By Bob Baker

In this issue, we will convert an existing HVAC System serving a 3,000-ft. home located in West Central Florida from a single balanced system with a central control to decentralize control into four separate zones. The home was built in 1992, faces West and backs up to a canal so has the humidity challenges so common in Florida. This home has a history of "near" IAQ problems that have only been averted through careful attention to preventative maintenance. Any change in envelope pressurization, inside moisture level of ventilation introduced by the new control scheme could well result in an environmental disaster.

I have decided I would like four separate control zones.b The first will be the two bedrooms and bath over the garage. Next is the daily living area consisting of the kitchen, family room, office and utility room plus a small bathroom. The third zone is the infrequently used formal living and dining rooms. Last is the master bedroom suite that has always been either too cold or too hot.

Survey Results

Before you can achieve a result, you have to know where you are coming from then decide what you need to do to get there. Armed with a floor plan, I set out to document the existing system and the desired objective. That meant a trip into the dreaded attic (No accident that December was chosen for the project.).

Good - Equipment consisted of a Carrier Heat Pump (60,000 BTU with thermal expansion valve on the inside coil) in reasonably good condition; located in a second floor equipment closet. Ducts were laid out according to the plan, accessible with a minimum of pain and appeared to be in good condition. The home has a radiant barrier tacked to the underside of the rafters so the attic space does not get as hot as many Florida homes. This probably accounts for the better than average condition of the ducts. Three of the planned four zoned areas have ducted returns that are more than adequate for the expected air volume. Good return airflow goes a long way toward assuring the success of a zoned system. Construction is wood frame with six-inch exterior walls and R-19 fiberglass bats in both the walls and floors plus loose fill fiberglass in the ceiling certified to R-30.

Bad - The system was installed before the use of sealing mastic became common. Although all seams and connections are taped with specification grade metallic tape and strapped, some of the external tape showed the effects of high temperature over time (although not apparently leaking).

Ugly - Future zone one consists of two West-facing bedrooms, each with a door leading to an outside balcony, and a shared bathroom. The return for this area is provided by small under cuts in the doors and may not be adequate. The afternoon heat gain to this zone is significant. The master bedroom suite is 25 feet from the air handler and is heavily shaded. As is typical of recent Florida construction, the duct system is a "spider" type system with flexible ducts connecting fiberglass board plenums and distribution boxes. It is essential to have a properly sized system free from leaks.

Changeover Plan

A list of components includes dampers and thermostats for each zone, a control panel to tie them together and to the existing equipment and all the wire connectors and so on to complete the job. Carl Peterson of Zonex out of Coca Beach, Florida was advising me so I selected a panel he recommended and dampers from the same manufacturer. This panel is especially made for a heat pump (important). It has capacity control so when only one zone is being served the outside unit can be cycled on and off if supply air is too hot heated (over 118° F) or cold (less than 45° F) and includes indicator lights that show damper and control status plus has built in time delay of four minutes between operations. The last feature is not necessary in my case as time delay is built into the existing system controls. It is important to be sure that all components work together so carefully follow specifications for the panel you choose. Critical components in addition to the panel include:

• Thermostats
  Most systems will accommodate any make or style of thermostats. Carefully read the control panel literature to be sure. In my case, heat pump thermostats were required and, if electronic, battery operated or models with a wired 24-volt return rather than the style that utilizes a trickle of power from the control wires. That constant trickle of power can confuse the sensitive electronic circuits in the zone control panel. The draw through a cooling anticipator resistor in a mechanical thermostat can cause like problems. I considered automatic setback thermostats but decided on run of the mill Honeywell mechanical models and test the addition of more exotic models later.

• Bypass Damper
  Often bypass dampers in zoning systems are seen as optional. This is a mistake. When only one zone is calling for air, only a fraction of the air handler capacity is being used. In my case, zone one only needs about 400 CFM and the air handler puts out 2,000. That excess has to go somewhere or it causes problems. A bypass damper routes that excess capacity back to the return. Most systems (including mine) use an atmospheric damper that (when adjusted properly) automatically keeps the static in balance. Some designs use an electric bypass damper. The further from the air handler you can install the bypass damper the better. In my case, the supply to the master suite and the return from that area run parallel for about 20'. I was able to place the bypass damper between them at that point.

• Connectors, elbows and junctions
  These are common components available at your neighborhood supplier but are listed here to make a point. Although I was not prepared to rip out my duct system and install an all metal one, I believe that metal ducts are better from an IAQ risk standpoint as there is less possibility of restricted airflow and they provide fewer places that can catch and hold particulate matter. Rather than build fiberglass distribution boxes I used all metal connectors, adapters and junctions. I also used plenty of elbows so each flexible duct was connected with no kinks or bends that could restrict air movement.

• Tape and mastic
  I also made another decision that added about half a day to the job but will pay off in the future. I lagged all the existing distribution boxes with a coating of mastic and redid all connections to the best current practice with specification tape, straps and mastic; in the process, eliminating any existing duct leaks.

• Insulation
  I used R-6 duct wrap on all the new components and to add extra insulation to the larger distribution boxes.

• Zone Dampers
  Not any real choice here. Pick the dampers that match your panel and the duct sizes. I used one 10" (second floor) 2 - 14" (kitchen/family room and living/dining) and one 12" (master suite). I was fortunate in that in both the first two zones, the supply ducts taking off the plenum served only the areas in that zone so I had only to cut the ducts, remove a small 2-3' piece and install the dampers. The other two zones required that I block the 12" outlet from the living room mixing box that served the bedroom suite and reroute that supply duct. I also installed a couple of sheet metal elbows in zone one to correct an overly sharp bend that restricted that duct (remember full air flow is vital for zoning success).

Once all the materials were assembled, I proceeded with the install which was straight forward involving the usual colorful language involved with tight spaces and joy of running the control wires (ran 5 wire for possibility of future electronic setback thermostats although 4 wire was all that was needed). Even though a contractor friend who was going to help never showed up (probably got lost), entire job took only two days of a long weekend with generous time outs for church, ballgame and refreshments. Next month we will look at the results.

Mr. Baker's field of expertise is the control of contamination in air-conditioning and ventilating systems by mold, mildew and bacteria. He writes and speaks frequently about the efficacy, legal risks, and regulatory issues involved in various control strategies. He serves on ASHRAE Technical Committee TC 2.3, TC 2.4, TC 9.8, and Sampling of Airborne Particulate Concentration in Commercial and Residential Buildings GPC 17P. He also serves as a member of ASTM D22.06 (Indoor Air Quality) and is on the Board of Directors of the Indoor Air Quality Association and the Florida Public Health Foundation. Because HVAC applications encompass new uses from an U.S. EPA regulatory standpoint, Mr. Baker works closely with the EPA and industry groups, including serving as the chair of the IAQ committee of the Consumer Specialty Products Association, to help formulate policy in this area.

Bob Baker is Chairman and CEO of BBJ Environmental Solutions, Inc., a company specializing in providing clean air through environmentally responsible products, such as BBJ MicroBiocide , BBJ Micro Coil Clean , "FreshDuct Odor Eliminator ", and BBJ Mold and Mildew Remover™ as well as the revolutionary new Power Coil Clean™. For additional information, Mr. Baker can be reached at (800) 889-2251 or through the company web site at http://www.bbjenviro.com.