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

DELInstallations said:
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.
Click to expand...
Thanks for your post.  I'm interested.  Who is offering that on residential installs?
 
In addition to Maytag, I notice that Carrier also offers 8-zone systems on their residential infinity lineup (http://www.carrier.com/homecomfort/en/us/products/controls-and-thermostats/)
 
Looks as though the use of variable speed has also yielded a big performance improvement in geothermal air conditioning:
 
GHP-Efficiency14.png

 
To go with it, the Waterfurnance 7 series also now offers up to 6 zones of zoning.
 
I've never looked into geothermal before, but the above performance numbers look quite impressive.  Also, I've read that if one is installed before 2016, there is a 30% federal tax credit on the total cost.  If all that's true, then Wow!  I have no idea what it costs, but I should probably get a quote....
 
I also went down the road you are charting here...
Surely, ground source heat-pumps, AKA geothermal systems are the most efficient. But they are pricey. Where I live on a rocky hill, the quote to replace my two old airsource heatpumps was $65K (5 wells drilled in hard rock and related systems). And I have a large, but single story home, with full basement and all duct work run in conditioned space, very accessible, and plenty of space to spare.
 
Word of advice: don't fall for marketing numbers, and make sure you understand the differences and difficulties of converting between SEER / EER / COP and the remainder of the alphabet soup. Most of these numbers are derived in controlled conditions with a like a 2' worth of duct work.
 
For example my Carrier Infinity air-source heat-pump has a COP of 3.9, i.e. for every 1000W used it is putting out 3,900W worth of heat. But even at this efficiency it pales to natural gas, where to produce 1M BTU with the heat-pump cost almost twice more versus burning natural gas to get 1M BTU.
In the end this help not a iota the enviroment and while might be saving some energy(money) for you, as you may be efficient but electricity is still generated by burning non-renewable fuel.
 
So I concluded that unless I had a sufficiently large solar system to produce free electricity and even store the excess for dark hours, my money is better spent to improve insulation and tightness in my home. I still replaced my old HVAC systems with a zoned system and even paid extra to have a heat-pump, just in case I get access to real renewable energy one day.
 
Another topic: The number of zones and range of operating capacity are less important. The zones were invented to keep an HVAC system in the 'sweet zone' i.e. where they are the most efficient, and this is NOT 0-100%. For most, this is in the 50-60% range. Your pursuit of a 0-100 percent range will have to trade efficiency.
 
There are requirements, such as when you want to keep the temperature variation within 0.1 and 0.5 degrees, where you will need a 0-100% modulating control, but in this case you are not concerned of efficiency, all you care is to keep the temp.
 
As I alluded in my earlier post, as long as the temperature is below about 90, I end up using less energy over a day keeping my home at 75, which means that my system hums along at 40% capacity during the day, with few spikes in the afternoon, versus doing a setback of 80 or even 85 during the day (i.e. 9AM-5PM) and do a recovery from 2-5PM (during which the AC runs at 100%) to reach 75 at 5PM. Your house where it is may be different. We had a very nice summer and I have not used more than 1200 KW/month (4BR+pool) with my 'gadget' budget in standby is 300W 24/7/365. While I think in my research circles this energy use is low, and is perhaps nothing remarkable compared to other (please do not take this comment as flaimbait to start who uses less...) I also know people in other parts of the world, where their monthly electric energy budget is 100-150KW.
 
So yes, energy efficiency is good, but always consider the cost and gain.
 
I think you mentioned, but Carrier Infinity can handle 8 zones on a single system, and the network interface with serial and IP access I have can handle 4 systems, each with 8 zones, and up to 4 remote temperature sensors averaged per zone. That translates to 32 zones with 128 temperature sensors. I cannot imagine such a house. One more thing, in new construction, one can do complete heat and energy recovery and recirculation, where your fridge, cooking and A/C may be heating your hot water, and in cooler months you could tap in your hot water for your minimal heating need a super-tight house may need. Edit: forgot to add the energy recovery in the sewer line, so that while you shower you also heat water or your home...
 
lleo said:
I also went down the road you are charting here....
Click to expand...
EXACTLY!!!  You have said exactly what I was thinking....
 
Instead of comparing the marketing hype of one system against the other, or looking at efficiencies you never see in the real world, I would start thinking about the payback period.  If a more efficient system takes 150 years to cover the cost of its added efficiency, than that doesn't sound like a great deal to me, PLUS the super efficient systems also tend to break down more often, and the parts can be more expensive.  The only one that gains from most of this is the manufacturer, not the home owner.
 
And also let me say a bit about zones. I never had a zoned system until recently, but since I live in AZ where the sun heat load can be high, I thought it would solve the problems I had with some rooms being too hot.  Most of the HVAC people i spoke with disagreed and said a properly sized and ducted system shouldn't need zoning.
 
So in the end I got the zoned system I wanted, with a variable speed HVAC unit, but I know acknowledge that on the zoning question, I was probably wrong and the HVAC people were probably correct.  I can now see that even with a zone (1/3 of my house) closed, the house stays 1 degree in all rooms, even in the section with the zone OFF.  The reality was the fan of my original HVAC system probably wasn't large enough and some of the ducting needed replacement.  The zoning was not only not required, but can make the HVAC work harder because it may have to squeeze air through less ducts.
 
Lets say you run each zone round-robin and are running your HVAC unit at 33% capacity vs. running all zones together and running the HVAC unit at 100% capacity.  The second system would be SO MUCH more energy efficient than the first. 
 
If you claim that a given HVAC system can run at 30% or 50%, then ask them what their efficiency is at that level?  I can guarantee, its VERY BAD and the 20 SEER system you bought is running at 7 SEER instead.
 
I just realized that I did not address a point was raised/discussed in earlier posts.
As I mentioned that the capacity limits are imposed for efficiency reasons, but these are paired with a certain CFM airflow., as ano had mentioned.
My condenser is 5 tons (the largest in carrier infinity and likely not the one used to establish the 20.0 SEER efficiency.
When is running at 40% is a 2 ton condenser, and needs about 830 CFM air to not freeze over.
So each and everyone of your zones should be able to take at least this much air, otherwise you will loose efficiency or create discomfort due to duct noise or even damage equipment. In my case I combined two existing systems into one, so the duct works in place were designed to take about 1000 CFM each, and the max CFM capacity of the new air handler is 2200 CFM
the 1% capacity of my system would 0.05 tons, which prorated from the 2 ton air need is about 24 CFM.
In a residential setting, I think such an about of airflow (at least in existing old construction) is worth a few recessed lights and the installed outlets. So there is never a need to go to 1%...
And at that range the unit is not efficient at all...
 
ano said:
The zoning was not only not required, but can make the HVAC work harder because it may have to squeeze air through less ducts.
Click to expand...
I would hope that's not how it works with the zoning that gets installed in a variable speed system, although with a 40% minimum, I suppose it could still happen if too many of the ducts were all closed at once.  If I abandon the notion that zoning will save any money but instead merely do dynamic balancing for greater comfort as heat loads vary throughout the day, then perhaps it would be easier to avoid closing too many zone dampers at once. If it turns out that too many dampers would need to be closed at once to adequately balance the load, then that would prove your earlier point that more insulation (at least in the chronically overheated areas) is needed.
 
I wish there were some simple computer simulations that would allow different scenarios to be compared.  Has anyone here found software that they like for that purpose?
 
lleo said:
lleo, on 05 Sept 2014 - 18:29, said:
I also went down the road you are charting here...
Surely, ground source heat-pumps, AKA geothermal systems are the most efficient. But they are pricey. Where I live on a rocky hill, the quote to replace my two old airsource heatpumps was $65K (5 wells drilled in hard rock and related systems). And I have a large, but single story home, with full basement and all duct work run in conditioned space, very accessible, and plenty of space to spare.

Word of advice: don't fall for marketing numbers, and make sure you understand the differences and difficulties of converting between SEER / EER / COP and the remainder of the alphabet soup. Most of these numbers are derived in controlled conditions with a like a 2' worth of duct work.

For example my Carrier Infinity air-source heat-pump has a COP of 3.9, i.e. for every 1000W used it is putting out 3,900W worth of heat. But even at this efficiency it pales to natural gas, where to produce 1M BTU with the heat-pump cost almost twice more versus burning natural gas to get 1M BTU.
In the end this help not a iota the enviroment and while might be saving some energy(money) for you, as you may be efficient but electricity is still generated by burning non-renewable fuel.

So I concluded that unless I had a sufficiently large solar system to produce free electricity and even store the excess for dark hours, my money is better spent to improve insulation and tightness in my home. I still replaced my old HVAC systems with a zoned system and even paid extra to have a heat-pump, just in case I get access to real renewable energy one day.

Another topic: The number of zones and range of operating capacity are less important. The zones were invented to keep an HVAC system in the 'sweet zone' i.e. where they are the most efficient, and this is NOT 0-100%. For most, this is in the 50-60% range. Your pursuit of a 0-100 percent range will have to trade efficiency.

There are requirements, such as when you want to keep the temperature variation within 0.1 and 0.5 degrees, where you will need a 0-100% modulating control, but in this case you are not concerned of efficiency, all you care is to keep the temp.

As I alluded in my earlier post, as long as the temperature is below about 90, I end up using less energy over a day keeping my home at 75, which means that my system hums along at 40% capacity during the day, with few spikes in the afternoon, versus doing a setback of 80 or even 85 during the day (i.e. 9AM-5PM) and do a recovery from 2-5PM (during which the AC runs at 100%) to reach 75 at 5PM. Your house where it is may be different. We had a very nice summer and I have not used more than 1200 KW/month (4BR+pool) with my 'gadget' budget in standby is 300W 24/7/365. While I think in my research circles this energy use is low, and is perhaps nothing remarkable compared to other (please do not take this comment as flaimbait to start who uses less...) I also know people in other parts of the world, where their monthly electric energy budget is 100-150KW.

So yes, energy efficiency is good, but always consider the cost and gain.

I think you mentioned, but Carrier Infinity can handle 8 zones on a single system, and the network interface with serial and IP access I have can handle 4 systems, each with 8 zones, and up to 4 remote temperature sensors averaged per zone. That translates to 32 zones with 128 temperature sensors. I cannot imagine such a house. One more thing, in new construction, one can do complete heat and energy recovery and recirculation, where your fridge, cooking and A/C may be heating your hot water, and in cooler months you could tap in your hot water for your minimal heating need a super-tight house may need. Edit: forgot to add the energy recovery in the sewer line, so that while you shower you also heat water or your home...
Click to expand...
Thanks for your great post. A lot of good info. You're right, I should find out what the efficiencies are at different speeds.

The experiment you did about running at 40% throughout the day versus doing the setback to 80 or 85 had a very interesting result. Most people, including me, would have guessed the opposite would be true, but then again most people (including me) haven't taken the initiative to discover the true facts like you have.
 
Anyhow, it illustrates that intuitions will only go so far when a lot of variables are in play, and a quantitative analysis would be better.  If I could find some kind of impartial HVAC engineer to model my house and do a blank page design as to what's best and most cost effective based on the actual particulars, I think it would be money well spent.  Based on previous interactions, I don't think I can rely on HVAC vendors alone for objective/accurate advice, and I'd prefer to have someone independent, competent, unbiased, and trustworthy who can specify a proper installation and later cross-check it for correctness.  But where to find such a person?  And how do I cross-check his work?  This is the part that typically gets insufficient attention, and yet it probably has the greatest impact.  How did you guys do it?  Engineer, self-design, or rely on vendor reputation (as best you can discern it by referral and/or reference checking)?
 
Here in AZ, in order to get a rebate from the utility, contractors have to do full sizing calculations from scratch. This involves measuring the sq. ft. X ceiling height, the window opening sizes, attic insulation, and a few other parameters. They enter it in their program and out pops your AC size. I had three contractors independently calculate this, and they each came out pretty close to my current AC units sizes, +/- 0.5 ton.

The capacity of n AC unit has nothing to do with the efficiency. If you need a 5 ton and a 4 ton units, that is true no matter the efficiency. And I don't know about other places, but here the calculations are based on a outside temp. maximum of 110. I can tell you, we often get higher than that.
 
@ Never,
 
A good, well rounded HVAC contractor that also installs and understands controls, not a hang and bang specialist. Usually not going to be the guys doing a 3K house in a subdevelopment.
 
I invested in some literature to understand basics, and got a time-limited version of a professional heat-load calculation program. I calculated my heat loads using multiple different environmental parameters to understand how the extremes affect sizing.
Than started calling in contractors. The ones that just eyeballed what I had and recommended a replacement were dismissed. In the end 2 guys spent the time and did proper calculations themselves. I chose the one who was more comfortable merging my oversized systems into one. The two contractor heat load calculations and the one I made for same conditions were within +/-5000 BTUs of each other.
Retrofit situations are even trickier as they will have to work with existing ducts. One contractor wanted to replace all my ducts if I insisted to merge my systems. Both contractors on my shortlist refused to do duct flow analysis to really know what my ducts were capable of. The guy I finally chose did measure the ducts and said that they will work. He was right.
Edit: forgot to add that if you do not want trust your contractor with the sizing/calculations, there companies that only do the sizing/calculations, and they have no vested interest in recommending any system/manufacturer over another.
 
lleo said:
I invested in some literature to understand basics, and got a time-limited version of a professional heat-load calculation program. I calculated my heat loads using multiple different environmental parameters to understand how the extremes affect sizing. Than started calling in contractors. The ones that just eyeballed what I had and recommended a replacement were dismissed. In the end 2 guys spent the time and did proper calculations themselves. I chose the one who was more comfortable merging my oversized systems into one. The two contractor heat load calculations and the one I made for same conditions were within +/-5000 BTUs of each other. Retrofit situations are even trickier as they will have to work with existing ducts. One contractor wanted to replace all my ducts if I insisted to merge my systems. Both contractors on my shortlist refused to do duct flow analysis to really know what my ducts were capable of. The guy I finally chose did measure the ducts and said that they will work. He was right. Edit: forgot to add that if you do not want trust your contractor with the sizing/calculations, there companies that only do the sizing/calculations, and they have no vested interest in recommending any system/manufacturer over another.
Click to expand...
Awesome.  Which program did you end up using?  As part of a remodel I previously built a exacting model of my house using ChiefArchitect, and the marketing videos made the process look a lot easier and faster than it actually was.  Alas that program is only good for visualization and drafting.  What a pity it can't do HVAC calcs, as all the geometry is already entered.  If there's an HVAC program that can leverage Sketchup, I might opt for that.
 
I sure do wish I had kept all my z-wave log data.  Then I could have zeroed in on the peak loads of the hottest days in the past and seen what percentage of the time my existing condensers had been running, and from that I might have quickly inferred an upper bound on the tonnage needed.
 
I was lucky that my ductwork included dedicated returns from each bedroom and from most areas, and returns were sized to match the supply trunks.
Also all my ductwork runs in the basement, easily accessible.
The Carrier system does evaluate each zone's capacity everyday and adjust limits as needed. Also does not need or work with bypass dampers to compensate for too small zones
 
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