The Benefits of a Variable Frequency Drive

Source

Commercial HVAC systems often operate on three phase power, as a standard method of alternating current electric power generation, transmission and distribution. Most conventional building HVAC applications are designed to operate the equipment at a constant speed. That being said, building loads aren’t constant and motors have to perform at full load at any given time. The technology itself controls the speed of a motor, converting incoming AC power to DC and then back to quasi-sinusoidal AC power using an inverter switching circuit, giving the advantage of more speed control.

Variable Frequency Drive is found to be very effective in assisting with energy management for HVAC systems. The main objective of this technology is to ensure that the motor only generates enough energy to power the compressor and no more. VFD provides constant load-matching capacity which results in the elimination of over-capacity running. Recently studied, current variable frequency drive benefits goes beyond the advantage of energy savings or energy efficiency. In conventional common application, the installation of variable frequency drive saves about 35% to 50% energy used by matching system capacity to the actual load.

In addition to energy savings, the equipment would benefit from savings on maintenance costs and enhanced motor lifetime. Installation of VFD applies low frequency and voltage to motors with controlled uprate, reducing vibration and motor wear which significantly contributes to longevity of the motor. Since VFD reduces the speed of compressors to match the need for performance, less mechanical stress is also applied to the component helping to reduce the chance of component failure.

VFD also affects starting currents, lowering a substantial amount of it without affecting the starting torque which would benefit the grid to affect less stress when the motors are powered up. With this capability, failure of electrical equipment can be reduced.

References:

http://blog.parker.com/5-reasons-to-control-your-compressor-with-a-variable-frequency-drive

http://hpac.com/motors-drives/applying-vfds-refrigeration-systems

Demystifying S1-S2 Optimization in Turbomachinery

  1. Historically turbomachinery development began with empirical rules postulated by early pioneers. With the need for jet engine for aircraft propulsion, dimensionless analysis became popular, followed by the 1 D mean line design and 2D meridional methods. Today 2D meridional methods with 3D blade to blade CFD/FEA methods are a necessity as efficiency and reliability requirements are further pushed.

 

  1. One key aspect of 2D meridional design is S1-S2 optimization, which is a time consuming, laborious task and hence subject to human errors. S1-S2 optimization is a task of reviewing, adjusting and optimizing the flow path in the Tangential (S1 or blade-to-blade or pitchwise) and the Meridional (S2 or span wise) planes. The main purpose is to:
  • Fit the flow path to specific meridional dimensional constraints
  • Adjust blade-to-blade parameters while taking into account structural constraints.

 

  1. The need for preserving the turbine performance (that has been selected) and then allowing alteration of flow path dimensions requires use of inverse solvers. The parameters that affect the blade-to-blade calculations are the number of blades and the chord. These can be optimized in the S1 optimization, while meeting structural requirements. For optimizing the spanwise distribution, the S2 optimization is chosen to modify/ fine tune the Mollier diagram (Heat drop or Enthalpy) to meet the desired performance. In the S1 optimization adjusting important pitch-wise parameters such as the chord, pitch and number of blades to preserve optimal “solidity”/”relative pitch” by  considering structural constraints. The S1 optimization can be performed either for the full turbine (cylinder) or for particular components (rotors/stators).

 

  1. An effective analysis requires six different criteria for optimization which is basically grouped into two categories. The groups are based on the chord that gives the maximum efficiency or minimum length that is required to meet the structural requirements. For both of these groups the optimization can be performed to:
  • Obtain the optimum chord, with a constant relative pitch
  • Get the optimum chord and optimum relative pitch
  • Obtain the optimum relative pitch while maintaining the chord constant

 

  1. If the max efficiency chord is selected then the chord optimization is done with first preference to the aerodynamic criteria and meeting the structural requirement for the given material. If the min length chord is selected, then the chord optimization is done with the objective to obtain the smallest value which meets the structural requirement and MSF (Margin of Safety) value nearer to “zero”.

 

  1. The AxSTREAM® software suite provides an  automated process for S1-S2 optimization enabling improved designs and reducing engineering hours.

 

What Happened to R22?

R-22Freon (brand name by DuPont) used to be the regulated and most used refrigerant in the HVAC market. The chemical (R-22) was introduced to the refrigerant system in 1920. It consisted of hydrogen, carbon, fluorine and chlorine. HCFC was used in replacement to CFC or chloro-fluoro-carbon which is considered more dangerous. Within a few years, HCFC took over CFC’s role as the safer option.

Even though it was found to be safer than the alternative at the time, various recent studies state that R-22 is detrimental to the environment as it is a substantial ozone depleting substance that leads to greenhouse effects. Since January 2015, the maintenance or servicing of existing refrigeration, air condition and heat pump equipment using R22 has been prohibited by the EPA (Environmental Protection Agency) and related international agencies. Based on the Montreal Protocol, which prevents more damage to the ozone layer by banning all ozone deteriorating substances, R22 can no longer be used in any kind of application.

Since the use of R22 is currently prohibited, end users are left with the option to change the working fluid from current appliances which can be done with the help of professionals –this process might require making changes/switching out installed components to match the new requirements of the new working fluid. Another option would be replacing your current appliances to newer equipment.

Replacing Freon, R410A is found to be the closest substance to take over R22’s functionality. Not only does it have similar characteristics, it comes with added the benefit of being more environmentally friendly and also causes less vibrations in equipment. With less vibration, stress performed on the machine is less and equipment will generally have a longer life time.

References:

http://www.brighthubengineering.com/hvac/61968-timhttps://learn.compactappliance.com/why-r22-freon-is-banned/eline-for-phase-out-of-r22-refrigerant/ 

https://www.out-law.com/en/sectors/core-industries–markets/real-estate/air-conditioning-costs-and-the-banning-of-r22/

http://www.epa.ie/air/airenforcement/ozone/r22andhaloncriticalusephase-out/

History of Refrigeration

RefrigerationIn its natural state, heat flows from higher to lower temperature regions. Refrigeration cycles are utilized to modify or reverse this cycle, using work obliging heat to flow with the direction that is desired, and align with increasing temperature from low temperature region to higher.

During the earliest records of the “cooling” process being invented, people harvested ice to refrigerate, cool and conserve food. As time progressed, humanity’s basic needs changed and new ways to manipulate temperature started being explored. Major research into refrigeration began with the creation of pup to create a partial vacuum container which absorbs heat from the air. That being said, while the experiment was successful it did not have any practical applications.

In the early 1800’s, people preserved their food by storing food and ice in iceboxes. General Electric decided to design a refrigeration unit that was powered by gas which eliminate the use of motors, decreasing the size,  and soon moved to a refrigeration system which was powered by electricity. The first commercial use of refrigeration was used to produce ice in regions with hotter climates. Refrigeration systems became the solution to ice shortages by enabling areas with environmental limitations to produce their own ice, thus reducing the products scarcity.

With the invention of chlorofluorocarbon, Frigidaire was able to make home and consumer use refrigeration systems better, cheaper, lighter and smaller. Of course, this was back in the times when CFC and Freon were still considered safe choices. Since then, many other refrigerants have been chosen to replace R22.

The thermodynamic cycle which is associated with the refrigeration process is known to be Carnot cycle -a reversible isothermal cycle, where heat is transferred at a constant temperature. To learn more regarding thermodynamic cycle of refrigeration please refer to one of our older post or contact our engineering team for our heat balance course and tool!

Design Process with AxSTREAM

Step 1: Basic inputs

– Input a set of boundary conditions, geometrical parameters and constraints that are known to the user.

Step 2: Design space generation

– Thousands of machine flow path designs can be generated from scratch
–  Explore a set of design solution points using the Design Space Explorer
–  Adjusting geometric parameters while retaining the desired boundary conditions is also possible

Preliminary Design
Figure 1: Design space
Post design geo modification B
Figure 2:  Post design geometry modification

Step 3: Streamline solver

– Determine streamwise and spanwise distribution of kinematics, thermodynamics and loss parameters as well as leakages and secondary air flows (including bleed) for a given set of boundary conditions.

Figure 3: Throughflow analysis window

Step 4: Optimization and performance maps generation

– Optimize the design using a DOE approach (Design of Experiment)
– Generate performance maps (and compare against previous results or experimental data) for any number of variables with AxMAP.

 

Figure 4: 3D Optimization Surface (DoE approach)
Figure 5: 2D map curves for off-design performance analysis

Step 5: 3D profiling

– Profiling of the 3D blades is done through inlet and outlet geometric parameters, beta, theta and channel thickness distributions for each of up to 49 spanwise sections while providing interactive and automatic visualization of the changes on the blade geometry while recalculating the outlet flow angle.
– Different profiling modes are available to ensure flexibility of the geometry editing for 3D blades, with interactive displays of the blade curvature which ensures a smooth surface therefore helping prevent flow separation and minimize losses.
– Blade re-staggering can also be performed to study how the throat area gets affected to allow for more or less flow rate. This re-staggering can even be optimized based on the rotation speed using user-defined rotation schedules.

Figure 6: 3D profiling
Figure 7: 3D geometry

Step 6: CFD and FEA

– An automated turbomachinery-specific, structured hexagonal meshing by customizable blocks is available for computational domain division.
– Select the problem formulation depending on whether you desire to calculate a pressure value (inlet or outlet) or the machine mass flow rate. Viscosity and different turbulence models (including k-ε, k-ω, k-ε RNG, k-ω SST) can be used for new calculations or to resume existing ones.
– Export of CFD results allows comparisons at design and off-design conditions between different calculations using the same or different solvers (1D, 2D, 3D) as well as experimental results.
– Import CFD loads for structural calculations and centrifugal, pressure and thermal loads can also be accounted for at design and off-design conditions.
– Perform static, modal, harmonic, “hot-to-cold” and “cold-to-hot” analysis, as well as Campbell and interference diagrams with AxSTRESS.

Figure 8: CFD
Figure 9: Structural analysis results

And this is just the beginning. Users can export flow path and stress analysis results and design the shaft of the machine with RotorDesigner module. Then, lateral and torsional analysis of the shaft can be performed including bearings properties with the use of Rotordynamics and Bearings modules. In addition, for cooling flows, secondary systems and hydraulics, AxSTREAM NET can be employed and with the use of our ION module, all the modules (as well as external software) can be wrapped under the same optimization/project scenario. If this is not complete, then what is? Ask a member of our team to demonstrate the capabilities of AxSTREAM live!

Figure 10: Rotordynamics analysis
Figure 11: Cooling scheme of entire gas turbine
Figure 12: Off design calculation of cooled gas turbine engine made in AxSTREAM ION

The Optimization Challenge in the Development of Turbomachinery

Optimization (or parametric studies) of a twin spool bypass turbofan engine with mixed exhaust and a cooled turbine can be considered one of the most complex problem formulations. For engine selection, determining the thrust specific fuel consumption and specific thrust is necessary against variables such as design limitations (Inlet temp, etc.), design choices (fan pressure ration, etc.) and operating conditions (speed & altitude). The task involves cycle level studies following machine, module, stage and component level optimization. This calls for an integrated environment (IE) and it is desirable to have such an IE operating on a “single” platform.

Historically IE was developed for the design of axial turbines (mainly steam). Later, it was expanded for gas turbines (especially blade cooling calculations) and axial compressors via plug-in modules. The new challenge designers face today is developing mixed flow machinery. An effective system for modern turbomachinery design needs to do the following: AxSTREAM_ION

  1. Involve a set of design modules necessary for design procedures under one operating platform (an umbrella, per se) that performs initial sizing and optimization, 1D formulations, and build 3D geometric blade models that are available for final refinement by means of 3D aerodynamic CFD and stress analysis
  2. Have the ability to automate and optimize calculations using embedded models
  3. Improve flexibility in carrying out interactive design scenarios including rollback to previous version(s), version support, project integrity, ensure expandability, scalability, and maintainability
  4. Provide users with convenient mechanisms to input, edit, display and export data to other systems.

The architecture presented below gives the designer an opportunity to design axial, radial and mixed flow turbomachinery in an integrated environment on a single platform. The objective is to review a large number of variants and design parameters to realize optimum results. From a software engineering perspective, the majority of modules are required to be compatible with every type of turbomachinery, and specific modules must be able to run simultaneously (axial and radial turbine, axial and radial compressor). Consequently, a solution using common modules (project data access, graphical display of information, multi-choice calculation and optimization, import/export, etc.) and specific machine modules operating in tandem emerges. It embodies cycle level analysis and further down to blade (impeller) 3D profiling, stress analysis, and 3D Flow analysis.

Such an IE platform shortens the design development process significantly, thereby decreasing engineering costs and improving productivity

To learn more about our new integrated software tool for automated design, register for our upcoming free webinar http://www.softinway.com/education/webinars/automated-design-of-an-industrial-steam-turbine/

Alternative Refrigerants to R-22

Gas tanks
Source

The majority of HVAC installations dating back to the 1990s have R-22 as their main working fluid. However, recent studies have proven that R-22 or as we commonly known as “Freon” (brand type) is not as environmentally friendly as we once thought it was. Ergo the use of this refrigeration type has been banned by the Environmental Protection Agency along with other substances which contributes to ozone depletion. With phasing out of R-22, HVAC manufacturers and end-users are forced to look into other comparable refrigerants which won’t negatively impact the environment as much.

R-410A offers a few benefits when compared to the traditional R-22 fluid – one of which is greater energy efficiency which translates into lower operational costs. This hydro-fluorocarbon has been approved for use in new systems and is classified as a non-ozone-depleting HFC. One note that has to be taken into consideration is that R-410A operates on roughly a 50% higher pressure than R-22, thus can only work with high pressure limit equipment.

R-407C has been set as the new standard for the U.S residential air conditioning system as of two years ago. Consequently, the commercial refrigeration system (including air conditioning and chilling units) R-407C was found to be the most frequent refrigerant to be used as a substitute of R-22. Of the higher temperature this type of refrigerant gives similar operating characteristic to R-22. R-407C, a non-ozone-depleting substance, gives better performance in comparison to Freon due to its higher pressure and refrigeration capacity.

R-134A is currently one of the most common refrigerant fluids; especially in HVAC applications in the automotive industry. Many machines are retrofitted to match this fluid from R-22; though one should be careful not to mix and cross contaminate R-22 with R-134A which can result to danger of raising compressor head pressure as well as unfavorable reliability. R-134A is made of one single component, which comes with the advantage of utilization of  a single recovery machine and adding into that, according to recent studies, R-134A is environmentally friendly which makes it an even more attractive choice.

References:

http://www.ac-heatingconnect.com/what-hfc-refrigerants-are-used-in-commercial-air-conditioning/

http://www.serviceexperts.com/blog/r-22-refrigerant-answers-from-the-ac-experts

https://learn.compactappliance.com/freon-alternatives/

 

 

Steam and Gas for Power Generation

Nowadays, gas and steam turbines are contributing to more than 80% of the electricity generated worldwide. If we add the contribution from hydro turbines too, then we reach 98% of total production.

The improvement of the flow path is crucial, and an advanced design can be achieved through several strategies. The aerodynamic optimization of gas and steam turbines can lead to enhanced efficiency. In addition to that, the minimization of secondary losses is possible by introducing advanced endwall shaping and clearance control. Moreover, further increase of efficiency can be achieved by decreasing the losses of kinetic energy at the outlet from the last stage of the turbine. This can be done using longer last-stage blades as well as improving the diffuser recovery and stability.

Flow Path
                     Flow Path of a Gas Turbine

Moreover, increased gas turbine performance is very much related to an increase of the turbine inlet temperature. However, the coolant mass flows will need to be minimized at the same time to achieve the highest performance benefits possible [1]. Therefore, effort must be put on the development of advanced cooling system concepts for the engine’s first stage components. New cooling surfaces as well as new cooling schemes should be studied by CFD modelling to use the coolant in the best possible way before it leaves the component.

A phenomenon that must be further addressed in this context is hot gas ingestion which can cause unacceptably high rotor temperatures. We need to develop more advanced technologies that will handle hot gas ingestion to make sure that the hot gases will be confined in the cavity without reaching the rotor itself. To use new sophisticated cooling methods based on porous structures a new method of thinking is necessary. Analysis methods, design concepts, and criteria must be developed and tested for such structures in order to optimize the design for components with porous structures. High temperature materials in gas turbines have properties that change significantly during the expected life of the component due to thermal exposure, mechanical load and the combination of the two. Issues that affect lifting and reliability and can cause serious problems are, for example, crack propagation usually due to creep or fatigue. In many components, early TBC (Thermal Barrier Coating) spallation will increase the material temperature of the component and reduce the safe life for which the component can be used [1].

Considerations for any power system, new or existing, include not only efficiency and optimization, but also cost, longer life-cycle of components, and keeping pace with current environmental restrictions. Given the scale of some of these projects, accurate early-stage design is critical for project success, whether it’s a new construction or retrofit.

At SoftInWay we have built our reputation on creating accurate preliminary design models for such projects. Our strength in engineering and power plant consulting combined with our AxCYCLE® heat balance calculation software are core offerings of success for turbomachinery design in the power generation sector.

References:

[1]http://www.euturbines.eu/cms/upload/publictaions/documents/EUTurbines_Roadmap_on_Turbomachinery_Research-final.pdf

 

Factors in your HVAC Selection

HVAC

A few decades ago, opening and closing a window was enough air temperature control. In modern days though, the standard bar of comfortable living has become higher and the occurrence of global warming, which raises the world’s temperature to the extremes, is abundant.  With all this in mind, temperature control becomes a major necessities. During this post, we will be exploring factors which should be considered for a new installation of a HVAC system either to modern or conventional homes.

Regardless of the size of property, ductwork that is balanced and well designed must be installed to make sure that the air and temperature circulation is optimal –especially for locations with extreme weather conditions. Externally insulated round ducts are found to be the most efficient. Installation of balance dampers in the ductworks should also be important to regulate airflow.

End users should also be paying attention to materials of the HVAC unit. The condenser coil type directly relates to the reliability and stability of the HVAC unit, which is even more important in harsh environments. In common applications, coils which are made from one types of metal are usually more reliable and generate better efficiency.

HVAC application has several types of working fluids also known as refrigerants. The main function of refrigerant fluid is to cool, dehumidify and distribute the low temperature air in the system. For a long time, R-22 or Freon happened to be the most common refrigerant in the market. Nowadays though, the use of Freon has been banned for the reason of being environmentally harmful.  Currently, there are a couple other refrigerants that are commonly implemented in such application including R-134a, R-407c and many more. Those refrigerants have their own advantages and disadvantages which end users should compare themselves to see what would fit their needs the best.

Efficiency should be the most important aspect to study before settling on a type of HVAC system. There is minimum efficiency which is settled by the government, though aside from legal limit, this would be an ultimate factor to be analyzed by users since efficiency directly correlates to operational costs (the higher the SEER, the lower utility bill you get). Thus, an up-front investment might benefit in the long run.

References:

http://www.hgtv.com/remodel/mechanical-systems/10-key-features-of-hvac-systems

http://www.ac-heatingconnect.com/what-hfc-refrigerants-are-used-in-commercial-air-conditioning/

SuperTruck II Program and Waste Heat Recovery Systems

Familiar to many, the 2011 SuperTruck program was a five-year challenge set by the U.S. Department of Energy to create a Class-8 truck that improves fuel efficiency by 50 percent.  Hoping for even more groundbreaking achievements this time around, the Department of Energy has initiated a second five-year program to bring further fuel-efficiency advancements and near closer to eventual commercialization.  Cummins, Peterbilt, Daimler Trucks North America, Navistar, and Volvo Group remain the five teams involved in this R&D endeavor.  Michael Berube, head of the Energy Department’s vehicle technology office mentioned “SuperTruck II has set goals beyond where the companies think they can be.”  SuperTruck II is looking for a 100 percent increase in freight-hauling efficiency and a new engine efficiency standard of 55 percent.  With such lofty goals, the SuperTruck II development teams will need to tackle improvements in freight efficiencies from all sides.

Figure 1 - Daimler SuperTruck
Figure 1 – Daimler SuperTruck

Material considerations, body aerodynamics, low-resistance tires, predictive torque management using GPS and terrain information, combustion efficiency, and several other improvements methods on the first iteration have demonstrated how the SuperTruck II will require a multi-phase and integrated systems approach to achieve equally successful numbers. However, with an engine efficiency target that is 31 percent above the SuperTruck’s first go around, special attention will be required on engine advancement to achieve an efficiency standard of 55 percent.

One of the main methods apart from auxiliary load and friction reduction is a comprehensive waste heat recovery (WHR) system dedicated to the engine.  From the existing works devoted to waste heat recovery, the following methods of efficiency increase can be highlighted:

  1. Addition of the internal heat recuperation to a WHR cycle
  2. Appropriate working fluid selection
  3. Increment of initial parameters of bottoming cycle up to supercritical values
  4. Maximize waste heat utilization due to the usage of low temperature heat sources
  5. Bottoming cycle complexification or usage of several bottoming cycles with different fluids

Figure 2 - AxSTREAM Platform for Radial Turbine Design
Figure 2 – AxSTREAM Platform for Radial Turbine Design

With regards to fluid selection, no universal organic fluid exists that is suitable for a wide range of ORC applications.  For this reason, each WHR project requires an extensive fluid selection analysis as one of the main design steps.  In general, working fluids are selected based on their thermodynamic properties, thermal stability, and environmental impact/safety.  Amongst the most popular options are water, ethanol, R245fa, and R134a.  Once the proper design range it set for the waste heat cycle, the designer can successfully set which fluid may be the best for its given application.

Later in the design process, the engineer must consider how to design a turbine that will create the optimal amount of power for the selected fluid type and operating ranges.  With high efficiency targets on the SuperTruck II, the proper experience and resources are required to create high-efficiency ORC turbines that can achieve these targets.  It is will be interesting to see what kind of engine advancements and technologies will be utilized from each design team throughout the outset and final completion of the SuperTruck II.  If you would like to learn more about SoftInWay’s AxSTREAM platform for design ORC Turbines in WHR cycles, please visit: http://www.softinway.com/software-applications/heat-balance-design-analysis/ 

References:

http://www.softinway.com/wp-content/uploads/2015/10/whr-based-on-SORC-10-2015.pdf

https://energy.gov/articles/energy-department-announces-137-million-investment-commercial-and-passenger-vehicle

https://www.trucks.com/2016/10/31/supertruck-program-5-year-phase/

https://energy.gov/sites/prod/files/2014/03/f8/deer12_sisken.pdf