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"Saving energy" in the sense of sufficiency

As stated in Energy sufficiency – an introduction. Concept paper for eceee (2018), “Energy sufficiency is a state in which people's basic needs for energy services are met equitably, and ecological limits are respected.”

It goes beyond energy efficiency: having enough but not using too much. In the past, some of these measures were enforced by law. However, this did not always contribute to acceptance among the public. Higher levels of public participation can be achieved by implementing energy efficiency measures, which require more minor behavioural change and compromise. Ideally, these measures will be executed when a building component already requires replacement at the right time in the part's lifecycle. If such improvements are undertaken systematically throughout the components' lifecycles, then the building's overall energy efficiency will be significantly enhanced9). Thus, legally enforced restrictions to implement energy sufficiency, often extremely unpopular, can be avoided.

However, sometimes sufficiency is necessary, especially when energy savings are needed rapidly. In this case, it would then be sensible to undertake such measures so that neither injury to health nor material damage to the structure arises - with these pages; we want to help provide the know-how for this.

Room temperature reduction

This measure is easy to achieve: heating less and lowering temperatures during winter always saves energy (and thus costs and emissions). This can include:

  • setting the average heating temperature to a lower level
  • temporarily decreasing the heating temperature and frequency
  • applying partial heating (not heating some rooms or heating less).

All three changes to our behaviour can be adopted in almost any building, whereby lowering the average temperature to heat can almost always be applied. However, when temporarily decreasing the heating temperature or frequency or using partial heating, increased humidity levels may occur in unheated rooms. This can lead to mould growth and ensuing structural damage or health concerns. However, this situation can be avoided by using additional ventilation in winter when air humidity levels are too high (relative humidity > 55%).

Thermal comfort in the room

Did you know that the internal temperature considered comfortable or “bearable” depends significantly on the clothing occupants are wearing? A sweater acts as an extra layer of thermal insulation for the body. The temperature required for optimal thermal comfort when wearing a sweater is approximately 3 degrees Celcius (5.4 Fahrenheit) lower than that with just a long-sleeved shirt. Lowering the average heating temperature by this can save 18 to 30 % heating energy. The percentage of energy saved by decreasing the thermostat is even higher in better-insulated buildings; however, in the case of the latter, the absolute values are so small that the difference plays a subordinate role.

Temporary reduction

If the set temperature is reduced only temporarily, e.g. when leaving the building or at night, then the internal temperature, especially of the building components and furnishings, only decreases gradually from time of reduction onwards. This reduces unnecessary energy use when the building is unoccupied, or the occupants are unlikely to notice the internal temperature change (e.g. are asleep). However, the heat output is initially much higher when switching on the heating after the setback because the building components must first be heated up again. Nevertheless, an energy-saving remains, but this is smaller than is often assumed. Even in already well-insulated buildings, this kind of “night setback” still saves energy, even if it's less than in uninsulated buildings, simply because the temperatures drop less due to lower heat losses through the building envelope. Compared to continuous heating, the savings from consistent night setbacks can amount to around 5% (in a Passive House building) and up to 20% (in an uninsulated existing building); on average, this would be an almost 8% saving across the Central European building stock.

A note for those living in multi-family buildings: out of regard for neighbours, the room temperature should not be below 15°C in Germany. The indoor air humidity should also be regularly checked and, in case of uncertainty, measured10). If it is higher than 55%, the moisture should be reduced by employing ventilation.

Partial heating

The results are similar when executing only partial heating in selected rooms. However, the risk of moisture damage is more critical. If the cold room (e.g. through the open door) is only heated 'a little' (e.g.15°C), and people stay in the warm room, the internal air change exchanges the heat and moisture. This can cause the humidity to be too high in the unheated room, particularly critical in old buildings. If a building is well insulated, the temperatures won't differ between the room and building envelope. Partial heating can still work. However, it doesn't have a pronounced effect.

In the paper [Ahn 2015], the authors show that the achievable range of energy-saving using partial heating can range from 13% (Passive House with high occupancy) to 48% (old buildings with unevenly distributed occupants), the average is around 20%. Partial heating has the most significant saving potential among other sufficiency measures. If users pay attention to the humidity level (in cold rooms in winter, it shouldn't be more than 55%), this measure can be implemented effectively.

Partial heating is already implemented in many old buildings, willingly or unwillingly. In cases of fuel poverty, some rooms are heated insufficiently for cost reasons. Sometimes, the thermostatic valve isn't correctly opened and these rooms remain unintentionally unheated. Therefore, the additional savings might be lower than expected in such cases.

Heating with a fan heater

In a nutshell, under normal circumstances, this is never recommended for several reasons:

  • The fan heater is loud and bothersome.
  • The resistance wires are heated electrically and become very hot. The organic dust in the air can be carbonised (or burned) when coming into contact with the wire. This often causes a noticeable smell.
  • The electric power is converted 1:1 into heat with the direct electrical heating systems. Again, this causes a series of undesirable consequences:
  • Cost! The electricity prices for general household use nowadays are regularly much higher than the heat from commonly used heating systems: Even though oil and gas prices are high, the kilowatt-hour price from traditional heating is always lower than that of electricity. Households that regularly use fan heaters or other similar equipment will notice this in the electricity bill. Besides, the heating consumption in old buildings is much higher than average household electricity use. For this reason, as long as the traditional heating is working, we do not recommend using a fan heater.
  • Seriously fails the goal! If the goal is to 'save gas' or limit CO2 emissions, then the user in most countries with significant heating needs will achieve the opposite. Especially in winter, when everyone uses a heating system, the electricity demand is higher, so there is usually no surplus from renewable energy. With the current renewable-energy limitations, fossil-fuel-based power generation is needed during this period. In the best conditions, this can achieve maximum efficiency of 55%. Each modern furnace using gas requires less fuel. With the fan heater, thus we consume even more gas and produce more CO2 than conventional heating. This situation might change with renewable energy, especially wind energy, in the future, but this will still need many years to be achieved.

The emergency - when the heating system fails

A traditional fan heater can reach 2 kilowatts (maximum). In an old building, a (small) single room may be heated using such equipment (when the doors remain closed). This only works when all residents in that district don't have the same idea. Otherwise, the electricity consumption in these areas will increase severely. This is the situation we don't want. Having several fan heaters in use simultaneously in the same district will quickly reach the limit of the electricity network's limit (not to mention the family's financial limit). In a supply crisis (e.g. for oil or gas), municipalities and energy companies will inform constituents and customers when and where fan heaters may be used, as well as how and by whom. They'll employ limited periods for energy use in different buildings and districts to do this. If this already unpopular approach doesn't work, this could cause even more significant problems with the electricity network.

Thus, electric space heating should use a heat pump system, which only uses about one-third of the electricity to provide the same level of heat. This will also curb overall CO2 emissions. At least when the electricity isn't generated using coal.


[Ahn 2015] A study on the impact of different occupant behavior on heating demand; Passive House Institute, Darmstadt 2015

Most people are surprised that e.g. the space heating demand in Passive Houses is only about one tenth of the contemporary average
low-cost electronic hygrometers are readily available today.
efficiency_now/sufficiency.txt · Last modified: 2022/08/24 14:05 by wfeist