3.5.10 Heat Transfer between Thermal Blocks

Applicability

All slab floors, optional

Definition

A unique name or code that relates the exposed floor to the construction documents

Units

Text: unique

Input Restrictions

None

Baseline Building

Not applicable

Applicability

All slab floors, required

Definition

One of two classes for floors in contact with ground. The classes are:

1. Heated slab-on-grade floors
2. Unheated slab-on-grade floors

Heated slab-on-grade floors include all floors that are heated directly to provide heating to the space. Unheated slab-on-grade floors are all other floors in contact with the ground.

Units

List: Heated or Unheated

Input Restrictions

None

Baseline Building

The baseline building slab floor type is unheated

Applicability

All slab floors, required

Definition

A geometric construct representing a slab floor in contact with the earth. The geometric representation can vary depending on how the energy simulation software models slabs-on-grade. Some models require that only the perimeter of the slab be entered. Other models divide the slab into a perimeter band within 2 ft of the edge and the interior portion or core area, such that the perimeter area and the core area sum to the total area of the slab.

Units

Data structure: as appropriate for the simulation tool

This may include: area, perimeter exposed

Input Restrictions

As designed

Baseline Building

The geometry of the slab floor in the baseline building is identical to the slab floor in the proposed design

Applicability

All slab floors, required input

Definition

A specification containing a series of layers that result in a construction assembly for the proposed design. The first layer in the series represents the outside (or exterior) layer and the last layer represents the inside (or interior) layer. See the building descriptors above for slab floor type.

A description of how the slab is insulated (or not). How the construction is described will depend on the energy simulation model. The construction can be represented by an F-factor that represents the entire construction (floor and insulation).

Simple models may include just an F-factor, representing an instantaneous heat loss/gain to outside air. The F-factor could be related to the configuration of insulation in the proposed design. Other slab loss models may require that the surface area of the slab floor be divided between the perimeter and the interior. The insulation conditions then define heat transfer between both outside air and ground temperature.

The insulation condition for slabs includes the R-value of the insulation and the distance it extends into the earth at the slab edge and how far it extends underneath the slab.

Units

List (depends on the model that is used)

For F-factor method: F-factor from Standard 90.1-2019 Normative Appendix A, Table A₆.3.1; this is one selection from list 1 and one selection from list 2. Note that some combinations from list 1 and list 2 are not allowed – see Normative Appendix A, Table A₆.3.1.

List 1: None, 12 in horizontal, 24 in horizontal, 36 in horizontal, 48 in horizontal, 12 in vertical, 24 in vertical, 36 in vertical, 48 in vertical, Fully insulated slab

List 2: R-0, R-5, R-7.5, R-10, R-15, R-20, R-25, R-30, R-35, R-40, R-45, R-50, R-55

Input Restrictions

For new construction, F-factors shall be taken from Table A₆.3.1 of Standard 90.1-2019, Normative Appendix A for both heated slab floors and unheated slab floors. For all methods, inputs shall be consistent with the construction documents. For alterations the same requirements apply.

Baseline Building

Slab loss shall be modeled in the same manner in the baseline building as in the proposed design.

Slab loss can be modeled with the simple method (F-factor) for unheated slabs. A layer-by-layer input can also be used. The base assembly is a slab floor of 6-inch concrete poured directly onto the earth (Concrete 140lb/ft³ – 6 in.), the bottom of the slab is at grade line and soil conductivity is 0.75 Btu/h-ft °F.

The configuration of insulation and the F-factors for the baseline building unheated slab floors are shown in Table A₆.3 in Normative Appendix A. The F-factors for the baseline building have been listed in the table below.