Transcript EnergyPlus Training Part 1

Lecture 24: Ground Heat
Transfer
Material prepared by GARD Analytics, Inc. and University of Illinois
at Urbana-Champaign under contract to the National Renewable Energy
Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved
Importance of this Lecture to the
Simulation of Buildings
 Almost all buildings have some connection to
the ground
 Depending on the building type, ground heat
transfer may play a significant role in
determining the response of the building to
its surroundings
 Ground heat transfer is often difficult to
calculate and often miscalculated
 Better simulation tools can help avoid errors
in predicting the effects of the ground on the
building
2
Purpose of this Lecture
Gain an understanding of:


Ground heat transfer in EnergyPlus
How to use the slab.exe utility program to
obtain better ground heat transfer
evaluation in EnergyPlus
3
Keywords Covered in this Lecture
GroundTemperatures
Inputs specific to the slab.exe utility
program
4
Ground Heat Transfer
Introduction
 It is difficult to link ground heat transfer calculations
to EnergyPlus since the conduction calculations in
EnergyPlus are one-dimensional and the ground heat
transfer calculations are two or three-dimensional
 This causes severe modeling problems for the ground
heat transfer calculation. But, it is necessary to be
able to relate ground heat transfer calculations to
that model
 Note that ground heat transfer is highly dependent
on soil properties and that soil properties can vary
greatly from location to location—even between
locations in the same city
5
Ground Temperature Object
Specifies the outside surface temp for
surfaces in contact with the ground (e.g.,
slab floors, basement walls)
GROUNDTEMPERATURES,
12.2,
12.7,
<etc.>
12.7;
!- Jan {C}
!- Feb {C}
!- Dec {C}
6
Ground Temperatures
(cont’d)
 Three sets of ground temperatures are tabulated in
the weather file.
 Ground temperatures are for “thermally undisturbed”
soil with a diffusivity of 2.3225760E-03 {m**2/day}.
- Monthly Calculated "undisturbed" Ground Temperatures °
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
0.5 m
9.8
9.5 10.1 11.5 13.4
15.1 16.3 16.7 16.0
2.0 m
11.0 10.4 10.6 11.4 12.6
14.0 15.1 15.7 15.6
4.0 m
12.0 11.4 11.3 11.6 12.4
13.3 14.2 14.8 14.9
Oct
Nov
Dec
14.6 12.8 11.0
14.8 13.5 12.1
14.5 13.8 12.8
 These values are not appropriate for computing
building floor losses.
7
Ground Temperatures
(cont’d)
 Use slab.exe utility to compute appropriate
ground temperatures at the exterior side of
any surface that is in contact with the ground.


This is a monthly value that establishes the outside
boundary condition (temperature) for a particular
surface in contact with the ground.
Documentation for slab.exe can be found in
AuxiliaryPrograms.pdf .
 Otherwise, take the indoor air temperature
and subtract 2C as a reasonable starting value
to use for most commercial applications in the
U.S.
8
Ground Temperatures
(cont’d)
Slab.exe utility will calculate:
 Monthly core, perimeter, and average
ground temperatures
 Given a description of the floor slab,
perimeter insulation, the average indoor
temperature, the soil conditions and the
weather file for a given location
 Will only compute temperatures for slabon-grade construction (i.e., not basements)
9
PreProcess Folder
PreProcess
 BLAST Translator
 DOE-2 Translator
 IDF Editor
 IFCtoIDF
 Weather Converter
 Ground Temp
Calculator
10
Ground Temperatures
(cont’d)
Slab.exe ground temperature utility
11
Slab.exe Utility Program
The slab program used to calculate the
results is included with the EnergyPlus
distribution. It requires an input file
named GHTin.idf in the input data file
format. The needed corresponding idd
file is E+SlabGHT.idd. An EnergyPlus
weather file for the location is also
needed. A sample batch file is shown
on the next slide.
12
Slab.exe Batch File Basic
Functions
echo ===== %0 (Run Slab Generation) ===== Start =====
: Complete the following path and program names.
: path names must have a following \ or errors will happen
set program_path=
set program_name=Slab.exe
set input_path=
set output_path=
set weather_path=
IF EXIST %output_path%%1.gtp ERASE %output_path%%1.gtp
IF EXIST %output_path%%1.ger ERASE %output_path%%1.ger
copy %input_path%%1.idf GHTIn.idf
if EXIST %weather_path%%2.epw copy %weather_path%%2.epw in.epw
ECHO Begin Slab processing . . .
%program_path%%program_name%
IF EXIST "SLABSurfaceTemps.txt" MOVE "SLABSurfaceTemps.txt" %output_path%%1.gtp
IF EXIST eplusout.err MOVE eplusout.err %output_path%%1.ger
ECHO Removing extra files . . .
IF EXIST GHTIn.idf DEL GHTIn.idf
IF EXIST in.epw DEL in.epw
13
Ground Slab Heat Transfer
 The simulation can go from a 1 to x (user
specified) years and uses an explicit finite
difference solution technique.
 Uses monthly average inside temperatures.
 Can use a daily cyclic hourly variation of
inside temperatures; main purpose is for user
experimentation.
 Will shortly have multiple ground temperature
capability in EnergyPlus
14
Slab Program Input
!
===========
Materials,
2,
0.158,
0.379,
0.9,
0.9,
0.75,
0.03,
6.13,
9.26;
ALL OBJECTS IN CLASS: MATERIALS ===========
!
!
!
!
!
!
!
!
!
N1
N2
N3
N4
N5
N6
N7
N8
N9
[NMAT: Number of materials: 2]
[ALBEDO: Surface Albedo: No Snow: 0-1]
[ALBEDO: Surface Albedo: Snow: 0-1]
[EPSLW: Surface Emissivity: No Snow: 0.9]
[EPSLW: Surface Emissivity: Snow: 0.9]
[Z0: Surface Roughness: No Snow: 0-10 cm]
[Z0: Surface Roughness: Snow]
[HIN: Indoor HConv: Downward Flow: 4-10 W/m**2-K]
[HIN: Indoor HConv: Upward: 4-10 W/m**2-K]
15
Slab Program Input (Cont.)
!
===========
MatlProps,
2300,
!
1200,
!
653,
!
1200,
!
0.93,
!
1;
!
ALL OBJECTS IN CLASS: MATLPROPS ===========
N1[RHO: Slab Material density: Validity: 2300.0 kg/m**3]
N2[RHO: Soil Density: 1200.0 kg/m**3]
N3[CP: Slab CP: Validity: 650.0 J/kg-K]
N4[CP: Soil CP: Validity: 1200.0 J/kg-K]
N5[TCON: Slab k: Validity: .9 W/m-K]
N6[TCON: Soil k: Vailidity: 1.0 W/m-K]
!
===========
BoundConds,
TRUE,
! A1
TRUE,
! A2
FALSE;
! A3
ALL OBJECTS IN CLASS: BOUNDCONDS ===========
[EVTR: TRUE/FALSE: Is surface evapotranspiration modeled]
[FIXBC: TRUE/FALSE: Is the lower boundary at a fixed temp.]
[OLDTG: TRUE/FALSE: is there an old ground temperature file]
16
Slab Program Input (Cont.)
!
=========== ALL OBJECTS IN CLASS: BLDGPROPS ===========
BldgProps,
2,
! N1[IYRS: Number of years to iterate: 10]
0,
! N2[Shape: Slab shape: 0 ONLY]
3.048,
! N3[HBLDG: Building height 0-20 m]
21.4;
! N4[TIN: Indoor temperature set point: 21 C]
!
=========== ALL OBJECTS IN CLASS: INSULATION ===========
Insulation,
0.,
! N1[RINS: R value of under slab insulation 0-2.0 W/m-K]
0.,
! N2[DINS: Width of strip of under slab insulation 0-2.0 m]
2.0,
! N3[RVINS: R value of vertical insulation 0-3.0 W/m-K]
1.0,
! N4[ZVINS: Depth of vertical insulation .2 .4 .6 .8 1.0
!
1.5 2.0 2.5 3.0 m ONLY]
1;
! N5[IVINS: Flag: Is there vertical insulation 1=yes 0=no]
17
Slab Program Input (Cont.)
!
=========== ALL OBJECTS IN CLASS: EQUIVSLAB ===========
EquivSlab,
5.08,
! N1[APRatio: The area to perimeter ratio for this slab: m]
TRUE;
! A1[EquivSizing: Flag: Will the dimensions of an equivalent
! slab be calculated (TRUE) or will the dimensions be input
! directly? (FALSE)]
!
=========== ALL OBJECTS IN CLASS: EQUIVAUTOGRID ===========
EquivAutoGrid, ! NOTE:EquivAutoGrid only necessary when EquivSizing is true
0.1016,
! N1[SLABDEPTH: Thickness of slab on grade, 0.1 m]
15;
! N2[CLEARANCE: Distance from edge of slab to domain edge, 15.0 m]
!
=========== ALL OBJECTS IN CLASS: AUTOGRID ===========
AutoGrid,
! NOTE: AutoGrid only necessary when EquivSizing is false
,
! N1[SLABX: X dimension of the building slab, 0-60.0 m]
,
! N2[SLABY: Y dimension of the building slab, 0-60.0 m]
,
! N3[SLABDEPTH: Thickness of slab on grade, 0.1 m]
;
! N4[CLEARANCE: Distance from edge of slab to domain
! edge, 15.0 m]
18
Building Properties IDD
Object
Slab Program uses the EnergyPlus input philosophy and uses its own IDD.
Example is shown below:
BldgProps,
N1, ! [IYRS: Number of years to iterate: 10]
N2, ! [Shape: Slab shape: 0 ONLY]
N3, ! [HBLDG: Building height 0-20 m]
N4, ! [TIN1: Indoor Average temperature set point for January: 22 C]
N5, ! [TIN2: Indoor Average temperature set point for February: 22 C]
N6, ! [TIN3: Indoor Average temperature set point for March: 22 C]
N7, ! [TIN: Indoor Average temperature set point for April: 22 C]
N8, ! [TIN: Indoor Average temperature set point for May: 22 C]
N9, ! [TIN: Indoor Average temperature set point for June: 22 C]
N10, ! [TIN: Indoor Average temperature set point for July: 22 C]
N11, ! [TIN: Indoor Average temperature set point for August: 22 C]
N12, ! [TIN: Indoor Average temperature set point for September: 22 C]
N13, ! [TIN: Indoor Average temperature set point for October: 22 C]
N14, ! [TIN: Indoor Average temperature set point for November: 22 C]
N15, ! [TIN: Indoor Average temperature set point for December: 22 C]
N16, ! [Daily sine wave variation amplitude: 0 C ]
N17; ! Convergence Tollerance : 0.1
19
Variable Inside Temperature
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
20
Heat Fluxes
Temperatures
Month
1
2
3
4
5
6
7
8
9
10
11
12
Heat Flux W/m^2
Average Perimeter Core Inside Perimeter
17.67
16.11
18.03
18
7.00
17.45
15.92
17.81
18
7.70
17.43
16.07
17.74
18
7.15
19
17.82
19.27 20
8.07
19.24
18.23
19.48
20
6.56
19.31
18.42
19.52
20
5.85
20.92
20.14
21.11
22
6.89
21.17
20.44
21.35
22
5.78
21.22
20.45
21.4
22
5.74
21.21 20.26
21.44 22
6.44
19.62
18.54
19.88
20
5.41
19.35
17.99
19.67
20
7.44
Average
1.22
2.04
2.11
3.70
2.81
2.56
4.00
3.07
2.89
2.93
1.41
2.41
21
Heat Fluxes with Hourly
Variation of Inside Temp
Month Av erage Perimeter
1
17.51
16.03
2
17.29
15.85
3
17.27
16
4
18.87
17.77
5
19.11
18.16
6
19.17
18.34
7
20.81
20.07
8
21.05
20.36
9
21.09
20.38
10
21.08
20.19
11
19.47
18.45
12
19.2
17.92
Perimeter Av erage
Heat Flux Heat Flux
W/m^2
W/m^2
Core
Inside
17.86
18
7.30
1.81
17.63
18
7.96
2.63
17.57
18
7.41
2.70
19.13
20
8.26
4.19
19.34
20
6.81
3.30
19.37
20
6.15
3.07
20.98
22
7.15
4.41
21.21
22
6.07
3.52
21.26
22
6.00
3.37
21.29
22
6.70
3.41
19.71
20
5.74
1.96
19.51
20
7.70
2.96
22
Hourly Temperature
Variation
Slab w ith Sinus oidal Ins ide Te m p
20
Perim Out Ts
15
Core Out Ts
10
Inside Temp
5
23
21
19
17
15
13
11
9
7
5
3
0
1
Temperature, C
25
hour
23
General Procedure for using
slab.exe with EnergyPlus
1.
Run the building in EnergyPlus with an
insulated slab or as a partition to obtain
monthly inside temperatures.
2.
Put those monthly inside temperatures in
the slab program to determine outside face
temperatures.
3.
Use resulting outside face temperatures in
EnergyPlus.
4.
Repeat 2 and 3 if inside temperatures
change significantly.
24
Example Results 100 X 300 ft
Warehouse, Minneapolis
25
Slab Results
Month Average Perimeter Core
1
4.78
3.90
4.99
2
4.68
3.85
4.87
3
6.13
5.40
6.30
4
10.54
9.90
10.69
5
17.56
16.83
17.73
6
22.56
21.73
22.75
7
24.96
24.14
25.16
8
24.31
23.51
24.50
9
20.03
19.33
20.19
10
12.89
12.31
13.03
11
7.07
6.56
7.19
12
5.17
4.51
5.33
Inside
4.4
4.5
6.3
11.8
20.0
25.1
27.1
25.6
20.1
11.9
5.8
4.4
Convergence has been gained.
26
Temperature Differences
between EnergyPlus Runs
I ns ide T emperature D ifferenc e, Step 2 to s tep 3
0 .3
0 .2
temperature difference C
0 .1
0
- 0 .1
1
2
3
4
5
6
7
8
9
10
11
12
- 0 .2
- 0 .3
- 0 .4
- 0 .5
- 0 .6
- 0 .7
mont h
27
Summary
Almost all buildings have some thermal
connection to the ground, but ground
heat transfer can be difficult to simulate
Slab Program allows more accurate
calculation of ground temperatures for
use with EnergyPlus
Use of Slab Program—EnergyPlus
combination may require iteration
between the two programs
28