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  1. #1

    Harmony III zoning retrofit

    Hi guys,

    I am looking to get retrofit zoning done on my system but wanted to check that it is actually possible since I have read that the AC must be dual stage for more than two zones.

    I would like to add 3 zones to our home, basement (2000 sq ft), main level (2000 sq ft) and loft (800 sq ft). The furnace is a Lennox G61MPV. I had a contractor at but he gave no details as to his plans and I am hesitant as its not supposed to work? He may be looking at using a different zoning panel, but I would like to get Lennox since our entire system is Lennox.

    The furnace is 5 ton but the key is that the AC is 2.5 ton. So I am wondering if it will be able to work almost like a two stage AC in this case, since its 50% the BTU of a 5 ton unit, which is what the home is designed for and what is used for heat/blower. The AC is an XC13-030.

    Does anyone know if its doable on a system like this? Perhaps the Staging could control just the fan? But the output would stick at a 2.5 ton and still be like the AC is running in first stage?

    Hope I dont need a new AC for this (

  2. #2
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    the control panel will work for what you want it to do and the blower can be staged for zones that are calling. just make sure the ducts to that loft area are large enough, might want to have a dump supply into the main floor off the loft zone.

  3. #3
    Quote Originally Posted by t527ed View Post
    the control panel will work for what you want it to do and the blower can be staged for zones that are calling. just make sure the ducts to that loft area are large enough, might want to have a dump supply into the main floor off the loft zone.
    We have four 6" ducts going up there. Do you think that's enough? Or do you think we still need a dump zone? I'm not sure how low the fan speed can run with the 2.5 ton single stage AC unit.

  4. #4
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    Quote Originally Posted by Lupinglade View Post
    We have four 6" ducts going up there. Do you think that's enough? Or do you think we still need a dump zone? I'm not sure how low the fan speed can run with the 2.5 ton single stage AC unit.
    Harmony III panel does not know/care what size the outdoor unit. What it does need is the setting for the CFM per zone.
    The minimum CFM for the 5 tons G61MV furnace is about 460 CFM.

    SO make sure the smallest zone is NO less than 500 CFM

    As for A/C and heating, it monitor its supplying air temperature and it will staging up/down/OFF the A/C or furnace.
    Last edited by just_opinion; 08-25-2012 at 01:56 PM.

  5. #5
    Thanks! Glad we can do it with the current AC. If the four 6" ducts to the loft are not enough is it possible to make the great room dampers open for both the loft zone and the main level zone? Since the air space is shared anyway.

  6. #6
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    Let me get this straight. You've got a furnace with a 5-ton blower for a 2.5-ton cooling system? Is that correct?

    The first thing that needs to be done is a real load analysis, IMO. Somebody screwed up somewhere when either the furnace or the AC was chosen. If the 5-ton blower can be reduced in capacity enough to accommodate the 2.5-ton cooling system then okay but generally that's not the case.

    All that said, any zone control system can be installed, provided the company doing the job knows how to properly design and install a zone control system. When zoning with anything but one zone on a single piece of equipment, there are basics and advance consideration. The basic is that the smallest zone should be able handle a minimum of 25% of the total load. The advanced consideration is what to do with the other 55% airflow that will need to go somewhere other than the smallest zone with it's calling. (55% + 25% = 80%, which is normally the minimum airflow the cooling coil will allow without icing.) The technical term for that decision is called the static relief strategy. Very few companies can actually properly do the design so I'd shop very carefully.

    As an aside, a properly designed and installed system should normally be quite comfortable without zone controls. Zones are generally indicated for rooms have a lot of glass or otherwise have a larger heat gain or loss than other rooms in the house.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  7. #7
    Quote Originally Posted by skippedover View Post
    Let me get this straight. You've got a furnace with a 5-ton blower for a 2.5-ton cooling system? Is that correct?
    That's correct. I think the AC is undersized for better dehumidification and energy savings (longer run times). We're right on the shore of Georgian Bay. We also have somewhat cold winters, so the larger heating capacity might make more sense. The furnace is 110BTU, 5 ton.


    The first thing that needs to be done is a real load analysis, IMO. Somebody screwed up somewhere when either the furnace or the AC was chosen. If the 5-ton blower can be reduced in capacity enough to accommodate the 2.5-ton cooling system then okay but generally that's not the case.
    The company that installed the equipment are professional and it seems like they knew what they were doing. And the furnace is capable of running at many different speeds from 1000-2000 cfm for cooling, or with Harmony III it can go as low as 460 as just_opinion stated. It does seem to work pretty well. The only issue is that the basement is half underground and does not have the large windows the upstairs has, so it is always much cooler. The main level has a great room with a very large window wall, so it is much hotter. And the loft is open to that great room, so all the heat goes up and its further even hotter. The system is holdings temperatures within about 6-8F per floor, give or take depending on weather, sun, etc. The goal is to lower the difference using the zoning system.

    All that said, any zone control system can be installed, provided the company doing the job knows how to properly design and install a zone control system. When zoning with anything but one zone on a single piece of equipment, there are basics and advance consideration. The basic is that the smallest zone should be able handle a minimum of 25% of the total load. The advanced consideration is what to do with the other 55% airflow that will need to go somewhere other than the smallest zone with it's calling. (55% + 25% = 80%, which is normally the minimum airflow the cooling coil will allow without icing.) The technical term for that decision is called the static relief strategy. Very few companies can actually properly do the design so I'd shop very carefully.
    That's where it gets interesting since the AC is under-sized. Right now its running the AC at 1900 CFM normally, 70% of that on call for dehumidification. But really, thats the speed for a 5 ton AC unit. The blower (furnace) is capable of being configured down to around 1000 CFM. But of course that may be too low for the square footage, hence why it is set to about double that right now. But once zoning is in place, we can definitely run it at the reduced CFM when only the smallest zone calls. The Harmony III can control the variable speed motor in the furnace. As far as heating goes there are no issues, as the Harmony III is designed for this and the furnace is two stage variable speed.

    So what I am thinking can be done is that the AC can take the place of a 5 ton two stage unit, since its as if its stuck at stage 1 on a 5 ton. This way, the fan will run at 700-1000 CFM when only the small zone is calling, or increase in capacity up to around 1900 CFM based on bigger/more zones calling. The Harmony can apparently handle this.

    As an aside, a properly designed and installed system should normally be quite comfortable without zone controls. Zones are generally indicated for rooms have a lot of glass or otherwise have a larger heat gain or loss than other rooms in the house.
    As I mentioned earlier, it is "quite comfortable", but the difference is still very noticeable when you go between floors and that's what I want to reduce. That vertical gradient caused by hot air going up, cold air going down (plus the fact that the way the house is built, its already colder downstairs and hotter upstairs).

    Hope this all makes sense. I've been doing a lot of research, but I'm not an HVAC guy

  8. #8
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    do the Harmony III keeping the a/c you have it will most likely work out very well with the description of your house.

    i would not use any zoning panel that does not have the ability to control blower speed.

    i also would not set it up to run anymore than about 1200 cfm with all zones calling, basement zone will not be open that much and 1900 cfm is just way to much air for a 2 1/2 ton unit.

  9. #9
    Quote Originally Posted by t527ed View Post
    i also would not set it up to run anymore than about 1200 cfm with all zones calling, basement zone will not be open that much and 1900 cfm is just way to much air for a 2 1/2 ton unit.
    Thanks for your input, it really helps to have another opinion. On the Harmony III, you can specify CFM per-zone. So if the basement is not calling, the CFM would not go as high as 1900 CFM. But I think if all zones were calling, wouldn't it make sense to be around the 1900 CFM mark just to make sure there is enough air flow for the entire house? As right now its working pretty well at that setting. Is there risk of damage to the AC unit because of too high a CFM?

  10. #10
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    As t527ed said, 1900 CFM on a 2.5-ton AC system is way too much and in fact, would do a very poor job of dehumidification. That alone could dramatically affect the comfort of the home. I'm surprised that a quality company would run the fan at such a high speed for cooling if in fact, it can be lowered to the nominal 1000 CFM a 2.5-ton system would use. Since Lennox requires a 2-stage condenser for a 3-zone system, I don't think the scheme will get you quite where you anticipate. I believe the 2-stage Lennox condenser using a standard unloading scroll compressor. If that's truly the case, then 1st stage of a 5-ton unit would actually be 67% of 5-tons or 3.35-tons, which would normally require a minimum airflow of 1072 CFM. That's not too bad for a 2.5-ton system, I'm just not sure you can get there from here. Perhaps one of the Lennox gurus can clear up my doubts.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  11. #11
    No problems with humidity in the home because the undersized ac runs for longer times and lots of water drains from it. We also have a whole house dehumidifier on top (but even before it humidity levels were reasonable except for the basement, where it would be worse due to the much lower temperature).

    I think the reason they have it at 1900 cfm is because otherwise the two stage heating would be at an even lower cfm. The entire system's fan speeds are percentages based off of the full cooling speed.

    With the Harmony though the fan speed can be set per zone from 460 to 1900 cfm (the top speed end can be moved up or down too). So with the zoning in place I think the AC size will actually be more appropriate and will also allow any needed speed to be set. My main worry was just short cycling or whatever reason Lennox wants a two stage AC, which isnt specified. But it's most likely so it can be scaled down in power when only one zone calls, which I think is not a problem if the AC is already undersized.

    Speaking of humidity, what about humidification/dehumidification with the Harmony... Would it be hooked up just to one zone or is it possible to zone that too somehow?

    We have a honeywell steam humidifier.

  12. #12
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    Quote Originally Posted by Lupinglade View Post
    I think the reason they have it at 1900 cfm is because otherwise the two stage heating would be at an even lower cfm. The entire system's fan speeds are percentages based off of the full cooling speed.

    Speaking of humidity, what about humidification/dehumidification with the Harmony... Would it be hooked up just to one zone or is it possible to zone that too somehow?

    We have a honeywell steam humidifier.
    heating speed is NOT based off cooling speed, it is set independently using dip switched on furnace control board.

    harmony will not slow blower down for dehumidification you will need to use a thermostat that allows overcooling for humidity control.

    the humidifier can be set up to run whenever needed with any zone calling.

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