Dual Fuel System Questions

[batman71]

I am replacing a dual fuel system that is 18 years old...heat pump with LP gas backup. The home is also 18 years old with about 2650 sq. ft. of living space. I am in central Ohio.
I have narrowed it down to two options both of which include the Carrier Infinity 80% furnace (80,000 BTU). This unit has the variable speed fan and 2 stage burner. I've decided that since the furnace will only be used at the coldest temps it would not make economic sense to spend the extra money for a high efficiency furnace such as the Carrier Infinity 96. In a typical winter I use only about 250 gallons of gas and the 80% furnace should cut that considerably.
On the heat pump (3 Ton),I'm trying to decide between the Carrier Performance 13 and their Infinity 17. The SEER rating of these two units are 14.5 and 17.5 respectively, a significant difference but the HSPF ratings aren't that different at 9.4 vs 9.5.
Since I live in Copeland "territory" and am personally acquainted with several engineers and marketing people employed there, I've been barraged with the benefits of the scroll technology. Therein lies part of the rub.
The Performance 13 HP has a scroll compressor whereas the Infinity 17 has a Bristol 2 stage reciprocating unit.
So, I'm torn between the less efficient HP with the scroll or the higher efficiency 2 stage design with recip'g. compressor. The cost difference is about $900.
My questions are as follows:

1)Is my logic sound going with the 80% furnace?
2)Infinity 17 or Performance 13 HP?
3)For the Infinity 17 HP and Infinity 80 furnace combination does $xxxx installed seem like a a fair price. Two contractors were within $100 of each other at this price.

Lastly, my current system has an electrostatic air cleaner that still works although I now have a preference for the simplicity of a media filter (EZ Flex). I am thinking of leaving the existing electronic air filter in place but removing the metal mesh pre-filter to minimize the pressure drop across it. Then, I would add ahead of this the new media filter. My logic is that the electrostatic filter would remove smaller particulate that the media filter won't. When the electrostatic filter "gives up the ghost" I'll just remove the cells rely on the media filter only from then on. In other words, I'll just take advantage of whatever life might be left in the electrostatic filter. Am I nuts thinking this way? Will this approach comprimise the overall syatem in any way?
Thanks for your input!


[Edited by lusker on 04-22-2005 at 08:29 PM]

[Dad]

http://hvac-talk.com/vbb/showthread.php?threadid=1241

[docholiday]

You probably wont get the savings you think with the 17 over the 13. Why? Because you nailed it by looking at the HSPF and if you look deeper, you will find the EER's arent that far apart either. Now there is a question of multiple stages which you may find comforting in your area, this makes for some fair argument to reconsider the big boy. I'm not impressed with the low latent capacity when in the lower stage but the longer run times might offset some of that.

I think for back-up heat, the 80 is fine. Im not a big fan of 90+ converted to LP anyway.

$xxxx sounds fair to me... ?????? Thanks for not posting pricing.

[protk1]

Doc H. I'm not disputing you but I'm curious why your are not a big fan of 90+ furnaces converted to LP. Thanks .....James

[docholiday]

Because LP is not the same no matter where you go but it gets treated the same by most installers. They simply use the orifaces supplied in the kit which are not always the right ones. Then you have the possiblilty of the HO changing LP companies or the LP company changing the mixture. When its not right, sooting is alot more prevelent and a secondary HX is a great place for fouling and difficult to clean. I rarely if ever hear of a natural gas furnace sooting once it is set up correctly but LP is another story all together.

I do understand the need to have LP, but unless your going to spend the time to set it up right and monitor it and as back up for a HP, it just isnt the wisest choice. I also know LP is expensive but the mere difference from an 80-90 in this application is, well, foolish. (Venting issues may be the deal breaker if there is no good chimney that can be lined or an exsisting b-vent.)

[beenthere]

You may find that the 13 seer scroll has better humidity control then the 17 seer bristol.

The bristol is a 50/100 compressor, and will give you a coil temp of about 50 degrees in first stage, the scroll is 67/100, and has a slightly cooler coil temp, 2 to 3 degees, which will help if your in a high humidity area.

[docholiday]

Thats made up in coil size though. (more surface area).

[wyounger]

The Performance 13 is a Copeland single stage scroll, so there is no 67%/100% split here. It's single stage or the Bristol TS 50/100%.

I agree with the 80% for dual fuel. It's just not going to run enough to make the fuel savings justify the extra cost of a 90+% furnace. There isn't a Carrier 80% 80,000 BTU furnace, though. There is an -070 model that is 66,000 BTU input, and an -090 that is 88,000.

As for the choice between the two heat pumps, check the ARI ratings and make absolutely sure that the numbers you're looking at are the real numbers for your exact prospective HP/coil/furnace combination. It can make a huge difference from size to size, coil to coil, etc., frankly it looks to me like the numbers you're looking at aren't correct.

I can't find ANY setup with the Infinity three ton that breaks an 8.3 HSPF with a furnace. Air handlers can get to 8.6. There is an odd-ball "037" three ton model that's higher, but still generally under 9 unless you use an air handler.

Assuming the more common vertical configuration and the -090 furnace, here are the numbers I find:
38YDB036, CK5...036 coil: 15.5 SEER, 8.2 HSPF (bigger coils are available, but don't boost heating efficiency, so skip them and get the best dehumidification.
38YDB037- only matches I can find for this furnace is 15.5/8.7. This is probably a rare and oddball setup (few matches, variable speed condenser fan motor).

38YXA036, CK5...042 coil: 13.5 SEER, 8.5 HSPF.
38YXA036, CK5...048 coil: 14 SEER, 8.8 HSPF (bigger coil is more efficient but won't dehumidify quiiiite as well).

I don't think you're going to pay for the upgrade to the Infinity 17 on energy savings- not in Ohio. Unless you're super-concerned about humidity control, I'd get the Performance 13 (YXA) with the CK5...042 size coil. The Infinity system does pretty well with humidity control even with a single speed outdoor unit (mine certainly does!). I'd only spring for the Infinity outdoor unit for the gadget value (direct digital communication between indoor and outdoor equipment for better diagnostics, etc.) or if there were severe humidity control concerns (Houston, Florida, etc.).

[beenthere]

So we need someone to tell us what size indoor coil each unit has.

[docholiday]

They do... called spec sheets or product data sheets.

I know you do beenthere but there are alot of HVAC guys that dont read these things, they might consider looking at several model and brands that best fit the need of the consumer. It really is interesting to find out the differences between mfg's performance numbers.

[beenthere]

Thanks wyounger, I didn't realize that the 13 seer he was talking about was single stage.

Alittle off topic, bit I like the bristol 50/100 for zoned systems, and i'm starting to lean more toward the scrol 67/100 for single zone systems.

York/Luxaire still uses 4 ton coils on 3 ton 15 seer equipment. Hard to get a cold coil on 2 stage 50/100 with their coil match ups.

[beenthere]

Originally posted by docholiday


I know you do beenthere

And how do you know that.

LOL...