Monday, June 14, 2010

Why does everything need to be so tricky?

 Malcolm Isaacs used the Passive House Planning Package to model the One Planet Reno.  The results were very useful, and a bit disheartening as we learned it would be a heckuva challenge to achieve the stringent standard for retrofits of 25kwh/m2.

In general terms, we simply have too many constraints on the tight urban lot.  We can only gain solar radiation on the upper two floors of the south façade due to shading of adjacent houses.  In January and February, given that our “south” façade is actually 30 degrees east of south, we simply can not get enough BTU’s from the sun to lower our heat demand.  Malcolm modeled the original wall sections as posted earlier before the great foam epiphany, and while we still thought we had to have non-combustible construction.  He modeled higher thermal resistance in the walls, floors, roof and windows to see what it would take to achieve 25, and concluded that the cost and the loss of interior space is going to make it an unfavorable option (thought about eliminating the bathrooms to save on space and reduce water consumption, but the 'ol backyard solution is going to be challenging with all that dog poo out there).  Depending on the choices we make, we should get below 30, but it is going to take a breakthrough to make 25.

Malcolm provided us with a great spreadsheet to plug in costs so that we can see the price of saved energy of proposed upgrades to the section.  This analysis helps show us that going beyond R70 or so on the roof has diminishing returns and we are better to invest in the walls.  It also shows us that diligence in air sealing will pay off well, and that the proposed imported HRV is probably going to be worth the investment.  We are going to re-work the wall sections with what we know now, and have Malcolm update the model for us. We're going to try to figure out how to post the report so stay tuned.

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