The Slab program produces temperature profiles for the
outside surface at the core and at the perimeter of the slab.
It also produces the average based on the perimeter and core
areas used in the calculation. This allows the user to apply
the Slab temperatures one of two ways in EnergyPlus:
Option 1 - Core and Perimeter Temperatures: The
EnergyPlus OtherSideCoefficients object can be used to provide
two sets of twelve monthly average ground temperature values.
In this way, both the perimeter and the core values from the
Slab program can be used in the succeeding EnergyPlus run.
This method assumes that the floor slab will be described
using at least two different heat transfer surfaces. The use
of OtherSideCoefficients to provide additional ground contact
surfaces is described in detail in the “Multiple Ground
Temperatures” section below.
Option 2 - Average Temperatures: Use the monthly
average temperatures produced by the Slab program in the
EnergyPlus GroundTemperatures object. This will provide an
average ground temperature at the outside face of any heat
transfer surface whose OutsideFaceEnvironment field is set to
“ground”.
EnergyPlus accepts twelve separate monthly average inside
temperatures. In addition, it is possible to add an hourly
sinusoidal variation of the inside temperature with a 24 hour
period sine function. This was included to show the effect of
something such as night setback on the face temperature.
Generally, the effect is quite small.
First the results for a monthly specified constant average
inside temperature. The location is Minneapolis, and the slab
is insulated.
The resulting heat flux is shown below. The inside heat
transfer coefficient and slab thermal properties are specified
in the input file. For this example the total thermal
resistance from the inside air to the slab bottom surface was
0.27 (m2 C)/W. This value is controlled by the user
with the inside heat transfer coefficient and slab thermal
properties values in the slab program input file.
Month
Average
Perimeter
Core
Inside
Perimeter Heat Flux
W/m2
Average Heat Flux
W/m2
1
17.67
16.11
18.03
18
7.00
1.22
2
17.45
15.92
17.81
18
7.70
2.04
3
17.43
16.07
17.74
18
7.15
2.11
4
19
17.82
19.27
20
8.07
3.70
5
19.24
18.23
19.48
20
6.56
2.81
6
19.31
18.42
19.52
20
5.85
2.56
7
20.92
20.14
21.11
22
6.89
4.00
8
21.17
20.44
21.35
22
5.78
3.07
9
21.22
20.45
21.4
22
5.74
2.89
10
21.21
20.26
21.44
22
6.44
2.93
11
19.62
18.54
19.88
20
5.41
1.41
12
19.35
17.99
19.67
20
7.44
2.41
Then for the same conditions, the results with a 2 degree C
amplitude 24-hour sine wave variation. Notice that the inside
temperatures are the same since they are monthly averages and
the daily variation oscillates about the mean. The core and
perimeter slab temperatures are affected slightly.
A plot of the daily profiles is shown below. Note that the
inside temperature change of 4 C produces only a small change
in the slab lower face temperature.
Daily Temperature Profiles
(Slab)
The resulting heat fluxes are shown below. They can be
compared with the fluxes shown above for the constant inside
temperature run. The changes resulting from a fairly large 4 C
daily temperature variation are probably not significant.
Use of the Ground Temperatures with Slabs[LINK]
The Slab program produces temperature profiles for the outside surface at the core and at the perimeter of the slab. It also produces the average based on the perimeter and core areas used in the calculation. This allows the user to apply the Slab temperatures one of two ways in EnergyPlus:
Option 1 - Core and Perimeter Temperatures: The EnergyPlus OtherSideCoefficients object can be used to provide two sets of twelve monthly average ground temperature values. In this way, both the perimeter and the core values from the Slab program can be used in the succeeding EnergyPlus run. This method assumes that the floor slab will be described using at least two different heat transfer surfaces. The use of OtherSideCoefficients to provide additional ground contact surfaces is described in detail in the “Multiple Ground Temperatures” section below.
Option 2 - Average Temperatures: Use the monthly average temperatures produced by the Slab program in the EnergyPlus GroundTemperatures object. This will provide an average ground temperature at the outside face of any heat transfer surface whose OutsideFaceEnvironment field is set to “ground”.
EnergyPlus accepts twelve separate monthly average inside temperatures. In addition, it is possible to add an hourly sinusoidal variation of the inside temperature with a 24 hour period sine function. This was included to show the effect of something such as night setback on the face temperature. Generally, the effect is quite small.
First the results for a monthly specified constant average inside temperature. The location is Minneapolis, and the slab is insulated.
The resulting heat flux is shown below. The inside heat transfer coefficient and slab thermal properties are specified in the input file. For this example the total thermal resistance from the inside air to the slab bottom surface was 0.27 (m2 C)/W. This value is controlled by the user with the inside heat transfer coefficient and slab thermal properties values in the slab program input file.
Then for the same conditions, the results with a 2 degree C amplitude 24-hour sine wave variation. Notice that the inside temperatures are the same since they are monthly averages and the daily variation oscillates about the mean. The core and perimeter slab temperatures are affected slightly.
An example of a 24-hour inside temperature profile for this case is shown below. The sine wave amplitude was 2 C.
A plot of the daily profiles is shown below. Note that the inside temperature change of 4 C produces only a small change in the slab lower face temperature.
The resulting heat fluxes are shown below. They can be compared with the fluxes shown above for the constant inside temperature run. The changes resulting from a fairly large 4 C daily temperature variation are probably not significant.
Documentation content copyright © 1996-2026 The Board of Trustees of the University of Illinois and the Regents of the University of California through the Ernest Orlando Lawrence Berkeley National Laboratory. All rights reserved. EnergyPlus is a trademark of the US Department of Energy.
This documentation is made available under the EnergyPlus Open Source License v1.0.