This article is a chapter of the paper “Passive House - the next decade” by Wolfgang Feist. Click here to the beginning of the article on Passipedia.

A version of PHPP 8.2 was enhanced with algorithms using the application-based PER factors discussed above [PHPP]. The spreadsheet was used to conduct comparative parameter studies regarding the influences of structural and technical parameters; Figure 10 shows an overview of the findings. The chart depicts

A) primary energy demand using contemporary conditions (nonrenewable! Top line, with circles)

B) renewable PER demand based on PER factors as discussed in this paper (bottom line, with diamonds)

One of the first things you may notice is that the renewable primary energy expenditure is generally much lower than the old nonrenewable primary energy expenditure. The main reason is that renewable sources mostly supply primary power directly; before, the average primary energy factor was in line with the conversion sector's efficiency rates, which were close to three than to two for fossil power plants. Such high primary energy factors can now only be found for heating, since it doesn't correlate well with renewable primary power and therefore requires seasonal energy storage, which automatically involves losses. On average, the PER is lower than today's PE by a factor of 0.52. For a better comparison, the PE curve scaled using this factor is also included in the chart below (smaller diamonds).

It is surprising that the old curve scaled to 52 percent is mostly in line with the new curve. For most of the parameters, very little has changed from the previous version.

Five new aspects, however, are noteworthy:

1. and 2. The relative importance of heating demand is greater as a result of the complex conversion/storage structure needed to provide enough energy in the winter. In the future, good insulation, better windows, heat recovery, and airtightness will be even more important than they are today. The efficient use of heat and renewable energy are perfect partners.

3. The influence of special measures for conserving summertime cooling energy is decreasing as renewable energy production and cooling demand become better aligned.

4. Direct biomass heating with wood stoves has a much higher PER value for two reasons. Such stoves are generally relatively inefficient today, which was previously not particularly noticeable because of a very low PE factor. At the same time, the PER factor for biomass should only be assigned a 1.1 below 20 kWh/(m²a); beyond this budget, the fuel must use the much higher figure assigned to the substitution fuel P2G (1.75). Biomass heat systems should therefore generally be combined with thermal solar arrays (even in Passive Houses) so that no heat needs to be generated from biomass in the summer. In addition, houses directly heated with biomass must have a very low heating demand (the Passive House Standard is ideal here). In this case, wood heating may actually be economically interesting, since one stove could be sufficient for an entire apartment [AkkP 36].

5. Heating systems with methane (biogas and P2G) heat generators are only sensible in terms of energy when the final energy demand for natural gas is below 20 kWh/(m²a). Using such systems for domestic hot water should be avoided; here, too, integrating a thermal solar array or a heat pump for service water is a good idea. Above a heating demand of 20 kWh/(m²a), direct electric heating (PER expenditure relative to useful heat about 2.2) is just about as good or as bad as methane heating (PER expenditure relative to useful heat about 1.9). This adjustment also changes earlier evaluations of energy sources. Gas heating systems are now hardly better than direct heating with electricity, although we don't recommend the latter, either, since a heat pump can further reduce consumption by at least a factor of 2. The practical consequences for domestic hot water systems are considerable. Circulation systems based on fuel heating no longer make sense – even electric tankless heaters would be a better option for heating up water. Here, too, heat pump systems are the best option. Such systems still hold great potential for development and optimization in terms of hygienic and efficient hot water supply (see [AkkP 49], Energy-efficient hot water systems).

Figure 10: Changes between the old PE evaluation (top line with circles) and the new sustainability evaluation (bottom line with large diamonds). The line with small diamonds represents the old PE line scaled to 52 percent. Except for the noted areas, the lines are surprisingly identical.1)

Passive House – the next decade - Focus, Consequences and outlook and References

Passive House – the next decade | Methodology

Passive House – the next decade | Example: Overall power provision for a Passive House

Passive House – the next decade | Determining application-specific PER factors