Looking at the incredible examples of green architecture featured on Inhabitat, you may have wondered what kind of mechanical equipment is used for these homes. Solar Decathlon competitors, Passivhaus designs, and other high-efficiency houses rely on highly efficient mechanical systems — in addition to the construction and design of the buildings themselves — in order to reach the level of performance they achieve. Obviously, there is not just one system used everywhere, but a number of features common to many of these systems are now being assembled into single, combined unit systems – read on for a look at these “magic boxes”.
Writing for Green Building Advisor, Martin Holladay calls the combined mechanical systems “magic boxes.” These are combination appliances that incorporate ventilation and heat pumps for heating and cooling. In may cases, they also include hot water heating. Because of their efficiency, “magic boxes” may offer reduced greenhouse gas emissions even in comparison with other efficient systems such as condensing furnaces or ground-source or air-source heat pumps.
While heat recovery and energy recovery ventilators (ERVs and HRVs) are not yet common to most homes, they are an essential part of the mechanical systems for Passivhaus homes and other high-efficiency buildings. Most high-efficiency buildings have very tight construction, therefore mechanical ventilation is needed to bring fresh air in and exhaust stale air from the building. ERVs and HRVs transfer energy from the outgoing air stream to the incoming one to recover some of the energy that would otherwise simply be lost in the exhaust.
Since high-efficiency buildings often need only limited heating and cooling, it can be possible to combine that function with the ventilation of an ERV into a single unit. While most of these “magic box” systems are larger than the furnaces they replace, because they incorporate several functions, the total footprint required for all mechanical systems is smaller than what would be required for all of the functions if provided by separate pieces of equipment.
Several of the units are not carried by distributors in the United States. These “magic boxes” are better suited for European conditions (with milder winters) than they are for those in North America. Holladay outlines the reasons for this, noting that the costs of these units are generally higher than the cost of individual pieces of equipment. Some manufacturers point out that the faster installation time for only a single piece of equipment helps offset the higher cost. However, unless space is at an absolute premium, in most cases it is probably better to use separate pieces of equipment.