Make-up Air Unit Research Articles

Demonstration of the carbon capture with building make-up air unit

Building-integrated carbon capture technology has the potential to reduce the cost of CO2 capture while improving indoor air quality (IAQ). To promote the adoption of CO2 capture in a building environment, this study investigated the possibility of integrating carbon capture technology with an existing rooftop make-up air unit (MAU) system to trap CO2. Here, a modular compact CO2 capture system containing amine-functionalized polymer fibers was examined. The system, which was installed at the exhaust of the MAU, captures CO2 before it leaves the building to enter the atmosphere as a greenhouse gas. The demonstrated average amount of CO2 captured was 1.1–1.4 mmol/g of absorbent material. Techno-economic analysis (TEA) was further performed on the CO2 capture system, considering material costs, energy costs, as well as transportation and regeneration costs. These results were then used to estimate the levelized cost per ton CO2 captured (LCOC). To achieve LCOC below $100/t-CO2, adsorbents should have working capacities of 4.9 t and 3 t-CO2/year for 5 years and 10 years of operation, respectively. In summary, this study highlights a viable path toward the decarbonization of the commercial buildings sector and provides quantitative performance and economic insight on the suitability of building-integrated carbon capture technology.

Integrated on-site collection and off-site analysis of airborne molecular contamination in cleanrooms for integrated circuit manufacturing processes

Both long-term on-site collection and off-site analysis methods were conducted to investigate airborne molecular contaminants (AMCs) in a semiconductor wafer cleanroom. The removal efficiency of SO2 and NO2 for chemical filters on a make-up air unit (MAU) in the cleanroom is approximately 50%, though this value does not meet the removal efficiency mentioned in the GB 36306 standard. The removal efficiencies of SO2, H2S, NO, NO2, NH3, and TVOC were approximately 76.5%, 50.9%, 83.5%, 99.3%, 94.8%, and 97.1% after the fan filter unit (FFU) was equipped with a chemical filter. AMCs mainly include benzene, toluene, ethylbenzene, xylene (BTEX), alkanes and alkenes, though BTEX accounts for 77% of the total. VOC concentrations in cleanrooms fitted with FFU chemical filters and where the process equipment was not in operation were found to be lower than those at domestic residences and slightly higher than those found in commercial aircraft cabin air. The daily average TVOC concentrations were negatively correlated with temperature (R2 = 0.46, p < 0.01) and positively correlated with humidity (R2 = 0.26, p < 0.01). The daily average NH3 concentrations were negatively correlated with T (R2 = 0.19, p < 0.05) and positively correlated with RH (R2 = 0.18, p < 0.01). Dibutyl phthalate (DBP) and dioctyl phthalate/diethylhexyl phthalate (DOP/DEHP) were detected in the new sealing joint strips in the HEPA filters. Phthalates and organophosphates were not detected in the new filter papers.

Studies on the control of kitchen pollutants by exhaust hood with air-filled slots

The make-up airflow organization is considered to be another important influencing factor for the capture performance of range hoods. Existing research has focused on the effect of make-up air devices on the performance of wall-mounted exhaust hoods and indoor air quality, and little research has been done on the parameters of make-up air devices. This article proposes a kitchen exhaust system make-up air method to improve the performance of the exhaust hood by establishing an air curtain between the stove and the exhaust hood. Numerical simulations were used to compare the airflow organization conditions of the kitchen with air-filled slots and no active make-up air conditions, and determines the influence of the width of the air-filled slot, the jet velocity and the exhaust air volume of the exhaust hood on the effect of the make-up air. It proves the positive influence of the air-filled slots on the performance of the exhaust hood. And according to the simulation results, an air-filled slot with a width of 20 mm was selected for experimental verification. The results show that when the air volume of kitchen exhaust system is 0.06 m3/s, the combination of 20 mm wide band exhaust and 0.08 m3/s exhaust has the best effect. This research establishes the optimal operating conditions of the island exhaust hood make-up air unit and improves the kitchen airflow organization.

Ground heat exchanger thermal imbalance prevention using dynamic long-term ground temperature predictions

ABSTRACT The authors present the development of a novel software and hardware package that dynamically predicts future ground heat exchanger temperatures to avoid thermal imbalance and future ground source heat pump system failure. In this study, an energy meter was installed on the ground heat exchanger of an office building and software was created on a remote server that collected the measured data. The future ground temperature was dynamically calculated, and the prototype was integrated with the building automation system to prevent future ground source heat pump system failure. The results showed that the building was cooling dominate and if the current mechanical system operation continued, the system would become inefficient in 16 years from high inlet temperatures to the heat pumps. A control sequence was developed for mitigating ground heat exchanger failure on the studied building. It was also determined by adjusting the set-point temperature of the make-up air unit from 12.8°C to 4.8°C, the amount of heating performed by the ground source heat pump system would increase to 49,230 kWh which maintained the calculated 20-year ground heat exchanger temperature below 32°C. The prototype developed in this paper is critical for maintaining an efficient ground source heat pump system and adequate ground heat exchanger temperatures. The outcome of this study provides the solution of ensuring a successful adoption of sustainable green technology on a large scale and eliminates ground source heat pump system failure due to thermal imbalance.

Feasibility analysis of canceling reheating after condensation dehumidification in semiconductor cleanrooms

Cold-heat offset problem occurs due to reheating after condensation dehumidification in the make-up air unit (MAU) of semiconductor cleanrooms . This study conducted on-site measurement and analyzed the indoor thermal balance in five tested factories A-E. Based on the measured results, this study focuses on the feasibility analysis of canceling reheating to avoid cold-heat offset. It is indicated indoor condensation will not be caused in the cleanrooms. Indoor subcooling is determined by air change rates of outdoor air ( A a ) and supplied indoor air ( A s ), and heat dissipation of indoor equipment ( Q in ). The larger A a , the less A s and the less Q in , the more likely indoor subcooling will be caused. When Q in is 0–100 W/m 2 , 100–200 W/m 2 and larger than 200 W/m 2 , the requirement range of A a to avoid indoor subcooling is 7–21/h, 12–26/h and 20–26/h respectively. It is concluded that canceling reheating is possible when factories A-D is within the operating parameters. In factory E, canceling reheating is impossible since indoor subcooling is unavoidable. The performance and energy saving potential of the proposed system which cancels reheating are then analyzed. Compared with the conventional system, the required cooling capacity and heating capacity are both decreased, and the energy saving ratio of the proposed system is 10.4%–38.3%. • Cold-heat offset is prominent in both make-up unit and entire system. • Canceling reheating will not cause indoor condensation, but may indoor subcooling. • Low outdoor air change rate and high sensible load do good to canceling reheating. • Energy saving ratio of the canceling reheating system is 10.4%–38.3%.

Performance analysis and energy saving potential of air conditioning system in semiconductor cleanrooms

Large energy consumption of air conditioning system occurs in semiconductor cleanrooms due to high demand for the control of temperature and humidity ratio. This study focuses on the operating performance and energy saving potential of the air handling process. On-site measurements of the air conditioning system were conducted in different seasons. The results reveal that cold-heat offset problem occurs in the current air conditioning system in summer, including 41.7% cold-heat offset between the heating in the make-up air unit (MAU) and cooling in the dry cooling coil (DCC), and 16.4% cold-heat offset in MAU. Feasibility of removing reheating in summer is simply verified. In winter, DCC has the potential to recover indoor heat for preheating the outdoor air. Therefore, high temperature chillers (Method A), canceling reheating (Method B) and heat recovery design from DCC system to MAU (Method C) are the energy saving methods adopting in this study. In order to analyze the annual energy saving potential of the proposed system, a dynamic calculation model is established. Cooling in DCC (Qc,DCC) is 42.8%–54.1% less than the current system annual. Heating in MAU (Qh,MAU) is 52.8%–94.3% less than the current system in transition season and winter (N ov.–Apr.), and is no required in summer (May–Oct.) in the proposed system. The proposed system can save 621 kWh/m2 annual, which is 20.2% less than the current system. It is indicated that both removing reheating and adopting heat recovery system in the current cleanrooms have certain energy saving significance.

Study on the Brine Storage Design During the Engine Running in the Climatic Facility

The engine will consume a large amount of air in the climatic environment facility when the engine is running in the test. The pressure in the chamber may decrease and the temperature in the chamber will change. In order to ensure the continuity and safety of the climatic test, the jet engine make-up air unit (JMAU) will compensate the cold/heat to guarantee the continuous and effective performance of the engine start-up test. Therefore, we should design the brine storage to ensure the supply of the brine.

Energy savings approaches for high-tech manufacturing factories

This study integrates a fab energy simulation (FES) tool and energy conversion factors to analyze energy consumption and identify energy savings opportunities of high-tech manufacturing factories. The data used is the 169,124 MW h annual energy consumption of a Taiwanese semiconductor manufacturing fab. We proposed a compressed/clean dry air (CDA) system as a two-pressure system using a heated-type dryer. The proposed method achieved 3050 MW h as the highest energy savings in the CDA system compared to the original fab data. The results also indicate that lowering the make-up air unit (MAU) operating temperature caused significant energy savings for the high-temperature water chiller system. When the outlet air temperature of the MAU system was 14 °C, the maximum energy savings were 3532 MW h. In addition, the process cooling water (PCW) system could potentially save energy by reducing the pumping head of water in its open system. Therefore, we suggested a closed PCW system that reached a maximum energy saving of 1541 MW h.

水熱源ヒートポンプユニットを用いた個別分散型空調システムに関する研究(第1報)低温再生デシカントロータを用いた水熱源外気処理ユニットの性能評価

水熱源ヒートポンプユニットを用いた個別分散型空調システムに関する研究(第1報)低温再生デシカントロータを用いた水熱源外気処理ユニットの性能評価

Energy-Saving Benefits of Adiabatic Humidification in the Air Conditioning Systems of Semiconductor Cleanrooms

This paper aimed to evaluate the applicability of adiabatic humidification in the heating, ventilation, and air conditioning (HVAC) systems of semiconductor cleanrooms. Accurate temperature and humidity control are essential in semiconductor cleanrooms and high energy consumption steam humidification is commonly used. Therefore, we propose an adiabatic humidification system employing a pressurized water atomizer to reduce the energy consumption. The annual energy consumption of three different HVAC systems were analyzed to evaluate the applicability of adiabatic humidification. The studied cases were as follows: (1) CASE 1: a make-up air unit (MAU) with a steam humidifier, a dry cooling coil (DCC), and a fan filter unit (FFU); (2) CASE 2: a MAU with the pressurized water atomizer, a DCC, and a FFU; and (3) CASE 3: a MAU, a DCC, and a FFU, and the pressurized water atomizer installed in the return duct. The energy saving potential of adiabatic humidification over steam humidification has been proved, with savings of 8% and 23% in CASE 2 and CASE 3 compared to CASE 1, respectively. Furthermore, the pressurized water atomizer installed in the return duct exhibits greater energy saving effect than when installed in the MAU.

水熱源ヒートポンプユニットを用いた空調システムに関する研究 （第２報）デシカント外気処理ユニットを用いた潜顕分離空調システムの性能評価

水熱源ヒートポンプユニットを用いた空調システムに関する研究 （第２報）デシカント外気処理ユニットを用いた潜顕分離空調システムの性能評価

A rapid tool for emission outlet concentration simulation of scrubber and make-up air unit at different inlet concentrations

Currently in the cleanroom-related industries, both the air quality of indoors intake and outdoors emission should be controlled at a certain level. Wet scrubbers and air washers are the main facilities to clean up air for the process required. However, previous studies have found that these devices typically have lower removal efficiency for low inlet concentration contaminations; little information is available to explain the efficiency deterioration and only on the empirical basis. A theoretical model is proposed, which applies Fick’s second law to derive a rapid efficiency simulating formula. This model is different from the empirical equations of former studies, and is able to describe the relationship between the inlet concentration and removal efficiency of the air washing facilities. Moreover, the calculation time of the nonlinear recurrence equation is effectively lessened by the Euler equation and proven to be practical and concise for the rapid efficiency determination. Confirmation of the simulation formula was conducted by using the experimental data from the previous studies of the wet scrubber and in situ historical record of a make-up air unit. In this article, we describe how an outlet concentration and removal efficiency can be predicted using a generic simulating formula, leading to better design with less effort. The proposed model and equation minimize the design complexity and help to optimize the sizing and operational control of the air washing facilities. This not only decreases the construction and operating costs, but also lead to better energy usage. Practical application: Engineers can use the output of this paper to optimize air washer facility designs instead of intuitively extending the rinsing duration or enlarging the scale of the equipment. The model can be applied to both residential and industrial air washers to predict the efficiency and evaluate the performance. It also allows the quantitative analysis and risk assessment of an abrupt air washer breakdown in the clean manufacturing industries.

Various Energy-Saving Approaches to a TFT-LCD Panel Fab

This study employs the developed simulation software for the energy use of the high-tech fabrication plant (hereafter referred as a fab) to examine six energy-saving approaches for the make-up air unit (MAU) of a TFT-LCD (thin-film transistor liquid-crystal display) fab. The studied approaches include: (1) Approach 1: adjust the set point of dry bulb temperature and relative humidity in the cleanroom; (2) Approach 2: lower the flow rate of supply air volume in the MAU; (3) Approach 3: use a draw-through type instead of push through type MAU; (4) Approach 4: combine the two stage cooling coils in MAU to a single stage coil; (5) Approach 5: reduce the original MAU exit temperature from 16.5 °C to 14.5 °C; and (6) Approach 6: avoid an excessive increase in pressure drop over the filter by replacing the HEPA filter more frequently. The simulated results are further compared to the measured data of the studied TFT-LCD fab in Taiwan. The simulated results showed that Approach 1 exhibits more significant influence on annual power consumption than the other approaches. The advantage/disadvantage of each approach is elaborated. The impact of the six approaches on the annual power consumption of the fab is also discussed.

Real-Time Fab-Wise Airborne Molecular Contaminant (AMC) Monitoring System Using Multiple Fourier Transform Infrared (FTIR) Spectrometers in a Semiconductor Plant

The objective of this study was to investigate the airborne pollutant emission sources and fluctuations around the indoor and outdoor environments of a semiconductor manufacturing plant using monitoring data that were collected over 4 consecutive days via three Fourier transform infrared (FTIR) spectrometers located near an outdoor make-up air unit and an indoor Fab and sub Fab. Based on a total of 1,032 five-minute-interval records, fourteen chemicals were detected. Six of these chemicals, namely, carbon tetrafluoride, nitrous oxide, carbon monoxide, silane, sulfur hexafluoride, and methane, had significant concentration correlations between the indoor and outdoor environments. With the exception of silane and sulfur hexafluoride, the percentage of indoor/outdoor concentration ratios that were greater than one ranged from 62.2% to 73.1%, indicating that the indoor chemical concentrations were typically higher than the outdoor concentrations. Based on the regression models derived for the indoor and outdoor nitrous oxide concentrations, the nitrous oxide was believed to be originally emitted from the sub Fab vented to the outdoors and then partially returned to the Fab. It was estimated that for one ppb of nitrous oxide detected in the Fab, 2.58 ppb of nitrous oxide could be detected at the make-up air unit, which might result from the sub Fab emission being at a high level of 6.60 ppb. Furthermore, elevated outdoor concentrations of chemicals, such as carbon tetrafluoride, nitrous oxide and carbon monoxide, were observed without previous indoor emission peaks, indicating that these chemicals might accumulate in the outdoor surrounding area. This study successfully illustrated the dynamically changing relationship between indoor and outdoor chemical concentrations in a semiconductor clean room. These results can be used to prevent subtle and potential adverse impacts of airborne molecular contaminant (AMC) in various manufacturing facilities of technological industries, including the semiconductor and optoelectronics industries.

Removal of Inorganic Gas Contaminants via the Air Washer of a Make-Up Air Unit in Clean Rooms

Removal of Inorganic Gas Contaminants via the Air Washer of a Make-Up Air Unit in Clean Rooms

Validation and application of adsorption breakthrough models for the chemical filters used in the make-up air unit (MAU) of a cleanroom

The dynamic adsorption capacity calculated from the breakthrough curves progressively decreased with the increases in the face velocity, suggesting that the effect of intraparticle diffusion and possibly the rate of adsorption as the rate-limiting mechanism were increasingly more profound for a chemical filter-type adsorber configuration. The Yoon–Nelson model generally matched well with the experimental breakthrough curved for breakthrough fraction less than 50%. However, the proportionality constant in the Yoon–Nelson model needed modification through the method from which the mass transfer coefficient ( k v ) in the Wheeler–Jonas equation is determined. Subsequently, a series of breakthrough curves for the hypothetical toluene concentrations and face velocities simulating realistic operating conditions was generated, and their validity was verified against the adsorption capacity predicted by the Dubinin–Radushkevich isotherm equation. The useful life of a chemical filter could henceforth be estimated with confidence using the breakthrough curves predicted by the modified Yoon–Nelson model.

Using phosphoric acid-impregnated activated carbon to improve the efficiency of chemical filters for the removal of airborne molecular contaminants (AMCs) in the make-up air unit (MAU) of a cleanroom

A coconut shell activated carbon precursor was modified by impregnation with phosphoric acid. The effects of the particle diameter of the impregnated activated carbons (IACs) on the thickness, pressure resistance, and face velocity of a chemical filter were investigated. Furthermore, volatile organic compounds (VOCs) adsorption experiments were carried out to determine the relationship between the removal efficiency and the chemical properties of the adsorbents. The effects of various parameters such as challenge gas concentration, saturated adsorption ratio, impregnation method and impregnant contents were investigated. The results showed that the effect of face velocity on pressure resistance is larger than that of the thickness, that 0.25 M phosphoric acid impregnation of activated carbon can raise VOC removal efficiency by 2–3% (toluene: from 95.8% to 98.1%, isopropanol: from 95.2 to 97.2%), and that the optimal impregnation time is around 1.5 h. A simple shaking impregnation method exhibited better performance than the ultrasonic method.

Saving energy in the make-up air unit (MAU) for semiconductor clean rooms in subtropical areas

The energy requirements to cool, dehumidify, preheat and/or humidify outdoor air are significant in the make-up air unit (MAU) of clean room air-conditioning systems, and can represent 30% to 65% of the total thermal energy required to maintain a clean room environment. Because of these high-energy requirements, cost-effective means to reduce energy costs can influence unit production costs. Reducing or displacing mechanical cooling or electrical heating requirements can achieve the greatest opportunity for significant energy savings. This paper, therefore, aims to improve the energy performance of the MAU system by properly arranging compositions of components of a typical MAU applied in a semiconductor clean room. Explicitly, we investigated the influence of various factors including the fan location (draft-through type vs. push-through type), chilled water system (single-chilled water temperature system vs. two chilled water temperature system) and reheating scheme (electrical heating vs. hot water provided by heat recovery chiller). The result shows that the draw-through type accompanied by two chilled water temperature system with heat recovery function exhibits the lowest electrical power consumption.

A comparative study on energy consumption for HVAC systems of high-tech FABs

The unique system dynamics of five different HVAC designs including the RCU (recirculation air unit) system, the MAU (make-up air unit) + RCU system, the MAU + RCU + FCU (fan coil unit) system, the MAU + axial fan system, and the MAU + FFU (fan-filter unit) system for a typical 200 mm DRAM wafer fabrication plant are discussed and compared. The energy performances of the RCU system, the MAU + RCU system, the MAU + RCU + FCU system, and the MAU + axial fan system are 3.8, 1.19, 1.12 and 1.08, respectively, folds that of the most efficient MAU + FFU system. The MAU + axial fan system exhibits slight less efficient in energy performance, compared with the MAU + FFU system. The most influential factor on energy performance between these two systems is the design of the noise abatement system, especially the pressure drop of the silencer, which dominates almost half of the internal static pressure of axial fan. When the static pressure of silencer of the MAU + axial fan system is reduced to 50 Pa, energy consumption of these two systems is comparable. Bypassing a certain portion of FAB return air to mix with make-up air can maximally reduce 50% of energy consumption of the RCU system.