The calculation of heating energy demand in Eturnity begins with the resource consumption of the existing heating system, which is either entered by the user or imported from the Eturnity heating calculator. To determine the actual heating energy demand required for the building envelope, the energy content of the resource (e.g., 2000 liters of oil) is corrected by the corresponding efficiency factors of the existing heating technology.

This process yields the annual heating energy demand, which is also displayed in Heating Expert. The calculation ensures that hot water demand is correctly included in the overall calculation.

When the existing heating system configuration changes, the energy calculation automatically adjusts. For example, if an existing oil heating system uses an electric boiler for hot water production, and the new heat pump is designed to cover both heating and hot water generation, the necessary energy for hot water production is added to the heating energy demand.

The hot water energy calculation is based on the number of persons that you enter on the Building page in the Number of people field. This person count is also imported from the heating calculator data when a project is created via the heating calculator.

Eturnity AG uses the BIN methodology, also known as the frequency summation method, for calculating building heating power. This methodology is described in the standards DIN EN 15316-4-2 / ÖNORM EN 15316-4-2 / SIA 384/3.

The BIN method assumes a linear relationship between decreasing outdoor temperature and increasing heating power demand. The total heating energy demand is distributed across corresponding temperature BINs between the minimum and maximum temperatures prevailing at the specific location.

This distribution follows data from a TMY (Typical Meteorological Year) temperature profile for the corresponding location, with hourly temporal resolution. The result is a frequency summation structure that provides precise heating load distribution across different temperature ranges.

Within each BIN, conditions such as outdoor temperature, heating power, supply and return temperatures are assumed to be constant, enabling precise performance calculations for each temperature range.

In Switzerland, both the heating calculator and Heating Expert offer the option to calculate the heating power with the heat pump system module; this method takes SIA stations into account. In Heating Expert, this add-on option must be enabled for your company; ask our customer support about it (support@eturnity.com or via chat). Once it is enabled, the Building page shows the Heat pump system module calculation next to the Standard calculation under Existing heating system. You choose which of the two applies on the Heating system page in the Base data for heater dimensioning table, in the Preferred calculation row: Standard calculation or WPSM Calculation.

The heat pump performance calculation leverages the BIN methodology's constant conditions assumption. For each temperature class (BIN), the system determines the operating point and calculates:

The calculations use data points from the EN 14511 standard, which are extrapolated to the corresponding operating point. The annual energy demand and Seasonal Performance Factor (SPF) are determined by summing across all BINs.

Air-to-water heat pumps: Use the outdoor temperature of the corresponding BIN as the source temperature.

Ground source heat pumps: Use source temperature calculated according to the ground probe calculation methodology.

Eturnity Heating Expert supports automatic calculation for probe length and arrangement, while allowing manual override at any time. The calculation follows the simplified calculation method of standard SIA 384/6. The ground probe appears on the Heating system page as soon as you select a ground source heat pump as the Heating technology. With Define the ground probe manually, you specify the Arrangement and Length yourself.

The calculated ground probe length directly influences the source temperature calculation for ground source heat pump simulation. This integration ensures that:

For each heating system (existing reference system and new heating system), Eturnity calculates three cost components:

In the offer, the three components appear on the “05 Heating system: overview” page in the legend of the cost chart, as Payback costs (the amortization costs), Energy costs and Operation & Maintenance (the maintenance costs). If a leasing model is active, the page shows Basic costs (the leasing rate) and Energy costs instead.

Amortization costs represent the costs allocated for heating system amortization: Eturnity spreads the investment evenly over the years of amortization and calculates without interest (0%), i.e. without equity capital costs. You cannot set an interest rate for this in Eturnity Expert; the Opportunity costs field in the PV System tab does not change this either. This differs from investment costs, which represent the initial investment amount.

Annual amortization costs are calculated using the annuity formula, providing a standardized approach to comparing different heating technologies over their operational lifetime.

Energy costs are calculated by applying the defined inflation rate over the entire heating system lifetime to the first-year energy costs (set under Financials › Profitability in the Heating system tab). The total energy costs over the lifetime are divided by the lifetime to provide an expected average value.

You enter the maintenance costs in Heating Expert under Financials › Profitability in the Heating system tab, Heating technology settings table, Maintenance row (excluding VAT). In the heating calculator, percentage definition based on investment sum is possible.

Recurring costs of the heating technology (Recurring costs page or bill of materials) count for the new heating system if Add new heat generator is switched on and they are recorded as Normal (in feasibility).

You enter the investment costs of the existing heating system per kW: under Financials › Profitability in the Heating system tab, Heating technology settings table, Investment costs of existing / reference heating system row. Eturnity multiplies them by the calculated heating power or, if you have entered it, by the Currently installed heating power.

The basis for the new heating system is the price of the heating in the bill of materials after discount. The offer shows it including VAT as Investment; if there are subsidies or Extended economic calculation is switched on, it shows Total costs instead, minus subsidies and tax savings. If a leasing model is active, neither line appears; instead there is a line with the costs under the leasing model (leasing rate and energy costs combined).

For each energy resource, you can set CO2 emissions per resource unit (e.g., 2.650 kgCO2eq/litre oil): under Financials › Profitability in the Heating system tab, Resource settings table, CO2 emissions row. The entered or simulated resource consumption of existing and new heating systems is multiplied by emission factors and prepared in a customer-friendly format.

On the “05 Heating system: overview” page, the CO2 emissions of each system appear as a percentage per person, not in kg; they are based on the Number of people on the Building page. In Switzerland, it is the share of a person's average CO2 emissions for heating; in other countries, it is not a comparison with the average for your country. The value cannot be compared with the “08 System: CO2 reduction” page.

The CO2 calculation methodology enables:

This provides clear environmental justification for heating system upgrades while supporting sustainability goals.

Number of people: Flows into hot water demand calculation, which influences heating energy demand and can affect heating power requirements when the existing or new heating system is responsible for hot water preparation.

Building Type: Different building types have different typical hot water consumption patterns stored in the system. These are multiplied by the number of persons to determine hot water energy demand. Together with the Heated area, the building type also flows into the calculated heating power.

Construction Year and Heated Area: In the heating calculator, these parameters generate appropriate estimated total energy consumption values for end customers. In Heating Expert, the year of construction is purely informational. The heated area, by contrast, feeds into the calculated heating power together with the building type and, with the Heat pump system module calculation, into the additional heating power for hot water.

This information is on the Building page in the Existing heating system section.

Heating (type of existing heating): Determines the heating type for the existing system to be compared with the new system.

Hot Water Generation: Determines whether energy required for domestic hot water is generated by the main heating system and must be included in heating load calculation based on annual consumption data, or handled separately.

Flow temperature and Return flow temperature: the temperatures of the existing heating system. For the Seasonal Performance Factor (SPF) of the new heat pump, what counts are the temperatures that you enter on the Heating system page under New heating system for Heat distribution system; they significantly influence the SPF.

Heat Distribution: Defines heat distribution from the boiler/heat pump to living spaces. The choice of heat distribution influences supply and return temperatures.

Hot water storage: Influences energy demand and heating power calculation for existing system hot water. Larger storage systems create higher storage losses, leading to increased energy consumption.

Resource usage of heating (Usage field; if the heat pump system module calculation is enabled, a table with the columns Year and Consumption appears there instead): Serves as the primary basis for heating load calculation required for the new heating system and has the greatest influence on calculations.

Currently Installed Heating Power: Does not change the simulation. If you switch on the Define currently installed heating power manually toggle on the Building page under Additional information and enter the value, the offer calculates the investment costs of the existing heating system with this value instead of the calculated heating power. For projects from the heating calculator, Eturnity enters the heating power calculated there in this field.

On the Heating system page under New heating system:

For technical support, parameter customization, or questions about these calculation methods, please contact:

Eturnity Customer Support:support@eturnity.com

You can also reach us via chat.