What to Expect with Service Call

[skizot]

I plan on having an HVAC tech come out and check out my system sometime soon, and I was wondering what all they would/should check for a problem with the A/C not being able to cool the house down to a comfortable temperature.

[bmathews]

I hope he would come out in a service vehicle. Have clothes on and not spewing profanity as he walks up to your house. How should we know what to expect. It depends on what is the matter with it. Talk about a giddy schoolgirl on a first date.

[yellowirenut]

hopefully with a better attitude than that of the above poster

[skizot]

I hope he would come out in a service vehicle. Have clothes on and not spewing profanity as he walks up to your house. How should we know what to expect. It depends on what is the matter with it. Talk about a giddy schoolgirl on a first date.
Do you have some sort of problem? Maybe I'll put you in touch with the idiot that did the HVAC system for the builder of this home, and you can quickly find out why I'm leery. If the tech showed up to my house with your attitude, I'd give him a few choice words. Do you talk to your clients like that?

[bmathews]

Do you have some sort of problem? Maybe I'll put you in touch with the idiot that did the HVAC system for the builder of this home, and you can quickly find out why I'm leery. If the tech showed up to my house with your attitude, I'd give him a few choice words. Do you talk to your clients like that?

Ease up. I'm giving you a hard time. Nobody on here can tell you what to expect unless we are there. What if the condenser isn't running? What if the condenser fan isn't running and the compressor is? What if everything is running and pressures, superheat and subcooling look ok? And the problem is showing up intermittently? Hopefully you get my drift. There are many different scenarios the tech could experience when he walks up. If somebody on here guides you down one path and it turns up to be something else. You're gonna get all squirrely with the tech and nothing will get accomplished and then come on here complaining about what a bad tech he is. And yes, if I have a customer get weird with me. I will talk to them that way. I don't need people like that questioning everything I'm doing. I will answer reasonable and intelligent questions, other than that I will tell them to back off.

[skizot]

Ease up. I'm giving you a hard time. Nobody on here can tell you what to expect unless we are there. What if the condenser isn't running? What if the condenser fan isn't running and the compressor is? What if everything is running and pressures, superheat and subcooling look ok? And the problem is showing up intermittently? Hopefully you get my drift. There are many different scenarios the tech could experience when he walks up. If somebody on here guides you down one path and it turns up to be something else. You're gonna get all squirrely with the tech and nothing will get accomplished and then come on here complaining about what a bad tech he is. And yes, if I have a customer get weird with me. I will talk to them that way. I don't need people like that questioning everything I'm doing. I will answer reasonable and intelligent questions, other than that I will tell them to back off.
Get all squirrely? I doubt it. I've learned quite a bit from reading this forum, other forums, and pretty much any piece of HVAC info I can get my hands on (mainly from NCI), so I do know a little bit. No, I don't think I know everything, and probably far from it since this isn't my profession. My point is that I just want to be sure I'm getting a competent tech, because although it may be hard for you to understand, there are plenty of incompetent HVAC techs out there (as there are in any profession). I just want to make sure they're going to do everything they can and should to diagnose the system, and not just try to sell me on another one, or work that isn't necessary. By asking what I should expect, I can better gauge that. Maybe I should have posted the symptoms first.

And as far as coming on here and badmouthing the tech, there shouldn't be any need to do that if they know what they're doing. As an example, I tried to talk to the owner of the HVAC company that installed everything in this house (I didn't have it built, so it was already in when I bought the house). I tried talking static pressure with him, because I've got 0.35" W.C. PD across a brand new blue fiberglass filter (something that should have a 0.05" - 0.10" W.C. PD new, like this one was), and he told me he had no idea what ESP was. I tried talking about the face velocity due to the dimensions of the main return drop, and he told me that I knew more than him (not something you want to hear as the customer, from the professional; they should know far more than I do on the subject, otherwise why would I be talking to them?). People like him give HVAC pros a bad image, and I know that not all of them are like that out there.

As for the symptoms, the system just won't cool the house below 77-78 degrees when it's above 90 outside. I was only able to get it down to 77 today because I set it at 77 and told it to hold the temp all day long. The temp outside right now is 93 with a heat index of 103. The temp split is about 17-18 degrees. The unit is not cycling, and has been running all day long. It only cycled a few times early this morning when the outside temp was in the low 80s. The house is fairly well insulated with R13 in the walls, and R50 in the attic, and has a natural ACH of 0.37. It's a 2300 sq. ft. home with no shading on the West or South (new construction so trees are all too young to provide much shade). The A/C unit is 3.5 ton with a 5-ton air handler. I've set the blower speed at Med. Hi which would be giving me about 1550 CFM due to my TESP (High would be too much air, Med wouldn't be enough; determined from manufacturer's blower performance table).

[katohvac]

What kind equipment do you have?

[skizot]

What kind equipment do you have?

Furnace
Brand: Armstrong Air
Model Number: G1N80BU100D20C-2A

A/C
Condensing Unit: 2SCU13LE142P-1 (Armstrong Air)
Coil: EC1P43CM (I couldn't find any information on this coil anywhere online)

[katohvac]

As it gets hotter your losing ground your either low on refrigerant or your condenser is dirty, without during a heat load on your house I can not tell if it is size prperly but I would say it is size fine, so I personally would make sure that the tech. that comes to your house be able to put gages on the unit and have the proper temp. tools to do superheat.

The condenser may not look dirty but it may be dirty between the fins, need to wash out with water very well, his gages will tell if the coil is dirty.

[lentz]

With a 2300 sq. house and a 3.5 ton condenser and not much shade-even with good insulation, tempertures in the mid 90s it will be hard to get to the low 70s. How is the infiltration? Seals on the exterior doors, shades on the windows, room ceiling penetrations. very high ceilings or well ventilated attic.

[skizot]

Thanks for the info, katohvac.


With a 2300 sq. house and a 3.5 ton condenser and not much shade-even with good insulation, tempertures in the mid 90s it will be hard to get to the low 70s. How is the infiltration? Seals on the exterior doors, shades on the windows, room ceiling penetrations. very high ceilings or well ventilated attic.
Mid to upper 90s are not uncommon at all during Summer here, and are pretty much the norm during the middle of Summer (I think the design dry bulb temp for this area is 100 for the Summer). Infiltration is not bad at 0.37 natural ACH. It's no where near as tight as it should have been for a new home, but I've done quite a bit to get it down to 0.37. Almost all ceilings are 9', with the family room being vaulted and 13' in the center. The attic has quite a few vents through out (gable, soffit, and static). All door and window seals are fine (everything is new, and I've adjusted a few things here and there as far as the seals go to get things in those areas a little tighter). There are wood blinds on all of the windows, and I keep them closed all day long to keep the sun out.

I've sealed every single penetration inside and out. :D Eletrical/switch boxes, can lights, fan boxes, smoke detectors, supply boots, to name a few.

[bradley wayne]

I just joined this site but if there are alot of jerks like bmatews, I wont be visiting here much.

[lentz]

Sounds like you have done a good job in getting the house ready for the Tech to come do his thing.
Good Luck on the getting the house cooler.

[jrgreene1968]

please post what the tech comes up with..i have the exact same problem:D i have had mine checked by 2 different companies, and keep getting told its doing all it can, its just hot out.

[bmathews]

I just joined this site but if there are alot of jerks like bmatews, I wont be visiting here much.

My wife tells me I'm an a^^hole. I'm a pretty tough pill to swallow. But that is me. If you need something fixed and don't have time for BS, call me. If you want to be courted, then don't call me. I don't have time for games, time is money, which most people don't realize. To the OP. You probably bought a tract home, they saved $50 for undersizing it. It is honestly probably doing all it can. Good luck with the call. I forgot Mr. Wayne, there are a quite a few more brutal than me on here. Be tough or you will be eaten alive.

[fenian]

I just joined this site but if there are alot of jerks like bmatews, I wont be visiting here much.

bye bye

[fenian]

"...I was wondering what all they would/should check for a problem with the A/C not being able to cool the house down to a comfortable temperature..."

not really sure why you are asking this.

i'm hoping for the tech's sake that you explain what your history of the house is in regards to your comfort/discomfort and what modifications you've made to the load and mechanics. Reading your earlier posts it's obvious there's a history here that some techs might see as a red flag and it seems something like an ambush if you're wanting him to hit a home run on the first pitch --especially given you've almost a hundred posts within this forum discussing to a great degree the relevant issues you'll be expecting him to command.

the problem could be anything.

this a tech someone you trust recommended to you, right?

[rojacman]

:D
I just joined this site but if there are alot of jerks like bmatews, I wont be visiting here much.hold up there pardner , you just hold on here and stick around , you'll find that this site is like no other on the net . most all of the experiences you'll have here with us will be pleasant , fun at times , sad at times when one of us has a tragedy or some bad times . in other words you'll feel like you're among friends . don't pass this learning experience!!!! just listen to an old timer , that poster may have been taken out of context or had a bad day , we're here for u 24/7 , welcome aboard , learn what u can and give some back when u can......Jack

[pacnw]

you may already know this, but as a general rule you can cool a house 1* an hour.

if it is already 80* before this unit comes on and it is hotter than that outside, then yes it is doing as good as it can.

if you start it earlier, does it get to your desired temp?

17-18* temp split is on the low end of things.

keep everyone posted.

[Some Dude]

Have you checked the temp across the unit? Temp in house and temp coming from vents?

[skizot]

"...I was wondering what all they would/should check for a problem with the A/C not being able to cool the house down to a comfortable temperature..."

not really sure why you are asking this.

i'm hoping for the tech's sake that you explain what your history of the house is in regards to your comfort/discomfort and what modifications you've made to the load and mechanics. Reading your earlier posts it's obvious there's a history here that some techs might see as a red flag and it seems something like an ambush if you're wanting him to hit a home run on the first pitch --especially given you've almost a hundred posts within this forum discussing to a great degree the relevant issues you'll be expecting him to command.

the problem could be anything.

Not really sure what you're talking about there. What posts have I made here in the past that says I've made "modifications to the load and mechanics". Either you're reading someone else's posts, or you haven't read my past posts correctly. There seems to have been some poor design on the HVAC company's part that installed the system into this house on several notes. I've discussed these in my past threads on this forum, and got helpful feedback from many. Why would I not talk to the tech about all of them? The more I re-read your post, the less it makes sense to me. I'm not really sure what your point in posting it was. I don't really know why you're making wild assumptions that I'm going to keep quiet and let them try to figure things out without telling them all I know about the system. This isn't a game to me; of course I'm going to discuss in detail all I know about the problem. And when I've given them all of the information I can, and they've looked at the system, I expect them to make recommendations or diagnose the problem, or problems with the system.


this a tech someone you trust recommended to you, right?
No one has recommended any tech to me. I'm looking to find a competent tech before I shell out $100+ to someone who doesn't even understand static pressure.

[skizot]

if you start it earlier, does it get to your desired temp?
Today I tried for 77 and was able to maintain it. I have not tried starting it early lower than that yet. I will try for 72 tomorrow (setting it in the morning), and see if it can maintain that all day. It looks like the high should only be in the mid 80s tomorrow after this cold front has passed through.


Have you checked the temp across the unit? Temp in house and temp coming from vents?
I got the 17-18* temp split from measuring the supply register closest to the air handler, and by taking an average of all of the returns (upstairs and downstairs). I will measure again tomorrow at the air handler itself.

[fenian]

"What posts have I made here in the past that says I've made "modifications to the load and mechanics". Either you're reading someone else's posts, or you haven't read my past posts correctly."

you set your blower speed.

you remind me of thebilli'llpay

[skizot]

"What posts have I made here in the past that says I've made "modifications to the load and mechanics". Either you're reading someone else's posts, or you haven't read my past posts correctly."

you set your blower speed.

you remind me of thebilli'llpay
Yes, I set it correctly. The company who installed it had it set on High. Again, that is a question I asked the owner of that company, and he said that they just leave the blower speed for cool and heat on whatever the factory presets on the board are. :( It's a 5-ton blower. Even with my TESP, that's over 1850 CFM. If you think 1850+ CFM is correct for a 3.5 ton coil, then that's a red flag to me that you don't know what you're talking about. ;)

Fenian, you remind me of the guy who designed and installed this system.

[fenian]

Yes, I set it correctly. The company who installed it had it set on High. Again, that is a question I asked the owner of that company, and he said that they just leave the blower speed for cool and heat on whatever the factory presets on the board are. :( It's a 5-ton blower. Even with my TESP, that's over 1850 CFM. If you think 1850+ CFM is correct for a 3.5 ton coil, then that's a red flag to me that you don't know what you're talking about. ;)

Fenian, you remind me of the guy who designed and installed this system.

fair enough. but my ac works.

[skizot]

Going to call up a tech tomorrow. Until then, here's some data from tonight:



Time Outside Temp (RH) Inside Temp (RH) SR Return Supply
5:40 PM 92 (32%) 76.4 (49%) 57.4 76.4 53.4
6:05 PM 91 (32%) 76.2 (49%) 57.4 76.3 53.0
6:25 PM 91 (36%) 76.1 (49%) 57.3 76.2 52.8
7:05 PM 90 (35%) 76.4 (48%) 56.9 75.8 52.2
7:55 PM 88 (46%) 75.7 (47%) 55.8 74.5 51.2
8:25 PM 84 (56%) 75.0 (47%) n/a n/a n/a


SR = Supply register in a room over from the tstat. Return and Supply columns are the return and supply temperatures measured at the air handler. When I came home from work, the AIR on the tstat had gotten it down to 76 and was still running (set to be 76 at 5:30 PM), but I'm not sure how long that took. I changed it from 76 to 74 when I got in. I would think it should have gone from 76.4 to 75.0 a lot quicker than almost 3 hours. Those outside temps and humidity are actually Spring-like compared to what it's been here for the last 2 weeks (the last two weeks are what we'll have a couple of weeks from now).

Note: the slight rise in temp at 7:05 was from cooking dinner (oven).

[aintitfun]

how old is the systm,how long since it was serviced?

[Ed Janowiak]

A little knowledge can be dangerous.

You set your blower correctly?
Based on what calculation?
Did you determine the sensible heat ratio of the load and try to match it with the airflow?

That 530 CFM per ton might have been where the system was supposed to be are you trying for a nominal number like 400 CFM per ton now?

[skizot]

how old is the systm,how long since it was serviced?
The system just turned 2 years and has never been serviced. I've cleaned the fins out on the condensing unit outside every Spring, and I replace the filter every 30-45 days.



A little knowledge can be dangerous.

You set your blower correctly?
Based on what calculation?
Did you determine the sensible heat ratio of the load and try to match it with the airflow?

That 530 CFM per ton might have been where the system was supposed to be are you trying for a nominal number like 400 CFM per ton now?
I do not have a load calculation for my home, and will be looking into getting one when I call a tech out. I used tonnage, temp split, TESP, and the Furnace Spec Sheet (http://www.eccohtg.com/files/eccohtg/product/Armstrong_Gas_Furnaces_-_Ultra_V.pdf) to calculate the blower speed. As I mentioned in a previous post, the HVAC company that installed the system said they leave the cool and heat blower speed taps set at the factory settings. The heat speed is probably set correctly since the blower is a component of the furnace, and I doubt the mfr. would ship the system out with the blower speed set incorrectly for heat (although it's always good to have someone check). However, the mfr. has no idea what size A/C unit with be paired with the system, so the cool speed would definitely have to be set by the tech (which it was not).



Did you determine the sensible heat ratio of the load and try to match it with the airflow?
I didn't realize that is how it should be done. If the unit is not sized correctly, setting the blower speed based solely on what you mention could cause several problems, right? If the unit is oversized, you might not be moving enough air across the coil. If the unit is undersized, you might be moving too much air. I thought there were several other factors that went into calculating blower speed. The cooling load (sensible and latent) should be used to size the equipment in the first place, right?

[Ed Janowiak]

Your putting the cart before the horse.

You need and accurate load done before you can determine what the total air flow required is.

Lets start out slow.

More air flow (higher sensible heat ratio) = more efficiency.

Less air flow (lower sensible heat ratio) = lower efficiency

More air flow quicker to satisfy the thermostat.

Less air flow longer to satisfy the thermostat.


What is you ultimate goal? As I read ti your not happy with the amount of run time you have (too much), lowering the fan speed will increase run time.

[skizot]

Your putting the cart before the horse.

You need and accurate load done before you can determine what the total air flow required is.

Lets start out slow.

More air flow (higher sensible heat ratio) = more efficiency.

Less air flow (lower sensible heat ratio) = lower efficiency

More air flow quicker to satisfy the thermostat.

Less air flow longer to satisfy the thermostat.


What is you ultimate goal? As I read ti your not happy with the amount of run time you have (too much), lowering the fan speed will increase run time.
The unit is only capable of removing a certain amount of heat from the air. It wasn't satisfying the t-stat any quicker when it was set for 530 CFM / ton (1850 CFM), than it is now at 440 CFM (1550 CFM).

My ultimate goal is to be able to cool the house lower than 78 degrees when it's 95 (or hotter) degrees outside (and not do a set and hold at the temp I want at 4:30 AM :D).

Quick question, are you saying that your "more air flow = more efficiency, and less air flow = lower efficiency" applies to heating as well?

[motoguy128]

The unit is only capable of removing a certain amount of heat from the air. It wasn't satisfying the t-stat any quicker when it was set for 530 CFM / ton (1850 CFM), than it is now at 440 CFM (1550 CFM).


Quick question, are you saying that your "more air flow = more efficiency, and less air flow = lower efficiency" applies to heating as well?

Generally speaking yes. But to a point. Much above 450CFM, I think you'll just be spending money to move air. Also, depending on your ductwork, as the static presure increases, you're spending money to compress and thereby heat the air.

Also, above 450CFM/ton, the fan itself is putting out more heat, so when cooling, it must be subtracted from the total system output. There is a point where getting another 170 BTU's will cost you another 50 Watts... so you've gained nothing.

If you have very restrictive ductwork, the point where your system is most efficient, might be closer to 400CFM/ton or even lower.

At some point you might gain more capacity, but lose efficiency as well. it really depends on each system and installation.

Also keep in mind that improving latent capacity, could be more efficnt if it allows you ot keep you home comfortable at a higher temprature because hte humidity is lower. This is something that has gotten missed in the rush to obtain ultra high SEER systems... that sometimes have inadequate latent capacity when compared to older lower SEER sytems.

[skizot]

Thanks, moto. I was just getting at this; the way I understand heating is that the you're adding a fixed amount of heat to the air inside your home (determined by the size of the furnace), and you're not going to be able to add more heat to the home by increasing the fan speed when heating. If your output is 80,000 btu/h, then you're adding 80,000 btu/h to the home, regardless of whether you're moving 1200 CFM across that heat exchanger, or 1600 CFM. You're just going to end up with different DeltaT's there (63.7 and 47.8, respectively). Obviously you run into problems when you don't move enough air across the heat exchanger (cracking), or coil (freezing). But, you can only add as much heat to the home as your system can output.

I assume the same is true about cooling. You can only remove as much heat from the air as your tonnage allows (42,000 btu/h in my case). Running the fan slower will remove more moisture, and yield a larger temp split. All increasing the fan gets you is a smaller temp split, less humidity removal (and good point on the added heat from the blower). If my total heat gain (latent + sensible) is more than 42,000 btu/h, and I want a comfortable temperature of less than 78 in the house, then adjusting the fan speed up or down gets me nothing (well, aside from extra humidity removal).

Am I correct with these assumptions?

[Ed Janowiak]

Your assumptions are not correct.

Heating is a 100% sensible process, cooling is (amost allways) both sensible and latent.

All Cooling BTUH's are not created equal, your sensible heat ratio changes with the amount of air you move.

This would be easier for me if I knew what part of the country you live. Designs will differ from desert to a green grass climate. A load calc would help too :p.

[skizot]

This would be easier for me if I knew what part of the country you live. Designs will differ from desert to a green grass climate.
Closest city to look at for design temperatures and normal humidity is Topeka, KS.

Still, I'm not understanding why you think setting the blower to 1850+ CFM would be correct for a 3.5 ton setup, even if I had a load calc sitting right in front of me to give to you the sensible and latent. I've never seen that much airflow recommended for cooling in all the posts I've read on this board. But maybe I'm not understanding things. :-p

[Ed Janowiak]

If your SHR is a 90 10 split, the faster you move the air the better.

I don;t know what your air flow should be with out a load calc, but I also know that I never automatically think less air flow is better unless noise is the major complaint.

[skizot]

If your SHR is a 90 10 split, the faster you move the air the better.

I don;t know what your air flow should be with out a load calc, but I also know that I never automatically think less air flow is better unless noise is the major complaint.
That's cool. Sorry if I come across as a smart-ass. :D I'm here to learn as much as I can, and posing my assumptions, and questioning answers is a good way to do that for me. Having people correct me and explain why is a good thing. :-)

[Ed Janowiak]

You don't come across like a smart anything ;) LOL.

Kidding, I looked up your area and you have both latent and sencible loads, design temp is 95 and if you can't maintain not recover but maintain 75 inside when it's 95 out with blinds draw and such something is wrong.

Could be lots of things, but from what you have listed I'd be confidant in saying it's not an air flow problem. I've been out on a lot of 3erd party complains and finding units too small almost never is the reason.

I'm sure you have read it here, if not in this thread, but look @ the temp of the air @ the return grill(s) and the temp of the air entering the coil and see if it's the same.

[skizot]

You don't come across like a smart anything ;) LOL.
Interesting. I guess my employer is paying me the money that they are, to do the work that I do, for nothing. ;) j/k


I'm sure you have read it here, if not in this thread, but look @ the temp of the air @ the return grill(s) and the temp of the air entering the coil and see if it's the same.
I will do that when I return home. Given the return temps I was seeing at the AH yesterday, I doubt much unconditioned air is being drawn into the return side of things.

[skizot]

Your putting the cart before the horse.

You need and accurate load done before you can determine what the total air flow required is.

Lets start out slow.

More air flow (higher sensible heat ratio) = more efficiency.

Less air flow (lower sensible heat ratio) = lower efficiency

More air flow quicker to satisfy the thermostat.

Less air flow longer to satisfy the thermostat.


What is you ultimate goal? As I read ti your not happy with the amount of run time you have (too much), lowering the fan speed will increase run time.
Reading this again, I have a question. What about the increased face velocity across the coil with higher air flow? The velocity increases when you increase the CFM. The higher the face velocity, the higher the coil bypass factor. The higher the coil bypass factor, the less efficient the coil is. This seems somewhat contradictory to what you've stated.

[Tech Rob]

You should expect your house to smell kinda funny for about a week or two after the service. :p

[ktechnical]

You can have a good air split, but not capacity. If you slow the blower down to get a better split, it doesn't mean there isn't a refrigerant issue.
You can have a dirty coil with a 23* split, and still be low on refrigerant and the system won't cool the home properly.
Let the tech check everything out before you present him with graphs and temp readings and such. He may find a problem and the time you spend discussing and going over all that info will be wasted time. Simply state the problem and let him do his testing. Leave him alone- you only slow things down and it's hard to concentrate with some one talking to you and following you around. At least it works best for me that way.
Then if he finds nothing wrong, present your info and see if he has any further ideas.
I always check the house out as I work- I look to make sure soffet vents haven't been covered or removed, the ridge vent is open, insulation is correct, windows and doors tight, or any infiltration issues. This takes little time while walking around the home inside and out and to the truck. Did the customer go from a white to a red roof, paint the house a dark color exposed to the sun (older homes mostly), loose a lot of shade, pour a new concrete slab that now directs reflected heat on a window side. Maybe not one issue, but add a few and it makes a difference.
The outdoor unit should be washed with water/cleaner- not blown out with compressed air as I found some have done. Changing filters is no guaranty the indoor coil is clean- in fact as a filter loads up it traps more and also bacteria or slim could be coating the surface of the coil- etc.
You could have any number of problems that would retard cooling.

[skizot]

You can have a good air split, but not capacity. If you slow the blower down to get a better split, it doesn't mean there isn't a refrigerant issue.
You can have a dirty coil with a 23* split, and still be low on refrigerant and the system won't cool the home properly.
Let the tech check everything out before you present him with graphs and temp readings and such. He may find a problem and the time you spend discussing and going over all that info will be wasted time. Simply state the problem and let him do his testing. Leave him alone- you only slow things down and it's hard to concentrate with some one talking to you and following you around. At least it works best for me that way.
Then if he finds nothing wrong, present your info and see if he has any further ideas.
I always check the house out as I work- I look to make sure soffet vents haven't been covered or removed, the ridge vent is open, insulation is correct, windows and doors tight, or any infiltration issues. This takes little time while walking around the home inside and out and to the truck. Did the customer go from a white to a red roof, paint the house a dark color exposed to the sun (older homes mostly), loose a lot of shade, pour a new concrete slab that now directs reflected heat on a window side. Maybe not one issue, but add a few and it makes a difference.
The outdoor unit should be washed with water/cleaner- not blown out with compressed air as I found some have done. Changing filters is no guaranty the indoor coil is clean- in fact as a filter loads up it traps more and also bacteria or slim could be coating the surface of the coil- etc.
You could have any number of problems that would retard cooling.
Thanks for the advice, ktechnical. I appreciate it. I will try my best not to follow him around, but I like to see what they're doing. :D

[skizot]

You should expect your house to smell kinda funny for about a week or two after the service. :p
Yeah, I heard you HVAC pros don't wash often. :p Nothing some Lysol shouldn't cure.

[skizot]

No response to my question about the CBF, Ed? I don't see how the coil is more efficient with more air flow (hence a higher coil bypass factor).

[Daltex]

I'm sure there may be some velocity limit to hinder efficiency but that's not your problem.

Regarding the furnace CFM- It was mentioned that to low CFM and the HX cracks but it's also important to hit the plate rating range because to high CFM can cause rusting of the HX. Don't think it was mentioned but I'm also not a pro but pretty sure about this.

Get the tech to give you all his readings:
Indoor wetbulb
OAT
liq. line temp and pressure
suction line temp and pressure

Post back after getting this if he doesn't find a problem.

Pro's may be able to add to what they would need to diagnose an issue.

Have him check each return/supply take off and connection for proper seal. Mastic is a plus.

Good luck.

[skizot]

Your putting the cart before the horse.

You need and accurate load done before you can determine what the total air flow required is.

Lets start out slow.

More air flow (higher sensible heat ratio) = more efficiency.

Less air flow (lower sensible heat ratio) = lower efficiency

More air flow quicker to satisfy the thermostat.

Less air flow longer to satisfy the thermostat.


What is you ultimate goal? As I read ti your not happy with the amount of run time you have (too much), lowering the fan speed will increase run time.
OK, I get what you're saying now after reading some more. The coil bypass factor still plays a role, but I see how you can remove more sensible heat with higher airflow. The only question there is, with higher airflow, your split will be lower, right? So, if I move 1400 CFM across the coil and get a 23 degree split, I can't also get that 23 degree split at a higher airflow of say 1700 CFM, correct? The temp split would be lower at the higher CFM.

[dash]

"because I've got 0.35" W.C. PD across a brand new blue fiberglass filter (something that should have a 0.05" - 0.10" W.C. PD new, "


That's very high,are you sure of it?

What size and cfms?

What ESP do you have and where did you test it?

[skizot]

"because I've got 0.35" W.C. PD across a brand new blue fiberglass filter (something that should have a 0.05" - 0.10" W.C. PD new, "


That's very high,are you sure of it?

What size and cfms?

What ESP do you have and where did you test it?
1550 CFM and 20" x 12"
The filter drop was tested right before and right after the filter.

[dash]

1550 CFM and 20" x 12"
The filter drop was tested right before and right after the filter.


Cfms are too high for that size filter,so PD will be high.

What about the ESP,or as you stated TESP?

[skizot]

Cfms are too high for that size filter,so PD will be high.

What about the ESP,or as you stated TESP?
I think that's the root of a lot of my problems. The return drop is way too small for the size of the furnace and A/C. [T]ESP is around 0.8 with the coil dry and the blue fiberglass filter. I calculated the face velocity to be about 930 FPM with that much airflow and that size of return drop. That's why I was asking about the coil bypass factor earlier; it's very high with a velocity of 930 FPM coming into the air handler.

[dash]

Can you post a link to the fan data chart?

.8 is high,what speed was it on when tested and where did you test supply and return,what was the supply and return ESP?
Can you post pics of the indoor unit and connecting ducts?

[skizot]

Can you post a link to the fan data chart?

.8 is high,what speed was it on when tested and where did you test supply and return,what was the supply and return ESP?
Can you post pics of the indoor unit and connecting ducts?
Here is the URL for the technical data sheet for the furnace: Furnace Spec Sheet (http://www.eccohtg.com/files/eccohtg/product/Armstrong_Gas_Furnaces_-_Ultra_V.pdf)

Model Number: G1N80BU100D20C-2A

The speed was Medium. Supply was 0.19" return was 0.20". Those were both taken by the auditor at the air handler as well. The return was measured before the filter, and by the looks of his diagram, the supply was measured at the coil.

[meoberry]

Not really sure what you're talking about there. What posts have I made here in the past that says I've made "modifications to the load and mechanics". Either you're reading someone else's posts, or you haven't read my past posts correctly. There seems to have been some poor design on the HVAC company's part that installed the system into this house on several notes. I've discussed these in my past threads on this forum, and got helpful feedback from many. Why would I not talk to the tech about all of them? The more I re-read your post, the less it makes sense to me. I'm not really sure what your point in posting it was. I don't really know why you're making wild assumptions that I'm going to keep quiet and let them try to figure things out without telling them all I know about the system. This isn't a game to me; of course I'm going to discuss in detail all I know about the problem. And when I've given them all of the information I can, and they've looked at the system, I expect them to make recommendations or diagnose the problem, or problems with the system.


No one has recommended any tech to me. I'm looking to find a competent tech before I shell out $100+ to someone who doesn't even understand static pressure.

I will tell you this. I know some real good techs that if you start spouting static pressure and some of the other technical terms you have used. In their mind they have already decided that you think you know more than them. So why should they bother helping you.

I happen to know what static pressure is but do you know what the symptoms are of low static or high static pressures and the best way to check for each without pulling out a manometer.

The best thing you can do is check with a neighbor or friend on who they use.

Then call them and sit back and let them do their job. The more you look over their shoulder or quiz them the less cooperation you will get.

[dash]

Here is the URL for the technical data sheet for the furnace: Furnace Spec Sheet (http://www.eccohtg.com/files/eccohtg/product/Armstrong_Gas_Furnaces_-_Ultra_V.pdf)

Model Number: G1N80BU100D20C-2A

The speed was Medium. Supply was 0.19" return was 0.20". Those were both taken by the auditor at the air handler as well. The return was measured before the filter, and by the looks of his diagram, the supply was measured at the coil.


Between the coil and furnace or exiting the coil?

Thought you stated the ESP was .8 in wc.

If the filter is .35 the return would e more then .20,unless that's the filter in the furnace,as it's included in the fan data.


Sounding like you may not be getting the cfms you think you are.

[skizot]

I will tell you this. I know some real good techs that if you start spouting static pressure and some of the other technical terms you have used. In their mind they have already decided that you think you know more than them. So why should they bother helping you.

I happen to know what static pressure is but do you know what the symptoms are of low static or high static pressures and the best way to check for each without pulling out a manometer.

The best thing you can do is check with a neighbor or friend on who they use.

Then call them and sit back and let them do their job. The more you look over their shoulder or quiz them the less cooperation you will get.
I don't know everything, nor do I claim to. I can tell you this though, it doesn't take me long to figure out what kind of tech is at my house.

[meoberry]

1550 CFM and 20" x 12"
The filter drop was tested right before and right after the filter.

20x12 way to small. You need at least 525 square inches. On a 3.5 ton unit I would recommend a 20x25 if you have available space.

[skizot]

20x12 way to small. You need at least 525 square inches. On a 3.5 ton unit I would recommend a 20x25 if you have available space.
Thanks. I think I have just enough room for a 20x25. The unit is in the garage, so the area where the water heater and furnace are at is pretty tight

[dash]

Air flow is not taught in many schools,and poorly in some schools,but techs need to know.

I'd say use a manometer,and the fan data,to many differences between brands/models when it comes to air flow.

[the dangling wrangler]

Air flow is not taught in many schools,and poorly in some schools,but techs need to know.


That's the truth.
I got extremely lucky when I learned the trade.
I apprenticed under an old time master. Learned everything from, sizing the tin, bending the tin, insulating the tin, installing the tin,I mean we did the total job.
It was like having a personal teacher.
Lot's of guys here think all the lettered manuals came out in the last five years.
They didn't.
So, I guess it would be hard as a home owner to find a throughly educated tech. In reality, there just isn't an over abundance of 'em.

[rubberduck]

I recommend that individuals looking for a good tech ask friends or relative. It is hard to argue with word or mouth.

Here is a link of things you can do to make the techs job easier
http://www.residential.carrier.com/support/preservice.shtml

As far as things that a technician should check just google ac service checklist or something similar. You will find a weatlth of information.

[skizot]

Thanks for the reply and link, rubberduck.

[spam'n'rice]

20x12 is only enough return for about 1 1/2 tons. The first thing about AIRconditioning is AIR until the AIR is right your system will not perform correctly The truth is you need a competent tech to assist you some one who knows airflow try asking company's if they have any NATE certified techs that have taken the air diagnostics NATE test. Of course you could get some one that is book smart and has no common sense but chances are you will get someone qualified to get you on the right track.

Also no one likes someone breathing down their neck (not saying you will do that) (well it kinda sounds like you will):D But seriously I personally like to get the customer involved and watch me work Because they see my worth that way and when they get the bill there is no complaints because they see that I know my $h!t. what im trying to say is that if the tech doesn't want you around or acts frustrated you might wanna get someone else (but dont be rude because he could be new to the trade, and we all started somewhere and it wouldn't be fair to start at your house:eek:

and dont forget to tip we love that:)

[gary_g]

...and dont forget to tip we love that:)

I had doughnuts and OJ for my installers for breakfast.

For lunch, I made them burgers on the grill, and sausage w/peppers and onions.

That was my tip.

[rojacman]

20x12 is only enough return for about 1 1/2 tons. The first thing about AIRconditioning is AIR until the AIR is right your system will not perform correctly The truth is you need a competent tech to assist you some one who knows airflow try asking company's if they have any NATE certified techs that have taken the air diagnostics NATE test. Of course you could get some one that is book smart and has no common sense but chances are you will get someone qualified to get you on the right track.

Also no one likes someone breathing down their neck (not saying you will do that) (well it kinda sounds like you will):D But seriously I personally like to get the customer involved and watch me work Because they see my worth that way and when they get the bill there is no complaints because they see that I know my $h!t. what im trying to say is that if the tech doesn't want you around or acts frustrated you might wanna get someone else (but dont be rude because he could be new to the trade, and we all started somewhere and it wouldn't be fair to start at your house:eek:

and dont forget to tip we love that:)put a tip jar on your toolbox???????????:)....Jack

[spam'n'rice]

put a tip jar on your toolbox???????????:)....Jack

No but I never turn one down

[meoberry]

Tip? What is that? In florida the tips you do get are from retired yankees. Local people very rarily tip.:(

[Armament]

I thought the first reply was in good humor. Jeese guys....

[AirDynamic]

Tip? What is that? In florida the tips you do get are from retired yankees. Local people very rarily tip.:(

The tips u get here in the mts. r the good kind like( dont eat yellow snow) or the rare jar of homemade honey or something fresh from the garden lol:p

[fenian]

a salon gave me a bottle of shampoo the other day...
i think they were trying to tell me something.

[Ed Janowiak]

Reading this again, I have a question. What about the increased face velocity across the coil with higher air flow? The velocity increases when you increase the CFM. The higher the face velocity, the higher the coil bypass factor. The higher the coil bypass factor, the less efficient the coil is. This seems somewhat contradictory to what you've stated.

What leads you to believe that?

You have made several statements in this thread as if they were facts based on what you have learned and they have been incorrect.

I make my statements based on what I have learned and use product application data and field measurements to be sure I am correct.

Going back to the bolded statement in the quote above, show me something that backs it up, I'd be interested in reading it.

In the mean time go to york.com or goodman.com (I like these manufacturers because they will allow access via the net where as some you need to be a dealer to access equipment info) and find some application data. Pick a system, any system and see what happens to capacity, efficiency and sensible heat ratio when the airflow is increased or decreased.

We can pick it up from there :).

[skizot]

What leads you to believe that?

You have made several statements in this thread as if they were facts based on what you have learned and they have been incorrect.

I make my statements based on what I have learned and use product application data and field measurements to be sure I am correct.

Going back to the bolded statement in the quote above, show me something that backs it up, I'd be interested in reading it.

In the mean time go to york.com or goodman.com (I like these manufacturers because they will allow access via the net where as some you need to be a dealer to access equipment info) and find some application data. Pick a system, any system and see what happens to capacity, efficiency and sensible heat ratio when the airflow is increased or decreased.

We can pick it up from there :).
This is the article I read:

http://www.iaqdirect.com/Main/Products/Fanhandler/Humidity.htm

It could be completely inaccurate.

I stated in a later post that I think I understand what you're saying now though. I didn't go look at either site, yet. I did come across this formula that I've seen before on here:

Delta T * CFM * 1.08 = BTU/h

That's for sensible heat removal, right? My question on that is the Delta T does not remain constant when you increase airflow though, right?

I'm pretty sure I understand the SHR in regards to airflow now though. The lower the fan, the more latent heat you'll be removing, dropping the humidity, but not as much temperature. Higher fan will remove less latent heat, and more sensible heat, therefor increasing the SHR. The 530 CFM you stated possibly being correct just seemed a little high (basing that on what I've read here). The VS blowers out there have a comfort mode (350 CFM / ton) and another mode of 400 CFM / ton, right? Do some have a setting for more than 400 CFM / ton?

[Ed Janowiak]

Everything you just wrote is correct.

I'll add: more air more efficiency, but to a point. I don;t think it's realistic to continue to move more air across a coil after the units capacity is 100% sensible.

ACCA's Manual S has the formulas for determining CFM based on space gain system capicity and SHR, thats accurate. The 350 a ton or 400 a ton values are starting points or nominal numbers, that's ball park.

I'm gonna go read the link.

[skizot]

Here is another link I found on the coil bypass factor. It states something similar to that first link:

Marks' Standard Handbook for Mechanical Engineers (http://books.google.com/books?id=oOKqwp3CIt8C&pg=RA5-PA1-IA118&lpg=RA5-PA1-IA118&dq=coil+bypass+factor+efficiency&source=bl&ots=P_8lzAYGzI&sig=P84nUE8usXMismydbEzA4QSiIkw&hl=en&ei=0i1NSsXjBcv6tgfQgpmhBA&sa=X&oi=book_result&ct=result&resnum=1)

[Ed Janowiak]

I know what bypass factor is, but I see why you though along the lines you did. I read the first one and as soon as the author stated taking about using a good motor and slowing the fan down I was expecting to see an add for fan handler, I scrolled down and what did I see? :).

To an extent your correct with regards to higher velocity lowering efficiency, but I can't think of why you would run a system outside the typical operating parameters of what the systems are made to perform under. If you stay within the velocity's in the application data it becomes a non issue.

Bad duct designs have to be really bad designs to get water to start blowing off the coil, these are the kinds of velocity's you're going to need to see capacities (or efficiencies) affected.

[skizot]

I know what bypass factor is, but I see why you though along the lines you did. I read the first one and as soon as the author stated taking about using a good motor and slowing the fan down I was expecting to see an add for fan handler, I scrolled down and what did I see? :).
LOL.


To an extent your correct with regards to higher velocity lowering efficiency, but I can't think of why you would run a system outside the typical operating parameters of what the systems are made to perform under. If you stay within the velocity's in the application data it becomes a non issue.
Yeah, but the system needs to be engineered by someone who understands airflow. Unfortunately, I don't think the company who designed the system in my house understood that. The velocity in the return drop right by my air handler is 955 FPM (1592 CFM / ((20" * 12") / 144)). The blower compartment has larger dimensions, as does the coil compartment, so I'm sure the air slows down some, but probably not a whole lot. Is 300-400 FPM across the coil what you should be shooting for? What type of velocities are we talking about that would affect coil efficiency?

[dash]

Originally Posted by skizot
Here is the URL for the technical data sheet for the furnace: Furnace Spec Sheet

Model Number: G1N80BU100D20C-2A

The speed was Medium. Supply was 0.19" return was 0.20". Those were both taken by the auditor at the air handler as well. The return was measured before the filter, and by the looks of his diagram, the supply was measured at the coil.





Between the coil and furnace or exiting the coil?

Thought you stated the ESP was .8 in wc.

If the filter is .35 the return would be more then .20,unless that's the filter in the furnace,as it's included in the fan data.


Sounding like you may not be getting the cfms you think you are.



One test of .8 static on a certain speed ,does not mean you use .8 for the other speeds to determine cfms,change the speed you must retest.

[skizot]

One test of .8 static on a certain speed ,does not mean you use .8 for the other speeds to determine cfms,change the speed you must retest.
I know, I need to retest the static on Med/Hi, but I don't own my own manometer. I assume the static will probably be higher on a higher speed, so the 1592 CFM on Med/Hi for 0.8" is probably not 1592, but less. How much less I'm not sure of until I have it measured again, but I'm sure I'll still be over 800 FPM, easily. 800 FPM is 1333 CFM (given my dimensions), which is less than what I get on Medium with a measured static pressure of 0.8.

BTW, the ESP is definitely 0.8" W.C. on Medium. The tech that was out the other day verified this.

[Ed Janowiak]

I know, I need to retest the static on Med/Hi, but I don't own my own manometer. I assume the static will probably be higher on a higher speed, so the 1592 CFM on Med/Hi for 0.8" is probably not 1592, but less. How much less I'm not sure of until I have it measured again, but I'm sure I'll still be over 800 FPM, easily. 800 FPM is 1333 CFM (given my dimensions), which is less than what I get on Medium with a measured static pressure of 0.8.

BTW, the ESP is definitely 0.8" W.C. on Medium. The tech that was out the other day verified this.


I think if you were moving the air across the coil that fast you see other problems.

You asked before about velocity's across the coil and the 300 to 400 number sounds OK ballpark, but that is not how the manufactures rate them. They do testing to an ARI standard that is making sure they maintain a minimum FPM that is a ratio from capacity to CFM. That kind of math makes my head hurt, so I stick to looking at the proper duct design and the units fan will move the air at the proper speed if I set it up right.

Do you have a slab coil? Or is it an N or a A? The shape matters if you want to do the math to estimate the velocity. I find it easier to just measure it myself.

http://lh6.ggpht.com/_2Lc9JtEUfFY/SleSdzSnznI/AAAAAAAAANM/FKErVy1O9xU/s512/DSCF1154.JPG