Internal Conditions

Indoor Climate Method

Within Indoor Climate Method, Controlled Values, ASHRAE 160 / DA07, EN ISO 13788, EN 15026 and Sine Curves can all be adopted to derive indoor temperature and humidity. Once adopted, the form updates to enable specific configuration for each Indoor Climate Method.

Internal relative humidity levels can affect the moisture transfer within building components. High internal relative humidity can lead to condensation within walls or roofs if these surfaces reach the dew point temperature. This can potentially lead to issues like mould growth and structural damage.

The relative humidity is typically uncontrolled in most buildings and is a function of external and internal conditions.

ASHRAE 160 / DA07

Indoor Temperature Method

The indoor temperature of a space impacts the heat flow through building components. High internal temperatures can increase the rate of heat transfer from inside to outside in colder weather and vice versa in warmer weather. This has a corresponding impact on moisture transfer.

Better Building defaults to the Intermediate method, where the indoor design humidity is ascertained from hourly weather data and the specific type of HVAC equipment used. Only the Intermediate method is suitable for building code compliance.

Auto

Select to auto derive the indoor temperature from the outdoor climate (DA07 Table 4.2).

Fixed Value

Select to set a fixed constant value.

HVAC System

Heating only

Select if a heating only space

Heating and cooling

Select if heating and cooling are present. Adopts cooling setpoint, as per DA07 Table 4.2

Heating, cooling and humidistat

Select if heating and cooling and humidistat are present. The humidistat holds the indoor RH at or below a maximum %.

Dehumidification

Select if dehumidification is present. The dehumidifier holds the indoor RH at or below a maximum %.

Ventilation

Air exchange, also known as air change or ventilation rate, plays a crucial role in hygrothermal simulations. It represents the amount of air that is added to (infiltration) or removed from (exfiltration) a building or a specific room within a given period.

Air exchange rates can vary significantly depending on the type of building, its construction, the effectiveness of its ventilation system, and how airtight the building is. These factors should be considered when defining the air exchange rate for hygrothermal modelling purposes.

Other standards, such as ASHRAE 62.1 for commercial and institutional buildings or ASHRAE 62.2 for residential buildings, would typically be referenced for specific air exchange rates.

Non-design - standard (0.2 ACH)

Nominate a standard non-designed air exchange rate of 0.2 ach, as per Q = 5.6 · 10-5 V m3/s (DA07 Equation 4-2).

Non-design - ait tight (0.1 ACH)

Nominate a standard non-designed air exchange rate of 0.1 ach, as per Q = 2.8 · 10-5 V m3/s (DA07 Equation 4-3).

Custom

Nominate a design mechanical ventilation systems used for the calculation of design indoor vapour pressure (DA07 Equation 4-1).

Moisture Generation Mode

Moisture generation mode refers to the methods or conditions through which moisture is produced or introduced into the indoor environment of a building. It's an essential aspect of simulations because moisture production can significantly affect indoor humidity levels and hence the hygrothermal performance of the building.

Three moisture generation modes are available, number of people, number of bedrooms, and custom.

Number of People

For design purposes, there will be a minimum of two occupants in a space, with an additional person for every bedroom beyond the master bedroom. The specific rates for design moisture generation can be found in ASHRAE 160/DA07.

Number of Bedrooms

For design purposes, the number of bedrooms can also determine moisture generation rates. The following specific rates for design moisture generation can be found in ASHRAE 160/DA07.

• For a 1-bedroom home with two occupants, the moisture generation rate is 7 litres/day or 0.8 x 10-4 kg/s.

• For a 2-bedroom home with three occupants, the rate is 9 litres/day or 1.0 x 10-4 kg/s.

• For a 3-bedroom home with four occupants, the rate is 10 litres/day or 1.2 x 10-4 kg/s.

• For a 4-bedroom home with five occupants, the rate is 11 litres/day or 1.3 x 10-4 kg/s.

• Add one occupant for each additional bedroom beyond four and increase the moisture generation rate by 1 litre/day or 0.1 x 10-4 kg/s.

Custom

For buildings with different occupancy types, the design values for moisture generation should be specified in kilograms per second (kg/s) and obtained from a mechanical services engineer.

Jetted Tub (no auto exhaust)

Specify to add the DA07 4.3.2.1.1 jetted-tub moisture allowance.

Indoor Relative Humidity Method

Auto

Select to auto derive the indoor RH from the DA07 4.3.2 moisture mass balance.

Fixed

Fixed overrides it with a constant value (capped at 70%).

Humidistat Maximum

The humidistat / dehumidifier holds the indoor RH at or below this value — a ceiling on the calculated RH, not a fixed override (that is the Specify option above).