adding heat recovery units, cooling and heating coil loads reduced by 7.8% and 43%, which in turn decreased the total required load of AHU by 17.84%. From the viewpoint of the second law and based on the results, incorporating the primary and secondary heat recovery units into the base AHU in hot and dry climate regions led to decrease in the total irreversibility up to 26.29%, while in hot and humid climate this figure is 14.25%. Consequently, the positive effect of using heat recovery units in the hot and dry climate region is superior to the hot and humid one.

Study of laser produced plasma in a longitudinal magnetic field

Laser produced plasma embedded in a longitudinal magnetic field was studied using a 1 MA pulsed power generator coupled with a 50 TW laser. Half turn coil loads with an internal diameter of 2.5–3.5 mm generate a 50–70 T axial magnetic field near the load. A subpicosecond laser pulse with an intensity of 1018–1019 W/cm2 irradiates a thin Si foil target in the magnetic field of the coil load. A laser produced plasma plume collimates within the longitudinal field to a narrow jet 0.2–0.3 mm in diameter with a length of 3–4 mm and an electron plasma density of (0.2–1) × 1020 cm−3 on the jet axis. The jet propagates with a velocity of 160–200 km/s in general agreement with magnetohydrodynamic simulations. X-ray spectral measurements show an increase in the plasma electron density resulting from the magnetic confinement of the jet.

Experimental platform for investigations of high-intensity laser plasma interactions in the magnetic field of a pulsed power generator.

An experimental platform for the studying of high-intensity laser plasma interactions in strong magnetic fields has been developed based on the 1 MA Zebra pulsed power generator coupled with the 50-TW Leopard laser. The Zebra generator produces 100-300 T longitudinal and transverse magnetic fields with different types of loads. The Leopard laser creates plasma at an intensity of 1019 W/cm2 in the magnetic field of coil loads. Focusing and targeting systems are integrated in the vacuum chamber of the pulsed power generator and protected from the plasma debris and strong mechanical shock. The first experiments with plasma at laser intensity >2 × 1018 W/cm2 demonstrated collimation of the laser produced plasma in the axial magnetic field strength >100 T.

Observation of impact of eddy current on laser targets in a strong fast rising magnetic field

Pulsed power generators are capable of producing strong magnetic fields. Foil laser targets for high intensity interactions with matter were characterized in a strong magnetic field produced by different types of loads. Longitudinal magnetic fields generated by coil loads were measured by Faraday rotation of the polarization plane of laser beams in a small glass sample at two wavelengths. Magnetic fields of 0.8–1.5 MG were measured in different coil loads at 1 MA current. For the first time, the impact of eddy current generated by the fast rising magnetic field with dB/dt = 109 T/s was observed in Al laser targets using shadowgraphy and interferometry. Material of the Al 10 μm foil target expanded from both sides at 0.1–0.2 mm. This effect was not observed in dielectric targets. The impact of eddy current on targets is important for designing experiments for laser plasma interactions in strong magnetic fields.

Energy benefit of a dedicated outdoor air system over a desiccant-enhanced evaporative air conditioner

The purpose of this study is to comparatively evaluate the energy performances of a dedicated outdoor air system (DOAS) and desiccant-enhanced evaporative air conditioner (DEVap) in building applications. The DOAS effectively accommodates latent cooling loads and some of the sensible cooling loads of the space by introducing cooled and dehumidified ventilation air into a building while integrating a parallel system aimed at reducing the remaining sensible load.The DEVap enhances the energy performance of a variable air volume system by reducing cooling coil loads through preconditioning of the supply air before it reaches a coil. The preconditioning is accomplished by using a liquid desiccant system and dew-point indirect evaporative cooler. In this paper, the operating and annual primary energy consumptions of both the DOAS and DEVap systems are compared based on detailed energy simulations. The results indicated the energy saving potential of DOAS to be greater than that of the DEVap. Specifically, a DOAS with ceiling radiant cooling panels experienced 20% less primary energy consumption compared to a DEVap.

Simplified thermodynamic modeling of chilled water coils based on bypass factors

This paper aims towards the development of a simple mathematical model for chilled water cooling coil based on the bypass factor as a principal input parameter. The methodology involves a temperature-based discretization of the coil that precisely shows when the coil will be dry, wet or partially wet. This procedure not only depicts the actual cooling–dehumidification profile of the coil, but also allows calculation of sensible and latent coil loads by the summations of individual loads of discrete coil elements. Maximum deviations in the range of ±5% for sensible and total coil loads are obtained between majorities of the findings from the theoretical model and experimental data available in literature. A close compliance with actual results and ease of application make this mathematical model a good choice for energy simulation tools.

재구성 다중포트 전력증폭기를 이용한 선택적 무선 전력 전송 구조

This letter presents a selective wireless power transfer architecture using a reconfigurable multi-port amplifier. The proposed wireless power transfer architecture is composed of a phase shifter part controlled by FPGA, two class-E power amplifiers, a four-port power combiner and two coil loads. Depending on the phase control of FPGA, the power ratio of outputs at the two coil loads becomes 1:1, 2:0 and 0:2. The manufactured system has delivered 1W DC power to loads at 125 kHz. The total DC-to-DC conversion efficiency shows more than 40 % including PA efficiency of 79 %.

A new theoretical formulation of dew point temperatures applicable for comfort air-cooling systems

Dew point temperature (DPT) of moist air plays a key role in ascertaining the comfort condition as well as indoor air quality for built environments. This article outlines a simple method to transform the fundamental relation between saturation pressure and temperature into a concise mathematical form for dew point temperatures of moist air that is applicable for normal comfort air conditioning systems. The error between the results from the derived equation and the ASHRAE correlation is found to be well within the accuracy limits of commonly used climatic sensors. Based on this equation, a simple computational method for wet bulb temperature (WBT) is proposed. The results from this method show minuscule error in comparison with the standard psychrometric data. Also, the DPT equation is used as a basis for plotting wet sensible and latent loads of a cooling dehumidifying coil by applying both temperature and humidity discretization schemes. Application of the inherently simple and aptly accurate DPT equation results in the representation of subtle variations in coil loads at varying psychrometric parameters of moist air, to be conclusive and theoretically conformal.

Automated tuning of an eight‐channel cardiac transceive array at 7 tesla using piezoelectric actuators

PurposeUltra-high field (UHF) MR scanning in the body requires novel coil designs due to B1 field inhomogeneities. In the transverse electromagnetic field (TEM) design, maximum B1 transmit power can only be achieved if each individual transmit element is tuned and matched for different coil loads, which requires a considerable amount of valuable scanner time.MethodsAn integrated system for autotuning a multichannel parallel transmit (pTx) cardiac TEM array was devised, using piezoelectric actuators, power monitoring equipment and control software. The reproducibility and performance of the system were tested and the power responses of the coil elements were profiled. An automated optimization method was devised and evaluated.ResultsThe time required to tune an eight-element pTx cardiac RF array was reduced from a mean of 30 min to less than 10 min with the use of this system.ConclusionPiezoelectric actuators are an attractive means of tuning RF coil arrays to yield more efficient B1 transmission into the subject. An automated mechanism for tuning these elements provides a practical solution for cardiac imaging at UHF, bringing this technology closer to clinical use. Magn Reson Med 73:2390–2397, 2015. © 2014 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Theoretical comparison of cooling loads of an air handling unit in blow-through and draw-through configurations

Blow-through (BT) and draw-through (DT) modes are the two common types of air handling unit (AHU) configurations that are prevalent in heating ventilation and air conditioning (HVAC) systems in existence. The arrangements of a supply fan and a cooling coil in these systems have advantages on each other in terms of cooling coil loads, moisture removal and noise levels. In the present work, a simple equipment load formulations for the two modes are shown, which may be used by designers for early diagnosis and decision making. From the comparison of derived loads for a cooling-dehumidifying chilled water coil, it is proved that DT type AHU shows higher cooling load than BT type, when supply air temperature from both these types of AHU is same. It is also seen that the difference between these coil-loads are actually affected by the AHU inlet condition and fan heat addition. An early choice between a DT and a BT system based on usage and requirement saves a lot of future hassles and untimely retrofits.

Energy Saving Potentials of a 100% Outdoor Air System Integrated with Indirect and Direct Evaporative Coolers for Clean Rooms

In general, HVAC systems for clean room facilities require significant energy to maintain the indoor environment. Due to high air change rates, reducing operating energy consumptions has been a critical issue. The purpose of this paper is to investigate the energy saving potentials of indirect and direct evaporative cooler assisted 100% outdoor air system (IDECOAS) serving a clean room. This research also provides a practical insight on how cooling and heating coil loads can be reduced and how to design the proposed system. In this study, it was assumed that a clean room is served by four different types of HVAC systems: a variable air volume system (VAV), an air washer system (AIRWASH), a dedicated outdoor air system (DOAS), and IDECOAS. It was found that DOAS and IDECOAS can reduce the annual cooling and heating coil loads by over 65.7% and 59.5%, respectively, compared with the VAV.

ESTIMATION OF MIXING ENERGY LOSS IN AN AIR-CONDITIONED ROOM BY A COUPLED ANALYSIS OF CFD AND HVAC SYSTEM SIMULATIONS

A coupled analysis of CFD and HVAC system simulations was carried out to assess the mixing energy loss in an air-conditioned office room where heating and cooling operate in the perimeter and interior zones simultaneously. To evaluate the mixing energy loss, we conducted two simulations; one was the case with the airflow mixing between the perimeter and interior zones and the other was the case without the airflow mixing. By comparing the required coil loads between the cases with and without the airflow mixing, the mixing energy loss was estimated. The accuracy of the coupled analysis was assessed by comparing the results with those from an experiment by Ito (1988).

Development and evaluation of optimization-based air economizer strategies

This paper describes two new strategies for controlling air economizers. The model-based control strategy uses a model to estimate the load on the cooling coil for 100% outdoor air and minimum outdoor air and transitions dampers between these two positions to minimize the load. The optimization-based control strategy uses a cooling coil model and a one-dimensional optimization routine to determine the fraction of outdoor air that minimizes the coil load. A coil model based on the contact–mixture analogy was adopted for this study and validated with experimental data. Simulations were used to compare the new economizer control strategies with traditional strategies. Simulations evaluated the sensitivity of the annual and peak cooling loads to outdoor air and return air sensor errors and climatic conditions. Incorrect control decisions stemming from sensor errors reduce the achievable energy savings and lead to higher peak hourly loads. For a scenario representative of poorly maintained sensors, the lowest annual coil loads of the economizer strategies investigated are 3.0–40.3% higher than those achieved for the ideal scenario of optimization-based control and ideal sensors (i.e., no sensor errors), and the lowest peak hourly loads for those cases are 6.8–84.1% higher than those for the ideal scenario.

A Method to Generate Effective Cooling Load Factors for Stratified Air Distribution Systems Using a Floor-Level Air Supply

A vertical temperature gradient is known to occur in an enclosure that is ventilated by stratified air distribution (STRAD) methods. Thermal stratification offers distinct energy-saving possibilities. For example, a portion of heat gains can be excluded when calculating the air supply rate and the air-conditioning load. The cooling load reduction of a heat source depends primarily on its vertical location and radiant and convective split. In this study, an effective cooling load factor (ECLF) was defined to calculate the effective heat gains, which can be used by design engineers for the determination of the reduced-supply airflow rate and reduced cooling coil loads for common- and split-return/exhaust configurations with STRAD. Numerical simulations used to obtain these factors for various internal heat sources in a small office were presented, and on-site measurements were carried out to validate the performance of computational fluid dynamics in predicting the thermal stratification in large spaces. A fully developed database of ECLFs will be very useful when designing such systems.

Primary energy and comfort performance of ventilation assisted thermo-active building systems in continental climates

This article presents a simulation study comparing the primary energy and comfort performance of ventilation assisted thermo-active building systems (TABS) relative to a conventional all-air (VAV) system in a compact office building featuring good thermal envelope performance, heat recovery, and solar gain control for the continental climate of Omaha, Nebraska with pronounced heating and cooling periods. TABS heating is accomplished using a geothermal heat pump and TABS cooling using a geothermal heat exchanger without an additional vapor compression cycle required. It was found that the coordination of the TABS and VAV systems is crucial, i.e., supply air temperature and active layer temperature setpoints and reset schedules greatly affect the performance of the overall system. The small contribution of TABS in the heating case shows the need for the adaptation of the ventilation system configuration to the TABS system. Annual cooling energy demand for the ventilation assisted TABS is higher than for the pure VAV system, which is due to lower occupied period room operative temperatures and thus a higher comfort provided. While a 4% useful energy penalty for the combined TABS/VAV was recorded, the VAV case requires 20% more delivered energy than the TABS case because of the displacement of compressor driven coil loads with low-exergy cooling through the ground heat exchanger in the TABS case. A primary energy intensity of 189 kWh/m 2 a was recorded for the TABS case; in contrast, the conventional all-air (VAV) equipped building incurs a primary energy intensity of 229 kWh/m 2a, which represents a penalty of 20%. Clear advantages of the TABS approach can be observed with respect to thermal comfort: during summer cooling periods, the mean radiant temperature of the TABS case is on average 2 K below that of the VAV case. Moreover, the VAV system is associated with a fairly constant predicted mean vote (PMV) value of 0.75, which is quite warm, while the TABS equipped system reveals an average of 0.56, which results in only 12% instead of 17% of people dissatisfied. Based on these results, ventilation assisted thermo-active cooling systems appear to be a very promising alternative to conventional all-air systems offering both significant primary energy as well as thermal comfort advantages provided the TABS is mated with low-exergy heating and cooling sources.

Quantitative single‐voxel spectroscopy: The reciprocity principle for receive‐only head coils

To correct MR spectra for local changes in the coil sensitivity for a widely used coil setup, consisting of a transmitting body coil and a receive-only head coil. The method relies on the reciprocity principle for the body coil and a correction factor for signal amplitudes between body coil and head coil. The correction is based either on the local flip angle dependence of the stimulated echo acquisition mode signal (TFC) or on the automatic RF calibration (RFC). Water phantoms of different volumes were used to simulate variable coil loads, and B1 field inhomogeneities were assessed by varying the voxel position. Furthermore, the correction was tested by longitudinal measurements in one volunteer. The correction in vitro yields a reduction of the variation coefficient of the water signal by about 77% (TFC) and 66% (RFC) for different coil loads, as well as 55% (TFC) for variable voxel positions. Slightly lower reductions were assessed for the variation coefficients of the metabolite signals in vivo. This approach adequately compensates for local changes in coil sensitivity, when acquiring MR spectra with a receive-only head coil.

東京とヨーロッパ5都市における空調機負荷特性の比較

This paper describes the simulation results of annual air conditioning load in the model office building in Tokyo and five European cities, Rome, Zurich, Paris, Frankfurt and London. The purpose of this study is to describe the characteristic of heating and cooling energy consumption in Japan in comparison with Europe where space heating is considered more important than cooling. From the comparison of annual air conditioning loads in the office building, the total load in Tokyo showed the greatest value which is 1.4 times of the total load in Paris. Since the space cooling load of office buildings is affected by solar radiation through windows and internal heat gains, the annual space cooling load is much greater than the space heating load in all cities. However, for the air conditioning coil loads, the heating load is greater than the cooling load in the most European cities due to cooling effect of outdoor air for ventilation reauirment. From the simulation results, it was confirmed that cooling is primarily important in Tokyo in comparison with the European cities where the heating shared the largest portion even for the office building.

The ITER-FEAT toroidal field structures

The magnet system of ITER-FEAT consists of 18 toroidal field (TF) coils, a free standing central solenoid, six poloidal field coils, and a set of correction coils. The TF coils are being designed to provide the magnetic field necessary to maintain plasma in a tokamak configuration with a current up to 17 MA and operate at a maximum field of 11.8 T as reported by Okuno et al. (Key Features of the ITER-FEAT Magnet System, Paper F-26, 21st Symposium on Fusion Technology, Madrid, Spain, 11–15 September 2000). The TF coil cases, which enclose the TF winding packs, are the main structural components of the magnet system. Extensive finite element (FE) analyses have been performed to investigate several design options by using 3D non-linear FE models, representing a 20° symmetry section of the TF coil magnet system. Evaluation of the results was mainly focused on the acceptability of static and cyclic stresses in the TF coil case and loads on keys/pins in the inner intercoil structures and outer intercoil structures.

A new procedure to evaluate creep data obtained by the helicoid spring specimen technique under conditions of non-viscous creep behaviour

A new procedure to obtain true creep rate—stress relation from data provided by the helicoid spring specimen technique considering non-viscous creep behaviour and redistribution of the stress across the coil wire cross-section is presented. Values of coil loads and coil deflections as measured directly in creep experiments are obviously expressed in terms of the initial elastic surface stress and surface strain rate. The creep equation proposed in the present work is transformed numerically into a relation between these integral values and fitted to experimental data. The stress distribution in the steady state is taken into account. It is shown that the true strain rate—stress relation differs markedly from the surface strain rate—initial surface stress relation when the behaviour of the creeping solid is non-viscous, e.g. when the viscous creep and power law (e.g. recovery) creep mechanisms operate in parallel and contribute to creep strain to comparable extents. Also, creep in which coupled viscous and non-viscous deformation mechanisms operate is considered.

A nomograph for estimating annual cooling and heating energy requirements in buildings dominated by internal loads

This paper describes a nomograph that can be used as a design tool for estimating annual cooling and heating coil loads in interior zones of office buildings. Based on simplified relationships between the heat load on an air-conditioning system, internal heat generation and outdoor air intake rate, the equations for normalized anuual cooling and heating coil loads in interior zones of office buildings are derived as a function of outdoor air enthalpy, two variables related to the intensity of internal cooling load, and the minimum and maximum outdoor air intake rates. Normalization of heat load on an ari-conditioning system made it possible to construct a design nomograph which can be used to calculate the energy-saving effects of an economizer cycle (passive cooling with ventilation air) and an exhaust air heat recovery unit on annual cooling and heating coil loads at the schematic design stage. Example calculations using the nomographs for three locations in Japan show that the energy-sacing effects of economizer cycle and exhaust air heat recovery units are heavily dependent on the profiles of regional weather conditions. A validation study showed that annual cooling and heating coil loads estimated from the nomographs were in good agreement with those from a detailed computer-based calculation.