| 36 | | For natural and paved surfaces in urban environments, PALM-4U employs PALM's land surface model. |
| | 36 | For natural and paved surfaces in urban environments, PALM-4U employs PALM's land surface model. The scheme consist of an energy balance solver for all different types of surfaces as well as an multi-layer soil model to account for vertical diffusion of heat and water transport in the soil. For natural vegetated surfaces, the energy balance solver will use the concept of a skin layer that has no heat capacity but considers the insulating effect of plants. In the absence of vegetation, no skin layer approach is used and the surface temperature is taken equal to the outermost soil, pavement, or wall layer. |
| | 37 | |
| | 38 | Vegetation can be either defined to be sub-grid scale (e.g. short grass) and is then purely treated in the land surface scheme. For tall vegetation (e.g. trees), PALM-4U offers a 3D canopy model which is based on a drag force approach and a leaf area density distribution. The canopy model is thus fully coupled to the soil model and an energy balance solver for the leaf temperature is solve at all grid volumen with a leaf area density. Also explicit transpiration of the 3D canopy elements will be realized. |
| | 39 | |
| | 40 | == Urban surface representation == |
| | 41 | For urban surface elements (i.e. building facades and roofs), an adapted version of the land surface scheme was developed. It consists of an energy balance solver for the surface temperature and a multi-layer wall material model. The wall model follows a tile approach so that fractions of solid walls, windows, and green facades are treated separately. Details of the preliminary urban surface model are given in Resler et al. (2017). |
| | 42 | |
| | 43 | == Indoor climate and building energy demand == |
| | 44 | In order to calculate the interaction of the buildings with the atmosphere, a holistic indoor climate model is available in PALM-4U. This model predicts the indoor temperature and also calculates both the energy demand of each building as well as the waste heat that is released to the atmosphere. The model is integrated as an optional module that is coupled to the wall model by using the temperature of the innermost wall layer of the respective building facades as input parameter. Also, the transmitted radiation by windows is transferred to the indoor model. The indoor temperature is then calculated based on building characteristics (e.g. insulation, air conditioning, and heating). In return, the indoor temperature is transferred to the wall model as boundary condition, while waste heat from heating or air conditioning is fed back into the atmosphere as an additional tendency in the prognostic equation for temperature at the roof top (representing the typical location of chimneys and air conditioning units). |
| | 45 | |
| | 46 | == Radiative transfer in the urban canopy layer == |
