what SEER is this

[jimbo]

We are still going round and round about my daughter's air cond., and she has had a few people out to look, but in my mind no one has yet done adequate testing. Anyway, the latest guy told her the system was too badly mismatched to ever work right. He says 14 SEER evap. cased coil, 8 SEER condensing unit. The coil is a year old, probalby 13 or 14 SEER. The outdoor unit is this: anyone know the SEER? It is 10 years old, min.

HEIL. VILLAGER. model ACS036A2C1 ( mfg. # NACS036A2C1).

[jadnashua]

My understanding is that the system SEER is a combination of the compressor, the refrigerant, and the evaporator coil. Change any one of those, and you may compromise the total efficiency. Depending on what refrigerant was in use, your compressor choices may be limited, as it must be compatible with what was used in the coil. Different coils perform different depending on the refrigerant.

[Dana]

My understanding is that the system SEER is a combination of the compressor, the refrigerant, and the evaporator coil. Change any one of those, and you may compromise the total efficiency. Depending on what refrigerant was in use, your compressor choices may be limited, as it must be compatible with what was used in the coil. Different coils perform different depending on the refrigerant.

And SEER presumes a certain duty cycle, yadda yadda...

The problem with SEER & AFUE is that they're fixed points on a continuous curve of real-world conditions, which doesn't tell you a whole lot about the real as-used efficiency. Oversized short-cycling beasts are gonna suck no matter what the compressor & coil technology or refrigerant. Those that run high duty cycles &/or long minimum cycles are gonna do pretty well. The configuration of compressor coils & refrigerants puts an upper bound on it, but there's no simple magic formula by which you can determine the as-used SEER (or AFUE). Even knowing the average load conditions only gives you a ball-park, with a lot of room for variation.

The question isn't really "what SEER is this?", but "will this coil air-handler, and that compressor work reasonably well together with that refrigerant". I'm not enough of an AC designer to answer that question, but it sounds like the guy who says there is a severe enough component mis-match to ever work right is probably onto something. But it has more to do with relative component sizing than it is with SEER. You can easily have a 14 SEER compressor that's way oversized for a 14 SEER air handler coil, if the compressor is 4 tons and the air handler was designed for 2 tons, or conversely.

Using a different refrigerant than one or the other was designed for makes it even more complicated. The 10 year old ACS036A2C1 is probably designed for R22 (it's specified on a plate somewhere on the unit.) The evaporator coil or it's ratings may have been specified for use with something else, like R410A. If you have to replace one or the other to get it to work right, replace the compressor- it's half the efficiency of newer better stuff, and R22 is going away, and is more than halfway through it's normal service-life anyway. (You may be able to get Federal & State subsidies for retiring it.)

But whatever you do, use a contractor that actually designs stuff- sounds like this may have been a hack by a well-intentioned but not fully competent installer when the new coil was installed.

[Thatguy]

If you find the generally accepted testing standards for SEER, you could get some bids on how much an HVAC company would charge to confirm/deny what overall SEER your system has.
It'd also come in handy if they could extrapolate from existing measurements to what the standard SEER test would say. This would involve curves supplied by the manuf. or just generic curves.
http://efficientcomfort.net/jsp/PsychroCoilCalc_Web.jsp
http://books.google.com/books?id=A7W...age&q=&f=false

It depends on what level of accuracy is good enough. A WAG by an HVAC tech. might get you within 50% of the true value. Many measurements might get you within 10% of the true value. Measurements at a NIST lab might get you within 1% and cost you dearly.

It is 10 years old, min.

Then it's lost 2 SEER off it's original value, by some reckoning.

[jimbo]

It is not really a question of what the system SEER is; the issue is ...is the mismatch so great that it cannot work.

I am really pushing them to just get a new condening unit, but her hubby is balking at the cost if it is not necessary.

[Thatguy]

. . .if it is not necessary.

There's comfort and there's payback period, and for the payback period somebody should make measurements.

If you know the heat gain for the building, indoor/outdoor temps., kw into the HVAC and the cost per kwh of elec. you can get the COP and then figure payback. I've heard of people who went from SEER 9 to SEER 18 and there was no change in the kwh.

Depending the kilobucks involved and the expectations for a new install you might to hire HVAC consulting engineers. This information has value.
http://en.wikipedia.org/wiki/Expecte...ct_information

If the hubby has more use for money than for comfort and the wife is the opposite, there are ways to resolve this besides rock/paper/scissors.