New replacement A/C System help/advice ??

[rkser]

Our 19 yr old TRANE A/C is dead -

It was a single phase condenser with a single speed Air Handler, 5 Ton, 10 SEER, was put in by the builder for a 2300 sq ft single story house in Orlando.

Life was good before it died...., the Two of us were comfortable enough, ignorant about the newer, more complicated systems out there, which we never previously had to know the professed increase in comfort. The Electric Bill was around $150 a month & was not a concern.

Our Echo Bee Thermostat did show humidity of 70% & above many times with our older system, which although concerning we took it as a part of living in the hot & humid climate of Orlando.

The Estimates which are being quoted for the new system with a variable speed fan motor & 16 Seers are $2000 higher for a 2 phase & $3000 higher for a variable stage Compressor respectively compared to a new single stage Compressor.

Any help/advice regarding which system to choose will be greatly appreciated .
Anyone who has lately changed to the newer, technically higher A/C systems care to put in a few lines about their increased comfort or increased maintenance complications with their newer systems ??

Thanks & with best regards

 

[SumDay]

We just had our new two stage (both units) Amana 96% furnace and 18 SEER 4 ton AC unit installed last week. They threw in a humidifier and wi-fi thermostat. We had bids from $7K to $14K and went with one in the middle of the pack.

On Monday, we had it set on heat and it blew cold air all night. The EIM board went bad and it was replaced, free of charge, thanks to the 10 year warranty. $hit happens, and they fixed it the next morning. Luckily, it wasn't a cold night.

I especially like the new "Circulate" option for the fan which allows you to set the fan to run a certain amount of time per hour. This evens out hot and cold spots, uses your high-efficiency filtration or UV system more effectively, and keeps energy usage from going through the roof. Or so we're told. Too early to tell on the utility bills for that but I do notice I'm not wearing a sweater as much as I used to. The heat seems more even.

I really do love the new thermostat, which can be controlled from the phone, and also has some fancy settings for vacation mode. It doesn't even have to be changed for daylight savings time.

Since we've only had it a little over a week, I don't have much else to add. We did decide to go with the most efficient we could get because summers are getting hotter here, and we are more & more sensitive to it as the years go by.

Happy to answer any questions you may have. I did want to go with a larger company who had lots of service techs so you didn't have to wait for the one guy at the little shop to get to you when your EIM board goes out.

This new HVAC purchase is our vacation for the year.

 

[samclem]

Life was good before it died...., the Two of us were comfortable enough, ignorant about the newer, more complicated systems out there, which we never previously had to know the professed increase in comfort. The Electric Bill was around $150 a month & was not a concern.

Our Echo Bee Thermostat did show humidity of 70% & above many times with our older system, which although concerning we took it as a part of living in the hot & humid climate of Orlando.

70% humidity is too high--I think 35-50% is considered most comfortable by most people, and 60% is about as high as you'd want it (due to mold, etc. If the sensor is reading 70%, there's a good chance it is 90%+ in some nooks and crannies of the house). High humidity in a home can be the result of an AC unit that is too big (it doesn't run long enough to remove enough moisture). Also, having a "too big" unit can result in larger temperature differences throughout the house (again, because the fan doesn't run often enough/long enough). You need someone to do a good "Manual J" heat load calculation on your home to determine the right size AC unit. Or, you can just replace it with one of the variable speed fan units you are considering, but that involves higher expense and higher system complexity for (perhaps) very little payoff.


How do you heat your home? I'm trying to figure out why the HVAC tech wants to replace your interior air handler. If you've got a gas or propane furnace, then that unit provides the fan for the AC and wouldn't necessarily need to be replaced just because the AC is dead. You don't say that your present unit is a heat pump, though that would be quite normal in Orlando.

 

[Sunset]

For us, the A/C unit sits outside, and the cold goes into the furnace.

It is the furnace that has a fan to blow the air past a radiator type thing inside the air duct (the radiator is cold from the outside A/C)

You can replace 1 of the two, no need to do both at the same time, I did that. For my replacement it is the furnace that has the variable speed fan, run continuous fan, etc. all high efficiency stuff.

The A/C which I got later replaced , was just a high SEER - it really has no knowledge of what type of furnace it's going to be connected to.

 

[Telly]

In an A/C system, the part that gets cold inside the furnace is called the evaporator. And in a heat pump system that is in Heat mode, a changeover valve swaps the function of the evaporator inside, and the condenser outside, so the heat exchanger outside gets cold, the inside heat exchanger gets warm.

Swapping or mixing and matching A/C compressor units with inside furnaces or fan coils was once easy, when everything was R-22 refrigerant. But since 2010, all new systems can not be shipped with R-22, R-410a is used instead. Which for all practical purposes requires different everything, including gauge set, as pressures are higher and saturation points are different temps.

For some years, it was possible for an owner of an existing R-22 system whose compressor unit died, to get a R-22 compatible replacement compressor unit, which was shipped with dry Nitrogen in it from the factory, getting around the law of no shipping w/R-22. The dry nitrogen would be purged onsite, and the system evacuated then recharged with R-22. But the years have gone by, and in 2020 by law, there is no more manufacture or importation of R-22, so people like me with two R-22 units I installed in the early 2000s will have to bite the bullet if there is a major failure, and do a total system replacement. Buying a R-410a compressor, line set, and finding compatible R-410a evaporators to try to fit my existing ~15 and + year-old furnace units would be a questionable effort.

 

[Telly]

Terminology:
"Single Stage" or "Two Stage" usually refer to a gas furnace that has one or two levels of firing. Ie, a Single Stage gas furnace the flame is either on, or its off. A Two Stage has a lower firing stage level, and if needed, kicks up to a higher flame level... so when the furnace is ON, the heat level it generates has two possibilities, rather than one. For my mild climate, a two stage gas burner makes no sense, to me.

EDIT - "Stages" have sometimes also referred in Heat Pump systems to whether the heat pump was transferring heat in heating mode by itself "First Stage", or had to turn on the backup resistance strip heaters, "Second Stage" to keep up the inside temperature. Usually the thermostat had a little indicator light that would turn on when in second stage resistance heat mode, to let you know: "yer really sucking up them amps now, baby!".

Blower (Fan) - Can be "Single Speed", which is a bit of a misnomer, as they are actually multi-speed tapped motors, which the tech selects which speed tap is used for heating, which for cooling, and which for just FAN ON air circulation, with no heating or cooling.
"Variable Speed", where the furnace or Air Handlers processor board controls the actual fan speed depending on the conditions it sees at its sensor inputs. Variable Speed fan motors have electronics, and are quite expensive compared to the age-old tapped multi-speed motors. Failures are not uncommon! I have never had a tapped multi-speed motor die... (actually I did, but it was because someone had not properly terminated an unused fan speed tap, and it grounded out in the electrical box, smoking the motor, not the motor's fault). There are pros and cons on single vs. variable speed fan motors, I think most today are sold variable, as the installed price, therefore the profit, is higher. Same with cars and just about everything, you go for it, or you don't, buyer chooses.

Compressor Speeds - Standard is a single speed compressor. It's either on, or off. Variable, well, the processor board controls the compressor speed, which varies the effective tonnage of cooling as the compressor runs, rather than starting-stopping a fixed-tonnage single speed compressor. I would think this would be of questionable merit in a cold climate where A/C isn't used much. In a warm climate, I can see the advantages, if you are willing to pay the price. Also, is a more complex system. As in life, more complex almost always means more $ to diagnose and fix failures.

 

[Bamaman]

I had to put a new A coil in my Trane heat pump last Summer, and it was quite costly--in a lake house. It's an old high quality unit, but has relatively low hours on it.

Next time my system goes down, I'm replacing it with two inverter style mini-split heat pumps. One will have two large evaporator heads for the great room and kitchen. The other will have 3 small evaporator heads--one in each bedroom.

Because each room has its own thermostat, each room can be shut off when not in use. And I would expect the initial cost to be much less--on top of heating and a/c half the cost to run as a conventional furnace or heat pump.

 

[samclem]

Next time my system goes down, I'm replacing it with two inverter style mini-split heat pumps. One will have two large evaporator heads for the great room and kitchen. The other will have 3 small evaporator heads--one in each bedroom.

Because each room has its own thermostat, each room can be shut off when not in use. And I would expect the initial cost to be much less--on top of heating and a/c half the cost to run as a conventional furnace or heat pump.

Your running costs will be lower and you may find it to be more comfortable (especially if there's a significant difference in the heat loads in various parts of the structure (upstairs/downstairs, sunny south side/shaded semi-buried north side, etc). I would be very surprised if the initial cost for the mini-split system is lower than a straight replacement of your present conventional split system. The equipment cost is higher, a new pad and possibly a separate electrical box for the additional compressor unit will be needed, new refrigerant lines will need to be snaked from the external units to every new head inside, each of those heads needs to be hung, have power run to it, etc. The existing ducts will at least need to be closed off. If you think you'll be more comfortable with the mini-splits, then it might make sense, but from a cost perspective, for a place that is infrequently occupied, the payback period might be very long (maybe longer than the life of the equipment).

 

[Texas Proud]

I went with the variable HVAC unit over the 2 stage... also have a split system that was installed a couple of years back to even out the temp variance from upstairs and downstairs... LOVE IT...


The price difference between 2 stage and variable was not that great for me... I got a credit (not sure from who) that effectively made it a decision between a single stage and variable.. I chose variable.


The system is much better than the single stage.. it can run a good number of hours when it is warm and humid as it is getting rid of humidity more than cooling IMO...



If you have a humidity problem go with variable... if you have 2 stories have them split the upstairs from downstairs... I control both from one thermostat vs two on the older one that was on the single speed unit..

 

[Lewis Clark]

Before making a purchase, I recommend contacting your power company. Some power companies around the country offer rebates for buying energy-efficient appliances. We've gotten rebates over the years buying a new heat pump and a new refrigerator.

It's worth the phone call.

 

[SumDay]

Before making a purchase, I recommend contacting your power company. Some power companies around the country offer rebates for buying energy-efficient appliances. We've gotten rebates over the years buying a new heat pump and a new refrigerator.

It's worth the phone call.

+1. We got rebates from the gas company, electrical company and the AC manufacturer. All total it was a little over $1k. FYI, our contractor was aware of what all these were and filled out all the forms for us.
Looking forward to lower utility bills as well.

 

[big-papa]

FYI - a similar discussion is going on over at bogleheads
https://www.bogleheads.org/forum/viewtopic.php?f=11&t=280317&newpost=4535921&view=unread#unread

 

[rkser]

Some more information -

Terminology - I need to mention the Compressors(inside the outdoor Condenser) come in 1, 2 & a variable stage. I mistakenly used the word phase for stage. These terms are new to me & I am sorry for the errors.

We had a Trane AC with a all electric Heat Pump with a 1 stage compressor with a 1 speed fan motor in the Air Handler(inside unit) which died. We are being quoted different replacement systems -

1) A 1 stage Compressor with variable speed fan motor - Around $7k

2) A 2 stage Compressor with "" "" """ """ - Around $9k

3) A variable stage Compressor with '' '''' ''''' - Around $11k


I understand we will have low humidity & more comfort as we climb the price ladder. But this will bring more complexity & may lead to more maintenance & repair headaches. As far as electric bills there will not be any substantial lowering because they run $150 to start with.

Many Techs from bigger AC companies are trained but 1 or 2 Man Teams who also do still service lot of Acs are not up to speed in the complex systems. The parts of complex systems are as not easily available as the more basic systems.

Never having the higher tech systems I am unable to decide among the above 3. I do not want to make any mistakes as I will have to live with it for the next 10 to 15 years.

Which option of the 3 given above would you choose ??

Thanks

 

[38Chevy454]

x2 that you want the system to provide good dehumidification as well as cooling. Proper unit sizing and also variable, or at least 2 stage, compressor and blower will allow for the best interior house climate. Higher SEER will be lower operating costs, but sounds like you are already fairly low. Too high of cooling capacity will lower the temps, but not allow for the needed run time for dehumidifying.

 

[ncbill]

One can always add a stand-alone dehumidifier.

 

[samclem]

I can't overemphphasize the need for a Manual J calculation for your house. You can even do a pretty good study yourself using an online calculator, it will take you less than an hour. This will also calculate the size heat pump required for your heating needs.
Your humidity issue indicates your AC may be oversized and your electric bill sounds (possibly) inconsistent with a house that needs a 5 ton AC unit. If you really need just, say, 3 tons, then you might get fine dehumidification and overall performance from a 3 ton single speed unit (IF that could also adequately heat your home). There are a lot of contractors unwilling to do a Manual J calc, which is a shame.
On Bogleheads you mentioned one bedroom didn't cool sufficiently. The best approach to that is to first try to bring that room into line with the average heat loss of the rest of your house (with shading/awnings, improved windows, better ceiling insulation there, etc). If that doesn't work, then you may need to improve duct capacity to that room and run the fan more often (there are thermostats that will do this), or consider a "zoned" system (unlikely to be needed unless you have a big problem).

 

[Sunset]

...
On Bogleheads you mentioned one bedroom didn't cool sufficiently. The best approach to that is to first try to bring that room into line with the average heat loss of the rest of your house (with shading/awnings, improved windows, better ceiling insulation there, etc). If that doesn't work, then you may need to improve duct capacity to that room and run the fan more often (there are thermostats that will do this), or consider a "zoned" system (unlikely to be needed unless you have a big problem).

OP
I have seen some people add an inline fan (its a short piece of ductwork with a fan inside) to blow extra hard into the room that is too hot/cold.
Maybe it's at the end of a very long run ?

 

[travelover]

I can't overemphasize the need for a Manual J calculation for your house. You can even do a pretty good study yourself using an online calculator, it will take you less than an hour...........

+1 Contractors are often too lazy to do the calculation and just oversize the HeVAC equipment. More profit for them and you can never claim it won't heat / cool. The downside is higher utility bills, short cycling equipment, uneven temperatures and high humidity in summer. I did my own Manual J and had little luck getting a contractor to do one, though one lied and said he did but wouldn't show his work.

Also, get a least 4 estimates. There is just too much temptation to pad on an extra grand of profit. There are places that sell HeVac equipment on line to give you an idea of the cost of the hardware, then you can extrapolate the labor and profit. Generally two guys can install an AC in a day.

 

[rkser]

Thank you,

I am going to ask these questions to the Guy who we are thinking of going with to install the system.

 

[Masquernom]

I had some problems with the AC for the house we bought 3 years ago. While trying to solve the problem, I read the residential HVAC forums online. The discussions break down into two camps.

The HVAC engineers say you want a smaller AC unit that runs longer and lowers the humidity in the house. It will cost less to run and the house will be more comfortable.

The installers say that might be correct, but if they install a larger AC unit on a house, they don't get customer complaints or have to go back to make changes.

 

[rkser]

Thanks UAL & every one for participation in this thread,

We finally signed up for a 5 Ton, 2 Stage Trane XR 17 Heat Pump with 16.25 SEER with a variable speed fan motor for $9220 cash.

Hopefully the installation scheduled for the coming week will go smoothly.

I am so thankful to this forum & its knowledgeable members where helpful ideas are exchanged & debated for many fruitful decisions.

Thanks for your help !

 

[travelover]

Thanks UAL & every one for participation in this thread,

We finally signed up for a 5 Ton, 2 Stage Trane XR 17 Heat Pump with 16.25 SEER with a variable speed fan motor for $9220 cash.

Hopefully the installation scheduled for the coming week will go smoothly.

I am so thankful to this forum & its knowledgeable members where helpful ideas are exchanged & debated for many fruitful decisions.

Thanks for your help !

The two stage should mediate any over sizing if it occurred.

 

[samclem]

The two stage should mediate any over sizing if it occurred.

Yes. OP, good luck with the install, you'll probably be happy with the performance. I'm surprised at the price, but I'm sure you got several bids for this work. Price can vary a lot between various companies, and especially between small companies and the larger ones with a lot of advertising and overhead.

 

[rkser]

Thank you !

 

[Telly]

"Updated" terminology - After doing some checking, I see that the A/C marketing folks have renamed a "two speed compressor" as a "two stage compressor". To me and many others, a "two stage" compressor has a totally different meaning, ie., a compressor, driven off the same shaft, that has two discrete compressor sections, in series flow-wise. The first section is high-volume, low-pressure, the second section it feeds into, is low-volume, high-pressure. Bigger air compressors, and quality vacuum pumps use this configuration.

History - Two speed compressors in A/C systems have been around for many years in top of the line residential systems. Had one for years from the early 80s, it was a two speed reciprocating compressor, this was before scroll compressors. The thermostat had two temperature-sensing sections, and created two separate contactor feeds to the outside unit. The two speed compressor had two separate motor windings, high and low, and there was an incredible amount of controls out there. A mechanically-interlocking contactor that absolutely prevented both motor windings from being energized at the same time, even in fault conditions, as that would destroy the motor ($$$). With all sorts of microswitches on it too, the big thing looked like it came out of an elevator controller! And there were all sorts of pressure and temperature transducers, and timers.
To change speeds, the energized speed had to be turned off, then it waited 5 minutes for the head pressure to subside, then it engaged the other speed winding. Sometimes, in a certain heat-load time of the day, usually later afternoon, the low speed couldn't hold temp, so it would shut down for its 5 minutes before starting up in high speed. And during that 5 minutes without any A/C running at all, it would start to get hotter inside, it was noticeable (whew! why isn't the A/C on?). Then the high speed would run, cool it down, then when it reached its thermostat limit, it would shut down to switch to low speed, which wouldn't hold it (especially after a 5 minute no-A/C time!), back to high, etc. With the timers, it wasn't a rapid flip-flop back and forth, but would feel warm and go look to see why (the thermostat had different color LEDs for low or high speed operation).

Back to the present - I hope that the dead-time issue between changing compressor speeds is not needed with a two-speed scroll compressor, and that the electrical method of changing speeds now does not require the complete isolation of motor windings/fields that the old method used!

Kudos to those past design Engineers - I should add, that the old two speed unit we had never failed due to its complexity, it was a real work of art. Can't see anyone selling, much less trying to manufacture something like that today. After many years of high A/C use climate, it's evaporator and line set started to slowly leak, then worse each year. I did a planned total system replacement of it at an opportune time (late winter, what winter we get).