How cool is considered reasonable?

[sdeemer]

I have posted a message yesterday about how my house is so hot and my A/C is not cooling the home (and has not been effectively cooling for awile). As I mentioned yesterday we have a new A/C unit and furnace 4 ton and 2850 sqft.

Well today the supervisor at the company told me that air conditioners are only rated to keep the house 20 degrees cooler than the outside temperature. I live in Houston - in average summers it gets 96-98 in the hottest part of the day...

Anyone who cares to give their opinion - does this mean I am asking to much to have my house cooled to 75 degrees all the time?

(As a side note my inside temp is 81 currently so it really is a mute point...but the lady said my A/C should not be expected to cool more than 20 degrees)

THanks everyone

[coolwhip]

what area do you reside?

[sdeemer]

I live in Houston long summers avg 95-98 during afternoon. RH 85-90%

[fl1]

It's common to size system for 17 to 20°F less then the outdoor design temperature(in our area),but it can be correctly sized for 75 or 72°F ,if that's what you want,and make it clear upfront.

[coolwhip]

The outside design conditions for your area are 95 and 33 deg., the inside design temperatures 75 and 70 deg. The system that was installed in your home should be able to maintain 75 deg. during the summer and 70 deg. in the winter.

If it is unable to handle the heat loss or heat gain, then the equipment selection was wrong or the system design is wrong or both.

[whitepoundog]

20 degrees is what I have always been taught.

[vlux]

My house is 70, outside temp 97, dam im goood

[coolwhip]

I have a 1.5 ton carrier and a 2 ton coil. It was 97 here today and my indoor temp is 73 degrees. I have a 1000 square ft. colonial plus the basement office which is 500 sq. ft.

[Mr Bill]

Originally posted by sdeemer
I have posted a message yesterday about how my house is so hot and my A/C is not cooling the home (and has not been effectively cooling for awile). As I mentioned yesterday we have a new A/C unit and furnace 4 ton and 2850 sqft.



Personally I have lived in Houston for 54 years and been in the a/c business 30 years and they probably used a manual J only to size your unit but I would have never in my life have installed a 4-ton system in a home "IN HOUSTON" with 2850 sq.ft. you would have had a 5-ton or I would not have done the job. A lot of folks here promote manual J and yes it is a good starting point but when you have been in the business here for 30 years it's helps to know Houston and use a little common sense, also I have a 5-ton 14 seer on my home 2500 sq. ft. and my system is tweaked out to the max and today it got to 78 in my home so go figure.

[Mr Bill]

Originally posted by sdeemer
I live in Houston - in average summers it gets 96-98 in the hottest part of the day...

Yes and don't forget that "heat index" today of 104 and that latent is removed first and then it can work on the sensible.

[coolwhip]

Thats exacty right Mr Bill!! I also take this into consideration when installing systems for the elderly. They like to keep their heat set at 80 degrees.

[bobr42]

MRBILL IS YOUR ANSWER I HOPE NEXT TIME YOU HAVE A MORE EXPERANCE COMFORT CONSULTANT

[bobr42]

VULX you have to have your house at 70 not very good dehumdifcation should be comfortbale at 73 72 should recalculate your heat load

[mark beiser]

According to the design conditions for Houston, the system is sized correctly if it keeps it 75 in the house when it is 95 outside.
If it is warmer than 95 outside, the indoor temp will creap up.

Designing systems that keep people comforterable in Houston can be tricky though. Generally you have to throw concerns about SEER out the window and match a larger outdoor unit with a smaller indoor coil to get high latent capacity for humidity control.

Since you already have the system, rather than throwing bigger equipment at the problem, you may want to look into a whole house dehumidification system.
If the humidity is being delt with by something other than your AC system, it will do a significantly better job of controling the temperature in the house when the outdoor temperatures are at or above the normal peak temperatures.
It will also result in a MUCH more comforterable house when the outdoor temperature AND humidity are in the 80's, wich is many many more hours than it is near peak temperature conditions.

Throwing bigger equipment at the problem would likely actually make the house more uncomforterably humid for much more of the time that it is warmer than you like with the smaller system.

[sdeemer]

i'm new on the website - everyone has been so helpful. you that lived in houston area that responded - is it against the rules to find out your contact info? or can people on this site recommend someone to me? thanks

[sdeemer]

i guess i need to call a technician to come to my home and evaluate my entire system and perform a manual J on my home - and then providing the info they have found shows my unit is undersized - get somthing printed out to take to the builder.

they do not want to put a larger unit in here. and if our home doesn't actually NEED it - i don't want that either. put if our home was sized incorrectly, maybe this is the only way. there has to be a good reason why our house can't cool under 82F from 4pm - midnight.

[bobr42]

We still on this subject sir I wouuld call another company not a tech even though most of us can tell you the problem .Look in the book the one that has been in buissness for a 20+ years have them to send you a comfort consultant a smooth name for a sales man have him do aheat load on your home talk to him a good company is not going to not down grade another company but help you for what you need thats our job . Thats how we work if you are not happy and you buy from us and if you not satisfied for any reason we will give your money back that is 100% buy back that us .So where is spell check on this system anyways

[Edited by bobr42 on 07-18-2006 at 11:41 PM]

[icyflame]

I hope the supervisor was refering to a 20 degree temp drop across the evap. as the entering air temp drop than the leaving air temp will drop. In simple terms you are moving the heat from the inside and "releasing" it to the outside. The thermostat is just an automatic on/off switch, It does not make the equipment operate at differnt temps. You should be able to have your inside temp as low as you like.
On new builds, builders and or hvac contractors will choke air flow due to space restrictions, or creative design. the second most abused procedure is the pump down, and third is the brazing the lineset and dryers. All three of these will effect system performance.

[Edited by icyflame on 07-19-2006 at 12:16 AM]

[perel]

A *lot* of HVAC companies will swear up and down that the 20 degree delta T is how much cooler you can get the indoors from outside. Sometimes the design conditions for the area mean you end up with about a 20-degree IAT/OAT difference at design conditions, but they don't put it that way. They definitely do insist that the systems are only designed for a 20 degree delta T, so it's impossible to have 75 inside when it's 100 outside! (I asked one such contractor how come people in the desert aren't 90 degrees inside when it's 110 degrees outside. He declined to answer.)

[gerger]

Installing your condensing unit under a tree will help more than you think on those hot sunny days. Being in the direct rays of the sun is really hard on a undersized unit. Even a properly sized unit works better if it has some shade from the sun.

[Steve Wiggins]

Outdoor temp has nothing to do with how cool the indoor temp can be. It has everything to do with heat load verses equipment capacity.

Your house is 82°F because you live in a brick oven with a second 140°F oven sitting on top of it and then you are taking the coldest air and passing it through your 140°F oven with the least amount of R-value seperating the two. Dark shingles and HUGE windows top it off as one of the dumbest ways to construct houses in Houston Texas. THAT is why you are hot. Oh yeah try sticking a thermometer in your bathroom exhaust housing.....you'll see where the heat is getting in esp. when you suck it in by running the clothes dryer.

[Panama]

It is unusual to find a truly undersized residential system. Cooling problems can almost always be solved by correcting the charge or by finding and repairing leaks in the ducts and air handler. In other words, most cooling problems result of poor installation.

But if the system is undersized it is usually better to fix the house instead of the AC system. That may not be cheaper now, but it will be cheaper over the long haul.

[coordinatesales]

Originally posted by Steve Wiggins
Outdoor temp has nothing to do with how cool the indoor temp can be. It has everything to do with heat load verses equipment capacity.


Exactly! It's really a simple matter of what is the heat load and having enough tonnage to handle that load. If you want to keep the house at 70 when it's 105 outside, that simply increases the heat load and requires larger equipment. Of couse, that equipment will then be oversized for most days. It's just a matter of design and that's why it's important to let the contractor know what you expect from the system. He/She will then let you know of any concerns and problems regarding under/over sizing.

The 15-20 degree delta that most people try to achieve is the difference between return air temp and supply air temp.

[perel]

I understand that. My point was that there are a lot of contractors out there telling customers that the 20 degree delta T is the IAT/OAT delta instead of the evap entering/leaving delta. As far as I can tell, this is because it's easier to blame the equipment/manufacturer than it is to explain design conditions and take the blame for having used inadaquate ones. It's incorrect information, but we should be aware that there are a lot of HVAC pros out there spreading it.

[engineerguy]

What Steve Wiggins and Panama said.

My own house stayed at 78 degrees inside when it was 101 degrees outside. The one ton AC was cycling on and off the whole time. The secret is R60 insulation in the attic, R30 in the walls, and all ductwork in conditioned space......

[alexb]

What's the effect of having the supply ducts in a basement, w/ such high humidity, that the ducts sweat? Will this actually remove the 'coolness' from the air in the ducts?

I forgot my physics; does condensation add heat, or subtract heat?

I"ve just solved this by buying a dehumidifier for the basement (no registers in basement). Basement is not finished, so I don't want that musty smell upstairs in the living area.

[Mr Bill]

"IF" your a/c has nothing to do with the outside ambient air then what are you designing the a/c to do, it must have something to do with heat load right? what is a local with 105 degree temps not considered to be used into a common sense heat load along with a manual J in warmer climates?
So if your concern is only size to home and installation proportion that would mean you should size a system in Alaska the same as Houston TX. I have to disagree with anyone saying the outdoor temps has nothing to do with unit sizing and I have even heard RUUD tell us at the dealer meetings that if you home is getting a difference of 20 degrees from out to in you are doing good and about what is expected unless you live in a cave with 40' thick walls.

[hvac hero]

Originally posted by mrbillpro

[i]


Personally I have lived in Houston for 54 years and been in the a/c business 30 years and they probably used a manual J only to size your unit but I would have never in my life have installed a 4-ton system in a home "IN HOUSTON" with 2850 sq.ft. you would have had a 5-ton or I would not have done the job. A lot of folks here promote manual J and yes it is a good starting point but when you have been in the business here for 30 years it's helps to know Houston and use a little common sense, also I have a 5-ton 14 seer on my home 2500 sq. ft. and my system is tweaked out to the max and today it got to 78 in my home so go figure. [/B]

AMEN Our climate is a lot like Houston, & I just know from experience that a 4 ton unit on a house that big is trouble. Especially with big vaulted ceilings & big windows. I have the man. J program & I betcha if the person that put that system in had used it they woulda put a 5 ton in or maybe even 2 systems. If I were the customer, I might be looking to pull the master bedroom & master bath off of the 4 ton unit & adding a small unit.

[bobr42]

Of course if you want to spend the money did we bring up 2 stage yet?With a varible speed system.Just another idea that will We have all the answers.