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Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

1 edit
reply to cowboyro

Re: Another a/c issue.

said by cowboyro:

A properly designed and working system will keep any reasonable inside temperature with any extreme but expected outside temperature. And cycle while at it. That means 65F inside with 105F outside if needed.
Humidity can be removed very well even if the unit is "oversized" by running the variable speed air handler in dehumidification mode. I said "properly designed" not "contractor special".
A unit that can barely handle the load isn't more efficient, as a matter of fact it may be unable to take advantage of any setbacks because it will have to run all day long for the house not to be an oven in the afternoon.

Can you provide your source of this information about "a properly designed and working system"? I've never seen this described in any technical literature or any real time calculations on new installations. I would be interested in studying the technical data behind the reasoning for this over sizing enough to provide 65 degrees with an outside temperature of 105 degrees.

How many people have a unit with a variable speed air handler? I just got one with my new upgrade system. That mode is only effective "if" the temperature is close to set point and maintaining. De humidification mode is a side effect of the unit running in a slower stage to maintain the set-point. To achieve 65 degrees with outside air of 105 I would need at least a 4 ton unit instead of the 3 ton I have.


SayWhat

@comcast.net
reply to cowboyro

said by cowboyro:

A properly designed and working system will keep any reasonable inside temperature with any extreme but expected outside temperature. And cycle while at it. That means 65F inside with 105F outside if needed.
Humidity can be removed very well even if the unit is "oversized" by running the variable speed air handler in dehumidification mode. I said "properly designed" not "contractor special".
A unit that can barely handle the load isn't more efficient, as a matter of fact it may be unable to take advantage of any setbacks because it will have to run all day long for the house not to be an oven in the afternoon.

Absurd. A properly designed system, one in which a Manual J Residential Load Calculation, Manual S Residential Equipment Selection, Manual D Residential Duct System Procedure and Manual T Air Distribution Basics for Residential and Small Commercial Buildings are performed, will run as long as possible to address the loads. In addition, a properly designed system will run close to 100% of the time at the outdoor design condition and proportionally less at temperatures closer to the inside design temperatures. Designing a system using peak heating and cooling loads based on extreme weather conditions that occur for only a few hours per season, such as the hottest day on record, will result in an oversized system. Over-sized systems in humid climates may not run long enough under some part load conditions to achieve humidity removal from the air and keep the house within the ASHRAE comfort zone.

An oversized HVAC system will have both a higher initial cost and a higher cost of operation. The frequent starting and stopping of short cycling can lead to premature failure of the equipment. Short cycling limits the total amount of air circulating through each room, and can lead to rooms that do not receive adequate duration of airflow. In the cooling season in humid climates, cold clammy conditions can occur due to reduced dehumidification caused by the short cycling of the equipment. The system must run long enough for the coil to reach the temperature for condensation to occur and an oversized system that short cycles may not run long enough to sufficiently condense moisture from the air. Excess humidity in the conditioned air delivered to a space may lead to mold growth within the house.


cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse
reply to Jack_in_VA

said by Jack_in_VA:

Can you provide your source of this information about "a properly designed and working system"? I've never seen this described in any technical literature or any real time calculations on new installations. I would be interested in studying the technical data behind the reasoning for this over sizing enough to provide 65 degrees with an outside temperature of 105 degrees.

Common sense. The system must be designed to keep the user comfortable at all times. Period. There is absolutely no excuse not to. If the outside may reach 105 and people may want 65 then the system must be designed to be able to handle that load.
said by Jack_in_VA:

How many people have a unit with a variable speed air handler?

All those who have at least a half-decent systems. Contractor specials are *not* included.


cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse
reply to SayWhat

said by SayWhat :

Absurd. A properly designed system, one in which a Manual J Residential Load Calculation, Manual S Residential Equipment Selection, Manual D Residential Duct System Procedure and Manual T Air Distribution Basics for Residential and Small Commercial Buildings are performed, will run as long as possible to address the loads.

Don't confuse a system that is *expected* to run morning to evening with a system that is expected to be turned off during day such as a residential setting.
Does it make any sense to keep filling a leaking bucket with a teaspoon or with a cup? Yeah, thought so...
said by SayWhat :

An oversized HVAC system will have both a higher initial cost and a higher cost of operation. The frequent starting and stopping of short cycling can lead to premature failure of the equipment. Short cycling limits the total amount of air circulating through each room, and can lead to rooms that do not receive adequate duration of airflow.

The difference in a residential system is insignificant. Few hundred on a $20k system. The system starts and stops the same number of times as most thermostats are set for a certain CPH rate. And of course the fan can be set to circulate the air at all times. Again, "contractor specials" are excluded. I have a properly sized system (some may call it way oversized) and it keeps humidity levels in the 50-55% range. In a 70's house that isn't so tight. Near the coast where humidity is a fact of life.
The only thing different from a system designed to the limit is that I don't have to run it all day so that I have under 80F when I get home. It can bring the house temperature to "nice" levels in a matter of 30 minutes.

iknow
Premium
join:2012-03-25
reply to Jack_in_VA

said by Jack_in_VA:

said by neonturbo:

I can hit a 68 degree setpoint in 100 degree weather and the unit still cycles. It is only off for 5-10 minutes at this temp, but still I am pushing it pretty hard.

My equipment is about 10 years old, and it is sized as close as they could for my house. When you get to houses smaller than 900 sf, you have a limited choice of system capacities. I think it is a 1 ton, but I am not where I can check at the moment.

I think the reason I can get it to cool so well is I have insulated the attic to R50, and added a radiant barrier. The rest of the house is fairly tight, but the 15 year old vinyl replacement windows don't seal perfectly.

IMO if you can pull your inside temperature down to 68 and still have the unit cycle you have a seriously over-sized unit.

that depends on the area, and what the homeowner likes the temperature to be, the standard is people are most comfortable at 72F which is what even small doctors offices and stores large and small are set at and these use freon systems in the smaller buildings. also, in places with high heat and low humidity, let's say las vegas and others. you don't want to remove any humidity.


SwedishRider
Rider on the Storm
Premium
join:2006-01-11
not Sweden
kudos:1
reply to aroberti

said by aroberti:

I've never seen a house that was 100% air-tight -- and even if it were, that would present a whole new set of challenges...

When building his house, a neighbor down the street went with Icynene insulation, and it's about as air tight as you can get without going closed cell. The downside is that it's expensive (about 3.5X the cost of fiberglass) and you are supposed to install air handlers to exchange the outside air because the home is sealed so well (or so said the salesman when quoting me a price).

I decided to go with traditional fiberglass with 2x6 exterior walls and a higher total R-value over the second floor. I just didn't want to get into additional equipment and I had heard of some buildings with interior problems because the house was sealed too well (mold, sickness, etc.) And I just thought it was simply too expensive. I don't think my heating and cooling bills are ridiculous either... 2x6 with vapor barrier has been great at maintaining interior heat and cooling.

My neighbor does like Icynene though... he recommended it and said he would use it again if he built again.


49528867
Premium
join:2010-04-16
Fort Lauderdale, FL
kudos:3
reply to chmod

Click for full size
downloadameristar.pdf 372,624 bytes
said by chmod:

Any help getting some info on this unit? I tried putting the model# into google with minimal results.

Per the model number it is a 2.5 ton 13 seer split system.

Wayne
--
Madness takes its toll, please have exact change ready…

scross

join:2002-09-13
Cordova, TN
reply to Viper677

said by Viper677:

said by alkizmo:

said by Viper677:

Get an infrared inspection done to check for insulation voids.

Can you rent those thermal cameras for 50$-60$ for a day or a couple of hours?

My biggest worry when I installed R55 insulation in my attic was having voids.

Next winter I want to check my ceilings for heat loss.

As far as I know you can rent a decent camera for about $100 - $125 per day. I dont think they let you have it for a couple of hours.

Now, I would also recommend you to hire someone to do the scan for you instead of just renting it. A thermal camera is not a point and shoot device and you need to have some experience to interrupt the anomalies.

Also, in order to get the best/right results you need to have a d-t of about 10C between inside and outside.

The best time to get someone to scan the house is in winter.

Most of the people who rent these cameras (that I know of) are the people who are professionals and already have a job lined up. So they rent the camera, get the job done and return the camera. They do it so they dont have to own a camera.

I have an inexpensive laser infrared thermometer which I used to scan my ceilings and outer walls. That's how I've located most of my known problem areas, which register much warmer than other areas when the sun is blazing down. An infrared camera would have been faster, but these aren't cheap.

Come to think of it, many modern digital cameras and video cameras have a night/infrared mode, which might work pretty well, too. No fancy colors, probably, but you don't really need them. I have a couple of these, so I may have to do some experimentation. This will probably be best done just after sundown, with all the lights out.

iknow
Premium
join:2012-03-25

said by scross:

Come to think of it, many modern digital cameras and video cameras have a night/infrared mode, which might work pretty well, too. No fancy colors, probably, but you don't really need them. I have a couple of these, so I may have to do some experimentation. This will probably be best done just after sundown, with all the lights out.

what i've heard is they have infrared blockers in the cameras now to stop the "infrared naked" pictures. to fix that, you have to disassemble the camera, and remove the filter, and replace it with plain glass of the same size, though. it's possible a camera that advertises it has infrared capability is still made though.(probably expensive).

scross

join:2002-09-13
Cordova, TN

said by iknow:

said by scross:

Come to think of it, many modern digital cameras and video cameras have a night/infrared mode, which might work pretty well, too. No fancy colors, probably, but you don't really need them. I have a couple of these, so I may have to do some experimentation. This will probably be best done just after sundown, with all the lights out.

what i've heard is they have infrared blockers in the cameras now to stop the "infrared naked" pictures. to fix that, you have to disassemble the camera, and remove the filter, and replace it with plain glass of the same size, though. it's possible a camera that advertises it has infrared capability is still made though.(probably expensive).

I have a camera that has night mode and a built-in IR lamp, so it should work pretty well. I doubt that it has any such filter, especially given that it's at least 10 years old now.

Kenbass

join:2007-05-10
Athol, MA
reply to chmod

System is undersized. End of story.


iknow
Premium
join:2012-03-25
reply to SayWhat

said by SayWhat :

said by cowboyro:

A properly designed and working system will keep any reasonable inside temperature with any extreme but expected outside temperature. And cycle while at it. That means 65F inside with 105F outside if needed.
Humidity can be removed very well even if the unit is "oversized" by running the variable speed air handler in dehumidification mode. I said "properly designed" not "contractor special".
A unit that can barely handle the load isn't more efficient, as a matter of fact it may be unable to take advantage of any setbacks because it will have to run all day long for the house not to be an oven in the afternoon.

Absurd. A properly designed system, one in which a Manual J Residential Load Calculation, Manual S Residential Equipment Selection, Manual D Residential Duct System Procedure and Manual T Air Distribution Basics for Residential and Small Commercial Buildings are performed, will run as long as possible to address the loads. In addition, a properly designed system will run close to 100% of the time at the outdoor design condition and proportionally less at temperatures closer to the inside design temperatures. Designing a system using peak heating and cooling loads based on extreme weather conditions that occur for only a few hours per season, such as the hottest day on record, will result in an oversized system. Over-sized systems in humid climates may not run long enough under some part load conditions to achieve humidity removal from the air and keep the house within the ASHRAE comfort zone.

An oversized HVAC system will have both a higher initial cost and a higher cost of operation. The frequent starting and stopping of short cycling can lead to premature failure of the equipment. Short cycling limits the total amount of air circulating through each room, and can lead to rooms that do not receive adequate duration of airflow. In the cooling season in humid climates, cold clammy conditions can occur due to reduced dehumidification caused by the short cycling of the equipment. The system must run long enough for the coil to reach the temperature for condensation to occur and an oversized system that short cycles may not run long enough to sufficiently condense moisture from the air. Excess humidity in the conditioned air delivered to a space may lead to mold growth within the house.

those manuals need to be updated to reflect the use of multi speed compressors, multi speed blowers, and thermostatic expansion valves, else it's useless. the maximum cooling can now be much higher, and still be lowered to normal levels and below to remove humidity and ensure proper circulation.


SayWhat

@comcast.net

What are you saying? Are you saying we should be installing 5-ton 2-stage systems in 3-ton homes just in case we need the additional BTU cooling capacity for those days when the temperature is above the outdoor dry bulb design temperature? Please elaborate. I'm fascinated by your theory.



alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1

Yes that's what he's saying... because why not afford super luxury

Have you seen the prices on those whole house dehumidifier? Better just splurge that money on pricier fancy AC.


iknow
Premium
join:2012-03-25
reply to SayWhat

said by SayWhat :

What are you saying? Are you saying we should be installing 5-ton 2-stage systems in 3-ton homes just in case we need the additional BTU cooling capacity for those days when the temperature is above the outdoor dry bulb design temperature? Please elaborate. I'm fascinated by your theory.

i'm saying some would want a constant temperature, and if they can afford it, it's doable. take for instance professional offices, even small one's like doctors and dentists, who keep the temperatures at a constant 72 deg. no matter what the temperature is outside. some homeowners may want that too. the 5 ton capacity would only be used on the hottest days, and it could switch down to 3 ton or less on cooler days.


cowboyro
Premium
join:2000-10-11
Shelton, CT
Reviews:
·AT&T U-Verse
reply to SayWhat

said by SayWhat :

What are you saying? Are you saying we should be installing 5-ton 2-stage systems in 3-ton homes just in case we need the additional BTU cooling capacity for those days when the temperature is above the outdoor dry bulb design temperature? Please elaborate. I'm fascinated by your theory.

If you can afford then yes... The extra investment may even pay off soon, if not only through the extra comfort.
If you can't afford then stick with the contractor special pack where you sweat when it's hot and have to keep the A/C running from 12PM just so it's bearable at 7PM.

iknow
Premium
join:2012-03-25

1 edit

said by cowboyro:

said by SayWhat :

What are you saying? Are you saying we should be installing 5-ton 2-stage systems in 3-ton homes just in case we need the additional BTU cooling capacity for those days when the temperature is above the outdoor dry bulb design temperature? Please elaborate. I'm fascinated by your theory.

If you can afford then yes... The extra investment may even pay off soon, if not only through the extra comfort.
If you can't afford then stick with the contractor special pack where you sweat when it's hot and have to keep the A/C running from 12PM just so it's bearable at 7PM.

here's a good example of a variable speed compressor, they DO make them. »www.analogzone.com/grnt0605.pdf
here's a few units using variable speed compressors. »www.energystar.gov/index.cfm?c=m···cac_ashp
Expand your moderator at work


mityfowl
Premium
join:2000-11-06
Dallas, TX
reply to cowboyro

Re: Another a/c issue.

said by cowboyro:

said by SayWhat :

What are you saying? Are you saying we should be installing 5-ton 2-stage systems in 3-ton homes just in case we need the additional BTU cooling capacity for those days when the temperature is above the outdoor dry bulb design temperature? Please elaborate. I'm fascinated by your theory.

If you can afford then yes... The extra investment may even pay off soon, if not only through the extra comfort.
If you can't afford then stick with the contractor special pack where you sweat when it's hot and have to keep the A/C running from 12PM just so it's bearable at 7PM.

I think you're being a little severe here.

They probably just stress until it gets real hot.

And that's usually for just 2 or 3 days in these areas. Not like Texas and Florida.


08034016
Hallo lisa Aus Amerika
Premium
join:2001-08-31
Byron, GA
reply to Msradell

said by Msradell:

An air conditioner should be able to return here about 20° cooler than the air it takes in, not than the outside temperature. If you don't think it's true just go to Las Vegas in the heat of the summer. It's 110°+ outside yet inside is extremely cool

That's about right it was in my City 107F and inside my home it was 74-75F.

My system ran 14Hrs straight with that Temp, we're having a Cooling Trend here now Low to upper 90's
--
Support
»www.minutemanproject.com/

Maniak

join:2008-03-29
Vail, AZ
Reviews:
·Wi-Power
·RuralNet

That is about how our system runs too.

The temperature split on our 2 stage heat pump is 16F when on the first stage and 21F when on the 2nd stage.

The 1st stage will keep our house at 73F up to about 100F outside temp Once it gets much over 100F the temp inside will climb 2 degrees above the set point and the 2nd stage will kick on. The 2nd stage will bring the temp back down. It doesn't bring it down quick enough to cycle in the hottest part of the day but it will slowly bring it back down. If the 2nd stage were to be used before the inside temp got 2f over the set point it probably would cycle.

~Mark