Zoning is an amazing enhancement to a single residential HVAC system. But there can be some real bugs in implementation if you’re not careful. Problems we encounter on service calls typically fall into two categories:
- Something is inherently incorrect in the installation or application (in these cases we always hope the installation wasn’t one of ours).
- There’s a glitch in a component or in the system’s operation. Glitches aren’t common in electronic zoning systems, but when they do occur they can be very tricky to pin down — especially if they occur only intermittently.
There are two basic types of zoning systems: pneumatic and electronic. The difference is how the dampers are opened and closed. Although much of what we’ll discuss here could pertain to either type of system, the focus of this article is troubleshooting electronic zoning systems on a service call.
Check the System First
On the initial evaluation visit, start with a full call for cooling from all zones. Depending on outside conditions, you may need to temporarily shut down power to the system’s condensers. You want to assess how the system is performing at full airflow, with all dampers open and the blower running on high fan speed. This is a good opportunity to verify that the zoning system’s dampers are not stuck. If a system is equipped with a bypass damper, it’s usually closed when the system is in full-call mode.
After confirming full system airflow, shut down a zone and observe the result. There should be an appreciable increase in air delivery in the remaining zones. This may be difficult to identify in variable-speed systems or systems that have a bypass damper, but at a minimum there should be no more air delivered to the zone that’s shut down. This may seem like an obvious step, but technicians often skip these basics and attempt to go right into hardware diagnostics.
Repeat that same zone shutdown test for each remaining zone and verify the changeover. You probably will have to wait through a slight delay in order to validate that the system has responded. Look for the same airflow confirmations as you did when running the system on full-call. While it would be possible to save some time by doing this at the zone board, you want to verify that each control and its corresponding wiring connections are good. Here a few problems you might find:
• System zone board. Many system zone boards have onboard diagnostic LEDs. Check these for possible trouble codes.
Board failure isn’t common, so when it does occur we want to identify a likely cause rather than just swap the board. For example, poor wiring work is a common cause of board failure. Has the wiring been labeled, organized, and correctly finished? Another cause of board failure is improper power. Most manufacturers suggest that a separate, dedicated 24V transformer be used to power their system. Has that been used in this case? Was it sized appropriately to the amount of hardware connected? Using a dedicated 60VA transformer is low-cost insurance that full low-voltage power will be available to run the system. Some installers take the extra step of putting surge protection on that circuit, which is a nice show of craftsmanship.
• Input sensors. These are used to measure leaving air temperature and return air temperature. If a high- or low-temp trip has occurred, did the sensor reset? What system operation would have to occur to cause that sensor to trip? Do you know the trip temperature points? They can vary by manufacturer. Placement of these sensors also can be an issue. Is the leaving-air sensor in a location where radiant heat from the furnace can trigger nuisance trips? Bypass dampers that are allowing too much flow can be another factor that causes sensors to trip.
• Bypass damper adjustment. Setting up a swing-weight barometric bypass can be tricky. With two different fan speeds (heating and cooling) where is the appropriate active bypass pressure? Is the pivot dry or in need of some lubricant? Pivots can stick and then loudly bang when they finally free up, and that can be a tough noise to track down.
• Control placement. Was a programmable thermostat used in each zone? What role (if any) is the program function of the thermostat having on zone function? Does the homeowner tend to designate one zone as occupied and leave the others shut down?
• Orphan zones. Although two-zone designs allow us to split system capacity pretty cleanly, a third or fourth zone can create some unintended consequences. For example, let’s say that you have a system in which zone one is 35% of the conditioned space, zone two is 40%, and zone three is 25%. What’s the probability of a system glitch with only 25% of the system calling? If the system receives a call for operation from zone three (only), the increased air delivery and noise level can result in complaints.
How you set up such a system is crucial. You might need to consider a dump zone or setting all zone dampers to permit some air bleed-off (i.e., never closing 100%). Try setting 80% closed as the maximum initially, then test for effect.
• Faulty thermostats. In our experience, this is more common than zone board failure. Nobody likes a callback after changing a zone board, only to find it was just a thermostat.
Make Customer Satisfaction Your Goal
With adjustable zone bleed, bypass adjustment, and fan speed selection, there’s much a technician can do to “tune” zoned system performance. But in the end there are two inescapable truths. The first is that if the original system was based on oversized equipment selection (highly likely) then a zoning retrofit will be a bit dicey. It can work, but it’s usually going to be necessary to modify and enhance the ductwork. The second truth is that homes that have zoning without a variable-speed furnace just aren’t getting the full benefit of what zoning can do to enhance comfort.
Having an almost silent system that holds correct temperatures reliably and unobtrusively is the promised land for comfort design. A great zoning system delivers that, and at a relatively low cost compared to multiple systems. In today’s economy, zoning really makes sense.
With so much focus on right sizing equipment matched to the structural load, we have found zoning to be a “must have” component, particularly in two-story homes. Becoming proficient at making sure these zoned systems are delivering the maximum comfort they’re capable of is crucial if we want the homeowner to be happy with the result of our service call.
Doug Vickery is president of Airplus of California Inc., a residential and light commercial HVAC contracting company in Corona, CA. Doug can be reached at 951/520-2704, or by email at firstname.lastname@example.org. For more information on Airplus, visit www.airplusca.com.
Understand the logic of zoning to simplify troubleshooting
BY DICK FOSTER
Zoned HVAC systems, for the most part, operate under the same basic logic as non-zoned systems. A thermostat in each zone still turns on and off the heating, cooling, or fan. However, with zoning, the thermostat also operates a motorized damper, either directly or through a central control panel.
A zoning system simply allows multiple thermostats to turn on and off the same HVAC system; sequence heat, cool, and fan calls; and use the dampers to direct the air to the zones requiring air.
Servicing a zoned system requires a basic knowledge of two HVAC skills: airflow and low-voltage controls.
In terms of low-voltage controls, troubleshooting zoning comes down to three basic control problems:
- On a call from any zone thermostat for heating, cooling or the fan; the heating, cooling, or fan doesn’t come on.
- When a zone thermostat is satisfied the heating, cooling, or fan doesn’t shut off.
- The zone dampers don’t open or close when they’re supposed to.
The key to troubleshooting zoning is knowing the logic of zoning. For the most part all systems operate similarly in that when any zone thermostat calls, be it for heating, cooling, or fan only, that thermostat closes its appropriate terminals, making the same terminals at the zoning panel. The panel then activates the corresponding HVAC outputs and closes the dampers to the zones not calling. When the zone thermostat’s call is satisfied, the thermostat breaks the circuits to the panel, and the heating, cooling, or fan is shut off.
Determining the cause of a problem simply requires looking at what is or is not being called for by the thermostat and tracing the circuit to see if the issue is with the zone thermostat, control panel, HVAC system, zone damper, or possibly in the wire to each component.
My experience over 35-plus years is that 90% of all problems can be traced to a field wiring issue. Wires may be crossed, broken, or shorted —typically to the zone thermostats as they are the longest runs.
The other side of zoning problems are not control-related and may be the duct system, its sizing, and airflow issues. The ability to view the system as a whole, then take the problem and isolate it, is the first step in troubleshooting zoning.
Keep in mind that troubleshooting zoning is often a total home issue. There can be multiple thermostats and dampers spread through the home, and it may take time to trace all the components of a system and check their operation. With zoning, the problem is not always at the furnace or air handler.
Dick Foster is president of ZONEFIRST, Elmwood Park, NJ. He can be reached at 877-FIRSTZONE (347-7896) or by email at email@example.com.
New ACCA manual a good resource
The Air Conditioning Contractors of America (ACCA) offers Manual Zr, the first ANSI recognized standard for residential zoning. Topics covered in Manual Zr include:
- Zoning advantages and appropriate use of the zoning concept
- Types of systems, equipment, and components used for air damper zoning
- Zoning metrics and methods
- Doable owner expectations
- Guidance for designing entire zone damper systems
- Limitations in design applications of bypass air
- Load calculations for zoned systems
- Strategies for excess air management.
ANSI/ACCA 11 Manual Zr – 2012 (Residential Zoning) is now available for sale and can be purchased at www.acca.org/store.