Carrier Greenspeed -- is it all it's cracked up to be?

[ndeverest]

Is the Carrier Greenspeed modulating compressor all it's cracked up to be? It sounds great on paper; instead of just a low and a high stage, you get essentially as many stages as you could ever want, and the system is smart enough to pick the optimal one for the current conditions. And the lowest stage goes all the way down to 40% of maximum, which gives you the potential for extremely good humidity control and comfort on mild days.

However, what looks good on paper doesn't always work so well in the field (as I am sure all you HVAC pros know). Sometimes things can be so complicated that they are just too smart for their own good (if you use Windows you know what I mean!). I had a standard two stage heat pump before, and for maximum comfort we kept it on the lowest stage whenever possible. Other than cold winter mornings and hot July afternoons, this was easy to achieve by just never moving the thermostat more than a degree or two off set point. Sometimes this might have made reaching our desired temperature take a little longer than it would have otherwise, but we got the maximum comfort that way. So with a standard two stage, the program (or algorithm) that determines which stage it utilized is easy to figure out and therefore control; just stay close to set point whenever possible and you will keep it on the low stage most of the time.

But is the program that controls the Greenspeed choice of stages so complicated that it just knows what I want more than I do (said with sarcasm)? Maybe it would force the system into higher stages when it wasn't really necessary - and not because the outdoor conditions required it but just because the program assumed that I wanted to get to my requested temperature more quickly than I was willing to wait? And then there would be no way to control my use of the system in such a way as to have it on the lowest stage whenever possible (as I was able to do with a standard two stage).

I hope this makes sense. My point is that although the Greenspeed sounds great, I wonder if in practice it is so automated that I would actually lose the flexibility to customize my usage of it to my particular needs.

[comfortdoc]

If the system is sized correctly, and the ductwork is designed properly for the lowest and highest airflows (tricky), the system will operate almost constantly at the speed necessary to maintain your comfort settings.

[ndeverest]

If the system is sized correctly, and the ductwork is designed properly for the lowest and highest airflows (tricky), the system will operate almost constantly at the speed necessary to maintain your comfort settings.

Thank you for your response. For what it's worth, we are reducting our entire house as we are putting a new system in. So we have the chance to do this right. That's why I want to think this all through carefully now.

I am concerned about getting a ductwork design that can handle both the low and high airflow properly as well. Is this even possible at these extremes? On a standard two-stage, where the low stage is 65-70% of maximum, this seems much more reasonable. But is it really possible to design ductwork than can handle the situation where the lower stage is just 40%? On a 5 ton system that would mean that the ductwork would need to handle 5 tons all the way down to 2 tons.

The other system I am considering is the Trane dual compressor, in which the lower stage is 50% of the higher stage. This would have a similar duct design problem to the Greenspeed, though obvious slightly less.

Any guidance would be greatly appreciated!

[dan sw fl]

MODULATION IS NOT REALLY THAT NEW of a CONTROL Concept in Residential Uses.

Similarly, Inverter technology has been used overseas for nearly 30 years.

http://www.achrnews.com/articles/117...g-gas-furnaces

[duckman06]

Thank you for your response. For what it's worth, we are reducting our entire house as we are putting a new system in. So we have the chance to do this right. That's why I want to think this all through carefully now.

I am concerned about getting a ductwork design that can handle both the low and high airflow properly as well. Is this even possible at these extremes? On a standard two-stage, where the low stage is 65-70% of maximum, this seems much more reasonable. But is it really possible to design ductwork than can handle the situation where the lower stage is just 40%? On a 5 ton system that would mean that the ductwork would need to handle 5 tons all the way down to 2 tons.

The other system I am considering is the Trane dual compressor, in which the lower stage is 50% of the higher stage. This would have a similar duct design problem to the Greenspeed, though obvious slightly less.

Any guidance would be greatly appreciated!

The carrier greenspeed is a great system. However it is limited to only heat pumps at this time. Where as the Trane XL20i and XV18-XV20i are avaiable in heat pump and straight a/c.

With the new XV 18-20i invertor you can go down as low as 30% the airflow all the way to 100% all the while the unit is adjusted air flow and outside compressor and fan to maintain the homes temp and humdity removel. With the XV models you can Chosse 30,40,50 to 100% of air flow at the outside CDA board.

In a nut shell choosing 50-100% would equal the XL20i using 2 compressors. Where as the XV18-20i use one. What that means is you can get the same performance out both at roughly the cost. The key to this systems is comfort and the XV18-20i will run 85-90% of the time when sized properly to keep you home comfortable and use less electricity in doing so then a system with 1 compressor that duty cycles on for 10-15 min then off for 10-15 mins as a example. If you look at the #'s the invertor will use less electricity when running most all the time then having a system that cycles on and off during the day.

Issiues that need to be addressed and or explained to customers about any 2 stage or invertor system:

1. System must be sized and installed properly per manual j. (Some contractors feel you can oversize the system due the fact it has mutilpe stages or speeds and bigger is better) wrong buy doing this the customer would be better off having single stage as 2 stage & or invertor will still want to duty cycle or come on and run for short periods of time and cycle off only to come back on. Oversized is oversized matter if single, mutple stage and or invertor.

2. Ductwork must be sized and installed properly for any system to work properly but speacial any system that has variable speed and 2 stage or invertor compressor. Why? Variable speed units will ramp up to overcome undersized or bad ductwork designs so it can try to do its job. Manual d should also be preformed to ensure duct system is sized and designed properly to deliver the correct amount of cfm/air flow to each air in the home. Along with proper return back to the unit so it can heat and cool the home properly.

3. Ductwork layout and sizing must be addressed for any system to work but with 2 stage or invertor with variable speed must be sized to move air flow correctly. Now with a system that can go down to 30-50% of the air flow a contractor must think the duct system sizing and layout before installing. Trial and error must be done to balance the air flow out and the propey settings set up at the new unit must be made to accomplish this. 30-100% in one home might work just fine but in the next it might need 40 to 50-100% air flow to keep the entire home comfortable. Where this comes into play is on a long trunk line system that has far drops at the end. When the air flow is decreased down to 30-50-100% those drops want get the proper amount of air flow to them to keep the room comfortable. It becomes a balancing act.

4. Contractors will have to explain in detail how this systems work and show data of how even though a proper sized system runs for longer times that the system is using less electricy and provides better comfort for the customers home.

All things listed above are important and must be addressed for any home to have true comfort but becomes very important with 2stage and invertor systems. Old ductwork must be reviewed and proper sizing for both equipment and ductwork must be done in order to have a system that will work properly as designed.

[bmathews]

Where do you live? It's real benefit is for heating. You can run the heat pump more efficient at lower temperatures. It is one expensive machine to be living in a predominantly cooling climate and I would recommend against it unless you just want it. You design the ductwork for the maximum, not the least. You size it properly per manual J then size it to D.

[energy_rater_La]

nice reply ductman.

[ndeverest]

The carrier greenspeed is a great system. However it is limited to only heat pumps at this time. Where as the Trane XL20i and XV18-XV20i are avaiable in heat pump and straight a/c.

With the new XV 18-20i invertor you can go down as low as 30% the airflow all the way to 100% all the while the unit is adjusted air flow and outside compressor and fan to maintain the homes temp and humdity removel. With the XV models you can Chosse 30,40,50 to 100% of air flow at the outside CDA board.

In a nut shell choosing 50-100% would equal the XL20i using 2 compressors. Where as the XV18-20i use one. What that means is you can get the same performance out both at roughly the cost. The key to this systems is comfort and the XV18-20i will run 85-90% of the time when sized properly to keep you home comfortable and use less electricity in doing so then a system with 1 compressor that duty cycles on for 10-15 min then off for 10-15 mins as a example. If you look at the #'s the invertor will use less electricity when running most all the time then having a system that cycles on and off during the day.

Issiues that need to be addressed and or explained to customers about any 2 stage or invertor system:

1. System must be sized and installed properly per manual j. (Some contractors feel you can oversize the system due the fact it has mutilpe stages or speeds and bigger is better) wrong buy doing this the customer would be better off having single stage as 2 stage & or invertor will still want to duty cycle or come on and run for short periods of time and cycle off only to come back on. Oversized is oversized matter if single, mutple stage and or invertor.

2. Ductwork must be sized and installed properly for any system to work properly but speacial any system that has variable speed and 2 stage or invertor compressor. Why? Variable speed units will ramp up to overcome undersized or bad ductwork designs so it can try to do its job. Manual d should also be preformed to ensure duct system is sized and designed properly to deliver the correct amount of cfm/air flow to each air in the home. Along with proper return back to the unit so it can heat and cool the home properly.

3. Ductwork layout and sizing must be addressed for any system to work but with 2 stage or invertor with variable speed must be sized to move air flow correctly. Now with a system that can go down to 30-50% of the air flow a contractor must think the duct system sizing and layout before installing. Trial and error must be done to balance the air flow out and the propey settings set up at the new unit must be made to accomplish this. 30-100% in one home might work just fine but in the next it might need 40 to 50-100% air flow to keep the entire home comfortable. Where this comes into play is on a long trunk line system that has far drops at the end. When the air flow is decreased down to 30-50-100% those drops want get the proper amount of air flow to them to keep the room comfortable. It becomes a balancing act.

4. Contractors will have to explain in detail how this systems work and show data of how even though a proper sized system runs for longer times that the system is using less electricy and provides better comfort for the customers home.

All things listed above are important and must be addressed for any home to have true comfort but becomes very important with 2stage and invertor systems. Old ductwork must be reviewed and proper sizing for both equipment and ductwork must be done in order to have a system that will work properly as designed.

Duckman,

Thank you for your thoughtful response. As a layman who is trying to make an informed decision this can all be overwhelming, and I appreciate the time you took to explain things. I read what you wrote probably 10 times to make sure I absorbed all of it!

Let me respond to a few points you made:

I completely understand about the whole oversizing issue. I am after comfort (more so than efficiency, but the way), and I want good humidity removal and long cycle times. That's why I was looking into the Greenspeed and/or the Trane dual compressor system (in which the lower stage is 50% of maximum). It seems to me that a standard two stage scroll compressors, in which the lower stage is just 65-70% of maximum, is not really taking of advantage of the lower stage as much as it could. My goal is to have the air just "ooze" gently out of the registers whenever possible - not blow me away - and to have nice long cycle times. So it seems to me that we want to have the lower stage be able to go as low as possible.

I am also VERY aware of how many HVAC contractors oversize things because it's easier to just use a "rule of thumb," round up, and then count on the fact that you have a two stage to pick up the slack from it being oversized. But then you lose a good part of the benefit of having a two stage. I have met with over a dozen contractors, and all but two barely knew what a manual J is, let alone a manual D! So you can see how, as a layman, this gets really frustrating; I really do have to understand many of the issues in order to know when I am talking to someone who does things right. That's why I came to this forum; I assume the pros on here work at a more advanced level than most in your field (or you would not have come to this forum to being with!).

First I have to decide whether not we even want a heat pump. We had one years ago, and although it was very comfortable (especially in the winter when we got a more gentle heating with a heat pump), we had an intractable mold problem with it (Dirty Sock Syndrome) and it was miserable. If you are so inclined, please see the thread I started called "are heat pumps more prone to mold problems." It explains the issues that I think are involved.

I know that many contractors (including some on this forum) don't think heat pumps are more prone to mold, but I think that is just because they don't live in the areas where this tends to be an issue. Many HVAC contractors in the southeast will absolutely swear that heat pumps are more prone to mold.

If we decide to go with a heat pump then the Greenspeed is an option, but if not we were planning to go with the Trane dual compressor system (so we could have a low stage that goes down lower than 65-70%). I am under the impression that Trane's invertor system is just coming on the market now, and I hate to be the guinea pig while they work the bugs out of the system, so that didn't really seem like an option. Do you disagree? Is Trane's invertor system ready for prime time?

And then the other concern I have too, as you discussed, is this: By having lower stages that go down so low (50, 40 or even 30%), are we just asking for problems in terms of the ductwork being able to handle such a wide range of airflows? I have had a couple contractors tell me that they did not think it was possible to design ductwork that will handle such a wide range of airflows, and that is why most two stage systems just have the lower stage only going down to 65-70% of maximum. So because of that we were considering just staying with a standard two stage scroll compressor, but then we might not be getting the level of comfort we might otherwise (and due to some health issues, we want to absolutely get the most comfortable system available; this is our priority). What do you think?

Thank you - everyone on here - for all your input. It is greatly appreciated!

[ndeverest]

Where do you live? It's real benefit is for heating. You can run the heat pump more efficient at lower temperatures. It is one expensive machine to be living in a predominantly cooling climate and I would recommend against it unless you just want it. You design the ductwork for the maximum, not the least. You size it properly per manual J then size it to D.

I live in Nebraska

[just_opinion]

There is something we need to be aware off is the air flow.

The unit can reduce down to 30%. But the duct is too bid for 30% of air flow.
Example: 5 tons system require (generally 2000CFM) at max speed. And your duct is designed for 2000 CFM.
NOW, we take the system down to 30%. This will make the blower to reduce speed down to approx 30% to get the best dehumidification. So 30% of 2000 is 600 CFM.
NOW, do we think the air will come out of the last room in the duct trunk. OR most of the air will go out the 1st couple of grills.

It is just something we need to look at.

It is a great system. We are Lennox and we installed few of this XC25 and XP25. But we use mostly on zoning system cause it has the ability to get as low as 30%. And it works wonder.

[beenthere]

There is something we need to be aware off is the air flow.

The unit can reduce down to 30%. But the duct is too bid for 30% of air flow.
Example: 5 tons system require (generally 2000CFM) at max speed. And your duct is designed for 2000 CFM.
NOW, we take the system down to 30%. This will make the blower to reduce speed down to approx 30% to get the best dehumidification. So 30% of 2000 is 600 CFM.
NOW, do we think the air will come out of the last room in the duct trunk. OR most of the air will go out the 1st couple of grills.

It is just something we need to look at.

It is a great system. We are Lennox and we installed few of this XC25 and XP25. But we use mostly on zoning system cause it has the ability to get as low as 30%. And it works wonder.

The air will flow to the last supplies, as there is little resistance to force it out the near registers.

If the duct system at 2000 CFM had a static of .5", then at 600 CFM, it would have a static of .045".

Its the under sized duct systems that will have problems.

[ndeverest]

There is something we need to be aware off is the air flow.

The unit can reduce down to 30%. But the duct is too bid for 30% of air flow.
Example: 5 tons system require (generally 2000CFM) at max speed. And your duct is designed for 2000 CFM.
NOW, we take the system down to 30%. This will make the blower to reduce speed down to approx 30% to get the best dehumidification. So 30% of 2000 is 600 CFM.
NOW, do we think the air will come out of the last room in the duct trunk. OR most of the air will go out the 1st couple of grills.

It is just something we need to look at.

It is a great system. We are Lennox and we installed few of this XC25 and XP25. But we use mostly on zoning system cause it has the ability to get as low as 30%. And it works wonder.

Thank you so much for responding. Yes, that is exactly the issue I elaborated on with Duckman, two posts up from yours. So I completely understand the problem ... but then my question is: can this actually be addressed? Or, as more than one contractor has told me, do we need to just stick with a standard two stage scroll compressor, where the lower stage is only 65-70% of maximum, in order to avoid the problem of one duct system handling such a wide range of airflows? We don't want to do this - we would rather have the lowest stage be smaller than this for maximum comfort (humidity removal, etc) - but if the duct system can't handle such a wide range, then maybe we have no choice.

You mentioned zoning. Can this issue be resolved by zoning with dampers?

[just_opinion]

...

You mentioned zoning. Can this issue be resolved by zoning with dampers?

Yes, definitely.

In my opinion, this inverter system is best with zoning. No dump damper and short-cycling of compressor as long as EACH ZONE is within 30%.

Like I have said on other post from another owner relating to zoning via this Inverter technology, you better have a GOOOOODDD mechanic to work on it. Otherwise, it will be YOUR nightmare.

[ndeverest]

Yes, definitely.

In my opinion, this inverter system is best with zoning. No dump damper and short-cycling of compressor as long as EACH ZONE is within 30%.

Like I have said on other post from another owner relating to zoning via this Inverter technology, you better have a GOOOOODDD mechanic to work on it. Otherwise, it will be YOUR nightmare.

Yes, you hit the nail on the head with my concern. This all sounds great in theory IF I can find someone who really knows what they are doing. If not, it seems I could just be setting myself up for a huge struggle.

And finding a good HVAC contractor is like find a good surgeon. How am I supposed to know if they are competent until they are done with the "surgery?" I think I am an unusually knowledgeable layman, but that's still all I am - a layman.

If I get someone who just uses a rule of thumb and then oversizes for a load calc, or someone that doesn't even think ductwork design is that important, I know to rule them out. But that only rules out the totally incompetent, and I think there are probably many HVAC contractors who would be perfectly fine on more conventional systems but might be in over their heads - and not even know it - in this more complicated situation.

How do I know if the person I am talking to understands these kinds of issues?

[teddy bear]

I have a couple years of data on the GS heat pump. They are a marvel of engineering. Complex, expensive, and difficult to adjust, but yet impressive.
They are also unable to maintain <50%RH during low/no cooling loads and +55^F outdoor dew points. The large cooling coil retains large amounts of moisture at the end of the cooling cycle, which evaporates back into the home at the end of the cooling cycle. The retain about 1 lb. per ton which will raise the indoor %RH about 8-10%.
If you want exact control of the temperature and the %RH in your home, get whole house dehumidifier like the Ultra-Aire whole house dehumidifier. You set the temp and the heating cooling system provides it. You set the %RH and the whole house dehu will provide supplemental dehumidification if the a/c can not provide it.
During the winter season, you will also need a whole humidifier for condition where the outdoor dew points are below 30^F.
The data on the GS shows three distinct speed of cooling. There are also variable supplies of air to the different areas of the home.

Regards TB

[just_opinion]

...

How do I know if the person I am talking to understands these kinds of issues?

....

How do I know if the person I am talking to understands these kinds of issues?

If you don't mind that I can ask you this question.

Let say you run water line to water your garden. The water comes from ONE water source (your back yard water spicket). The hose you ran are BRANCHING over your garden. Now, you turn your water ON BUT VERY LOW pressure.

Question: Which branch will get more water?

a) The one closest to the spicket.
b) The one farther away from the spicket
c) They all come out the same rate

My point is that you don't have to know how to fly the air plane. But we sure know if the pilot is good or bad.

Good luck

[hurtinhvac]

Just be sure to carefully weigh your comfort and energy conservation aspirations against the cost and complications of this higher end technology. One bad component after the labor warranty expires can significantly impact your comfort, energy savings and satisfaction levels.

I personally do not advise systems like this unless you are one of those kids that just has to have the coolest stuff and will bore your neighbors to tears talking about it.

Or some kind of medical condition that demands your air be conditioned as best as possible.

[just_opinion]

...

How do I know if the person I am talking to understands these kinds of issues?

Believe it or not, but this kind of system is MUCH easy to diagnose. In facts, it tells you what is wrong. The problem is to find the person to interpret its bible. AND this person don't make things complicated or start to re-engineer it. The you are OK.

I cannot talk for carrier or trane. But Lennox has about 3 pages of error code.

[hvacvegas]

Just be sure to carefully weigh your comfort and energy conservation aspirations against the cost and complications of this higher end technology. One bad component after the labor warranty expires can significantly impact your comfort, energy savings and satisfaction levels.

I personally do not advise systems like this unless you are one of those kids that just has to have the coolest stuff and will bore your neighbors to tears talking about it.

Or some kind of medical condition that demands your air be conditioned as best as possible.

exactly what I was going to say.

Our pricing, you could buy 2 "standard efficiency" systems for the price of the green speed. If not more.

I can only imagine out of warranty repair costs.
Variable speed blowers are crazy expensive anyways.

[duckman06]

The air will flow to the last supplies, as there is little resistance to force it out the near registers.

If the duct system at 2000 CFM had a static of .5", then at 600 CFM, it would have a static of .045".

Its the under sized duct systems that will have problems.

Beenthere is correct if a ductsystem is designed correctly per manual d then there will be some minor adjustments and depending on the layout it will work just fine but again trail & error is needed to address the airflow simple things so every ductsystem and home is different that's why they give us and u the option to adjust air flow.

To the OP I understand not wanting the 1st one of the Trane systems like the XV18-20i but I know Trane has 80-90 trial units in Trane reps homes that have been running over a year with little to no probelms. If the XV 18-20 interests u ask the company that is installing it if you can be the 1st customer with one and could they help out on price due to this? Not to say give it to you for free but discount non the less to use your home a poilet for them. I have done this in the past with the XL19i & Hyperion air handler etc... Just a thought.


2 stage/invertor systems are not for everyone or every home. If you are looking for total comfort, eff., latest bells & whiles etc.... This systems are for you. If u want a cost effective system I would look at in Trane XR17 (2) stage system with variable speed. Hvac system sized properly & Duct system sized propely with this system and you can get the best of both worlds.