Chapter IX
Mechanical Systems
Mechanical systems help us to make sure we stay warm in winter and cool in summer, and they provide us with adequate water, power, and lighting. The building’s mechanical system includes the heating, ventilation, air conditioning, plumbing, and electrical systems. Most of these systems are hidden from view in the walls, ceiling, soffits (drop ceilings), and the floor.
THE MOST SUSTAINABLE MECHANICAL SYSTEMS:
Let nature do the work for you.
Aggregate uses.
Match technology to need.
It is critical to design mechanical systems early and alongside the structure because many times, the systems and structure try to inhabit the same space, and the mechanical system may be heavy enough to influence structural loading. Without careful planning, these systems get crunched and result in details that are not just ugly... but sometimes threaten the way the systems work or inhibit your ability to do maintenance and repair. We also want to make sure we use the latent heat created by the mechanical system in the most beneficial way possible.
Mechanical, solar, electric, and water systems… especially those designed for Earthships and PassivHauses… are somewhat of a high tech solution. There will be maintenance necessary which you can most likely not perform on your own due to the complexity of the system. Most of the systems are designed and manufactured in Europe, and oftentimes they only come with instructions in those languages, and the tools required to repair them may not be readily available. This can be frustrating for those wishing to be self-sufficient.
In many, if not most, cases... we really cannot achieve human comfort with only natural means. Passive solar helps. Shading helps. Ventilation helps, but only insofar as it is a) needed and b) in the right humidity range. In order to attain true comfort year-round, we most often need to provide additional heating, cooling, humidification, or de-humidification through mechanical means.
UNDERLYING THEMES OF HVAC
The human body loves to be kept at a temperature of between 75° F to 80° F. As humidity increases, air temperature is more comfortable when it is towards the cooler edge of the 75-80° range.
Heating, Ventilation, and Air Conditioning (HVAC) systems provide us with adequate ventilation when we cannot open the windows. They allow us to move the air around so it does not get stale. They control thermal performance and humidity. These systems also help to control dust and minimize odors.
Regular air movement should be above 10 feet per minute (FPM) to provide the right amounts of oxygenation to our bodies. Air velocities greater than 50 FPM create “drafty” conditions that make us uncomfortable.
Low humidity can create static charges and prematurely dries out wood, so we want to try and keep humidity above 20% and below 50%. High humidity causes the opposite effect - condensation - which we see on many Earthships because they lack adequate ventilation and de-humidification is not provided in humid environments.