OT: Two speeds vs. two compressors vs. two units vs. two zones or any combination?

[Chance]

Every summer there seems to be at least one HVAC thread. So here is my question.

My old large single air conditioning unit has a slow evaporator leak that may not be economical to fix. Looking ahead and doing a little research in advance just in case it needs total replacement, it seems there are many options for higher efficiency and improved comfort. But at a cost.

My question is not about the physical aspect of these options but rather more about how they perform and hold up in everyday life. Technical differences seem relatively easy to understand but what’s more important is feedback from people who have switched from a single large unit to other types (or have other types) on how they like them. Are savings as much as expected? Did comfort improve? Reduced noise? Did maintenance increase due to number of units or added complexity?

It’s very possible that we will be charged for peak demand during peak hours in the near future, so units that can be run at lower capacity during those hours interest me. Yeah, it may get a little “too” warm during the middle of the afternoon in middle of summer, but that would be OK most of the time.

Any feedback you have is appreciated.

[Ken Robb]

I'd weigh the extra cost of two complete systems vs. the ability to have the best control of temps throughout the house. Buying extra cooling capacity can backfire because that system will cool the area so quickly it will be "off" most of the time which allows humidity to rise which provides a cool but clammy feeling. If you get into power rationing or "punitive" pricing with escalating pricing tiers based on usage you might want to cool only part of your home during heat waves.

The new units are much more efficient than those of just a few years ago so I wouldn't be willing to spend much to repair an old system that's out of warranty. I bought a new HVAC system a couple of years ago with a full 5 year warranty and I think that is probably an industry standard.

[Smiley]

Ten (10) years parts and labor warranty to go along with SEER 16 compressorand Variable speed fan. google them as they don't advertise to consumers but rather to dealers whom will tell you about this gem of a secret.

[Chance]

......
Buying extra cooling capacity can backfire because that system will cool the area so quickly it will be "off" most of the time which allows humidity to rise which provides a cool but clammy feeling.
......

Ken, to be clear, the systems described above would be of equal total capacity. Say, a 5-ton unit replaced with two 2-1/2 ton units (or a 2 and a 3 depending on need) or a single unit with a 2-1/2 and a 5 ton compressor so only one runs at a time, and so on. The two speed (or dual capacity???) unit would run at 5 tons at 100 percent or at roughly 2/3 capacity depending on need. The intent is not to oversize in any way.

[Ralph]

I'm not very knowledgeable about these systems.....but do live in Florida......

We have variable speed air handler fan and variable speed compressor, along with a fancy thermostat to control it. Don't know how this affects max cooling, but it does seem to help with light cooling needs. Also.....A huge improvement over units of our past is our digital thermostat that allows control over temps and humidity and can be programed for temp and humidity for different times of day. With variable speed fans the unit can run at very low speed to lower humidity without making rooms too cold. Along with ceiling fans in every room, and ability to keep humidity in the 55 percent range, our new unit allows us to run the room temps a little higher than we did in past. We think we are saving evergy and are more comfortable than years ago. We're not set up for dual units, or have an ideal home for dual units, but if we had the right house layout for dual units, would prefer that. Could just cool a portion of house at different times, all thermostatically controlled. BTW....ours is the new type freon.

[rwsaunders]

Single story or two? What zone of the country? Gas, electric or oil for the heating system? Filtration and humidity concerns? Current condition of the home including insulation values? There are a boatload of questions that are relavent before selecting an HVAC system.

Sometimes you can start with your local utility company for a complimentary energy audit and rebate review. Don't install a system that is proprietary to one specific dealer as well, as you will need to do maintenance and repair work at some point.

http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12330

[handsomerob]

I wish I knew more about HVAC as well. I have a larger unit for the downstairs (5T?) and a smaller unit for upstairs (2.5T?) and they are both in need of replacement. I have had them both "recharged" and cleaned the coils... but the fact is they just can't keep up with the heat when it is 90+ outside.

I don't plan on moving so whatever solution I choose will be best for long term. Anyone in the know have a 2nd on the Amana recommendation?

FWIW... we have natural gas heat and it seems to work fine... it is just the A/C that needs attention... and soon.

[Chance]

I'm not very knowledgeable about these systems.....but do live in Florida......

We have variable speed air handler fan and variable speed compressor, along with a fancy thermostat to control it. Don't know how this affects max cooling, but it does seem to help with light cooling needs. Also.....A huge improvement over units of our past is our digital thermostat that allows control over temps and humidity and can be programed for temp and humidity for different times of day. With variable speed fans the unit can run at very low speed to lower humidity without making rooms too cold. Along with ceiling fans in every room, and ability to keep humidity in the 55 percent range, our new unit allows us to run the room temps a little higher than we did in past. We think we are saving evergy and are more comfortable than years ago. We're not set up for dual units, or have an ideal home for dual units, but if we had the right house layout for dual units, would prefer that. Could just cool a portion of house at different times, all thermostatically controlled. BTW....ours is the new type freon.

Thanks Ralph. That's the kind of practical feedback of most interest to me. Technical matters are OK too but how they affect the homeowner is of more importance at this stage. Do you mind mentioning the brand? Also, notice any difference in noise level when unit operates at partial speed?

[Earl Gray]

Single story or two? What zone of the country? Gas, electric or oil for the heating system? Filtration and humidity concerns? Current condition of the home including insulation values? There are a boatload of questions that are relavent before selecting an HVAC system.

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Gets it.

Speculation otherwise.

[Chance]

Gets it.

Speculation otherwise.

With due respect, neither of you gets it at all. Sorry, but it’s true. At least from the perspective of the person asking.

The request was purposely worded for general and practical information as it has affected homeowners under their given circumstances (in lieu of specific and or technical) because no one knows better than me that a bunch of cyclists can’t solve or comment on a technical problem they know little about, and even if they had AC experience, without seeing and analyzing the house. That should be so obvious anyway that it shouldn’t have to be mentioned in the first place.

So while I appreciate your comment, it’s completely unnecessary. Regardless, thanks for sharing your point of view.

By the way, how is Ralph sharing his experience speculation? From my perspective he "GOT" the question 100%. Just figured others would share similar personal experiences with whatever type of system they upgraded to.

[Ralph]

Thanks Ralph. That's the kind of practical feedback of most interest to me. Technical matters are OK too but how they affect the homeowner is of more importance at this stage. Do you mind mentioning the brand? Also, notice any difference in noise level when unit operates at partial speed?

Ours is a Bryant. But imagine all systems are comparable. We use the newer environmentally friendly R 410 refrigerant VS the older R 22. When the fan is barely running to lower humidity, we don't hear anything. The compressor doesn't cycle much to do that.

To me....again as not really knowledgeable about HVAC.....it's about having a programable thermostat for both temps and humidity, at different times of day, and having an AC system that can respond to the thermostat. It takes a system designed to all work together. Plus ceiling fans, moving air, in all rooms allow comfort at a couple higher degrees. Lower humidity also allow comfort at higher temps, and it takes less energy to gradually remove a couple percentage points of humidity than to just cool. We're usually comfortable now with room temps around 80 degrees (and in middle of day I program it for 81), VS 76-78 of our old system, which just blasted out cold air when called upon. And....if room gets a little warm....I can always walk over to thermosat and push button to lower temp setting....over riding programed setting.

Also....a free energy audit turned up leaks in our duct work, which we fixed, and we also sealed up the base of the air handler. Being in Florida, these things matter.

I think our home is as comfortable as anywhere in US.

[Chance]

I wish I knew more about HVAC as well. I have a larger unit for the downstairs (5T?) and a smaller unit for upstairs (2.5T?) and they are both in need of replacement. I have had them both "recharged" and cleaned the coils... but the fact is they just can't keep up with the heat when it is 90+ outside.



Spent significant time researching different options and as expected they are diverse for certain making a decision difficult. Some of this information may help you get started in your own research.

Making the decision based on basic comfort and financials seems easiest. Include incremental comfort and it gets a lot harder because it affects costs very rapidly. “Environmental” concerns beyond basic systems can make decision even tougher unless you have money to burn.

Replacing my leaking Trane R-22 evaporator is not a good option for various reasons. Can be done for around $2,400 but entire system would have to last at least another 3 or 4 years for cost to be lower than depreciation on any new system that would also save some on energy costs. My system is too old to gamble that much. Plus it would still use R-22 which is incredibly expensive and harms the environment.

Going to two smaller but independent systems was also easy to dismiss due to cost and space. Each smaller unit doesn’t drop in size or cost very much even when size is cut in half. Higher long-term maintenance costs would also be an issue.

A basic replacement 5-ton unit like mine cost from about $6,100 (Bryant) to about $7,200 (Trane). SEER ratings would be slightly higher than mine but not by much. Mine was top of the line at its time. Not that it affects economics since it’s in the past. More concerned about durability of these “builder’s grade”. Warranties are generally shorter too.

Many “independent” experts not trying to sell me a high-cost (and presumably higher-margin too) system seem to think “economics” alone presently favor systems with a SEER of 16 or thereabouts. To get much higher, like around a SEER of 20, costs go up significantly. These top-end units typically need some capacity control to run at partial load in order to achieve higher seasonal performance (think average over time). The most common seems to be using a two-stage scroll compressor (many refer to them as two speed, although they seem to “rotate” at one speed). This allows the compressor to run at 2/3 capacity (not to be confused with rotating speed). Trane uses two separate compressors because using a compressor at partial load lowers their efficiency by a small amount. Installed costs for these units range from $11,800 (Bryant) to $12,700 (Lennox) to $12,900 (Trane). These higher end systems also add incremental comfort (lower humidity and noise) so the decision is not strictly limited to economics.

Two-stage systems are required if one wants to separate the house into two separate zones (like upstairs versus downstairs) so they can be cooled independently and or more uniformly. That adds about $2,000 to above prices.

Some very new systems have even higher SEER ratings up in the 23 range (maybe higher). One of them uses an inverter to run the compressor at various speeds as needed to keep up with cooling demand. Technically it sounds great but the cost is hard for me to justify at this time.

In reality none of these higher-end units solve my main concern about future peak power penalties from the utility company because in the middle of summer they will kick up to high capacity when the temperature is in the 95 to 100 degree range anyway. And at peak periods their efficiency won’t be that different.

Tough choices.