2 stage AC or heat pump?

[beenthere]

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[ga-hvac-tech]

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.

[motoguy128]

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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[SkyHeating]

+1. IF you have propane, dual fuel all the way for sure. The effciency of heat pumps is actually slightly lower in 1st stage, so you don't gain much with 2 stage. 2 stage is more for comfort and effciency in cooling than heating.

I assume you mean 1st stage(low stage) is HIGHER efficiency, all equipment that I have seen shows much higher COP ratings.

[Quantumstate]

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[jpsmith1cm]

Quantumstate

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[motoguy128]

I assume you mean 1st stage(low stage) is HIGHER efficiency, all equipment that I have seen shows much higher COP ratings.

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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[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