In order to achieve a sustainable design for residential houses, it is essential to optimize the energy consumption for heating, ventilating, and air-conditioning (HVAC) systems and the use of an energy recovery the ventilator (ERV), which can recover the sensible and latent heat, is considered as one of the most effective ways to reduce the ventilation load in buildings. In this study, we clarify the heat and moisture transfer mechanism in the energy recovery ventilator (ERV) unit and focus on the development of a mathematical model for predicting the hygrothermal transfer efficiency by integrating computational fluid dynamics (CFD) analysis in ERV. Toward this end, firstly we arranged the governing equations of the hygrothermal transfer models applied in the ERV unit and conducted fundamental experiments to measure the adsorption isotherm (constant volume method) and moisture conductivity (cup method) in order to identify the model parameters. Secondly, we established a coupled numerical simulation model of CFD (convective heat and moisture transfer in air) and hygrothermal transfer model (simultaneous heat and moisture transport equations in solid material) to predict the temperature and enthalpy exchange efficiency in the ERV unit. As a result of the coupled analysis of the CFD and hygrothermal transfer model, we confirmed that our proposed numerical models showed reasonable agreement with the experimental results. In addition to the fundamental analysis for discussing the prediction accuracy, we carried out sensitivity analyses for targeting three types of flow channel models in the ERV unit. As for the staggered flow channel model, the improvements in the convective heat transfer coefficient and fin efficiency were confirmed. The flow channel model with the patch that introduces the discontinuous adiabatic surface was confirmed to have a possibility to improve the temperature and enthalpy exchange efficiencies without increasing the exchange surface area.
At present, there is a need to significantly reduce the energy consumption of the air conditioning systems used in commercial buildings. For that purpose, it is necessary to utilize renewable energy and unused energy in addition to improving the performance of the air conditioning unit. Therefore, we aim to develop an individual distributed air conditioning system that utilizes heat source water, which is easier to handle and more expandable than the Freon refrigerant. As a first step, we developed a water heat source makeup unit, which utilizes a low-temperature desorption-type desiccant rotor, and evaluated the performance of the single unit. As a result, it was possible to confirm the dependency of the cooling / heating capacity, dehumidification / humidification amount, and COP on the heat source water temperature. In addition, we confirmed that this unit demonstrates high performance throughout the summer and intermediate seasons, and by introducing renewable thermal energy and unutilized thermal energy etc. it demonstrates high performance even in winter.
Since businesses are required to save energy according to the Strategic Energy Plan by the Agency for Natural resources and Energy of Japan, it is necessary to reduce the energy utilized for building operation as much as possible. Therefore, a new air conditioning system, which makes the indoor environment cool or warm by applying both heat radiation and micro-flow convection from the ceiling, has been developed and introduced to the new office building at Takamatsu. In this paper, the actual energy consumption report and the indoor environment survey conducted in this building are discussed. Firstly, the annual primary energy consumption reduction rate reached 58.52% (or 68.7% if renewable energy is included) in the first year of operation: in other words, this building has become <italic>ZEB (Net Zero Energy Building) READY</italic>. Furthermore, in the second year, the reduction rate was increased to 60.7% (or 71.1% if renewable energy is included) by improving the operation, for example, by tuning up the water pumps for this air conditioning system. However, further studies must be conducted to reduce the heating energy during winter. Secondly, the survey of indoor environment during summer showed that the indoor air temperature during working hours (from 8:30 to 17:10) fluctuated within 2.7°C (from 25.0 to 27.7°C), the air temperature difference in the vertical direction fluctuated within 0.5°C, and the ambient air velocity was under 0.19m/s. A small temperature difference in the vertical direction and a small air flow velocity are features of the space controlled by the radiant air conditioning system. On the other hand, the radiant temperature was slightly higher than the air temperature, and the PMV (Predicted Mean Vote) was 0.50 to 0.95, corresponding to “slightly warm”. There was probably caused not only by the calm air flow and slightly high air temperature but also by the large perimeter zone and glass walls. However, the results of the questionnaire show that almost all the occupants in this building felt comfortable and were satisfied, and the indoor environment controlled with this system impressed 30% of them that their intellectual productivity improved slightly. In summary, this report suggests that it is possible to maintain a high level of thermal comfort and satisfaction even if energy saving is applied.