Cascade control is one of the most successful methods for improving single loop control performance. This control can stabilize the system, minimalize both of oscillation and integral error of interference in manipulation variables. Cascade control structure consists of two controllers where loop feedback in the loop feedback. This research takes a case on original shell-and-tube heat exchanger and simulated using Matlab/Simulink. Cascade control is used to stabilize outlet temperature even there is interference. Shell-and-tube heat exchanger is modeled using first order plus delay time (FOPDT). The type of controller is used PID standard with Ziegler-Nichols tuning method. Performance of cascade control is tested by providing inlet fluid flow disturbance. The experiment got the best performance on PI control (secondary controller) with parameter of Kp and Ti worth 1.375 and 2. PI control produces smallest IAE amount 34.57. Test control of cascade (primary controller) obtained a result that control of PID produces the best response. PID control with parameter values Kp, Ti, and Td of 2.85, 53.06 and 13.265 gave the smallest IAE of 601.54 and the fastest rise time of 121.5 seconds. From this research, it is concluded that the shell-and-tube heat exchanger system can use cascade control to regulate the temperature stably even with an unstable fluid flow.

The slinky ground heat exchanger (GHE) is the most widely utilized horizontal-type GHE, however, this GHE has a low curvature coil. The GHE has poor thermal mixing, especially at a low flowrate. At this flowrate, the coil heat exchanger has similar performance to a straight tube heat exchanger. Discrete double-inclined ribs (DDIR) are well known for their good thermal mixing by generating a vortex in straight tubes. In this paper, a numerical analysis of thermal performance for the plain coil and DDIR coil is discussed. It was found that the thermal performance of the DDIR coil was slightly higher than that of the plain coil in laminar flow. In turbulent flow, the DDIR coil was superior to the plain coil only in the first 149-min operation. The first 60-min analysis shows that in laminar flow, the average heat transfer rate in the plain coil is 59 W/m and in the DDIR coil is 60.1 W/m. In turbulent flow, the average heat transfer rate is 62 W/m, and the plain coil is 62.3 W/m. The copper DDIR coil material produced a better heat transfer rate than that of the composite and High-Density Polyethylene (HDPE). Sandy clay has the highest heat transfer rate. The influence of ground thermal conductivity on the performance of the GHE is more dominant than convection in the DDIR coil.

Photovoltaic (PV) based power generation system has been considered massively as one of renewable energy resource. However, the performance of PV system is sensitively affected by many factors including the weather and solar irradiance. The hybrid system is taken for solving this system output uncertainty. For improving the power management performance such this hybrid systems, the forecasting of power output of PV system has been proposed in some previous research. The precision of this forecasting has to be considered for building a high performed power management system especially for remote area where the very small power output is very important. Therefore, this paper proposes a novel approach of forecasting of power output of PV systems using ensemble neural network with four base forecasters. The PV system used in this research is equipped with 2-axis automated tracking with maximum output 10Wp. As base forecasters of ensemble structure, this research employs the multi-layer perceptron network with two hidden layer. According to the research results, the proposed method provides high accuracy prediction. Moreover, this method outperforms the individual MLPN based forecaster commonly used in the forecasting research.

The twisted tape is inserted into the hairpin heat exchanger generate secondary flow to improve heat transfer performance. The study investigated at the effect of twisted tape on the exchanger. Flow was pumped at the rate from 0.011 to 0.022 kg/s. From the experimental data, heat transfer coefficient, heat load, and effectiveness on the addition of twisted tape is calculated and compared to plain tube data. The results showed that there were improved performance heat transfer coefficient, heat load, and effectiveness, and discovered the effectiveness twisted tape was better than plain tube by 20%.

In this study, the thermal and hydraulic characteristics in low curvature coil with Discrete Double Inclined Ribs (DDIR) were investigated. Water is selected as a working fluid, and flowrate range from 1 to 5 L/min, which is a low flowrate condition. Effect of geometry parameters such as distance between ribs, curvature ribs, and ribs inclination angles was observed. Results obtained by numerical simulations show that the heat transfer in DDIR-coil is 7.7 to 29.11% greater than that in plain coil, while the pressure drop was approximately 12.7 to 89.5% larger than that of plain-coil. A COP improvement factor that is calculated based on energy loss by pressure drop and energy saving by heat transfer enhancement was found to vary between 0.25 and 5.29. Flow visualization shows that there are two vortexes in cross-section at the downstream, and local vortexes arise around the ribs of DDIR-coil, which shows similar pattern and strength to DDIR-straight tube. The vortex makes a long fluid particle path and strengthens the turbulent mixing between the wall and the core flow of the coil. Based on these findings, DDIR-coil is recommended for applications in Slinky Ground Heat Exchangers, especially at low flowrates.

One of the most common passive methods used to improve heat transfer in a circular pipe is twisted tape. Heat transfer increases when twisted tape generated secondary flow in pipe. In this paper, Nusselt number, pressure drop, effectiveness and NTU were investigated experimentally on double pipe heat exchanger with twist ratio variation on perforated twisted tape. Hot water and cold water flow rate were changed 20, 40, 60, 80 and 100 lph. The hole diameter of perforated twisted tape was 8 mm and twist ratio were 4, 6, 8, 10 and 12. The results of this research showed that at Reynolds number of 3488, the different value of Nusselt number had a maximum value of 5.73% from plain inner pipe to twist ratio of 4. When this value was compared to the condition without perforated twisted tape, the bigger pressure drop change occurred in twist ratio of 4. Twist ratio of 4 caused the average value of pressure drop greater 350% from 19.55 Pa to 87.98 Pa. Besides that, twist ratio of 4 had average different value in the effectiveness of 45.22% and NTU of 83.19% from a plain inner pipe.