^^^^^ 2 stage is about comfort. You won't likely see any significant savings in operating costs.

Like I said before, a 2spd heat pump is more likely to see the savings. Significant? probably not. But it will probably recoup the difference within 15 years or so depending on a long list of various factors.

If you have any long humid laced summers and mild winters this is where the 2 speed heat pump will shine on operational costs (when installed properly).

Just be sure to get the 'communication controller' that the system is designed for. It's called the 'observer' for the brand you posted a link to.

We don't have super long, high humidity issues in Indiana and I don't consider our winters mild. This year it has been above average but over all it can stay pretty cold. After researching last night and talking to several HVAC installers I think I am going to stick with the 14 seer single stage. Right now money is tight and I don't feel the benefit of the 2 stage would be worth the price for me right now.

Thanks for all the input.

Is that a $2100 difference for two units or just one? And each unit is doing a single zone unto itself?

I think a $1000+ difference between 14 and 16 is a bit much.

If you're going to do single stage, still ask about a variable speed blower. That will get you a step along the path to better humidity removal.

2 speed is about comfort especially humidity. Even with your rebate, you will never ever recover any operating cost savings versus cost difference. For your location, you want a matched AHRI system with minimum 9 HSPF heating efficiency. And for your location, you definitely want the HP condenser to have electronic demand defrost feature over the cheap time/temp defrost method. Depending on size heat strips indicated, you want the strips staged based on demand. You don't need 2 stage equipment for removing humidity as long as you have matching var speed air handler, the correct thermostat and have dehumidify on demand properly set up for AC cooling.

IMO

Thanks guys. I decided to go with the single stage 14 seer units. Partly based on price, but I also brought it up to all for HVAC companies that I have quoting me this job. All four of them immediately said the 2 stage units are more likely to have issues due to additional parts and they cost more to work on. If some of them thought they were good and some thought they were bad I might consider. But all 4 of them without question told me to stay away from 2 stage units.

Glad you're happy with your decision but the companies you spoke to appear to employ Luddites!

;)

The question that comes immediately to my mind is, what is the efficiency of the 2-stage unit in high vs. low speed.

They are comparable - the high speed efficiency (COP) is marginally higher than the low speed (see page 7 and on in your linked document and look for COP at high and low temps). You may be able to find a table of COP vs temperature instead of just "High and Low" for a more detailed analysis; look on the manufacturer's site.

It is really hard to compare equipment that is not fixed speed. My understanding is that ratings lock variable speed compressors at a fixed frequency and give that rating. I don't know about 2-speed. For the former, it seems like a useful approach would be to rate at 100%, lowest output and then for a cycle that might be viewed as typical for a home. I am thinking of the kind of drive cycle that is used for automobile fuel consumption ratings.

The question that comes immediately to my mind is, what is the efficiency of the 2-stage unit in high vs. low speed.

The efficiency is the combination of the two speeds in my opinion. The heat of the day is typically between 3-7pm.

Because of that high speed is typically only engaged during that time depending on other loads being placed on the structure.

That means that 1/6 of a day the full capacity of the system is needed. The efficiency comes from reduced capacity. (If you don't need capacity, it's just wasted.)

A car gets 30 miles per gallon on the freeway, but only 25 miles per gallon in the city. What is the efficiency in MPG of this car? (This is a poor comparison, but the best one I could think of at the time.)

Please, share your proposals for rating systems for 2-speed and variable-speed AC, and for automobile fuel consumption that will be useful to consumers.

I have looked at the product data sheets of 2-speed AC condensers. I have not seen separate efficiency rating for low and high stages. I also don't know if the reported SEER and EER rating is the worst efficiency of the two stages. You would think with all the government regulation on HVAC efficiency that manufacturers would have to report that information.

I think, but do not know for sure, that the SEER rating is at full load, not partial or an average of high and low loads.

I believe the government uses the 'full cool' mode to determine efficiency... which means on a 2 speed machine they would rate it from the stage 2. Which in my opinion is foolish because the machine 'when installed properly' will run in 1st stage 90% or more of the time.

Remember 1/6 of a day is the heat of the day. Unless the sun gets stuck, this will not change. (3pm-7pm)

I think you all are going about it wrong... comparing a single speed 16 SEER to a 16 SEER 2 speed. You should compare the 2 against what it is replacing. Realizing the 2 speed will provide better comfort. Which is the whole reason for air conditioning in the first place.

This 'IMHO' is like comparing high definition TV to Ultra high definition TV.

Is there really a 'need' for Ultra High Definition?

Your home is an asset. I know a good many who treat it like a liability. I also know that it doesn't matter one bit what I think. People do what people do.

on output, usually low stage in a 2 stage is 65-70% of high stage output BTUs...

yes, that's true to an extent. It will vary some from manufacture to manufacture. In addition to these there are machines that have as many as 5 stages and some that are true variable speed machines that can run in 10% increments more or less.

So it really depends on which machine you are referring to.

I think that I get your perspective on homeowners and investment in their homes, Austin. The trouble is that in modern times, people change homes so much, they really have to judge how much they invest in mechanical systems with that perspective. My parents always upgraded and renovated with living there in mind and little if any thought to resale value. I am not sure that I have that privilege. I never really though about it this way, but a lot of tradespeople who are small business owners are tied to locale and have a very different perspective than modern homeowners.

My HVAC equipment is variable-speed. I know that with variable speed like mine, one coil at low speed means an oversized outdoor coil. (The outdoor blower is not even operating some times.) The result of that an probably other characteristics is increased efficiency at partial output. It seems to me that there is a great variety of systems design out there. I guess that there are two-speed, two-compressor systems, two-speed single compressor systems. I don't know if there are outdoor coils in common or separate for the former, but I am guessing they are separate. The increased complexity in operational characteristics makes it very difficult to decide what will work best in equipment to install and how to run it (setbacks or no) from an energy cost standpoint.

I thought the discussion was on Sgl stage vs two stage, not multiple stages beyond 2 or the latest and greatest true variable condensers that move up and down in small increments within a specified range.

IMO

Sure tigerdunes, but hijacking threads is an internet forum tradition. In this case, the OP has made a decision and probably checked out so there is no harm done.

I realize this is single stage vs. two stage thread. My goal in stating what I stated was to show there is a realm above 2 stage, more or less as well as to show there are differences from one manufacturer from another. It wasn't my purpose to hijack a thread. There are those out there that say 2 speed equipment is unnecessary... so why would manufacturers make 5 stage equipment and variable speed equipment on top of an already unnecessary system?

Many times in the field I've heard of people saying 'I don't want to gold plate anything'. Part of my response was geared to show that 2 stage systems these days are middle tier systems.

People change homes so much: yes, this is why my job can be really challenging. Many times it's not replacing a whole system (which would be required to go to a 2 stage machine... in most cases*).

Many times my job involves retro fit decisions. Replacing one or two pieces of an older system. In situations like that it's more about repairing the existing system and give a homeowner a solution they want.

If I find out a home owner is only planning to stay in the home a few short years I rarely if ever even offer the 2 stage equipment. 2 Stage equipment is for those of you looking to stay in the home for at least a decade or longer.

HVAC is not a one size fits all market. I am more likely to repair an existing system in some fashion than to replace. But replacement in some cases is the better option regardless of how long you plan to live in the home. If you live in my climate (Katy, Texas), you will have a tough time to sell a home without a functioning AC system.