Exhaust Air Stream Research Articles

Combined Mote System PM10 Emission Factors and Rates for Cotton Gins: Hope Method 201A PM10 Sizing Cyclones

This report is part of a project to characterize cotton gin emissions from the standpoint of stack sampling. The impetus behind this project was the urgent need to collect additional cotton gin emissions data to address current regulatory issues. A key component of this study was focused on EPA emission factors for particulate matter with a particle diameter nominally less than or equal to 10 µm (PM10). The 1996 EPA AP-42 emission factors were assigned quality ratings, from A (Excellent) to E (Poor), to assess the quality of the data being referenced. Emission factor quality ratings for cotton gins were extremely low. Cotton gin data received these low ratings because they were collected almost exclusively from a single geographical region. The objective of this study was to collect additional PM10 emission factor data for combined mote systems at cotton gins located in regions across the cotton belt based on EPA-approved stack sampling methodology, Method 201A. The project plan included sampling seven cotton gins across the cotton belt. Key factors for selecting specific cotton gins included: 1) facility location, 2) production capacity, 3) processing systems, and 4) abatement technologies. Two of the seven gins were equipped with combined mote systems where the 1st and 2nd stage mote system exhaust airstreams were combined. In terms of capacity, the two gins were typical of the industry, averaging 35.1 bales/h during testing. The combined mote system average emission factors for PM10 and total particulate were 0.098 kg/227-kg bale (0.215 lb/500-lb bale) and 0.141 kg/bale (0.310 lb/bale), respectively. System average PM10 and total particulate emission factors were higher than those currently published in EPA AP-42. The combined mote system PM10 emission rate test averages ranged from 2.57 to 4.28 kg/h (5.66-9.44 lb/h). The ratio of combined mote system PM10 to total particulate was 69.3%.

A study of passive ventilation integrated with heat recovery

To meet the demand for energy demand reduction in heating, ventilation and air-conditioning systems, a novel design incorporating a heat recovery device into a wind tower was proposed. The integrated system uses a rotary thermal wheel for heat recovery at the base of the wind tower. A 1:10 scale prototype of the system was created and tested experimentally in a closed-loop subsonic wind tunnel to validate the Computational Fluid Dynamics (CFD) investigation. Wind towers have been shown to be capable of providing adequate ventilation in line with British Standards and the Chartered Institution of Building Services Engineers (CIBSE) guidelines. Despite the blockage of the rotary thermal wheel, ventilation rates were above recommendations. In a classroom with an occupancy density of 1.8m2/person, the wind tower with rotary thermal wheel was experimentally shown to provide 9L/s per person at an inlet air velocity of 3m/s, 1L/s per person higher than recommended ventilation rates. This is possible with a pressure drop across the heat exchanger of 4.33Pa. In addition to sufficient ventilation, the heat in the exhaust airstreams was captured and transferred to the incoming airstream, raising the temperature 2°C, this passive recovery has the potential to reduce demand on space heating systems.

Optimization of Ammonia Absorption Using Acid Spray Wet Scrubbers

<abstract> <bold><sc>Abstract.</sc></bold> Packed-bed wet scrubbers are effective for abatement of ammonia (NH₃) emissions from animal feeding operations (AFOs) but result in high air resistance. Spray scrubbers generally have relatively low air resistance and high NH₃ removal potential. This study aimed to develop a spray scrubber module (SSM) through optimization of the design and operating parameters of spray scrubbing for recovering NH₃ emissions from the exhaust air streams of animal facilities. The design parameters, including nozzle type, scrubber column size and geometry, and number of stages of the spray scrubber module, were optimized. Effects of operating parameters such as acid concentration, superficial air velocity, retention time, and inlet NH₃ concentration were quantified. Superficial air velocity adversely affected scrubber performance significantly due to its direct relationship with air residence time. The inlet NH₃ concentration was inversely proportional to the scrubber efficiency. The SSM was optimized as a hexagonal scrubber column with a diameter of 45.7 cm (18 in.) equipped with three stages of PJ40 spray nozzles, spraying 1% (w/v) H₂SO₄ scrubbing liquid counter-current to the exhaust air stream with superficial gas velocity of 3 to 4 m s^-1, equivalent to air retention times of 0.55 to 0.41 s. The SSM recovered about 91% of the NH₃ at an operating liquid pressure of 0.51 MPa, a superficial air velocity of 4 m s^-1, and an inlet NH₃ concentration of 30 ppm_v when operated with a single stage of spraying. For high inlet NH₃ concentration of 100 and 400 ppm_v, the SSM was able to reduce NH₃ by 86% and 74%, respectively, when operated at a maximum pressure of 0.62 MPa with three stages of spray nozzles and a superficial air velocity of 4 m s^-1. The pressure drop of the spray scrubber was mainly caused by the mist eliminator. The total static pressure drop of the SSM was under 15 Pa when the air velocity ranged from 2 to 4 m s^-1. The results of this study demonstrate that acid spray scrubbers could be a very effective and feasible NH₃ mitigation technology for U.S. animal farms.

Thermo-economic performance of a solar membrane liquid desiccant air conditioning system

A solar membrane liquid desiccant air conditioning (S-M-LDAC) system is proposed and investigated in this study. Liquid-to-air membrane energy exchangers (LAMEEs) are used for humid air dehumidification and dilute desiccant solution regeneration in the S-M-LDAC system. This eliminates the problem of desiccant droplets carry over in supply and exhaust air streams, which limits the wide use of conventional direct-contact liquid desiccant air conditioning systems in commercial/residential applications. Eight systems configurations, which mainly differ in the heating and air systems, are simulated using the TRNSYS building energy simulation software. Four heating systems are investigated as follows: (i) natural gas boiler, (ii) electrical heat pump, (iii) solar thermal system (STS) with natural gas boiler backup, and (iv) STS with electrical heat pump backup. Two air systems are studied – one with and one without an energy recovery ventilator. Parametric studies are performed to study the influences of the collector area and storage volume of hot water tank relative to collector area on the annual solar fraction, annual collector efficiency and life cycle cost. The size of the STS is optimized to give the lowest life cycle cost, and then the economic and environmental performances are evaluated for the systems studied by calculating the initial cost, annual operating cost, life cycle cost, payback period and annual CO2 emissions. Results show that using a STS to cover the thermal energy required to regenerate the dilute desiccant solution significantly improves the economic and environmental performances of the systems studied, with more significant reductions when a natural gas boiler is used as the backup heating system and there is no energy recovery ventilator.

Heat recovery in an air-conditioning system with air-to-air heat exchanger

In comfort applications, air-to-air heat exchangers (HEs) lower the enthalpy of the building supply air during warm weather and raise it during cold, by transferring energy between the outdoor ventilation and exhaust airstreams. In this paper, a 250 person capacity auditorium located in Thessaloniki, Greece, is used as a model to calculate (i) the heating and cooling energy that can be recovered, (ii) the reduction in heating, ventilation, and air conditioning equipment, and (iii) the expected payback period from the installation of a fixed-plate, cross-flow HE in the air-handling unit of the system. An energy analysis with the modified bin method energy calculation was used to compare the energy consumption with and without HE, and with full or half occupancy. It is proved that, at the climatic conditions of Thessaloniki much more heating than cooling energy can be recovered and that the payback period of the HE is between 1 and 2 years.

Formaldehyde transfer in residential energy recovery ventilators

The rotary enthalpy wheel design used in many energy recovery ventilators (ERVs) is designed to transfer heat and moisture between supply and exhaust air streams. The wheel, however, can also transfer formaldehyde and other indoor contaminants from the exhaust stream to the supply stream through air leakage, entrainment in the porous wheel, and adsorption/desorption to the filter medium. This contaminant transfer reduces the benefit of the mechanical ventilation provided by the device. Field and chamber experiments were used to quantify the formaldehyde transfer efficacy (the fraction of formaldehyde transferred from the exhaust stream to the supply stream) in a common ERV model under varied conditions. In field experiments, the transfer efficacy was approximately 29%. Chamber tests showed formaldehyde transfer efficacy between 10 and 29%. The bulk of the transfer was due to air leakage and entrainment within the wheel, with up to 30% of the transfer attributed adsorption/desorption from the filter medium. The transfer efficacy decreased with increasing air exchange rate and supply air temperature. The transfer efficacy increased as the supply and exhaust streams were unbalanced in flow rate. Overall, the air leakage through the device substantially exceeded the product rating of 10%, with 27–28% air leakage measured in field experiments and 12–19% air leakage in chamber experiments.

Storage Method Impacts on Ammonia Flux from Broiler Cake and Acid Scrubbers for High Ammonia Concentration Measurements

Ammonia emissions from poultry farms, including waste stockpiles, can degrade the environment and may be regulated in the USA. The main purpose of this study was to see how different poultry waste storage methods impacted ammonia loss. During a 13-day lab study, ammonia flux from uncovered (Control), covered with an inexpensive blue tarpaulin (Tarp), and stockpiles twice the depth of the Control stockpiles (Double-depth) were compared. Ammonia concentrations in the exhaust airstream from the stockpiles were measured using boric acid scrubbers. Ammonia loss per unit surface from the Tarp treatment was 45 % lower than the other treatments, while on a volume basis, losses from the Tarp and Double-depth treatment were 45 % vs. the Control stockpile. A less-pervious cover might have reduced ammonia losses even more. Ammonia flux per unit area from the Control and Double-depth treatments were comparable to those from large stockpiles in a shed monitored in a companion study though flux per unit volume was much higher from the lab stockpiles due to larger surface area per unit volume. Therefore, compared with a flatter stockpile, a more compact stockpile with a lower surface area per unit volume would have lower ammonia loss. Ammonia diffusion from the core of the stockpile to the surface may control ammonia flux, even in larger stockpiles in the short term (≤15 days), with nitrogen mineralization playing a smaller role. The 250-mL 3 % boric acid scrubbers were suitable for sampling air streams with ammonia concentrations up to 1,000 mg m−3 at 25 °C. At 25 °C, three moles of boric acid seemed adequate for each mole of ammonia to be trapped.

Annual evaluation of energy, environmental and economic performances of a membrane liquid desiccant air conditioning system with/without ERV

In this study, a membrane liquid desiccant air conditioning (M-LDAC) system is modeled using the TRNSYS building energy simulation software. Liquid-to-air membrane energy exchangers (LAMEEs) are used as a dehumidifier and regenerator in the proposed M-LDAC system to eliminate the carryover of desiccant droplets in supply and exhaust air streams, which may occur when direct-contact conditioners are used. A sensitivity study on the sensible, latent and total effectivenesses of the LAMEEs is performed under 36 operating and design conditions. The technical, environmental and economic performances of the proposed M-LDAC system are evaluated, and compared to those of a conventional air conditioning (CAC) system. The influences of installing an energy recovery ventilator (ERV) under balanced and unbalanced airflow rates conditions are investigated. Results show that the annual primary energy consumption and the life cycle cost (LCC) of the proposed M-LDAC system are 19% and 12% lower than that of the CAC system, and they reach 32% and 21% when an ERV, which operates under balanced airflow rates, is installed in the M-LDAC system.

Contaminant transfer in run-around membrane energy exchangers

The run-around membrane energy exchanger (RAMEE) is a novel membrane-based energy recovery system, which uses liquid desiccant to transfer heat and moisture between air streams. VOCs may transfer from the exhaust air to supply air due to (i) air leakage and (ii) dissolution of VOCs into liquid desiccant in the exhaust exchanger and subsequent evaporation into air stream in the supply exchanger. Experimental tests were conducted at different operating conditions using two RAMEE prototypes. Sulfur hexafluoride (SF6) was used as tracer gas to test air leakage, and toluene (C7H8) and formaldehyde (HCHO) were used to test VOC transfer fraction. Results show that the exhaust air transfer ratio (EATR) of SF6 was 0.0±3.6% for both prototypes, which means the air leakage is negligible. The transfer of C7H8 was 2.3–3.4±3.5%, while the transfer of HCHO was 4.5–6.4±3.6% in the prototypes. It implies that there is a negligible transfer of low water soluble VOCs (i.e. C7H8), but possibly a small detectable transfer of very water soluble VOCs (i.e. HCHO) between the exhaust and supply air streams in RAMEEs. Moreover, the EATR values for both prototypes were insensitive to changes in air flow rate, liquid desiccant flow rate, latent effectiveness and environmental conditions.

Improving heat recovery using retrofitted heat pump in air handling unit with energy wheel

The world is facing a challenge to reduce energy use to meet the environmental goals set for the future. One factor that has a great impact on the energy performance of buildings is the ventilation losses. To handle these losses, heat recovery systems with rotating heat exchanger are often implemented. These systems have been shown to recover about 60–70% of the energy in the exhaust air on an annual basis.After a heat recovery system is installed it is hard to improve the efficiency of the installed recovery system with an acceptable economic payback period. In the present paper one way to improve the energy performance of a building with this type of heat recovery system by the use of a heat pump is investigated by simulations in TrnSys.The heat pump system is arranged so that the evaporator is connected to a heat exchanger mounted in the exhaust airstream after the energy wheel, and the condenser of the heat pump is mounted so that the temperature of return water from the heating coil is increased.The simulations show that there is a possibility to increase the heat recovery rate of the air handling unit in a significant way by retrofitting a heat pump to the system.

Combining liquid desiccant dehumidification with a dew-point evaporative cooler: A design analysis

This article uses a numerical model to analyze a concept combining a liquid desiccant dehumidifier with a dew-point indirect evaporative cooler. Each of these components, or stages, consists of an array of channel pairs, where a channel pair is two air channels separated by a thin plastic plate. In the first stage, a liquid desiccant film lining one side of the plates removes moisture from the process (supply-side) air through a membrane. An evaporatively cooled exhaust airstream on the other side of the plastic plate cools the desiccant. The second stage sensibly cools the dried process air with a dew-point evaporative cooler. This article uses a parametric analysis to illustrate the key design tradeoff for this concept: device size (a surrogate for cost) versus energy efficiency. The analysis finds the design parameters with the largest effect on this tradeoff and finds the combinations of design parameters giving near-optimal designs, which are designs with the highest efficiency for a given device size. The results indicate that there are two key parameters contributing to this tradeoff: the supply-side air channel thickness and the exhaust-air flow rate in the evaporative cooler.

Dichloromethane emissions from automotive manufacturing industry in Iran: case study of the SAIPA automotive manufacturing company

The primary data about the role of automotive manufacturing industry in emitting dichloromethane (DCM) to the environment in Iran are provided by a case study of SAIPA Automotive Manufacturing Company in 2012. The average emission rate and emission factor of DCM in the stack exhaust air streams of the solvent-based automotive painting plant were 6.8 kg·d−1 and 19.5 g per car, respectively. The spray booths had the highest portion (about 85%) of DCM emission in the stack exhaust air streams. The average concentration of DCM (± standard deviation) in the generated wastewater of the factory was 64 ± 12 μg·L−1, but in the effluent of the factory wastewater treatment plant, it was reduced to a nondetectable level. DCM was also observed in three groundwater wells out of five monitored water resources. To control DCM emission and prevent pollution, the replacement of solvent-based paints with water-based paints is highly recommended.

A hybrid energy efficient building ventilation system

The present paper presents a high performance cooling/heating ventilation system using a rotary heat exchanger (RHE), together with a reverse-cycle heat pump (RCHP) that can be integrated with various heat sources. Energy consumption in the building sector is largely dominated by the energy consumed in maintaining comfortable conditions indoors. For example in many developed countries the building heating, ventilation and air conditioning (HVAC) systems consume up to 50% of the total energy consumed in buildings. Therefore energy efficient HVAC solutions in buildings are critical for realising CO2 targets at local and global level. There are many heating/cooling concepts that rely upon renewable energy sources and/or use natural low temperature heat sources in the winter and heat sinks in the summer. In the proposed system, waste energy from the exhaust air stream is used to precondition the outdoor air before it is supplied into the building. The hybrid system provides heating in the winter and cooling in the summer without any need for additional heating or cooling devices as required in conventional systems. Its performance is better than a typical reheat or air conditioning system in providing the same indoor air quality (IAQ) levels. It is shown that an energy saving up to 60% (heat energy) is achieved by using the proposed hybrid system in building ventilation applications.

Analytical model based performance evaluation, sizing and coupling flow optimization of liquid desiccant run-around membrane energy exchanger systems

A run-around membrane energy exchanger (RAMEE) is a novel energy recovery system which can avoid carryover of desiccant solution while transferring both heat and moisture between non-adjacent supply and exhaust air streams. In this study, an analytical model for a flat-plate counter-cross-flow liquid-to-air membrane energy exchanger (LAMEE) is compared with experimental test results and numerical simulations for a single LAMEE and a RAMEE system under various operating conditions. Agreements are obtained among the analytical, experimental and numerical results. The effectiveness of a RAMEE system under balanced and unbalanced airflow conditions is evaluated by using the analytical model. Optimization studies for exchanger size and solution flow rate in RAMEE systems are investigated. Results show that RAMEE systems with equal-sized supply and exhaust exchangers can achieve the highest effectiveness in most conditions for both balanced and unbalanced airflow. Optimization control of the solution flow rate can enhance annual energy recovery rate up to 7%.

Influence of constructive parameters on the performance of two indirect evaporative cooler prototypes

Two equally-sized cross-flow heat-exchanger prototypes have been designed with a total heat exchange area of 6 m2 and 3 m2 respectively, constructed with polycarbonate hollow panels of different cross section. They are connected into a heat-recovery cycle within the whole experimental setup constructed for the tests, which mainly consists of: an Air Handling Unit to simulate the outdoor airstream conditions, a conditioned climate chamber, and a water circuit to provide the water supply required. They have been experimentally characterised in two operating modes in order to determine how evaporative cooling improves heat recovery in each case, focussing on the influence of modifying the constructive characteristics. To perform the evaporative cooling process, water is supplied to the exhaust airstream. Results are studied considering how constructive issues, outdoor air volume flow rate and temperature, as well as operating mode influence on the performance obtained. An Analysis of Variance shows how outdoor airflow has a key role in the performance of the systems; whereas entering outdoor air temperature determines cooling capacities. Improvements introduced by larger heat exchange areas compensate with their corresponding smaller cross sections, which hinder water–air distribution on the exhaust air side of the heat exchanger. Finally, these small devices achieve cooling capacities of up to 800 W, being able to partly support ventilation load and achieving around 50% of energy saving in ventilation cooling.

A desiccant-enhanced evaporative air conditioner: Numerical model and experiments

This article presents modeling and experimental results on a recently proposed liquid desiccant air conditioner, which consists of two stages: a liquid desiccant dehumidifier and an indirect evaporative cooler. Each stage is a stack of channel pairs, where a channel pair is a process air channel separated from an exhaust air channel with a thin plastic plate. In the first stage, a liquid desiccant film, which lines the process air channels, removes moisture from the air through a porous hydrophobic membrane. An evaporating water film wets the surface of the exhaust channels and transfers the enthalpy of vaporization from the liquid desiccant into an exhaust airstream, cooling the desiccant and enabling lower outlet humidity. The second stage is a counterflow indirect evaporative cooler that siphons off and uses a portion of the cool-dry air exiting the second stage as the evaporative sink. The objectives of this article are to (1) present fluid-thermal numerical models for each stage, (2) present experimental results of prototypes for each stage, and (3) compare the modeled and experimental results. Several experiments were performed on the prototypes over a range of inlet temperatures and humidities, process and exhaust air flow rates, and desiccant concentrations and flow rates. The model predicts the experiments within ±10%.

Application of neural networks to predict the transient performance of a Run-Around Membrane Energy Exchanger for yearly non-stop operation

Application of soft computing methods (i.e. neural networks and genetic algorithms) for modeling and controlling the dynamic and transient behavior of systems has been increasing during the last decade. In this study, a neural network (NN) model is developed to predict the transient heat and moisture transfer performances (i.e., the sensible and latent effectivenesses) of a novel HVAC energy exchanger, called the Run-Around Membrane Energy Exchanger (RAMEE), which is able to transfer both heat and moisture between exhaust and supply air streams. The training data set for the NN model covers a wide range of outdoor conditions and system parameters and is produced using a Transient Numerical Model (TNM) that has been experimentally validated for some transient applications. Two separate NNs (one for sensible and one for latent energy transfer) each with 12 inputs and one output, are selected to represent the RAMEE. The ability of NN models to predict the performance of a given RAMEE design in different climates is numerically validated. The mean absolute difference (MAD) between the results of TNM and NN models for different locations are 0.5 °C for the sensible model and 0.2 gv/kga for the latent model, which indicates satisfactory agreement for energy exchange calculations. These NN models are very fast and easy to use therefore, they might be used for design purposes or estimating the annual energy savings in different buildings with continuous operation and a RAMEE in their HVAC system.

QUALITY IMPROVEMENT OF INDOOR AIR BY USING HEAT RECOVERY WHEEL

An energy recovery device transfers sensible and latent heat between the exhaust and supply air streams of a building. There are several different types of energy recovery devices utilize for this project. A rotary air-to-air energy exchanger that can transfer both sensible and latent heat. Two Air Conditioning systems will be studied - one without an energy wheel (termed as the base case) and one with an energy wheel. The air conditioning system is based on the vapour compression refrigeration system. There are various heat recovery devices which gives the different methods of heat recovery. There are two main purpose of this research project. The first is to determine the relaxed relative humidity levels temperature in a building and class room can be possible using an energy wheel. The second is to determine whether any energy and cost savings can be realized with the use of an energy wheel. Keyword: Indoor Air Quality, Energy Recovery, Wheel Selection, Cost Analysis.

Energy performance of a lightweight opaque ventilated façade integrated with the HVAC system using saturated exhaust indoor air

The energetic performance of an integrated system basically consisting of an adiabatic humidifier, a lightweight mechanically ventilated opaque façade equipped with a direct evaporative air-cooling device, and an air-to-air heat exchanger for energy transfer from the outdoor airstream to the exhaust airstream leaving the air space, is analyzed numerically using an in-house-developed computer code. The minor energy consumptions with respect to a basic configuration consisting of a traditional closed cavity wall and a recovery equipment wherein energy is transferred from the outdoor air to the exhaust air extracted from within the building, are also calculated by introducing a cooling performance index and discussed in full details. A dimensional empirical correlation that expresses such cooling performance index as a function of the several independent variables considered is also proposed.

Odor and Odorous Chemical Emissions from Animal Buildings: Part 6. Odor Activity Value

There is a growing concern with air and odor emissions from agricultural facilities. A supplementary research project was conducted to complement the U.S. National Air Emissions Monitoring Study (NAEMS). The overall goal of the project was to establish odor and chemical emission factors for animal feeding operations. The study was conducted over a 17-month period at two freestall dairies, one swine sow farm, and one swine finisher facility. Samples from a representative exhaust airstream at each barn were collected in 10 L Tedlar bags and analyzed by trained human panelists using dynamic triangular forced-choice olfactometry. Samples were simultaneously analyzed for 20 odorous compounds (acetic acid, propanoic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, hexanoic acid, heptanoic acid, guaiacol, phenol, 4-methylphenol, 4-ethylphenol, 2-aminoacetophenone, indole, skatole, dimethyl disulfide, diethyl disulfide, dimethyl trisulfide, hydrogen sulfide, and ammonia). In this article, which is part 6 of a six-part series summarizing results of the project, we investigate the correlations between odor concentrations and odor activity value (OAV), defined as the concentration of a single compound divided by the odor threshold for that compound. The specific objectives were to determine which compounds contributed most to the overall odor emanating from swine and dairy buildings, and develop equations for predicting odor concentration based on compound OAVs. Single-compound odor thresholds (SCOT) were statistically summarized and analyzed, and OAVs were calculated for all compounds. Odor concentrations were regressed against OAV values using multivariate regression techniques. Both swine sites had four common compounds with the highest OAVs (ranked high to low: hydrogen sulfide, 4-methylphenol, butyric acid, isovaleric acid). The dairy sites had these same four compounds in common in the top five, and in addition diethyl disulfide was ranked second at one dairy site, while ammonia was ranked third at the other dairy site. Summed OAVs were not a good predictor of odor concentration (R2 = 0.16 to 0.52), underestimating actual odor concentrations by 2 to 3 times. Based on the OAV and regression analyses, we conclude that hydrogen sulfide, 4-methylphenol, isovaleric acid, ammonia, and diethyl disulfide are the most likely contributors to swine odor, while hydrogen sulfide, 4-methyl phenol, butyric acid, and isovaleric acid are the most likely contributors to dairy odors.