Air Conditioner Sizing 13.5 vs 15

[Cumminsfan]

Originally Posted by Big Vic

Another consideration: 13.5K can probably run off a 2K genny, whereas a 15K may need a larger wattage genny.

It's rare that you can run a 13.5 off a 2000w gen. I've tried multiple times to try. I'm at 135' el and it won't do it with my Honda 2000W. Being higher up will make it even worse.
A yamaha 2400 should be able too. If the OP wants to run the AC off a gen then a 3000W would be better.

[rideandslide]

Just A Final Comment !!!

To me is a no Brainer ! Bigger is better ! We run are's on 30 amp service, with our other appliances running , no problem ! Once ! we popped the breaker, when the wife was using the micro, can only presume the water heater was on at that time !

We have a 2015 Grey Wolf 26RL,with the 15m air, i really wanted a all season TT, but prices, and de wife ( i insisted on rear living ) we found a great deal on our unit.

I know it's far as a top of the line unit, but we love it !!!! And most likely not very well insulated.

Back to the A/C On a recent trip, we were at a very semi shaded site, and the temps that day reached 104 deg. The 15m unit was able to maintain about 80 inside !!!
I guess not great, but happy ! Sure will have some feedback !

[Sweetbriar]

About the only very remote down side would be have too much cooling capacity and the A/C cools down faster than if can pull the humidity out and the rig feels like a cave, cold and damp. 30 amp will run a single 15K A/C all day. Add a second and you'll probably trip the breaker.

If the builder offers a 15K heat pump option that would be even better.

[wrvond]

Our old TT (a 1989 model) had a 13.5k BTU non-ducted unit. Once in a great while on a southern beach it seemed like the unit was working hard and the space wasn't as cool as I'd like it. So this time we got the 15k BTU ducted unit. We've never had a problem with power, but I have frozen the coils up once or twice. I think I had the thermostat set at 60* and it simply got too cold inside. I've since set the thermostat at 75* and haven't had any problems. I tend to think that with the ducting, a 13.5k unit would work just as well but I'd hate to go with a smaller unit and find I was wrong.

[Badlands Bob]

With our 15K ducted AC unit in a 22 foot trailer, I can hang meat in about 30 minutes. My wife discovered that she can't run the hair dryer and the coffee pot with the AC on. It's a learning curve.

[docj]

The posts to this thread omit one important factor with respect to air conditioning, both RV and residential. Over the past decade there have been major improvements in the energy efficiency of virtually all air conditioners sold in the US. So people's experience with older A/C's with 30A hookups isn't entirely relevant to the situation with new units. Furthermore, the energy efficiency of air conditioners usually depends on the placement of the specific model unit in a manufacturer's product line; more simply put, the more expensive units are usually more energy efficient,

That being said, there doesn't have to be much of a difference in energy usage between a 13,500 BTU unit compared with one producing 15,000 BTU of cooling. For example, according to Dometic its 13,500 BTU Penguin II will use 12.7A under normal operating conditions whereas the 15,000 BTU unit will use 12.9A. Both are designed to run on a circuit protected by a 30A breaker. Hardly enough difference to notice under most circumstances IMO.

In comparison, the less expensive Brisk II A/Cs use 15.3A and 15.98A for the 13,500 BTU and 15,000 BTU models.

So, if I were trying to run one of these in an RV rated for 30A connections I would want to have a more energy efficient model. Unfortunately, I suspect that many manufacturers choose to keep costs and prices down and probably don't equip their RVs with the higher priced, energy efficient units.

[Old Crows]

What DocJ has eloquently pointed out..... today's Heatpumps/AC units are more efficient and many will put out more BTU with less power demand than a smaller unit.

You need to look at the specs on the offered 15K BTU model and compare with the 13.5 unit. More BTU at less AMP draw is the key.

This also means that you can use a smaller generator.

Since campers/trailers are metal/fiberglass 'tents'..... cooking, bathing, breathing, pets, wet clothes, etc., add to the moisture inside the camper. De-humidification is very important, regardless of the temperature. So a larger unit will do a better job in in those areas where there is high temperatures and high humidity.

A last point is to look at the CFM of the interior fan. You need one with the best CFM you can get to make sure that the air circulates well throughout the camper. (Mighty important if you don't have a 'ducted' unit....)

[wingnut60]

I would think one would really need the startup amps to know what to expect. When quoting 'normal operating conditions' does this account for startup amps?
And, IMHO, there is definitely a difference in a generator output and a 30amp shore power--but I'm not smart enough to explain it.

Joe

[docj]

Originally Posted by wingnut60

I would think one would really need the startup amps to know what to expect. When quoting 'normal operating conditions' does this account for startup amps?

No, the normal operating load I cited was from the manufacturer's specs and doesn't include the starting load which, I understand, is typically 10-15 amps greater. When such units are run off of a 20A breaker, the starting load will momentarily exceed the breaker rating but it (usually) won't trip because the surge has a very short duration. I did find one RV A/C manufacturer that cited a "locked rotor" current draw of ~60A which would be a worse case situation for a compressor that wouldn't start.

Some air conditioner compressors do trip their breakers and this situation can become more common as a unit ages or when operating at reduced voltages. It sometimes is necessary to install "hard start kits" on A/C's that repeatedly trip their breakers. Such kits primarily consist of larger starting capacitors.

[D Lindy]

What is the amperage draw of a 13.5 A/C unit? My Coleman 15 pulls about 14 amps.

[docj]

Originally Posted by D Lindy

What is the amperage draw of a 13.5 A/C unit? My Coleman 15 pulls about 14 amps.

It depends on the brand and the specific model. The Dometic Penguin II only draws 0.2A less in a 13,500 model than it does as a 15,000 one.

[rideandslide]

OK ! Here's the scoop on our brand new ( replaced under warrentee ) Dometic Brisk II 15M, using my brand new Watt Miser use meter, set to read amps. We have 20 amp service to the TT, and till this point, don't run the A/C on but could as you will see.

Use when A/C unit turned on ( fan kicks in first ) 4.6 amps when it kicks on, and 2.08 running, Then when compressor kicks in, the meter when to 16 amps ( although it has a max of 15 amps ) then dropped quickly to 11.72 amps ( up and down a few points while running. Mean't to switch to KWPH but forgot, next time !! the voltage hovered around 110v-115 v. so i feel save should we want to run the A/C, no ele. water heater or Microwave while the A/C is running of course.

So i just run the Fridge on propane , stock it up with beer, and de wife gets pissed at me, i just head to the TT

Love this meter, i get to show de wife how but power this and that uses !!!!!!

[SailorSam]

Jim,
A lot of good info. Since I keep the S&B AC at 82 in the summer, being able to get down to 80 would be overkill for me.
Also, based on your numbers, a genny that has 2000 running watts would be enough to run your AC. Good to know. If your lighting is all LED and you ran the fridge on propane, you could get thru a night that way.
Al

[wildtoad]

Originally Posted by Sweetbriar

If the builder offers a 15K heat pump option that would be even better.

Bingo!

Also,

If you tow the trailer all day in a southern climate in say August with the sun beating down, you will want as much cooling and dehumidifying capacity as possible once you setup camp.