2 stage AC or heat pump?

[ga-hvac-tech]

I know the oversized coils preform but putting a 3.5t on a 2t unit to get to 8.5hspf and 15 seer will kill latent cao when i looked at ratings goodman reached 9 hsPf on the 16 seer single stage ho written only a 2.5 ton coil. Performance above 40f was over a cop of 4 i think.

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I know intuition suggests latent capacity suffers with over-sized coils... however field experience does not always agree. Do you think AHRI is ignoring this?

And now just for fun, I will ask you the same question you asked me: How many of these have you installed?

[ga-hvac-tech]

In cooling yes, but in heating ive looked at carrier, york and geocomfort and with all, teh cop is higher in high stage than low stage in heating. I think Beenthere explained it once. In heating I think the higher mass flow of refrigerant has an advantage plus running on a fixed orifice not a txv has something to do with it.

It still nice for comfort and teh efficiency gained from long run times and more eventemperatures provides some effiency. A dual fuel size right with a 2 stage furnace in a cold climate should run almost continously under about 45f in any one of the 4 stages of heat.

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I will agree that running higher pressures will produce higher heat transfer... regardless of whether one is heating or cooling.

OTOH: I do not think you said this, however: there is NO way a piston is going to perform better than a TXV.

[motoguy128]

I thought the TXV is bypassed in heating mode and is metered by a fixed orifice when flow is reversed.

Eer is based on total capacity to total Watts. Larger indoors coils always increase output with a less that proportional increase in Watts although its diminishing returns at some point.

A larger coil surface with similar BTUs means a warmer coil which equals higher dewpoints. Standard ahri conditions do not reflect ideal indoor comfort. It also takes longer to wet a larger coil so in part load conditions moisture removal suffers. So them you run airflow lower giving up the shadowy gains our find the temp nerds to be set lower for comfort




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[54regcab]

Most 14SEER+ units are TXV anyways. Many have 2 TXVs one in the condenser, the other at the coil. I'd go single stage, I don't think 2 stage is worth the money.

[ga-hvac-tech]

I thought the TXV is bypassed in heating mode and is metered by a fixed orifice when flow is reversed.

Eer is based on total capacity to total Watts. Larger indoors coils always increase output with a less that proportional increase in Watts although its diminishing returns at some point.

A larger coil surface with similar BTUs means a warmer coil which equals higher dewpoints. Standard ahri conditions do not reflect ideal indoor comfort. It also takes longer to wet a larger coil so in part load conditions moisture removal suffers. So them you run airflow lower giving up the shadowy gains our find the temp nerds to be set lower for comfort




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In a HP installation, there are two metering devices... one at each end (indoor coil and outdoor coil). The indoor coil TXV meters for cooling and the outdoor TXV meters for heating. Each is a 'bypass' design TXV... that meaning when refrigerant flows in one direction it is metered, when it flows in the other direction it bypasses. One of the issues we had with higher SEER equipment when it first came out was bypass TXV's (most supply houses only stock coils with bypass... it is less inventor issues). The bypass in some Chinese TXV's (read that cheap) would not close during AC mode... thus not allowing adequate cooling and less humidity control.

Agree with EER... agree about diminishing returns also. This is why larger indoor coil sizing needs to be based on both AHRI matching as well as experience.

Ah yes grasshopper... yet you are not factoring in the ramping profiles of ECM motors... both at startup AND at shutdown... There is more to this than what is apparent... and what the books claim is not always correct in teh field... just one of those things.

[troyport]

I will check the part numbers on what my guy is planning on, but I am pretty sure it was going to be a matched unit... that is a 3 ton inside and out. And I was under the impression that since Goodman bought Amana (or vise-versa) that the warranty was the same? In reading stuff on this forum, I think I saw that I should have a TXV on both the cond and evap... My installer has a TXV listed, but only one... I assume there is one built in to the condenser? Why isn't there one built into the evap too if it is needed? thanks, Mike

[motoguy128]

GA thanks for clarifying that. I still see higher COP's listed for high stage heating in the mfg data sheets. AHRI will match a 3.5 ton indoor coil with a 2 ton condenser. Very common for example on the Yorks' I've looked at trying to get 8.5HSPF and 15 SEER while staying in the more economical LX line rather than jumping to the 2 stage Affinity series. Same with Carrier. Goodman however, matches better and seems to have better ratings on heating... which is why I asked about it earlier. On top of try to give some advice here and there I'm also learning and doing some of my own research for myself.

[ga-hvac-tech]

You are welcme... there is a certain amount of information one can learn from the books, yet also some one can only learn in the field... I shudder to remember all the spouting off I did before I had enough field experience... Lots of folks were patient with me.

I really do not know much about York/Coleman/(whatever other clone). I do know some about Rheem/Ruud, Goodman/Amana, and my brand AlliedAir (AirEase, ArmstrongAir, Concrod, Ducane). Generally, I see matches of 1/2 ton larger coil up to 3 ton, a few matches of 4 ton coil to 3 ton AC/HP. When we get to 3.5 and 4 ton outdoor units most of them are 5 ton coils, just a few 4 ton coil with 3.5 outdoor. That extreme match you noted; a 3.5 ton coil with a 2 ton outdoor unit... well I do not remember seeing one that 'extreme' in the lines I am familiar with.

I did a HUGE volume of 'tax credit' systems in 2010... when the govt would give you a $1500 tax credit for installing a 16 SEER system. I was more or less familiar with almost any match in the three manufacturers noted above. Out of all three manufacturers, I still like Rheem/Ruud equipment the best... Those rectangle outdoor units seem to be tougher and work better... albeit they cost more. I put in a 16 SEER 4 ton HP a few weeks ago; according to AHRI Ruud actually did test out at 16 SEER using a 4 ton AH... I used a 5 ton AH anyhow for other reasons (existing plenums matched the 5 ton Ruud). The 5 ton tested out about 1/4 ton better. The outdoor units are sooo quiet!

[superfittertech]

Amana and Goodman have the same exact warranties 10 yr labor warranty with goodcare

The Goodman communicating system is similar to Rheem/Ruud's system... a good system.

I would definitely use the larger coil with Goodman, be sure you get an all aluminum coil... and I would upgrade to Amana... you get a better warranty for the same hardware and you get access to a 10 yr labor warranty.

Plan to have annual service on the system; HP's and especially high SEER units need regular cleaning.

Sounds like you are gonna have a nice system.

[troyport]

Okay, thanks for all the replies! So, is it okay that my installer wants to put in a 3-ton HP with a 3 tone evap.. and.. he has a TXV on his parts list for the evap, but nothing listed for the condenser, so is the TXV part of the condenser? I trust he will do a good job, but I like to be armed with the correct info because I just want to be sure. thanks guys! Mike.

[ga-hvac-tech]

I think Goodman coils do not come with TXV's... some brands do (Rheem/Ruuds ALL do). If the outdoor unit is AC, there is no need. If the outdoor unit is a 16 SEER HP, I suspect it already has a TXV in it. Might want to verify that.

I would ask your contractor to show you the AHRI matches... either online or in the Goodman spec book.

[troyport]

hello, I am posting to an old thread because my question is related to this thread.. I hope that is okay.. My installer gave me the parts list, here is what my system will be comprised of, please let me know if this seems okay.. GMVM96 80K propane furnace installed last summer, now want to upgrade the AC to: 3ton 2-stage HP DSXC160361, CAPF3743C6 coil, TXV #TX3N4. I also have the best comfortnet t-stat. All Goodman stuff. According to what I can find, that coil is generally matched with either a 3 or a 3.5 ton HP.. Does this coil sound big enough? He also says a hard start kit is not needed.. opinions on this? Thanks, Mike

[beenthere]

Scroll compressor doesn't nee a hard start kit.

[hvacvegas]

Scroll compressor doesn't nee a hard start kit.

Goodman wants hard starts on "systems using non-bleed txv", which their TXV's happen to be.

Unless there's something I haven't heard of.

[beenthere]

Thought that was only on non scroll units.

[hvacvegas]

Thought that was only on non scroll units.

"Units with rotary or reciprocating compressors and non-bleed TXV’s
require a Hard Start Kit."

Thats the new slogan from the install instructions.

I know for a fact that the older models used to say scroll instead of recip. Sounds like someone made a typo and changed it.

Thanks for getting me to double check.

[ga-hvac-tech]

"Units with rotary or reciprocating compressors and non-bleed TXV’s
require a Hard Start Kit."

Thats the new slogan from the install instructions.

I know for a fact that the older models used to say scroll instead of recip. Sounds like someone made a typo and changed it.

Thanks for getting me to double check.

This reminds me of when R410 first came out in resi units... At first they said NO mixing of oil... now some say as much as 5% mineral oil is OK... so which one is it?

The manufacturers tend to say what they want when they want... IMO it is more a liability than a technical thing.

[troyport]

thanks for the replies guys.. but you have confused me because I don't know the technical terms.. so with this set up that he wants to install, do I need the hard start kit? He does not have it on his parts list but I am sure he would add it if I asked him to. And is that coil big enough for the HP? I have read on this forum that a lot of you like to put in a slightly bigger coil to put less strain on the HP. Thanks, Mike.

[ga-hvac-tech]

Yes, I would ask for the hard start. As long as they provide it... go ahead and get it. Outdoor units with hard starts tend to last longer (compressor) than units without... so it is worth it.
Ask your contractor to show you an AHRI match (he should be able to look it up on the internet in front of you). If a HP and a coil and furnace are an AHRI match... they are good.

[beenthere]

"Units with rotary or reciprocating compressors and non-bleed TXV’s
require a Hard Start Kit."

Thats the new slogan from the install instructions.

I know for a fact that the older models used to say scroll instead of recip. Sounds like someone made a typo and changed it.

Thanks for getting me to double check.

I was getting worried I would have to go back to some units and install hard starts.