Fig. 2: Comparison of Measurement and Simulation for data collected in the scientific research project "Passive House Passivhaus Darmstadt Kranichstein". (Click on the diagram to show higher resolution. The simulation program used was DYNBIL; the comparison was published in [AkkP 5]).

Fig .3: Comparison of Results Obtained by dynamic simulation (DYNBIL) with calculations done with PHPP (Monthly Method of EN 832 and Annual Method) The agreement of the results of the simplified stationary calculation method with the dynamic method is very good. In doing such a comparison, however, one has to be very accurate in using identical input data for all methods. (Right click and "Open image" in your browser to show the diagram in higher resolution.)

Fig. 4: Comparison of Measured Consumption Data (Statistical Data) with PHPP-calculation results. It is important to compare the average values from a sufficiently large sample, as the individual consumption values will vary a great deal due to differences in user behavior. The average values compare very favorably with the PHPP-results (Click on the diagram to show a higher resolution).

Fig. 5 This balance (right side) was calculated by PHPP; it is corresponding to the very first Passive Houses realized in Darmstadt Kranichstein (Architects: Prof. Bott, Ridder, Westermeyer). The results of the monitoring program (left side) compare quite well to the calculated balance. The measurement was done using calibrated heat flow meters and natural gas meters. (Right click and "Open image" in your browser to show the diagram in higher resolution.)

The good compatibility of the calculation and the measurement results are not just by chance in the projects documented here. Experiences with some 1000 projects designed with the aid of PHPP are excellent.

Fig . 6 An example of a PHPP-Balance-Sheet with Data for a Passive Row House Unit. An annual heat requirement of 12 kWh/(m²a) indicates that the criteria for the Passive House Standard has been fulfilled. (Click on the table to show a higher resolution).

Abb. 7 Monthly Heat Balances of the Darmstadt Passive Row House, using PHPP. (Source: [AkkP 13])

Fig. 8 Annual Heat Balance (added up from the monthly balances) for the Kranichstein Passive House, calculated using PHPP. Solar gains and internal heat sources are more important than the remaining active heating. (Source: [AkkP 13]; Click on the diagram to show a higher resolution) An explanation of the energy calculations can be found here: EnergyBalance.html

Where can you get PHPP?

More information at the website of the Passive House Institute: PHPP - from PHI .

Read more about the coming
International Conference on Passive Houses
2008-April-11 to 12th
in Nuernberg:

www.passivhaustagung.de.

The Passive House Planning (Design) Package (PHPP) includes:

• energy calculations (incl. R or U-values)
• design of window specifications
• design of the indoor air quality ventilation system
• sizing of the heating load
• sizing of the cooling load
• forecasting for summer comfort
• sizing of the heating and domestic hot water (DHW) systems
• calculations of auxiliary electricity, primary energy requirements of such (circulation pumps, etc.), as well as projection of CO2 emissions
• verifying calculation proofs of KfW and EnEV (Europe)
• Climate Data Sheet: Climate regions may be selected from over 200 locations in Europe and North America. User-defined data can also be used.
• ... and a lot more tools useful in the design of passive houses, e.g. a calculation tool to determine internal heat loads, data tables for primary energy factors, etc.
• a comprehensive handbook, not only introducing PHPP use, but also highlighting crucial topics to be considered in Passive House design.

The Scientific Background: Simulation Program Solidly Rooted In Principal Equations of Physics

For the first Passive Houses, it was indispensable to use sophisticated modeling, employing many sets of high-resolution dynamic data. Calculating the energy balance of buildings with very low energy consumption is a demanding task - existing codes and standards proved too inaccurate (in that, little has changed to this day). The challenge: the input data for an intermittent simulator routine are very extensive – our computer model for Darmstadt Kranichstein requires over 2000 independent input data (without the climatic data set). If the simulation is to provide reliable results, these data must be in accordance with the actual geometry of the building. This is indeed possible, as we can see from the comparison between simulations and plotted actual measurement data ([AkkP5] Fig. 2, above left). The expenditure for such a model is extensive, and not all the necessary data are of equivalent importance. Nevertheless, we have identified in the meantime the critical factors for preparing reliable calculations - with tools that are simple to use and with acceptable effort in terms of data input. The technique for designing well-performing passive houses has now been tried, tested and optimized in thousands of cases.

A Pragmatic Solution: Simplified Model, Well Defined Input Data

In comparing different simulation models and tools, we were able to distill which elements are truly important. In this way it was possible to devise simplified models to be used with an affordable effort and which still provide reliable results [Feist, 1994]. The development of the simplifications is published [AkkP 13]. It may be surprising, but accuracy sufficient for practical planning purposes can be achieved using a quite simple model. That is:

• treat the whole building as one zone of energy calculation
• use monthly energy balances in lieu of dynamic simulation with short time steps.

(see fig. 3 in the column left hand side).



Transparency of calculation is not the only advantage. More importantly:

• Much smaller expenditure on data acquisition (only the data of the building envelope and of the ventilation have to be determined),
• The sources of errors are reduced and it is simpler to inspect the data and the calculation (a quality controller would be horrified to have to examine and assure the propriety of a numerical simulation data set).
• The designer can concentrate on the important variables…
• ...and can be sure to include all of these in her/his design.

To briefly discuss this last point: Most highly developed simulation programs are very accurate with respect to certain of the physical processes (e.g. non-stationary thermal transmission or for radiant heat transfer), but these models serve to distort in other areas (e.g. angle-dependent radiation transmission through glazing; the shading of solar radiation by balconies, lintels, etc). So far, no single program has been able to fully address all relevant processes to the exacting satisfaction of physics. Even at future such a program would be highly complex, which will create additional potential for errors.

Naturally, any such simplification implies a lost in accuracy - but each datum that is not fully correct when put into a complex model will also lead to losses of accuracy. And, pragmatically viewed, the computational accuracy possible is, at any rate, limited by the precedent case of data not predictable with high accuracy – the weather! We do not argue here expressly against the use of detailed simulation programs: On the contrary, these programs are the only acceptable way for scientific research. But for the practical purpose of building design, employing already well-tested building concepts, the use of simplified, optimally adapted computing tools will reduce the probability of errors and might therefore be even more accurate.

The tool optimally adapted for the design of Passive Houses is the well-proven PHPP (Passive House Planning Package). The PHPP has been calibrated with simulation calculations using complex dynamic models.

Why is PHPP more accurate for energy efficient buildings than other tools?

PHPP was systematically developed by aligning the utilization rate function with the results of dynamic simulation models [AkkP 13]. For this development only such models were used as had been validated against monitoring results of built passive houses (see fig. 2 in the left column). By this method was the standard for Passive Houses aligned, as well as a standard for buildings with low, but not as low, energy requirement for heating. However, for such buildings the calculation differs slightly from what is given in the European standard EN 832 (ISO 13 790). But the difference is not important for conventional buildings - it is only of influence for buildings with very long time constants. In this class of buildings the ISO 13 790 tourns out to be a little bit too optimistic.

The results from PHPP-calculation have been repeatedly compared with monitoring results of sufficiently large samples of built Passive Houses (see fig. 4 on the left side). These comparisons have always shown a very good correlation.

The PHPP clearly uses boundary conditions that are significantly different from the calculation process used for the German Energy Conservation Ordinance (EnEV). There are important reasons for this - these are discussed in detail in [Feist 2001] and given in short here:

• For internal heat sources in residential buildings using efficient appliances, during the heating season values of some 2.1 W/m² (±0.3) are realistic (and not 5 W/m², as frequently assumed). In the PHPP, there is an additional calculation sheet to determine the internal heat sources of given building projects. However, if internal heat gains are assumed to be higher than realistic, this will result in significantly lower heating energy requirements and may even lead to the illusion that a "zero heating house" can be built with a building envelope of mediocre quality. Practice shows this to be untrue.
• The average indoor design temperature in German dwellings can be assumed to be 20°C. This is more realistic than the 19 °C given in the German ordinance. The PHPP user can adjust this indoor design temperature to his or her specifications.
• To calculate solar gains it is important to take into account realistic shading factors (the environment, balconies, etc.) and also to account for ever-present dirt and dust on surfaces.
• Temperature-correction-factors (F-factors) very often were chosen too optimistically for super-insulated buildings. E.g. for insulated ceilings under uninsulated roofing, the F-factor values are not in the range of 0.8, but nearer to 1.0.
• The assumption to add an "additional air exchange rate" due to user-opening of windows is given by EnEV to be 0.15 h^-1 for exhaust systems; 0.2 for balanced ventilation systems with heat recovery. Those values are assumed far too high. To be correct, one needs to base values on achieved air-tightness; which means based on actual measured n₅₀-value, as in the PHPP and DIN EN 832 / ISO 13 790.

These and additional topics result in differences in calculation results, which are significant for energy efficient buildings.

More than just an Energy Calculator

The PHPP was not primarily developed just to calculate energy requirement verifications. Much more, the PHPP is a design-tool, which can be used by the architect and the engineers to design and optimize their Passive House project. In the PHPP they will find dimensioning tools for the windows (with attention to optimal comfort), for the heat recovery ventilation system (with attention to good indoor air quality and sufficient relative humidity), for the mechanical systems and for summer comfort. Within PHPP, the building and the mechanical equipment are treated as one overall system.

The PHPP-handbook is not restricted to explaining the use of the spreadsheets and the compilation of the input data. Rather, the handbook gives advice on how to optimize the design (e.g. how to build very air-tight, how to avoid thermal bridges, how to minimize construction costs). All this is very useful during the planning phase and for quality control work as well.

This link leads to the main site of the Introduction to Passive Houses.

	Author: Dr. Wolfgang Feist, director of the PHI   Link to the homepage of the Passive House Institute:

Literature:

[AkkP 5] Energiebilanz und Temperaturverhalten; Protokollband Nr. 5 des Arbeitskreises kostengünstige Passivhäuser, 1. Auflage, Passivhaus Institut, Darmstadt 1997 GERMAN (Link zur Publikationsliste, PDF, 200kB)

[AkkP 13] Energiebilanzen mit dem Passivhaus Projektierungs Paket; Protokollband Nr. 13 des Arbeitskreises kostengünstige Passivhäuser, 1. Auflage, Passivhaus Institut, Darmstadt 1998 GERMAN (Link zur Publikationsliste, PDF, 200kB)

[AkkP 20] Passivhaus-Versorgungstechnik; Protokollband Nr. 20 des Arbeitskreises kostengünstige Passivhäuser, 1. Auflage, Passivhaus Institut, Darmstadt 2000 GERMAN (Link zur Publikationsliste, PDF, 200kB)

[Feist 2001] Stellungnahme zur Vornorm DIN-V-4108-6:2000
aus Sicht der Passivhausentwicklung, CEPHEUS-Bericht, 1. Auflage, Passivhaus Institut, Darmstadt 2001 GERMAN (Link zur Publikationsliste, PDF, 200kB)

An English version is available:

[PHPP 2004] Feist, W.; Pfluger, R.; Kaufmann, B.; Schnieders, J.; Kah, O.: Passive House Planning Package 2004/2007, Passive House Institute Darmstadt, 2004/2007 (Link: PHPP-contend).

A complex model, based on the fundamental physics of heat transfer and suitable for systematic scientific research. The "circuit diagram" shows a part (one room) of the DYNBIL-model used for the Passive Houses in Darmstadt Kranichstein. Using this model the fundamental research was done to develop the concept. And a comparison of the accurate measurements, which took place in the realized building, was made to the simulations later (fig. 2 on the left side). This Model was also then used to calibrate the PHPP calculation. (Click on the figure to show a higher resolution).

(updated: 2007-05-26 Author: Wolfgang Feist;
The author thanks Katrin Klingenberg, Mike Kernagis and David Stecher for doing extensive proof reading of this article.
© Passive House Institute; unchanged copy is permitted, please give reference to this site)