The present paper presents a high performance cooling/heating ventilation system using a rotary heat exchanger (RHE), together with a reverse-cycle heat pump (RCHP) that can be integrated with ...various heat sources. Energy consumption in the building sector is largely dominated by the energy consumed in maintaining comfortable conditions indoors. For example in many developed countries the building heating, ventilation and air conditioning (HVAC) systems consume up to 50% of the total energy consumed in buildings. Therefore energy efficient HVAC solutions in buildings are critical for realising CO2 targets at local and global level. There are many heating/cooling concepts that rely upon renewable energy sources and/or use natural low temperature heat sources in the winter and heat sinks in the summer. In the proposed system, waste energy from the exhaust air stream is used to precondition the outdoor air before it is supplied into the building. The hybrid system provides heating in the winter and cooling in the summer without any need for additional heating or cooling devices as required in conventional systems. Its performance is better than a typical reheat or air conditioning system in providing the same indoor air quality (IAQ) levels. It is shown that an energy saving up to 60% (heat energy) is achieved by using the proposed hybrid system in building ventilation applications.
•Hybrid ventilation system: the hybrid ventilation system uses a rotating regenerator and a reversible heat pump.•Heat recovery: heat recovery from exhaust air stream by rotary wheel type heat exchanger.•Reversible cycle heat pump (RCHP): additional heating or cooling of the supply air is provided by the RCHP.•Energy efficiency: energy savings of up to 60% using the proposed system are achievable.
The present article numerically optimizes the thermal performance of a rotary heat exchanger (RHEx) where its internal structure is modeled as a porous medium. The objective is to maximize the RHEx's ...heat transfer rate per unit of frontal surface area (
q″). The flow velocity through the porous matrix respects Darcy's law. Two thermal conditions between the solid matrix and the fluid are considered: (i) local thermal equilibrium – LTE and (ii), non-local thermal equilibrium – NLTE. The numerical calculations, which are implemented using a finite volume formulation, allow us to optimize two design variables, the length
L of the heat exchanger and the porosity
φ. The numerical results show that the figure of merit is substantially affected by both design variables and that optimal values of
L and
φ can be obtained. The numerical experiments also show that the optimum porosity is not a function of the pressure difference driving the flow across the RHEx. The study ends by addressing the effects of the porosity distribution and differential periods between the hot and cold sides of RHEx on the figure of merit. The numerical results are supported by a scale analysis.
The performance characteristics of a commercially available rotary heat exchanger or were determined using CFD. A rotary air pre-heater of a thermal power plant (fuelled by natural gas), situated in ...Ramin, Iran, was numerically modelled with full scale dimensions using 3D approach. This model was then validated against the experimentally measured values. After a satisfactory validation of the CFD model, a design modification was applied to the model by modelling the heat exchanger with four ducts, with hot and cold fluid ducts arranged alternatively. This was done to improve the heat the heat transfer from hot gases to cold air. The medium of heat exchange (core) is modelled as porous media, since the core in the actual equipment has many number of fine passages arranged in complex manner, which would make the modelling difficult. The model was subjected to same boundary conditions as the validation model. The temperature of the outlets and effectiveness of both the models were compared and was found out that the 4-ducts model is around 12% more effective than the base model.
This work is a first-of-a-kind feasibility study investigating technology options with gas/gas rotary heat exchangers for the water management in the integration of Natural Gas Combined Cycle (NGCC) ...plants with post-combustion carbon capture, with and without exhaust gas recirculation (EGR). A range of configurations are examined for wet and dry cooling of the flue gas entering a post- combustion capture (PCC) absorption system, and regenerative heating of the CO2-depleted flue gas prior to the power plant stack. First, this work examines the addition of a gas/gas rotary heat exchanger to transfer heat from the exhaust gas entering the absorber into the CO2-depleted gas stream leaving the absorber. It then investigates the performance of a configuration with an additional air/gas rotary heater to further reduce exhaust flue gas temperature and water consumption, and, eventually, a more compact arrangement which combined the two heaters into a single gas/gas/air heater with a trisector configuration. A thermal performance analysis was conducted for each of the previous configurations, in order to evaluate the dimensions and the operational parameters of the heaters. By replacing the direct contact cooler traditionally used in PCC technology by a dry-cooling system, a significant reduction in the overall process water usage and cooling water consumption associated to the capture plant can be achieved. The second part of this work examines the use of a similar system for NGCC plant with EGR. This strategy increases CO2 concentration in gas turbine exhaust gases and reduce O2 induced solvent degradation. In addition to the heat and water balance around the absorber column of the PCC process, an important aspect of EGR is that recirculated gas stream temperature should be as low as possible so that the gas turbine performance is not compromised. The performance of the rotary heat exchanger configurations is analysed at different recirculation ratios.
Rotary-heat exchanger which have three functions as a blower, a heat exchanger and a pump have been developed on the basis of a cross flow fan. In the first paper, the blower and pump performances of ...the rotary-heat exchanger were clarified. In the present paper, we report the heat transfer characteristics of it as a heater and a cooler. The experiments as a heater have been done using with several kinds of rotors that differ in shape. As a consequence, the experimental relation between the heat transfer coefficients and the parameters of the rotary-heat exchanger was obtained. And in the experiments as a cooler, it is clarified that the heat transfer coefficient is higher than that of a heater. In particular, condensed water droplets on the blades of rotor which are heat transfer surfaces are rapidly and continually blown off by the centrifugal force.
The developed rotary heat exchanger has three principal functions as follows, a blower, a heat exchanger and a pump. Structure is similar to cross flow fan. The blades also work as heat transfer ...surfaces. Further more, this rotor is equipped many circular tubes, liquid collection and distribution tanks to flow the cooling liquid. So previous studies about cross flow fans are not able to apply to this type of rotor directly. We prepared various samples which have different parameters in rotor diameter, length, diameter ratio of inner to outer and fin pitches. Throughout series of studies, we found the relation between the airflow rate and various parameters that mentioned before. A stationary guide impeller attached to the outlet side of rotor and a rotary impeller attached to the inlet side are necessary to support the pumping action. And we indicate the relation between the water flow rate and the impeller's shapes.
With the rise of acceptable operating temperatures for information technology (IT) equipment, using ambient air has been a growing trend for data centers. In this computational study, a thermal wheel ...is used as a rotary air-to-air heat exchanger extracting heat from IT equipment and dissipating it to the ambient. The wheel is made of a metallic honeycomb material that enables air to pass through while convectively transferring heat. A computational model has been developed to calculate the volumetric air flow rate required for an assigned cooling load. When the ambient temperature is too high, direct expansion cooling is used as a secondary approach and modeled in building energy usage estimation software, EnergyPlus. The integrated computational model calculates overall power usage effectiveness (PUE) for data centers. Using weather data for a specific location, PUEs for several different climates can be obtained. Even without considering the energy savings that is produced through less air quality and humidity control, for a cooling load of 400 kW, it was found that overall PUE can be as low as 1.10 in Helsinki, Finland and 1.20 in Atlanta, Georgia. The presented model can be used to determine the system performance with varying location, cooling load, and regenerative heat exchanger parameters.
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