A coil/Condensor sizing

[MechAcc]

[:-bigeyes The hvac guy, and I am one, may not be full of crap. Mismatching of coils has been a concern of the Dept of Energy when the government mandated 10 seer efficiency ratings in the early 90's. And is a bigger concern with the updating of minimum efficiencies to 13 seer. The DOE contracted a manufacturer to test new air conditioning condensers with older evaporator coils. With a mix of txv's and capillary tube metering devices. Their findings back then the system in many instances needed extra refrigerant added in order for the system to provide any adequate cooling. The down side was that additional refrigerant put extra stress on the compressor and electrical consumption ended up being equal to and in some cases greater than the wattage that of the replaced condensing unit.

Bristol Compressors recently did their own test when the 13 seer minimum efficiency was mandated. Their findings closely corresponded that of the test contracted by the DOE in the 90's. In the case of a heat pump unit it was found that the charge had to be readjusted when changing from heating to cooling mode.

It is going to be really interesting when 2010 arrives and R-22 equipment can no longer be sold. The hacks that have been cobbling in new condensers on old evaporators are going to be in for a shock when they don't install a matched indoor coil.

[energy star]

Originally posted by fyrmnk

Here's the info off what's installed. Any feedback on this installation?

Furnace by International Comfort Products

Evaporator Coil

model no. EPA42F19B1

mfg. no. NEPD42F19B1

serial no. L984436333

Forced Air Furnace

model no. GNE100F14A1

mfg. no. GNE100F14A1

serial no. L984122059

Air Conditioner by Goodman Manufacturing

model no. CKT481AB

serial no. 9904473052

Thanks again

Evap 3.5 ton, A/C unit, 4 ton = not good.

[kajer]

A under sized evap. coil will decrease efficiency. Were a over sized evap. coil by 1\2 a ton will increase the efficiency.

[Jim Baird]

ScottPat said

"...The house had many moisture problems all attributed to the over sized A/C system..."

Pardon my ignorance, but I have slogged all the way across the icy tundra of this thread and have not seen this statement elucidated.

Just how does an oversized system create moisture problems in a house?

I looked at a house where the occupant claimed "mold" problems, but mostly what I saw was plain old dirt. The only moisture source inside was the vertical clothes dryer exhaust that looked like it stayed clogged all the time. Then there was an unattended return filter that fit miserably. Advised occupant that dryer exhaust would have to be cleaned often and ought to be re-routed, and that the filtration scene should be tightened up, A-coil likely clogged up.

The claim of mold was accompanied by vigorous affectation of coughing. (Very relevant factor: I noticed that other yet sold homes in the little 'hood had signs advertising "owner financing". Most substandard dwelling complaints I have attended to were from occupants who were behind on rent or mortgage payments)

Pardon the digression.

Again brethren, how does oversized system create moisture problem?

[Terence McCann]

When an a/c system is ovesized it will maintain house temperature but will not dehumidify properly due to the fact that it doesn't run long enough - cold clammy feel.. The longer the system runs the better dehumidification. Not good for an a/c system to short cycle either which happens when they are too big for the load.

I've never heard of this type of thing causing moisture problems though, just comfort problems.

[Jim Baird]

Thanks for the reply Terry.

I had heard the short cycling argument, but am still trying to grasp just how short that cycle might become to result in non-circulation to the point that the ambient air becomes clammy.

There has to be a certain amount of circulation to cool things at all.

I think that refrigeration theory is one of Natures first orders of mystery anyway.

My HVAC man installed me a programmable T-stat a cpl of yrs back and warned me not to put too great a spread between my settings, lest I defeat the purpose of modulation.

[Terence McCann]

Thanks for the reply Terry.

I had heard the short cycling argument, but am still trying to grasp just how short that cycle might become to result in non-circulation to the point that the ambient air becomes clammy.

There has to be a certain amount of circulation to cool things at all.

I think that refrigeration theory is one of Natures first orders of mystery anyway.

My HVAC man installed me a programmable T-stat a cpl of yrs back and warned me not to put too great a spread between my settings, lest I defeat the purpose of modulation.

It's not an air circulation problem but a problem with the unit not running enough. With an oversized system it will cool the room space quicker than it can remove humidity. As setpoint is reached the unit shuts down but the humidity still remains.

There are some fixes for an oversized system but they really only make sense for a commercial system. With residential it would be a better bet just to bite the bullet and replace it.

[Jim Baird]

Thanks again Terry.

It's not that I like to argue or claim to be an HVAC xpert, but the thinking that drove my prior post went like this.

Let's say there's a volume of air in a building that, due largely to its relatively expanded state at its current temp, contains X amount of moisture in the form of vapor.

When that air is cooled by the action on it of HVAC equipment of whatever size, it has to give up moisture that is changes state into liquid as condensate. Does not that air contain the amount of vapor that is commensurate to its density as determined by its temp?

Whether the refrigerant coils it passes over are colder or haotter, doesn't it give up that moisture not as a function of how cold the refrigerant is but as a function of its drop in temp?

I have been in a house where a dirty A-coil kept the air from cooling and thus felt clammy, but it wasn't cold and clammy. It felt, rather, like a jungle.

[Terence McCann]

Hey Jim:

Here is a pretty good write up on the subject:

http://www.proctoreng.com/articles/bigger.html

A tidbit from it: The ability of the air conditioner to remove moisture (latent capacity) is lowest at the beginning of the air conditioner cycle. The moisture removed from the indoor air is dependent upon the indoor coil temperature being below the dew-point temperature of the air. The moisture then wets the indoor coil and, should the unit run long enough, will begin to flow off the coil and be removed out of the condensate drain.

For short cycles, the coil does not have time to operate at the low temperature and when the unit stops, the moisture on the coil evaporates back into the indoor air. Thus, in humid climates, a properly sized air conditioner will do a far better job of removing moisture from the air than oversized units

The article is a little simplistic but gets the point across.

If I have a four ton air conditioner but only a two ton load it will drop the room temperature quickly (sensible load) but won't stay on long enough to remove moisture (latent load).

Coil design however is out of my league - you'll need a guy with a pocket protector for that discussion.

Hope this helps.

[Jim Baird]

Muchas gracias Terry.

What I like about this site is that questions get answered so well.

[ebtorqued]

Something to look for is recently replaced windows in a larger home. I have designed systems that required a 5 ton with single pane windows and poor insulation but a 4 ton with double pane windows and added insulation. This was found out by doing a heat load calculation with both situations. (The home owner was in the middle of a energy efficiency remodel).

Unfortunately there are to many "Heat 'em and Cheat 'em companies that will also replace a unit with the same size as the failed unit without doing a heat load.

[inspectorholmes]

Question for Scott Patterson;

How do you check both the evaporator coil size to the exterior componets. I would like to here this.

[Bain]

Scott speaks for himself just fine, but the coil sizing is nearly always listed in the model number.

[plummen]

Quote:Originally posted by fyrmnk

It is a 4 ton condensor and 3 1/2 ton A-coil.

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That's a bunch of crap anyway... a 12.5% mismatch on sizing either way makes no difference. The system will flow at the rate the expansion valve allows.

how do you know it was a txv system and not just a 10seer with a piston/orifice? the high side of compressor will be restricted by wrong size of piston causing high head pressure shortening life of condensing unit.

[plummen]

Kevin

The HVAC guys are full of crap!

Captain

what is your experiance in hvac field,or am i being too abrasive asking such a thing as ive been told? and yes i do refrigiration work also

[plummen]

I agree with Chad, Captian and Terrance.

I've specifically asked HVAC guys why I sometimes see mismatched coils on coolings systems and they've explained that it was deliberate and calculated. However, they have explained that it should always be (I believe) it was the evap coil that should be larger. (Don't quote me on that part because I honestly don't remember and hope someone will chime int and nail that part down.)

For a small period of time I used to actually report mismatched coils until I realized this is beyond our expertise and more than likely the HVAC guy knew what he was doing. (Even though they can't seem to assemble systems airtight worth a hoot.) [:-magnify

this is how you gain efficiency in a cooling system by making the coils bigger more surface area/more freon .look at the size of the coil on a 10seer condensing unit then compare to a 13 seer

[plummen]

Well said, Brian!

Speaking of miss-matches, the equipment gets better and the installations get worse cancelling all the manufacturer's good efforts and the poor consumer's alleged benefits.

HVAC contractors have a huge gap to close, themselves!

They're not high on my list these days simply because their shortcomings spell flat out laziness and carelessness. And, you know that the installations on their own homes are perfection.

In example: Yesterday's new construction home inspection revealed the HVAC system had:

- Holes at the corners of the metal ductwork junctions as round as a dimes!

- Gaps around the suction line where it entered the evap coil big enough to plunge your pinky finger into.

- Gaps where the blower and evap coil cabinets joined big enough you could see right into the unit and the same where the ducts joined the unit.

If a surgeon sewed his patient up like that they'd bleed to death. A boat built like that would sink to the bottom in seconds.

It's just downright shameful and inexcusable! I mean WHY BOTHER to show up for work? In fact, please do EVERYONE a favor and DON'T show up for work!

Nice to know us contractors are all a bunch of hack artists! have you taken into consideration that lots of stuff gets installed by bozos working out of pickup trucks and not actual contractors? some of us do go out of our way to make sure our work is very nicely done above and beyond any building codes! [:-censore

[plummen]

Yep, what they all said. Not our job, well beyond the scope, and probably not even the problem to start with. No way I'd cover that, and I don't believe for a minute they could make me either.

The service guys and contractors (all kinds) seem to be getting more and more into the mode of claiming anything they find or fix should have been caught at inspection. I don't know if it's revenge or they're just trying to look good for having *out-done* us. All I can say is that if most of them were doing thier job as thoroughly as I do mine, we'd all be out of work. I'm not worried.

Brian G.

Not An HVAC System Engineer [:-irked]

Im not worried either! [:-slaphap

[plummen]

There's really little variation in standard line sets. I have the Carrier design manuals as well as the Trane design manual however, these get more into commercial/industrial applications.

Attached is a link for a pretty good PDF on sizing. http://www.thermopride.com/Manuals/13_SEERAC_I&O.pdf

As you can see the sizing doesn't vary a whole lot and assuming (bad word, I know) that the installation was correct to begin with not changing out the line set doesn't cause any red flags to pop up however, I do point out if the condensing unit is newer and the liquid line dryer is still old, if the armaflex is shot or if the disconnect is rusted and in need of replacement. You should always install a new liquid line dryer whenever you have to open up the system as well as pulling a good vacuum to purge moisture and non-condensible.

In commercial applications where there is a remote condenser, not condensing unit, it is advisable to change out the hot gas line. The hot gas line really takes a pounding from the constant high temperatures and the expansion and contraction during cycles. This is an area that is prone to leaks over time.

the liquid line is the high side of condensor that pumps liquid freon to the A coil and already has a filter installed from the factory on every unit ive ever seen.The suction line on the other hand pulls freon/vapor back to the unit.If you need to replace the condensing unit the suction side should have a filter/dryer installed before condensing unit to catch anything from being pulled back into the condensor and or compressor.

[plummen]

Well, just to be clear on my question, sometimes I'll see that the old line set diameters are significantly smaller that the lines on the new equipment and they've just crimped and soldered them. Is that OK?

that qualifies as butchering in my book since you can buy any size ofreducer you want at a supply house

[plummen]

I guess I'm having difficulty trying to decide what should be called out as mismatched units or components on an air conditioning unit. As an example:

The condenser and evaporator being two different sizes/ratings. For the most part, trying to figure out the size of the unit becomes a guessing game. Especially if you are trying to read the model number or serial number. I've been told that you take the first set of numbers that you can divide by 12 and that will tell you the tonnage. However I see numbers like 604842. Is that a 5 ton unit or a 4 ton unit?

I'm under the impression that if you have a Carrier condenser and a York evaporator (different name brands) you now have a mismatched unit. It may not work efficiently. Do you call these out?

Yesterday's inspection had a 8 year old condenser unit and a 21 year old evaporator. Is this a matched unit? As seer ratings change it's my understanding that coil size changes also. So this unit may not work very efficient.

I have heard that you can go 1/2 size larger on an evaporator if it is an air conditioning unit. However, if it is a heat pump it must be the right size.

Currently I would think that if you are going to call out mismatched units or components, you need to do everything and not only size.

Jeff Euriech

Peoria AZ

In my experiance goodman and summit coils normally go up by 1/2t inciments.2t and 2 1/2t are same coil,piston is differant.

the biggest thing is to match the tonnage brand doesnt matter much,sometimes differant brand of coil must be used because of clearance issue.

[plummen]

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31.43 KB lets see if i can make this work

[plummen]

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71.92 KB heres a 15 seer heatpump install from differant job last month,yes i straightened out the feet before i was done! []

[plummen]

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50.61 KB funny nobody noticed the tape on bottem of flue pipe when this one was inspected! [:-yuck]

[Jim Katen]

I agree with Chad, Captian and Terrance.

I've specifically asked HVAC guys why I sometimes see mismatched coils on coolings systems and they've explained that it was deliberate and calculated. However, they have explained that it should always be (I believe) it was the evap coil that should be larger. (Don't quote me on that part because I honestly don't remember and hope someone will chime int and nail that part down.)

For a small period of time I used to actually report mismatched coils until I realized this is beyond our expertise and more than likely the HVAC guy knew what he was doing. (Even though they can't seem to assemble systems airtight worth a hoot.) [:-magnify

this is how you gain efficiency in a cooling system by making the coils bigger more surface area/more freon .look at the size of the coil on a 10seer condensing unit then compare to a 13 seer

It's interesting that the engineers who design these systems didn't think of that.

- Jim Katen, Oregon