Surface Heat Balance With Moveable Insulation[LINK]
Basic Heat Balance Cases[LINK]
A heat balance must exist at the outside surfaceair interface. The incoming conductive, convective, and radiative fluxes must sum up to zero:
In contrast to the internal surface heat balance that treats all surfaces simultaneously, the external thermal balance for each surface is performed independent of all other surfaces. This implies that there is no direct interaction between the individual surfaces.
TARP includes four possible representations for the basic outside surface heat balance. The first two depend on which of the optimal surface conductance algorithms the user selects. The simple outside surface conductance that includes both the convective and thermal interchange between the surface and the environment in a single coefficient, is represented by the thermal network in Figure 28. Equation can also be expressed as:
This can be solved for the outside surface temperature.
The detailed outside surface conductance model considers convection and radiant interchange with the sky and with the ground as separate factors. Its use in the outside thermal balance is shown in Figure 29. In this case, equation can be expanded to give
This can be solved for the outside surface temperature:
The third and fourth representations occur when the outside surface has been covered with movable insulation. The insulation has a conductance of UM. The thermal network in Figure 30 represents this case. The insulation must be massless because it is not generally possible to perform a correct thermal balance at the juncture of two surfaces each modeled by CTF.
The equation for the thermal balance between the surface and the insulation is
Which can be rewritten to solve for TO :
Depending on whether or not the detailed or simple algorithm for surface conductance is being used, there are two expressions for TM, the outside temperature of the insulation. For the simple conductance:
For the detailed conductance:
In this case the values of HA, HS and HG must be found by using an estimated value of TM in place of TO.
Heat Balance Cases[LINK]
TO_{t}and TI_{t}are related through the Y_{0}CTF_{.}However TI_{t}is also unknown. While it is possible to combine the outside and the inside surface heat balances to compute TO_{t}and TI_{t}simultaneously, TARP uses a simpler procedure where TO_{t}is based on a previous value of TI. When Y_{0} is small, as occurs in well insulated or very massive surfaces, TI_{t}can be replaced by TI~t 1~(which is known for the previous hour’s heat balance) without significantly effecting the value of TO~t .~When Y_{0} is large, TO and TI can so strongly be coupled that separate outside and inside heat balances do not work because the environment and zone temperatures have negligible influence on the heat balances. The TARP uses the inside surface heat balance to couple TO_{t}with TZ and TR. These two temperatures are less strongly influenced by TO and allow a reasonable heat balance. On the first heat balance iteration, TZ and TR are the values at time t1. The user may optionally require that TO_{t}be recomputed with every iteration of TI~t .~ In this case TZ and TR have values from the previous iteration and a true simultaneous solution is achieved. In most conventional constructions, recomputing TO_{t}does not significantly change the computed zone loads and temperatures. The inside surface heat balance is given by
The surface heat balances can be combined in eight ways according to conditions for calculations of the outside surface temperature
Case1: Y_{0} small, simple conductance, no movable insulation:[LINK]
From Equation
Case2: Y_{0} not small, simple conductance, no movable insulation:[LINK]
From Equations and
Case3: Y_{0} small, detailed conductance, no movable insulation:[LINK]
From Equation
Case4: Y_{0} not small, detailed conductance, no movable insulation:[LINK]
From Equations and
Case5: Y_{0} small, simple conductance, with movable insulation:[LINK]
From Equations and
Case6: Y_{0} not small, simple conductance, with movable insulation:[LINK]
From Equations , and
Case7: Y_{0} small, detailed conductance, with movable insulation:[LINK]
From Equations and
Case8: Y_{0} not small, detailed conductance, with movable insulation:[LINK]
From Equations , and
Fortran Algorithm Examples[LINK]
Case5: Y_{0} small, simple conductance, with movable insulation:[LINK]
From Equation
! Outside heat balance case: Movable insulation, slow conduction, simple convection
F2 = DBLE(HmovInsul) / ( DBLE(HmovInsul) + DBLE(HExtSurf(SurfNum)) )
TH(SurfNum,1,1) = (CTFConstOutPart(SurfNum) &
+DBLE(QRadSWOutAbs(SurfNum) ) &
+Construct(ConstrNum)%CTFCross(0)*TempSurfIn(SurfNum) &
+F2* ( DBLE(QRadSWOutMvIns(SurfNum)) &
+ DBLE(HExtSurf(SurfNum))* DBLE(TempExt) ) ) &
/( Construct(ConstrNum)%CTFOutside(0) + DBLE(HmovInsul) &
 F2* DBLE(HMovInsul))
Case6: Y_{0} not small, simple conductance, with movable insulation:[LINK]
From Equation
! Outside heat balance case: Movable insulation, quick conduction, simple convection
F2 = DBLE(HmovInsul) / ( DBLE(HmovInsul) + DBLE(HExtSurf(SurfNum)) )
TH(SurfNum,1,1) = (CTFConstOutPart(SurfNum) &
+ DBLE(QRadSWOutAbs(SurfNum)) &
+F2*( DBLE(QRadSWOutMvIns(SurfNum)) &
+DBLE(HExtSurf(SurfNum))* DBLE(TempExt) ) &
+F1*( CTFConstInPart(SurfNum) &
+ DBLE(QRadSWInAbs(SurfNum)) &
+ DBLE(QRadThermInAbs(SurfNum)) &
+ DBLE(HConvIn(SurfNum))*MAT(ZoneNum) &
+ DBLE(NetLWRadToSurf(SurfNum)) ) ) &
/( Construct(ConstrNum)%CTFOutside(0) + DBLE(HmovInsul) &
F2* DBLE(HMovInsul ) F1*Construct(ConstrNum)%CTFCross(0) )
Case7: Y_{0} small, detailed conductance, with movable insulation:[LINK]
From Equation
! Outside heat balance case: Movable insulation, slow conduction, detailed convection
F2 = DBLE(HMovInsul)/ ( DBLE(HMovInsul) + DBLE(HExtSurf(SurfNum)) &
+DBLE(HSky) + DBLE(HGround) )
TH(SurfNum,1,1) = (CTFConstOutPart(SurfNum) &
+DBLE(QRadSWOutAbs(SurfNum)) &
+Construct(ConstrNum)%CTFCross(0)*TempSurfIn(SurfNum) &
+F2*( DBLE(QRadSWOutMvIns(SurfNum)) &
+DBLE(HExtSurf(SurfNum))*DBLE(TempExt) &
+DBLE(HSky)*DBLE(SkyTemp) &
+DBLE(HGround)*DBLE(OutDryBulbTemp) ) ) &
/( Construct(ConstrNum)%CTFOutside(0) &
+DBLE(HMovInsul)  F2*DBLE(HMovInsul) )
Case8: Y_{0} not small, detailed conductance, with movable insulation:[LINK]
From Equation
! Outside heat balance case: Movable insulation, quick conduction, detailed convection
F2 = DBLE(HMovInsul)/ ( DBLE(HMovInsul) + DBLE(HExtSurf(SurfNum)) &
+DBLE(HSky) + DBLE(HGround) )
TH(SurfNum,1,1) = (CTFConstOutPart(SurfNum) &
+DBLE(QRadSWOutAbs(SurfNum)) &
+F1*( CTFConstInPart(SurfNum) &
+DBLE(QRadSWInAbs(SurfNum)) &
+DBLE(QRadThermInAbs(SurfNum)) &
+DBLE(HConvIn(SurfNum))*MAT(ZoneNum) &
+DBLE(NetLWRadToSurf(SurfNum)) ) &
+F2*( DBLE(QRadSWOutMvIns(SurfNum)) &
+DBLE(HExtSurf(SurfNum))*DBLE(TempExt) &
+DBLE(HSky)*DBLE(SkyTemp) &
+DBLE(HGround)*DBLE(OutDryBulbTemp) ) &
/( Construct(ConstrNum)%CTFOutside(0) &
+DBLE(HMovInsul)  F2*DBLE(HMovInsul) &
F1*Construct(ConstrNum)%CTFCross(0) )
Fortran Variable Descriptions[LINK]
Fortran Variables and Descriptions
TH(SurfNum,1,1)

Temperature History(SurfNum,Hist Term,In/Out), where: Hist Term (1 = Current Time, 2MaxCTFTerms = previous times), In/Out (1 = Outside, 2 = Inside)

TO_{t}

C

Temperature of outside of surface I at time t

Construct(ConstrNum)%CTFCross(0)

Cross or Y term of the CTF equation

Y0

W/m^{2}K

Cross CTF term

Construct(ConstrNum)%CTFInside(0)

Inside or Z terms of the CTF equation

Z0

W/m^{2}K

Inside CTF term

Construct(ConstrNum)%CTFOutside(0)

Outside or X terms of the CTF equation

X0

W/m^{2}K

Outside CTF term

CTFConstInPart(SurfNum)

Constant inside portion of the CTF calculation

KIP_{t}

W/m^{2}

Portion of inward conductive flux based on previous temperature and flux history terms

CTFConstOutPart(SurfNum)

Constant Outside portion of the CTF calculation

KOP_{t}

W/m^{2}

Portion of outward conductive flux based on previous temperature and flux history terms

F1, F2, F3

Intermediate calculation variables

F1, F2, F3


Radiation interchange factor between surfaces

GroundTemp

Ground surface temperature

T_{g}

C

Temperature of ground at the surface exposed to the outside environment

HConvIn(SurfNum)

Inside convection coefficient

HI

W/m^{2}K

Inside convection coefficient

HExtSurf(SurfNum)

Outside Convection Coefficient

HO, HA

W/m^{2}K

Overall outside surface conductance

HGround

Radiant exchange (linearized) coefficient

HG

W/m^{2}K

Radiative conductance (outside surface to ground temperature

HmovInsul

Conductance or “h” value of movable insulation

UM

W/m^{2}K

Conductance of Movable insulation

HSky

Radiant exchange (linearized) coefficient

HS

W/m^{2}K

Radiative conductance (outside surface to sky radiant temperature

MAT(ZoneNum)

Zone temperature

TZ

C

Temperature of zone air

NetLWRadToSurf(SurfNum)

Net interior longwave radiation to a surface from other surfaces

HR*TR

W/m^{2}

Net surface to surface radiant exchange

QRadSWInAbs(SurfNum)

Shortwave radiation absorbed on inside of opaque surface

QSI

W/m^{2}

Short wave radiant flux absorbed at inside of surface

QRadSWOutAbs(SurfNum)

Short wave radiation absorbed on outside opaque surface

QSO

W/m^{2}

Short wave radiant flux absorbed at outside of surface

QRadSWOutMvIns(SurfNum)

Short wave radiation absorbed on outside of movable insulation

QSM

W/m^{2}

Short wave radiant flux absorbed at surface of movable insulation

QRadThermInAbs(SurfNum)

Thermal Radiation absorbed on inside surfaces


W/m^{2}

Longwave radiant flux from internal gains

SkyTemp

Sky temperature

T_{s}

C

Sky temp

TempExt

Exterior surface temperature or exterior air temperature

TM, T_{a}

C

Temperature of external surface of movable insulation or outside ambient air temperature

TempSurfIn(SurfNum)

Temperature of inside surface for each heat transfer surface

TI_{t1}

C

Temperature of inside of surface I at time t1

: Fortran Variables and Descriptions
Walton, G.N. 1983. “The Thermal Analysis Research Program Reference Manual Program (TARP)”, National Bureau of Standards (now National Institute of Standards and Technology).
Surface Heat Balance With Moveable Insulation[LINK]
Basic Heat Balance Cases[LINK]
A heat balance must exist at the outside surfaceair interface. The incoming conductive, convective, and radiative fluxes must sum up to zero:
In contrast to the internal surface heat balance that treats all surfaces simultaneously, the external thermal balance for each surface is performed independent of all other surfaces. This implies that there is no direct interaction between the individual surfaces.
TARP includes four possible representations for the basic outside surface heat balance. The first two depend on which of the optimal surface conductance algorithms the user selects. The simple outside surface conductance that includes both the convective and thermal interchange between the surface and the environment in a single coefficient, is represented by the thermal network in Figure 28. Equation can also be expressed as:
This can be solved for the outside surface temperature.
The detailed outside surface conductance model considers convection and radiant interchange with the sky and with the ground as separate factors. Its use in the outside thermal balance is shown in Figure 29. In this case, equation can be expanded to give
This can be solved for the outside surface temperature:
The third and fourth representations occur when the outside surface has been covered with movable insulation. The insulation has a conductance of UM. The thermal network in Figure 30 represents this case. The insulation must be massless because it is not generally possible to perform a correct thermal balance at the juncture of two surfaces each modeled by CTF.
The equation for the thermal balance between the surface and the insulation is
Which can be rewritten to solve for TO :
Depending on whether or not the detailed or simple algorithm for surface conductance is being used, there are two expressions for TM, the outside temperature of the insulation. For the simple conductance:
For the detailed conductance:
In this case the values of HA, HS and HG must be found by using an estimated value of TM in place of TO.
Thermal Network for Simple Outside Surface Coefficient
Thermal Network for Detailed Outside Surface Coefficient
Thermal Network for Outside Moveable Insulation
Heat Balance Cases[LINK]
TO_{t}and TI_{t}are related through the Y_{0}CTF_{.}However TI_{t}is also unknown. While it is possible to combine the outside and the inside surface heat balances to compute TO_{t}and TI_{t}simultaneously, TARP uses a simpler procedure where TO_{t}is based on a previous value of TI. When Y_{0} is small, as occurs in well insulated or very massive surfaces, TI_{t}can be replaced by TI~t 1~(which is known for the previous hour’s heat balance) without significantly effecting the value of TO~t .~When Y_{0} is large, TO and TI can so strongly be coupled that separate outside and inside heat balances do not work because the environment and zone temperatures have negligible influence on the heat balances. The TARP uses the inside surface heat balance to couple TO_{t}with TZ and TR. These two temperatures are less strongly influenced by TO and allow a reasonable heat balance. On the first heat balance iteration, TZ and TR are the values at time t1. The user may optionally require that TO_{t}be recomputed with every iteration of TI~t .~ In this case TZ and TR have values from the previous iteration and a true simultaneous solution is achieved. In most conventional constructions, recomputing TO_{t}does not significantly change the computed zone loads and temperatures. The inside surface heat balance is given by
The surface heat balances can be combined in eight ways according to conditions for calculations of the outside surface temperature
Case1: Y_{0} small, simple conductance, no movable insulation:[LINK]
From Equation
Case2: Y_{0} not small, simple conductance, no movable insulation:[LINK]
From Equations and
Case3: Y_{0} small, detailed conductance, no movable insulation:[LINK]
From Equation
Case4: Y_{0} not small, detailed conductance, no movable insulation:[LINK]
From Equations and
Case5: Y_{0} small, simple conductance, with movable insulation:[LINK]
From Equations and
Case6: Y_{0} not small, simple conductance, with movable insulation:[LINK]
From Equations , and
Case7: Y_{0} small, detailed conductance, with movable insulation:[LINK]
From Equations and
Case8: Y_{0} not small, detailed conductance, with movable insulation:[LINK]
From Equations , and
Fortran Algorithm Examples[LINK]
Case5: Y_{0} small, simple conductance, with movable insulation:[LINK]
From Equation
Case6: Y_{0} not small, simple conductance, with movable insulation:[LINK]
From Equation
Case7: Y_{0} small, detailed conductance, with movable insulation:[LINK]
From Equation
Case8: Y_{0} not small, detailed conductance, with movable insulation:[LINK]
From Equation
Fortran Variable Descriptions[LINK]
: Fortran Variables and Descriptions
References[LINK]
Walton, G.N. 1983. “The Thermal Analysis Research Program Reference Manual Program (TARP)”, National Bureau of Standards (now National Institute of Standards and Technology).
Documentation content copyright © 19962014 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.