The upside to an oversized ac

[Old Man Roger]

South Florida, ac is on 24/7/365. There are the rare “cold spells“ that allow me to turn it off occasionally, but they don’t last long.

The bill is about 200 during the hottest s months, and about 100 the rest of the year.

 

[reader2580]

How hot does it get in Minnesota?

101 degrees one day this year plus quite a few days in the 90s already. The dew point is the real issue. It was in the 90s yesterday and the dew point hit 75 degrees yesterday. Hot enough that the majority of houses and apartments in the Minneapolis area have central A/C or a window A/C at least.

I open the windows occasionally in early to mid June when the dew point is low and the outside temperature is below the set point for my A/C. I still leave the A/C on as it won’t run.

it is 9:30 pm here and my A/C just came on even though it isn’t real hot outside.

 

[rharman]

South Florida, ac is on 24/7/365. There are the rare “cold spells“ that allow me to turn it off occasionally, but they don’t last long.

The bill is about 200 during the hottest s months, and about 100 the rest of the year.

Our bill would probably be $1500 or more. We have Time-Of-Day pricing. It saves us a ton as we're diligent about usage.

Summer rate is $0.19/kwh between 9:00pm and 4m. But, from 4:00pm to 9:00pm, it jumps to $0.54/kwh.
We do get a kickback as we've allowed SCE to install remote switches on our two A/C units. They can turn them off if they run short on power.

At 4:00pm, we stop using pretty much everything that is a big draw.

 

[Old Man Roger]

Our bill would probably be $1500 or more. We have Time-Of-Day pricing. It saves us a ton as we're diligent about usage.

Summer rate is $0.19/kwh between 9:00pm and 4m. But, from 4:00pm to 9:00pm, it jumps to $0.54/kwh.
We do get a kickback as we've allowed SCE to install remote switches on our two A/C units. They can turn them off if they run short on power.

At 4:00pm, we stop using pretty much everything that is a big draw.

You’ve been trained very well.lol California looks great on tv, but I wouldn‘t want to live there.

 

[bobg03]

If you live in Texas or California, doesn't the utility company shut it off a few times a day do for you?

 

[Old Man Roger]

Florida has a similar system, but you have to opt in, it’s not mandatory. The price break they give you for joining is minimal, and not worth having your ac turn off just when you need it most.

I can see it now, my girl wondering why all those candles she loves melted..lol

 

[jar944]

Not sure why everyone loves the ac running 24/7 must be the same people who complain about a $500 electric bill.

Mine kicks on in May and shuts off in September.. it's undersized for the house, but only has issues on 100+ days. To be fair it's only one of the 2 hvac systems and it's the smaller of the 2.. so in reality the combination of the 2 systems are 2x or more oversized based on actual need.

So in this case running one full time is cheaper then 2 some of the time and makes for a better living experience.

I don't have half of a $500 electric bill and I'm cooling 6000sqft.

 

[engineer2]

So what's the point?

It takes time to cool off all the stuff in your house. I get that question all the time. "I turned on the AC an hour ago and it still feels warm." Well yes, you cooled the air, but it takes more time for everything inside your house to cool down from 85°F.

 

[reader2580]

My A/C system is just about the perfect size for my house. It will run a good portion of every hour on a really hot 95 to 100 degree day. On the other hand if it is in the high 70s with a high dew point it won't run enough to remove the humidity. I really need a two stage or similar A/C unit.

The day it hit 101 degrees this summer my A/C was on load control from 4 pm to 7 pm. It got up to 78 degrees inside the house. The A/C ran non-stop for nearly three hours to get it back down to 75 degrees inside. I thought it would cool down much faster once the sun started to set, but it didn't stop running until well after dark.

 

[justinjoyal]

Not sure why everyone loves the ac running 24/7 must be the same people who complain about a $500 electric bill.

Not 24/7, but as much as needed.

A properly sized system will consume less electricity and provide better comfort (less temperature swing, lower RH, constant filtration, etc.) A multi-stage/inverter system is the best.

I don't want my A/C kicking in and out all the time. I would hate that.

 

[White Shadow]

I was always told that you don't want to oversize an A/C system because it will not have enough cycle time to remove humidity. In that case, you want the A/C running longer, not shorter cycles, no?

 

[Hobby_Man22]

I was always told that you don't want to oversize an A/C system because it will not have enough cycle time to remove humidity. In that case, you want the A/C running longer, not shorter cycles, no?

Mine shuts off after 8-15 minutes when it's like 85-90 outside. Then 20-30 minute cycles when it's above 90 and shuts off for about 8 minutes and kicks back on

 

[65ranchero]

When the humidity index is predicted to be high the 1st thing I do is close all the windows pull down the double wall cell shades, and close all insulated drapes for the window that have them.

Then I run my Fujitsu mini split in "dry " mode when it it'd going to be a miserable day.
the E bill is only about $25/30 extra month.
the system only runs about 25 days /yr when it is needed for cooling.

 

[rharman]

You’ve been trained very well.lol California looks great on tv, but I wouldn‘t want to live there.

Born & raised here - coming up on 67 years. Same house for 42 years, same wife for 41 - and she's a local native as well. We ain't going anywhere.

We went into the TOU/TOD plan with our eyes wide-open. It's served us well - you just adapt your schedule. Probably took 40% or more off our average bill.

If you live in Texas or California, doesn't the utility company shut it off a few times a day do for you?

The A/C cycling program is an opt-in and there are a several tiers and the kickback varies. One tier gives you the option to override it if they shut you down. You're limited as to the # of times that can be done.

We've always taken the biggest discount tier (actual amount is based on tonnage) - they can shut it down up to 6 hours per day total.
In practice, it's not been much of an inconvenience - it's actually pretty rare that it gets shut down.

 

[Old Man Roger]

Born & raised here - coming up on 67 years. Same house for 42 years, same wife for 41 - and she's a local native as well. We ain't going anywhere.

We went into the TOU/TOD plan with our eyes wide-open. It's served us well - you just adapt your schedule. Probably took 40% or more off our average bill.




The A/C cycling program is an opt-in and there are a several tiers and the kickback varies. One tier gives you the option to override it if they shut you down. You're limited as to the # of times that can be done.

We've always taken the biggest discount tier (actual amount is based on tonnage) - they can shut it down up to 6 hours per day total.
In practice, it's not been much of an inconvenience - it's actually pretty rare that it gets shut down.

40% off sounds great, but you mentioned your bill would be 1500 bucks. Mine is 200 on the hottest month and I’m in south Florida. If I remember correctly, they only offer us like 6 bucks a month discount. They can keep their 6 bucks, and I will keep my ac running when I need it.

 

[rharman]

40% off sounds great, but you mentioned your bill would be 1500 bucks. Mine is 200 on the hottest month and I’m in south Florida. If I remember correctly, they only offer us like 6 bucks a month discount. They can keep their 6 bucks, and I will keep my ac running when I need it.

That $1500 was a SWAG if we ran 24x7. We've never come anywhere close to that but $500 was doable in the old days if we overused.

Way under that now.

 

[dsimatt]

I suppose my situation is a bit different. Not sure where you hail from. I have ductless minisplits which are mildly oversized in upstate NY. . I wouldn’t, but If i were to ever let the house get to 90+(which it could easily, we are forcasted for 99°f thursday) my splits can easily have the house down to 72 in 30-45 min. they recover and dump heat FAST. My home is always dry and i prefer mildly oversized to undersized any day with splits and dc driven inverter motors/compressors.

I have a single 18k unit in my house and it gets the job done sort of, not as good as it did 5 years ago. We used a local company and sized it just right at the time, we lost all out shade trees and added 2 humanoids so on hot days it really struggles to maintain temp and forget dropping temp.

They now have these ducting models you can mount in a basement or attic so i would like to add that to the bedrooms which is oversizing for the house but would be much more comfortable when needed.

 

[Old Man Roger]

That $1500 was a SWAG if we ran 24x7. We've never come anywhere close to that but $500 was doable in the old days if we overused.

Way under that now.

I don’t understand your use of the word SWAG, but we have to run the AC 24/7 in South Florida.

 

[Hobby_Man22]

What is TOU/TOD?

 

[JohnKal]

What is TOU/TOD?

Time of use/time of day

 

[Hobby_Man22]

I guess time will tell if the short 8-10 minute run cycles will be detrimental. I asked a youtube havac company if this mattered and he said the oil pretty much continued to circulate regardless. I think the have traps now in certain areas of the system to keep oil from pooling in certain areas and not making it to the compressor.

 

[TRITOON]

I guess time will tell if the short 8-10 minute run cycles will be detrimental. I asked a youtube havac company if this mattered and he said the oil pretty much continued to circulate regardless. I think the have traps now in certain areas of the system to keep oil from pooling in certain areas and not making it to the compressor.

OP.....

Have you looked into your thermostat settings?

On my primary house we have units that are only about 0.5-1 ton oversized. But during times of the year when its coolish outside or cloudy, the upstairs can seem to want to over cycle. All the cool air would fall downstairs, ac would come on for 5 minutes, shut off for 2-3 minutes, then come on again (sensor at top of stairs) and it drove me crazy when we first installed the new upstairs unit that replaced a 20 year old unit. We have ecobees that came with the house, and i went into the settings and could set minimum cool and off cycles. I set them for 15 minutes minimum each and it resolved the problem. I can handle 2 on cycles per hour.

You could also set the temperature swing settings to let it go 1-5 degrees before turning back on. Each house is different depending on insulation, layout, materials, etc, but you may look into adjusting those settings.

 

[bonneyman]

I had a maintenance contract on a building that was built for small individual suites that was later opened up to accommodate one large office. Flex duct above drop ceiling, holes cut in walls for doorways to allow workers to travel between the original suites, 3.5 ton combo units on the roof. As people came and went over the years they'd put up new walls and cubicles and knocked down others. Floorplan changed regularly. And then they started calling me for no cooling in certain spots.
Found out on the roof that they'd had units go down, and the contractor then replaced the units. The office manager had them install 5 ton units in place of the original 3.5 tonners just to get more cooling. But the place never cooled right, and their electric bills were crazy. The ductwork on the roof was undersized and had too many elbows to attach the newer units. And the flex ducts downstairs were tucked into nooks and crushed with the remodeling and ever increasing computer and phone lines added. It was a real mess.

Upshot is they had 5 tons units in place of 3.5 tons and STILL were not comfortable.

 

[u3b3rg33k]

This is going to sound like a stupid question, maybe it is a stupid question, but I’ll ask anyway..lol

It’s a three parter. Could you compensate for an oversize system by having a multi speed blower motor? Meaning you would leave the motor on high speed, if let’s say, the AC has been off all day and you want to cool the house quickly, then switch to a lower speed once the desired temp is reached?

My second thought was a type of zone system. Would it keep the system running longer if it cooled one section of the house at a time? Maybe include the attic? Or even vent some of the air out of the house? Probably not very efficient, I know, but the person having an over sized system probably isn’t to worried about efficiency.

I’m asking for the sake of lowering humidity with an over sized system.

They have two stage systems where the compressor changes size

Not 24/7, but as much as needed.

A properly sized system will consume less electricity and provide better comfort (less temperature swing, lower RH, constant filtration, etc.) A multi-stage/inverter system is the best.

I don't want my A/C kicking in and out all the time. I would hate that.

seems like the "perfect" heat pump for this application is the 5 ton bosch BOVA 2.0 system. 5 ton, auto-adjusts from 25-110% nameplate capacity, so you can run a super low first stage for quiet/dehumidification then have stage two be whatever you want it to be.

a decent PI logic 2 stage stat would pair nicely with that, you can basically let the thermostat stage it by airflow, and it'll tune itself based on the resulting coil temp, and the compressor will run at whatever RPM it needs to accomplish the goal.

you can set the compressor for two different coil temp targets, 37F and 47F, so you get to choose how aggressively it dehumidifies.

 

[Jsf721]

I did that and it’s a
Bad idea. Until blows too much cold too fast and shuts down till it gets warm and freezes is again.

Trying to figure out a solution.

Don’t do it.

 

[Hobby_Man22]

I did that and it’s a
Bad idea. Until blows too much cold too fast and shuts down till it gets warm and freezes is again.

Trying to figure out a solution.

Don’t do it.

I'll go with a 4 ton the next time I replace it and then just insulate it better.

 

[bigdav160]

It's hard for our northern members to imagine that it doesn't get below 80 degrees here 4 months of the year. And for 2 months the temperature will be in the 90's up till midnight. Like Roger said the A/C runs 24/7

I have 4200+ sq/ft with 16 exterior doors (big mexican hacienda) and only 7 tons of cooling. The electric bill can be painful at times

 

[Hobby_Man22]

It's hard for our northern members to imagine that it doesn't get below 80 degrees here 4 months of the year. And for 2 months the temperature will be in the 90's up till midnight. Like Roger said the A/C runs 24/7

I have 4200+ sq/ft with 16 exterior doors (big mexican hacienda) and only 7 tons of cooling. The electric bill can be painful at times

The northerners are the ones who can cool a 4000 square foot house with a 2 ton mini split.