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 enhanced. 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.

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%).

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 lower than that with just a long-sleeved shirt. Lowering the average heating temperature by three degrees can save 18 to 30 % heating energy. The percentage of energy saved by decreasing the thermostat is even higher in better-insulated buildings; however, the absolute values are so small that the difference plays a less significant role.

If the setpoint temperature is reduced only termporarily, e.g. during absence or at night, then the temperatures especially of the building components and the furnishings decrease only gradually from the time of the setback onwards… the heat losses are reduced because the interior temperature always remains below the daytime setpoint. However, the setback value may not be achieved at all because the building capacity is not discharged to that extent. When switching on again after the setback the heat output is initially much higher because the building components are first heated up again; a saving remains nevertheless, but this is smaller than is often assumed when viewed naively. Even in excellently insulated buildings this kind of “night setback” still saves energy, even if less than in uninsulated buildings, simply because the temperatures drop barely noticeably due to the long time constants. The savings through consistent night setbacks compared to continuous heating can amount to between around 5% (in a Passive House building) and up to 20% (in an uninsulated existing building); on average this would be around 8 % in the Central European building stock. Legal note: out of regard for neighbours (if there are any), the room temperature may not be decreased to below 15°C in Germany. Attention should also be given to the reference regarding checking of the indoor air humidity (in case of uncertainty this should be measured and if it is higher than 55%, this should be reduced by means of ventilation¹⁾; low cost electronic thermohygrometers are easily available today).

The situation is similar to executing only partial heating in a selected room, and the 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, both the heat and moisture would transfer by the internal air change, and too high humidity could be caused in the unheated room. This is important for old buildings.

If a building is well insulated, the temperatures won't have a huge difference between the room and building envelope. The partial heating can still work, however it doesn’t have a prominent effect.

In the paper [Ahn 2015], it is shown that the achievable range of energy saving can be from 13% (Passive House with high occupancy) to 48% (old buildings with unevenly distributed occupants), the average is around 20%. In fact, partial heating has the greatest saving potential among other sufficiency measures. If users pay attention to the humidity level (in winter and in a cold room, it shouldn’t be more than 55%), this is definitely the measure that can be implemented successfully.

Considering the achievable expectation, it must be taken into account that the situation described here (few heated rooms) has already been partially „implemented“ in many old buildings, either willingly or unwillingly; often some rooms are heated insufficiently or for cost reasons the thermostatic valve isn’t opened in some rooms. Therefor, in such cases the additional savings might be lower than expected.

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

• The fan heater is loud and disturbing.

• The resistance wires are heated electrically and become very hot - with these wires passed by the room air; the organic dust in the air can be carbonised (or burned) by the wire. This often causes noticeable smell.

• With the direct electrical heating systems, the electric power is converted 1:1 into heat. Again this causes a series of undesirable consequences:

• Cost! Today the electricity prices for the general household use is regularly much higher than the heat from commonly used heating systems: Even though oil and gas prices are expensive, the kilowatt-hour price from traditional heating is always cheaper than that of electricity. The household which uses fan heaters regularly or other similar equipment will clearly notice this in the electricity bill. Besides, the heating consumption in old buildings is much higher than normal household electricity use. For this reason, as long as the traditional heating is working, we do not recomend the use of a fan heater. In contrast different claims are sometimes made in commercial advertisements.

• Seriously fails the goal! If the goal is to „save Gas“ or to restrain CO₂ emissions, then the user in most countries with significant heating will achieve the opposite²⁾. Especially in winter, when everyone uses a heating system, the electricity demand is higher, so there is usually no surplus from renewable energy³⁾. During this period (usually when the fan heater is working), conventional fossil power generation will be needed. In best conditions this can achieve a 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 compared with conventional heating. However, the situation might change by having renewable energy, especially wind energy in the future; but this will still need many years to be achieved.

The traditional fan heater can reach 2 kilowatts (maximum). In an old building, a (small) single room may remain to be heated with such an equipment (when the doors⁴⁾ remain closed). This will only work when all residents in that district don’t have the same electricity demand, otherwise the electricity consumption in these areas will increase severely. This is the situation that we all probably don’t want to experience. Having several fan heaters in the house at the same time will reach the limit of the electricity network (not to mention the cost). In the situation of a supply crisis (e.g. for oil or gas), municipalities and electricity suppliers will inform who, when, and how fan heaters may be used. (The supply will be limited in certain periods. If it doesn’t work this could cause even bigger problems with the electricity network.)

Thus, electric space heating normally should use a heat pump system, which only uses about one third of the electricity to provide the heat. This will also restrain the overall CO₂ emission. At least, if electricity isn't generated by coal.

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