Two stage - what's the point?

[prec_mktg]

Copeland 2-stage compressor is around 70% capacity on "low". Most, if not all, manufacturers only make the two stage products in even tonnages. If I use a 2-stage in a 3.5 ton house, I need to use a 4 ton unit, which would be about 2.8 tons on low. Hardly much difference.

[ehsx]

Copeland 2-stage compressor is around 70% capacity on "low". Most, if not all, manufacturers only make the two stage products in even tonnages. If I use a 2-stage in a 3.5 ton house, I need to use a 4 ton unit, which would be about 2.8 tons on low. Hardly much difference.

More than you might think. Properly sized it would continually run fully loaded < 10% of the time. Most of it run time will be at reduced speed. Speed reductions less than 50% can cause oil and refrigerant management issues. Run a load calculation and you may find that it is matched fairly well. Matching that up to air flow thru the coil, air throw/room mix from the diffusers, there may be good reasons.

[CircusEnvy]

Less cycling, more even temperature in the home, quieter operation running in first stage most of the time.

[ga-hvac-tech]

Less cycling, more even temperature in the home, quieter operation running in first stage most of the time.

All this...

And in humid climates... better humidity control.

AND the added bonus: usually one has to go to a slightly oversized unit in high stage (the example of a 3/5 ton LC and a 4 ton unit)... one has some reserve capacity for a heat wave!

[Snapperhead]

I dunno man , to me it seems like more shit that can go wrong , so you wont find one in my place

[litjoe]

better humidity control i have a 18 seer amana been great

[ga-hvac-tech]

Two points...

First... we have NEVER had a customer, who we installed a 2 stage for... who did not like it...
And...
We have not really had any more service issues with 2 stage, than single stage... with one exception:
HP's have defrost boards... 2 stage have 2 stage boards... both can loose a board in a storm.
Something interesting about my brand (AlliedAir)... they use the same board for defrost and 2 stage... the board was designed to handle the features of both needs.

It becomes a question of comfort... do I want to pay the extra for added comfort???
Some do, some do not...

[prec_mktg]

I'm in complete agreement with the advantages, just that I don't think 70% power is enough reduction to be worthwhile in a situation where the unit has to be upsized by half a ton. Like ehsx says, maybe it only runs on high power <10% of the time. More than 50% of the time it is still way to big for the job even on low power. Yes, it seems that proper lubrication and refrigerant operation makes it impossible to make a two-stage scroll with lower than 65-70% capacity.

I have the same problem with the length of my pants. I wish somebody would make odd size lengths!

Variable speed can produce 25-30% power makes a lot more sense for good humidity control in the shoulder seasons. If we pretend that the companies could build control boards that last long and are not so expensive when they fail. We will eventually get to variable speed being the most common setup in another 10-15 years I suspect.

[pecmsg]

Then you need Variable speed

That get expensive to purchase and maintain.

[ga-hvac-tech]

I'm in complete agreement with the advantages, just that I don't think 70% power is enough reduction to be worthwhile in a situation where the unit has to be upsized by half a ton. Like ehsx says, maybe it only runs on high power <10% of the time. More than 50% of the time it is still way to big for the job even on low power. Yes, it seems that proper lubrication and refrigerant operation makes it impossible to make a two-stage scroll with lower than 65-70% capacity.

I have the same problem with the length of my pants. I wish somebody would make odd size lengths!

Variable speed can produce 25-30% power makes a lot more sense for good humidity control in the shoulder seasons. If we pretend that the companies could build control boards that last long and are not so expensive when they fail. We will eventually get to variable speed being the most common setup in another 10-15 years I suspect.

In my area...

Design temp is 22/92...

This summer 2020, we have recorded a high above design 4 or 5 times...
Last summer (2019), we recorded close to 2 months of highs over design and almost a month of high 90's (had a couple of 100's)... and lots of humidity!

If a system was installed that just barely made design... you would have one HOT (both temperature and angry) customer!
And I can tell you this: You will LOOSE referral business if you do not make it right!
People around here do not care about the tech stuff... they want to feel comfortable.
So reserve capacity is a MUST!

Enter the 2 stage unit... with a VS furnace...
It resolves the capacity and humidity issues... the system is energy efficient... and the customer is happy...
And the contractor gets referrals.

Comprende...

[beenthere]

I'm in complete agreement with the advantages, just that I don't think 70% power is enough reduction to be worthwhile in a situation where the unit has to be upsized by half a ton. Like ehsx says, maybe it only runs on high power <10% of the time. More than 50% of the time it is still way to big for the job even on low power. Yes, it seems that proper lubrication and refrigerant operation makes it impossible to make a two-stage scroll with lower than 65-70% capacity.

I have the same problem with the length of my pants. I wish somebody would make odd size lengths!

Variable speed can produce 25-30% power makes a lot more sense for good humidity control in the shoulder seasons. If we pretend that the companies could build control boards that last long and are not so expensive when they fail. We will eventually get to variable speed being the most common setup in another 10-15 years I suspect.

In your size example in your opening post. The 2 stage would be operating at 80% of the capacity of a 3.5 ton A/C. Giving 25% longer run times on days below design.

Plius, with a VS blower, and a good thermostat, the blower can be slowed when the indoor RH is above set point, raising latent capacity, and lowering sensible capacity, which would increase run time also.

[Hurst11]

I dunno man , to me it seems like more shit that can go wrong , so you wont find one in my place

I think that a lot of us who don’t completely understand how something works or have seen the benefit of said thing,whatever that thing may be are quick to write em off as unnecessary or over engineered. I’m the same way about things as well. Took me a long time to convert to the dark side and actually like txvs where before I despised them with a passion,untill i finally seen the benefit of it. At present time I’m not a fan of variable speed blowers but I’m slowly warming up to em.

[Makeitcold]

Run a manual J, you might be able to get away with a 3 ton, or check the static pressure, might not be moving 1400 cfm anyrate. I've never met a customer who regretted going multi-stage equipment, if it was installed well, loved it at my last house and I've rarely ever had problems with them because they arent turning on and off nearly as often

[Adlerberts-Protege]

Undersize it a little and install a ductless or keep a portable ready to go, under extreme conditions. Done deal.

[pecmsg]

Undersize it a little and install a ductless or keep a portable ready to go, under extreme conditions. Done deal.

👍

[billygoat22]

my particular model is 50/100%, most of tranes at the time were 60/100%. mine runs on first stage majority of time for ac.I also have the 825 tstat, so controls variable speed motor directly to match airflow to capacity and dehumify mode as well.

[theoldscroll]

Undersize it a little and install a ductless or keep a portable ready to go, under extreme conditions. Done deal.

You say this in jest right? Or help me grasp how that is a great solution. That's like sayin my kids need 2200 calories a day to live, but I'll only give them 1900 because they can get by on that a good part of the time, and if they can't, they know the cabinet holds a bunch of those peanut butter cheesey crackers if they're too hungry.

2 stage works great for most applications. Only issues are during weather where it don't hit hi stage but still kinda hot, the bedrooms at the far ends may suffer from the airflow/capacity reduction. The duct didn't change when the airflow did. Clients who have had them for long periods express things like a 30% reduction in summer electric bills from a previous system. but in the afternoon the BR on the SW part of the house is warmer than it used to be.Remember the something gained , something lost rule always exist. Oh, I see mini split fix here.

Embrace multistage equipment or look for another way to make a livin. Soon that will be all they sell. Just look they already took away PSC motors from furnaces, What? this year.

[Makeitcold]

Most systems are so oversized to begin with that you end up with higher comfort, my last house I put 2 stage on, it stayed in low stage until a couple degrees above design temp. Connected to a HW Prestige IAQ, I never had to overcool in the mornings or evenings to control humidity=$$$ saved. I'd argue that if your home is so large that your losing critical cfm on long duct runs, then you really should have 2 systems or at least zone the multi-stage

[niceguypmp3]

When i upgraded to a 3 ton 2 stage from a single stage 3 ton HP, i have noticed that except on mild days, it would take forever for first stage to satisfy the thermostat. I should have had them move up to a 3.5 ton unit so that first stage would work better and then on temp extreme days 2nd stage would work more efficiently and not run as long. I will have to make sure to do that for my next unit!

[BNME8EZ]

I tend to embrace the new tech, just not right a way. Being in the middle of the country the coasts always get the new stuff before they send it here. Once it is here I like to see the issues that others have before I jump on the band wagon, which also gives me time to learn and understand what I will be putting in. After the first one, the rest are an easy sale as you start to see and understand the benefits to the customer.

The thing to remember is just because it is a furnace, A/C or heat pump does not mean that you install 2-stg the same way you do 1stg. The same can be said for high end equipment. If you install the top of the line 1 stg system the same way you install a base line or even bottom tier brand equipment you will have unhappy customers. Most of the issues I see with equipment are install issues where full consideration of the needs of the equipment is not done. VS blowers are great but not for long on undersized ducts. 2 stg equipment is great but not every house is the proper application or maybe I should say not every customer. If they want a unit that will run for 2 minutes and shut off they will not be happy with 2 stg and especially not VS equipment. Some of this can be overcome with education, some not so much.