Recommendations for replacement system in Tampa?

[KMorley]

Our house currently has a fairly sophisticated Trane system. But it's getting old, our power bills keep rising and I need to start planning for replacement.

The house is 3333 sq feet in Tampa and we use AC about 275 days per year. We typically heat less than 10 days out of the year.

The existing system consists of two 3T Trane XL1200 TTX036C100A1 straight cool condensors, a TWE062E13FB dual-circuit VS air handler, a hot water coil (driven by two natural gas hot water heaters) in the return duct, a Trane ZSASSMAL010 Integrated Zone System controller, electric dampers for five zones, a Trane Master Scheduler and a Trane Electronic Air Cleaner.

I have been VERY pleased with the comfort this system has provided over the years. You are almost never aware of it running and it keeps humidity well below 50% with the indoor temperature set at 78F and it being 92-95F with close to 100% humidity outside in the heat of the day.

The only exception has the upstairs bonus room, which is surrounded by attic on 3 sides. The bonus room would heat up rapidly when the house system shut off, so I added a 1T Mr Slim in the bonus room to smooth out the temperature swings.

The problem is that the main system seems to be running more than it has in the past and seems to be having trouble maintaining 78 during the heat of the day with both condensors running. This has resulted in some $400 - $500 monthly electric bills this summer. When the system was brand new, it seemed like the 6T total was plenty, but now it seems barely adequate.

I've cleaned the two condensor coils and the evaporator coil and had the charge levels checked on both circuits. They match the TXV Refrigerant Charging Curve published by Trane. At 88F outside, each condensor draws about 11.7A at 240VAC, which seems reasonable. At higher OD temps, the current draw will rise to about 12.5A. But each 3T condensor draws less current than a 2T window unit I measured under indentical conditions, so they can't be too inefficient. Also, one condensor had it's coil replaced about two years ago and the two condensors measure almost identically.

When the system was originally being designed, the combination of the 3T XL1200 and the dual-circuit air handler was around SEER 13.7, but I don't remember if that was with one or both condensors operating.

In Tampa, it seems like the contractors all want to sell the same recipe: a 5T single-stage HP and air handler. But I don't want to take a step backwards either comfort or energy-efficiency wise. I definitely want some kind of multi-stage and zoned cooling. We run the heating so infrequently that I don't really care about the heating fuel. It's cooling performance, comfort and efficiency that I'm after.

Here's what I'm thinking so far:

1) The Air Handler is currently mounted horizontally in unconditioned space in the garage. This causes it to sweat, rust, grow mold inside, etc. Our attic has plenty of available space and so I intend to build an insulated room off the upstairs bonus room and connected to the conditioned air in the house. I have plenty of space for one or two vertical air handlers.

2) The current hot water coil is mounted in the attic in the return ductwork and is not easily accessible. So, even though I use quality pleated filters, the coil still catches and holds dust. I have to take apart the ductwork to clean it and it's an all day job. If I use a hot water coil for the new system, I want it to be out of the airstream alltogther in cooling mode and more easily accessible for cleaning. I don't care if I have to manually move dampers in December and March to changeover from cooling to heating.

3) I don't think Trane or anyone else makes a residential dual-circuit VS air handler anymore. If they still do, someone please enlighten me.

4) Trane has a newer ZSASSMAL012 Integrated Zone System that will accomodate dual-stage condensors. Does anyone know if that will accomodate two 3T dual-stage condensors?

5) If Trane still makes a Dual-Circuit VS Air Handler and the ZSASSMAL012 will accomodate two 3T dual-stage condensors (like the XL20), that might make my decision easier. I could duplicate the existing system with the improvements mentioned in 1 and 2 above. If there are no Dual-Circuit Air Handlers, I will probably have to install two seperate systems (2 3T XL20's, 2 VS Air Handlers, 2 Electronic Air Cleaners and 2 zoning systems). That would be major expensive.

In addition to the above, I intend to replace some or all of the existing ductwork to accomodate the change in AH location. The attic insulation is R33, but it's settled some and I need to have additional blown in AFTER the ductwork changes. I may also add some powered ventilators in the attic. Longer term, I intend to replace the cheap builder's windows with dual glazed types.

Any thoughts or suggestions to any of this would be appreciated!

[dash]

1. Okay idea if the same insulated space can't be built where the air handler is now.

2.I think the extra duct required may be adverse ,both in space required,and the extra restriction caused by more ducts and fittings.

3.I don't think soeither.a 5 ton two stage and some increase in insulation to reduce the load may be the way to go. Plus check the actual btus of the old system ,may not be much more than 5 tons,buillt today.

4.Don't know,but you can't couple variable speed air handlers to the same duct system,their motors controls will fight each,and the motor(s) will fail.

Using standard motors,you still have half the air going thru a coil that has no cooling,I think you be unhappy with the indoor humidity.

5.See #4. Replacing all the duct system will be costly.
If you change the windows now,5 ton two stage will likely handle the load,load calc to be sure.


Bonus rooms,often allow air from the surrounding attic to circulate under the floor,check for that. Additionally the wall insulation that is exposed to the attic,need to be sealed on the attic side to prevent hot air circulating(vrtically ) thru the insulation. Those are often the reasons bonus rooms don't cool well,in your area.

We are in New Port Richey,and have found a lot of bonus rooms with these issues.

[KMorley]

Dash:

Thanks for the suggestions and I'll comment on your points:

1) It's not feasible to build insulated space where the AH is currently located. But where I'm considering building the insulated space should reduce the ductwork required as the AH will be more in the center of the house rather than at one end in the garage. The bonus room has a framed and insulated dead area that's walled off. I could pretty easily put a lovered door there and finish the area out. It would be plenty big enough for a vertical AH. I don't know why the builder didn't make it a closet - the joists, plywood flooring, wall framing and insulation are already there.

2) If Trane doesn't make a dual-circuit VS air handler, that's going to simplify the decision some: I'll have to get by with a 5T two-stage for the majority of the house. You are right about the total BTU capacity being not much more than 5T. Although the two 3T condensers make 6T, the existing AH has a huge A-Coil but it's minimal for the application. I remember seeing somewhere that it's rated for up to 65K BTU, so it's reasonable to assume that I got 5.5T capacity when it was all new.

Another thought is that I might be able to take some load off the current system by buying a bigger Mr. Slim and removing the bonus room and upstairs bath from the main system. The AH being minimal for 6T input is part of the problem: when both condensers are running and the AH fan is on high tilt, water sprays all over the inside of the AH. Since it's in the garage in 90+ degree heat, it grows mold like crazy. I'm hoping that using a vertical AH installed inside will mitigate that problem.

3) I mistated the bit about "two systems". I meant "two seperate systems" not sharing any components or ductwork. I know you can't twin the air handlers.

4) I consider the current ductwork to be minimal: It's round R4.2 flex with black plastic inner tube and silver mylar outer. It is all sealed with mastic where the flex connects to ductboard, but where flex is spliced to flex it's just taped. The attic is accessible enough that installing new ductwork wouldn't be problematic in most areas. There are a few areas that the installer would have to bend over to get to, but in most places you can stand up straight. Being just R4.2 means the existing duct loses a lot of the cooling, so I would like something more efficient. I wouldn't want to spend thousands on that, but I would at least replace some of the longer runs with better flex.

A load calc is my very next move. I'm measuring rooms and windows, etc. so my wife can get an engineer at work to run it through their software.

5) The bonus room has a band of R33 stapled around the joists. It's not air tight, but shouldn't allow too much circulation. Plus it's then covered with R33 blown insulation, so you can't see the band unless you dig for it. The bonus room has R33 in the walls, but the walls are 2x4 framed and the insulation is much thicker than the wall itself. I'm sure it would be more efficient if the insulation was fully contained in the wall, but there's not much way to do that I can think of. How would you seal the insulation on the attic side?

Thanks again for the suggestions.

[KMorley]

Dash:

I know that the bonus room insulation is not very effective, even though it's R33 because of the gaps and lack of facing on the attic side.

I did a little research and found that house wrap is recommended for that application. To do that, I would have to make some kind of spacer that I can attach to the existing studs on the attic side that would extend wood out to about the thickness of the insulation. Then I could staple house wrap to that to encapsulate the insulation or even add a layer of Thermaply ( expensive).

I'm thinking that effectively insulating the bonus room might remove enough load that I can cool that with the existing 1T Mr Slim and free up that capacity from the house system. The bonus room and upstairs bath are a total of 462 sq feet with 8' ceilings or 3696 cu feet with one 96" x 40" 26.6 sq ft window. I can easily get above the bonus room ceiling to add insulation, etc.

You've got me thinking that fixing the bonus room insulation might be the most cost-effective solution over the long term and might get the load down to 5T. That could save a LOT on equipment, not to mention electricty going forward.

Any idea where I can buy spacers to make the stud wall the depth of the insulation? Might make a good project for this winter...

Thanks again!

[dash]

Not idea about spacers,we usually recommend high R sheeting over the insulation to air seal and add R-value. Wrap,staples to existing wall studs could seal it well.

Did you check to make sure attic air can't circulate under the bonus room floor? That's been a big issue in many homes in y/our area.

[KMorley]

Dash:

Thanks for the replies and good suggestions.

Keep in mind that the insulation between our attic and bonus room is roughly 12" thick batts. While you could compress that down to fit in a 2x4 wall and then seal it with Thermo-Ply or wrap, you would lose much of the insulating ability by doing so. Sealing it and maintaining the current thickness would mean making the wall about 12" thick and that's why I'm looking for spacers or something.

Out bonus room sits directly over the living and dining room downstairs. There is a band of batt insulation around the joists. Then, the attic has blown insulation about a foot deep. You can't see the joist band unless you dig for it under the blown insulation. While I'm sure this is not air tight, I doubt there is much circulation under the joists.

Thanks again.

[dash]

Dash:

Thanks for the replies and good suggestions.

Keep in mind that the insulation between our attic and bonus room is roughly 12" thick batts. While you could compress that down to fit in a 2x4 wall and then seal it with Thermo-Ply or wrap, you would lose much of the insulating ability by doing so. Sealing it and maintaining the current thickness would mean making the wall about 12" thick and that's why I'm looking for spacers or something.



Out bonus room sits directly over the living and dining room downstairs. There is a band of batt insulation around the joists. Then, the attic has blown insulation about a foot deep. You can't see the joist band unless you dig for it under the blown insulation. While I'm sure this is not air tight, I doubt there is much circulation under the joists.

Thanks again.

I was thinking "house wrao,stapled to each 2X4 ,without compressing the insulation too much.

Shoot the floor of the bonus room with an infrared thermometer ,on a hot afternoon and see what the temp. is, that an easy way we find them. Check the walls too.