A real first world problem: balancing my A/Cs

[LVSteve]

Like most medium to large two-storey homes in Vegas, I have two A/C systems. Well, I'm having fun with them right now. I had the attic insulation done properly in January, and it changed the thermal properties of the home drastically.

http://smith-wessonforum.com/lounge/609879-those-cursed-1990s-vegas-builders.html

My issue is that when the temps outside are in the high 80s to low 90s, I seem to get into a freeze or fry fight between the two systems. If I set the upstairs to 78°F then my wife is super comfortable in the upstairs office and the bedroom with the cathedral ceiling is kinda OK. The A/C runs maybe once an hour for 10-15 minutes. If I set it to 77°F, the A/C comes on earlier in the day and still runs about as often. Trouble is the wife gets frozen out when it comes on. It is a SEER 14 R-410 unit.

The downstairs A/C is a very well maintained 3.5 ton R-22 unit. Last year it was found that the cap on the fan for the outside unit had gone soft and slowing the fan. After it was fixed, I named it the freeze machine. With the upstairs at 78°F, if I set the downstairs to 77°F, the hall where the thermostat lives is fine, but the family room eventually gets stuffy. If I set it to 76°F the A/C runs about once an hour and it is freezing while it's on. I thought about fiddling with the swing (I have digital stats) but making the swing bigger will likely make the issue worse, IMHO.

None of this happens when the temperature gets up nearer 100°F. Then everything seems to run very happily, with the downstairs coming on maybe twice and hour, or three times every two hours. I'm fine with that as it gives me headroom for the 110°F+ days when they come.

I have no doubt that the new insulation is doing what's required, so maybe I should just shrug about these in between days and look for smaller bills in the summer than I had in previous years.

Like I said, first world problems, eh?

 

[s&wchad]

If your home is like mine, you have dampers in the ductwork and/or built into the outlet grates. Try restricting the flow to rooms that get too cold. Partially blocking airflow to one area will increase flow to others, so you need to experiment to get it balanced properly.

You might also consider installing a few ceiling fans. Our great room and downstairs master bedroom have cathedral ceilings and the fans really help even out the temperature. You want to run them clockwise in the winter and counterclockwise in the summer.

 

[bigwheelzip]

My in-law's Florida home had wide daytime temperature swings between rooms on the north and south side of the house. The majority of it's windows were south facing, and inefficient. The thermostat was in a hall off the north facing rooms.
If the condition became uncomfortable during a visit, we'd flip the fan switch from Auto to On during sunny daytime hours, letting the constant air circulation even out the temperatures throughout the house.

Sent from my Moto G (5) Plus using Tapatalk

 

[steelslaver]

I put an addition in my house and after it was done the duct to the addition was not keeping the 2 new bedrooms warm enough, I was assured the furnace was large enough. Solution was installing a duct fan in the ducting going to the addition. It causes more air to flow to those rooms and even when the furnace kicks off this fan keeps going and slowly sucks air from main house vents to the addition and of course that flows back, keeping the heat in the whole house very even.
Maybe adding a duct fan or 2 to you system will help keep it more even.

 

[Gamecock]

I have same problem, but it is more pronounced with heating. Closing vents not an option. I am reasonably successful by adjusting thermostats, but have to make changes 2-3 times a day.

 

[Big Cholla]

Steve: As a long time house builder in the LV area and a lessor of multiple houses with renters that just will never understand how an air conditioner works IMHO multiple ceiling fans work best to address problems like yours. All rooms that humans occupy for some periods of time during the day should have good ceiling fans. During the summer the fans should be set to blow the air up towards the ceiling and during the winter just the opposite. As of late I have become a big fan of the remote controlled fans. I set down to this 'puter and if I need a little air to cool myself I turn on the ceiling fan to low with the remote. If I need just a little more cooling I raise it to the next temp. No getting up and running to the thermostat which will affect the rest of the house not just my space. And an important "and"......My wife likes the house warmer than I. She prefers 79 deg. while I prefer 77. I use the ceiling fan for my comfort in the room that I am occupying. That is the first reason to purchase the latest version of ceiling fan with the remote control.

Also, with local a/c units most are set to deliver air at the register that is at about 60 deg. + or - depending on the brand. That cold blast of air needs to be controlled as to where in the room it is being directed. There are multiple devices out there to do this controlling. Good luck. In my previous career in commercial buildings the satisfactory use of the A/C system by the occupants was always the biggest problem.

 

[LVSteve]

Steve: As a long time house builder in the LV area and a lessor of multiple houses with renters that just will never understand how an air conditioner works IMHO multiple ceiling fans work best to address problems like yours. All rooms that humans occupy for some periods of time during the day should have good ceiling fans. During the summer the fans should be set to blow the air up towards the ceiling and during the winter just the opposite.

That's interesting. Your advice on fans is the exact opposite of what I have read on the Web.

Yeah, I should run the ceiling fan in the family room, but it makes a faint noise that annoys me, my fault for having good hearing, lol.

 

[LCC]

A/C systems from the 90's were typically sized for max needs during average high temps days, and are typically 'overkill' when during lesser temp days, and short cycling typical with those systems on lesser heat days.
And now that your orginal 'demand' sizing has changed with the new insulation package, it will just short cycle more.
New systems today employ variable speed central fan motors, variable demand compressors, multi sensor points in the house controlling in duct modulators, and an intelligence controller mixes it all up to provide appropriate air flow and compressor load.
So with those set-ups, regardless of temp, required air flow to maintain set-point temperatures in the various rooms is delivered as the a/c compressors chug along supplying minimum required as well.
Would reccomend bringing in a commercial company to look at your systems, see what they reccomend to upgrade your current system for a more even a/c delivery.

 

[Big Cholla]

Steve: I am aware of the multitude of web advisors advising the opposite. I can only hearken back to my college engineering physics class. Hot air rises. During the winter one will lessen their heating bills by using that supply of hot air that is nestled against the ceiling to warm the lower parts of each living space. During the summer the last thing one wants is a column of warm air coming down and working against the A/C unit. Of course there is air current along the walls in the opposite direction of the ceiling fan. But, the mixing is more gradual and less of a contrast to what one wants by doing the direction control the way I stated. .....

 

[LVSteve]

Steve: I am aware of the multitude of web advisors advising the opposite. I can only hearken back to my college engineering physics class. Hot air rises. During the winter one will lessen their heating bills by using that supply of hot air that is nestled against the ceiling to warm the lower parts of each living space. During the summer the last thing one wants is a column of warm air coming down and working against the A/C unit. Of course there is air current along the walls in the opposite direction of the ceiling fan. But, the mixing is more gradual and less of a contrast to what one wants by doing the direction control the way I stated. .....

Oh, I'm with you on the hot air rises thing. However, I doubt I will ever run my fans "uphill" because this home has all the ceiling vent in close proximity to the fans. Bit of a design fault IMHO. With registers in the wall this wouldn't be a problem.

 

[Gamecock]

New systems today employ variable speed central fan motors, variable demand compressors, multi sensor points in the house controlling in duct modulators, and an intelligence controller mixes it all up to provide appropriate air flow and compressor load.
So with those set-ups, regardless of temp, required air flow to maintain set-point temperatures in the various rooms is delivered as the a/c compressors chug along supplying minimum required as well.
Would reccomend bringing in a commercial company to look at your systems, see what they reccomend to upgrade your current system for a more even a/c delivery.

But the old system is paid for. This surely isn't a $10,000 problem.

 

[LVSteve]

But the old system is paid for. This surely isn't a $10,000 problem.

Funny yo u should come up with that number. When the upstairs system had to be replaced research showed that a multi-speed system would have cost about $10k. Takes a while to get that level of investment back in reduced bills or at house sale time.

Looks like the A/C systems are going to get a workout next week. Temps up to 108°F are forecast. The bigger test will be for the new insulation. I have high hopes given what we've experienced so far.

 

[Heymatt]

Ceiling fans cool people, not rooms.

 

[LVSteve]

Ceiling fans cool people, not rooms.

Ah yes, that subtle difference between comfort and actual temperature.