Typically, very large heating and cooling systems are installed in homes, and often these are oversized in terms of their space conditioning capacity.
Heating and cooling a low-energy-use home requires an extra degree of care in the sizing of mechanical systems to ensure comfort and efficiency. In other words, you will not be shopping for conventional space conditioning systems.
Rather, you want systems that efficiently deliver low quantities of space conditioning and that allow you to modulate those levels according to the weather and indoor comfort needs.
Choosing a System
When researching and selecting the best heating and/or cooling system for your home, be sure to assess the heat requirements of the house, installation costs, and local fuel costs (and carbon content). Get help from a professional heating contractor or energy consultant to find an appliance that matches the new heating and cooling requirements of your improved home, or one that can meet your needs now and still be appropriate after your next stages of energy improvements.
Following are some popular equipment options for low-load homes.
Gas-Fired Heating
Many highly efficient homes can be effectively heated with a wall- or floor-mounted gas space
heater or with a high-efficiency, modulating gas furnace or boiler. These heating plants adjust
their flame to deliver varying amounts of heat to the air or hot water circulating in baseboard or
radiant floor distribution systems. Look for efficiency ratings in the mid-90 percent range.
Heat Pumps
There are two main types of heat pumps: ground source and air source. Ground source heat
pumps remove heat from the ground by way of a working fluid flowing through tubes that are in
contact with the ground. The fluid goes through a compression and evaporation cycle to extract
heat from the ground and deliver it to the house.
One advantage of a heat pump is that it can also work in reverse and act as a space-cooling system, removing heat from the house and transferring it to the ground.
Disadvantages of ground source heat pumps are that they are quite complex, can be costly to install, and can use quite a lot of electricity. They are generally most effective in cooling-dominated climates, and some studies show that in heating-dominated climates the actual efficiencies are somewhat less than rated levels.
Air-source heat pumps can be efficient and versatile for both heating and cooling a home. They
operate by transferring, or pumping, heat between indoor and outdoor air. Sometimes called “minisplits” or “ductless mini-splits,” these units are similar in operation to central air conditioners, but they do not use ductwork to deliver the conditioned air.
Instead, one or more indoor units are connected (via a refrigerant line set) to a single outdoor unit. This setup allows for different temperature zones within the house. The absence of ductwork eliminates the problem of leaky ducts, a potentially large loss of energy.
Other Heating and Cooling Options
Additional options to consider for heating include cordwood wood stoves, pellet boilers or stoves,
and masonry heaters. These options require more frequent attention by the owner than automatic,
fossil fuel systems.
Evaporative coolers work well in dry climates by taking advantage of the same principle that our
bodies use to remove excess heat by sweating.
Evaporating water absorbs and dissipates heat energy. When it’s humid, moisture can’t evaporate
from our skin, and we feel hot and sticky. In hot, dry climates, moisture added to the air evaporates,
absorbing heat energy and cooling the surrounding air in the process. Evaporative coolers are sometimes called “swamp coolers” because they use a steady supply of water to cool the air while also making
it more humid. Evaporative cooling equipment requires no compressor and therefore consumes much less electricity than a conventional air conditioner.
Though not as effective as conventional air conditioners, swamp coolers can provide sufficient
comfort under the right conditions. Because they rely on the evaporation of moisture, they work only in dry climates where relative humidity levels are below 40 percent.
More novel approaches to cooling very efficient homes include a ground coupling system, where
fluid is circulated in underground pipes and then through a “fan coil” (something like a car radiator) that lives inside the ductwork of a space conditioning or ventilation system. Air blows over the cool coil and delivers cool air to the house.
Another innovative system, called the NightBreeze (see Resources), allows you to use cool nighttime air to ventilate your home at night through a balanced ventilation distribution system. Such systems can be found by exploring the cutting-edge work being done to promote the Passive House Institute U.S. efficiency standard, which primarily addresses new homes (see Resources).
This extremely efficient standard has taken a strong foothold in Europe and is just beginning to gain traction in the United States.
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