To Zone Or Not To Zone

March 4, 2005
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Zoned HVAC systems are those that control HVAC delivery to specific areas of a home or business. Which rooms are zoned together? It depends on the activities going on there, and the length of time those activities last. For a single-family residence, for instance, bedrooms would be a separate zone from the family room or kitchen.

Zoning can help customers save money by controlling when zones are heated or cooled. However, they also improve customer comfort in many ways by providing heating or cooling to areas that may have received inadequate conditioning in the past.

Most customers could benefit from zoning, as long as the ventilation system is working as it's meant to, delivering the amount of airflow it was designed for. Zoning can offer comfort corrections for homes with poorly designed ventilation systems, but what ductwork there is needs to be in good condition.

Archaic Zoning

The most basic home heating-cooling design uses one furnace or boiler, one air conditioner or heat pump, and one thermostat. (Indeed, hydronic systems have used zoning for years thanks to zone valves. These heating systems can have multiple thermostats running to one heating system, allowing temperatures to be raised or lowered as occupant use and comfort dictated.)

If a home had two floors and the thermostat was located on the main floor, this would lead to the upstairs rooms being too hot - anywhere from 4 degrees to 10 degrees F warmer than the downstairs - because heat rises. This is also a problem in summer; in order for upper rooms to be comfortable, lower rooms would wind up being overcooled.

For many years, forced-air systems needed multiple furnaces and/or air conditioners if the owner wanted more than one zone - something that could completely shut off heat in unused portions of the home or business, beyond shutting doors and registers. Of course, dampers have been used for this purpose in commercial buildings, but the controls were much more complicated than your typical residential system.

Technology has come a long way. Control systems have been designed that allow residential contractors to offer uncomplicated, multiple zones using one furnace or air conditioner and multiple thermostats.

Today's Zoning

With a zoned system, the unitary equipment needs to be sized to satisfy the cooling-heating loads of the entire house. Variable-speed motors can be used to supply individual or multiple zones at partial load, or all zones at full load, as needed.

One type of zoning method uses a bypass damper. A branch of ductwork (typically in the supply plenum) connects the supply to the return. As dampers close, this creates back pressure to the unit. The bypass damper opens to relieve the back pressure and recirculate the air through the return.

Bleed-through dampers and modulating dampers also can be used for residential zoning systems. Some zoned systems use what is called a dump zone, an area of a building where excess air is essentially dumped. In addition to wasting energy, the zone has no control and its temperatures can influence an adjacent zone.

The thermostat, of course, needs to be compatible for zoning. However, these thermostats are not necessarily more complicated, from the contractor's perspective, than more basic thermostat models. Manufacturers of unitary products and thermostats have worked hard to make their installation as simple and as efficient as possible. Many products do not get more complicated than a basic three-wire hookup.

Do They Want It?

Contractors seem reluctant to tell homeowners about zoning, or to offer it as an option, because they don't think the customer would want it. These contractors are missing some golden opportunities.

In 1999, Professional Builder magazine asked Baby Boomers to rank desirable home features and options. Out of 72 possible items, zoning came in second. "Fireplace" and "home security" ranked underneath comfort system zoning. Still, market penetration for zoning is very, very low.

It spells opportunity for contractors willing to get into this lucrative comfort area. If you can wire a thermostat, you can wire a zoning system.

For more information, click on the Emerson Climate Technologies logo above.

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