Home


About us
PALM
PALM-4U
Installation
Release notes
Documentation
Getting Help
Gallery
Developers area

Urban surface model (USM)

TracNav

Main page of the urban surface model under construction. Click here for first information about capabilities and model steering. Also available, the related article PALM-USM v1.0: A new urban surface model integrated into the PALM large-eddy simulation model (Resler et al., Geosci. Model Dev., 10, 3635–3659, ​10.5194/gmd-10-3635-2017)

This page is part of the Urban Surface Mod (USM) documentation.
It describes the physical and numerical realization of the USM.
Please also see the namelist parameters.

Overview

Since r19xx an urban surface model (USM) is available in PALM (see urban_surface_mod.f90​). It consists of a multi layer wall and soil model, predicting wall and soil temperature and moisture content, and a solver for the energy balance, predicting the temperature of the surface or the skin layer. Urban surfaces (building surfaces) are simulated using a tile approach. Each surface element consists of a fraction of bare wall/ roof, window and green elements (green roofs/ facades) with underlying soil layers (green roofs only) and a bare wall/ roof structure.

Energy balance solver

The energy balance of the urban surfaces reads

\begin{equation*} C_0 \dfrac{dT_0}{dt} = R_\mathrm{n} - H - LE - G \end{equation*}

where C0 and T0 are the heat capacity and radiative temperature of the surface skin layer, respectively. Note that C0 is usually zero as it is assumed that the skin layer does not have a heat capacity (see also below). Rn, H, LE, and G are the net radiation, sensible heat flux, latent heat flux, and ground (soil) heat flux at the surface, respectively.

The energy balance is calculated for each urban surface tile individually and the three radiation surface temperatures are combined together.

The parametrisation of the sensible heat flux, latent heat flux and ground heat flux of the wall/ window/ soil is equivalent to the Land Surface Model (LSM).

The wall heat and green heat model consist of prognostic equations for the bare, window and soil temperature and the volumetric soil moisture which are solved for multiple layers. The models only take transport into account that is orthogonal to the urban surface layer orientation and no ice phase is considered. By default, the wall heat model and the green heat soil model consists of four layers each (see Fig. 1 below), in which the orthogonal heat and water transport inside the soil is modelled.

urban surfaces (bare, window, green) in PALM-4U, adoption of concept of urban surfaces by Björn Maronga

Figure 1: urban surfaces (bare, window, green - horizontal and vertical) in PALM-4U

The physical properties of the urban surfaces and wall, window and green soil elements can be set using values from a building database where different types of buildings are defined. The insulation value of windows are there only characterized by the U-value and and the heat capacity and heat conductivity is evenly distributed (no real glas or gas layers are taken into account.

The green heat model calculates the transport of soil moisture but neglects the extraction of water from the respective soil layers.

Window transmissivity: representation

The radiant flux received by the window (incident radiant flux, ΦI) is partially reflected back (ΦR), partially absorbed by the mass of the glass (ΦA which is simulated by four discretized layers of window depth) and partially transmitted through the window, where the transmitted flux ΦT may be processed by the indoor model (if enabled), therefore

\[ \Phi_{\mathrm{I}}=\Phi_{\mathrm{R}}+\Phi_{\mathrm{A}}+\Phi_{\mathrm{T}} \]

Most of the reflection happens as specular reflection on the frontal and rear boundary between the glass and air. The radiant flux reflected at the rear boundary is partially reflected again at the frontal boundary, then partially at the rear boundary again and so on, however, these fluxes are typically negligible, as are the non-specular reflections, the absorption of the reflected fluxes and the scattering inside the glass; a bias can be avoided by adjusting the parameters of the non-neglected processes. The reflected radiant flux can thus be simplified as ΦR=ΦRF+ΦRR, where ΦRF is the radiant flux reflected at the frontal boundary and ΦRR is the radiant flux reflected at the rear boundary.

The total transmissivity T=ΦT/ΦI is the fraction of transmitted and received radiant flux, i.e. it includes loss by reflection and absorption together. The internal transmissivity TI=ΦTT/ΦTI describes the loss by absorption by a single pass of the light through the glass, where ΦTI=ΦI-ΦRF is the radiant flux entering the glass after frontal boundary reflection and ΦTT=ΦTI-ΦA is the radiant flux leaving the glass before rear boundary reflection. The frontal reflectivity RF=ΦRF/ΦI and rear reflectivity RR=ΦRR/ΦTT express the fraction of radiant flux reflected at each boundary. Together, the radiant flux passing through the glass can be described sequentially as it is diminished by frontal reflection, absorption and rear reflection. (2) describes this process additively while (1) describes the fractions multiplicatively:

\begin{align} T & =(1-R_{\mathrm{F}})T_{\mathrm{I}}(1-R_{\mathrm{R}})\\ \Phi_{\mathrm{T}} & =\Phi_{\mathrm{I}}-\Phi_{\mathrm{RF}}-\Phi_{\mathrm{A}}-\Phi_{\mathrm{RR}} \end{align}

The internal transmissivity is described by the Beer–Lambert law. For a homogeneous material with width z, it is equal to

\[ T_{\mathrm{I}}=e^{-az} \]

where a is the absorption (attenuation) coefficient.

Window transmissivity: modelling

The window fraction of surfaces in PALM is described by two parameters: albedo (total reflectivity in the respective band, R=ΦR/ΦI) and transmissivity (total, T).

The frontal and rear reflectivities of glass are similar. From simple Fresnel equations they are equal, in reality the frontal reflectivity is slightly stronger. In PALM they are modelled as equal and they are calculated from the total reflectivity.

\begin{align*} \Phi_{\mathrm{R}} & =\Phi_{\mathrm{RF}}+\Phi_{\mathrm{RR}}\\ \Phi_{\mathrm{R}} & =\Phi_{\mathrm{I}}R_{\mathrm{F}}+(\Phi_{\mathrm{T}}+\Phi_{\mathrm{R}}-\Phi_{\mathrm{RF}})R_{\mathrm{R}}\\ R & =R_{\mathrm{F}}+(T+R-R_{\mathrm{F}})R_{\mathrm{R}} \end{align*}

Using RF=RR we get:

\[ R_{\mathrm{F}}=\frac{R+T+1-\sqrt{(R+T+1)^{2}-4R}}{2} \]

In order to simulate the absorption by the discretized window layers, the absorption coefficient has to be calculated from the parameters:

\begin{align*} T_{\mathrm{I}} & =\frac{\Phi_{\mathrm{TT}}}{\Phi_{\mathrm{TI}}}\\ T_{\mathrm{I}} & =\frac{\Phi_{\mathrm{T}}+\Phi_{\mathrm{R}}-\Phi_{\mathrm{RF}}}{\Phi_{\mathrm{I}}(1-R_{\mathrm{F}})}\\ e^{-az} & =\frac{T+R-R_{\mathrm{F}}}{1-R_{\mathrm{F}}}\\ a & =\frac{-\log\frac{T+R-R_{\mathrm{F}}}{1-R_{\mathrm{F}}}}{z} \end{align*}

In the prognostic equations, the absorbed flux is added to the temperature tendency in the Runge–Kutta method for each layer l, depending on layer width and. The absorbed flux is equal to

\[ \Phi_{\mathrm{A},l}=\Phi_{\mathrm{I}}(1-R_{\mathrm{F}})(e^{-az_{l-1}}-e^{-az_{l}}) \]

where zl-1 is the depth of the previous layer (cumulative width of all previous layers) and zl is the depth of layer l.

Boundary conditions

Neumann boundary conditions are used for the transport of heat at the upper boundary (surface). The values are given by the energy balance. At the bottom boundary either a fixed temperature of the inner wall and window layers is set or the ground heat flux from the inner wall and window surface is used that is calculated by the indoor model (Dirichlet conditions).

Building database

A model database is used for the parametrization of the building indoor model and the urban surface model. The database provides building physical parameters of the building envelope, geometry data and operational data (incl. user behavior, control strategies and technical building services). The only available building information is often the age of the building, its construction material of façade and coating, the façade and window area, and the cubature. Hence, the model database defines all building physical parameters and operational data based on those basic parameters according to a building typology (Helbig et. al., 2018). The model database contains four areas:

  • The building description is based on geometry, fabric, window fraction and ventilation models.
  • The user description is based on (stochastic) user models regarding window opening and use of solar control, and user profiles regarding attendance and internal heat gains.
  • The person description is based on the metabolic rate and the clothing value.
  • The HVAC energy supply system is simulated with simplified models based on characteristic line models (considering the applicable standards) for different air-conditioning concepts. The model database contains also operation strategies for the energy supply system.

The parametrization of the façade is separated in four different parts:

  • Roof
  • Above Ground floor level façade second floor, where normally residential areas take place
  • Ground floor level façade the first floor, where nonresidential areas like shops with store windows in residential buildings could be. This could reason for example a higher window surface, than in residential buildings.
  • Ground plate parameters integrated, algorithm not integrated in source code yet

All of these parts are separated in four layers of different material. For façades and roof it´s possible to add an optional surface layer for greening (see figure 2).

structure of building for parametization

Figure 2: structure of the building construction for parametization in PALM-4U

The standard database contains six building types according to the German building topology (Helbig et. al., 2018), i.e. building age from the 1920s, 1970s and the 1990s for residential and non-residential buildings. Furthermore, there is a non-building type for bridges or car parks. The summer heat protection corresponds to the minimum requirements with regard to DIN 4108-2 (2013). Typical attendance and internal heat gains are taken from DIN V 18599 (2011) and empirical values (Voss et al., 2006).

Parameterlist

Building year before 19501950-2000after 2000
ISE typology 1920er 1970er passive house
on the base of (Helbig et. al., 2018) MFH_B MFH_F RH_J
arameter number (1) parameter name symbol/unit description
GEOMETRIE 132 height_storey h[m] 2.90 2.50 2.70 height of the storey
133 heigth_cei_con d[m] 0.20 0.20 0.20 clear space for ventilation
1 agfl, 22gfl, 102 r AF/AW [m2/m2] 0.18 0.25 0.29 window fraction
0 agfl, 21 gfl, 89 r, 51 gp AF/AW [m2/m2] 0.82 0.75 0.71 wall fraction
2 agfl, 3 agflr, 23 gfl, 24 gflr AF/AW [m2/m2] 0.00 0.00 0.00 green fraction
20 gflh [m] 2.90 2.50 2.70 ground floor level height
GLOBAL PRARMAETERS 124 eta_ve WRG[-] 0.00 0.00 0.80 heat recovery
125 factor_a [m2/m2] 3.00 3.50 2.50 specific effective surface
126 factor_c [J/m2/K] 260000.00 370000.00 165000.00 inner heat storage capacity
127 lambda_at [m2/m2] 4.50 4.50 4.50 view factor
128 phi_h_max [W/m2] 100.00 80.00 40.00 max. spec. Heating capacity
129 phi_c_max [W/m2] 0.00/-100.00 0.00/-120.00 0.00/-80.00 max. spec. Cooling capacity (ZERO for residential buildings)
heating / cooling technology gas boiler / cooling unit district heating / adsorption chiller heatpump / thermal componing activation
134 waste heat for heating [Wwasteheat/Wnetto_energy] 0.10 0.00 -2.00 waste heat heating
135 waste heat for cooling [Wwasteheat/Wnetto_energy] 1.33 2.54 1.25 waste heat cooling
WINDOWS just glas without window frame window type box type window double-layer glazing tripple-layer glazing DIN 4108-4
121 U-value for indoor model U[W/m2/K] 2.90 1.70 0.80 DIN 4108-4
120 g-value for indoor model g[-] 0.80 0.70 0.60
Layer 1-4 17 agfl, 35 gfl, 114 r transmissivity tau[-] 0.70 0.65 0.57
albedo [-] 0.12 0.15 0.18
40 agfl, 77 gfl, 115 r albedo_type [-] 37 37 38 specified in radiation model
119 indoor model FC[-] 0.75 0.75 0.15 4108-2, reduced
49 tc[thermal capacity] of surface lambdaS[W/m2/K] 23.00 23.00 23.00 1 cm air
47 hc [heat capacity] of surface rho x cS[J/m2/K] 20000.00 20000.00 20000.00 1 cm air
shading type curtain, inside curtain, inside blinds, outside
16 agfl, 33 gfl, 113 r emissivity epsilon[-] 0.91 0.87 0.80 just longwave radiation
67-70 gfl, 79-82 agfl, 103-106 r thick [thickness] (2) s[m] 0.02 0.02 0.03 approximatly
86-87, 145 agfl, 74-76, 143 gfl, 110-112, 149 r tc [thermal capacity] lambda[W/m/K] 0.45 0.19 0.11
rho[kg/m3] 2480.00 2480.00 2480.00
c[J/kg/K] 700.00 700.00 700.00
71-73, 142 gfl, 83-85, 144 agfl, 107-109, 148 r hc [heat capacity] rho x c[J/m3/K] 1736000.00 1736000.00 1736000.00
T1[s] 1531.00 3643.00 14081.00
a[mm2/s] 0.26 0.11 0.06
resulting U value (3) U[W/m2/K] 2.90 1.70 0.80
FACADE layer 1 (outside) material mortar plaster mortar plaster mortar plaster DIN 4108-4
46 tc[thermal capacity] of surface lambdaS[W/m2/K] 23.00 23.00 23.00 1 cm air
45 hc [heat capacity] of surface rho x cS[J/m2/K] 20000.00 20000.00 20000.00 1 cm air
38 agfl, 66 gfl albedo_type [-] 36 36 36 specified in radiation model
14 agfl, 32 gfl emissivity epsilon[-] 0.93 0.93 0.93 emissivity only for facade in indoor model implemented as h_is
41 agfl, 62 gfl thick [thickness] (2) s[m] 0.02 0.02 0.02
9 agfl, 29 gfl tc [thermal capacity] lambda[W/m/K] 0.93 0.93 0.93
rho[kg/m3] 1900.00 1900.00 1900.00
c[J/kg/K] 800.00 800.00 800.00
6 agfl, 26 gfl hc [heat capacity] rho x c[J/m3/K] 1520000.00 1520000.00 1520000.00
T1[s] 654.00 654.00 654.00
a[mm2/s] 0.61 0.61 0.61
layer 2 material solid brick thermal insulation thermal insulation DIN 4108-4
42 agfl, 63 gfl thick [thickness] (2) s[m] 0.18 0.06 0.20
10 agfl, 30 gfl tc [thermal capacity] lambda[W/m/K] 0.81 0.046 0.035
rho[kg/m3] 1800.00 120.00 120.00
c[J/kg/K] 840.00 660.00 660.00
7 agfl, 27 gfl hc [heat capacity] rho x c[J/m3/K] 1512000.00 79200.00 79200.00
T1[s] 60480.00 6198.00 90514.00
a[mm2/s] 0.54 0.58 0.44
material solid brick concrete brick DIN 4108-4
layer 3 43 agfl, 64 gfl thick [thickness] s[m] 0.18 0.24 0.36
11 agfl, 31 gfl tc [thermal capacity] lambda[W/m/K] 0.81 2.10 0.68
rho[kg/m3] 1800.00 2400.00 1600.00
c[J/kg/K] 840.00 880.00 840.00
8 agfl, 28 gfl hc [heat capacity] rho x c[J/m3/K] 1512000.00 2112000.00 1344000.00
T1[s] 60480.00 57929.00 256151.00
a[mm2/s] 0.54 0.99 0.51
layer 4 (inside) material gypsum plaster gypsum plaster gypsum plaster DIN 4108-4
44 agfl, 65 gfl thick [thickness] (2) s[m] 0.02 0.02 0.02
137 agfl, 138 gfl tc [thermal capacity] lambda[W/m/K] 0.70 0.70 0.70
rho[kg/m3] 1400.00 1400.00 1400.00
c[J/kg/K] 1090.00 1090.00 1090.00
136 agfl, 139 gfl hc [heat capacity] rho x c[J/m3/K] 1526000.00 1526000.00 1526000.00
T1[s] 872.00 872.00 872.00
a[mm2/s] 0.46 0.46 0.46
resulting U value (3) U[W/m2/K] 1.57 0.62 0.16
ROOF layer 1 (outside) material roof tiles bitumen ground (4) DIN 4108-4
101 albedo_type [-] 42 42 42 specified in radiation model
100 emissivity epsilon[-] 0.90 0.93 0.93
90 thick [thickness] (2) s[m] 0.02 0.02 0.02
97 tc [thermal capacity] lambda[W/m/K] 0.52 0.16 0.52
rho[kg/m3] 1800.00 1000.00 2040.00
c[J/kg/K] 840.00 1700.00 1840.00
94 hc [heat capacity] rho x c[J/m3/K] 1512000.00 1700000.00 3753600.00
T1[s] 1163.00 4250.00 2887.00
a[mm2/s] 0.34 0.09 0.14
layer 2 material wooden formwork thermal insulation wooden formwork DIN 4108-4
91 thick [thickness] (2) s[m] 0.04 0.15 0.04
98 tc [thermal capacity] lambda[W/m/K] 0.12 0.046 0.12
rho[kg/m3] 415.00 120.00 415.00
c[J/kg/K] 1710.00 660.00 1,710.00
95 hc [heat capacity] rho x c[J/m3/K] 709650.00 79200.00 709650.00
T1[s] 9462 38739.00 9462.00
a[mm2/s] 0.17 0.58 0.17
layer 3 material planks concrete thermal insulation DIN 4108-4
92 thick [thickness] (2) s[m] 0.02 0.20 0.30
99 tc [thermal capacity] lambda[W/m/K] 0.12 2.10 0.035
rho[kg/m3] 415.00 2400.00 120.00
c[J/kg/K] 1710.00 880.00 660.00
96 hc [heat capacity] rho x c[J/m3/K] 709650.00 2112000.00 79200.00
T1[s] 2366.00 40229.00 203657.00
a[mm2/s] 0.17 0.99 0.44
layer 4 (inside) material gypsum plast gypsum plast gypsum plast DIN 4108-4
93 thick [thickness] (2) s[m] 0.02 0.02 0.02
147 tc [thermal capacity] lambda[W/m/K] 0.70 0.70 0.70
rho[kg/m3] 1400.00 1400.00 1400.00
c[J/kg/K] 1090.00 1090.00 1090.00
146 hc [heat capacity] rho x c[J/m3/K] 1526000.00 1526000.00 1526000.00
T1[s] 872.00 872.00 872.00
a[mm2/s] 0.46 0.46 0.46
resulting U value (3) U[W/m2/K] 1.41 0.27 0.11
GROUNDPLATE layer 1 (outside) material solid brick concrete concrete DIN 4108-4
52 thick [thickness] (2) s[m] 0.18 0.20 0.20
59 tc [thermal capacity] lambda[W/m/K] 0.52 2.10 2.10
rho[kg/m3] 1800.00 2400.00 2400.00
c[J/kg/K] 840.00 880.00 880.00
56 hc [heat capacity] rho x c[J/m3/K] 1512000.00 2112000.00 2112000.00
T1[s] 94209.00 40229.00 40229.00
a[mm2/s] 0.34 0.99 0.99
layer 2 material solid brick thermal insulation thermal insulation DIN 4108-4
53 thick [thickness] (2) s[m] 0.18 0.06 0.12
60 tc [thermal capacity] lambda[W/m/K] 0.52 0.05 0.05
rho[kg/m3] 1800.00 120.00 120.00
c[J/kg/K] 840.00 660.00 660.00
57 hc [heat capacity] rho x c[J/m3/K] 1512000.00 79200.00 79200.00
T1[s] 94209.00 5702.00 22810.00
a[mm2/s] 0.34 0.63 0.63
layer 3 material screed screed screed DIN 4108-4
54 thick [thickness] (2) s[m] 0.06 0.06 0.06
61 tc [thermal capacity] lambda[W/m/K] 2.10 2.10 2.10
rho[kg/m3] 2400.00 2400.00 2400.00
c[J/kg/K] 880.00 880.00 880.00
58 hc [heat capacity] rho x c[J/m3/K] 2112000.00 2112000.00 2112000.00
T1[s] 3621.00 3621.00 3621.00
a[mm2/s] 0.99 0.99 0.99
layer 4 (inside) material floor board carpet floor board DIN 4108-4
55 thick [thickness] (2) s[m] 0.03 0.02 0.03
141 tc [thermal capacity] lambda[W/m/K] 0.12 0.04 0.12
rho[kg/m3] 415.00 190.00 415.00
c[J/kg/K] 1710.00 1880.00 1710.00
140 hc [heat capacity] rho x c[J/m3/K] 709650.00 357200.00 709650.00
T1[s] 5322.00.00 3572.00 5322.00
a[mm2/s] 0.17 0.11 0.17
resulting U value (3) U[W/m2/K] 1.12 0.67 0.37
GREEN Surface 4 r, 5 agfl, 25 gfl LAI [Leaf area index] LAI[m2/m2] 1.50 1.50 1.50
39 agfl, 78 gfl, 117 r albedo_type [-] 5 5 5 specified in radiation model
15 agfl, 34 gfl, 116 r emissivity epsilon[-] 0.86 0.86 0.86
118 r green type roof [-] 0 0 0
18 agfl, 36 gfl z0 roughness z0[m] 0.001 0.001 0.001
19 agfl, 37 gfl roughness heat/humidity z0h/z0q[m] 0.0001 0.0001 0.0001
50 tc[thermal capacity] of green surface lambdaS[W/m2/K] 10.00 10.00 10.00
48 hc [heat capacity] of green surface rho x cS[J/m2/K] 20000.00 20000.00 20000.00

(1) r=roof, agfl=about groundfloor level, gfl=groundfloor level, gp=groundplate

(2) thickness for layers are implemented kommulative (e.g. thickness_layer_2 = thickness_layer_1 + thickness_layer_2)

(3) against outside air calculated, dependend of modeling the earth temperature not to compare wih U-value after DIN 12831

(4) same values like dry gravel

User behaviour

All parameters for user behavior is taken from DIN 4108-2.

Parameter name Parameter_number residential office unit description
T,set (heating) 13 20.00 20.00 °C setpoint temperature for room in winter
T,set (cooling) 12 26.00 26.00 °C setpoint temperature for room in summer
qint_low (5) 131 4.20 3.00 W/m2 internal heat without presence after schedule
qint_high (5) 130 0.00 7.00 W/m2 additional internal heat with presence after schedule
100.00 142.00 Wh/(m2 d)
air_change_low_summer (5) summer_pars in indoor model 0.50 1.00 l/h air change without presence after schedule in summer
air_change_high_summer (5) summer_pars in indoor model 1.50 1.00 l/h air change without presence after schedule in summer
air_change_low_winter (5) winter_pars in indoor model 0.50 0.20 l/h air change without presence after schedule in winter
air_change_high_winter (5) winter_pars in indoor model 0.00 0.80 l/h air change without presence after schedule in winter

(5) for total internal heat and total air change always = LOW + Schedule(0/1)* HIGH

(6) presence in office buildings from 8:00 - 18:00 else no presence. presence in residental buildings 18:00 - 8:00 else no presence.

References

  • A. Helbig, J. Baumüller, and M.J. Kerschgens. Stadtklima und Luftreinhaltung, Springer-Verlag 2013. Institut für Wohnen und Umwelt IWU: Deutsche Gebäudetypologie, 2018
  • DIN 4108-2:2013-02 (2013). Thermal protection and energy economy in buildings - Part 2: Minimum requirements to thermal insulation, Beuth-Verlag, Berlin, 2013
  • DIN V 18599:2011-12 (2011). Energy efficiency of buildings - Calculation of the net, final and primary energy demand for heating, cooling, ventilation, domestic hot water and lighting, Beuth-Verlag, Berlin, 2011
  • Voss et al.. Bürogebäude mit Zukunft, Solarpraxis, 2006.
  • DIN 4108-4:2017-02 (2017). Thermal insulation and energy economy in buildings - Part 4: Hygrothermal design values, Beuth-Verlag, Berlin, 2017
Last modified 2 years ago Last modified on Oct 17, 2022 9:12:22 AM

Attachments (2)

Download all attachments as: .zip

                                                                                                                                                                                                                                                                                                                                                                               
  | Impressum | ©Leibniz Universität Hannover |