[Greenbuilding] Passive house standard for retrofits

[Bob Waldrop]

The article below references a Passive House standard for retrofit 
situations where the standard is a "maximum heating demand of 25 kWh per 
meter squared.  How is this determined?  Do I --

- add up my winter kilowatt hours,
- subtract the base load, which gives me the heating kwh, and
- then divide by the area of the house in square meters.

http://www.passiv.de/en/03_certification/02_certification_buildings/04_enerphit/04_enerphit.htm
Begin quote:
The use of Passive House components in refurbishments of existing 
buildings leads to extensive improvements with reference to thermal 
comfort, economic efficiency, absence of structural damage and climate 
protection. A reduction of the heating demand by 90 % was achieved in a 
large number of projects. Achieving the Passive House standard in 
refurbishments of existing buildings is not always a realistic goal, one 
of the reasons being that basement walls remain as barely avoidable 
thermal bridges even after refurbishment.

For such buildings, the Passive House Institute has developed the 
“EnerPHit – Quality-Approved Energy Retrofit with Passive House 
Components” Certificate. This requires either a maximum heating demand 
of 25 kWh/(m²a) or alternatively the consistent use of Passive House 
components in accordance with the requirements for PHI certification of 
components. The heating demand calculated by the PHPP, and the quality 
of thermal protection of the individual
components are indicated in the certificate. (end quote)

This paragraph --

(being quote) Today, ‘passive house’ is a clearly defined standard 
across most of Europe for buildings of a very high energetic 
performance. Experience has shown that a single definition of the 
passive house can be used at least from 40°–60° latitude, and passive 
house definition has been tested in both Scandinavia and southern 
Europe. Key parameters are a specific space heat demand maximum of 15 
kWh/m2 TFA, a specific primary energy demand for space heating, cooling, 
domestic hot water, electricity for pumps and ventilation and household 
appliances at a maximum of 120 kWh/m2 TFA, a maximum heat load of 10 
W/m2 TFA, and an airtightness of n50 0.6/h maximum.(end quote)

from http://www.viking-house.ie/passive-house-retrofit.html

says "120 kilowatt hours per meter squared," for total energy use. For 
our house, which is 144 square meters, if it were a passive house, we 
would have to come under a total of 17,280 kilowatt hours, with no more 
than 2,160 kwh attributable to heating.  I am assuming this is "per year."

Are these interpretations of the standard correct?

Bob Waldrop, OKC