Your choices:
1 Biomass (solid); 2 Local heating (ind. house); 3 Comfortable indoor climate
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | 3 Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| 1 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 | 2 Local heating (ind. house) |
The characteristic for single family houses is that the variations in energy need may be very different from hour to hour. For example will the fact that one person in the household takes a shower suddenly demand a rise in heat supply to the hot water system and if windows are opened for intensive ventilation the demand for heating suddenly increases radically. Also the opposite is true: A party with 20 participants will suddenly increase the heat supply to the house with about 2-3 kW (one person releases approximately 100 W only in the form of body heat and if they are dancing the heat release increases) and there might suddenly be a demand for cooling!
In case cooling is needed in a single-family house, this is usually arranged by installing separate AC-units in the rooms where the need is most pronounced, or to have a mobile AC-unit that is moved to the room where it is needed. For single houses only compressor cooling machines are applicable.
Hence, the stationary energy system in single houses can have only two roles, namely to provide heat and to provide tap water. Houses without central heating systems are not considered in this material.
Central heating in single-family houses can be water-borne – which is preferred in case of biofuel – or it may be air-borne. In case of water-borne heating, the production of tap water is normally integrated in the same boiler but – of course – with a separate heat exchanger coil. In case of air-borne heating, the production of tap water becomes a completely separate system.
With water-borne systems, the boiler may be complemented with an accumulator tank to even out thermal load. The accumulator tank shall be large enough to cover the average heat demand of the house, tap water and heat combined, during 24 hours with a temperature drop of about 20 °C. With an accumulator tank integrated in the system it is simple to integrate solar heating with the system by a separate heat exchanger coil in the accumulator. There are also some domestic boilers that have extra-large water volumes – though not as large as can be obtained by a separate accumulator – and also comprising solar heating connections. The energy system in single-family houses cannot take very high investments and is thus controlled using a simple on-off system. With water-borne systems the control parameter is normally the water temperature in the boiler or the accumulator while air-borne systems, especially if the system is distributed with several stoves and heat sources, may have thermostats in several rooms. With water-borne systems the temperatures in individual rooms are set by aid of radiator thermostats.
Like single-family houses will larger buildings – be they apartment houses, office buildings or commercial like shopping centres – exhibit a pronounced daily variation in the energy need.
Office buildings will quite frequently have a pronounced need for cooling during office hours because of the excess heat delivered by office electronics and by the fact that the number of persons per m2 in an office building is usually more than the number of people per m2 in homes. The indoor climate in an office building should be adapted to the fact that most people in the building will be sitting most of the day.
Shopping centres, sports centres, schools, hospitals, official buildings and such, aimed to host a large number of people of varying ages and constitutions and not primarily a cadre of sitting middle-aged people, will again pose new demands on the indoor climate control.
The energy system in larger buildings may sometimes be able to take rather high investment costs. This depends of course on the type of building and the tenants. Opposed to the case in single-family houses, the boiler will typically operate using modulating control.
As with any type of heating system; the larger the total heat production becomes, the more dominant becomes the operational (variable) cost. In energy consuming applications – such as greenhouses – will this put a demand on the system to be based on the cheapest (i.e. the most raw) fuel while, in less energy consuming applications like for example a smaller school, a more upgraded fuel such as briquettes or pellets may prove the most economical in the long run.