Multiple Zone Retrofit Carrier Infinity Residential HVAC System

I upgraded my residential central heating system three years ago with a new variable-speed Carrier Infinity Greenspeed 4 ton heat pump and fan coil. The previous system was about 22 years old, and had some upgraded components, but ultimately, the 22 year old fan coil developed a refrigerant leak in the coil, and replacements were no longer available. I looked at having a custom coil fabricated, but ultimately, decided to go with a full variable speed system for efficiency, low temperature capability, and greatly reduced outdoor noise with the variable speed heat pump.

Close duct - basement supply. Far duct - main floor supply with Belimo Damper Actuators

My house has three levels - main floor, basement and first floor. The house was originally constructed with three ductwork branches, one for each level, and each branch had a bypass damper installed. The bypass dampers allow excess air from any one zone to recirculate within the mechanical room back to the furnace. In my case, the bypass was open to the room and not ducted, for this reason, the large mechanical room in the basement was always very warm in the heating season, or very cold in the cooling season - a tremendous waste of energy.

At one time, the dampers were controlled with an industrial PLC which was also connected to thermostats on each level of the house. By the time I purchased the house, the PLC controller was no longer functioning and the system was operating as a single zone system, however, the thermostats were still installed on the walls, and the dampers could be controlled manually with toggle switches on the original PLC panel.

Manual Damper Controls on Legacy PLC Panel Cover

With the Covid-19 lockdown, my wife and I were working from home full time, from our office in the basement. In the summer time, the basement was too cold, and I began manually modulating the dampers to heat the basement in the summer for better comfort. This was laborious, especially considering the dampers had a 45 second full cycle time - you had to manually hold the spring loaded control switch for 45 seconds to make the damper position change. I quickly scrapped this idea and thought about upgrading the Carrier Infinity system with its Damper Control module and retrofit damper actuators. 

Components required for the retrofit - 2 Zone Thermostats, 3 Zone Actuators and the Zone Control Module

Researching how the Infinity Damper Control module controls its dampers, I learned that it expects the damper actuator to have a 15 second cycle time from full open to full close. If the Damper Control module needs to modulate damper position partially open or partially closed, it will simply actuate the damper for a fraction of 15 seconds - for example, half open - it will power the actuator for 7.5 seconds from full open or full closed. It also has a current limit of 1A at 24VAC. My Belimo dampers would not be compatible, so I would have to replace them. Carrier sells two damper actuators which are compatible with the Infinity system - standard damper actuators complete with the damper for new installations, and a retrofit damper actuator designed for round shaft dampers - in two versions - 90 degree rotation and 45 degree rotation. I needed the 45 degree versions. 

New Carrier Retrofit Damper Actuator DAMPACT45DEG-R on the Left - Old Belimo Actuator on the Right

So - I ordered all the parts and got started. The first order of business was replacing the actuators. I could take my time with this without affecting the normal system operation. 

First step before removing old actuators - mark shaft with damper blade orientation

And for each damper - mark the blade orientation - Damper Open and Closed

In my case - the damper opened with counter clock wise (CCW) rotation, but the markings on the Carrier actuator are for clock wise (CW) opening. So - I simply relabled the actuator cover with open and close positions reversed, both for the electrical connection and for the orientation sketches. Not only does this help yourself keep things straight during installation and cabling, but it will really help the next guy that comes along sometime in the future and has to figure out what you've done. 

Carrier DAMPACT45DEG-R Damper Actuator Cover Relabelled for CW Opening

I expected this to be fairly quick and straightforward and it was - until I tested the actuator with 24VAC. The actuator could not supply enough torque to move the damper for the basement or main floor dampers which were installed horizontally. The first floor damper, which was installed in a vertical duct, was properly balanced and the Carrier actuator had no problem with it. 

Measuring torque required to move damper blade

So - to check to see how much trouble I was in, I took a pair of vice grips and gripped the damper axle. Then, I took a digital fish scale and hooked it on the vice grips at a measured distance from the axle (8") and pulled the damper open - careful to keep the scale oriented exactly 90 degrees to the radius to the axle. I measured approximately 2lb of force required at 8" - which works out to 16 in-lb of force. The Carrier Actuators are rated for 10 in-lb of force, and the old Belimo actuators were rated for 133 in-lbs. So - the new Carrier actuators were 13 times weaker than the Belimo actuators, and half as strong as what I needed. What to do now..... 

The axles did not protrude from the other side of the duct, so I would have to come up with a solution on the actuator side of the axle. I checked out counterweights - some are available online, and the principle is that you have a weight on an arm that is fixed to the axle at a particular orientation - with the weight at a particular distance from the axle to balance the damper blade. I didn't have enough space to use a balance weight because I had ductwork above each actuator installation - I only had about 3" of clearance above the two horizontal duct actuators. 

I thought about using springs to assist with opening the actuator, to reduce the torque required. Luckily, I had a mixed kit of Power Fist extension and compression springs from another project. I realized that I could simply replace the short shaft lock screw with a longer lock screw - the screw thread is 5/16" diameter, and I had some 2" bolts in my hardware stores. 

Damper actuator assist first attempt - extension spring attached directly to 2" bolt

First I tried connecting an extension spring directly to the 2" bolt - however, very finicky to retain the other end, and I found that the spring yielded easily because of the relatively long travel of the head of the lever (2" lock bolt) compared to the relative short length of the extension spring (about 3" compressed). So, I selected some additional extension springs and cobbled together a spring assembly using zip ties. 

Prototyping an assist spring for the damper

I ran out to the local home improvement store, and found some 3" fully threaded 5/16 bolts to allow me to use a washer and nut to attach the spring assembly near the head of the lever bolt. 

2nd Try - 3" fully threaded lock bolt with spring assembly

Upgraded with small turnbuckle for Tension Adjustment

I was able to get these adjusted to reliably assist the opening and closing of the dampers. In my case, if the furnace fan was running - it greatly impacted the torque on the axle. I adjusted the dampers to reduce the opening and closing effort without the fan running, because I expected that the Damper Control module would only actuate the dampers at a reduced fan speed. I turned out to be correct. 

With damper actuators resolved, I moved onto installing the remote thermostats. You have the option of installing 2 wire thermocouples, or 4 wire communicating thermostats. I went with the thermostat option, which Carrier calls a "Smart Zone Temperature Sensor", Carrier part number SYSTXCCSMS01. Luckily, I had a 4 conductor cable already in the wall from a Legacy home automation system - so I just reused the existing cable. 

Smart Zone Temperature Sensor baseplate and 4 wire communicating cable connections

Smart Zone Temperature Sensor installed in the upstairs master bedroom

With the actuators and zone thermostats installed, it was now time for installation of the Zone Control module. Before undoing any connections, shut power off to the furnace, fan coil and thermopump, to ensure that the 24V control transformer is powered down. 

In my installation, I had a Carrier Network Interface Module installed to control my whole house air exchanger. This ended up greatly simplifying my installation, because all system cables already ran to a location just above my fan coil, so I didn't have to move any cables. 

Carrier Network Interface Module

As I removed the cables from the Network Interface module, I labelled each cable with 6mm Brother TZ tape, with clear heat shrink to protect the label. This provides a durable label that won't fall off or become illegible over time. Helps avoid errors during installation, and greatly assists the next guy that has to come along and maintain or modify the system. 

As I disconnected cables from the Network Interface Module, I labelled them

The new Zone Control module installed on the ductwork above the fan coil in place of the old Network interface module. I labelled all the new thermostat and damper actuator cables and brought them into the Damper Control module enclosure. Zip ties help keep the cabling neat. In my case - the master thermostat (what Carrier calls the "User Interface") connects here, as well as the 4 wire communication cable to the fan coil. 

Damper actuator cables connected to the terminals on the Damper Control module

Cabling complete - Thermostats, Damper Actuators, Air Exchanger

Once all the cabling is complete, double check all of your connections, and then reapply breaker power to the fan coil and thermopump, this powers up the 24V system transformer and powers up the User Interface (Master Thermostat) and the Zone Thermostats (Smart Zone Temperature Sensors).

The first thing you need to do is program the Smart Zone Temperature Sensors with the correct zone number. This is done at the Zone thermostat - because it is a communicating device and the commications cable connects to a common interface ABCD bus, and not a particular terminal on the control board. 

Program the zone number on the Smart Zone Temperature Sensors

With the zone sensors programmed, you then need to reset the installation at the User Interface. This will force the User Interface to query the Carrier communication bus and identify all connected components - the fan coil, the thermopump, the two smart zone temperature sensors, and the zone control board. 

Carrier User Interface queries the communications bus and identifies connected equipment

Carrier User Interface identifies the Zone Control Module, and 2 Additional Zone Thermostats

With all equipment identified, the system automatically starts a duct assessment, and checks the flowrate (duct sizing) of each zone.

Duct Assessment in Progress

When the duct assessment is complete, it displays the results. In my case, I have relatively high leakage and I later realized that the humidifier bypass duct is open - this will cause air recirculation that appears as a leak. I intend to redo the duct assessment with the humidifier bypass duct closed and see what effect this has. 

Results of duct assessment

Then - the setup process finishes, and you can now control all three zones independently from the user interface / main thermostat. You can control the remote zones using the Smart Zone Temperature sensors as well. This worked perfectly from initial startup, and I really like the new capability. 

System status - temperature control screen - shows setpoints and temperatures of all zones

System status - temperature control screen on the Carrier iPhone app - Same information

System has been running for 2 days now - I've programmed the the first floor where we have our bedrooms for cooler temperatures at night to promote better sleep, and the basement during daytime hours to be warmer for comfortable working temperature from home. I'll be fine tuning the programs going forward to optimize energy consumption. Stay tuned for an update once I have some operating experience and data.