Property Information Page
Use this as a guide to entering data on the Property Information page.
The first step in creating a property is supplying basic building information and defining all ventilation zones and heated rooms that exist within the dwelling.
Location Data
Country
The country will be predetermined based on the postcode entered. The country is used to determine the correct Standard Assessment Procedure (SAP) region for retrieving reference data.
Altitude
The altitude will also be predetermined based on the postcode entered and effects the level of infiltration in high and exposed buildings. The altitude of the building at ground level should be entered, however, it will only make a difference to the heat loss if the height is over 100m above sea level.
Design Conditions
Design conditions are the parameters under which the heat load will be calculated.
Design external air temperature
This is the temperature of the outside air under design conditions, sometimes called Design Outdoor Temperature (DOT).
It is used to determine the temperature difference between the room and the external air when calculating the peak heat load of exterior walls, roof, windows and doors as well as exposed floors.
By default, the temperature is obtained from the closest reference weather station to the property (based on straight line distance).
NOTE
For default values for external design temperatures, see Design Conditions.
Mean annual external air temperature
This is the mean external air temperature over an entire year. It is used as the assumed ground temperature when calculating the heat loss of solid ground floors and basement walls.
By default, the temperature is obtained from the closest reference weather station to the property (based on straight line distance).
NOTE
For default values for mean air temperatures, see Design Conditions.
Heating degree days
The number of heating degree days is a value that quantifies the amount of energy that is required to heat a building over an entire year. This figure is used to estimate the annual heating energy (in kWh) based on the peak space heating load.
By default, each postcode area is assigned a heating degree days figure using a base temperature of 15.5°C.
NOTE
For default values for heating degree days, see Design Conditions.
Property Details
Dwelling type and attachment
The dwelling type and attachment are used to determine the number of heat loss surfaces and exposed facades for the property.
Age band
The age band helps determine the most accurate U-value to apply to external walls, floors and roofs. Where a property has been extended or had major renovation works, the age band to select should be that of the original house.
Number of occupants
Entering the number of occupants, including all adults and children that live at the property, helps determine if any additional ventilation rate is required for high occupancy.
Dimension Specification
The dimension specification can be selected that will be used for all walls, floors and ceilings. It is important to select the correct option based on the dimensions that you will be entering to produce an accurate heat loss calculation.
NOTE
For more information on dimension specification, see Core Concepts.
Building Airtightness
When calculating the ventilation heat loss of individual rooms, the calculator will determine the highest heat loss figure from either: the design air change rate of the room itself; the intentional ventilation provided by mechanical systems; or the building infiltration rate proportioned volumetrically by the room size. The choice of airtightness method will determine this last factor.
Standard method
The system will assume an infiltration rate of the building based on the number of bedrooms. An additional infiltration allowance will be added for properties with a large floor area or high occupancy level.
NOTE
For more information on how the infiltration rate is assumed, see Ventilation Rates.
Measured air permeability
Allows you to enter a measured air permeability from an airtightness test performed on the property. When using this option, the building envelope area and volume that were recorded during the airtightness test also need to be entered.
NOTE
The building envelope area should be measured as per CIBSE TM23 (Testing buildings for air leakage) and is expected to include any party walls. Refer to CIBSE TM23 Section 2.2 for more information.
Design air change rate
If you have a whole-house air change rate that you are designing to, you can enter this value instead.
Room Air Change Rates
Separately to defining the airtightness level of the entire building, you can also enter design air change rates for each room.
Thermal Performance
Heat Transfer Coefficient
A Heat Transfer Coefficient (HTC) is a key metric of whole-house heat loss that encompasses all of the heat lost from a dwelling through the walls, roof, floor and windows, and by air movement from outside to inside the home. A HTC, measured in W/K, is obtained from a thermal performance test carried out on the property.
When used, the total heat loss and all room heat losses will be calibrated against the measured HTC to produce an accurate heat load calculation.
MIS 3005-D Compliance
Please be aware that using a measured HTC may require justification if the heat load calculation is to be used for MCS compliance purposes.
NOTE
For more information about measuring heat transfer coefficient, please visit Thermal Performance Measurement of Buildings.