Air-to-air membrane enthalpy exchangers using semi-permeable membranes are widely used in building ventilation systems to pre-condition the supply air by exchanging energy with the exhaust air stream. Moisture diffusivity is one of the most important properties of porous membranes. This property has a significant influence on the design and performance of membrane enthalpy exchangers. In this study, moisture diffusion resistances of five porous membranes were measured, and the effects of the

more »

... brane pore size on the moisture diffusivity were evaluated under different test conditions. The five porous membranes tested included: I) two PVDF (Polyvinylidene difluoride) membranes with mean pore diameters of 0.22 μm and 0.45 μm respectively, ii) two Nylon membranes with 0.1 μm and 0.45 μm pore sizes respectively, and iii) a PES (Polyethersulfone) membrane with a 0.1 μm pore size. A theoretical model to predict the effectiveness of a crossflow membrane enthalpy exchanger was also developed with respect to the latent heat transfer. The experimental results showed that the PVDF membrane with a mean pore diameter of 0.45 μm outperformed the others in terms of the moisture diffusivity. The results from the theoretical model of the enthalpy exchanger agreed well with those from the experiments reported in the literature. The latent effectiveness was found to be insensitive to the outdoor air conditions. Abstract District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand -outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Air-to-air membrane enthalpy exchangers using semi-permeable membranes are widely used in building ventilation systems to pre-condition the supply air by exchanging energy with the exhaust air stream. Moisture diffusivity is one of the most important properties of porous membranes. This property has a significant influence on the design and performance of membrane enthalpy exchangers. In this study, moisture diffusion resistances of five porous membranes were measured, and the effects of the membrane pore size on the moisture diffusivity were evaluated under different test conditions. The five porous membranes tested included: i) two PVDF (Polyvinylidene difluoride) membranes with mean pore diameters of 0.22 µm and 0.45 µm respectively, ii) two Nylon membranes with 0.1 µm and 0.45 µm pore sizes respectively, and iii) a PES (Polyethersulfone) membrane with a 0.1 µm pore size. A theoretical model to predict the effectiveness of a crossflow membrane enthalpy exchanger was also developed with respect to the latent heat transfer. The experimental results showed that the PVDF membrane with a mean pore diameter of 0.45 µm outperformed the others in terms of the moisture diffusivity. The results from the theoretical model of the enthalpy exchanger agreed well with those from the experiments reported in the literature. The latent effectiveness was found to be insensitive to the outdoor air conditions. Abstract Air-to-air membrane enthalpy exchangers using semi-permeable membranes are widely used in building ventilation systems to pre-condition the supply air by exchanging energy with the exhaust air stream. Moisture diffusivity is one of the most important properties of porous membranes. This property has a significant influence on the design and performance of membrane enthalpy exchangers. In this study, moisture diffusion resistances of five porous membranes were measured, and the effects of the membrane pore size on the moisture diffusivity were evaluated under different test conditions. The five porous membranes tested included: i) two PVDF (Polyvinylidene difluoride) membranes with mean pore diameters of 0.22 µm and 0.45 µm respectively, ii) two Nylon membranes with 0.1 µm and 0.45 µm pore sizes respectively, and iii) a PES (Polyethersulfone) membrane with a 0.1 µm pore size. A theoretical model to predict the effectiveness of a crossflow membrane enthalpy exchanger was also developed with respect to the latent heat transfer. The experimental results showed that the PVDF membrane with a mean pore diameter of 0.45 µm outperformed the others in terms of the moisture diffusivity. The results from the theoretical model of the enthalpy exchanger agreed well with those from the experiments reported in the literature. The latent effectiveness was found to be insensitive to the outdoor air conditions. (Z Ma) Ahmed K. Albdoor et al. / Energy Procedia 160 (2019) 499-506 2 Albdoor et al. / Energy Procedia 00 (2018) 000-000