Re: [EnergyPlus_Support] F-factors

My goal is to reverse engineer an equivalent slab-on-grade construction for simulations as per ASHRAE 90.1 Appx G.

F * Pexp = Ueff * A

= 1/Reff * A

This gives

Reff = A / (F * Pexp)...the user inputs

...therefor for a insulation rating value that matches the standard's rated insulation requirement for the required F-factor and
substituting for the construction build up as defined by ASHRAE 90.1 A6

Reff = Rairfilm_in + Rconcreate + Rrequired_rated_insulation + Rsoil + Rother + Rairfilm_out

where
*********************************

Rairfilm_in = 0.77 hr-ft2-F/Btu (0.14 m2-K/W)

is the average of the air film resistance for heat flow up 0.61 hr-ft2-F/Btu (0.11 m2-K/W) and heat flow down 0.92 hr-ft2-F/Btu (0.16 m2-K/W), as per ASHRAE 90.1 A9.1.4 and Winkelmann

*************************************
Rconcreate = 0.07 m²K /W

as per ASHRAE 90.1 A6 for 0.5ft (150 mm) concrete from ASHRAE 90.1 Table A3.1B, and density 2304 kg/m³

**********************************

Rrequired_rated_insulation can be found by fitting a curve through the values in standard 90.1 Table A6.3 for fully insulated slab-on-grade:

ASHRAE 90.1 F-Factors for fully insulated slabs and Unheated as per Appendix G
SI Units
R-values	0	0.9	1.3	1.8	2.6	3.5	4.4	5.3	6.2	7	7.9	8.8	9.7
F-factors	na	0.8	0.71	0.62	0.52	0.45	0.4	0.37	0.34	0.32	0.3	0.29	0.28

we can find the curve fit equation as

Rrequired_rated_insulation = 0.6065 * ( F )-2.165

****************************************

Rsoil is assumed 1 ft (0.3 m) at k=1.3 W/m²-K as per Table A9.4D, which corrisponds to recommendations in UNDERGROUND SURFACES: HOW TO GET A BETTER UNDERGROUND SURFACE HEAT TRANSFER CALCULATION IN DOE-2.1E, Winkelmann

therefore

Rsoil = 0.22 m²K /W
**************************************

Rairfilm_out = 0.0299387 m²K /W as per ASHRAE 90.1 A9.4.1
*************************************

Therefore the only unknown, Rother can be calculated.

Rother = A / (F * Pexp) - (0.14) - (0.07) - (0.6065 * ( F )-2.165) - (0.22) - (0.0299387)

it is assumed Rother has material properties for density and specific heat, the same as that of soil.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Now I can build up an equivalent construction for the "slab" espectially honed to exclusively "slab-on-grade" for Appendix G of ASHRAE 90.1. If Rother is negative, Rrequired_rated_insulation must be "derated" to effect the difference. See the spreadsheet attatched.

Thanks for all the help.

Jean.

PS other material properties one can use to build up this construction in e+ could be as follows

Concrete	150 mm	Construction as per A6.1:
	Properties as per A3.1B for 150 mm, 2304 kg/m³ --> Rc = 0.07, HC = 294 -->
	specific heat =	850.694444	J/kg-K
Insulation R-		0.36521482	m²K/W
	Properties as per HOF Expanded Polystyrene extruded smooth skin 40 kg/m³, 0.030 W/m²-K
	thickness =	0.01095644	mm
Soil	to account for thermal mass effects of the soil as per DOE-2 Articles from the Building Energy Simulation User News, January 2003 and ASHRAE 90.1 table A9.4D
	k =	1.3	W/m²-K
	thickness =	0.3	m
	density =	1840	kg/m³	as per DOE-2 referenced above

On 29 April 2013 10:19, Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Jean,

My comments follow your questions below.
Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 4/29/2013 12:05 AM, Jean Marais wrote:

Hi Joe,

I'm not getting any further on this issue. Perhaps you can lend me some insight. You say that the F-factors in standard 90.1 were the result of parametric simulations that you ran for different configurations of perimeter insulation...so let me see if I understand this right.

1) your model (1988) assumed the walls were Adiabatic so that only the heat loss through the slab-on-grade was captured

No, the 2-D simulations I did were with a finite-difference program for a vertical 1 ft. slice through the foundation extending 15 ft into the building.
In the original analysis done for the Foundation Design Handbook in 1988, I multiplied the heat flow of each FD element by the annulus length of a 1540-ft2 house (55 ft x 28 ft) to derive the total heat flow through the foundation. For the simpler method described in Winklemann and Huang,
I took the total heat flows across the entire 15 ft foundation slice and divided that by temperature difference (Tin - Tout) to derive the F-Factors per lineal foot of perimeter. This actually overestimates the heat flows due to the core section, but is a lot easier to calculate. So, I repeat - no heat losses
are being ignored, just that their magnitude is assumed to be a function of the perimeter length.

2) you considered vertical, horizontal AND fully insulated configurations

I did 88 foundation configurations for slab on grade, 8' full basements, 4' half basements, and ventilated crawl spaces. Slab configurations include two depths of vertical perimeter edge insulation (2' and 4') either R-5, R-10, or R-15, on the outside or inside of the slab, and also combinations of vertical and horizontal extending down 2' and out 2' (this turned out to be the most effective, as it decoupled more of the soil from the outside air temperatures). Basement insulation is similar, 4' 8' insulation outside, inside, and integral (for a wood frame foundation), crawl space configurations are similar to the slab configurations. I think all 88 cases are described in both the 88 ASHRAE paper as well as the Winkelmann Huang paper.

3) you used a 2D slab simulation program

Yes, it was a 2-D finite difference program written by Lester Shen at the Univ. of Minnesota Underground Space Center. We did 5 years of initialization, 4 on a monthly time step, 1 on a daily time step, followed then by one year on a daily timestep. The program was very robust, no problems at all.

My questions

4) what inside air film resistance did you use?

You have to distinguish the air film resistances used in the 2-D simulations, and the ones used in the whole building simulation incorporating the 2-D results. I think we used pretty standard ASHRAE values for the air film, maybe 0.77 Btu/hr-ft2-F . This actually gets rather academic because the total effective R-value of the foundation including the soil is quite high, R-20 to R-40, especially when "coupled" with the outside air temperature.

5) what outside air film resistance did you use?

I believe it was a constant 0.17 Btu/hr-ft2-F in the 2-D simulation, but in the whole house simulation, this varied depending on wind speed. Not a big effect.

6) what inside temperature did you use?

Same caveat applies here. In the 2-D simulation, Tin was constant 74F for the slab, lower for the basement and crawl space, either 60 F or 65F. In the DOE-2 simulation, the zone temperature varies quite a bit, for which DOE-2 does a UA delta T correction using the same F-Factor. This adjustment was
especially large for the basement and crawl space, and Lester and I came up with a crude response factor to take into account the thermal lag due to the large amount of thermal mass. That was written up in the 1988 paper, but I did not emphasize it in the simpler models.

7) what outside temperature did you use? If it varied over time, how is it that the F-factor can be constant? If it varied by Climate Zone, R-value, or other, could you tell me the breakdown?

The outside temperature is the daily outdoor air temperature. There's also a constant deep ground temperature 50 ' down in the model. Think of the F-Factor as a conductance, so it scales with the temperature difference (Tin - Tout). It's the crudest first-order approximation because it doesn't take
the thermal lag of the soil into account, nor does it distinguish between the temperatures of the air, ground, and deep ground. What I did were linear
regressions of the heat flux through the foundation against the instantaneous temperature difference Tin - Tout, averaged for 12 different climates.

That was why when I did the project for the Energy Commission a decade later, I split the foundation into different domains and did separate regressions for 3-week air temperature, 5' ground temperature, and deep ground constant temperature.
Kind regards,

Jean Marais
On 25 April 2013 12:09, Joe Huang <yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Jean, others,

It was quite a surprise to read your e-mail and find that the old F-Factors that I calculated back in 1988 are still being referred to in Standard 90.1. If you're interested in more details of that effort, there's an ASHRAE Transaction paper
Huang, Y.J., L.S. Shen, J.C. Bull, and L.F. Goldberg 1988. "Whole-house simulation of foundation heat-flows using the DOE-2 program",
ASHRAE Transactions, Vol. 94-2.

and a 1998 User News article written by Fred Winkelmann on its implementation in DOE-2 (see attached).

The F-Factors are per lineal feet of perimeter from Tout to Tin of the space containing the foundation. There are actually several ways to implement this model: (1) model a monolithic foundation as an exterior wall and adjust the R-value of the layer so that U*A = F*PL (Perimeter length) -- this is the method shown in the Winkelmann article, (2) decompose the foundation into two regions - a perimeter strip 1-2 ft wide and a core for the remainder; model the perimeter as an exterior wall, adjusting its R-value accordingly, but model the core as an adiabatic layer. When I was working with DOE-2, there was a practical problem that layers can't be too thick or the response factor would fail, so I could only add at most 2.5 ft of soil. I don't know if EnergyPlus has similar limitations. Ideally, you would want to model as much soil as possible to get the thermal dampening effect.

The main deficiencies with this technique are (1) Tout is the outside air temperature, (2) the foundation is treated as a single layer. I know there's a temptation to model the foundation as a underground layer tied to the soil temperature, but that would be wrrong since the F-Factors are calculated air-to-air.

In the late 90's (1998-2000), I worked with Fred Winkelmann and Vladimir Bazjanac for the Calif. Energy Commission to develop what I think is a much better model that is now the approved method for Title-24. This model uses a similar approach as before, except instead of a single F-Factor, there are six Foundation Conductances for two domains (perimeter and core) and three heat flow paths ("quick" to the outdoor air temperature the past 3 weeks, "slow" to the monthly ground temperature, and "constant" to the deep ground temperature). The model is not only more accurate, but more flexible for different building conditions. If anyone's interested in the report, it's available at www.whiteboxtechnologies.com/downloads/00_02.YJH.CEC_Fdn_Model.pdf

If I have it in my power, I would urge everyone to stop using the 1988 model and switch to the 2000 model, but since the F-Factors seem to have been institutionalized by now, that would be irresponsible. So, I'll be happy to answer questions about the use of either model.

Joe
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 4/24/2013 9:34 PM, Jean marais wrote:

Dear Group,
e+ has a documented technique of converting the user inputs of F-Factor, Area and Perimeter into a Equivalent U-Value Contruction. It seams however that ASHRAE 90.1 and HOF has too little information on how the F-Factors in standard 90.1 were created (for example, which T_in and T_out were used, how were losses into the soil accounted for, which air film resistances were used, etc.) for me to trust this technique as a compliance tool.

I propose the following solution:
Baseline case...
In a nut shell, a curve fit for the "fully insulated" case of the F-factor table in 90.1...R-insulation is then a function of F-factor input. Thus an equivalent construction can be created that satisfies the Standard in terms of Rated R-insulation covering the entire slab, concrete thickness and soil conductivity as per the description in Appx A. As Dr Huang suggested, use a 0.3 (also noted for this thickness at the back of 90.1 appx A) at the soil conductivity perscribed by 90.1 to catch the thermal mass effects of the soil.

As a check, a construction defined in this way can be looked up for its F-factor and should give the right R-value using interpolation.

Proposed case...
1) look at the actual design
2) deturmin the F-factor from Table A6.3
3) Calculate equivalent slab construction as for Baseline case using the F-factor from step 2)

It should be said that if your slab does not meet the criteria for "slab-on-grade" as per 90.1, then the standard has no requirement of it and it should be modelled identically to that of the proposed case model (e.g. Basement slabs are not slab-on-grade)

Your comments please, after reading some of the rest of these corrispondances.

Kind regards,

Jean

Further reading...

I would like to draw your attention to how COMcheck software handles slab-on-grade F-factors.
http://www.energycodes.gov/sites/default/files/documents/BECP_Technical%20Support%20Document%20for%20Version%20391%20of%20the%20COMcheck%20Software_Sept2012_v00.pdf

Another interesting take is that of DOE2 http://simulationresearch.lbl.gov/dirpubs/un_articles02.pdf
The tabled F-factors here were deturmined by Huang using 2D parametric studies...the tabulated values don't match those in ASHRAE 90.1. See the onebuilding forum note by Joe Huang http://www.gard.com/ml/bldg-sim-archive/msg01047.html

Comments, please.

Kind regards,

Jean Marais

On 19 April 2013 16:59, Tianzhen Hong <thong@xxxxxxx> wrote:
Jean,

When we developed this feature for EnergyPlus, we did quite some research on the topic and you also pointed out, ASHRAE did not have every details on F-factor. A few years back, I was developing EnvStd, a tool used for ASHRAE 90.1 envelope tradeoff, F-factor was used to calculate the equivalent heat transfer between the zone and outdoor, there is no such a term of "heat flow into soil environment".

Tianzhen

On Fri, Apr 19, 2013 at 2:32 AM, Jean Marais <jeannieboef@xxxxxxxxx> wrote:
HOF 18.31 equation 41 with equation 42 for "at grade surfaces" can be combined as follows:
q = Pexp*F*delta_t ...unfortuanately delta_t is not defined here...judging from the previous section for slabs below grade, I must currently assume delta_t = (T_in - T_ground), though for perimeter losses delta_t = (T_in - T_ODA) may be more appropriate.

In context of slabs below grade, I see that the for heat to travel from T_in to T_ground, it must travers Rfilm_in, Rcon, Rinsulation (if any) and possibly a R_soil_to_slab (probably negligable). However, for slabs at grade the heat travels partly into the ground and partly into the ODA via the ground. i.e. I could assume that the F-factors were calculated somewhat as below:

qtot = heat flow into soil environment + heat flow into outdoor environment through perimeter effects
       = [Area * U_slabconstructionwithinteriorairfilmresistances * (T_in - T_ground)] + [Pexp * F * (T_in - T_ODA)]
       = [Area / (Rfilm_in+Rcon+Rins) * (T_in - T_ground)] + [Pexp / (Rfilm_in+Rcon+Rins+Rsoil_path_to_outdoors+Rvertical_insulation+Rfilm_out) * (T_in - T_ODA)]   ...there is a small overlap here, but should be negligable.

As you can see, if this is the case,it is very important to establish what Rsoil_path_to_outdoors was used for the F-factor ratings in 90.1. Alternatively,
1) soil conductivity used for the F-factor ratings in 90.1 = 1.30 W/m-K as per A6.1
2) soil heat flow path length for the F-factor ratings in 90.1...can be assumed the distance of the corrisponding F-factor insulation and type. E.g. F-0.90 corrisponds to R-1.8 and 600 mm vertical insulation, which approximates a soil travel path of 2x600 mm.

HOF does not mention any air film resistances in chapter 18.31, but 90.1 lists these for rating values in A9.4.1. Assuming an average for heat flow up and down is probably a good approximation for the interior air film resistances as the temperature of the soil cycles over the annual average for half the year and under the average for the other half (sinusoidal).

The values in HOF table 24 are in the same range as those in 90.1 table A6.3. Furthermore, HOF equation 42 defines q = heat loss through perimeter...this leads me to believe that the F-factor rating values in 90.1 express only heat losses of perimeter effects and does not include those to the soil.

In summary:

INPUT VALUES
F-factor
Pexp
Area
T_ground = anual_mean_ground_temperature used for the F-factor rating values is assumed at 0.3 m...0.3 from Winkelmann's slab-on-grade model...we assume the rating values of 90.1 included variation per climate zone and that this corrisponds to user input.
T_in = anual_mean_indoor_temperature used for the F-factor rating values is assumed to have been assumed at 20ºC for conditioned spaces
T_ODA = annual_mean_outdoor_temperature ...it is assumed that the F-factor rating values had assumed the annual_mean_outdoor_temperature for calculation and that climate zone variation was taken into account. It is assumed this temperature will closely match the user input.

GIVEN / ASSUMED VALUES
Rcon = 0.077 m2-K/W ...as in EngRef which co-insides closely to values in 90.1 Table A3.1B
Rfilm_in = 0.14 m2·K/W ...which is the average of the 0.11 m2·K/W for heat flow up and 0.17 m2·K/W for heat flow down as per 90.1 A9.4.1...this differs from EngRef!
Rfilm_out = 0.03 ... as per EngRef and 90.1 A9.4.1 for all exterior facing up or sideways surfaces...NB not for external floors
k_soil = 1.30 W/m-K ...as per A6.1

LOOKUP VALUES
Insulation_configuration_best_fit_for_F-factor_from_Table_A6.3 (Perimeter_Insulation_is_Vertical, Ins_mm, R-value)

CALCULATED VALUES
Soil_Heat_Flow_Path_Length
Rins
the rest

Someone may shed some more light on how the rating values were calculated so that we can back calculate the U-value of the slab construction.

Kind regards,

Jean.

On 19 April 2013 08:50, Jean Marais <jeannieboef@xxxxxxxxx> wrote:
Thanks Mike, I will check the handbook and see if revers calculatiosn can bring some light.

Funny thing that definition...the definition is aimed at slabs that lay exposed above the grade line and are exposed to the OD environment (that means that their is no requirement for basement slabs!, i.e. for basement slabs the baseline is modeled as proposed case), but includes "or is less than or equal to 600 mmj below the final elevation of the nearest exterior grade".

If I learn anything more, I'll post it.

Kind regards,

Jean.

On 18 April 2013 17:46, Michael J Witte <mjwitte@xxxxxxxx> wrote:
Jean:

Just to clarify, for "slab-on-grade" the slab edge is exposed to the air (directly or through insulation). From Std. 90.1 Appendix A, section A6.1 "For the purpose of Section A1.2, the base assembly is a slab floor of 6 in. concrete poured directly on to the earth, the bottom of the slab is at grade line, . . ."

It seems there are several issues here.

1. How to convert from F-factor to equivalent U-value. This is what your users need to know, regardless of how F-factor has been implemented or documented in EnergyPlus. There appears to be some guidance here, but I do not have access to my handbook at the moment to check this:

http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/2010-March/003573.html

2. The second issue is whether EnergyPlus has implemented and documented the f-factor model as intended.   I don't have the answer to that at the moment. What I can tell you is that the source code matches the v8.0 documentation. It creates two material layers (which you should be able to report in the eio output using Output:Constructions).

Concrete layer (inside layer):
! Add the 6" heavy concrete for constructions defined with F or C factor method
IF (TotFfactorConstructs + TotCfactorConstructs >=1 ) THEN
    MaterNum = MaterNum + 1

    Material(MaterNum)%Group=RegularMaterial
    Material(MaterNum)%Name = '~FC_Concrete'
    Material(MaterNum)%Thickness     = 0.15d0       ! m, 0.15m = 6 inches
    Material(MaterNum)%Conductivity = 1.95d0       ! W/mK
    Material(MaterNum)%Density       = 2240.0d0     ! kg/m3
    Material(MaterNum)%SpecHeat      = 900.0d0      ! J/kgK
    Material(MaterNum)%Roughness = MediumRough
    Material(MaterNum)%AbsorpSolar = 0.7d0
    Material(MaterNum)%AbsorpThermal = 0.9d0
    Material(MaterNum)%AbsorpVisible = 0.7d0
    NominalR(MaterNum) = Material(MaterNum)%Thickness / Material(MaterNum)%Conductivity
    Material(MaterNum)%Resistance = NominalR(MaterNum)

Rcon = Material(iFCConcreteLayer)%Resistance

The second layer is the insulation layer (outside layer) with Rfic:

      Reff = Area / (PerimeterExposed * Ffactor) - Rfilm_in - Rfilm_out
      Rfic = Reff - Rcon

   ! ASHRAE Handbook Fundamental 2005
   !Thermal resistance of the inside air film, m2.K/W. Average of 0.14 (heat flow up) and 0.11 (heat flow down)
REAL(r64),PARAMETER :: Rfilm_in = 0.125d0
    !Thermal resistance of the outside air film used in calculating the Ffactor, m2.K/W. 0.17/5.678
REAL(r64),PARAMETER :: Rfilm_out = 0.03d0

Looking at example file 1ZoneUncontrolled_FCfactor_Slab_UGWall.idf
Construction:FfactorGroundFloor,
    slabconst,               !- Name
    0.12,                    !- F-Factor {W/m-K}
    232.26,                  !- Area {m2}
    61.0;                    !- PerimeterExposed {m}

! <Material CTF Summary>,Material Name,Thickness {m},Conductivity {w/m-K},Density {kg/m3},Specific Heat {J/kg-K},ThermalResistance {m2-K/w}
Material CTF Summary,~FC_Insulation_1, 0.0000,         0.000,      0.000,        0.000,   31.50
Material CTF Summary,~FC_Concrete, 0.1500,         1.950,   2240.000,      900.000, 0.7692E-01

When the Ffactor surface heat balance is done, the inside convection coefficient is varying as it does for any surface in EnergyPlus. This seems reasonable.

However, the outside surface temperature is set directly to the current value of Site:GroundTemperature:FCfactorMethod, so there is no outside film coefficient resistance during the simulation. This makes me question whether Rfilm_out should be dropped from this equation:

      Reff = Area / (PerimeterExposed * Ffactor) - Rfilm_in - Rfilm_out

And as you ask, where did the values for Rfilm_in and Rfilm_out come from? Do they match the ASHRAE f-factor calculations.

3. Finally, is the DesignBuilder team planning to implement the F and C-factor option?

Mike

On 4/18/2013 1:08 AM, Jean Marais wrote:
Hi Linda,

Mr. Hong is not responding...

Sorry. This issue is not going away. As stated, yes, the documentation has changed in v8, but still refers to air on the outside of the slab and no soil is mentioned, i.e.
"Q = Area * Ueff * (Tair,out – Tair,in) = (Tair,out – Tair,in) * (Pexp * F-factor)", "Tair,out is the outside air temperature in °C", "The outside air film resistance Rfilm, out = 0.03 m2·K/W.", etc.

If a slab is "on-grade" then I fail to see how air_outside can factor into the equation. Mr. Hong has insinuated that these issues have been corrected "The air film (either inside or outside) is not included in the calculation of effective U-factor. The soil layer is modeled as part of the 6" concrete and an insulation layer to come up with the equivalent U-factor.", but the documentation of the last v8 release does not reflect it. As I am supporting DesignBuilder, and DesignBuilder does not currently support the F-factor objects for e+, it is important for me to explain to clients how to calculate the Ueff to properly reflect the f-factors in 90.1. No one has been able to explain this to me. I need to know what R-soil ASHRAE was using for these f-factors AND which film factors (if any) are included in the f-ractor rating values.

This information would help many users who have been ignoring this issue for many years. I'm always supprised how long people have been "conforming" to ASHRAE 90.1 for simulations.

Kind regards,

Jean

On 17 April 2013 14:51, Linda Lawrie <linda@xxxxxxxxxxxxxx> wrote:
I presume he meant the current V8 release. But I'm not sure.

At 11:21 PM 4/16/2013, jeannieboef@xxxxxxxxx wrote:
May I ask for your source of information? Do you mean the next release, as the v8 documentation includes the film resistances?

Kind regards,

Jean

Sent from my iPhone

On 16.04.2013, at 22:36, Tianzhen Hong <thong@xxxxxxx> wrote:

Jean,

We clarified the documentation in the coming E+ 8.0 release.

The air film (either inside or outside) is not included in the calculation of effective U-factor. The soil layer is modeled as part of the 6" concrete and an insulation layer to come up with the equivalent U-factor.

Tianzhen
To: linda@xxxxxxxxxxxxxx
Subject: [EnergyPlus !7333]: F-factor method engineeringreference documentation error?
Date: Wed, 10 Apr 2013 09:39:30 +0000
Jean Marais updated #7333
-------------------------

F-factor method engineeringreference documentation error?
---------------------------------------------------------

Ticket ID: 7333
URL: http://energyplus.helpserve.com/staff/Tickets/Ticket/View/7333
Full Name: Jean Marais
Email: jeannieboef@xxxxxxxxx
Creator: User
Department: General
Staff (Owner): -- Unassigned --
Type: Issue
Status: Open
Priority: Medium
Template Group: Default
Created: 10 April 2013 09:39 AM
Updated: 10 April 2013 09:39 AM
Due: 11 April 2013 09:39 AM (1d 0h 0m)
Resolution Due: 12 April 2013 09:39 AM (2d 0h 0m)

Dear Team,

How can there be an air-resistance-film on the underside of the slab? I am comparing to DOE-2E
http://www-esl.tamu.edu/docs/terp/2012/ESL-TR-12-02-01.pdf
Surely a soil layer should be assumed here. And then which soil layer was used for the F-factors listed in ASHRAE 90.1?

Please advise.

Kind regards,

Jean.