Commonly HVAC systems are grouped into four main systems starting with the heating and air conditioning split system, which is the most ordinary implementation of residential applications encompassing both inside and outside installations. The application, which can be controlled with a central thermostat, consists of air conditioning system which cools the refrigerant to drop the temperature, and heating system which involves gas furnaces. Ducts used to circulate the adjusted air from both heating and conditioning, with the help of evaporator/fan coils – a terminal unit which is used to provide heating or cooling to the targeted space.
The configurations of the expanders used in the oil and gas industry makes it not only ideal but mandatory to perform train torsional analysis. Expander trains are commonly used in CCU and FCU units and in the production of nitric acid. Serving the purpose of energy recovery, various arrangement for power recovery train are illustrated to the left:
While the term of air conditioning in relation to automotive might instantly correlate to a system which provides passenger with a comfortable air temperature/environment, HVAC systems also are used for heating and cooling of batteries in such application as well as cooling of the vehicle fuel systems. Thermal management for automotive application isn’t easy though. Many factors have to be accounted for in order to build a dependable cooling system.
While talking about HVAC concerns and challenges which arise in automotive application, the biggest inconvenience commonly comes down to the lack of cold air produces. Mobile refrigeration/air conditioning systems come with quite a few concerns from two sides: the refrigeration side, where it removes heat and injects cold air, and from the electrical side which provides control. From the system, the most common challenges are found in moisture –which would fail the cooling system if present in the air, soiled condenser which would block air flow, and various other mechanical complications which might occurs.
A humid climate is defined as a condition where the average monthly latent load (energy required to remove moisture from the air) of environment’s air is the same or higher than the average monthly energy needed to cool the air during the cooling season. Using air with high latent load easily brings moisture in and accumulates it in building materials.
Maintaining humidity control isn’t an easy task. The HVAC unit has to be able to support a proper pressurization system using dehumidified air to entire the building. In order to provide the right dehumidification, a HVAC system must be able to dehumidify the air that flows across the cooling oil (which means the precise sizing of cooling coil must be selected to meet the load of both outside and return air). That is not the only criteria that an HVAC system needs to fulfill though. The system must also meet the sufficient run time to remove moisture from the interior air. In a humid condition, temperature control is not enough. Moisture control comes second on the priority list ( though this has to be fulfilled without scarifying the main goal of giving comfortable temperature to users).
The application of oil-free bearings have started to emanate due to the overall consistency of their performance and the minimized heat loss associated with air as the damping fluid. Studies on these bearing types for turbomachinery applications are neither trivial nor unique, as they have seen plenty of exposure within the commercial and military aircraft industries within turbo compressors and turboexpanders. However, the success of these specific applications are due to the fact that these turbomachines operate with light loads and relatively low temperatures. The main design challenges with foil air bearings are a result of poor rotor dynamic performance, material capabilities, and inadequate load capacities at high temperature/high load applications.
The complexity of combined cycles, without any turbine inlet air cooling, poses significant challenge in design of steam system and HRSG due to competing factors such as pinch point, heat and mass flows optimization etc. Knowledge of fluid viz properties of standard air (psychrometrics), standard gas for Joule Brayton cycle, steam for bottoming Rankine cycle and refrigerant for cooling system( for refrigerated inlet air cooling) as applied to complete cycle makes the process complete as well as complex. AxCYCLE™ is one such unique tool to simulate such combined cycle processes with multi fluid-multi phase flows including refrigeration. The standard HVAC features can easily be used for inlet air cooling refrigeration and integrated into the CCPP. Once a digital representation of the complex process is replicated and successfully ‘converged’ at design point, the challenge of optimization emerges. To facilitate optimization various tools namely AxCYCLE™ Map, Quest, Plan and Case are embedded integrally. As a first cut, users based on their experience apply AxCYCLE™ Map and vary one or two parameters to see the effect of operational parameters on cycle performance. AxCYCLE™ Quest opens the gates by allowing users to vary unlimited parameters, according to quasi-random Sobol sequences. mutli-Parameter optimization tasks are possible using AxCYCLE™ Plan – it uses design of experiments concepts. Once optimized the AxCYCLE™ Case tools allows off design simulation tasks. Exhibit below represents complexity of a combined cycle plant represented conveniently:
The majority of land based gas turbines can be assigned in two groups : (1) heavy frame engines and (2) aeroderivative engines. The first ones are characterized by lower pressure ratios that do not exceed 20 and tend to be physically large. By pressure ratio, we define the ratio of the compressor discharge pressure and the inlet air pressure. On the other hand, aeroderivative engines are derived from jet engines, as the name implies, and operate at very high compression ratios that usually exceed 30. In comparison to heavy frame engines, aeroderivative engines tend to be very compact and are useful where smaller power outputs are needed.
With the rate of how quickly technology in the HVAC industry is currently growing, the pool of talent in the market can’t quite seem to catch up. Day by day due to increasing demand and competition, leading companies in this industry is required to come up with new design and new technology with better efficiency, easier operation, and better control is needed. Demanding increase in technology does not meet with the current available skill pool. As a result, the hiring process for skilled labor takes considerably longer. Finally, once you take into account calculation of training and orientation, the entire hiring process requires a lot of investment both in time and money.
Lateral rotor-dynamic behavior is the most critical aspect in determining the reliability and operability of rotating equipment in the oil and gas industry – be it a centrifugal pump , compressor, steam or gas turbine, motor or generator. One way to evaluate operating reliability is identifying lateral rotor response to unbalance, i.e. by analytically determining damped unbalanced rotor response. Torsional response is sought only for train units comprising three or more coupled machines (excluding any gears). Experience suggests that the effect of other equipment in the train is normally not included in the lateral damped unbalanced response. Hence brief summary of various characteristics and a technique for analytical predictions of lateral behavior deserves attention by all.
The purpose of damped unbalanced rotor response is to identify critical speeds, associated amplification factors-AF (as per API standards AF greater than or equal to 2.5 is considered critical) and ability of rotor dynamics system to meet the separation requirements (margin of operating speed away from critical speed/s). The first step is ‘undamped’ unbalance response analysis for identifying mode shapes and critical speed-support stiffness map. ‘Damped’ unbalanced response analysis then follows for each critical speed within the speed range of 0 % to 125 % of trip speed. Unbalance or side load is placed at the locations that have been determined by the undamped analysis to affect a particular mode most adversely. The magnitude of the unbalances is four times the value of U as calculated by U = 6350 W/N. The aim then is to identify the frequency of each critical speed, frequency-phase and response amplitude data, deflected rotor shape due to unbalance and bode plots to compare absolute shaft motion with shaft motion relative to the bearing housing (support stiffness < 3.5 times the oil-film stiffness).