SEER in the real world.

[Glennhvac]

Maybe I am missing something or my casual test was a bit haphazard but I was underwhelmed. Just for the fun of it a few years back I did a before and after amp draw test on a new installation. I replaced one of those condensing units that was like an upside down U with the double shaft fan. Maybe a York? It was the type that took forever to dry out to check pressures after you washed it out. They also were sold under anther name as DIY units. I'll venture a guess that maybe it would have been equal to 8 or 9 SEER.

Anyway I replaced this 5 ton system, TXV coil (13 SEER) and the furnace. When all was said and done my TD was within a degree or so of the old system and the running amp draw was about one whopping amp less. That is the same as one average light bulb!

To sum it up, ever since that installation I have been very hesitant to make much of a point about how much more efficient new systems are or how they will pay for themselves. There are nowhere near enough cooling days in the Chicago area to justify that as reason alone.

I am curious about thoughts on this. The power consumption change was almost meaningless as far as payback time. So what am I missing?

[ar_hvac_man]

I generally see a sizable amp drop when changing old equipment. Its very hot here though. Maybe newer units draw less under heavy load?

Good question, interested in what others think about it

[doc havoc]

Sorry Glenn, no input here. Just tagging along to see other replies.

[FLSTC]

IMHO, in the northern regions going from a 8 seer to a 13 seer will not save enough to justify cost. But the reason for replacement is not based on eff. alone, most of the time it should be balanced on warranty, matched system, sight appeal, etc....
In the north we base most of our jobs on heating, I would imagine in the southern states it is reversed and they would replace a/cs based on eff. and not the heating.

One thing to keep in mind. Your best eff. upgrade is to ECM equipment. Always do a load cal as well, most of the time older equipment was oversized and as a result ended up being really inefficient.

[vstech]

I remember the old singer units looking like you describe. I'll bet it was more like a 5 seer unit, the 8's didn't come out until the mid 80's. what's the dataplate minimum circuit ampacity of the old unit? max breaker size? on the units I've installed, it's been nearly 1/2 what the old 70's or 80's units required... 1 amp? possibly your system is overcharged? possibly there was very little demand on the old system when in operation... possibly the system is drawing in hot air from the attic to the return, seriously overloading the unit... I don't know.

[Glennhvac]

Update from VSTECH post. Yep it may have been closer to a 5/6 seer unit which only makes the payback scene worse! That is over doubling the SEER rating on the new for one amp. Maybe 2 if my meter is off a bit.

[hvacrmedic]

What was he indoor WB temp before and after? What was the ambient temp before and after. What was the capacity before and after. Without that data you can't draw any conclusions about relative efficiency.

[Glennhvac]

What was he indoor WB temp before and after? What was the ambient temp before and after. What was the capacity before and after. Without that data you can't draw any conclusions about relative efficiency.

I did not take a ton of readings. I may next time. I can only say that the ambient outdoor temps and the indoor load were nearly the same when I checked the draw on the old unit and the new unit. These people never open windows and on both occasions the system was merely cycling on and off to maintain indoor temp.

[Ron223]

Interesting stuff.... With that said, what does the SEER designation consist of? What factors are measured to surmise the the rating? Is it mostly based on COP? Maybe that will help me understand whats distinguishes an 8 from a 15 in general. Cause if its just current draw, it doesn't sound so good base on whats being posted.

[SkyHeating]

It all depends on outdoor temp and run time. If one unit was running for 20 minutes and it was 75 degrees out and the other was just started up and it is the end of the day and now 90 yes there may not be much difference... Let's see if I can get my numbers right here.

Cooling SEER is based on an 82 degree outdoor temp and 80 degree indoor temp, this is not realistic. Now SEER means for each watt of energy X BTU's are removed, so 20 SEER means that at above conditions for each watt of energy expelled 20 BTUs of heat were removed, now EER is more realistic because I think it again assumes a 80 degree indoor and now a 95 degree outdoor, at this point that same 20 SEEER unit is only a 14EER.

[Ron223]

It all depends on outdoor temp and run time. If one unit was running for 20 minutes and it was 75 degrees out and the other was just started up and it is the end of the day and now 90 yes there may not be much difference... Let's see if I can get my numbers right here.

Cooling SEER is based on an 82 degree outdoor temp and 80 degree indoor temp, this is not realistic. Now SEER means for each watt of energy X BTU's are removed, so 20 SEER means that at above conditions for each watt of energy expelled 20 BTUs of heat were removed, now EER is more realistic because I think it again assumes a 80 degree indoor and now a 95 degree outdoor, at this point that same 20 SEEER unit is only a 14EER.

So then wouldn't COP be a more accurate way of measuring this?

[SkyHeating]

But COP does not measure cooling its heating. A COP of 1.0 ias electeic resistance heat there is not really the same standard to compare to for cooling. But SEER and EER are BS because as temp changes so does efficiency. A customer that I buys 13 SEER will rarely ever see their equipment operating that well.

[Ron223]

But COP does not measure cooling its heating. A COP of 1.0 ias electeic resistance heat there is not really the same standard to compare to for cooling. But SEER and EER are BS because as temp changes so does efficiency. A customer that I buys 13 SEER will rarely ever see their equipment operating that well.

I know how to do it for all forms of heating btu's but I guess I assumed we could do it for measuring cooling btu's.... I understand now. So SEER and EER are the comparable measures for cooling btu's? Hmmm, it does seem with all the emphasis on these eff. Ratings it would be a better way of really being able to translate it. So the ratings are only based on being yielded at design conditions?

[SkyHeating]

The ratings are only at AHRI conditions not design conditions as those vary by job and location.

Now look at variable compressor units like a ductless or the greenspeed and it might as well be all but impossible to accuratly rate. But with an invertor units are often running at higher efficiency than rated vs conventional running at lower efficiences.

[Ron223]

Ok. Thanks.

[hvacrmedic]

I did not take a ton of readings. I may next time. I can only say that the ambient outdoor temps and the indoor load were nearly the same when I checked the draw on the old unit and the new unit. These people never open windows and on both occasions the system was merely cycling on and off to maintain indoor temp.

Even with identical indoor and outdoor conditions there may have been a half ton or more difference in capacity, due only to low indoor airflow on the old system.

[Senior1]

IMHO, in the northern regions going from a 8 seer to a 13 seer will not save enough to justify cost. .

You are correct, same in the south.

Clean the cond/evap/blower wheel of an old system, you just saved the same amount as new system. (all else being same, correct charge, air flow,etc.)

I have advised a comp change, even with one year warr if a system is ok, leak free and good airflow. Sales weasels will tell you different.

[Glennhvac]

Even with identical indoor and outdoor conditions there may have been a half ton or more difference in capacity, due only to low indoor airflow on the old system.

That would help with shorter run time for sure. From what I see as far as amp draw it's all going to have to come from a shortened run time. If they say a 13 seer should cost half as much to run as a 7 seer it sure is not coming from one or two less amps running on a five ton unit.

[rdholder]

How SEER is Calculated

ARI 210/240 Conditions

SEER is calculated by dividing the net total cooling capacity (in Btu/h) by the total power input (in Watts) with indoor temperatures of 80°F dry bulb and 67°F wet bulb (26.7°C/19.4°C), an outdoor air temperature of 82°F (27.8°C) and includes a penalty for cycling degradation. Tests for determining cycling degradation also are conducted with an outdoor temperature of 82°F (27.8°C). For equipment that uses a condenser coil condensate evaporation technique, the outdoor wet bulb is specified to be 65°F (18.3°C). At this condition the outdoor enthalpy (30 Btu/lb) is lower than the indoor value (31.5 Btu/lb). For two-speed or two-compressor equipment, a bin method calculation is used in which 66% of the outdoor bin temperatures are actually less than the indoor temperature.

[mark beiser]

If you were to take the full load of readings to determine the actual capacity the old system was operating at vs the new system, you likely would have found that the old system was in much worse shape than you thought.