Multi-zoning driven by true variable speed air conditioning. Is it finally here?

NeverDie

NeverDie

Senior Member
I  recently checked the Lennox and Trane websites, and both now appear to offer genuine variable speed centralized air conditioning (it looks as though Carrier still doesn't have it).  In terms of multi-zoning, that might be the sea change I've been waiting for.  Prior to now if you wanted fine grained zoning (where many if not most rooms are on their own zone) for central air, the options for getting it in the United States borrowed from commercial technology that was not within the mainstream for residential HVAC.  Previously, the closest substitute I could find would have been a custom chiller system.   However, if major vendors are now offering mainstream variable speed central air for residential, the whole thing should become a lot more affordable and easier to get reliably installed and repaired.  It would probably eliminate a lot of the custom control and zone automation that would have otherwise been required.  I'm excited about this.  I really doubt that even best efforts at "balancing" a conventional one or two stage compressor system would come anywhere close to either the comfort or performance of a multi-zoned variable speed system.  Has anyone else here given it a hard look?
 
[Note: I recently posted the above on another thread (http://cocoontech.com/forums/topic/27011-where-to-start-with-hvac/?p=218623 ) because of how it related to that thread, but it got immediately buried.  I think the topic is worthy of its own thread, so I moved it here.]
 
Frederick C. Wilt said:
What part is variable?
Click to expand...
The condenser (aka air conditioning compressor).  Previously, in the US nearly all residential condenser's were either single speed or two speed.  In the case of single speed, it's either all-on or all-off, and residential systems built around it often had a fixed fan speed blowing over the coil to keep it from freezing into a block of ice.  The problem with that, from a zoning point of view, was that when you turned off zones by closing dampers, the same volume of air as before had to be diverted elsewhere.  That, in turn, made it hard to put many zone dampers onto the system and to ever have most of them shut-off (e.g. to unoccupied rooms at night).
 
In contrast, with a variable speed condenser, you can reduce both condenser output and the speed of the coil fan as you turn-off zones or throttle zones.  The advantage: no short cycling (in theory leading to lower operating costs) and every thermostat zone gets just exactly cool as you want it to be all the time.
 
NeverDie said:
The condenser (aka air conditioning compressor).  Previously, in the US nearly all residential condenser's were either single speed or two speed.  In the case of single speed, it's either all-on or all-off, and residential systems built around it often had a fixed fan speed blowing over the coil to keep it from freezing into a block of ice.  The problem with that, from a zoning point of view, was that when you turned off zones by closing dampers, the same volume of air as before had to be diverted elsewhere.  That, in turn, made it hard to put many zone dampers onto the system and to ever have most of them shut-off (e.g. to unoccupied rooms at night).
 
In contrast, with a variable speed condenser, you can reduce both condenser output and the speed of the coil fan as you turn-off zones or throttle zones.  The advantage: no short cycling (in theory leading to lower operating costs) and every thermostat zone gets just exactly cool as you want it to be all the time.
Click to expand...
 
Thanks much for that information.
 
Having been through this I can tell you there are no easy answers, despite what the marketing materials for HVAC manufacturers might tell you. For an AC to be efficient, the cooling must be precisly balanced to he airflow. So foregetting fan speed for an instant, just making a variable speed compressor that is efficient at different speeds is impossible. Trane has a unit with two compressors for this reason. most other have two speeds. Anything more than that is taking too many comprimises that HVAC designers are not going to do.
 
The next problem is airflow, which certainly needs to vary with zonning. I installed my unit with three zones, which is the best compromise. At anytime one, two, or three zones could be running. So a three to one ratio. You don't want one zone running with lots of airflow, or three with very little. It required a large amount of duct work to get it all balanced out.
 
A third factor is control. Yes, the HVAC manufacturers make great systems with proprietory thermostats, but try to control those with a home automation system. Trying to balance all these things is a giant untertaking.
 
Most homes with plain old single zone HVAC systems with single speed compressors are perfectly comfortable inside.  In my home, even when I turn one zone completely off, and its 110 outside, those rooms are MAYBE one or two degrees higher than the others, so zoning in a correctly balanced home makes little difference.
 
So my advice is to not disregard basic HVAC design like home insulation, good duct layout, correct sizing and air balancing, and then just use the extra technology for just tweaking, if that. The zoning and variable speeds are NOT going to magically fix the other issues.
 
ano said:
Having been through this I can tell you there are no easy answers, despite what the marketing materials for HVAC manufacturers might tell you. For an AC to be efficient, the cooling must be precisly balanced to he airflow. So foregetting fan speed for an instant, just making a variable speed compressor that is efficient at different speeds is impossible. Trane has a unit with two compressors for this reason. most other have two speeds. Anything more than that is taking too many comprimises that HVAC designers are not going to do.
 
The next problem is airflow, which certainly needs to vary with zonning. I installed my unit with three zones, which is the best compromise. At anytime one, two, or three zones could be running. So a three to one ratio. You don't want one zone running with lots of airflow, or three with very little. It required a large amount of duct work to get it all balanced out.
 
A third factor is control. Yes, the HVAC manufacturers make great systems with proprietory thermostats, but try to control those with a home automation system. Trying to balance all these things is a giant untertaking.
 
Most homes with plain old single zone HVAC systems with single speed compressors are perfectly comfortable inside.  In my home, even when I turn one zone completely off, and its 110 outside, those rooms are MAYBE one or two degrees higher than the others, so zoning in a correctly balanced home makes little difference.
 
So my advice is to not disregard basic HVAC design like home insulation, good duct layout, correct sizing and air balancing, and then just use the extra technology for just tweaking, if that. The zoning and variable speeds are NOT going to magically fix the other issues.
Click to expand...
Thanks for your post.      
 
I hadn't realized that the thermostats being used in new systems would be proprietary and difficult to interface with home automation.  That seems very much counter to the current trend.  Are there any that do offer a good home automation interface?    
 
When I had my roofing redone, I was able to buy a 10 year performance guarantee from the product manufacturer (GAF) that only best practices (which were detailed in the guarantee) would be used by any one of its certified installers (listed on their website), and it covered 100% the material and labor costs of fixing it if there were ever any problems of any kind during the warranty period.  GAF even sent their own inspector to look at the work afterward.  Roofing is a notoriously shady business, but I've had absolutely zero problems with that roofing installation.  I wish there was a guarantee like that for HVAC as a way to cost-effectively address concerns about the potential for improper design and installation.  It does seem that some kind of third party oversight would be beneficial, and I'm quite sure city building permit inspectors (at least the ones here) are inadequate for cross-checking an HVAC installation.
 
NeverDie said:
Fantastic!  What sort of config do you have (e.g. how many thermostat zones per condenser)?  Is it the cat's meow, or are there parts you wished behaved differently?
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We've got 3 zones on 1 condenser. I love this system, no complaints at all. The only weird thing is that it does a duct as assessment once a day at 1 PM. It takes about 3 minutes and at times ramps the fan to the max which is somewhat noisy. The rest of the time the fan and compressor just loaf along and are unnoticeable. We've got a humidifier and HRV connected and thus the air handler fan runs quite a bit, although very slowly. 
 
There are some zone controllers out there that can be connected to home automation thermostats, like an OmniStat2, for example, but there are considerations.  For example Honeywell makes several zone controllers that can support a two-stage HVAC unit, and it offers many ways to select the stage, but none are perfect.  For example, maybe one zone calling would be stage 1 and two or more zones are stage 2. Not perfect, but O.K. This will cause stage 2 quite often.  Or maybe ANY thermostat calling for stage 2 will cause stage 2 for the HVAC unit. Or maybe stage 2 is called after the AC runs for a certain period.  None of these are perfect.
 
Trane, and most others now have zone controllers with proprietary thermostats that can fine-tune things better, but these can't be controlled.
 
One of my systems is a three zone, controlled with a Honeywell zone controller and OmniStat2 thermostats.  I had to do some programming to make it more efficient, like for example, when ALL three thermostats are not calling for cooling or heating, I turn off all the thermostats for 12 minutes. If I don't, the main HVAC unit may turn off and on too often because each thermostat would otherwise be independant of the other, and if one is calling for AC, and another ALMOST is, then you need a way to sync these. This works pretty good. If you don't sync these, your main AC unit might be on all the time, but just for one zone. Say zone 1 then zone 2 then zone 3. This would be teribly inefficient. You want to have all zone on at once, when you can.
 
There is a duct damper out there that rather than fully closing and opening, it goes from 50% to 100%. This means that all zones are open at least 50% all the time, reducing backpressure. Then if more AC/HEAT is needed, it goes to 100%. So you might have one zone open 100% and two at 50%.  If I had to do it again, I would get these. They would reduce many of the problems of zoned systems.
 
ano said:
There are some zone controllers out there that can be connected to home automation thermostats, like an OmniStat2, for example, but there are considerations.  For example Honeywell makes several zone controllers that can support a two-stage HVAC unit, and it offers many ways to select the stage, but none are perfect.  For example, maybe one zone calling would be stage 1 and two or more zones are stage 2. Not perfect, but O.K. This will cause stage 2 quite often.  Or maybe ANY thermostat calling for stage 2 will cause stage 2 for the HVAC unit. Or maybe stage 2 is called after the AC runs for a certain period.  None of these are perfect.
 
Trane, and most others now have zone controllers with proprietary thermostats that can fine-tune things better, but these can't be controlled.
 
One of my systems is a three zone, controlled with a Honeywell zone controller and OmniStat2 thermostats.  I had to do some programming to make it more efficient, like for example, when ALL three thermostats are not calling for cooling or heating, I turn off all the thermostats for 12 minutes. If I don't, the main HVAC unit may turn off and on too often because each thermostat would otherwise be independant of the other, and if one is calling for AC, and another ALMOST is, then you need a way to sync these. This works pretty good. If you don't sync these, your main AC unit might be on all the time, but just for one zone. Say zone 1 then zone 2 then zone 3. This would be teribly inefficient. You want to have all zone on at once, when you can.
 
There is a duct damper out there that rather than fully closing and opening, it goes from 50% to 100%. This means that all zones are open at least 50% all the time, reducing backpressure. Then if more AC/HEAT is needed, it goes to 100%. So you might have one zone open 100% and two at 50%.  If I had to do it again, I would get these. They would reduce many of the problems of zoned systems.
Click to expand...
Thanks for the good info.  The 50% damper does sound like a good idea, especially for one or two stage systems.  Do you recollect who makes it?
 
When I last looked into this, years ago, I found some motorized iris dampers.  They could be set to any percentage you want.  IIRC, they were priced around $100 each, so definitely more than the open/shut type, but not really excessive compared to the overall installed system cost.  I seem to recall they had fixed open/close stop-points that you manually set, but perhaps now there are ways to  vary the iris diameter using the motor to whatever you want whenever you want it.
 
With a chiller system, there isn't the risk of the coil freezing over, so you have more latitude over fan speed.  IIRC, the fan speed on a chiller system ramps up/down to achieve a target static pressure to conform to however the dampers are set.  There's a simple elegance to that approach that would give a lot of freedom over how the dampers are set.  Then, to supply cooler/less-cool air, the system ramps up/down the pump speed on the chilled water circulating between the coil and the outdoor chiller, which is variable capacity and would self-adjust to maintain the chilled water at a particular setpoint.  I would think something analogous could be done with a variable speed condenser, except perhaps there would be temperature sensors on the coil and/or the air stream after the coil that would govern whether the condenser speed ramps up or down.  Therefore, I was hoping a variable speed condenser system would be a perfect substitute for a chiller system.  However, I'm not sure if that's true or not.  Anyone know?   I think I'd be very happy with a chiller system, except that it's unconventional for a residence and not easily sourced, and there wouldn't be much of a go-to list when it comes to repairs.
 
I also have the heatpump linked in post #3 above, paired with a 98% efficient variable-speed furnace serving two zones. This zoned system actually replaced two indentical HVAC systems that my house came with, each with a 100K BTU furnace and a 3 ton AC condenser. Since there was no communication between them, you could set one to heat, and another to cool and watch your money burn away...
It is typical in the HVAC industry to oversize, "just in case..." but this will always be cause of problems.
 
Technically there is only one thermostat, but each zone has temp sensors. There are actually temperature sensors in each of the bedrooms that are averaged by the thermostat for that zone. I also have a serial interface that is hooked to Elk for basic control. One could build very sofisticated algorithms to manage the temperature, but tracking the power/energy use, lead me to the conclusion that drastic set backs are actually not saving money. Of course I am not talking about the week long vacation, but on a daily basis. Both my furnace and heat-pump (for now electricity is much more expensive, so heat pump does not see lot of use for heating) are variable that modulate dynamically their output between 40% and 100% of capacity. The air handler (built into the furnace) has an infinitely variable speed ranging from 0 CFM to 2200 CFM. This keeps us very comfortable, and much more economical than what I had before.
 
I am not fond of proprietary solutions, but in few cases, (this being one) a purposefully engineered solution that just works as expected together, while giving you a serial port to change things if needed is OK for me.
 
lleo said:
I also have the heatpump linked in post #3 above, paired with a 98% efficient variable-speed furnace serving two zones. This zoned system actually replaced two indentical HVAC systems that my house came with, each with a 100K BTU furnace and a 3 ton AC condenser. Since there was no communication between them, you could set one to heat, and another to cool and watch your money burn away...
It is typical in the HVAC industry to oversize, "just in case..." but this will always be cause of problems.
Click to expand...
Carrier was the one company that did have a system that can be controlled by a home automation system (with the addition of an $800 box). This can be controlled by HAI controllers as well, but last I heard, the interface has been discontinued, and new HVAC units no longer support it.  I looked into it last year when I was shopping for a system.
 
By the way, Honeywell zone controllers can heat and cool at nearly the same time as well. One zone can call for heat, and when that is done, another can call for AC, and the HVAC unit will go back and forth. No way to shut off that ability as far as I have seen.
 
lleo said:
lleo, on 02 Sept 2014 - 14:25, said:
lleo, on 02 Sept 2014 - 14:25, said:
I also have the heatpump linked in post #3 above, paired with a 98% efficient variable-speed furnace serving two zones. This zoned system actually replaced two indentical HVAC systems that my house came with, each with a 100K BTU furnace and a 3 ton AC condenser. Since there was no communication between them, you could set one to heat, and another to cool and watch your money burn away...
It is typical in the HVAC industry to oversize, "just in case..." but this will always be cause of problems.

Technically there is only one thermostat, but each zone has temp sensors. There are actually temperature sensors in each of the bedrooms that are averaged by the thermostat for that zone. I also have a serial interface that is hooked to Elk for basic control. One could build very sofisticated algorithms to manage the temperature, but tracking the power/energy use, lead me to the conclusion that drastic set backs are actually not saving money. Of course I am not talking about the week long vacation, but on a daily basis. Both my furnace and heat-pump (for now electricity is much more expensive, so heat pump does not see lot of use for heating) are variable that modulate dynamically their output between 40% and 100% of capacity. The air handler (built into the furnace) has an infinitely variable speed ranging from 0 CFM to 2200 CFM. This keeps us very comfortable, and much more economical than what I had before.

I am not fond of proprietary solutions, but in few cases, (this being one) a purposefully engineered solution that just works as expected together, while giving you a serial port to change things if needed is OK for me.
Click to expand...
I hadn't realized the adjustable operating range of the Carrier heat pump was 40%-100%, not 0%-100%. Given the 40% minimum, I suppose that to easily add a lot more zones than two it might require making all the dampers be of the type that close 50%, as mentioned above.
 
Maytag has IQZone to facilitate zoning. Maytag says that adding IQZone to its 25.5SEER IQDrive airconditioner will yield up to an additional 12% in energy savings (http://www.maytaghvac.com/Maytag-iQ-Zone-p/iq_zone.htm). However, no less significant, is that the IQZone zoning allows the creation of up to 8 different comfort zones per air conditioner. At least on paper, that sounds like a big improvement over the quotes I got from the major brands (including Maytag) 5 years ago, where the most any of them could offer was 4 zones per air conditioner. It appears that the current variable speed Lennox air conditioner also supports only 4 zones, not 8, or so I infer from the current Lennox brochure (http://www.lennox.com/pdfs/brochures/Lennox_iHarmony_Zoning_System.pdf) and website.    

The 26.00 SEER Lennox XC25 air conditioner has a  35%-100% operating range, supporting 1% increments in-between.  The 25.5 SEER Maytag PSA4BI iQ Drive claims to modulate betwee 40%-118% of capacity (according tohttp://www.maytaghvac.com/Maytag-iQ-Drive-Air-Conditioner-p/psa4bi.htm) .  Presently I'm unclear as to what Maytag means by modulating at greater than 100% capacity.   Is it code for 22%-100%?  Assuming 40% is the real minimum, I'm not sure how Maytag manages to offer up to 8 zones when competitors with similar minimums offer only up to 4 zones.  I would have thought that 8 zones would imply a modulating range more like 0%-100%, so what kind of compromises does the 40% minimum imply?  Perhaps the 8 zones are more for tweaking, as suggested by ano above, using "fully modulating dampers", which is the type that  Carrier uses in its commercial 8 zone installs: http://www.commercial.carrier.com/wcs/proddesc_display/0,,CLI1_DIV41_ETI4926_PRD676,00.html
 
I notice that back in January Trane announced a 27.5 SEER variable speed air conditioner, the XV-S (http://www.achrnews.com/articles/125609-thursday-jan-23-2014-trane-introduces-ultra-high-efficiency-variable-speed-system).  That's quite a performance jump over it's existing 21 SEER XV20i.  Unfortunately, so far it's vaporware, as I don't yet see it being offered as an actual product on the Trane website.  The article says that "S" in SV-S  stands for Scability.  What's being scaled?  Is it a greater than 5 ton condenser?  As to home automation integration, it looks as though Trane has opted for Nexia solutions (wi-fi or z-wave):  http://www.trane.com/residential/en/products/thermostats-and-controls/connected-controls.html  Previously I was able to interface my z-wave to some Nexia products as ordinary z-wave (without a Nexia subscription), so maybe there's hope.
 
Anything else in the pipeline? 
 
You don't use modulating dampers, you use VAV boxes. The only variable is the equipment on the other end of the duct. How the boxes are controled is a simple item, but does require balancing and should have a somewhat smart head end to take advantage of knowing the flow and position of the VAV percentage, as well as the temperature of incoming and outgoing air.
 
It's how it's done in the real controls world outside of the erector sets that everyone seems to want in their houses. If you do it right, it's the cat's meow, but people get hung up on the bottom dollar sticker vs. effeciency and control.
 
Once you get away from the basic embedded dumb circuit boards that all HVAC guys seem to want to mount on their ductwork or AH it's a different world.
 
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