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03-20-2005, 11:09 AM #1
This is a tough couple questions to ask. Please forgive the length of the post. This message is spurred by a call-in to the Tom Tynan radio show in Texas. The caller complained of AC monthly bills in the $350-400 range (meaning 3500-4000 kwh) while living in a 2700 sqft home using 3.0 ton AC system. He said the system ran "all the time".
Now Tynan has more experience than I will ever have, on building matters in general. I would buy a home built by him and trust in his craftsmanship and good construction methods, as much as any builder I know of -- even when they are not what Lstiburek would do. But occasionally Tynan sounds off his strong opinions that don't seem to reflect education.
Tynan came down hard on this guy's AC sizing, saying the long runtimes were the source of high bills. He strongly advocated a larger unit which would cycle even during the hottest days, saying the shorter runtime would result in lower bills -- he strongly suggested a similar house built by him would see summer bills no higher than $160/mo.
Tynan exclusively uses Central City Air for his AC systems, so I am very confident he gets a quality install even if not exactly to Manual J specs. And I am confident CCA would make sure the ductwork was well sized (Tynan's apparent awareness of ductwork is nil). I am hoping Airman would be willing to say why Tynan might be believing a larger system would be better for energy consumption. Would anyone else care to argue in favor of Tynan's claim that a larger system with shorter runtimes, would result in lower energy bills?
Question for the other board experts -- At 900 sqft/ton this does not seem to be the classic old leaky Texas house. It seems as if someone tried to use modern building practices and botched it. What would you think would be the LEADING CAUSES TO SUSPECT for high energy bills in a case like this one?
While I would *like* to believe all the answers can be found with Lstiburek and Manual J etc., it seems necessary to look and see if answers can be found elsewhere as well. Hence the devil's advocate type of question.
Thanks -- P.Student
03-20-2005, 11:52 AM #2Banned
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- Aug 2002
- Office and warehouse in both Crystal River & New Port Richey ,FL
Assuming the house is maintaining the desired temperature,and that you replace it with a larger system of the sme SEER,I don't see that the bill would go down.
If the house needed two tons and we installed a 4 ton system,the 4 ton would run half as much(not accounting for short cycling,humidity,etc.),but the 4 ton would cost twice as much to operate per hour.
The home in question likely has ,duct leaks,infiltration,exfiltration,system problems,etc.,etc..
Now ,sized by CCA,yes it will cycle on the hottest day,and have better part-load humidity control.
03-20-2005, 12:16 PM #3
From his post, CCA designs the entire system for max humidity control, and temp. using a large condenser, and a smaller indoor coil with a txv sized to the oudoor unit.
Did the caller say what he was setting his stat at.
If the system was originally designed to maintain 78 indoor, and they have the stat set fo 70, that will raise the old elec bill alot.Contractor locator map
How many times must one fix something before it is fixed?
03-20-2005, 12:26 PM #4
The home I presently own was initially installed with HVAC per manual J. 1950 sq. ft., 2.5 ton HP. We bought it when 10 years old. In the summer, we culd not get the temp below 75 if outside was 85 or better, 78, if outside temp was 90 or better.
Well I like to tun my a/c about 72-73.
Ran constantly with high electric bills. Would not get to 73
One reason, I don't like manual J, calculates for efficiency only, with no regard to comfort.
The original folks in the house were elderly, and I guess they were satisfied with 78 degree home.
If yo size per manual J,here, you size for 75 indoor @ 92 outdoor. Some summers we have many days above 92. And some customers, like me, like to be cooler than 75.
So when I size jobs, I use 72 inside and 95 outside for calcs. Would have been a 3 ton in my home that way.
Also manual J does not take into account that windows & doors get old and leak more. So after several years the home has more infiltration, not accounted for by man j.
During the hot part of the summer, I will have several calls for no A/c and find that the unit is operating as designed, but just not big enough for the outdoor temps.
Customers don't like it when I explain that system is doing all it can.
[Edited by bornriding on 03-20-2005 at 12:29 PM]
03-20-2005, 01:22 PM #5
Another thing Manual J does not allow for is wether the duct system is actually delivering all the available BTU's from the equipment.
The installation needs to be tested to insure it is delivering the BTU's from the equipment into the building envelope as calculated by Manual J.
I could not begin to tell you how many times we have had a request for a proposal for larger equipment due to long run times & unable to keep temperature under control during high outside temperatures.
With some investigation it was found the culprit wasn't the size of the equipment it was the duct system being inadequate.Have you set up a Google alert for Carbon Monoxide yet?
Click here to find out how.
03-20-2005, 09:12 PM #6Member-bad email
- Join Date
- Aug 2003
Pstudent---This thread is a contiueum of our last. You need to be carefull who you believe is an expert. Tom Tynan is dead wrong on this issue and is misleading the public. Dr. Joe has forgotten more about building energy effecient, moisture free, comfortable homes than Tom Tynan will ever know. I suggest you do more research into the Building America program that Dr. Joe is involved in.
He designed the methods and trained production builders to build thousands of better homes that guarantee energy savings and comfort for the same cost as code built homes. I would love to test Tynan's homes to see if he even comes close.
Manual J is the only way to size HVAC properly. Is it as accurate as we would like it? No, it is only as good as the person using it, and actually oversizes because of things like leaky, poorly designed ducts, and not testing, but guessing air infiltration. The statement that manual J sizes for effciency and not comfort is not true in many areas of the country that are humid. Too many things are blamed on manual J, rather than the real problems as Dash has mentioned.
03-20-2005, 09:45 PM #7Regular Guest
- Join Date
- Apr 2004
- Niantic, Illinois
I would also like to ask if anyone has checked the refrigerant charge. If it is not properly charged it will not properly cool. It may not be sizing or ductwork, but all are good culprits to look at.
03-21-2005, 12:04 AM #8
We get Tynan up here in DFW on Saturdays. Sometimes I find him to be kind of a blowhard. Last Saturday he was going off about how attic insulation is so much more important than wall insulation. Maybe that's true down in Houston, but up north here we've had some nasty experiences with the Arctic Express at times.
True, it's not Minnesota here, but think about it. If you want a 70 degree house on a day that stubbornly will not climb out of the low 20's all day, will you feel cozy being near a wall with marginal insulation with that kind of temperature difference between indoors and out? Even with great insulation overhead?
I didn't read in your post that the phone caller was living in a Tynan built house with a CCA system installed. Even if Tynan built the house and CCA put in the system, there could be a number of things we're not hearing that could be causing the high energy bills. Some of which other posters have already mentioned, but I'd add to that a sub that could've skimped on insulation or didn't install it properly, infiltration greater than expected by the Manual J load calc, etc.
I've been up in attics where batts of insulation have been tossed around over the years as post construction work was done on the house, and nobody was thoughtful enough to place it back when they were finished. People up in attics don't mix well with ductwork. It gets stepped on, shoved around, insulation torn loose, etc.
What approach Tynan might have taken, especially if one of his star contractors was being singled out, is to advise the homeowner to have his HVAC system undergo a thorough performance check, which CCA sounds quite capable of doing. If the system is found to be performing as designed, and was indeed sized correctly for the expected heat load, then the focus of the long run times needs to shift away from blaming the equipment and toward the construction of the house, IMO. The HVAC contractor may have acted in good faith on Manual J, only to have the questionable construction integrity of the house hamstring his efforts. Since we're not there, it's just my best speculation at this point."In this house we obey the laws of thermodynamics!"
- Homer Simpson
03-21-2005, 06:26 AM #9Professional Member
- Join Date
- Feb 2003
all of this seems to promote having a record left with all units showing data from startup, including design assumptions | conditions.
03-21-2005, 07:45 AM #10
Thanks very much for all the ideas so far.
Almost certainly the house was not *built* by Tynan, and he SHOULD HAVE touted his chosen partner company CCA at that time. I must agree Tynan can be a bit of a blowhard on certain subjects (but IMO so can other talented people). This is one of those subjects -- he self-righteously zeroed in on the tons/sqft measurement. However CCA itself has gone on record favoring mucho tons/sqft and I can see where Tynan might have got the idea this is valid.
Duct problems, system charging, infiltration, exfiltration, all of the things you guys are familiar with as problem sources (and I much less so) are good leads on looking for the problem. That directly helps me with one of my questions. I observe that were CCA to address the problem, I would expect them to prescribe a much larger system, and of course the ductwork would have to all be replaced, thereby wiping out one class of problem sources.
In asking where Tynan could have got his ideas, I was honestly hoping Airman would see fit to speak and either sort-of support Tynan's position or sort-of provide a correction. I understand on the subject of system sizing there are educated and experienced "heretics" and I would dearly appreciate the opportunity to hear one of them speak at length.
By my guess this appears to be a failed attempt to build with modest AC sizing, and it would be most revealing to learn just how it went wrong. As you all have said, there could be many possible ways, some of them quite ordinary.
Best wishes -- P.Student
03-21-2005, 07:57 AM #11Member-bad email
- Join Date
- Aug 2003
Pstudent--there is no "modest" sized HVAC. Hvac is undersized, correctly sized, or oversized according to the heat gain/loss of the home.
03-21-2005, 08:57 AM #12In asking where Tynan could have got his ideas, I was honestly hoping Airman would see fit to speak and either sort-of support Tynan's position or sort-of provide a correction. I understand on the subject of system sizing there are educated and experienced "heretics" and I would dearly appreciate the opportunity to hear one of them speak at length.
I've studied the material on CCA's website and I can conclude his entire approach appears to design for the humid Houston climate. He's apparently had good success with evap coils sized smaller than the condenser (since it is the compressor and condenser that ultimately determine system capacity) because he can run a colder coil, thereby removing more latent heat. His setup likely wouldn't work as well in, say, Phoenix, where sensible heat is a far greater issue in summer months.
The disadvantage you have, as a listener of the show, is the same disadvantage we have here on this board when homeowners come seeking advice on their systems. Without personally visiting the home, we're only able to give replies based on our experience and training. Perhaps Tynan was doing the same, going on the scant info he's received from the caller. If he lacks training on the proper sizing of HVAC systems, he could either get that training or defer to someone who has it.
Nevertheless, you won't catch me willfully advocating oversizing systems, since that's a recipe for trouble. The right size system for the anticipated heat load of the building is the best route.
So when he's talking about "oversizing", perhaps he's discussing the condensing unit vs. the entire system."In this house we obey the laws of thermodynamics!"
- Homer Simpson
03-21-2005, 09:23 AM #13
he is a builder with a radio show and he should show more responsabilty with his show. it is like one of us saying code calls for 8 in rafters but he should have but in 14 in rafters with out any idea of what we are talking about
if the house is cooling and humidity on down it most likely is right thay want cheaper bills turn the stat up a few dagrees
manual j loads are there for a reason and there is a precentage of room to be within
square foot per ton is rule of thumb and realy does not apply at all when you do it right
do it right the first time or keep going back