Does it cost more money to run a 2 ton AC condensor or a 2 and a half ton AC condensor?

Question

I am a maintenance tech at an apartment complex in Phoenix, AZ. We do all of our AC work in-house ( service , installs etc. ). There is a guy who lives in the complex who has his own AC company and is trying to sell us condensers for our split-system straight-cool units. His price is less than our usual supplier so that is well and good. But rather than just pocket the savings, the property manager is considering taking that money saved and spending it on a larger condensor.

Our air-handlers are theoretically convertable to a larger tonnage by simply changing out the piston /metering orfice so we probably could accomodate the larger condensor.

My opinion on this matter was asked and I was against the idea because the stated reason for doing it is to save the residents money on their power bill. The idea being that a larger condensor would have to run less often to acheive the desired temperature inside the apartment. My counter-argument is that it may well have to run less often but it will be running a larger compressor and a larger fan motor ( and therefore have a larger amp draw ) when it IS running.

 The higher power consumption when it is running seems like it would counteract to a large extent the savings gained when it isnt running. 

But that is just my opinion and I am not an engineer, just a lowly technician with hands-on experience.

So my question is this- all other factors being equal- same heat load, same thermostat setting, same seer rating, same brand etc.- is it cheaper to run a 2 ton condensor or a 2 and a half ton condensor? 

It seems to me that there is no free lunch and that if you want to transfer X amount of heat BTU's then you are going to have to expend the same power to move that heat whether you do it with a 2 ton unit running more often or a 2 and a half running less often. 

Additional info: I am aware that it is possible to acheive more actual cooling with a 2 and a half ton system, and that it could certainly save money running a larger condensor if it was a situation where the 2 ton wasnt sufficient for the load and therefore ran all the time, but that is not the case here. 

Nobody is complaining that their system is failing to acheive the desired temperature with their new 2 ton system, it's just that some residents are whining about their high power bills. Our property manager just wants to help lower the bills for the residents by giving them a larger unit if it would in-fact save them money .

So to sum up, are we going to acheive great power savings with the larger condensor for our residents, or is it a waste of money?

Another factor in all of this, is that on some of the air-handlers, it is well-nigh impossible to actually see or work on the piston/metering orfice because the units are crammed up into a tiny little space above the air-return grille, so unless there is mad-money to be saved for the residents I really don't want to upsize our systems!

Hopefully there are some knowledgable AC folks who can shed some light on this qestion / debate...

Boe · Accepted Answer

Here is how I see this. 
If the original systems were designed and spec'd out to be 2 ton units. Then the duct work in place more than likely can not handle the additional BTU;s off cooling.  
To me its a complete waste of money. 
Invest in digital thermostats 1. 
2nd you need to CLEAN the coils on the condensing units chemically 
3 dont use cheap mesh style filters, and use pleated filters. Ideally every 30 days would be great, but that aint gonna happed. So, if you can at least 4 times a year change these out that will help out. 

You also need to inspect the evaporator coil esp if these units are a couple of years old and they have been running mesh filters in the. You will find that the evaporator coils are probably very dirty. 
So couple a dirty evaporator coil, dirty condensing unit, say the thermostats are mechanical. And that = $$$ to the end user. Also. by not maintaining the equipment it shorten the service life of the unit as it works harder and long to try and achieve the cooling results. 
You can get setup with a supply house to buy the pleated filter which are your cost around 3-3.50. There would be a greater discount if you buy them in bulk (as the unit all take the same size filter.) 

You can reduce electrical consumption in excess of 180.00 per year per unit by maintain the equipment correctly.  So this in turn by having a true maintenance program in place not only save the renter money, but also the Apt complex in the long haul as the equipment with proper maintenance should see a good service life of 15-17 Years. 
No maintenance or half **** so to speak and you be band aiding / replacing stuff in 7-8 years. 
If all this equipment is R410A its even more sensitive to  keeping that outdoor and indoor coil clean. And R410A runs at much higher pressure than that of and R-22 System. R-22 system are more forgiving and can be neglect to all hell and still run. They just dont see the high pressures that R410A does.  I cant tell you how many R410A systems Ive seen take a crap in 1-2 years. When condensers too dirty, and with the already high opperating pressures it runs at the compressor can not sustain the added abuse of a dirty coil which drives the pressssue up even more. Somethings got to give and typically from what I saw was a dead compressor.  Yes, the pressure switches are suppose to stop that from happening. But the "contractors" grade or "builders" grade units dont have the pressure switch incorporated into the unit So while it preforms the same function, it also lower the cost of the actual unit. Thats typically what would be sold and installed. While nothing wrong with it.  That the common issue. Guessing thats whats being proposed here contractor grade. 
The price is probably killer. But youd really or they I should say would be wasting there money. Take that money and set whats needed aside for the maintenance of the equipment. 

BTW 2.5 Tons of cooling vs 2 tons of cooling. You would gain roughly 6000 BTUS of additional cooling. And you are correct if the coils are size for 3 tons then yes, you could change out the piston to match the OD unit if you went the 2.5 Ton. But to me my concern is the duct work is NOT size nor will it handle the additional BTUS of cooling. The unit will run LONGER!!! Bigger IS NOT always better. Its sized off a Jload calculation and this would have been done pre-constrcition and size accordingly to the spec of the Apt.  Its got disaster spelled all over it if the go bigger. Trust me.  The cost factor would be insane to swap all of these out. I cant see the savings even if they claimed it would work.   Its just a bad idea if you ask me, and I have not even see the job. 
Have a reputable company come in and present to you a maintenace plan. If they are any good at what the do. they will be able to show you hard number on what you can expect to save. 
A rule of thumb is take the current bill do as I suggested and you should see an average savings of 18% which is more real world.

Marko · Answer

I'd agree with the others here who don't see a significant, if any, money savings when you factor in the higher amp draw at start up on a bigger compressor. On the other hand . .
The increased humidity with a larger ecoil may be a benefit, especially in Phoenix, plus it will make the room feel more comfortable and the user can lower the setting on the stat a degree or two because of that, which is a savings for them. Also, more humidity requires a little more maintenance for the drain pans and drain lines but that may not be when you're in a dry climate.
If I was the owner, I'd be more inclined to use that capital for insulation and new windows.
Additionally, if they're wanting to upgrade the units for their long term plans, I'd do it a few units at a time, or, as they breakdown. In that case, they could buy two of them and have them ready to install when the time comes, and see how it goes.

Chuck · Answer

Well, first of all you have to understand that system efficiency is increased with run time. it's the start up that costs.

Now, if the outside units are really new, then they are 13 SEER efficient and the air handler may need a TXV valve rather than a piston to achieve that efficiency and to save the compressor  from freon back flow. By the way, are these air handlers the "above the tub" fan coil type?

You can check the specs. but a lot of stop and start is going to cost more and likely increase humidity.

Anonymous · Answer

Ton Ac

? · Answer

I can't see much of a savings by simply swapping out condensing units. You're essentially going to be mixing used, new and off-sized componants (ducts were sized to be used with a 2 ton system) together. 

 That's not a formula for higher efficiency, in my opinion.

CALIBOY · Answer

ok that was alot and i didnt read it all heres what u need to know 220v. cost less than 120v. cuz it uses less amps to run its the amps u need to look at on the unit it will say for example 220 v. 30 amp max compare the 2 units amp max and the lower amps will cost less to run

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Does it cost more money to run a 2 ton AC condensor or a 2 and a half ton AC condensor?

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