Upstairs always much warmer.

[Tim Frank]

Re: Upstairs always much warmer.

If you understand the concept I am trying to explain it is absolutely correct...

Just because someone does not agree with you does not mean that THEY don't understand the concept....
You made a blanket pronouncement...(which is not accurate) and then a few sentences later explained that it is not an absolute situation (OK, point taken..)

In my area, .when you are dealing with an RH of 85% and a temp of 78 in a house, just reducing the RH by 15% makes major difference in comfort...and you haven't dropped the temp one iota.

So the sensible cooling value would be....???

If you want to discuss why I believe your original statement was not correct, PM me and I'll explain.(doubt anyone in here would be interested) More relevant, your subsequent points (all correct) contradict that first statement...it is actually the sensible cooling ratio that would suggest what direction to change your fan speed...if appropriate.


****Edit: I just took a second, and actually looked up humidity levels for Arizona just to get a sense of what you guys have to deal with.... as low as 5-10 %??
So you are dealing almost entirely with sensible cooling....and 100 degree plus?...that is seriously hot. It said 102 degrees ..."feels like 92".
Totally upside down on what we have here.
Last Week we had a day that was 80...RH 90+....felt like a sauna.

 

[hrdwrkingacguy]

Re: Upstairs always much warmer.

I pulled this from This article...

Air Flow

When it comes to airflow, the laws of physics apply. Air follows the line of least resistance. So many of the duct systems are poorly designed that ductwork problems can seriously curtail proper system performance. These factors usually show up in uneven temperatures through the conditioned area. In addition, airflow across the cooling coil can affect humidity removal. Too much air will result in poor dehumidification. Too little air can cause the registers to sweat. The right amount of air is usually between 325 CFM and 400 CFM per ton. Lower airflow will produce increased humidity removal, but compromises sensible heat removal. Finding the right air flow and run time balance can eliminate most of the comfort zone humidity problems.



I guess I should have said "The faster the air goes through the unit the more sensible heat is removed in relation the the latent heat load" faster air = more sensible, less latent heat removal, slower air = less sensible, more latent heat removal...

 

[Tim Frank]

Re: Upstairs always much warmer.

I pulled this from This article...




I guess I should have said "The faster the air goes through the unit the more sensible heat is removed in relation the the latent heat load" faster air = more sensible, less latent heat removal, slower air = less sensible, more latent heat removal...

Would have saved us both some typing....

I have often thought that up here a humidistat instead of thermostat would make a lot of sense on a central A/C ~ here that is really just a whole-house dehumidifier.

I am not sure that I can comprehend RH values like you have.

 

[hrdwrkingacguy]

Re: Upstairs always much warmer.

For the record I don't deal with any residential AC anymore...I am a heavy commercial/industrial technician...I work on chillers, fluid coolers, water source heat pumps, server rooms, & anything else that's is annoyingly large...A lot of the buildings I deal with have more humidity then they care to deal with...At luke AFB I had to deal with the simulator room that was at 100% RH and needed to be exactly 46%...What we did was install a unit with re-heat...Basically strip heaters in the return that warmed up the air so the indoor coil could pull the latent heat out of it...So anything is possible, it's just a matter of getting it right...in a 1600 sq/ft house a 4 ton unit isn't going to work in a situation with high humidity, it will cycle off to fast and not dehumidify at all...You need a undersized unit that runs longer...Slower fan speed with more run time with the right refrigerant charge and it's all good...

 

[DJ]

Re: Upstairs always much warmer.

Where are the returns in this house? Downstairs would be my guess...

Not to insult anyone intelligence but an air conditioner does not blow cold air into a house...It uses the supply air to pressurize a room to move the heat out of it, and back to the return that is under negative pressure and to the indoor coil to remove the heat from it...The air that comes out of the supply registers isn't "cold" it is air that gave up its heat to the refrigerant in the system...

If you don't have enough pressure out of the registers upstairs, and the return is a long way away, the upstairs will always be hot...If you have to right type of registers you can close down some(depending on design of the house) close to the return and drive more air upstairs...

Describe with a little more detail how the system is laid out...

Agreed. You have to have air for the A/C unit to cool.

I live in AZ, so I know a thing or two about A/C air movement.

In our two story, the downstairs family room is always a good 10* warmer than the rest of the house, upstairs included. I do know why. It's because it is the farthest way from the air return. Unfortuneately, there is no way to remedy it.

 

[ac0j]

Re: Upstairs always much warmer.

I live in central nebraska, My 1 &1/2 story has the same problem. I have contacted a few ac/heat companies about this problem. They ALL told me it is a common practice around here to install a second smaller ac/heat unit for the upper floors, controlled by its own thermostat. I have been looking at newer houses, and all multi story homes around here built within the last 10 years, have a seperate system for each level.

 

[NW Redneck]

Re: Upstairs always much warmer.

Tim and ACGuy pretty much covered the main principals of how AC works. I work in resi HVAC too, and the problem you describe is very common. Upper floors are always warmer, or I should say have more heat gain, than lower. The two most common (but hardly ever done, because it costs more $$) ways of dealing with this are, 1. Zoning the ductwork on a single system. This is where the upper and lower floors have separate duct systems, each with a motorized damper, that tie in together at the air handler. Each floor has it's own t-stat that controls the damper for that floor which in turn turns on the AC. 2. Installing separate systems with totally independent ductwork for each floor. This is a more expensive option, but gives you a redundant system where one unit still functions if the other fails so you at least have one floor that is comfortable. Clear as mud?

 

[hrdwrkingacguy]

Re: Upstairs always much warmer.

All you really need is a return upstairs...problem solved...hot air rises...in my 3800 sq/ft house both systems returns are upstairs in the hallway...It works pretty well...doors are undercut a little so the air can get out when they are closed...

 

[Fishing Dude too]

Re: Upstairs always much warmer.

Have an old house use 3 window ac units, 2 upstairs are both 5000 btu units, one downstairs iss 7500 house is always nicer than the moble home unless we run the 5000 btu unit with the central air. Then the central air runs less and bedroom always nice.

 

[DJ]

Re: Upstairs always much warmer.

My house (2 story) has two central A/C units.

It is interesting, and fact, that the two coolest rooms in the house are those closest to the return air vents, not those closest to the A/C units.

 

[hrdwrkingacguy]

Re: Upstairs always much warmer.

My house (2 story) has two central A/C units.

It is interesting, and fact, that the two coolest rooms in the house are those closest to the return air vents, not those closest to the A/C units.

That's because every ounce of air coming out of the system has to make its way by those rooms to get back to the unit...You remove heat from a house, you don't blow cold in...