Your choices so far:
1 Comfortable indoor climate; 2 District heating
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | 1 Comfortable indoor climate |
| Biomass (fermentable sludge) | 2 District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | ocal heating (ind. house) |
When it comes to space heating, district heating is always the preferred choice in case the buildings are situated in a sufficiently densely populated area. In case the total load in the district heating network is large enough – and the central production unit is fuel fired – also district cooling may be available and then the system solution as a whole becomes even better.
Except from the fuel-firing cases (biogas firing and solid fuel firing) may district heating be produced from geothermal energy and from solar energy. However, solar energy will always only serve as a complement in systems where the main source is something different.
District heating is distributed by the aid of hot (>100 °C) or warm (<100 °C) water.
The internal distribution of heat in a building with a central heating system is often done so that warm water is produced in a local boiler and the warm water is distributed to the individual rooms and given the chance to heat up the room through radiators, floor heating or other systems.
In buildings without central heating systems the heat is instead distributed using warm air as the distribution medium. However, there will still be a need for hot-water production for tap-water and for hygiene.
The practical difference when the central AC-unit in – for example – a school or an office building is replaced by district heating is that heating function in the main, central, air-conditioning unit is replaced by a heat exchanger. The heat exchanger will need two separate circuits: one for heating of the ventilation air or for the radiator water and one for the production of tap water.
In case the district heating plant is not big enough for tri-generation, so that cooling must be produced locally using air-conditioning unit, but the district heating plant is big enough for CHP-production, then the electricity delivery should be contracted so that also the electricity used for the AC-unit is provided from the biogas-fired CHP-plant.