Whats the deal with new seer standards
user-144543
| Posted in Energy, Heating & Insulation on
I have some older apartments which from time to time will need new outdoor condensing units. The apartments are roughly 900sf. Whats the deal with the new seer ratings. Can I use a new condensing unit on an older system, and what size condensing unit do I need for this size apartment. I was told the rule of thumb is 1 ton per 700sf. Does this still hold true?
Replies
Can I use a new condensing unit on an older system
No, but people will do it anyways. Condenser, evaporator and lineset must be matched for best performance and long life. 13 SEER condenser + 10 SEER coil = short life (and around 7 actual SEER).
A bigger problem for you will be the phaseout of R22 systems for 410A... the two are not compatible. Old poorly installed linesets will have oil traps and the oils are not compatible. Metering devices are not compatible. Flushing linesets to an acceptable condition is questionable. Anyone that tells you otherwise is full of it.
Cheap customers will insist on a mismatch, and hack companies will do it.
I was told the rule of thumb is 1 ton per 700sf
Rule of thumb? Hackery.
Load calculation will tell you for sure.
Edited 2/5/2009 4:32 pm ET by danski0224
As Dan said, rule of thumb is worthless, do a load calc.
There has been a volumous discussion of reuse of line sets and evaporators. Very divergent opinions.
Would have no problems reusing evaporators with R22, an old 10 SEER 1-1/2 T unit would function well with a 1 T new condensor unit and probably be over 13 SEER as a combo, but no way of knowing without detailed data on the evaporator (indoor unit). As for converting to 410A, getting mineral oil out of traps is a problem, removal/replacement using N2 fill is the most reliable. Would not try to reuse an aluminum coil evaporator with 410A due to the much higher (2x or more) pressures.
...an old 10 SEER 1-1/2 T unit would function well with a 1 T new condensor unit and probably be over 13 SEER as a combo...
That is a possibility, but how many people will downsize the condenser- especially the hacks that don't do a load calc?
Would not try to reuse an aluminum coil evaporator with 410A due to the much higher (2x or more) pressures.
Well, you shouldn't be reusing an old *R22* evaporator for a new *R410A* condenser in the first place... it won't work unless you change the metering device, and then there is the issue of all that trapped oil in the old part. The R410A will not pick up the mineral oil, so it is there forever, reducing the efficiency of your system.
Anyone desiring a 15, 20 or more year old component to be mixed in with a new AC component is using poor judgement... especially now with the phaseout of R22.
Trane and American Standard are offering *new* evaporator coils made out of aluminum.
ACCA has a "white paper" out on mixing different SEER split AC components. In a nutshell, don't do it.
The hacks that can't/won't install R22 stuff properly will be doing the same with R410A systems, and those systems will die an early death.
"Whats the deal with the new seer ratings."
On January 23, 2006, a new government mandate took effect that raised the minimum efficiency standard for all newly manufactured central air conditioners and heat pumps from 10 SEER to 13 SEER. The regulations require that all products manufactured after that date meet the new standard.
"Can I use a new condensing unit on an older system, and what size condensing unit do I need for this size apartment. I was told the rule of thumb is 1 ton per 700sf. Does this still hold true?"
You can still buy R-22 units and they can be installed on an existing system. R-22 will no longer be produced or exported in the near future (2010, I believe) but the availability of R-22 will be relatively unaffected for the next 2 or 3 decades.
There is a kernal of truth about mixing refrigerants. IF you change to R-410a, change everything.
Installing a 13 SEER condenser in a system previously "designed" for a 10 SEER will not result in a SEER of 7, nor will it result in a SEER of 13. The manner in which units were revised to achieve increased efficiency ratings are complicated and beyond the scope of your question, but basically, the statements about shortened life and lowered efficiency ratings in slightly "mismatched" systems are not based in reality.
The only Rule of Thumb that holds true: Don't hit yours with a hammer!. Construction, climate, and exposure all play into the correct sizing of equipment. Replacing like for like is a good start unless known problems exist.
Thanks, that kind of clears things up for me.