10 Ton air conditioner

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Elfmaze

Elfmaze

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Just bought a new A/c for the house. Swapping the old 10 ton out for a new energy efficient 14 Ton.

Now as i look at the spare 10Ton...... Think it would run a walk in closet sized cold room? I don't know if it would actually be useful but it would be good for wine storage at least.


Btw: Ops if a mod sees this i meant for the DIY forum.
 
I think you meant 14 SEER...Not ton (a measurement of heat exchange capacity).

How old is the unit? If it's more than 15 years old, I would recycle it...
 
Hmm maby it was seer. The unit is about 10 years old. But as its getting pulled out the compressor unit still looks pretty good.

Mainly swapping because the heat exchanger was shot and gettin gthe government kick back. I was just thinking about the window a/c glycol units and wastinking that would be one hella cooler. Lol
 
Yeah, you meant seer. Either way, it'd make a hell of a cooling unit for anything brewering related but it would be kind of expensive to run and require a lot of power be run to it.

Seeing as how it's a split unit (I/m assuming) it would be kinda nice though if your 'closet' were in the middle of the house or otherwise hard to exhaust hot air from.
 
Running a 10 year old unit with a shot heat exchanger (condenser, evaporator?) isn't a good idea. Even if it was usable, it would be way over-powered (probably around 3 tons/36,000 BTU) for a walk-in cooler. It would cycle infrequently and the temperature of the cooler would be erratic. Overly large A/Cs can also be a source of humidity problems. The unit cools before it has time to remove the moisture. I've got a 5000 BTU window A/C for my brewery cooler and is does a good job.
 
Yup. You meant SEER.

I have a 3.5 ton, 10 SEER, on my 2300sqft house right now. I too am upgrading to a 4 ton, 14.5 SEER.

Ditch it and get one of those packaged in room air conditioners. Because keep in mind that the box outside is only 1 of 3 pieces to the system (4 actually) in addition to that you have to have the evaporator coil, some kind of fan to move the air, and mebe some ductwork to channel the air properly.

Not to even mention an additional disconnect and a 40 amp circuit for it. It would definitely do the job, just not very efficiently.
 
GilaMinumBeer said:
Yup. You meant SEER.

I have a 3.5 ton, 10 SEER, on my 2300sqft house right now. I too am upgrading to a 4 ton, 14.5 SEER.

Ditch it and get one of those packaged in room air conditioners. Because keep in mind that the box outside is only 1 of 3 pieces to the system (4 actually) in addition to that you have to have the evaporator coil, some kind of fan to move the air, and mebe some ductwork to channel the air properly.

Not to even mention an additional disconnect and a 40 amp circuit for it. It would definitely do the job, just not very efficiently.
Click to expand...

Do yourself a favor and go with the same size as your old, unless you had REAL problems keeping cool. I had a small 1500 sq ft house and had a replacement unit put in. The salesman tells me, "My software says 2-tons should be fine, but you could go 2.5 tons if you want to really be cool!" A typical "rule-of-thumb" HVAC guys use is 800 sq ft per ton. Rules of thumb suck. Get a real energy analysis.

So, back to my story. Yes, my house was cool. But, my AC would also run for 10 minutes and turn off for 10, back on, back off. It's called short-cycling and it is because the unit was oversized. If I knew what I know now, I would have gotten the 2-ton. AC units don't reach their rated SEER until equilibrium is reached. That usually takes 30-40 minutes for a modern unit. Don't forget it is cheaper to run a smaller unit longer than a big unit in short bursts.

So, you can do what you want, but my suggestion is to go with the smaller of what they recommend. If you're hot, the installers know you'll call to complain. So, they always recommend a "little big" to have a satisfied customer. Oh, and they make a little more money on the sale of a larger unit. Plus more Freon. Plus, it costs you more every month in energy. Just my $0.02.
 
2-0turbo said:
Do yourself a favor and go with the same size as your old, unless you had REAL problems keeping cool. I had a small 1500 sq ft house and had a replacement unit put in. The salesman tells me, "My software says 2-tons should be fine, but you could go 2.5 tons if you want to really be cool!" A typical "rule-of-thumb" HVAC guys use is 800 sq ft per ton. Rules of thumb suck. Get a real energy analysis.

So, back to my story. Yes, my house was cool. But, my AC would also run for 10 minutes and turn off for 10, back on, back off. It's called short-cycling and it is because the unit was oversized. If I knew what I know now, I would have gotten the 2-ton. AC units don't reach their rated SEER until equilibrium is reached. That usually takes 30-40 minutes for a modern unit. Don't forget it is cheaper to run a smaller unit longer than a big unit in short bursts.

So, you can do what you want, but my suggestion is to go with the smaller of what they recommend. If you're hot, the installers know you'll call to complain. So, they always recommend a "little big" to have a satisfied customer. Oh, and they make a little more money on the sale of a larger unit. Plus more Freon. Plus, it costs you more every month in energy. Just my $0.02.
Click to expand...

Your problem is/was due to a poor control loop (i.e., thermostat), not an oversized unit. It is generally recommended to go slightly larger than you need since a larger capacity system will theoretically (1) run less and (2) last longer (due to #1).

Just so you know, the quickest way to kill a compressor is to undersize a unit...Bad advice.
 
lamarguy said:
Just so you know, the quickest way to kill a compressor is to undersize a unit...Bad advice.
Click to expand...

Agreed.

And generally, HVAC use 500sqft/ton but YRMV and the 500ft/ton is actually a sales technique to get people to buy oversized equipment which can be a cause of short cycling. However, newer units avert this to a degree with variable speed fans (as opposed to single speed on/off) to circulate air through the home constantly. A "Manual J" heat load/cooling load calculation is the industry standard way to calculate acvtual btu needs (and losses) to match to the appropriate equipment.

I did have a heating and cooling load analysis done (Manual J) by 3 contractors and by myself (with the instruction of a Mechanical Chief Inspector). This is what I need for my situation. 3.86 tons to be exact but, most brands now make full tonnage jumps.

You also have to take into account that btu outputs are different now too. 10 years ago energy was cheap and units pumped out more btu's. Todays equipment has become more efficient but many (not all) systems kick out fewer btu's per ton. Thus, oft times a step is needed.

However, in "some cases" a smaller unit is justifiable in that window technology and door seal technology has improved as well as insulation performance so, if some or all of those aspects have been updated a smaller tonnage may suffice.

Another problem with some installs is that codes have changed from that of yore and a bigger service is mandated or sometimes even required by the unit. Unfortunately, some of the smaller HVAC companies don't take notice of this (as many don't carry a electrical license) and it causes problems with the unit.
 
GilaMinumBeer said:
Agreed.


You also have to take into account that btu outputs are different now too. 10 years ago energy was cheap and units pumped out more btu's. Todays equipment has become more efficient but many (not all) systems kick out fewer btu's per ton. Thus, oft times a step is needed.
Click to expand...

I thought 'ton' in HVAC speak was a direct conversion for BTU/hr?:confused:? I.E. one ton of refrigeration = 12 MBTU/hr.
 
MMW said:
I thought 'ton' in HVAC speak was a direct conversion for BTU/hr?:confused:? I.E. one ton of refrigeration = 12 MBTU/hr.
Click to expand...

It is, but like I said, the rules have changed for how many btu's/hr are needed. And, not all makers follow 3 ton = 36k/btu. For example, my 1999 American Standard 3.5 ton, 10 SEER system was rated at 46k total btu/hr with about 30 of them being "sensible".

That was my point, older systems kicked out more btu less efficiently because energy standards weren't as big a concern. things are different now and the 3t = 36k holds more weight.

Additionally, I am also having my furnace replaced with equivalent sizing but higher efficiency. The btu output on the old unit "was" 180k btu/hr (60% AFUE) and a new system does it with 100k btu/hr but with an 80% AFUE.

They use less enerrgy today but, get more of whats used into the structure than they did before. with the old, 40% of the energy went up my flue to atmosphere and that was when it was new. Today, that furnace is 26 years old.
 
2-0turbo said:
The salesman tells me, "My software says 2-tons should be fine, but you could go 2.5 tons if you want to really be cool!" A typical "rule-of-thumb" HVAC guys use is 800 sq ft per ton. Rules of thumb suck. Get a real energy analysis.
Click to expand...

And this is precisely why I obtained 7 quotes, 3 Manual Load calcs, AND talked to the Authorities Having Jurisdiction. Sales men say lots of interesting things especially when they stack $$$$. For what many co's are charging $12k, I am getting done for less than $5k. and with the $7k savings I can use elsewhere (I need better windows) or for service "if" needed. I have researched my chosen contractor with the Inspections department(has failed 2 inspection in a 15 year history), the BBB, the Licensing department (liscence has never lapsed), and with the Equipment Manufactuerer he is representing (4 warranty claims in 15 years).

If this guy botches the install, it will be a rare occasion, and he has a good standing reputation fo work done right.
 
lamarguy said:
Your problem is/was due to a poor control loop (i.e., thermostat), not an oversized unit. It is generally recommended to go slightly larger than you need since a larger capacity system will theoretically (1) run less and (2) last longer (due to #1).

Just so you know, the quickest way to kill a compressor is to undersize a unit...Bad advice.
Click to expand...

You sound like a heat pump salesman. I don't disagree that the controls on my unit were crappy. It was the latest and greatest programmable thermostat, variable speed air handler, single speed compressor. Unfortunately, the deadband on the thermostat could not be adjusted. So, one-degree above/below my setpoint and the unit would cycle on/off.

You can't really undersize a compressor. It will happily move XXX BTU's from one place to another all day long. Your logic is similar to saying a deskfan will die quicker than a 16" floor model if it is not properly sized for the room. True, if it runs all year long, that is 8000 hours per year and it will wear out quicker than a unit that runs 3 hours per day (1100 hs/year)--this is comprehended by most people. Where you can screw up is sizing your evaporator wrong. Of course, these are usually matched together, so manufacturers/installers make some compromises (you can't have a small outdoor unit with a huge evaporator/air handler or vice versa).

But, a PROPERLY sized HVAC SYSTEM will move the most amount of heat for the least amount of work. If you oversize it, it is not going to be as efficient and will use more energy than a properly sized unit. Will it cool? Yes. Will it heat? Yes. Might it use more energy that a properly sized unit? Quite likely. My other suggestion is to get advice from someone other than the person selling you the unit--this really goes without saying. Remember, they don't want you calling back saying it is not cooling. Does that mean you'll call them back and complain about spending $7 more per month on your electric bill? No, you won't, because you'll be cool, you'll never see the extra $7, which is why they tend to oversize.

See here for some more info. I do stand corrected and upon doing some reading, most manufacturers say their units hit their rated SEER and reach equilibrium in about 10-15 minutes instead of 30-40. Sounds likes they are making some improvements in this area. But, this means if your unit runs for 15-minutes and shuts off, you just got to max efficiency before it turned off.
 
2-0turbo said:
You sound like a heat pump salesman. I don't disagree that the controls on my unit were crappy. It was the latest and greatest programmable thermostat, variable speed air handler, single speed compressor. Unfortunately, the deadband on the thermostat could not be adjusted. So, one-degree above/below my setpoint and the unit would cycle on/off.

You can't really undersize a compressor. It will happily move XXX BTU's from one place to another all day long. Your logic is similar to saying a deskfan will die quicker than a 16" floor model if it is not properly sized for the room. True, if it runs all year long, that is 8000 hours per year and it will wear out quicker than a unit that runs 3 hours per day (1100 hs/year)--this is comprehended by most people. Where you can screw up is sizing your evaporator wrong. Of course, these are usually matched together, so manufacturers/installers make some compromises (you can't have a small outdoor unit with a huge evaporator/air handler or vice versa).

But, a PROPERLY sized HVAC SYSTEM will move the most amount of heat for the least amount of work. If you oversize it, it is not going to be as efficient and will use more energy than a properly sized unit. Will it cool? Yes. Will it heat? Yes. Might it use more energy that a properly sized unit? Quite likely. My other suggestion is to get advice from someone other than the person selling you the unit--this really goes without saying. Remember, they don't want you calling back saying it is not cooling. Does that mean you'll call them back and complain about spending $7 more per month on your electric bill? No, you won't, because you'll be cool, you'll never see the extra $7, which is why they tend to oversize.

See here for some more info. I do stand corrected and upon doing some reading, most manufacturers say their units hit their rated SEER and reach equilibrium in about 10-15 minutes instead of 30-40. Sounds likes they are making some improvements in this area. But, this means if your unit runs for 15-minutes and shuts off, you just got to max efficiency before it turned off.
Click to expand...

A well functioning A/C system is about acheiving balance. Too large, like you said, the system never reaches it's efficient operating range before cycling. Too small, and the compressor runs all day.

Constant overheating is the primary cause of compressor failure, followed by hard stops which slowly weaken the valves. Overheating can be caused by long running cycles (undersized unit) and/or running low on freon (evaporator ices-over).

I installed A/C systems for 6 years in my previous life (paid for my college education). Based on that experience, my recommendation is to always slightly oversize the unit to prolong the life of the compressor.

There are other tricks too, like installing a slightly larger evaporator and swapping the orifice or expansion valve accordingly to achieve a small (5%) gain in efficiency. Of course, the gained efficiency comes at the price of a more expensive evaporator coil...
 

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