Cooling Coils Research Articles

Vapor-selective active membrane energy exchanger for high efficiency outdoor air treatment

As much as 40% of the total load on air conditioning systems can be attributed to condensation dehumidification. However, new water vapor-selective membranes present a unique opportunity to greatly reduce the power requirements for moisture removal by avoiding phase change and have thus been ranked as a top alternative to traditional HVAC systems. To date, however, all such systems have relied on the assumption of constant temperature, even terming the technology “isothermal dehumidification.” This work proposes a membrane-based air cooling and dehumidification approach, referred to as the Active Membrane Energy Exchanger (AMX), which is the first to provide simultaneous, yet decoupled, air cooling and dehumidification. The suggested AMX configuration uses two vapor-selective membrane modules with a water vapor compressor in between them, using the second membrane module to reject vapor into the exhaust stream. Cooling and heating coils in each membrane module channel move heat between the air streams using a vapor compression cycle. A detailed steady-state, thermodynamic model is presented for the AMX integrated within a 100% outdoor air conditioning system. The AMX’s limiting parameters and design considerations like compressor efficiency are systematically analyzed for a broad range of outdoor air conditions and compared against standard and state-of-the-art dedicated outdoor air systems. This new high efficiency approach is found to outperform all other standard and state-of-the-art systems, achieving 1.2–4.7 times the COP over conventional dedicated outdoor air treatment. Lastly, a building simulation case study predicted cooling energy savings as high as 66% in hospital buildings with 100% outdoor systems in hot, humid climates.

Ultraviolet germicidal coil cleaning: Decreased surface microbial loading and resuspension of cell clusters

Cooling coil surfaces within building ventilation systems are ideal sites for biofilm formation due to the presence of adequate nutrients (deposited particles) and moisture (condensate). In this study, a heating, ventilation, and air-conditioning (HVAC) test apparatus was built consisting of two parallel ducts, each with its own cooling coil. One coil was exposed to ultraviolet germicidal coil cleaning (UVG-CC) while the other was the comparison control to investigate the impact of UVG-CC on surface microbial loading and bacterial attachment. Surface samples were collected by swabbing a uniform area of coil surface and airborne samples were collected isokinetically with sterile funnel filters. All samples were quantified via direct epifluorescent microscopy. Prior to irradiating, higher concentrations of surface microbial loading were found on the downstream side of both cooling coils under condensing conditions. Conversely, under dry surface conditions with downstream UV irradiance, surface concentrations were higher upstream. UVG-CC (at an average 200 uW/cm2 on the coil surface) reduced surface microbial loading by 55% on average during condensing conditions and inhibited bacterial attachment causing clusters of bacterial matter to become airborne downstream of the cooling coil. Additionally, it was found that desiccation also inhibited surface microbial loading and yielded cluster detachment but to a lesser degree than UVG-CC treatment.

Optimum Conditions for the Efficacy and Safety of Cryofiltration Apheresis: An Analysis of Circuit Temperatures Depending on Plasma Flow Rate and Cooling Coil Lengths/Turns.

A system providing both appropriate cooling and warming are needed for the efficacy and safety of cryofiltration (CF) plasmapheresis. We measured some points of CF circuit temperatures with varying plasma flow rates (QP = 10-40 mL/min) and the numbers of connecting cooling coils (one or two) under the conditions of blood flow rate (QB ) 100 mL/min with 7700-mm coil length, 19 turns, and 50-mL priming volume. We measured the respective temperatures of each point of starting/returning for an extracorporeal circuit (TA /TV ), intracooling coil (TC ), and post-plasma fractionator (PF) (TPF ). The subtraction of TV from TA (ΔT) was used as an indicator of safe return. There were no significant differences in TC , TPF , or ΔT in accordance with each QP between that of one and two coils. All of the Tc values under the condition QP ≤ 20 mL/min achieved <4°C. The TPF under the condition QP ≥ 20 mL/min was not significantly different compared to that of QP 30 mL/min (the lowest condition). Although the ΔT increased depending on the QP increase, the ΔT under the condition QP ≤ 15 mL/min was not significantly different from that of the control (one-way double-filtration plasmapheresis [DFPP]) group. We conclude that (i) one coil is enough for effective cooling in CF, and (ii) an ideal QP that fulfills the required conditions for both effective cooling and sufficient warming of returning fluid does not exist, but QP from 15 to 20 mL/min may be a relevant range.

Optimisation of Direct Expansion (DX) Cooling Coils Aiming to Building Energy Efficiency

Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.

Performance study of a constant temperature and humidity air-conditioning system with temperature and humidity independent control device

To reduce the large energy penalty for constant temperature and humidity control in conventional air-conditioning systems, a novel temperature and humidity independent control (THIC) device is developed for typical cooling coils. The working principle of the THIC device is to adjust the chilled water flow rate in a cooling coil (CC) to maintain constant temperature and to adjust the apparatus dew point temperature of the CC to maintain constant humidity. A split-range control strategy is developed to control the cooling coil with the THIC device, the heater and the humidifier to achieve reliable control of indoor temperature and humidity while minimizing energy use.Control performance of the THIC device was tested in an existing constant temperature and humidity air conditioning system serving a storeroom in a museum. The field test shows that the indoor temperature and humidity were well controlled in the required range. Energy performance of the THIC was tested using simulation tests on TRNSYS platform. Seven testing cases with different typical load conditions were conducted. The energy performance of the THIC is compared with conventional air conditioning systems. The results show that the THIC device can achieve power saving of 30–50%.

Experimental investigation of dehumidification process in cooling coil by utilizing air-to-air heat exchanger in humid climate of Iran

Energy recovery systems can be used in HVAC to reduce energy consumption by recovering wasted energy from the exhausted air to pre-cool inlet fresh air. In this paper, experimental study of utilizing cooling coil (CC) and cooling coil combined with heat exchanger (CCHE) has been developed. Considering the different climate zones in Iran, the experimental study has been done for the areas with high humidity content. In each case, the effects of air-to-air heat exchanger (HE) on the sensible and latent cooling load are investigated. The analysis gives the applicability of HE in Iran for various operational conditions to obtain air with lower moisture content. In CCHE systems more latent load quota is allocated in cooling coils and lower air humidity ratio can be obtained. Also in the cities with higher dew point depression (difference between dry-bulb and dew point temperature) more humidity reduction is achieved and the difference between latent load quotas of CCHE system is higher than CC system.

Fungi on Air-Conditioning Cooling Coils and Drainage Pans, Identified with Polymerase Chain Reaction Assays

Fungi on Air-Conditioning Cooling Coils and Drainage Pans, Identified with Polymerase Chain Reaction Assays

Evapotranspiration Measurement in Controlled Environment Chambers: A Comparison between Time Domain Reflectometry and Accumulation of Condensate from Cooling Coils

The measurement of water fluxes from canopy and soil surfaces is performed in sunlit controlled environment chambers by measuring condensate draining from cooling coils in a constant humidity environment. This provides a direct measure of evapotranspiration (ET). However, in growth chambers with soilbins, this does not give information on soil water status or root activity. The objective of this study was to compare ET measurements from the condensate system with ET calculated from measurements of water content by TDR. Data from an irrigation × carbon dioxide (CO2) study on potato (Solanum tuberosum L.) were used for this study. The soil water contents in the growth chamber soilbins were monitored once an hour at five vertical depths with three measurement locations per depth using an automated TDR system. The correspondence between daily ET rates for the two systems was good. Maximum daily ET rates were near 6.1 to 7.1 mm cm−2 d−1 (7–8 L d−1 on a chamber basis) and differences were on the order to 0.89 to 1.8 mm cm−2 d−1 (1–2 L d−1). At the higher daily ET rates, the daily values from the two methods were closer. The correspondence between hourly measurements of ET measured from the condensate system and calculated from TDR water contents was poor due to instrument and soil variability. A significant source of error was vertical variation in water content in the soil between horizontally placed TDR probes, especially during irrigation events. Evapotranspiration estimates from TDR measurements were much more robust for calculation of water use over a period of time. Data from the condensate system were most useful for quantification of diurnal transpiration rates and were better correlated with radiation.

Quantitative Comparison of Temperature Control of Reactors with Jacket Cooling or Internal Cooling Coils

This paper presents a quantitative comparison of the effectiveness of two alternative heat-removal schemes in the control of continuous stirred tank reactors (CSTRs). The chemistry features an exothermic irreversible reaction A → B, and different design levels of conversion are explored. Two mechanisms for removing the heat of reaction are studied: (1) a cooling jacket surrounding the vessel or (2) an internal cooling coil. Controllability is shown to become more difficult as the design conversion decreases. Results demonstrate that internal coil cooling provides better dynamic controllability than jacket cooling in terms of being able to handle larger disturbances. A generic “reactor controllability index” (RCI) is proposed that can be used to assess the dynamic robustness of any CSTR. The RCI is the dimensionless ratio of the temperature difference between the reactor and jacket (or the log-mean temperature difference for coil cooling) and the maximum available temperature difference (reactor temperatu...

Simplified Model for the Operation of Chilled Water Cooling Coils Under Nonnominal Conditions

This study presents a cooling coil model for calculating energy consumption in air-conditioned buildings that has a minimal number of inputs. The model accurately determines the cooling energy rate and dehumidification energy rate under nonnominal conditions, and takes into account operation under variable air and water flows. In this manner, the model enhances the simplified ASHRAE Toolkit model without requiring more input data. The main assumptions are justified considering the common existing configurations of cooling coils in the air-conditioning industry. The parameters of the model are identified from only one nominal rating point. The model has been validated on a VAV facility with an average deviation of 5% for total energy rate. Errors are mainly due to the assumption that the coil is either completely wet or dry even if the surface is partially wet.

Performance of Chilled-Water Cooling Coils

A model capable of predicting the performance of wavy-fin-tube chilled-water cooling coils has been developed. It includes formulas for calculating the heat transfer coefficients and pressure drops on the air and water sides of the coil, as well as a procedure for calculating the condensation rate on the air side. The model was tested by comparing its predicted heat transfer rates and pressure drops with experimental data from the literature. The heat transfer rates were predicted to within 5% of the experimental value for seven corrugated-fin coils representing a wide range of geometries. Air-side pressure drop predictions were less accurate. The model was able to predict the air-side pressure drop within 25% for three of four coils whose geometrical parameters were within the range of applicability of the model. A parametric study of the effects of various water- and air-side geometric factors revealed that the choice of coil circuiting can affect the heat transfer performance by as much as 90%. Water-s...

Titanium Cooling Coils for Surface Ship Applications

High machinery space temperatures and generally inadequate ventilation air cooling in many Navy ship machinery compartments influenced a David Taylor Research Center (DTRC) decision to reevaluate seawater cooling coils as a principal means of compartment cooling. Earlier Navy designed and fabricated copper-nickel seawater coils had suffered numerous reliability problems due to fouling, corrosion, and erosion and, thus, were removed from ship use. Advanced plate-fin and integral fin cooling coil designs were evaluated as a means of improving reliability and thermal performance of the previous Navy seawater cooling coils. Math models were developed to analyze the effects of (1) seawater and air temperature, (2) seawater and air flow rates, and (3) coil material on thermal performance. Unique fabrication techniques were assessed for both coils to allow fabrication using titanium in place of copper-nickel for all seawater-wetted components. Finally, various cooling coil waterbox de signs were evaluated to improve the seawater flow patterns and thus reduce fouling and increase component reliability. Results showed that both cooling coil designs can satisfactorily handle cooling requirements of machinery spaces on existing and future class ships without the need for large increases in air conditioning capacity. Furthermore, both seawater coil designs can be fabricated from titanium by modifying fabrication techniques used in the previous design. The recommended general design approach, as concluded from the study, can be summarized as follows: 1 Increase air velocity across the coil to maximize thermal performance; 2 Increase seawater flow rate in the tubes and water-box to prevent biofouling accumulation; 3 Limit the compartment ventilation air to only that amount needed for life support; 4 Provide a small chilled water coil in the compartment for latent heat removal and; 5 Utilize titanium as the seawater-wetted component material to increase reliability over the copper-nickel coil previously used.

Thermal Detailed Analysis for Various Types of Finned Serpentine Counterflow Cooling Coils and Applications for System Design

Thermal Detailed Analysis for Various Types of Finned Serpentine Counterflow Cooling Coils and Applications for System Design

Tin Coating for Aquarium Cooling Coils

Tin Coating for Aquarium Cooling Coils

COOLING COILS CLEAN AFTER 2 YEARS

COOLING COILS CLEAN AFTER 2 YEARS

On the preparation of drying oil

As much as 40% of the total load on air conditioning systems can be attributed to condensation dehumidification. However, new water vapor-selective membranes present a unique opportunity to greatly reduce the power requirements for moisture removal by avoiding phase change and have thus been ranked as a top alternative to traditional HVAC systems. To date, however, all such systems have relied on the assumption of constant temperature, even terming the technology “isothermal dehumidification.” This work proposes a membrane-based air cooling and dehumidification approach, referred to as the Active Membrane Energy Exchanger (AMX), which is the first to provide simultaneous, yet decoupled, air cooling and dehumidification. The suggested AMX configuration uses two vapor-selective membrane modules with a water vapor compressor in between them, using the second membrane module to reject vapor into the exhaust stream. Cooling and heating coils in each membrane module channel move heat between the air streams using a vapor compression cycle. A detailed steady-state, thermodynamic model is presented for the AMX integrated within a 100% outdoor air conditioning system. The AMX’s limiting parameters and design considerations like compressor efficiency are systematically analyzed for a broad range of outdoor air conditions and compared against standard and state-of-the-art dedicated outdoor air systems. This new high efficiency approach is found to outperform all other standard and state-of-the-art systems, achieving 1.2–4.7 times the COP over conventional dedicated outdoor air treatment. Lastly, a building simulation case study predicted cooling energy savings as high as 66% in hospital buildings with 100% outdoor systems in hot, humid climates.