Mechanical systems are a necessary evil in most buildings. We’d prefer to rely entirely on natural ventilation and passive solar heating and cooling, but that’s not usually feasible. But we can design buildings so that the architecture does most of the work, and use mechanical systems to take care of the reduced heating, cooling, and ventilation loads that remain. Done right, this approach allows us to invest in highly efficient equipment and without spending more, because the equipment is so much smaller than it would otherwise have been.
Reducing HVAC loads
Some types of mechanical equipment don’t provide heating or cooling directly, but they reduce the amount of heating or cooling that’s needed. Air-to-air heat recovery systems, for example, exchange heat between outgoing and incoming air streams, so less energy is needed to condition the fresh air coming in. And ice storage systems using chillers to make ice and night, so that ice can be used during the day to cool the building. That reduces the size of the cooling equipment needed to maintain comfort, and reduces peak loads on the utility grid.
Solar energy isn’t just for photovoltaics (PVs) that generate electricity; it can also be used to heat water, to heat incoming air, or to heat a space directly. Heating needs can also be met with biomass, in the form of cordwood, pellets, or other cellulosic materials. Cogeneration systems that simultaneously generate heat and electricity, make the most complete use of the energy available from combustion. Cogeneration systems are covered under Electrical.
High Efficiency Equipment
Once loads have been reduced as much as possible with smart design and targeted use of equipment, it’s desirable to handle the remaining loads as efficiently as possible. High-efficiency boilers, furnaces, air conditioners, chillers, heat pumps, and the like all contribute to that efficiency. New split-system air conditioners or heat pumps are especially promising for homes and small commercial buildings due to their flexibility and efficiency. In larger buildings, cooling towers are key to releasing unwanted heat; these can be more or less efficient in both the amounts of energy and water they require.
Distributing the Comfort
Mechanical systems don’t just generate heat or cooling, they also have to deliver it to the occupied spaces. Traditionally this is done by blowing air through large ducts, often combining recirculated indoor air with specified amounts of fresh air to provide good air quality. But it takes much less energy to move heat using water than using air, so radiant heating and cooling systems are becoming more common. And keeping ventilation separate from comfort systems usually results in better overall control, higher efficiency, and better air quality.