Heat Balance Analysis of Thermal Energy Storage

A primary challenge of meeting the increased demand in energy is that energy supply and accessibility isn’t consistent throughout different geographical areas. Availability of energy sources is considered extremely critical in clean/renewable energy applications such as wind and solar where energy source is quite scarce and unreliable. Thermal energy storage in particular is often being looked into with the universal rise of energy demand from every part of the world. With the help of energy storage technology, it allows any excess of thermal energy to be stored and used at a later time/date where it’s needed.

Energy Storage
Source: http://www.climatetechwiki.org/sites/climatetechwiki.org/files/images/extra/storage.jpg

Thermal energy storage can be achieved with widely diverse technologies, including molten salt application. By heating the salt and storing it in insulated containers, users can pump out the salt to release the heat stored when the energy is needed. For example, with solar application the molten salt stores the excess heat that is produced during the day and releases it at night to produce electricity.
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Importance of Preliminary Design for Centrifugal Compressors

Preliminary Design in AxSTREAM

Centrifugal compressors span a number of applications including oil compression systems, gas shift systems, HVAC, refrigeration, and turbochargers. It works by using energy from the flow to raise pressure, using gas to enter the primary suction eye (impeller). As the impeller rotates, the blades on the impeller push the gas outwards from the center to the open end of impeller to form a compression. Compressors are commonly used for combustion air supplies on cooling and drying systems. In HVAC system application, fans produce air movement to the space that is being conditioned. As a key component of an energy cycle, design/performance requirement must be met. While a design can easily be scaled from an existing design through appropriate parameters, a tailored design from scratch to confirm with design requirement for the specific cycle would give a better match and improve overall cycle performance.

There are variants of non-aerodynamic constraints in centrifugal compressor design practice, from frame size to durability and ultimately cost. An optimized impeller design should also ensure that aerodynamic problems associated with the all compressor components are minimized. With all of these (aerodynamic and non-aerodynamic) design constraints, there is no better way to optimize your compressor design than starting from the preliminary step, making sure that your compressor meets your criteria from a one dimensional basis ( a step that is often overlooked in practice).
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The Economics of Power Generation

Economics of Power GenerationThere are two crucial factors in any power generating system: performance and economy. As we know, higher efficiency is naturally more desirable, though higher efficiency plants usually come with the price of high cost investment. A power system would simply not be feasible should one neglect one of the two main factors. A highly efficient plant would not be feasible in practice if it gives no financial incentives to the producer as well as the end-user. A good power plant design must possess a good balance of efficiency and economy.

One of the main goals in power generation practice is to deliver the lowest possible cost per unit of electricity to meet the growing demand. Often in practice, economic assessment of a power plant is depicted by their levelized cost of energy (LCOE), also known as  levelized energy cost (LEC), which is the average price per unit of power delivered to break even with total cost (capital and operating) over the length of its operating lifetime.

Generally, cost factor which contributes to power generation can be categorized into two main groups: capital cost and operating charges. Capital cost (usually consisting of a series of fixed cost factors which do not vary with the level of output) encompasses equipment, rent/land cost, and any other costs associated with the establishment of the power generation plant, up until when it’s ready to operate. This is a critical data point needed for accurate investment decision making. Whereas operating cost (combination of fixed, semi-fixed and variable charges) covers all costs related to daily operational and/or production cost incurred – which should include maintenance, fuel, feed water, etc.

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The Use of SCO2 in Power Generation

Lab imageGlobal warming and the growing demand for energy are two primary problems rising in the power generation industry. A simple solution to these problems has been researched for a number of years. The SCO2 Brayton cycle is often looked into as an alternative working fluid for power generation cycles due to its compactness, high efficiency and small environmental footprint. The usage of SCO2 in nuclear reactors has been studied since the early 2000s in development of Generation IV nuclear reactors, but the idea itself can be traced back to the 1940s. During this time however, no one really looked into the potential of supercritical CO2 since steam was found to be efficient enough, not to mention it was the more understood technology when compared to SCO2. In modern times though, demand of more efficient energy continues to rise and with it, the need for SCO2.

The potential of supercritical CO2 implementation is vast across power generation applications spanning nuclear, geothermal and even fossil fuel.  The cycle envisioned is a non-condensing closed loop Brayton cycle with heat addition and rejection inside the expander to indirectly heat up the carbon dioxide working fluid.
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Identifying Compressor Problems

Centrifugal Compressor for Refrigeration Because the most vital part of a refrigeration and HVAC system is to function optimally, compressors are used to raise the temperature and pressure of the low superheated gas to move fluid into the condenser. Consequently, refrigeration compressors must be properly maintained through regular maintenance, testing and inspection. There are a couple conditions which would indicate compressor problem or failures. However, with the right supervision it is possible to avoid further damage. Through this post we will identify and discuss some of these conditions:
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The Benefits of a Variable Frequency Drive

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.

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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.

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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.

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Alternative Refrigerants to R-22

Gas tanks

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.

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Factors in your HVAC Selection


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.

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