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.
Monthly Slab Outside Face Temperatures, C
Perimeter Area: 304.00 Core Area: 1296.00
Month Average Perimeter Core Inside
1 17.67 16.11 18.03 18.0
2 17.45 15.92 17.81 18.0
3 17.43 16.07 17.74 18.0
4 19.00 17.82 19.27 20.0
5 19.24 18.23 19.48 20.0
6 19.31 18.42 19.52 20.0
7 20.92 20.14 21.11 22.0
8 21.17 20.44 21.35 22.0
9 21.22 20.45 21.40 22.0
10 21.21 20.26 21.44 22.0
11 19.62 18.54 19.88 20.0
12 19.35 17.99 19.67 20.0
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.
|
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.
Monthly Slab Outside Face Temperatures, C
Perimeter Area: 304.00 Core Area: 1296.00
Month Average Perimeter Core Inside
1 17.51 16.03 17.86 18.0
2 17.29 15.85 17.63 18.0
3 17.27 16.00 17.57 18.0
4 18.87 17.77 19.13 20.0
5 19.11 18.16 19.34 20.0
6 19.17 18.34 19.37 20.0
7 20.81 20.07 20.98 22.0
8 21.05 20.36 21.21 22.0
9 21.09 20.38 21.26 22.0
10 21.08 20.19 21.29 22.0
11 19.47 18.45 19.71 20.0
12 19.20 17.92 19.51 20.0
An example of a 24-hour inside temperature profile for this case is shown below. The sine wave amplitude was 2 C.
Day Hour Perim Out Ts Core Out Ts Inside Temp
1 1 17.30827 19.15832 18.51749
1 2 17.29503 19.15274 18.99974
1 3 17.30236 19.16732 19.41389
1 4 17.32258 19.19376 19.73175
1 5 17.34834 19.22526 19.93166
1 6 17.37288 19.25529 20.00000
1 7 17.39023 19.27798 19.93212
1 8 17.39544 19.28838 19.73265
1 9 17.38485 19.28117 19.41517
1 10 17.35602 19.24733 19.00130
1 11 17.30590 19.18686 18.51924
1 12 17.23507 19.10210 18.00180
1 13 17.14650 18.99703 17.48425
1 14 17.04291 18.87713 17.00183
1 15 16.92873 18.74895 16.58738
1 16 16.81076 18.61963 16.26915
1 17 16.69609 18.49656 16.06881
1 18 16.59243 18.38671 16.00000
1 19 16.50669 18.29626 16.06741
1 20 16.44276 18.23010 16.26645
1 21 16.40369 18.19161 16.58356
1 22 16.38873 18.18218 16.99714
1 23 16.39435 18.19834 17.47902
1 24 16.41942 18.23298 17.99639
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.
|
1
|
17.51
|
16.03
|
17.86
|
18
|
7.30
|
1.81
|
|
2
|
17.29
|
15.85
|
17.63
|
18
|
7.96
|
2.63
|
|
3
|
17.27
|
16
|
17.57
|
18
|
7.41
|
2.70
|
|
4
|
18.87
|
17.77
|
19.13
|
20
|
8.26
|
4.19
|
|
5
|
19.11
|
18.16
|
19.34
|
20
|
6.81
|
3.30
|
|
6
|
19.17
|
18.34
|
19.37
|
20
|
6.15
|
3.07
|
|
7
|
20.81
|
20.07
|
20.98
|
22
|
7.15
|
4.41
|
|
8
|
21.05
|
20.36
|
21.21
|
22
|
6.07
|
3.52
|
|
9
|
21.09
|
20.38
|
21.26
|
22
|
6.00
|
3.37
|
|
10
|
21.08
|
20.19
|
21.29
|
22
|
6.70
|
3.41
|
|
11
|
19.47
|
18.45
|
19.71
|
20
|
5.74
|
1.96
|
|
12
|
19.2
|
17.92
|
19.51
|
20
|
7.70
|
2.96
|
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.
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.
Documentation content copyright © 1996-2014 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.