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1 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 | 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 | Local heating (ind. house) |
Houses may either be part of a municipality or they may be isolated, single houses. Nevertheless, those living in the house will want to have a comfortable indoor climate.
A comfortable indoor climate – looking now only at the thermal aspects of climate control – consists of heating during cold days, cooling during hot days and access to hot tap water all days. Though not part of the indoor climate electricity must also be supplied for the use of household electronics.
For buildings in densely populated municipalities, heating and cooling are, or should be, supplied by district heating and cooling systems. With modern insulation materials district heating systems may become economical once the annual heat load in a geographical area exceeds approximately 10 kWh/m2 and year. For any building outside such areas, 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, in apartments in apartment houses and again in single rooms in hotels. In office buildings will the ventilation system often be equipped with a central AC-unit.
For the use of renewable energy in combination with AC-units there is mainly one alternative and that is to provide at least part of the electricity need for the house by local, individual, generation. This can be achieved by solar cells, by a micro-hydropower installation or by a small wind turbine. Electricity from renewable sources can also be contracted for delivery via the grid. However and generally speaking electricity should not be used as the primary energy carrier for indoor climate control.
A comfortable indoor climate is maybe the most common energy service and is one of the most important ones.
Since the indoor climate is a low-temperature service, temperatures ranging from room temperature up to 50-70 oC in tap water and at the most 80 oC in radiator water, the demands on the energy carrier are low and low-exergy carriers such as district heating can be used. There is one exception to this, and this is the energy supplied for illumination which is best supplied as high-exergy, i.e. electricity. Typically, this results in a demand for energy where low-exergy sources are dominant.
With low-energy houses or passive houses, the demand becomes different since the "low-energy" definition is interpreted so that the low demand shall be for low-exergy energy carriers, i.e. for heating. Passive houses or low-energy houses will instead demand an increased supply of electricity for their heat-recovery and control systems. In case a large fraction of houses in an area or a municipality are low-energy and if the district heating system is supplied by a CHP-plant, this may upset the situation so that the demand for electricity increases while the possibilities for electricity production decreases.
Theoretically, there are a large number of possible ways to reduce the energy use in buildings but in reality there are a number of limitations connected to the indoor climate. One important aspect is, just as an example, the actual architecture that may well limit the use of solar irradiation (i.e. daylight) for illumination.
"Indoor climate" is in itself a complex phenomenon composed of light, temperature, air quality, noise and draught. The picture is further complicated by the interaction of the "real" (quantifiable) climate parameters and the climate as experienced by the occupants, be they tenants, customers or workers. Social factors – private as well as work related – are sometimes reflected in questionnaires aimed to investigate the quality of indoor climate. Hence, though several parameters such as temperature, relative humidity, sound level, air velocity and illumination may be measured and quantified and may well be within the set limits, it is not sure that the occupants appreciate the indoor climate when interviewed.
The building energy system cannot be blamed for social problems but can only be well aimed for the technical supply and to keep the quantifiable parameters temperature, relative humidity, CO2-content, particle concentration, smell, noise, illumination and air velocities within the set limits. There is also a sanitary aspect so that, especially in the case of forced ventilation systems mould or other allergenic or hazardous organisms may not establish in the system. Hence, the building climate system does not only require energy input for heating, cooling, ventilation and illumination but also annual maintenance.
At northern latitudes the outdoor air during winter is very dry and the ventilation system will have to provide a moisture addition for comfort, during summer the situation is the opposite and excess moisture must be removed from the outdoor air before it enters the building.