- Email: [email protected]
02760 Optimal chiller sequencing by branch and bound method for saving energy
13 Space heating and cooling temperatures can be tailored to appropriate value by preparing a eutectic mixture of the lauric and the palmitic acids. In the present study, the thermal analysis based on differential scanning calorimetry (DSC) technique shows that the mixture of 69.0 wt% LA and 31 wt% PA forms a eutectic mixture having melting temperature of 35.2°C and the latent heat of fusion of 166.3 J g 1. This study also considers the experimental determination of the thermal characteristics of the eutectic mixture during the heat charging and discharging processes. Radial and axial temperature distribution, heat transfer coefficient between the heat transfer fluid (HTF) pipe and the PCM, heat recovery rate and heat charging and discharging fractions were experimentally established employing a vertical concentric pipe-inpipe energy storage system. The changes of these characteristics were evaluated with respect to the effect of inlet HTF temperature and mass flow rate. The DSC thermal analysis and the experimental results indicate that the L A - P A eutectic mixture can be a potential material for low temperature thermal energy storage applications in terms of its thermo-physical and thermal characteristics.
05•02753 Long-term validated simulation of a building integrated photovoltaic system Mondol, J. D. et al. Solar Energy, 2005, 78, (2), 163-176. Electrical and thermal simulations of a building integrated photovoltaic system were undertaken with a transient system simulation program using real field input weather data. Predicted results were compared with actual measured data. A site dependent global-diffuse correlation is proposed. The best-tilted surface radiation model for estimating insolation on the inclined surface was selected by statistical tests. To predict the module temperature, a linear correlation equation is developed which relates the temperature difference between module and ambient to insolation. Different combinations of tilted surface radiation model, global-diffuse correlation model and predicted module temperature were used to carry out the simulation and corresponding simulated results compared with the measured data to determine the best combination which gave the least error. Results show that modification of global-diffuse correlation and module temperature prediction improved the overall accuracy of the simulation model. The monthly error between measured and predicted PV output was lied below 16%. Over the period of simulation, the monthly average error between measured and predicted PV output was estimated to be 6.79% whereas, the monthly average error between measured and predicted inverter output was 4.74%.
05•02754 Maintaining uniform surface temperature along pipes by insulation Sahin, A. Z. and Kalyon, M. Energy, 2005, 30, (5), 637-647. An analytical solution is obtained for the insulation thickness variation over a pipe to maintain a uniform outer surface temperature. A high temperature fluid is considered to be flowing through the pipe. The amount of the insulation material is assumed to be limited. Heat transfer from the outer surface of the pipe is thr.ough convection and radiation. The solution of the insulation thickness is found to be independent from the outer surface convective and radiative heat transfer coefficients. In addition, the solution is found to be very close to linear variation, which is very easy to implement in practice.
05102755 Neural computing thermal comfort index for HVAC systems Atthajariyakul, S. and Leephakpreeda, T. Energy Conversion and Management, 2005, 46, (15-16), 2553-2565. The primary purpose of a heating, ventilating and air conditioning (HVAC) system within a building is to make occupants comfortable. Without real time determination of h u m a n thermal comfort, it is not feasible for the HVAC system to yield controlled conditions of the air for h u m a n comfort all the time. This paper presents a practical approach to determine human thermal comfort quantitatively via neural computing. The neural network model allows real time determination of the thermal comfort index, where it is not practical to compute the conventional predicted mean vote (PMV) index itself in real time. The feed forward neural network model is proposed as an explicit function of the relation of the PMV index to accessible variables, i.e. the air temperature, wet bulb temperature, globe temperature, air velocity, clothing insulation and h u m a n activity. An experiment in an air conditioned office room was done to demonstrate the effectiveness of the proposed methodology. The results show good agreement between the thermal comfort index calculated from the neural network model in real time and those calculated from the conventional PMV model.
05•02756 Numerical analysis of a PCM thermal storage system with varying wall temperature Halawa, E. et al. Energy Conversion and Management, 2005, 46, (1516), 2592 2604.
Numerical analysis of melting and freezing of a PCM thermal storage unit (TSU) with varying wall temperature is presented. The TSU under analysis consists of several layers of thin slabs of a PCM subjected to convective boundary conditions where air flows between the slabs. The model employed takes into account the variations in wall temperature along the direction of air flow as well as the sensible heat. The paper discusses typical characteristics of the melting/freezing of PCM slabs in an air stream and presents some results of the numerical simulation in terms of air outlet temperatures and heat transfer rates during the whole periods of melting and freezing. Considerations in the design of the TSU are also given.
05•02757 Numerical simulation on performance band of automotive air conditioning system with a variable displacement compressor Tian, C. and Li, X. Energy Conversion and Management, 2005, 46, (17), 2718-2738. A mathematical model of an automotive air conditioning (AAC) system with a variable displacement compressor (VDC) is developed in order to simulate and analyse its steady-state performance. A test system is established to validate the system model, and the simulated results agree well with the experimental data. The simulation results show that there is a performance band for the system parameter relationship due to the frictional forces between the moving components of the VDC within which all the steady-state points fall. Different from the one-one parameter relationship in an A A C system with a fixed displacement compressor, it is a multiple one-parameter relationship in the A A C system with a VDC. The influence of the compressor rotary speed, air temperature at the condenser inlet and air flow rate through the evaporator on the performance band is simulated. The evaporating pressure performance band moves in the direction of increasing evaporator inlet air temperature and increasing evaporating pressure when the compressor rotary speed increases. The evaporating pressure performance band moves in the direction of decreasing evaporating inlet air temperature and decreasing evaporating pressure when air temperature at the condenser inlet or air flow rate through the evaporator increases.
05•02758 Numerical study for enhancing the thermal conductivity of phase change material (PCM) storage using high thermal conductivity porous matrix Mesalhy, O. et al. Energy Conversion and Management, 2005, 46, (6), 847 867. In this paper, the melting process inside an irregular geometry filled with high thermal conductivity porous matrix saturated with phase change material PCM is investigated numerically. The numerical model is resting on solving the volume averaged conservation equations for mass, m o m e n t u m and energy with phase change (melting) in the porous medium. The convection motion of the liquid phase inside the porous matrix is solved considering the Darcy, Brinkman and Forchiemer effects. A local thermal non-equilibrium assumption is considered clue to the large difference in thermal properties between the solid matrix and PCM by applying a two energy equation model. The numerical code shows good agreement for pure PCM melting with another published numerical work. Through this study it is found that the presence of the porous matrix has a great effect on the heat transfer and melting rate of the PCM energy storage. Decreasing the porosity of the matrix increases the melting rate, but it also damps the convection motion. It is also found that the best technique to enhance the response of the PCM storage is to use a solid matrix with high porosity and high thermal conductivity.
05102759 One-zone simulation model of an oil-injected screw chiller Le, C. V. et al. International Journal of Energy Research, 2005, 28, (15), 1343-1359. This paper presents a one-zone steady-state system model of an oilinjected screw chiller. The model can be used as a design and opfimisation tool for system performance of multiple-chiller plant in process industries. All major components of the system are modelled in a modular format including the oil-injected screw compressor, shell and tube condenser, flooded evaporator and a high side-float value. The model results are validated with the experimental data from a multiple-chiller plant at a process industry. The validated results show that the part-load ratio and the glycol-water temperature at the evaporator inlet significantly affect the system performance as compared to the temperature of cooling water entering the condenser.
05•02760 Optimal chiller sequencing by branch and bound method for saving energy Chang, Y.-C. et aL Energy Conversion and Management, 2005, 46, (13 14), 2158-2172. This paper proposes a method for using the branch and bound (B&B) method to solve the optimal chiller sequencing (OCS) problem and to eliminate the deficiencies of conventional methods. The coefficient of
Fuel and Energy Abstracts
November 2005 401
13 Space heating and cooling performance (COP) of the chiller is adopted as the objective function because it is concave. The Lagrangian method determines the optimal chiller loading (OCL) in each feasible state. The potential performance of the proposed method is examined with reference to an example system. The proposed method consumes much less power than the conventional method and is very appropriate for application in air conditioning systems.
05•02761 Parametric study on the silica gel-calcium chloride composite desiccant rotary wheel employing fractal BET adsorption isotherm Zhang, X. J. et al. International Journal of Energy Research, 2005, 29, (1), 37-51. In this paper a family of new silica gel-calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using calcium chloride as impregnated salt can be controllably modified by varying the amount of the salt inside the pores. The thermodynamic performance of such desiccant rotary wheel is analysed based on the adsorption equilibrium equations obtained through nonlinear regressions using fractal BET theory. The simulation results show that the new composite desiccants can be effectively used in a rotary wheel dehumidifier and to improve its performance, various optimum operational/system parameters have been identified.
05•02762 heating
PCM-facade-panel for daylighting and room
Weinl/ider, H. et al. Solar Energy, 2005, 78, (2), 177-186. Double glazings combined with phase change materials (PCM) result in daylighting elements with promising properties. Light transmittances in the range of 0.4 can be achieved with such facade panels. Compared to a double glazing without PCM, a facade panel with PCM shows about 30% less heat losses in south oriented facades. Solar heat gains are also reduced by about 50%. This results in calculated U,f~values of -0.3 to -0.5 W m - 2 K - 1 depending on PCM used. For an optimized panel, the authors calculated an Ueff-value of -0.6 W m ~ K - . Although the U~ff-value of a double glazing is -0.8 W m -2 K -1, the PCM-systems may prove advantageous in lightweight constructed buildings due to their equalized energy balance during the course of day. Facade panels with PCM improve thermal comfort considerably in winter, especially during evenings. In summer, such systems show low heat gains, which reduces peak cooling loads during the day. Additional heat gains in the evening can be drawn off by night-time ventilation. If a PCM with a low melting temperature of up to 30°C is used, thermal comfort in summer will also improve during the day, compared to a double glazing without or with inner sun protection. A homogeneous appearance of the PCM-systems is achievable by use of a concealment, like a screen-print glazing.
05/02763 Performance of components of ice slurry systems: pumps, plate heat exchangers, and fittings Nc~rgaard, E. et al. International Journal of Refrigeration, 2005, 28, (1), 83 91. In recent years, a lot of important work has been carried out in order to gather knowledge of the fundamental behaviour of ice slurry in piping systems and heat exchangers. The scope of this work has been to bring ice slurry one step closer to practical application, i.e. to provide a basis for selecting distribution pumps and investigating flow in piping system components. The performance of different multiple-stage centrifugal pumps has been measured with ice concentrations in the range from 0 to 30 wt% of ice. It was found that the pump operation is reliable in the entire range of ice concentrations. The pump performance decreases with increasing ice concentration due to the increasing viscosity of the ice slurry. A viscosity model has been applied to compare the manufacturer data on the viscosity dependency. From the results, it cannot be concluded whether the pump performance is entirely determined by the increasing viscosity or whether the solid particles have an additional effect. The flow behaviour of ice slurry has been investigated in a test rig with transparent pipes to allow visual observation of flow patterns in various single components such as fittings, valves and heat exchangers. Finally, pressure loss coefficients in selected fittings have been measured to reveal the dependency of ice concentration.
05•02764 systems
Real-time tuning of PI controllers in HVAC
Qu, G. and Zaheeruddin, M. International Journal of Energy Research, 2005, 28, (15), 1313-1327. The problem of tuning single-loop controllers in heating, ventilating and air conditioning (HVAC) systems is explored. The HVAC process was described by a first-order-plus-dead-time (FOPDT) model. By using recursive least squares method, the model parameters were updated while the system remained in closed-loop. The H ~ loop-
402
Fuel and Energy Abstracts
November 2005
shaping tuning rules published in the literature were transformed to discrete-time tuning rules and were implemented in an adaptive PI control strategy. The methodology was applied to a discharge air temperature (DAT) control system. The output responses of adaptive PI controller were compared with a LQR optimal adaptive controller. Simulation results show that the adaptively tuned PI controller is able to track setpoint changes very well in the presence of changes in plant parameters, disturbances and external noise acting on the system.
05/02765 Residential building envelope heat gain and cooling energy requirements Lain, J. C. et al. Energy, 2005, 30, (7), 933 951. The autrhors present the energy use situation in Hong Kong from 1979 to 2001. The primary energy requirement (PER) nearly tripled during the 23-year period, rising from 195,405 to 572,684 TJ. Most of the PER was used for electricity generation, and the electricity use in residential buildings rose from 7556 TJ (2099 GWh) to 32,799 TJ (9111 GWh), an increase of 334%. Air-conditioning accounted for about 40% of the total residential sector electricity consumption. A total of 144 buildings completed in the month of June during 1992-2001 were surveyed. Energy performance of the building envelopes was investigated in terms of the overall thermal transfer value (OTTV). To develop the appropriated parameters used in OTTV calculation, long-term measured weather data such as ambient temperature (1960-2001), horizontal global solar radiation (1992-2001) and global solar radiation on vertical surfaces (1996-2001) were examined. The OTTV found varied from 27 to 44 W / m z with a mean value of 37.7 W/m e. Building energy simulation technique using DOE-2.1E was employed to determine the cooling requirements and hence electricity use for building envelope designs with different OTTVs. It was found that cooling loads and electricity use could be expressed in terms of a simple two-parameter linear regression equation involving OTTV.
05•02766 Response of conventional and energy-saving buildings to design and human dependent factors Filippfn, C. Solar Energy, 2005, 78, (3), 455-470. During the year 2000, energy-efficient buildings for low-income students at La Pampa University were designed and constructed. Buildings are located at the centre of La Pampa province, in a temperate semi-arid region of central Argentina Socio-economic, educational and environmental reasons have driven the design. Energy conservation devices, passive solar heating, natural ventilation and solar protection were the main strategies. The resulting design comprises two blocks of apartments with a useful floor area of 700 m 2 and main spaces. Two bedrooms, a dining room and essential services make up each apartment. Solar windows are provided for all main spaces. Northern shading devices and metallic pergolas protect all windows in summer. Once the building was finished, a monitoring plan started on December 2000. This paper shows the results of the thermal and energy behaviour of apartments. The evolution of internal temperature was different in each apartment. The consumption of natural gas varied among dwellers, but the volume consumed was lower than that of conventional dwellings. Without extra building cost dwellers live under good higrothermal conditions at 50% of the auxiliary energy consumed by conventional dwellings.
05•02767 Sensor fault detection and validation of VAV terminals in air conditioning systems Wang, S. and Qin, J. Energy Conversion and Management, 2005, 46, (15 16), 2482-2500. Sensor failure and bias are harmful to the process control of air conditioning systems, resulting in poor control of the indoor environment and waste of energy. A strategy is developed for the flow sensor fault detection and validation of variable air volume (VAV) terminals in air conditioning systems. Principal component analysis (PCA) models at both system and terminal levels are built and employed in the strategy. Sensor faults are detected using both the T2 statistic and square prediction error (SPE) and isolated using the SPE contribution plot. As the reliability and sensitivity of fault isolation may be affected by multiple faults at the system level, a terminal level PCA model is designed to further examine the suspicious terminals. The faulty sensor is reconstructed after it is isolated by the strategy, and the F D D strategy repeats using the recovered measurements until no further fault can be detected. Thus, the sensitivity and robustness of the F D D strategy is enhanced significantly. The sensor fault detection and validation strategy, as weI1 as the sensor reconstruction strategy for fault tolerant control, are evaluated by simulation and field tests.
05/02768 Simulation of a cavity insulated by a vertical single band cold air curtain Chen, Y.-G. and Yuan, X.-L. Energy Conversion and Management, 2005, 46, (11-12), 1745 1756. The cold air curtain used for cavity insulation in the present study is a fundamental idealization of a refrigerated air curtain in display cases. Flow and heat transfer characteristics of vertical single band cold air
05•02753 Long-term validated simulation of a building integrated photovoltaic system Mondol, J. D. et al. Solar Energy, 2005, 78, (2), 163-176. Electrical and thermal simulations of a building integrated photovoltaic system were undertaken with a transient system simulation program using real field input weather data. Predicted results were compared with actual measured data. A site dependent global-diffuse correlation is proposed. The best-tilted surface radiation model for estimating insolation on the inclined surface was selected by statistical tests. To predict the module temperature, a linear correlation equation is developed which relates the temperature difference between module and ambient to insolation. Different combinations of tilted surface radiation model, global-diffuse correlation model and predicted module temperature were used to carry out the simulation and corresponding simulated results compared with the measured data to determine the best combination which gave the least error. Results show that modification of global-diffuse correlation and module temperature prediction improved the overall accuracy of the simulation model. The monthly error between measured and predicted PV output was lied below 16%. Over the period of simulation, the monthly average error between measured and predicted PV output was estimated to be 6.79% whereas, the monthly average error between measured and predicted inverter output was 4.74%.
05•02754 Maintaining uniform surface temperature along pipes by insulation Sahin, A. Z. and Kalyon, M. Energy, 2005, 30, (5), 637-647. An analytical solution is obtained for the insulation thickness variation over a pipe to maintain a uniform outer surface temperature. A high temperature fluid is considered to be flowing through the pipe. The amount of the insulation material is assumed to be limited. Heat transfer from the outer surface of the pipe is thr.ough convection and radiation. The solution of the insulation thickness is found to be independent from the outer surface convective and radiative heat transfer coefficients. In addition, the solution is found to be very close to linear variation, which is very easy to implement in practice.
05102755 Neural computing thermal comfort index for HVAC systems Atthajariyakul, S. and Leephakpreeda, T. Energy Conversion and Management, 2005, 46, (15-16), 2553-2565. The primary purpose of a heating, ventilating and air conditioning (HVAC) system within a building is to make occupants comfortable. Without real time determination of h u m a n thermal comfort, it is not feasible for the HVAC system to yield controlled conditions of the air for h u m a n comfort all the time. This paper presents a practical approach to determine human thermal comfort quantitatively via neural computing. The neural network model allows real time determination of the thermal comfort index, where it is not practical to compute the conventional predicted mean vote (PMV) index itself in real time. The feed forward neural network model is proposed as an explicit function of the relation of the PMV index to accessible variables, i.e. the air temperature, wet bulb temperature, globe temperature, air velocity, clothing insulation and h u m a n activity. An experiment in an air conditioned office room was done to demonstrate the effectiveness of the proposed methodology. The results show good agreement between the thermal comfort index calculated from the neural network model in real time and those calculated from the conventional PMV model.
05•02756 Numerical analysis of a PCM thermal storage system with varying wall temperature Halawa, E. et al. Energy Conversion and Management, 2005, 46, (1516), 2592 2604.
Numerical analysis of melting and freezing of a PCM thermal storage unit (TSU) with varying wall temperature is presented. The TSU under analysis consists of several layers of thin slabs of a PCM subjected to convective boundary conditions where air flows between the slabs. The model employed takes into account the variations in wall temperature along the direction of air flow as well as the sensible heat. The paper discusses typical characteristics of the melting/freezing of PCM slabs in an air stream and presents some results of the numerical simulation in terms of air outlet temperatures and heat transfer rates during the whole periods of melting and freezing. Considerations in the design of the TSU are also given.
05•02757 Numerical simulation on performance band of automotive air conditioning system with a variable displacement compressor Tian, C. and Li, X. Energy Conversion and Management, 2005, 46, (17), 2718-2738. A mathematical model of an automotive air conditioning (AAC) system with a variable displacement compressor (VDC) is developed in order to simulate and analyse its steady-state performance. A test system is established to validate the system model, and the simulated results agree well with the experimental data. The simulation results show that there is a performance band for the system parameter relationship due to the frictional forces between the moving components of the VDC within which all the steady-state points fall. Different from the one-one parameter relationship in an A A C system with a fixed displacement compressor, it is a multiple one-parameter relationship in the A A C system with a VDC. The influence of the compressor rotary speed, air temperature at the condenser inlet and air flow rate through the evaporator on the performance band is simulated. The evaporating pressure performance band moves in the direction of increasing evaporator inlet air temperature and increasing evaporating pressure when the compressor rotary speed increases. The evaporating pressure performance band moves in the direction of decreasing evaporating inlet air temperature and decreasing evaporating pressure when air temperature at the condenser inlet or air flow rate through the evaporator increases.
05•02758 Numerical study for enhancing the thermal conductivity of phase change material (PCM) storage using high thermal conductivity porous matrix Mesalhy, O. et al. Energy Conversion and Management, 2005, 46, (6), 847 867. In this paper, the melting process inside an irregular geometry filled with high thermal conductivity porous matrix saturated with phase change material PCM is investigated numerically. The numerical model is resting on solving the volume averaged conservation equations for mass, m o m e n t u m and energy with phase change (melting) in the porous medium. The convection motion of the liquid phase inside the porous matrix is solved considering the Darcy, Brinkman and Forchiemer effects. A local thermal non-equilibrium assumption is considered clue to the large difference in thermal properties between the solid matrix and PCM by applying a two energy equation model. The numerical code shows good agreement for pure PCM melting with another published numerical work. Through this study it is found that the presence of the porous matrix has a great effect on the heat transfer and melting rate of the PCM energy storage. Decreasing the porosity of the matrix increases the melting rate, but it also damps the convection motion. It is also found that the best technique to enhance the response of the PCM storage is to use a solid matrix with high porosity and high thermal conductivity.
05102759 One-zone simulation model of an oil-injected screw chiller Le, C. V. et al. International Journal of Energy Research, 2005, 28, (15), 1343-1359. This paper presents a one-zone steady-state system model of an oilinjected screw chiller. The model can be used as a design and opfimisation tool for system performance of multiple-chiller plant in process industries. All major components of the system are modelled in a modular format including the oil-injected screw compressor, shell and tube condenser, flooded evaporator and a high side-float value. The model results are validated with the experimental data from a multiple-chiller plant at a process industry. The validated results show that the part-load ratio and the glycol-water temperature at the evaporator inlet significantly affect the system performance as compared to the temperature of cooling water entering the condenser.
05•02760 Optimal chiller sequencing by branch and bound method for saving energy Chang, Y.-C. et aL Energy Conversion and Management, 2005, 46, (13 14), 2158-2172. This paper proposes a method for using the branch and bound (B&B) method to solve the optimal chiller sequencing (OCS) problem and to eliminate the deficiencies of conventional methods. The coefficient of
Fuel and Energy Abstracts
November 2005 401
13 Space heating and cooling performance (COP) of the chiller is adopted as the objective function because it is concave. The Lagrangian method determines the optimal chiller loading (OCL) in each feasible state. The potential performance of the proposed method is examined with reference to an example system. The proposed method consumes much less power than the conventional method and is very appropriate for application in air conditioning systems.
05•02761 Parametric study on the silica gel-calcium chloride composite desiccant rotary wheel employing fractal BET adsorption isotherm Zhang, X. J. et al. International Journal of Energy Research, 2005, 29, (1), 37-51. In this paper a family of new silica gel-calcium chloride composite adsorbents is presented for desiccant rotary wheel in dehumidification system. For these desiccants the water sorption equilibrium has been measured in a wide relative vapour pressure range. This experimental study shows that the vapour adsorption properties of the composites using calcium chloride as impregnated salt can be controllably modified by varying the amount of the salt inside the pores. The thermodynamic performance of such desiccant rotary wheel is analysed based on the adsorption equilibrium equations obtained through nonlinear regressions using fractal BET theory. The simulation results show that the new composite desiccants can be effectively used in a rotary wheel dehumidifier and to improve its performance, various optimum operational/system parameters have been identified.
05•02762 heating
PCM-facade-panel for daylighting and room
Weinl/ider, H. et al. Solar Energy, 2005, 78, (2), 177-186. Double glazings combined with phase change materials (PCM) result in daylighting elements with promising properties. Light transmittances in the range of 0.4 can be achieved with such facade panels. Compared to a double glazing without PCM, a facade panel with PCM shows about 30% less heat losses in south oriented facades. Solar heat gains are also reduced by about 50%. This results in calculated U,f~values of -0.3 to -0.5 W m - 2 K - 1 depending on PCM used. For an optimized panel, the authors calculated an Ueff-value of -0.6 W m ~ K - . Although the U~ff-value of a double glazing is -0.8 W m -2 K -1, the PCM-systems may prove advantageous in lightweight constructed buildings due to their equalized energy balance during the course of day. Facade panels with PCM improve thermal comfort considerably in winter, especially during evenings. In summer, such systems show low heat gains, which reduces peak cooling loads during the day. Additional heat gains in the evening can be drawn off by night-time ventilation. If a PCM with a low melting temperature of up to 30°C is used, thermal comfort in summer will also improve during the day, compared to a double glazing without or with inner sun protection. A homogeneous appearance of the PCM-systems is achievable by use of a concealment, like a screen-print glazing.
05/02763 Performance of components of ice slurry systems: pumps, plate heat exchangers, and fittings Nc~rgaard, E. et al. International Journal of Refrigeration, 2005, 28, (1), 83 91. In recent years, a lot of important work has been carried out in order to gather knowledge of the fundamental behaviour of ice slurry in piping systems and heat exchangers. The scope of this work has been to bring ice slurry one step closer to practical application, i.e. to provide a basis for selecting distribution pumps and investigating flow in piping system components. The performance of different multiple-stage centrifugal pumps has been measured with ice concentrations in the range from 0 to 30 wt% of ice. It was found that the pump operation is reliable in the entire range of ice concentrations. The pump performance decreases with increasing ice concentration due to the increasing viscosity of the ice slurry. A viscosity model has been applied to compare the manufacturer data on the viscosity dependency. From the results, it cannot be concluded whether the pump performance is entirely determined by the increasing viscosity or whether the solid particles have an additional effect. The flow behaviour of ice slurry has been investigated in a test rig with transparent pipes to allow visual observation of flow patterns in various single components such as fittings, valves and heat exchangers. Finally, pressure loss coefficients in selected fittings have been measured to reveal the dependency of ice concentration.
05•02764 systems
Real-time tuning of PI controllers in HVAC
Qu, G. and Zaheeruddin, M. International Journal of Energy Research, 2005, 28, (15), 1313-1327. The problem of tuning single-loop controllers in heating, ventilating and air conditioning (HVAC) systems is explored. The HVAC process was described by a first-order-plus-dead-time (FOPDT) model. By using recursive least squares method, the model parameters were updated while the system remained in closed-loop. The H ~ loop-
402
Fuel and Energy Abstracts
November 2005
shaping tuning rules published in the literature were transformed to discrete-time tuning rules and were implemented in an adaptive PI control strategy. The methodology was applied to a discharge air temperature (DAT) control system. The output responses of adaptive PI controller were compared with a LQR optimal adaptive controller. Simulation results show that the adaptively tuned PI controller is able to track setpoint changes very well in the presence of changes in plant parameters, disturbances and external noise acting on the system.
05/02765 Residential building envelope heat gain and cooling energy requirements Lain, J. C. et al. Energy, 2005, 30, (7), 933 951. The autrhors present the energy use situation in Hong Kong from 1979 to 2001. The primary energy requirement (PER) nearly tripled during the 23-year period, rising from 195,405 to 572,684 TJ. Most of the PER was used for electricity generation, and the electricity use in residential buildings rose from 7556 TJ (2099 GWh) to 32,799 TJ (9111 GWh), an increase of 334%. Air-conditioning accounted for about 40% of the total residential sector electricity consumption. A total of 144 buildings completed in the month of June during 1992-2001 were surveyed. Energy performance of the building envelopes was investigated in terms of the overall thermal transfer value (OTTV). To develop the appropriated parameters used in OTTV calculation, long-term measured weather data such as ambient temperature (1960-2001), horizontal global solar radiation (1992-2001) and global solar radiation on vertical surfaces (1996-2001) were examined. The OTTV found varied from 27 to 44 W / m z with a mean value of 37.7 W/m e. Building energy simulation technique using DOE-2.1E was employed to determine the cooling requirements and hence electricity use for building envelope designs with different OTTVs. It was found that cooling loads and electricity use could be expressed in terms of a simple two-parameter linear regression equation involving OTTV.
05•02766 Response of conventional and energy-saving buildings to design and human dependent factors Filippfn, C. Solar Energy, 2005, 78, (3), 455-470. During the year 2000, energy-efficient buildings for low-income students at La Pampa University were designed and constructed. Buildings are located at the centre of La Pampa province, in a temperate semi-arid region of central Argentina Socio-economic, educational and environmental reasons have driven the design. Energy conservation devices, passive solar heating, natural ventilation and solar protection were the main strategies. The resulting design comprises two blocks of apartments with a useful floor area of 700 m 2 and main spaces. Two bedrooms, a dining room and essential services make up each apartment. Solar windows are provided for all main spaces. Northern shading devices and metallic pergolas protect all windows in summer. Once the building was finished, a monitoring plan started on December 2000. This paper shows the results of the thermal and energy behaviour of apartments. The evolution of internal temperature was different in each apartment. The consumption of natural gas varied among dwellers, but the volume consumed was lower than that of conventional dwellings. Without extra building cost dwellers live under good higrothermal conditions at 50% of the auxiliary energy consumed by conventional dwellings.
05•02767 Sensor fault detection and validation of VAV terminals in air conditioning systems Wang, S. and Qin, J. Energy Conversion and Management, 2005, 46, (15 16), 2482-2500. Sensor failure and bias are harmful to the process control of air conditioning systems, resulting in poor control of the indoor environment and waste of energy. A strategy is developed for the flow sensor fault detection and validation of variable air volume (VAV) terminals in air conditioning systems. Principal component analysis (PCA) models at both system and terminal levels are built and employed in the strategy. Sensor faults are detected using both the T2 statistic and square prediction error (SPE) and isolated using the SPE contribution plot. As the reliability and sensitivity of fault isolation may be affected by multiple faults at the system level, a terminal level PCA model is designed to further examine the suspicious terminals. The faulty sensor is reconstructed after it is isolated by the strategy, and the F D D strategy repeats using the recovered measurements until no further fault can be detected. Thus, the sensitivity and robustness of the F D D strategy is enhanced significantly. The sensor fault detection and validation strategy, as weI1 as the sensor reconstruction strategy for fault tolerant control, are evaluated by simulation and field tests.
05/02768 Simulation of a cavity insulated by a vertical single band cold air curtain Chen, Y.-G. and Yuan, X.-L. Energy Conversion and Management, 2005, 46, (11-12), 1745 1756. The cold air curtain used for cavity insulation in the present study is a fundamental idealization of a refrigerated air curtain in display cases. Flow and heat transfer characteristics of vertical single band cold air