Houses without Heating Systems
by: Paul Kando
Is it possible to reduce energy use to near zero in an existing building without reducing comfort? Definitely. Improved efficiency means more comfort while consuming less energy and passive house (PH) technologies are as applicable to existing structures as they are to new buildings. Regardless of the age of a building, a PH window will have over 70% lower heat loss than an ordinary double pane window. Insulation added to an existing structure will cut up to 90% of the heat lost through the wall, ceiling or floor to which it is applied. And a heat recovery ventilation system will reduce ventilation heat loss by 75 to 90%. PH products and technology will work in any building, new and old. Still, existing buildings offer different challenges since their energy upgrade often involves modifications to the existing structure and associated costs. For this reason, it is best to combine a full PH upgrade with other remodeling work. Another opportunity arises when a costly replacement of a boiler or furnace must be contemplated.
The same performance requirements apply to a PH rehab as to new construction: 10 kW/m2 heat load or 15 kWh/m2/year energy used for heating, 120 kWh/m2/year total energy; and 0.6 air changes per hour at 50 Pascals (Pa) indoor/outdoor pressure difference. (1 kWh = 3412 Btu; 1 meter2 = 10.7639 square feet; 1 Pa = 2.953x10-4 inches of mercury (at 32°F) = 0.00014504 Lbs./square inch (PSI). The means to meet these standards are also the same: super-insulation, no thermal bridges, thermally efficient windows, airtight construction, and heat-recovery ventilation.
The challenge lies in the existing structure. Therefore the process begins with its thorough assessment, i.e. an energy audit. The results of this audit are then entered into the Passive House Planning Package (PHPP) to determine the specific upgrade requirements. Needless to say, to avoid extra steps and possible confusion, it helps when the energy audit and its software are fully compatible with the PHPP. The Midcoast Green Collaborative's audit procedure and software, unlike any other we are aware of, has been designed with this compatibility in mind. The Collaborative also owns the latest version of the PHPP and is a member of the International Passive House Association. In fact, a MGC energy audit report's recommendations (usually focused on efficiency measures that pay back from energy savings in 7 years or less) can be viewed as interim steps toward a possible full PH upgrade. These suggestions usually include beefed-up insulation within the limitations of the existing structure (e.g. wall thickness); improvements to existing windows; and sealing the structure. We also indicate when the installation of a heat recovery ventilator becomes necessary. However, unless part of a PH upgrading, (or the existing windows are beyond repair), we do not recommend replacing windows. This is because it makes no economic sense to pay fort the cost of installing any but the most energy efficient windows. Projected savings in heating fuel bills associated with each recommended step are also indicated in the energy audit report.
Further steps on the way to a full PH upgrade may involve adding insulation outside the physical boundaries of existing walls, in a way that thermal bridges are also eliminated; tightening the structure; installation of high efficiency heat recovery ventilation; sealing and super-insulating the attic and the basement ceiling; and the installation of PH rated windows. The existing heating system maybe left in place as backup, or removed, depending on the circumstances. This is where systemic thinking comes in handy: Instead of looking at the task ahead adding things to the building as "afterthoughts": Insulation, windows, doors, ventilation etc, we are configuring a system that will deliver certain services, like comfort, warmth, cold and warm water, lighting, fresh air, sanitation, friendly atmosphere, eco-friendliness, etc. Large economies may be realized from such systemic thinking. For example, since a PH requires less energy for space heating than water heating, there is an opportunity to combine both with heat recovery ventilation.
When remodeling, it seems foolhardy not to include a PH energy upgrade as well: The marginal cost of insulation and tightening a structure is not high and other benefits may also be realized. Otherwise we advise a stepwise approach, with subsequent improvement steps paid for by savings realized from previous steps. In any event, near- PH performance should be the ultimate goal. After all neither the climate nor the oil merchants are likely to cut a better deal for us.
An upcoming article will compare Passive House and LEED certification.
Continue Reading: Part 1 or Part 2