ZEH1 Near Zero Energy House:

The near zero energy home described in the ASHRAE paper "The First Attempt at Affordable Zero Energy Houses", Christian has some features that puzzle me.

The envelope construction using SIPS seems well thought out, and in particular the low infiltration rates achieved are impressive. The way in which infiltration rates were measured for conventional frame vs SIP construction also seem well thought out and produced impressive data.

The use of the heat pump water heater puzzles me. In effect the solar panels on the roof produce electrical energy at about 10% efficiency, which is then used (in part) to power the heat pump water heater that has a coefficient of performance of about 2 (at best). So, in rough terms, the overall efficiency of the water heating system might be around 20%. The system has a high initial cost due to the PV panels and the heat pump water heater. Why not just use a conventional solar water heater, which would have been much more efficient in turning solar energy into heated water, and would have cost much less?

The roughly 2KW solar electric system adds around $20,000 to the price of a $100,000 house. The all electric house uses 10,000KWH per year, and the solar electric system system provides about 20% of that. A 20% increase in house price to lower the energy bill by 20% (about $150 worth of electricity) does not seem like a stellar deal to me. I wonder if forgoing the solar electric system in favor of solar water heating and more emphasis on passive (or active) solar heating and cooling would have provided equally good or better results at a lower cost?

If you clarify this please contact me.