This study discusses the effectiveness of “demand-supply coordinated control” in reducing conveyance power consumption of District Cooling and Heating (DHC) systems. Demand-supply coordinated control is introduced to address the problem of increased power conveyance, which is required by the DHC systems while providing heating to consumers. However, the effectiveness and limitations of this control have not yet been clarified. In our previous reports, therefore, we have numerically examined the operation of DHC systems with demand-supply coordinated control, and discussed its effectiveness and limitations for systems with simple configuration and a short piping length. Following the previous reports, this study deals with the effects of piping length on the supply temperature and conveyance power consumption, focusing on the fact that the longer the piping length, the further the occurrence of the disturbance in temperature mixing in the heat medium, which is caused by the unstable operation of the heat source machine. First, we determined the piping length at which the supply temperature does not deviate from the target temperature this is observed to become shorter as the thermal load following speed of the heat source machine and the thermal load fluctuation rate increase. We also showed that the relationship between the nondimensionalized factor of the supply temperature fluctuation range and the piping length is not unique even when the relative value of the thermal load fluctuation rate to the thermal load following speed of the heat source machine is constant. This is because the influence of the thermal load fluctuation period on the mixing is greater than that of the thermal load following speed of the heat source machine. Next, the effects of the piping length on the conveyance power consumption were discussed. The numerical results showed that when the relative value of the thermal load fluctuation rate to the thermal load following speed of the heat source machine is approximately 1.6 (or more), the conveyance power is approximately 1.25 times (or more) higher than when that value is less than approximately 1.6, regardless of the piping length. This result can be explained by the following facts: When the piping length is long, the inlet temperature of the heat source machine and the heat exchanger is not disturbed and therefore is stabilized due to a mixing effect, resulting in less-distorted shapes of the pump flow rate and the pump head. There is an increase in the pump flow rate and pump head due to a decrease in the outlet temperature of the heat source machine, which in turn is caused by control delay. However, this increase does not substantially differ from that when the piping is short. Terefore, under this condition, the conveyance power increases regardless of the piping length.
This experimental study aims to determine the control characteristics of new variable water volume control methods without using differential pressure for heat supply to buildings. The experiments in the study investigated not only the new methods for controlling the pump speed without using differential pressure, but also the general methods for controlling the pump speed using differential pressure. The experiments have been based on the assumption that heat is supplied to two buildings. Furthermore, the basic data such as the power used for the conveyance of heat by each control method were obtained and the control characteristics were analyzed. It was found that the pump speed could be controlled even by the variable water volume control methods without using differential pressure as is used in methods such as methods using secondary side water temperature control and valve opening control, and it was shown that the methods are effective for reducing the power consumption for the conveyance of heat.
In this study, we proposed partial variable temperature water supply system that uses return water. The demand for systems that can bring down the temperature of the heat medium close to room temperature, thereby saving the heat source by air conditioning through sensible and latent heat separation and radiation cooling and heating has been increasing. But, it is necessary to provide a temperature-mitigated water piping network and heat source systems separated from the standard systems. However, despite the increasing demand which has the capability to mitigate the temperature of the water supply, the energy saving opportunities are missed owing to cost constraints. In this study, we have proposed the piping network, and a control system that can be adjusted to the mitigated temperature for each demand by using return water. This enables partial variable temperature water supply and the heat source system that improves the heat source efficiency by cooling and heating water which has a large temperature difference using return water in stages of the reverse Carnot cycle. We examined the system construction and its effects. Taking advantage of the temperature difference at the heat source, we demonstrated that the system is capable of reducing the power of the first-stage refrigerator by 19%, by through staged cooling. Furthermore, we proposed an increase in the number of refrigerators in staged cooling to a certain range by adopting an overflow refrigerator. We also proposed a control system that copes with the various patterns of standard and mitigatable demands. The case study showed that the proposed system reduced power consumption by 18%, while the annual refrigerator power was reduced by about 30% at the highest cascade utilization in this system compared with the case without temperature mitigation. As the temperature difference tends to be large in the case of hot water, performing staged heating and showed that the energy saving effect is also large. However, the issues that need to be considered in the actual design of the system and the necessary improvement required for the heat source are issues for future study.
In commercial kitchens, the oil and soot deposited on the surface of the exhaust duct may cause fire and odor problems. To prevent such problems, the effect of ultraviolet (UV) rays has been investigated in this study. The influence of UV on the oil layer adhering to the inner surface of the exhaust duct was observed for a long period of time. The results showed that UV can resolve the oil/soot layer at the duct surface near the UV lamp. Furthermore, the concentration of acrolein was measured in the exhaust duct to obtain the basic data for calculating the appropriate ventilation rate.