Options for hydronic air handler control: properly coordinate ECM blower motor and variable-speed condenser compressor
First post. Not sure if this is best in Mechanicals or Energy Efficiency. Please move as you see fit.
High level: Replacing condenser unit and air conditioner coil. Since the work is being done, now is the time to upgrade the air handler mechanicals and controls as well. I need help understanding options for properly coordinating an ECM infinitely variable blower motor with a multi-stage/variable speed condenser compressor. And this needs to work with my hydronic heat too (currently air, but will be adding radiant at some point).
Details: Current system is comprised of a modulating condenser boiler (Buderus GB142-60) with a closed loop to an indirect water heater for domestic hot water. The home heating utilizes the remnants of an older all-in-one system air handler with a heating coil, and the original control board for that system (Lennox CompleteHeat AM30). The A coil sits above this air handler. The blower motor is capable of multiple speeds, but I believe when the system was retrofitted to work with the new boiler, it was reduced to single speed duty.
There are 3 zones, managed by mechanical duct zone dampers. Technically, there is a 4th, AC-only zone in the house, but that is managed independently (a smaller AC unit and air handler in the attic to cool an upstairs easier). As mentioned above, I do intend to add infloor radiant in the future. This might end up being a mix of under existing floors and in a concrete slab in newly renovated areas. Due to unknowns/variables of the future, the number future of radiant zones is also an unknown. If I had to guess, I would say anywhere from 2 to 6 radiant zones. The radiant zones don’t necessarily need to be managed by the same controller system.
The old AC uses R22. The new will obviously use R-410a and require a new A coil. The air handler has a number of water pipes in front of the part of the plenum with the A coil, which will increase labor on swapping out the A coil.
Since all this work is being put into a new AC system, I’ve decided the time is right to upgrade the hydronic air handler system at the same time. I’m looking at all components and looking at options to take advantage of the current technology out there. Specifically, I’d like to go with a variable speed ECM blower motor and a variable or 2-stage AC condenser unit. I realize ROI might be weak on some of these systems, but I’m looking more at the comfort factor.
Where I am struggling is in a control board that will drive an infinitely variable ECM blower motor in support of the mod-con boiler to a hydronic heat coil, as well as interfacing properly with a variable speed condenser compressor. In a perfect world, this would be a third party control board so that I’m not locked into a particular vendor’s system. It would just be a normal, 24 volt system and I’d be free to mix and match other, third party thermostats.
What I seem to be finding is that when the vendors went to variable speed (more than 2 speed) condensers, they decided to lock customers into their electronics, forcing control board and thermostats to be from the same vendor as the condenser. From the little research I’ve done, it seems that using 3rd party thermostats with these systems, for example, reduces a variable stage condenser to use only 2 stages and may limit other benefits of the system. At that point, it makes no sense to buy a variable speed unit if it is going to be restricted to 2 stages.
Side note: I’m sure some people would decide to not buy the variable speed condenser because of this. I sure hope the vendors reconsider the path they are taking.
One last question I have regards infinitely variable speed ECM blower motors. I say “infinitely variable,” because it appears the term “variable” usually means a fixed number of speeds (much the way variable for compressors does). The motors may be capable of infinite speed adjustments, but they are being restricted to set speeds. In such a use case, will the ECM motors still independently adjust to air pressure variations, or will they be forced to stay at the speed set by the control board?
Products: Here is a list of products I’ve jotted down. I have no loyalty to any brand. I will say that due to problems with the Lennox product, I probably won’t be buying more from them. That doesn’t mean that they don’t have good systems, but I’m still not doing it. 🙂
- Variable speed Bryant (189BNV)
- Variable speed Carrier (24VNA9)
- 2 stage Goodman (DSXC18)
Hydronic air handler products:
- Ecologix (EZT – Zone Comfort Tall System)
- First Company (possibly model VMB-277 Series (Variable Speed), but their website is confusing)
- Summeraire (TC3550E)
- Lennox CBWMV — as noted above, there would have to be a darn good reason to go with it
3rd party controller products:
- Tekmar (tN2 House Control 402)
- Aprilaire (Aprilaire Model 6504 Zoned Temperature Control)
- Honeywell (model??)
I’m assuming the boiler can’t be dynamically adjusted by the system and that I’ll simply be adjusting the temperature that it will hold (for house heat) and relying on the modulation of the blower air speed and duration to account for higher or lower demand. If there is a product that dynamically/magically adjusts this particular boiler (GB142), I’m all ears.
Although I listed hydronic air handler products and 3rd party controllers, I don’t really know if they will accomplish my goal of properly integrating components in this system.
I appreciate any help people can provide!
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