Your choices:
1 Comfortable indoor climate; 2 Biomass (digestible sludge); 3 Local heating (ind. house)
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| 2 Biomass (digestible sludge) | District cooling | 1 Comfortable indoor climate |
| Biomass (fermentable sludge) | 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 | 3 Local heating (ind. house) |
For any building outside such areas where district heating and cooling systems are feasible, the only alternative will be to organise the climate control system locally.
Todays' air-conditioning units will provide air-borne heating as well as cooling in one single unit and often such units will be found in the individual rooms in single-family houses. For cooling purposes in single-family houses and also in larger building there is no realistic alternative to the use of electricity-demanding compressor cooling.
For the use of renewable energy in combination with AC-units there is then only one alternative, and that is to provide at least part of the electricity need for the house by local, individual, generation. Generally, this can be achieved by solar cells, by micro-hydropower installations or by small wind turbines.
For farms large enough to host and individual digester, there will be one more alternative, and that is to use the gas in an internal combustion engine – basically a modified car or ship engine – with a generator connected to it. The cooling water from the engine is used for heating, maybe with an extra temperature boost for cold winter days. Such an extra temperature boost can be achieved in an external combustion chamber again fired with the raw biogas and maybe with a pilot flame. A system like this will exhibit a limited flexibility with respect to the ratio between produced electricity and produced heat. Electricity production may amount to at the most 20-30% of the biogas input and down to 5-15% in small-scale applications and the total efficiency can be up to about 80%, less in small scale.
For individual house heating, the alternative when local biogas is at hand is to use the raw biogas in a gas-fired boiler for heat and tap-water production. It must then be remembered that for safety reasons, the biogas quality is variable, there will be a need for a pilot flame to ensure a stable ignition of the flame. Also the gas burner in the boiler will have to be replaced. With such a system solution, however, only heating and tap-water will be produced from biogas. If the first system solution is chosen, with the IC-engine, then also at least part of the comfort cooling is produced from biogas via electricity...