When natural cooling just isn’t enough, you have several options for mechanical cooling. They are
If your objective is to cool some spaces some of the time—a home office or living room by day, bedrooms by night—then smaller units may be a good choice. If the whole house needs long-term cooling, a central system is better.
Cooling with Fans
Sometimes a fan is all the boost you need to stay cool—and fans generally use much less electricity than A/Cs.
Why does moving air on your face feel so cool? In hot weather, our bodies try to dissipate heat by evaporation. The more we sweat, the faster we want that sweat to evaporate, and moving air aids evaporation. Because we’re acutely conscious of anything that accumulates on our face, especially sweat, that fan on our face is especially sweet.
Ceiling fans have a great feature—visibility. They’re always rotating, reminding us that cooling is happening. Many ceiling fans are reversible, allowing you to choose whether to feel the moving air directly on your skin (downward flow) or more indirectly (upward flow).
Smaller desk fans are affordable, portable, and easy to direct as needed. They can’t cool an entire room, but they can make a personal workplace more comfortable, and they use very little energy. Variable-speed desk fans give you finer control, and can be set to rotate their direction of flow.
Exhaust fans can be set in an open window, but they should be surrounded by barriers to avoid readmitting the exhausted air. Also, avoid facing exhaust fans into the prevailing summer wind.
If you live in a very dry climate with hot summers, the evaporative cooler (also called a swamp cooler) is a simple and relatively inexpensive way to cool. Evaporative coolers use far less electricity than A/Cs. They also generally provide warmer and wetter—but fresher—air than refrigeration A/Cs. So they must deliver more air to do the same job.
Most evaporative coolers blow air into the house via a single diffuser in the hall ceiling or a modest duct system in the attic. If you live in a mild, dry climate, this system can meet all your home’s cooling needs.
An evaporative cooler consists of a fan, a water source, and a wet pad. A small pump circulates water from a built-in water reservoir to keep the pad wet. The fan draws hot, dry outside air through the wet pad, cooling and humidifying the air. This air is blown into the house, forcing the warmer house air out through open windows or a vent into the attic.
There are two basic types of evaporative cooler. Direct evaporative coolers move outside air through a wet pad directly into the house. Two-stage (also called indirect/direct) evaporative coolers are like two evaporative coolers in one. The first precools the air indirectly, so no humidity is added. The air then travels through the second cooler, where it is directly cooled. Because the precooled air can’t hold much moisture, the result is cooler, drier air. Two-stage coolers are more expensive than direct evaporative coolers, but they perform better during extremely hot, dry days.
Evaporative coolers use much more water than refrigeration A/Cs. Using water heavy in minerals means frequently replacing the pads. Unfortunately, the best climates for evaporative cooling are usually the ones with the least available water, and that water is often mineral rich. In some water-starved cities, evaporative coolers for residences are illegal.
To prevent the water reservoir from becoming saturated with minerals, evaporative coolers use water to flush them out. This can be done in one of two ways. A bleed-off can drain a small amount of water from the cooler whenever it is running. Or a sump dump can evacuate the water from the reservoir every half hour or so. Sump dump systems are more effective than bleed-off systems, because they discharge not only brackish water but also some of the filtered dirt that collects in the reservoir. This waste water is rarely suitable for reuse.
Most evaporative coolers are mounted on the roof (the least expensive installation) and have a blower that discharges cool air out the bottom. However, foot traffic and water leaks can damage the roof. Rooftop coolers also produce slightly warmer air, because they are directly exposed to sunlight. The easiest installation to maintain is a ground-mounted cooler that discharges out the top or the side. Put the cooler on the north side of the house for shade.
In areas with hot, humid summers, the A/C excels. It transfers heat from the air inside the house to the air outside. An A/C consists of a compressor, a condenser, an evaporator, refrigerant lines, a blower fan, and, for a central A/C, ductwork to distribute the cooled air throughout the house. A refrigerant transports the heat from the evaporator coil inside to the condenser coil outside. In fact, an A/C functions much like a refrigerator.
Heat pumps and A/Cs have identical components, except that the heat pump has a reversing valve that allows it to supply either heating or cooling; in winter the inside coil works as the condenser and the outside coil as the evaporator, heating the house. If your home is heated by a heat pump, your A/C is built into that system.
A mini-split system is a type of heat pump in which refrigerant loops connect an air handler in each room or zone with the outdoor compressor/evaporator, eliminating the need for ducts.