June-bearing strawberry plants (Fragaria × ananassa Duch. cv. Benihoppe) were grown in a growth chamber with florescent lamps as light source at the light periods of 12 h and the temperature of 22 / 10°C (light / dark periods). The diurnal change of diameters of a fruit and a fruit stalk were measured with a digital displacement sensor. The sugar flux through the cut section of fruit stalk was attempted to estimate by EDTA method. A fruit grew faster in light periods than dark periods. The fruit growth rate was the highest at the start of light periods. Short-time shrinkage of the fruit was observed at the start of dark periods. The change of fruit diameter and the change of diameter of the fruit stalk were closely associated. When vapor pressure deficit changed greatly in a short time because of the operation of the air conditioner, these changes were closely associated with the change of vapor pressure deficit. Water flux through the cut section of fruit stalk took negative value in light periods and positive value in dark periods. It might be estimated that the contribution to the water flux was higher through phloem (56.9%, 59.4%) than xylem (43.1%, 40.6%) in both of light and dark periods. Sugar flux through the cut section of fruit stalk was much higher in dark periods than in light periods. The sugar flux through the cut section of fruit stalk in light periods and dark periods were estimated as 20.2% and 79.8% of total flux, respectively.

The purpose of this study is to develop a new control method of vapor injection cycle with a flash tank in order to achieve optimal COP. In this cycle, temperature of vapor injection doesn't change due to the saturation in a flash tank. Therefore, there is no simple method to detect how much vapor in a flash tank has been injected into the compressor. Hence, it has been an issue to develop a simple injection flow control method. This study proposed a new control method using a superheat index generated by active heating using discharge refrigerant from the first compression chamber. The experiment was conducted to verify the effectiveness of this index. The experimental results show that this new superheat index varies with the injection flow rate and is useful for controlling the injection flow rate properly to achieve the optimal COP.

From the viewpoints of energy and environmental problems in the world, an effective thermal energy utilization has been one of the most important issues in the world. Chemical Heat Pump (CHP) is one of the technologies which is considered to contribute to the issue. By using the refrigeration mode of CHP, Chemical Refrigerator (CR) which generates cold heat below 273 K can be driven by chemically stored thermal energy such as solar heat, waste heat etc. In order to improve the evaporator performance of CR, the experimental and theoretical studies on the effects of aqueous solution components and mass transfer were performed. The results were shown as follows. (1) CR using Ethylene glycol 30 wt% - NaCl 10 wt% aqueous solution in the evaporator can release cold heat under 258 K similarly in the case of using Ethylene glycol 40 wt% aqueous solution. Ethylene glycol 30 wt% - NaCl 10 wt% aqueous solution is suitable for keeping CR longer bellow 258 K. (2) The evaporator performance was enhanced in early reaction stage by using a stirrer and changing the evaporator position. Furthermore, the synergistic effects of combining a stirrer use and evaporator position change, cold heat power in early reaction stage increased 1.9 times.

To improve and maintain the refrigerant wettability of the evaporative heat transfer surface and improve the evaporative heat transfer performance from the thin liquid film, we focused on the fiber flocked heat transfer surface where rayon fibers were electrostatically flocked onto the surface of a cross-fin type heat exchanger. In this study, to clarify the shape of the liquid film formed on the flocked surface and the evaporative heat transfer characteristics, this heat exchanger was immersed in water refrigerant and the liquid film on the fin was observed. It was confirmed that two types of liquid films were formed, a bridge liquid film extending between the fins and an inter-fiber liquid film on the fin surface. Then, a method for estimating the thickness of both liquid films was proposed, and its validity was confirmed. Next, comparative experiments on non-flocked surfaces confirmed that the flocked surface did not inhibit heat transfer. Furthermore, it was found that when the fin surface was covered with the inter-fiber liquid film, the thermal resistance was reduced to about half that of the non-flocked surface. Finally, we proposed a model for predicting the thermal resistance of the inter-fiber liquid film and confirmed its application range.

The defrosting process is important to keep the heat transfer performance of the heat exchanger for the frosting condition. The frost layer is a porous structure of ice crystals and air pores. Thus, the meltwater penetrates into the remaining frost layer by the capillary effect during the defrosting process. In this study, the meltwater penetration behavior on the single vertical aluminum-plate was measured by using X-ray radiography. The water deposition distribution on the aluminum plate was estimated quantitatively by the X-ray beam attenuation in every 10 seconds. The meltwater behavior was estimated by comparing the frost deposition distribution before melting. Frost layer melting was started from the leading edge of the aluminum plate by increasing the temperature to 0 C. deg., then, the meltwater penetrated into the remaining frost layer along the aluminum plate in the vertical direction. The meltwater penetration behavior can be observed by the X-ray radiography.

The heat exchanger of air conditioners installed in windy seaside areas may suffer from corrosion. This corrosion reduces the heat transfer coefficient of the heat exchanger and reduces the performance of the air conditioner. It also damages the refrigerant pipes and may cause refrigerant leakage. In this study, corrosion was produced on fin-tube heat exchangers by an accelerated corroding test with salt water mist. The corrosion level on the heat exchangers is the same as the damage in the area suffering from salt damage for 3-15 years. To estimate the heat transfer decrease from corrosion, the quantity of heat exchange between air and hot water in the refrigerant pipe of the corroded heat exchanger was measured. The overall heat transfer factor decreased by 48% with the corrosion, which level is same as the damage in an area suffering from salt damage for 15 years.

As a measure to improve the energy saving of air conditioners, we paid attention to the loss of piping systems that had not been actively improved until now. The air-conditioning refrigeration cycle uses copper pipes, and especially the compressor suction pipe tends to have a large pipe diameter. In order to prevent stress concentration due to the vibration of the compressor, the small air conditioner has a length of 1000 to 1500 mm with 2 to 3 U-shaped turns. This prevents stress concentration due to compressor vibration. Since the suction pipe is in a low-pressure gas state, the pressure loss is large and it is desirable to shorten the length as much as possible in order to improve the performance. In order to solve this problem, we changed the material of the suction pipe from a copper pipe to a rubber hose pipe, and tried to achieve both the reduction of stress concentration in the entire pipe and the reduction of pressure loss by shortening the pipe length. A trial calculation of the energy saving effect of the air conditioner system and a comparative analysis of the stress and vibration of the piping system were performed, and good results were obtained. In addition, we evaluated the vibration test and the 5000-hours endurance test using the prototype, and confirmed that there were no problems.

The spread of ground source heat pump system (GSHP) in Japan is delayed due to high installation cost compared with airsource vapor compression heat pump system. A new air + ground source hybrid heat pump system whose outside air heat exchanger and ground source heat exchanger are connected in series was suggested in this study. The installation cost of this system can be reduced by reducing boring length for setting ground source heat exchanger and by reducing development cost by using commercial air source heat pump system. However, the performance of the hybrid system seems to be lower than ground source heat pump system due to using air heat source. Therefore, evaluation of the system is required regarding cost performance. This study deals with field test, numerical simulation and estimation of cost performance of the hybrid system. This paper is mentioned about the results of field test of the hybrid system as the 1st report. The results show that this hybrid system can be driven using 70% reduced borehole length compared with the general GSHP system. However, the performance of the hybrid system is lower than expectations due to using control system of commercial air source HP.

The objective of this study is to evaluate the performance of a GSHP that uses the direct expansion method, in cooling and heating air conditioning applications. This pump utilizes the steel pipe foundation pile of the house to accommodate its heat exchanger. To achieve the same, 12 underground heat exchangers were inserted into the foundation piles. Experiments were conducted to study its performance in both cooling and heating operations, and the coefficient of performance (COP) was obtained by measuring the amount of heat transferred and the electricity consumption for running the GSHP. From the experimental result obtained, the COP was approximately from 4.4 to 4.7 in the cooling operation and approximately from 4.8 to 5.0 in the heating operation. Additionally, no performance deterioration was observed in the intermittent cooling or heating operation for 5 days. On the other hands, the COP value for continuous cooling and heating operations slightly decreased of 12 % for cooling and 6 % for heating during 5 days.

This paper described the experimental results regarding the air conditioning performance of ground source heat pump that use direct expansion method. An underground heat exchanger consists of three parallel copper tubes and one insulated copper tube. The power output of the heat pump was 6.8 kW for cooling and 8.9 kW for heating. The underground heat exchangers were inserted into the three casing pipes made of steel which is 30 m depth. The three-parallel U-shaped underground heat exchanger were connected with the refrigerant circuit in the out-door unit. Experimental results are as follows. During the cooling operation, the average value of the output power, the power consumption, and COP was 1.9 kW, 0.3 kW, and 6.8, respectively. During the heating operation, the average value of the output power, the power consumption, and COP is 3.9 kW, 0.48 kW, and was 8.1, respectively.

In cold regions of Japan, the energy required for heating and hot water supply accounts for 81% of the energy consumption of the whole household, and this reduction can be expected to have high energy saving effect. However, in cold regions, the outside air temperature is low and the efficiency of the heat pump is reduced, so that it is not widely used and kerosene is mainly used. In this study, a thermosiphon type heat pipe using CO₂ as working fluid is applied to heat recovery to prevent the efficiency from decreasing by using the underground surface heat of the underground as the heat source of the evaporator. Attempts to improve the performance of CO₂ thermosiphon that can be considered when using, such as the shape of the heat pipe container, the effect of changing the temperature of the condenser and auxiliary heating to the lower part of the evaporator on the performance, and a simulation incorporating the obtained data are carried out. As a result, when the condenser temperature was set to 0°C, the maximum heat exchange amount of the condenser was obtained without a corrugated tube heater and the encapsulation rate was 45%. The maximum heat exchange in the condensation section was shown at a rate of 40%. It was confirmed that the auxiliary heater was installed to suppress the rise in wall temperature at the bottom of the evaporator. Using the heat transfer coefficient rearrangement formula obtained from the measured values, 8 smooth tubes are needed at 10 m long, 5 at 15 m long, and corrugated tubes are also 7 at 10 m and 5 at 15 m, with a COP=2.8. Achieved.

The optimal design of ground heat exchangers is essential to reduce the life cycle cost of shallow geothermal systems, therefore the fast computation is desired for a long term simulation. The temperature in the ground heat exchangers field is expressed as a convolution product of the incremental heat loads and the temperature response function for a unit heat load, and that can be calculated efficiently using the fast Fourier transform. This work aims at the fast convolution using the fast Fourier transform by graphics processing unit. This method indicates 22.8 s computation time for 25 years at 60 seconds interval convolution, that is 2.5 times faster than the calculation without graphical processing unit.

The effective thermal diffusivities of shallow ground to a depth of 10 m was investigated by a heating method from 2015 to 2018. The measurement point was the College of Engineering, Nihon University in Koriyama city, Fukushima prefecture. The effective thermal diffusivities were from 0.42 mm²/s to 2.72 mm²/s. Precipitation and ground temperature were considered as factors affecting thermal diffusivities. The daily mean precipitation ranges from 1.9 mm to 3.3 mm, and the ground temperature ranges from 4.6 ℃ to 23.9 ℃. The regression analysis shows the effective thermal diffusivities deeper then depth 5 m depend on the aforementioned factors, and the correlation coefficient between the effective thermal diffusivities at each depth and precipitation was 0.63, while in the case of ground temperature it was 0.38. As a result, the effective thermal diffusivities deeper then depth 5 m are found to be influenced by precipitation.

The Fukushima Demonstration House (80.6 m²) for the shallow ground-source heat-pump system developed by Nihon Univ., which have 10 shallow (10 m) heat wells, was built in 2013. The results of heating experiments from Jan. 2014 to March 2020 are reported in this presentation. The ground source fluid temperature was 3°C or above throughout each winter season when the heat of 220 MJ/day (2.5 kW) or below was extracted. Time dependent decrease in the temperature was negligible. The energy efficiency of the system ranged from 2.5 to 3.7 depending on the operating conditions. The height distribution of the room temperature was ±1°C for floor heating and 6 to 10°C for air heating. The overall heat transfer coefficient of the house estimated from the results is 0.78 W/(m²･K), where the heating power to keep the room 20°C higher than the ambient is 3.5 kW with the system efficiency of 2.5.

First of all, the effect of thermal storage was clarified by comparing the rooms with different thermal storage in winter, targeting the experimental building "House of LOHAS 3" constructed on the Koriyama Campus of Nihon University. Next, in order to clarify the effect on the indoor environment and the improvement method when the thermal storage was made larger, the heat storage effects due to the difference in thermal storage in Fukushima were examined by simulation calculation. In semi-cold regions, it was expected that the improvement of indoor thermal environment due to large heat capacity and reduction of annual heating/cooling load would be expected by improving heat collection/insulation performance. Finally, the effects of the temperature of the regenerator and the ambient temperature on the room temperature were clarified by using the "variable heat capacity system" of the house No. 3 in the experimental building Roxas. It was confirmed that a large heat capacity can be utilized by making good use of the variable heat capacity system even when heat collection cannot be expected.

In the previous report, the effect on the indoor environment and the improvement method when the heat capacity was increased in winter were clarified for the experimental building "House of LOHAS 3" constructed on the Koriyama campus of Nihon University. Furthermore, t the influence of the difference in heat capacity in summer and the influence of the temperature of the regenerator and the ambient temperature on the room temperature were clarified by using the "variable heat capacity system". The annual cooling load was reduced to 0 by securing the heat capacity and introducing the outside air at night. Furthermore, the measured results also showed a decrease in room temperature due to an increase in heat capacity. In addition, by using a variable heat capacity system, it is expected that the cold storage effect during the daytime and the ambient air introduction effect due to the small heat capacity at night will be reduced at room temperature.

In response to the “Fukushima Smart Community Building Support Project” that the Fukushima Prefectural Government publicly recruited, Fukushima University applied for and was adopted by “Project Study for Utilization System of Mainly by Renewable Energy thermal in Fukushima University”. Fukushima University has developed plan aiming to introduce efficient renewable energy thermal for the future by investigating the potential of available energy on the campus. In this project, we estimated the heat / electric energy demand and grasped the power demand characteristics. We have compiled a plan for introducing renewable energy such as photovoltaics and wind-generated electricity generation. In addition, ground source heat information utilization potential map was created by conducting geological information, a column diagram of existing buildings (geological boring data), and TCP test. This led to the introduction plan of the utilization of ground source heat used for air conditioning system, hot water supply system, road snow melting system and thermal source water network system in the next report.

Whole planning process and method for introducing ground source heat used for heat pump air conditioning system to three buildings was described. Method of calculating total extension and required area of ground heat exchanger from setting of cooling and heating load for air conditioning systems was described. When introducing groundwater heat used for hot water supply system for heat pump in student dormitory, procedure for setting heating load and selecting heat pump and hot water storage tank capacity for hot water supply system was shown. In addition, road snow melting system by free heating that uses the heat of wastewater treatment equipment as unused thermal (temperature difference thermal) is also described. Utility tunnel (common ditch) has been set up on the campus from beginning. Heat source water network plan was established to effectively utilize ground source heat through heat source water network system in this utility tunnel. There is large gap in electricity demand between during day and night hours on the campus. Consideration was given to installing thermal storage tank in order to eliminate electricity demand difference between day and night hours. At some future date, thermal storage tank is likely to be used for purpose of operating heat pump and storing heat by using surplus electric power of photovoltaics.