??? Which uses less energy ??? 2 air conditioners on low or 1 air conditioner on high ???

[SamKnause]

This refers to identical window units bought at the same time.

All help appreciated.

[Kali]

1. probably the 2 uses more

you are at least running 2 fans, and I think they are what really uses the most electricity, but the truth is probably more complex - length of run time, volts or amps or whatever (I do NOT understand that shis LOL), stress on machines etc.

[SamKnause]

3. From what I understand, (which is very little) the compressors are what use the most energy and

the fans use very little energy.

If this is true, than 2 air conditioners on low would use more energy then 1 air conditioner on high.

Thanks so much for your input.

[Kali]

4. don't EVER take electrical advice from me!

it is basically voodoo magic to my brain

[ProfessorGAC]

7. The Fans Are A Fraction Of Energy Usage

You're right about that.
I don't have my manuals handy, so I'm making an experienced guess here; i seriously doubt low is 50% power, or 50% duration.
If I had to make a bet, I'd pick 2/3rds.
So, 2 on low probably uses 33.3% more power.
I guarantee that a window unit on low doesn't run only half as much as on high.
You can hear when it's on.
That's where my 2/3rd guess comes from.

[SamKnause]

10. Thank you so very much for your input.

I think your experienced guess is right.

[Blue_true]

41. You are ignoring the temperature target, that determines the duty cycle before

the compressor shuts off.

If he is trying to cool a big space with one AC unit, the bet here is that the compressor never shuts off. Cooling the same space with two units would most likely result in the compressors being idle a considerable amount of time because the space cooling would be more efficient.

[ProfessorGAC]

44. I Didn't Ignore Anything

I said I was guessing from experience.
Our entire house is window A/C. We have circulating hot water heat. We could never bear the disruption of having walls ceiling, and floors to run central air ducting. So, we never went central.
As we added units to cool more rooms (3 to 4 to 5) we saw a more than linear increase in electric costs.
Your scenario would apply here. 3 units for the whole house, we would think, would run a lot more often, than 4 or 5. Hence running more units would mean less compressor time. But, we didn't see that.
Also, my thoughts were on two at low, or one on high.
I would have had the same idea as you, if we're talking 1 or 2 units running the same power setting.
But, that wasn't how I read the OP.
So, we don't disagree, but I think we're talking about 2 different things.

[Blue_true]

36. You are right if the two ACs are cooling to the same temperature target as the one.

Last edited Sat Aug 8, 2020, 11:00 PM - Edit history (1)

But, why would you do that? You would have two ACs to make cooling near space more efficient, that would result in less duty for their compressors. The compressors drive the Refrigeration Cycle in the ACs (along with the coolant), as long as that cycle is needed to cool air, the compressor will be running.

Edit: I used a biological term for a thermodynamics term. Updated to correct term.

[tblue37]

20. You're essentially "refrigerating" a space when you air condition it, so it takes more

energy than a mere fan does.

I don't know the answer to the OP's question, though.

[Kali]

21. oh I do know that

but I thought I had read that fans use more electricity than compressors - but I fully admit I have no clue where I got that

[SheltieLover]

2. Prob 2 units on low

It's the compressor cycling that runs up bill.

If you can get a ductless, variable speed mini-split, you will save a ton of money on power because the unit runs constanptly, rather than cycling.

Sounds crazy, I know. But I've had one for over a year & my power bill is never more than $100. (I keep it cold - 65 F.)

[SamKnause]

5. That's what I thought.

2 compressors would use more energy.

I don't run my A.C.'s all the time.

I just turn them on as needed.

There is no cycling on or off involved.

Thanks so much for your input.

[SheltieLover]

6. The compressors do cycle

Whether you know it or not. They do in cars, too!

Many of the mini-split units come fully charged & only take an hr or so to install. 👍

[SamKnause]

8. Thank you.

I did not know that.

By cycling I thought you meant kicking on and off like central air.

Thanks for the information.

[SheltieLover]

11. No. The fan will still run

But compressors go on & off. 👍

Yw. Feel free to message me if you need help. 😊

[SamKnause]

13. Thank you so very much.

The reason I asked the question is I love to conserve energy and save money.

I bought my 2 new air conditioners in July of last year.

I am good to go for now.

I don't have a problem with high electric bills in the summer.

That is only a winter problem for me.

Again thanks.

[SheltieLover]

14. You are most welcome!

Glad you are all good. 😊👍

[Amishman]

42. Just need to second this mention of ductless minisplits

This lets old homes without ducting take advantage of the exceptional energy efficiency of heat pumps.

IMO, there should be a huge government program to retrofit and insulate older homes. Heat pumps need to become ubiquitous in this country to help limit climate change.

[SheltieLover]

43. Even in homes with ducts

Mqkes an enormous difference to not be blowing cold air through ducts in hot attic or crawl space. Same with heat in winter.

I was skeptical, but I love it! And comparatively a much much cheaper unit & install! 😍

[doc03]

9. I would say one on high. Most of the power is consumed

by the compressor. Puting them on high is just the fan speed. That's my guess. Want to know for sure measure their amperage.

[SamKnause]

15. Thank you.

[doc03]

12. I would say one on high. Most of the power is consumed

by the compressor. Puting them on high is just the fan speed. That's my guess. Want to know for sure measure the the current.

[SamKnause]

17. Thank you so much for your input.

[doc03]

19. When I was young I lived in a mobil home for a while

I had one on each end of my trailer I could get it like a meat locker.

[SamKnause]

22. I hear that.

The 2 small units I have only cost $138.00 each.

They will turn this place into a meat locker as well.

They work so much better then my central air ever did and much cheaper.

[doc03]

25. I had a 12k on one one end and 5k on the other.

I think the 12k was the biggest I could use with 120 volts.

[fescuerescue]

16. We can only guess - but 2 is probably worse

But it all depends on the specific units.

Get one of these and you'll know precisely

https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU

[SamKnause]

18. Thank you so much.

[Happy Hoosier]

37. If only there were people who did this kind of thing!

Let’s call them engineers.

In almost all cases one unit will be more efficient than two, assuming all three units are identical.

There are some possible corner cases, however.

[LeftInTX]

23. I don't understand the question...

Are you trying to cool one room?


Or are you trying to cool two separate rooms?

[SamKnause]

26. Sorry I should have mentioned 1 large room.

All doors to the room are closed.

My question has been answered.

2 compressors use more energy then 1 compressor.

Thanks so much.

[LeftInTX]

28. Got it...Yes one unit in one room

Two separate rooms, two units are best.

[SiliconValley_Dem]

24. 2 on low will be more energy but more effective across larger area

[SamKnause]

27. Yes, I find this to be true.

It is one large room.

All doors to the room are closed.

I notice when I have the 2 AC's on low it will freeze me out.

Thanks for your input.

[Kaleva]

29. A furnace or air conditioner runs most efficiently when in steady state (running most of the time)

[SamKnause]

30. I am not sure what you are saying.

Does this mean you should never use the low setting on the AC ???

[Kaleva]

31. Set it where it runs pretty much continuously during the hottest time of day while...

maintaining the temp you want.

[SamKnause]

32. There are 4 settings for the AC's or fans only:

On

Off

Low

High

[Blue_true]

33. Depends upon the duty cycle.

I assume that when you say “low” and “high” you are referring to the temperature target. Of course if you have two air conditioners in different parts of your home chilling the space around them to say 65 F, versus one air conditioner in say your living room chilling the near space to 65 F, the two air conditioners will use more power.

Here is the deal. Air conditioners of the window variety are best at cooling a near space. The air conditioner in your living room will likely cool the living room fairly well, but your bedroom(s), bathroom(s) and kitchen likely will be warmer, unless they are open to your living room. So, if you use two AC units, why not run each to cool the near space to 70 F?. If you follow the last idea, the total duty cycle of the two ACs could be lower than for the one cooling to 5 F lower.

[SamKnause]

38. I should have mentioned it is 1 large room with all doors closed.

There are also ceiling fans above each AC.

I was just curious about the energy usage.

I thought 2 compressors would use more energy and that has been confirmed.

Thank you so much for your input.

[Blue_true]

48. The ceiling fans help with air circulation. But.

Last edited Sat Aug 8, 2020, 10:56 PM - Edit history (1)

If you have two ACs cooling a space to the same temperature target as one AC, the compressor duty cycle for the two ACs will be significantly lower. Even if you go with what the Prof pointed out, if the compressors on each of the two ACs are running at anything less than 55-60% of the time that the one AC is running, then you are better off with two well placed ACs. The efficiency of the Refrigeration Cycle is dependent on the time based deltaT of air being cooled, that deltaT has a high value a long time for the one AC, even with a ceiling fan, so the Cycle for the one AC will be inherently less efficient than that of either of the two ACs. My guess, depending upon how far down you are cooling the room, the one AC never shuts off.

Maybe you should go online to an AC design site and ask this question of AC engineers, giving them all the information about how your room is laid out (ie, ceiling fans-and their size, and location of windows in the room). You can also maybe go the AC manufacturers help lines and ask the question.

Updated: don’t know where my brain was. I used a biological process term for the refrigeration cycle where a gas is compressed then expanded, cooling during the expansion.

[SamKnause]

50. Thanks for all you input and helpful suggestions.

[Mosby]

34. My two cents

the reason why one unit is probably more efficient is that it can take up to 10 minutes for a compressor to reach its SEER rating. So if two units cycle on and off quickly they lose efficiency every time the compressor kicks on, and if they don't run long enough they never hit the advertised SEER number.

[SamKnause]

39. Thank you.

[Flaleftist]

35. Can you read your meter?

If you can see your meter, do a test and find out. Record where your meter is and run one on high for a few hours and note the difference. Then run two on low and compare. You might also be able to log on to your account and see the usage online. Duke energy lets you see the charts of your energy usage down to the hour.

[SamKnause]

40. Thank you for the suggestion.

[SheltieLover]

45. If you have a friend with an amp clamp

It would only take 2 min to measure draw of each unit on different speeds.

Looks sort of like a claw & they just open it & clip around wires to measure draw. 👍

[moondust]

49. Or get a cheap usage meter.

https://wiki.ezvid.com/best-electricity-usage-monitors

Run AC for a while on high and then on low (x2).

[Happy Hoosier]

46. In almost all cases, one will be more efficient that two.... cases

Here’s why...

Air conditional compressors tend to operate digitally... they are either on or off. The “high and low” refers to the fan speed. I assume for this analysis that the target room temp is the same in both situations. There will be some baseline losses in each unit which, being identical, means the two units will consume twice as much as the one unit, but these loses are small... these are line losses, the power lost in the control system, etc. the fans on the two units, being set on “low” will consume less energy individually for sure. Without knowing the characteristic of the speed settings and motor efficiency, it’s not definitely possible say if together they would use as much energy as the single unit on high, but I suspect so. The compressors are where the vast majority of energy goes. And so the question really is, will the duty cycle of two compressors be low enough to overcome the additional losses of have two units.

The answer is almost certainly no. The effect of two air conditioners would be a lower duty cycles on the compressors. But to be able to get more efficient than the single unit, they would have to be on for considerably less than half the time than the single unit. But the lower fan speed means that 2 units will not be likely to cool twice as fast as the single unit, even if we assume the energy use scales linearly.

And this makes sense. After all, if this trick worked, we likely see spaces cooled by multiple smaller units. We mainly see multiple units when a single larger unit is not convenient or the duct system isn’t suitable (my house an upstairs and downstairs unit, for example).

In the end, your choice is really between two smaller units, or one larger one.

[SamKnause]

47. Thank you for your input.

[Blue_true]

51. I believe that if he is really trying to save money, he should go to the

manufacturer and ask this question. They would almost surely want to know a lot about his room setup.

Two ACs are not for sure more energy consuming than one AC. There is a lot of conditionality that AC design people would take into account.

[Happy Hoosier]

54. Unless the space being cooled...

Is shaped such that it can't treated more or less as a single space, the two will use more than the one almost for sure. There are some corner cases where the two would be better, but they are academic than practical. In order for the two to be more efficient, the compressors of the two would have to be operating in.p manner where they considerable more efficient than the one. You can construct some scenarios, but they are not really reasonable.

Now if the OP is talking about putting them in different rooms on the same floor of a house or apartment, that is a different question.

[Shermann]

52. Any energy usage difference either way will be marginal at best

Run them in a way which is most comfortable to you.

[SamKnause]

53. Thank you.