Overview · Fundamentals · Documentation · Examples
Heat demand calculation
Heat demand is the basis of every design. EPOS-Plan determines it not as an annual figure but as a complete time series over 8,760 hours – only this resolution shows when which output is required and how generators and storage actually behave.
Modelling approach
A single building could be reproduced with a detailed dynamic model. For district heating areas with many buildings of differing construction, however, the necessary survey effort bears no sensible relation to the gain in accuracy – especially as user behaviour, that is room temperatures, setback times, heated floor shares and hot water demand, can only be captured statistically anyway. EPOS-Plan therefore uses a deliberately robust method: for each of the 365 days a daily heat load is balanced and then distributed to hourly values through a type-dependent daily distribution curve.
The daily balance includes solar gains through the window areas, separated by south, north and east/west and weighted with the window transmittance, transmission losses through external wall, windows, roof, ground floor and other components with their U-values, thermal bridge losses through the associated connection lengths, ventilation losses from air change rate and room volume, and internal gains. The thermal mass of the structure – classified as light, heavy or very heavy – damps the daily variation and ensures that setback phases do not translate immediately into heating output.
Use and boundary conditions
Besides building physics, use determines the result: set room temperature during the day, night setback, weekend setback, maximum room temperature and four freely definable holiday periods with their own setback temperature. Particularly in non-residential buildings – offices, schools, sports halls – this block decides the level and timing of the load peaks, for example when reheating after weekends and holidays.
For distributing the daily values over the hours, type-dependent curves are available: eight curves by season and weekday for residential buildings, five curves by season and cloudiness for non-residential buildings. The assignment is automatic through the building type and the day-type classification derived from the climate data. Own curves can be created in the catalogue and edited hour by hour.
Demand from consumption data
In existing buildings, measured consumption is often the most reliable information. Instead of the floor area you can therefore enter the annual consumption – heating oil in litres, natural gas in cubic metres or megawatt hours, fuel in general in megawatt hours. Together with the annual utilisation ratio of the old plant EPOS-Plan derives the useful heat and scales the building model to produce exactly this demand. The annual profile remains physically based while the annual total matches the bill.
Hot water, process heat and network losses
Hot water and process heat are kept separate, each with twelve monthly values and a weekly profile of 168 hourly values. This separation matters because hot water demand alone determines summer operation and is often more decisive for sizing heat pump and storage than the heating load; where a circulation line exists, its losses belong in the annual consumption. Process heat is recorded as a separate entry per temperature level or process, with the weekly profile representing shift operation. A measured heat load profile can be imported as an hourly series and is added directly. Network losses are entered as a percentage of total demand or as an absolute annual figure and distributed evenly over the year, raising the summer load in particular.
Results
From the sum of all components the annual profile of heat output, the maximum heat load, the monthly values and the ordered load duration curve are derived. The duration curve immediately shows which share of output is needed for how many hours – the classic argument for sizing the base-load generator small and the peak-load generator large.