ALF help

Design help

On the Design pages you enter information about the particular house design and location to perform an ALF analysis on it.

Insulation & Thermal Mass

Insulation

The entering of all insulation R-values on one dedicated page is a significant change from the previous software version of ALF 3. Using this page, it is now possible to increase insulation levels in the whole house from one simple interface. It is hoped this method will allow for a quick and easy investigation into the buildings insulation levels relationship to the overall heating energy requirement.

The R-value of the insulation material of the different building elements are entered on this page. The R-value of the construction (i.e. the selected construction with the specified insulation material and R-value) is calculated automatically by the program when the insulation value is selected.

If the INSULATION R-value that you have chosen significantly exceeds the highest tabled value for this type of construction then the resultant CONSTRUCTION R-value can only be estimated and is therefore unreliable.

In this case you may first check that it is physically possible to install the selected/proposed insulation into the construction type being considered.

If this is the case then the actual CONSTRUCTION R-value should be calculated using recognised methods/first principles i.e. NZS 4214:2006 or it should be based on values derived directly from thermal resistance test data that may be available from manufacturers on a specific system.

Where such a value is to be used it can be entered directly by selecting the construction type 'Custom' (the first construction type in the list).

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Thermal Mass

Thermal mass describes the ability of materials to store heat. Estimating the amount of thermal mass involved in the heat flow process requires some judgement because thermal mass is most effective when it is exposed to the indoor climate and particularly the solar radiation. 'Thermal floor area' is floor area which is not carpeted and which is exposed to the inside. In the cells on this page you can enter the areas of the components, which contribute to the thermal mass. Thermal floor is floor, which is not covered by any insulation. Carpet and underlay have to be treated as insulation. Their R-value is approximately 0.4 m2 °C/W. Therefore you must not include any floor area, which is carpeted. Most other floor coverings, such as tiles and vinyl have rather small R-values and can therefore be included in the floor area.

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Ground Floor Insulation

Enter the insulation R-values for the floor type and insulation strategy previously specified in the 'Floors' page.

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Slab Insulation

For a fully insulated slab floor; enter the insulation R-value.

For an edge insulated floor enter the insulation depth and thickness and half the width of the slab floor.

Slab & Ground R-value

This cell shows you the R-value of the slab and the soil underneath taking account of the ratio of Slab Floor Area and Perimeter Length, the External Wall Thickness and the Soil Conductivity. It also includes the insulation contribution of any full or edge insulation underneath the slab and the floor covering.

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Timber Floor Insulation

In this cell the R-value of any bulk insulants to be placed in the timber floor are entered.

Total Suspended Floor R-value

This cell shows the total R-value of the suspended floor. It includes the Subfloor R-value, the Floor Insulation R-value and the Floor Covering R-value.

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Wall Insulation

Enter the R-value of the insulation to be used in the walls. ALF automatically returns the construction R-value for the wall and insulation.

Wall Construction R-value ('Constr. R')

This is the R-value of the construction material including the insulation. The framing material has generally lower R-values than the insulation material. Therefore more heat escapes through the framing parts of the walls than through the insulation parts. This effect is called 'thermal bridging'. The construction R-value is generally lower than the R-value of the insulation material, because of the wall framing.

Hint:
If you want to include some corrections for the construction type and the corrections can not be entered through the available framing options and insulation R-values you can use the 'Custom' wall construction type and enter the construction R-value directly in the Insulation Material Cell on the 'Construction' page. For the 'Custom' construction type the program does not correct for the influence of the building structure but instead takes the entered insulation material R-value as the construction R-value.

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Roof Insulation

Enter the R-value of the insulation to be used in the roof. ALF automatically returns the construction R-value for the roof and insulation.

Roof Construction R-value ('Constr. R')

This is the R-value of the construction material including the insulation. The framing material has generally lower R-values than the insulation material. Therefore more heat escapes through the framing parts of the walls than through the insulation parts. This effect is called 'thermal bridging'. The construction R-value is generally lower than the R-value of the insulation material, because of the roof framing.

Hint:
If you want to include some corrections for the construction type and the corrections can not be entered through the available construction detail options and insulation R-values you can use the 'Custom' roof construction type and enter the construction R-value directly in the Insulation Material R-value on the 'Construction' page. For the 'Custom' construction type the program does not correct for the influence of the building structure but instead takes the entered insulation material R-value as the construction R-value.

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Thermal Concrete Floor

Uncarpeted concrete floor contributes a large amount of thermal mass to the building. If the slab is laid on top of the ground, the ground underneath also contributes to the thermal mass. If the concrete floor is suspended or the full area under the slab is insulated the thermal mass depends on the thickness of the concrete slab.

Slab-on-ground floors have a thermal mass of 300 Wh/m2°C.

Suspended concrete floors and fully insulated floors have the following thermal mass: 50 mm slabs have 28 Wh/m2°C, 100 mm slabs 56 Wh/m2°C and 150 mm slabs 83 Wh/m2°C. Intermediate thicknesses can be interpolated.

If only the edge of the slab is insulated the uninsulated slab on ground option can be selected.

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Thermal Timber Floor

The area of the timber floor, which is uncovered by carpet contributes to the thermal mass in the building. The type of floor covering determines the amount of thermal mass per m2.

Exposed and vinyl covered timber floor has a specific thermal mass of 10 Wh/m2°C.

Carpeted floor has no accessible thermal mass.

A tiled timber floor has 20 Wh/m2°C.

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Exterior Walls

The thermal mass of exterior walls depends on their construction. The following thermal mass values are used for the available constructions:

Construction

Thermal Mass[Wh/m2°C]

Any internally lined construction

9

Solid timber wall (44 mm)

7

Solid timber wall (62 mm)

10

Concrete blocks (inside exposed)

42

Brick (inside exposed)

38

The area of external walls is counted only once, i.e. do not count the internal side of the walls again.

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Interior Walls

The thermal mass of internal wall construction types is the same as listed in the table for exterior walls.

Also in this case only one side of each wall is to be counted.

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Total Thermal Mass

The Total Thermal Mass is the sum of the four individual thermal mass components plus a contribution for furniture and ceiling. The program automatically assumes that ceiling and furniture contribute 4.5 Wh/m2°C and 2.5 Wh/m2°C respectively. This value is multiplied with the total floor area as an approximation of ceiling area and furniture density.

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Effective Thermal Mass

Not all the thermal mass actually takes part in the daily heat flows. The effective thermal mass shows the mass, which actually contributes to heat flows. Once the Total Thermal Mass reaches a certain threshold the Effective Thermal Mass stays almost constant. The estimation of thermal mass in the building is therefore particularly important for low thermal mass houses because in those cases small changes in the Total Thermal Mass can lead to significant changes in the Effective Thermal Mass.

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Thermal Mass Background

One of the significant extensions of this ALF procedure is the modified treatment of thermal mass. The method is a refinement of the previous method, which was based on other overseas results generally concerned with a fixed 24-hour heating schedule. This means that only the benefits of thermal mass as a heat sink, which supplies free heat in the early evening hours, were considered. The introduction of intermittent heating schedules necessitated taking account of the disadvantages of high thermal mass. In the case of insufficient free heat (small windows, unsuitable climate, etc) the thermal mass absorbs heat, which is supplied through purchased heating and thus increases the amount of required heating.

The consideration of both aspects of mass in the calculations, the 'mass warm up' energy as well as the thermal storage of free heat, allows a specific evaluation of the disadvantages and benefits of thermal mass as a function of building design and heating habits. The method allows a decision as to the appropriate amount of mass.

Particularly in cases of high thermal mass only a fraction of the total thermal mass actually takes part in daily energy flows. This thermal mass is called the Effective Thermal Mass.

The data necessary to calculate the thermal mass level of the house is the area, construction type and finish of the floors and walls. The effective thermal mass is calculated by adding all the significant contributors of thermal mass together (i.e. floors, external and internal walls, ceilings and furniture). The thermal mass of each of the contributors is calculated by multiplying its area with its specific thermal mass. Note that the area used to calculate the thermal mass of a component is always only the surface area of the material exposed to indoor air (wall, ceiling, and floor areas). The total thermal mass is then divided by the total floor area. The resulting thermal mass density provides an indication of the accessibility and effectiveness of thermal mass in the building.

This approach does not explicitly account for orientation or placement of the thermal mass. More research is currently under way to shed light on the effects that different components of the thermal mass have on the thermal performance of the building. The thermal mass calculation method in later ALF versions may be modified according to these findings.

Effective thermal storage is that exposed to the inside of the building. Some judgement is required to decide whether particular floor and wall areas of the building should be included in the thermal mass. This is more critical for low mass building designs (suspended timber floors, timber framed constructions) since small variations in available thermal mass have a larger impact on the useability of gains. In heavy mass houses the decision is less critical as there is usually a large surplus of thermal mass available which is not utilised for thermal storage. In particular exposed slab-on-ground floors have such high thermal mass that the effects of walls and furniture may become negligible.

The effective thermal mass density depends on the applied heating schedule. The units of the effective thermal mass density are chosen to be compatible with the Specific Heat Losses (W/°C). Multiplying the value of the total floor area and the ALF-value gives the energy needed to warm up the effective thermal mass from ambient temperature to the temperature defined in the heating level.

Please note that houses with a larger thermal mass generally have more uniform temperatures, and are thus less likely to have condensation problems. However, for houses with low solar gains, thermal mass can be a liability.

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 Create an ALF account

Register now to create your free ALF account.

Every user needs to create an ALF account. Creating an ALF account will ensure:

  • Confidentiality for your project.
  • Allow BRANZ to record usage of the ALF tool – BRANZ cannot access any individual projects. Your privacy is assured.

 Contact and Feedback

Contact us at Branz for further information about the ALF 3.2: Annual Loss Factor.