I’ve been discussing a lot with my colleagues how best to reach Passive House standards in a green Brooklyn brownstone renovation. Passive House (a German building system not to be confused with passive solar) is a good benchmark because if you do it correctly you really don’t need a heating system.

Here is one comment I thought worth sharing. It is a little technical but the idea is very simple: a sun house arrangement on the roof to capture heat and pass it into the building as well as water tanks to collect the extra heat for use later (evenings, cloudy days).

Bottom line with this arrangement it is possible to heat the house and the household water using only the sun. Makes your super fancy expensive heating system look a little silly, no?

Here s what my colleague Nick Pine says:

NREL says January is the worst-case month for solar heating in NYC: 610 Btu/ft^2 falls on the ground and 980 falls on a south wall on an average 31.5 F day with a 37.6 high. An equilateral A-frame sunspace on a flat roof with 5 $200 R2 4’x16′ double-glazed argon-inflated polycarbonate panels with 80% solar transmission could provide a dramatic venue for fundraising cocktail parties and gain 0.8×20’x16′(610sin(30)+980cos(30)) = 295K Btu/day. At 100 F, it would lose about 6h(100-34.6)16’x20’/R2 = 63K Btu, for a net gain of 233K Btu (68 kWh), with 79% efficiency.

With common brick walls and lots of new roof insulation under some OSB and a 20’x80′ piece of EPDM rubber, the brownstone could stay 70 F in January with a thermal conductance G = 295K/(24h(70-31.5)) = 319 Btu/h-F, eg 2×20’x24′ = 960 ft^2 of exposed brick walls with 960/319 = R3 insulation. This would not meet the Passive House standard 🙂

With a fan-coil unit (eg a 20 watt car radiator) we might store heat for 5 cloudy days (with a 1-2^-5 = 0.97 solar heat fraction) and heat water for showers in 2 140 F East-West plywood tanks lined with EPDM rubber at the base of the north and south sunspace walls. With soft cushions, these could also serve as seating and a ballast foundation.

We could refine this with an elegant interior decorator and a simple simulation using NYC TMY2 weather data.