Are AC contractors "pushing" Trane XR13's?

wcweaver3

Hi there,
I have a 2300 square foot home served by a Unico AC system with a 3 ton American Standard compressor outside using R22 refigerant. The unit was installed 17 years ago (2005). The current American Standard unit is an Alligence 14, model number 2A7A4036B1000AA. As I read the model number, the "4" means the SEER is 14. Not bad for 17 years ago.

As it's 17 years old, I am inclined to replace it. I've had a number of contractors come in to take a look. They all say that since I have a Unico system, I am locked into a new 3 ton Unico coil and a 3.5 ton Unico air handler. And, I have to replace those to upgrade to R-410A. OK, I accept that.

I am looking at Trane units and two of these contractors say this: ..."You need a Trane XR13 and the SEER will be around 13 to 14. It doesn't matter if you get the Trane higher level SEER unit (like a XR17) with the two stage compressor and all that because you are locked into the Unico coil and air handler."

That seems a little far fecthed to me. If I buy a Trane XR17 with a two stage compressor that has an SEER of 18, it seems to me that it has to have a higher realized SEER than the XR13 even if the coil and airhandler are Unico. I would think that an AC unit (XR17) running a compressor at 30% at least some of the time would be more efficient than an AC unit (XR13) running a compressor at 100% all of the time.

My thought is that if I am going to spend the money, I want more SEER. If I go with an XR13 with an SEER between 13 to 14, I am not doing any better than what I have now with the old unit which is an SEER of 14.

Have I missed something?

EBEBRATT-Ed

Your only going to get the seer rating if the condenser is installed with a matching coil no matter what equipment you install.

If I recall are you in Pittsburgh?? If you figured out how much electricity you will use with a higher SEER versus a lower SEER in Pittsburgh in a year it won't be very much. AC equipment installed in northern locations just dosent run enough hours to make much difference but that's up to you

Jon_blaney

UNICO FAQ:24. Can any condenser or heat pump work with a Unico system?
Almost all makes of condensing units will work quiet well. You will lose about 2 points on a 13 seer and 5 to 15% Btu capacity at certain conditions. This is because we are operating at 250 cfm per ton instead of 400 which lowers Btu capacity. Unico operates at a higher duct static which lowers cfm per watt. SEER = BTUH / WATTS. The Unico duct system is much more efficient at delivering BTU’s to the space that we regain the efficiency and capacity because of our more efficient duct system.

25. How high a SEER rating can I install with a Unico System?
If the highest rated unit efficiency on paper is what is required by the homeowner then Unico will not equal a conventional systems matched combination. Even though the Unico’s delivered efficiency can be higher. A 13 SEER to a two stage 19 SEER will work very well with Unico air handlers. Be sure the control scheme is compatible. Some units have communicating indoor and outdoor sections. We use standard 24 volt control.

TAG

I only had one house w/ high velocity. It was my understanding that since the flow is constant you can't use a two stage compressor -- or anything other than a single stage output. Well you can ...but, there is no way to get the benefit.

I did read somplace where the newish Bosch condensing unit that works off pressure was installed and gave some added benifit. One thing to note -- Most of the higher end system use brand specific thermostats to get the benifits .. so that's another restriction.

Unless there is a thought that the unit is about to fail I'm not sure this is the time to switch it out .... also not much you gain

wcweaver3

Hi - many thanks for the great advice. I've been on the Unico website many times, but was unable to find the guidance about SEER dropping by 2 points - thank you! And, I agree - if the unit isn't about to fail (I don't think it is), why replace it? You've saved me thousands! Appreciate it!

wmgeorge

Does your old Evaporator coil have a TXV for a metering device? My concern would be its a old R22 coil and your going to put R410a in at lot more pressure, I have worked on commercial two stage units or with unloaders and never had an issue with the AHU speed, its just set at what is needed for the max BTUs of the condensing unit.
If its ok to run R410a you will need the TXV changed out. Most of the efficiently is gained with the new condensing unit.

Buts its been suggested in your part of the country as ours ((Iowa) , the A/C only runs perhaps 4 months of the year, so its more than likely got at least 5-6 more years of life...

EdTheHeaterMan

No, contractors are not pushing low efficiency. The unique design of a Unico High Velocity Duct system is more efficient than a standard "Large Duct" HVAC system. There is a SEER rating system in place since the 1970s (or before) so the regular home owner can more intelligently decide if paying a thousand dollars more for "High Efficiency" equipment is actually going to save on energy cost. But you already knew that.

The problem is that Unico does not make an air handler unit to match to a high efficiency dual or variable speed compressor. So in your case paying a thousand dollars more for the outdoor unit will not get you a lower operating cost to justify the price, because there is no matching Unico air handler that can produce that savings. The refrigerant dynamics and physics of the refrigeration cycle in a High Velocity Duct system does not lend itself to the higher price outdoor units of any brand name equipment. It is easy to see by going to AHRI directory and plugging in the Unico model number of the new air handler and see what Trane units will match up.

In this picture you can clearly see that a 3 Ton Trane unit will not get much over 12 SEER in any combination.



Go to www.ahridirectory.org and enter the Unico air handler you will install, then see what will match in the Trane XR17 and higher and see if you get a match. You won't

in these listings you can also see the to get 3 ton of cooling you must purchase a 3.5 ton outdoor unit and match it with a 3.5 ton air handler.

Now if you were insistent on wanting to get "The Best," most efficient Unico system, and I was the type of guy that thought, "Well this guy just won't listen to reason" so I'll sell him what he wants, I might just find that the system will never work right on low speed. After a year of listening to and trying to solve all the problems this miss-match caused, I would just put a jumper wire on the low speed relay to the high speed relay so the darn thing will just operate in high speed no matter what I set the thermostat to. either High or Off. that is all you get and it is working now!

Now you have spent extra for a feature you can't use anymore. and you think that I'm incompetent because i tried to do something that you insisted on that just won't work. That would make us both idiots. As your contractor offering you an estimate, I would offer you the XR13 and walk away if you wanted anything more. The extra $$$ will only get you and me aggravation that I would like my competitors to deal with.

I hope I wasn't to harsh

Mr Ed

GW

You’re gonna yank a conventional duct system and install a Unico? That’s going to take some dough. 

Unico is 1/2 the air flow (cfm)

BTU is cfm x delta t x 1.08

Their claim to fame is “better dehumidification”- but if you want BTU, just say with the normal ducts (unless the old ducts are sub par—- then chuck it or make never improvements)

EdTheHeaterMan

GW said:

You’re gonna yank a conventional duct system and install a Unico? That’s going to take some dough. 

Unico is 1/2 the air flow (cfm)

BTU is cfm x delta t x 1.08

Their claim to fame is “better dehumidification”- but if you want BTU, just say with the normal ducts (unless the old ducts are sub par—- then chuck it or make never improvements)

??? Gary... read the first line! ???




I think OP wants a high efficiency condensing unit and a new 410a Unico coil to match his existing 17 YO duct system. I believe he also wants the lowest operating cost he can get. this makes sense because the old system lasted 17 years. That's a good run. Spend an extra $$$ today for 17 more years of lower electric cost. Makes sense to me.

wcweaver3

Thank you for the insightful comments. Yes, the current system installed is a Unico with a Unico coil and Unico air handler. Mr. Ed - really appreciate the coil/comperessor SEER cross reference - I had hoped something like that existed, but wasn't able to find it. And, no not harsh at all - I now understand why they were landing on the XR13 and I REALLY appreciate the honest, thoughful reponse.

EdTheHeaterMan

wcweaver3 said:

Thank you for the insightful comments. Yes, the current system installed is a Unico with a Unico coil and Unico air handler. Mr. Ed - really appreciate the coil/comperessor SEER cross reference - I had hoped something like that existed, but wasn't able to find it. And, no not harsh at all - I now understand why they were landing on the XR13 and I REALLY appreciate the honest, thoughful reponse.

I did a search of a 3-3.5 ton coil on the ahridirectory.org and plugged in a coil only. left all others fields blank. less than 150 certificates available. sort by SEER and this one was the highest

Did not see Trane on the list but I did see American Standard (same stuff, same factory, same model numbers.)
I also tried that Unico coil on AC only (not heat pump) and nothing came up.
So not all equipment is listed on AHRI but that does not mean it won't work. Your Unico dealer will know what outdoor equipment they have the most success with in your area.

GW

Ed OK I don’t read very well 

EdTheHeaterMan

GW said:

Ed OK I don’t read very well 

No problem Greg Winslow Oops, I mean Gary Wilson... I have had my Emily Litella moments too

GW

Way too triggered Ed, you need more hobbies. If you would have just stated the math in the beginning, we would all be in a better place. 

TAG

OP -- My guess is the 13 seer is being recommended because it's the best match for what you have ... there is no way to harness what the higher seer units have to offer. Remember hearing the 2 point SEER drop as well ... not something that Unico wants to boast about. They have always said the system performs in different ways and I know they addressed the SEER difference ... my system did work well and nothing else would have been able to have been retrofitted.

With the change in refrigerant you have no choice but to change out the inside evaporator as well --- I'm assuming the air handler is still usable. They had different types .... I'm just not sure how much you will save doing what is basically like for like? Even if you save 25% ... what's the AC cost to run for the season and the potential savings.

I would call Unico and see if they can give you any feedback. They were nice to me many years ago when I was trying to silence a couple of outputs. Sometimes you get a talker who will give you the lowdown -- maybe you can find out is there is any benefit to the higher single speed SEER equipment .. or what they are using for condensers.

Manufacturers do make odd components for special applications. When I was doing my NJ house in order to get the rebates I had to get a special Carrier condenser just for some markets .... Carrier makes what is a 3 ton unit in a 4 ton case -- more surface area. It changes the heat-pump curve and better matches the area (actually 37k BTU). I ordered the same unit for my house in PA as that will be used about the same. There are odd things out there for specific applications

wcweaver3

Thank you! I will give Unico a call.

John Mills_5

Check your duct system. Last 2 HV systems we replaced we had to add runs to meet their instructions. We had trouble with 1 and even though we put in the minimum they wanted for a 3 ton, they told us probably should have added a couple more even.