Why is equipment sizing such and ongoing problem?

[joeselectric]

I am not in the HVAC industry but became very interested as I was researching my future gas furnace purchase. I learned much here and it has become an interesting hobby to visit here and learn. I would like to request feedback from all of you on what seems to be such a widespread problem of oversized equipment that has been installed. It amazes me all of the problems (and various complaints) inquired about here after an install. (i.e. short cycling, noise, hig utility bills, too humid...) This is certainly not directed at anyone, either the homeowners or the technicians that installed. This seems to happen so often. Whose shoulders should the selection and installation of the improperly sized equipment rest on? It would seem that the manufacturers should focus on this issue and provide the training needed to install the [I]properly [I] sized equipment. My compliments to all of the very knowedgeable professionals here that do so much to help the consumers of your trade. Guys, never underestimate the value of the information you all provide here. You have steered so many in the right direction.
Best wishes to all,
joe

[Southern Mech]

oversized equipment leads to poor humidity control, which leads to mold growth and poor home health down the road. It also is wasted power. They are starting to set higher standards for power consumption and if your house needs a 2.5 ton vs someone who would just drop in a 3 ton, thats alot over the life of the system. Also as general building practice change, better insulation,windows,and methods for tighter structure, one has to stop the rule of thumb heat and a/c designers. ie I have known some to design 5-600sq ft a ton, well I have designed some system's that were like 9-1000sq ft per ton. Can you see what would happen if you had a 3000sqft house done by rule of thumb vs a real precise load calculation. Now yes there is a differance between a 3000sqft house with 8-9' ceilings and one with 14-18ft ceilings.

[joeselectric]

Southern, Yes, I see. There is just so much to all of this. Is not doing a proper load calc. almost like throwing darts in the dark?
Thanks for the reply!
Joe

[Southern Mech]

no it's more like throwing them straight up in the air, you still don't know where they will land but 1 or 2 is going to bite ya.

[garya505]

I have wondered why oversizing is so common and have come to some conclusions.

1. Contractors don't want to leave any chance of undersizing, as this almost guarantees a tear-out and replacement at the contractor's expense. In new construction, they just seem to put in whatever they have in stock, as long as it's big enough. If it's not new construction, there is some guesswork in a load calculation, so it's "safer" for the contractor to error on the large size.

2. Everyone understands undersizing, where the unit can't heat or cool the house. However, most people don't understand that you can have too much heat or cooling capacity. This requires a little more thought and understanding of how things work, somewhat more than the typical homeowner's ability. Most people think bigger is better. When I try to explain to people why this is not true, I often get the "deer in the headlights" look from them.

Put 1 and 2 together, and you have a the oversizing mess we're in.

[joeselectric]

gary, that makes sense. So consumers have expectations that no matter how cold or hot it gets the temp in the living space had better be exactly what it is set to. Has anyone been succussful in finding a homeowner that can be educated to understand that in extremes of weather the system won't always maintain set point and be okay with that?
Thanks!
joe

[simplyrollin]

I have not had a homeowner that is satisfied unless that thermostat setpoint is reached on a 100 degree day with high humidity. Most contractors still oversize slightly for just this reason. Nothing more irritating than ripping out a system because it wont get below 78 on a 100 degree day. Hopefully, in the future, you will see more and more 2 stage equipment installed, this helps greatly.

[garya505]

gary, that makes sense. So consumers have expectations that no matter how cold or hot it gets the temp in the living space had better be exactly what it is set to. Has anyone been succussful in finding a homeowner that can be educated to understand that in extremes of weather the system won't always maintain set point and be okay with that?
Thanks!
joe

Well, I educated myself, does that count? :LOL:

But seriously, I've seen this when I talked to my contractor. Initially he wanted to put in larger equipment. After we talked a while, and he realized that I had done my homework, he looked at my sizing and agreed. But then he understood that I knew my system might struggle to reach setpoint on the occassional -0F or +110F day. Implicit in his agreement was that I take the risk for undersizng.

BTW, I didn't hold it against him for wanting to oversize. He's experienced and knows his installations, but he also knows that expectations matter, so the "safe" approach is to avoid any possibility of the system not reaching setpoint on those extreme days, however infrequent they might be. I can understand that point of view.

His recommendation: 100000 BTUH, 3.5-ton
What's really going in: 80000 BTUH, 2.5-ton
(the 80000 is already in, and is probably slightly oversized)

[joeselectric]

I am understanding this better. The cotractors are almost in a no win situation in many cases. If they properly size then you have those extremes when it doesn't reach setpoint. Oversize and maybe all of those typical problems show up. I also learned just in time and have the proper size for my climate and load. Good idea for the contractor to have the homeowner sign that he knows the capabilities of the system.

[bmathews]

I have not had a homeowner that is satisfied unless that thermostat setpoint is reached on a 100 degree day with high humidity. Most contractors still oversize slightly for just this reason. Nothing more irritating than ripping out a system because it wont get below 78 on a 100 degree day. Hopefully, in the future, you will see more and more 2 stage equipment installed, this helps greatly.

Bingo. Give this man a prize. This is exactly why they are oversized. I have a lot of customers that live in very high end homes. $2 million +. As many have told me that they don't give a squat about manual J or how much energy they use or whatever else I want to tell them. All they want is for the thermostat to reach whatever temp they want when they want it. I have one customer right now that wants his house 65ish or less no matter what the temp is. If we can't do it. Rip the equipment out and give him his money back. If we have a problem giving him his money back, around $50K, he'll sue us.

[Roadhouse]

This is a good topic as I myself, never having done a heat load for a system size, have often wondered how two experienced professionals using the exact same man j or software for the exact same home in the exact same location will come to two entirely different system sizes and yes, I have asked on here if this is the case and the pro's themselves have said that yes, more common than not for this to ocur.

My guess is the educated guess' are not so educated after all, too many variables and what one person sees and thus makes an educated guess on conflicts with how another sees it and makes his educated guess with.

Need more scientific fact based entries and not these educated guess', IMO.

I hope something of concrete comes about sooner rather than latter because I will feel so bad if I get it wrong come my time to do so and I am not impressed with the fact that a Man J is so if-sh in result nor do I stand by it whole heartedly from what I understand of it and judging by what I have read of everyone's contradicting stories concerning system size.

Luckily I just installs so I'm not too conflicted as I am more worried about getting it right in the event I need to perform a home analysis.

[garya505]

I am understanding this better. The cotractors are almost in a no win situation in many cases. If they properly size then you have those extremes when it doesn't reach setpoint. Oversize and maybe all of those typical problems show up. I also learned just in time and have the proper size for my climate and load. Good idea for the contractor to have the homeowner sign that he knows the capabilities of the system.

You got it, man!

That's why I got a guy who was good at installation and let me take the responsibility (and risk) for sizing. However, that's not a viable solution to the problem. Very few homeowners are obsessed with proper HVAC sizing like I am. :gah:

[Lambo]

I am new to the forum, but have a few things to add on this subject. If a contractor’s design engineer performs a true "Manual-J" load calculation, then the new tighter construction and higher insulation values of modern building products would be accounted for. There are also geographic considerations to take into account. Any given region has a historically based set of design temperatures to go with it. At some point during the extremes of the winter or summer, you are going to exceed these design parameters. You can't account for everything, or you will be over sizing. It's hard to drive this one home with homeowners. Just like trying to convince them that refrigerant doesn’t get consumed or that the system doesn’t work faster if you bury the needle on the thermostat.

[Southern Mech]

another thing I may add is we are held by state and local code to abide by man J calcs. Therefore that design criteria is what stands. in my neck of the woods it's 78 inside and worst case 93 out, as long as my sysem does that, I am right, the owner may not be happy but that is the law and I met it. Every contractor has the oportunity to sit down with the owner and discuss real live design realities. As long as the owner and contractor have a written and signed document, you can alter the design criteria.

[Roadhouse]

Georgaphical location is just a small piece of the pie. Here is one of four videos on heat load calculations given by The Indian Institute for Technology.

Solar radiation and the angles of solar radiation and what not and if you can stand the accent, it's in English but Indian instructor so heavy accent, these guys know a lot, highly intelligent and scientific, and break it down.

Energy transfer to and from, inside and out, tilt of the earth's axis and that's just the sugar that makes the icing on the cake.

These full and complete lecture vids are all on youtube, btw. I found them when I was hunting for info on heat loads a few months ago and IMO, well worth a watch.

http://www.youtube.com/watch?v=Dj8ATzgrxyA&playnext=1&list=PLB7EC2253F814ACB9&index=23

[joeselectric]

Whew! Wow this is as deep as it is wide! I thank each and every one of you for taking the time. Bmathews, your scenario would be even more chalenging. I can't imagine trying to cover every aspect of their expectations. There is so much at stake with your reputations for future referrals. You could get a bad rap even when you did everything right. Last summer we had a terrible hot spell and humid as all get out. My inside temp was a couple degrees warmer than set temp...BUT my humidity was running between 38-40%. I called and left a message on his machine... thanking him for a job well done. I'll bet he worked his butt off that day. I have him check my A/C every spring, he's never had to do anything since the install but screw the caps back on.
joe

[garya505]

another thing I may add is we are held by state and local code to abide by man J calcs. Therefore that design criteria is what stands. in my neck of the woods it's 78 inside and worst case 93 out, as long as my sysem does that, I am right, the owner may not be happy but that is the law and I met it. Every contractor has the oportunity to sit down with the owner and discuss real live design realities. As long as the owner and contractor have a written and signed document, you can alter the design criteria.

I like that approach. Are Manual J calcs required for both new construction and existing? Seems doign this for existing structures could be problematic due to some parameter estimates that are required.

[Airmechanical]

Well, my name "is" Robin:CU:

Just to make something clear; I do not promote to "undersize" systems. I promote to properly size systems .

from robo this morning!

.

[carolincarolina]

I'm a homeowner and from my perspective......
There are a lot more issues to be dealt with other than the state codes when dealing with customer satisfaction. Price, service, reliability, and clarity matter to people and each one carries different weight with each person.

I am in the process of getting a a new system installed and I can tell you it has been a roller coaster ride. I am sure I am a contractor's nightmare because if it doesn't seem right o me I'll ask question until everything is clarified and I cannot trust someone who cannot explain things to me. I also don't want anyone getting over on me. We just fired our contractor after I learned somethings on this site and I found out that our installer was not really a Goodman rep but was ordering our system from a website called acwholesalers. I don't know anything about them but when the guy kept saying that the units were in the "warehouse" I trusted him until I saw his help drop my contract and it had a shipping notice fromt that website. When I asked him he said that was where the units were shipped from and I thought there was something fishy. The other thing I did't like was the service contract the guy was trying to sell us and why the guy could never explain to me why he needed to put in a 3.5 ton system to replace our 3 ton system. I'm not dumb just explain to me why. These guys also never produced my manual J calculation. If I know what it is and they didn't know what it was or wouldn't do it that made me think that they were not worth it.

So once again I will be searching the Triad area for someone to do it and do it right.

[Southern Mech]

Caroline all your issues are good point's, I wouldn't get wrapped up in the where he get's the equipment from though, not everybody stocks or can afford to stock a warehouse, the manufacture does not do this for you it's the company that pay's upfront and hopes to sell.

[garya505]

My wife says equipment sizing is a big problem. She said, "I think bigger is better".

Funny, I didn't think she knew anything about HVAC. :confused:

[Southern Mech]

My wife says equipment sizing is a big problem. She said, "I think bigger is better".

Funny, I didn't think she knew anything about HVAC. :confused:

Funny LOL

but bigger is not better in the HVAC industry, and I do know the above was ajoke about your ''unit'' size.

[George2]

Caroline all your issues are good point's, I wouldn't get wrapped up in the where he get's the equipment from though, not everybody stocks or can afford to stock a warehouse, the manufacture does not do this for you it's the company that pay's upfront and hopes to sell.

I agree that most do not "stock" the equipment, but that does not mean you should lie to the homeowner.

There are to many "white lies" that go unchecked.

[Gimmered]

Bingo. Give this man a prize. This is exactly why they are oversized. I have a lot of customers that live in very high end homes. $2 million +. As many have told me that they don't give a squat about manual J or how much energy they use or whatever else I want to tell them. All they want is for the thermostat to reach whatever temp they want when they want it. I have one customer right now that wants his house 65ish or less no matter what the temp is. If we can't do it. Rip the equipment out and give him his money back. If we have a problem giving him his money back, around $50K, he'll sue us.

My house isn't anywhere near that 2 million dollar mark and I must say I expect my system to handle all the extremes. Where I live I get to enjoy the best of both worlds. I can enjoy 100-110° in the summer and -15° to -20° in the winter.

[commerce48]

I have wondered why oversizing is so common and have come to some conclusions.

1. Contractors don't want to leave any chance of undersizing, as this almost guarantees a tear-out and replacement at the contractor's expense. In new construction, they just seem to put in whatever they have in stock, as long as it's big enough. If it's not new construction, there is some guesswork in a load calculation, so it's "safer" for the contractor to error on the large size.


If there was a larger incremental cost to different sizes of residential gas furnaces, that might give a contractor some pause about oversizing. For the most part, cost difference between sizes is irrelevant to decision making. AC sizing costs are very different of course.

[commerce48]

Very few homeowners are obsessed with proper HVAC sizing like I am. :gah:

You are not alone, young Luke. The force is with you.

[garya505]

You are not alone young Luke. The force is with you.

My psychiatrist says there's a good chance that the obesssion will go into remission once my new system is totally installed and running.

[hvac_two]

Good question. Most of this falls on three parties and really is not the equipment manufacturers obligation.

Consumer: I know this may suprise you but I have my reasons. Consumer's on average do very little research on what they are getting into. So many times they fall prey to catchy sales schemes introduced by an ever increasing base of crooked contractors. There are so many tools made available to the consumer. Here in Virginia they can visit the DPOR website and search the contractor and its employees for license info and complaints. Do not waste your time with the BBB, Angie's List, etc.
Contractor: Contractors, in my opinion, have a moral obligation to be totally upfront with the consumer. It has become a bad trend in the recent years for contractors to get sketchy with their business practices. In addition , contractors need to make sure their sales folk have prior field experience...a tradesmen license would be great as well. Some sales folk intentionally oversell...b/c the company makes more money on a larger system .
State: States, including VA, need to do a better job of making the consumer aware of all the tools that are available to the consumer at no cost. These tools are much more powerfull to the consumer than those offered by the likes of BBB or other contractor reporting services b/c there is no benefit to the contractor by paying extra to be accredited, and the State can revoke licenses as well...Tends to get the contractors attention.



~~There are great contractors out there...You just have to look a little to find them. A good HVAC contractor will not oversize a system. AND...You will not have what looks like a spider of flex duct in your attic or crawl.

You can find more info on contractors and other topics at Link removed by Admin

[hvac_two]

Anyone know what is the cause for posts disappearing from a thread??

[k-fridge]

Anyone know what is the cause for posts disappearing from a thread??
It's under review because of the link you posted. We'll be in touch after the mods discuss it.

[hvac_two]

Thanks for the update. I have posted that link in other posts as well and this is the first to be reviewed....by the way that link is for a blog where I post and sometimes I may have already posted something regarding a similiar topic here.

Been a member here for a long while. Thanks.

[jerrod6]

another thing I may add is we are held by state and local code to abide by man J calcs. Therefore that design criteria is what stands. in my neck of the woods it's 78 inside and worst case 93 out, as long as my sysem does that, I am right, the owner may not be happy but that is the law and I met it. Every contractor has the oportunity to sit down with the owner and discuss real live design realities. As long as the owner and contractor have a written and signed document, you can alter the design criteria.

I am glad I don't live within your code range. If I choose to have 78F inside during the summer and 65F in the winter fine, but I don't want an entity that is not going to live with me and has no clue about possible medical issues, to tell me what temperature I have to keep my house.

[jimj]

I am glad I don't live within your code range. If I choose to have 78F inside during the summer and 65F in the winter fine, but I don't want an entity that is not going to live with me and has no clue about possible medical issues, to tell me what temperature I have to keep my house.


Just so you know manual J calls for 70* winter 75* summer, but goes on to say that if other temps are needed or wanted for medical or personal preference they can be changed.

[commerce48]

My psychiatrist says there's a good chance that the obesssion will go into remission once my new system is totally installed and running.

Do you think that could be a valid generalization, or applies just to your particular case? I'm hoping the former, because after my install is polished off tomorrow, I could use a break! Too much research, thought, and lurking.

I have to say I'm pretty darned please with my new tankless and furnace so far. I think I will have to post pictures because to my untrained eye, it just looks great! I'd like to finish the basement just to be able to spend more time with my new install. I got really lucky with a company with a great culture. One of the techs whipped out a pocket level putting the thermostat in and I asked him if that was his idea, or the company's. He said the company! Color me very impressed, and I'm about as fussy as they get.

[thorton]

I believe that most cooling and especially heating systems are over sized because it's the safe thing to do. In new construction the contractors have no way of knowing what people's expectations are of the heating and cooling system. People who use steep set backs in heating want a heating system that will heat the house back to set point fairly quickly. Same with cooling systems. A lot of people set back during the day when at work and then want the house cooled down as quickly as possible when they arrive home. Systems that are properly sized have trouble accomplishing these things. In a retro fit, it is a bit easier to determine what ho's expect from their heating and cooling systems. I even had a refrigeration mechanic tell me that he wants his own over sized because "when he wants his house cool, he wants the capacity to do so in a hurry." Adding to this he said I don't my cooling system running for hours to slowly bring down the temperature. So a person has to determine what exactly they want their heating and cooling system to do for them.

thorton
___________________________
In fact, air at –0.4 F contains about 85 percent of the heat it contained at 70 F

[Dad]

Anyone know what is the cause for posts disappearing from a thread??

You need to join the pro membership before you can advertise your company. You may not at anytime post a link to another HVAC Blog website.

This is why you received a 10 point infraction "warning" from me this morning as this was not the first time you posted your web blog. If you post it again the warning becomes a real time ticket and you will receive time off.


Thx

[cmanbrazil]

I personally am not happy with the information available to consumers from the hvac industry. Something is amiss, and even consumer reports has little to offer consumers. I have been very frustrated by the whole process. Everything else I buy I can find reviews, or have it evaluated, etc.
If it wasn't for this website, I would be totally in the dark, and while the info here is good, you still can't get detailed professional or consumer reviews of specific products.

And this whole issue of its not the manufacturer but the quality of the install is really confusing because few contractors offer the type of system analysis professionals on here recommend. I had an authorize dealer install my furnace and I knew more about what the particular furnace was supposed to do than the installer. He didn't know anything about the cycles per hour, what york recommended regarding the install on its site, etc.

I am disappointed in the industry in general. I am also disappointed in consumers, and consumer review sites for not sharing more info on the topic. That is why I am going to share in as many places as possible about my reflections on the york mod I bought.

I do thank the professionals and consumers on this site for being so thorough and passionate about hvac. If any professional on here is in Columbus Ohio, please let me know.

Lusker, is that too much info? Its like the parent showing up to school and spanking the child in front of the class. I understand communicating what is allowed and not allowed, but learning what infraction someone received and future warnings is a little much.

[Dad]

Lusker, is that too much info? Its like the parent showing up to school and spanking the child in front of the class. I understand communicating what is allowed and not allowed, but learning what infraction someone received and future warnings is a little much.

I gave him the same respect as he showed this forum. This is not his first venture outside the rules. He knows better than to put a link on our site to another HVAC Blog. As per the rules, if I were to follow them to the letter, he would be banned. I gave him a warning and a public slap on the hand. Seems fair to me.

[OSURanger]

Long time lurker. Sizing is indeed the achillies heel of our industry. This post talked about the issues of both over and undersizing. While someone posted that 2 step machines would help, I'd argue that is not what they are designed for. 2 stage units are designed for comfort, dehumidification, and energy savings--not to make up for an improperly sized unit. This is partially due to efficiency in the lower stage generally not as high as the high stage.

The coming or return of variable speed compressors may help sizing. They are as efficient in part load as they are in full load. If configured properly, they can match the output to the building load, including turbo mode for extra capacity. Of course these units will be expensive, but the sensitivity to sizing (on top of comfort and energy efficiency) will be one of their advantages.

[cmanbrazil]

I gave him the same respect as he showed this forum. This is not his first venture outside the rules. He knows better than to put a link on our site to another HVAC Blog. As per the rules, if I were to follow them to the letter, he would be banned. I gave him a warning and a public slap on the hand. Seems fair to me.

got it. Thanks for the additional explanation

[hvac_two]

I gave him the same respect as he showed this forum. This is not his first venture outside the rules. He knows better than to put a link on our site to another HVAC Blog. As per the rules, if I were to follow them to the letter, he would be banned. I gave him a warning and a public slap on the hand. Seems fair to me. __________________
I have been a member here for several years and this was a first. Lusker I can respect your decisions so next time the private message will suffice and really doesn't need the extra kick in the pants.

I was merely answering what I thought was a good question by a consumer and decided to add a link to a blog where I post. The post contains some reviews and such.

If posting a link to an informational blog, THAT IS NOT MY COMPANY, is bad than perhaps I need to rethink my membership here.

[Southern Mech]

I am glad I don't live within your code range. If I choose to have 78F inside during the summer and 65F in the winter fine, but I don't want an entity that is not going to live with me and has no clue about possible medical issues, to tell me what temperature I have to keep my house.


Understood, and most good system designers don't do that but,

that is the minimum required by code, it also states as long as I can keep less than 4 degree differance between rooms is ok. This is just minimum, requirements for a contractor to keep, now a good system designer would crap all over himself to be that slack.

Just something to think about when you see these low budget low income homes that go up by the hundreds, They are designing these to that minimum, so when you go buy that cheap house you can understand why.

[Dad]

__________________
I have been a member here for several years and this was a first. Lusker I can respect your decisions so next time the private message will suffice and really doesn't need the extra kick in the pants.

I was merely answering what I thought was a good question by a consumer and decided to add a link to a blog where I post. The post contains some reviews and such.

If posting a link to an informational blog, THAT IS NOT MY COMPANY, is bad than perhaps I need to rethink my membership here.

Posting links to other HVAC blogs has always been against the rules yet you say you've been here a long time, so, you should have known. Doesn't matter if the other site belongs to you or not. Your XMas greetings post clearly named your company as well. As stated, you should become Pro to post your info and you will be allowed to advertise your company as well.

Until you become a Pro Member you do not have access to the private message system here.

You may "rethink" your membership here as needed but you will find that there will be more of an open door policy around this site. (as seen in the private Pro Areas) If you muck up you will be told where all can see. The "behind closed doors" scenario hasn't worked in the past without dozens of emails back and forth. I can see new members not reading the rules but someone that has been here for a long time? Well... no excuse.

Now, If you want to banter back and forth so be it. If you want to complain about your hand slap, OK. I have no issue with that but... the more you complain the more you make this public. I suggested you become a Pro Member (several times now) so if you are wanting to be helpful to new members here you should see what this site is really about.

[hvac_two]

Posting links to other HVAC blogs has always been against the rules yet you say you've been here a long time, so, you should have known. Doesn't matter if the other site belongs to you or not. Your XMas greetings post clearly named your company as well. As stated, you should become Pro to post your info and you will be allowed to advertise your company as well.

Until you become a Pro Member you do not have access to the private message system here.

You may "rethink" your membership here as needed but you will find that there will be more of an open door policy around this site. (as seen in the private Pro Areas) If you muck up you will be told where all can see. The "behind closed doors" scenario hasn't worked in the past without dozens of emails back and forth. I can see new members not reading the rules but someone that has been here for a long time? Well... no excuse.

Now, If you want to banter back and forth so be it. If you want to complain about your hand slap, OK. I have no issue with that but... the more you complain the more you make this public. I suggested you become a Pro Member (several times now) so if you are wanting to be helpful to new members here you should see what this site is really about.

Lusker,

Look, I totally respect your decision whether or not I agree...so this will be my last post regarding this particular issue. I like HVAC-TALK and have recommended this site. There will be no further banter back and forth on this as this site has rules and if I did not fall within them so be it...and the rules have to be enforced or else what good are rules right.

In regards to professional membership...I thought about it but the minimium posts might be a problem as I tend to disapear when I get super busy. It would be nice to have PM access so this does have to mess up someone's thread. Lastly....the service company I work for was posted in a Merry Christmas thread thanking our customers.

Anyways...you are just doing your job Lusker so keep on getting it.

As to my response to why oversizing systems is such an ongoing problem Lusker reposted it, I believe, earlier for members to read.

[Airmechanical]

While someone posted that 2 step machines would help

I'd argue that is not what they are designed for

2 stage units are designed for comfort, dehumidification, and energy savings

not to make up for an improperly sized unit

i see you joined up this month, welcome

now, can you translate your point!


.

[OSURanger]

i see you joined up this month, welcome

now, can you translate your point!


.

I will try.

The primary benefit of two stage units is longer run times in the low stage, to give better comfort and to dehumidify. This is done with a low stage with less capacity than the primary. That low stage is better suited to provide cooling in moderate days, during summer nights, etc. when the load is far below the design conditions. The power consumed in the low stage is less than the high stage, which leads to some energy efficinecy and savings.

Most two stage units use the Copeland stepped capacity compressor, which gives 100% capacity in the primary stage, and about70% capacity in the low stage.

So, let's say a manual J calls for a 2.5T. Most HVAC manufacturers do not have two stage units in 1/2 tonnages. So you up size to a 3T, which can run at full stage and give 3T, and at low stage and give a bit more than 2T. The issue is that this split is not big enough to overcome the oversizing. 2T is not 'small' enough relative to the 2.5T building requirement, so you wont get long enough run times in the low stage to get the full comfort and dehumidification benefits that a two stage system is meant to offer. So, the two stage unit does in some ways cover up the oversizing, it doesnt give the comfort or energy savings benefit the consumer would expect-->Unhappy customer.

The difference with a fully variable speed compressor is that it is not bound by discrete steps. It is infinitely variable. It is rated at 100%. It likely can give some turbo capacity on really hot days (maybe up to 120%), and can slow down to about 30% of rated capacity. And, it is very efficient at all of those points.

So back to the prior example. A 3T variable speed system is installed, when the building really needed a 2.5T. On rating days, it will run at 83% and deliver 2.5T. On hotter days, it can run faster than that and meet the load. On moderate days, it can slow down to about 30%. This allows the system to slow down on moderate days, still give the long run times to give dehumdification and comfort. While not as efficient as a properly sized 2.5T variable speed system, the 3T system has enough turn down that the homeowner would likely never know the difference if the system is installed and set up properly because the variable speed system can slow down to match the load and it has infinite steps, not 2.

So, while a 2 stage HVAC will cover up some degree of oversizing, it cannot then deliver the same comfort benefit. A variable speed compressor can still give comfort while covering up some degree of oversizing because it has more steps.

We just need Trane to bring back the XV1500, or for Carrier to introduce their variable speed system. Or turn to mini/multi splits who already have the variable speed compressor technology.

Airmechanical--does that make sense?

[garya505]

Do you think that could be a valid generalization, or applies just to your particular case? I'm hoping the former, because after my install is polished off tomorrow, I could use a break! Too much research, thought, and lurking.

I have to say I'm pretty darned please with my new tankless and furnace so far. I think I will have to post pictures because to my untrained eye, it just looks great! I'd like to finish the basement just to be able to spend more time with my new install. I got really lucky with a company with a great culture. One of the techs whipped out a pocket level putting the thermostat in and I asked him if that was his idea, or the company's. He said the company! Color me very impressed, and I'm about as fussy as they get.

Coincidently, the rest of my stuff is also going in today.

[Airmechanical]

I will try, The primary benefit of two stage units is longer run times in the low stage, to give better comfort and to dehumidify This is done with a low stage with less capacity than the primary That low stage is better suited to provide cooling in moderate days, during summer nights, etc. when the load is far below the design conditions. The power consumed in the low stage is less than the high stage, which leads to some energy efficinecy and savings
ok.

Most two stage units use the Copeland stepped capacity compressor, which gives 100% capacity in the primary stage, and about70% capacity in the low stage.
this is incorrect, we can discuss that later

So, let's say a manual J calls for a 2.5T. Most HVAC manufacturers do not have two stage units in 1/2 tonnages
none of them do

So you up size to a 3T, which can run at full stage and give 3T, and at low stage and give a bit more than 2T. The issue is that this split is not big enough to overcome the oversizing. 2T is not 'small' enough relative to the 2.5T building requirement, so you wont get long enough run times in the low stage to get the full comfort and dehumidification benefits that a two stage system is meant to offer
yes you would, if you knew about dehumidification on demand you would understand, we can discuss that later as well

So, the two stage unit does in some ways cover up the oversizing
that's not what it's used for

it doesnt give the comfort or energy savings benefit the consumer would expect-->Unhappy customer.
when the incorrect 2 speed system is selected, there will be unhappy customers

The difference with a fully variable speed compressor is that it is not bound by discrete steps. It is infinitely variable. It is rated at 100%. It likely can give some turbo capacity on really hot days (maybe up to 120%), and can slow down to about 30% of rated capacity. And, it is very efficient at all of those points.
i have actually repaired those Trane XV's years ago, so what was your point?

So back to the prior example. A 3T variable speed system is installed, when the building really needed a 2.5T. On rating days, it will run at 83% and deliver 2.5T. On hotter days, it can run faster than that and meet the load. On moderate days, it can slow down to about 30%. This allows the system to slow down on moderate days, still give the long run times to give dehumdification and comfort. While not as efficient as a properly sized 2.5T variable speed system, the 3T system has enough turn down that the homeowner would likely never know the difference if the system is installed and set up properly because the variable speed system can slow down to match the load and it has infinite steps, not 2.
ummm and?

So, while a 2 stage HVAC will cover up some degree of oversizing, it cannot then deliver the same comfort benefit. A variable speed compressor can still give comfort while covering up some degree of oversizing because it has more steps.
yes i agree, now whoever said that a true varible system was not the best?

We just need Trane to bring back the XV1500
i still have the special green repair brochure put out by Trane to repair those things
i agree bring them back

or for Carrier to introduce their variable speed system. Or turn to mini/multi splits who already have the variable speed compressor technology Airmechanical--does that make sense?

it makes sense that you wish they brought back the XV

i do too but was there any other point?



.



.

[Southern Mech]

The XV system was the deal, gotta wonder why Trane never grew on that, other then they were an arm and a leg, but 2 stage and dual compressors aren't much cheaper compared to today.

The only thing I don't like about 2 stage, dual comp, or variable speed compressors is in heat mode. When I want heat I want it now, not to sit there and run churn and dry out a house.

[teddy bear]

Contractors are expected to provide specific temperatures and %RH with loads that vary from only sensible to only latent or any varible load extreme mix inbetween. We use sizing charts that calculate the extreme sensible and extreme latent loads in homes varible occupancy and imperfect structural quality. We do our best to provide a specific size of equipment to do the job. Some of us are bold enough to state that we will meet the occupants expectations without even getting a written description of the expectations.
In reality, most systems installed today are unable to handle the extremes. Handling high sensible cooling loads is large enough equipment, properly installed. High sensible and latent is usually properly insulated ducts with right amount of air flow to remove enough latent. As the sensible cooling declines while the latent load remains high is where the fun starts. At some point there is not enough sensible cooling load for typical a/cs to remove enough latent to provide low %RH.
This is especially true high all latent cooling with high occupancy and adequate fresh air ventilating.
As contractors, we need some explaination for the imperfect results. If question is raised with a system installed by someone else, we raise a question. Did they do a manual J? Clearly, the system is oversized or the home as excessive air leakage, really? If we did manual J, must be equipment adjustment or improper use. Like, you setting the t-stat up when are not in the home? Fortunately, after retraining the occupant or readjusting the equipment, and(or) the weather returning to more normal conditions, life goes on.
As an industry, we are now over-cooling/dehumidistat, air tightening homes/ducts and using varible speed equipment to fix this problem. Occasionally we install a/c reheat or whole house dehumidifiers as a fix.
Fortunately, these low/no sensible/high latent conditions are not often long lasting. If we had a months of this condition in green grass climates, we would agree that reheat or whole house dehumidifiers are the only solution to mainting 70-78^F, <50%RH with high occupancy and adequate fresh air ventilation.
We fix many houses every year with the good installs and good equipment by providing a method of removing latent load without over-cooling the home. Even a small whole house dehu helps alot.
Thanks for allowing me to input 2 cent, maybe more.
This is like doing a burn-out on the town square with police watching. No brands mentioned.
Regards TB

[Roadhouse]

I personally am not happy with the information available to consumers from the hvac industry. Something is amiss, and even consumer reports has little to offer consumers. I have been very frustrated by the whole process. Everything else I buy I can find reviews, or have it evaluated, etc.
If it wasn't for this website, I would be totally in the dark, and while the info here is good, you still can't get detailed professional or consumer reviews of specific products.

And this whole issue of its not the manufacturer but the quality of the install is really confusing because few contractors offer the type of system analysis professionals on here recommend. I had an authorize dealer install my furnace and I knew more about what the particular furnace was supposed to do than the installer. He didn't know anything about the cycles per hour, what york recommended regarding the install on its site, etc.

I am disappointed in the industry in general. I am also disappointed in consumers, and consumer review sites for not sharing more info on the topic. That is why I am going to share in as many places as possible about my reflections on the york mod I bought.

I do thank the professionals and consumers on this site for being so thorough and passionate about hvac. If any professional on here is in Columbus Ohio, please let me know.

Lusker, is that too much info? Its like the parent showing up to school and spanking the child in front of the class. I understand communicating what is allowed and not allowed, but learning what infraction someone received and future warnings is a little much.

The trades have masters and helpers, installers and techs. It takes a long time to be considered a master, a lifetime or two in many cases. Myself being an installer of 12 years can find out the info if needed such as cycle per hour and what not. My job is to install and get system running as I work my way up to tech. My boss who has been in this business for 30+ years will be the one talking to the customers for technical support and he's the one to answer those questions in my case. Most times I learn these answers on a job while talking inbetween my boss and the customer. Nothing wrong with that as most if not all hvacr work and learning is in the field in one way or another.

In other words, just because one person, the installer, doesn't know every technical aspect of a system at a company does not mean that the higher ups who have been around forever and a day also do not.

Just ask and let them find a way to find out for you, that's why they call it TEAMWORK.

[jimj]

The trades have masters and helpers, installers and techs. It takes a long time to be considered a master, a lifetime or two in many cases. Myself being an installer of 12 years can find out the info if needed such as cycle per hour and what not. My job is to install and get system running as I work my way up to tech. My boss who has been in this business for 30+ years will be the one talking to the customers for technical support and he's the one to answer those questions in my case. Most times I learn these answers on a job while talking inbetween my boss and the customer. Nothing wrong with that as most if not all hvacr work and learning is in the field in one way or another.

In other words, just because one person, the installer, doesn't know every technical aspect of a system at a company does not mean that the higher ups who have been around forever and a day also do not.

Just ask and let them find a way to find out for you, that's why they call it TEAMWORK.


Well said

[Airmechanical]

As an industry, we are now over-cooling/dehumidistat, air tightening homes/ducts and using varible speed equipment to fix this problem

agree with most of your post but,

dehumidification on demand

it's the ability of the system to slow the blower down to dehumidify

it can also be run to where it does not overcool to dehumidify

it's one of the benefits of the communicating systems

the IAQ t-stat can accomplish the same thing (slow down blower) and not overcool to dehumidify

of course this is all depends on there being a load

.

[cmanbrazil]

The trades have masters and helpers, installers and techs. It takes a long time to be considered a master, a lifetime or two in many cases. Myself being an installer of 12 years can find out the info if needed such as cycle per hour and what not. My job is to install and get system running as I work my way up to tech. My boss who has been in this business for 30+ years will be the one talking to the customers for technical support and he's the one to answer those questions in my case. Most times I learn these answers on a job while talking inbetween my boss and the customer. Nothing wrong with that as most if not all hvacr work and learning is in the field in one way or another.

In other words, just because one person, the installer, doesn't know every technical aspect of a system at a company does not mean that the higher ups who have been around forever and a day also do not.

Just ask and let them find a way to find out for you, that's why they call it TEAMWORK.

I hope so, and I am going to approach it with the company in the same spirit in which you wrote your post.

My mother went from a 120,000 system to a 70,000. I went from a 105,000 to an 80,000. Both of us could live with systems at least 10,000 btu less. Its a guess on my part, but when it gets to 9 here and I have the temp on 73 in my house, and it doesn't run on high most of the time and still cycles off I think my system is oversized. I would have never thought that an 80,000 btu furnace would be enough for a 2,200 sq ft home. Its a definite learning curve. However, look how long people go before buying another furnace. Imagine going twenty years before buying another car.

[jerryd_2008]

... Initially he wanted to put in larger equipment. After we talked a while, and he realized that I had done my homework, he looked at my sizing and agreed. But then he understood that I knew my system might struggle to reach setpoint on the occassional -0F or +110F day. Implicit in his agreement was that I take the risk for undersizng.

...

His recommendation: 100000 BTUH, 3.5-ton
What's really going in: 80000 BTUH, 2.5-ton
(the 80000 is already in, and is probably slightly oversized)

So what was your payback, Gary? More comfort? Possible longer equipment life (maybe taken on faith)? That you figured out after much work what he should have proposed in the first place (not many want to do as much work - about 2 years for you now, right)? Cheaper (hopefully, much cheaper)?

[jerryd_2008]

This is a good topic as I myself, never having done a heat load for a system size, have often wondered how two experienced professionals using the exact same man j or software for the exact same home in the exact same location will come to two entirely different system sizes and yes, I have asked on here if this is the case and the pro's themselves have said that yes, more common than not for this to ocur.

...

Need more scientific fact based entries and not these educated guess', IMO.

...

Sounds like an honest man. IMO and I am NOT a HVAC expert, there are at least 2 explanations for differing Manual J's. One - person doing it isn't trained and/or possibly does not understand the climate parameters at the given location. Two - person doing it isn't doing a good job or doesn't put in enough time to consider some important factors.

IMO, all of the factors that go into this calculation, both inside and outside, are not straight forward. After all, how many of us remember doing our chemistry experiments and how often did those come out as we expected. And that scenario was much more constrained and simple than a house and surroundings, no?

[jerryd_2008]

I'm a homeowner and from my perspective......

... The other thing I did't like was the service contract the guy was trying to sell us and why the guy could never explain to me why he needed to put in a 3.5 ton system to replace our 3 ton system. ..

I came up with the same question but before I had contractors in the house. Since I expected to move up from a single stage AC to 10 SEER at at least 13 SEER and preferably higher and also get a multi-stage unit (turned out to be a DFHP) and the current system was adequate, in writing I gave each contractor a spec that said very clearly that they were in no circumstances to propose a system that exceeded the capacity of the existing system. Period. No discussion.

[jerryd_2008]

I personally am not happy with the information available to consumers from the hvac industry. Something is amiss, and even consumer reports has little to offer consumers. I have been very frustrated by the whole process. Everything else I buy I can find reviews, or have it evaluated, etc.
If it wasn't for this website, I would be totally in the dark, and while the info here is good, you still can't get detailed professional or consumer reviews of specific products.

...

Brazil, one of the important differences between HVAC purchases and other consumer purchases, is that it is a custom install. Each location and most houses (unless 1 of a large number of the same model in a fairly generic location) are different, as well as the expectations and education of the buyer. Custom installs need a contractor that understands the parameters of both and puts in the work to get it right. That can be hard if you wait until 100 or -10 and call when your system fails.

PS: (Tried to add this to post below but it timed out on me) It seems that better fits would be possible if the manufacturer made their units more flexible like handling the 1/2 ton ranges that they don't provide. While this may be more expensive, it may be possible that if all units were made this way the extra flexibility would come at a very low cost to the buyer, and he would get a system that fits his house. (Don't ask me how to do this. I am neither an engineer nor a HVAC expert. Let the experts take the requirement and provide the solution.)

[Southern Mech]

Brazil, one of the important differences between HVAC purchases and other consumer purchases, is that it is a custom install. Each location and most houses (unless 1 of a large number of the same model in a fairly generic location) are different, as well as the expectations and education of the buyer. Custom installs need a contractor that understands the parameters of both and puts in the work to get it right. That can be hard if you wait until 100 or -10 and call when your system fails.

PS: (Tried to add this to post below but it timed out on me) It seems that better fits would be possible if the manufacturer made their units more flexible like handling the 1/2 ton ranges that they don't provide. While this may be more expensive, it may be possible that if all units were made this way the extra flexibility would come at a very low cost to the buyer, and he would get a system that fits his house. (Don't ask me how to do this. I am neither an engineer nor a HVAC expert. Let the experts take the requirement and provide the solution.)

Ummm, they do come in 1/2 ton increments 1.5,2,2.5,3,3.5,4,5 no 4.5 ton though.

[commerce48]

Coincidently, the rest of my stuff is also going in today.

Not so surprising considering that a huge tax credit is ending in just three days!

[garya505]

So what was your payback, Gary? More comfort? Possible longer equipment life (maybe taken on faith)? That you figured out after much work what he should have proposed in the first place (not many want to do as much work - about 2 years for you now, right)? Cheaper (hopefully, much cheaper)?

Well, if you're asking if it was worth the risk, I'd say yes. I didn't have any proposals for less than 90000 anyway.

[jerryd_2008]

Ummm, they do come in 1/2 ton increments 1.5,2,2.5,3,3.5,4,5 no 4.5 ton though.

My multi-stage York HP only comes in 2,3,4,5 tons with no in-between. I thought that this was not unusual.

[ubacool12]

Fortunately, I sell mostly 2 stage replacements, after the heat load is done, and I know everytime I do the customer will be satisfied.

[Southern Mech]

My multi-stage York HP only comes in 2,3,4,5 tons with no in-between. I thought that this was not unusual.

multi stage only comes in full ton size.

[just_opinion]

Hey Airmechanic,

I have some question to ask you to elaborate for us tech here to learn. Please detail as possible.

1) you said on post #53 that communicating sytem has the dehum on demand and "it can also be run to where it does not overcool to dehumidify". Please tell us its logics behind your statement. So we know how trane can dehum without overcool the house. I assume trane since I know you said you are trane man

2) On your post #48, you mentionaed about the XV15 - those old variable speed compressor. I call them DC comp. We have 2 of them in our small town and I served them both. Still DO one. The other one was dead few years back. Do you know that in the 90's there was no motor can vary with that compressor capacity. In those old day the ICM motor was those SQUARE BUTT. These compressor COULD at that time matched with those A/H with old ICM motor. These A/H only has 4 speeds - G, Y1, Y2, and W. There was NO board can give the signal to vary the speed of these motors. Thus, these DC compressor (XV15) were not a good application.

Today, we have variable speed motor ICM motor, that can be controlled at infinite speeds. And the compressor with infinite stage/capacity like digital scroll or those in old XV15. WE STILL cannot apply it to a house to get those infinite capacity to match those infinite loads.

Example: We cannot use the sytem that capables of reducing the capacity down to 10% to match the house load of 10%. Or 20%, 28%, 35%, etc..

Why not ? I already gave the answer.

[Airmechanical]

Hey Airmechanic,

I have some question to ask you to elaborate for us tech here to learn. Please detail as possible.

1) you said on post #53 that communicating sytem has the dehum on demand and "it can also be run to where it does not overcool to dehumidify". Please tell us its logics behind your statement. So we know how trane can dehum without overcool the house. I assume trane since I know you said you are trane man
they dehumidify by slowing the blower down, the parameters can be set to where dehumidification does not overcool at all!

2) On your post #48, you mentionaed about the XV15 - those old variable speed compressor. I call them DC comp. We have 2 of them in our small town and I served them both. Still DO one. The other one was dead few years back. Do you know that in the 90's there was no motor can vary with that compressor capacity. In those old day the ICM motor was those SQUARE BUTT. These compressor COULD at that time matched with those A/H with old ICM motor. These A/H only has 4 speeds - G, Y1, Y2, and W. There was NO board can give the signal to vary the speed of these motors. Thus, these DC compressor (XV15) were not a good application.
well your wrong, the xv's air handlers used true variable speed technolgy

Today, we have variable speed motor ICM motor, that can be controlled at infinite speeds. And the compressor with infinite stage/capacity like digital scroll or those in old XV15. WE STILL cannot apply it to a house to get those infinite capacity to match those infinite loads.
read above

Example: We cannot use the sytem that capables of reducing the capacity down to 10% to match the house load of 10%. Or 20%, 28%, 35%, etc..

Why not ? I already gave the answer.

if you really served the 2 xv's in your town, you would know that the air handlers are true variable speed

i have that special green pamphlet in front of my face right now for the xv's!

what else would you like to know about the xv

do you want to learn more, email me your number and i will attempt to teach you!

or ask your question here if it's not to technical for this forum



.

[jimj]

if you really served the 2 xv's in your town, you would know that the air handlers are true variable speed

.

:ditto::ditto::ditto::yes:

[just_opinion]

:ditto::ditto::ditto::yes:


if you really served the 2 xv's in your town, you would know that the air handlers are true variable speed

i have that special green pamphlet in front of my face right now for the xv's!

what else would you like to know about the xv

do you want to learn more, email me your number and i will attempt to teach you!

or ask your question here if it's not to technical for this forum



.


See how do you again. You must be great a playing dodgeball when you were young. Why don't you just tell everyone so we all learn. Why email and stuff and being so selfish. The whole world is waiting. Explain how the communicating system can dehum without over-colling the house.

And for you and Jimj -- those old trane A/H in the 90 was not a true variable speed a/h. Because it does not communicate with the stat via a speeding ramping signal or such. Those stat will send a analog signal to the O/D but through a control panel BUT it does not tell the a/h blower to ramp/run at certain speed to match the compressor load.

Today, it became true variable becasue we can control it speed infinitely. I.e. 200cfm, 250, 300, etc..

So both of you need to know that. Like I said, the a/h only has those signal to run according to 24 volt AC signals. Eventhough, the blower will ramp up/down base on air-load and or static. THERE WAS NO ANALOG SIGNAL TO RAMP UP/DOWN THE MOTOR IN THOSE OLD A/H in those system

Once again the blower did not vary with the compressor load. :ditto: :ditto: :ditto: jimj

[hvac_two]

See how do you again. You must be great a playing dodgeball when you were young. Why don't you just tell everyone so we all learn. Why email and stuff and being so selfish. The whole world is waiting. Eaplain how the communicating system can dehum without over-colling the house.

And for you and Jimj -- those old trane A/H in the 90 was not a true variable speed a/h. Because it does not communicate with the stat via a speeding ramping signal or such. Those stat will send a analog signal to the O/D but through a control panel BUT it does not tell the a/h blower to ramp/run at certain speed to match the compressor load.

So both of you need to know that. Like I said, the a/h only has those signal to run according to 24 volt AC signals. Eventhough, the blower will ramp up/down base on air-load and or static.

Once again the blower did not vary with the compressor load. :ditto: :ditto: :ditto: jimj

Can you feel the love tonight??

Can't we all just get along?

Trust me, I know what I'm doing.

How do you confuse a blonde? Put her in a circle room and tell her to find the corner.

Ease up fella's

[Airmechanical]

See how do you again. You must be great a playing dodgeball when you were young. Why don't you just tell everyone so we all learn. Why email and stuff and being so selfish. The whole world is waiting. Eaplain how the communicating system can dehum without over-colling the house.

And for you and Jimj -- those old trane A/H in the 90 was not a true variable speed a/h. Because it does not communicate with the stat via a speeding ramping signal or such. Those stat will send a analog signal to the O/D but through a control panel BUT it does not tell the a/h blower to ramp/run at certain speed to match the compressor load.

So both of you need to know that. Like I said, the a/h only has those signal to run according to 24 volt AC signals. Eventhough, the blower will ramp up/down base on air-load and or static.

Once again the blower did not vary with the compressor load. :ditto: :ditto: :ditto: jimj

do yourself a favor, QUIT GUESSING AND SQUABBLING GARBAGE and get the Trane publication 22-8058-2

that has all the information that you don't understand ABOUT THE XV SYSTEM WHICH DOES USE A TRUE VARIABLE SPEED AIR HANDLER

we don't mind your attitude, but when your wrong it looks rediculous

as far as the dehumidification on demand what part don't you understand on that

as stated above, it's not magic

THE DEHUMIDIFICATION MODE SLOWS DOWN THE VARIABLE SPEED MOTOR TO DEHUMIDIFY ON DEMAND, PARAMETERS CAN BE SET WHICH ELIMINATES OVERCOLING BY NOT LETTING THE SYSTEM DEHUMIDIFY UNDER THE COOLING SETPOINT


.

[hvac_two]

If you have lost your sense of smell and you have BO do you really have BO??

[just_opinion]

as far as the dehumidification on demand what part don't you understand on that

as stated above, it's not magic

THE DEHUMIDIFICATION MODE SLOWS DOWN THE VARIABLE SPEED MOTOR TO DEHUMIDIFY ON DEMAND, PARAMETERS CAN BE SET WHICH ELIMINATES OVERCOLING BY NOT LETTING THE SYSTEM DEHUMIDIFY UNDER THE COOLING SETPOINT


.

See how easy it is when you go straight to the point. That's all I ask.

Now, according to your aswer, WHAT IS SO GREAT ABOUT THAT ?

Or I can easily accomplish that SECIFIC task by using a mercury stat and a mechanical humidistat. Stat to run a/c and dehumidistat to break the Bk signal.

I want to know what is so great about that.
It stop removing humidity even though the humidity level is still high. What is so good about that.

Pint #2) On the old XV15 system, what signal control the blower ramping ? I mean the analog signal. once again I don't want email and don't tell me it's proprietary

[Airmechanical]

On the old XV15 system, what signal control the blower ramping ? I mean the analog signal

ICM-2 MOTOR CONTROL BOARD controls the indoor blowermotor on the XV

.

[RoBoTeq]

OK then! I see that airmaniacal has already trashed up this thread by tossing a bunch of crap on the wall to see if any of it would stink.....er....stick:whistle:.

Sizing of HVAC systems? Hmmmm. The down and dirty fact is that there is no pat formula for each and every application, even for dwellings that appear to be identical.

Manual J calculations are a very good base for properly sizing systems. The reason we don't upsize cooling systems any longer is because newer, higher efficient systems do not dehumidify as well as the older systems did, when installed as per manufacturer's guidelines. Therefore, we must be more cogniscent of dehumidification issues with new cooling systems.

Heating systems cannot be upsized the way they used to be because heating systems cannot take the heat....literally...that the older systems could. So, for the same amount of heat with a new system, we need a lot more air. When the ducting cannot handle the additional amount of air needed for today's heating systems, the equipment overheats and shuts down on limits.

For new construction, we should be doing "accurate" Manual J calculations with real numbers and not slightly "better" numbers, "just to make sure". If you plug in average low and high temperatures into Manual J, you can be comfortable increasing the equipment capacity to the next larger size for both heating and cooling. If you are plugging in extreme low and high temperatures, and there is more then 10k difference (for heating, 6k for cooling) between next larger capacity equipment, you should absolutely go to the next size lower capacity. Vice versa, if there is more then 10k difference (for heating, 6k for cooling) between the next lower capacity equipment, you might want to think about going to the next larger capacity equipment.

For existing homes, start with a Manual J calculation and then have an in depth discussion with the home owners about what their specific concerns and needs from an HVAC system are and how the existing system performs during extreme high and low temperatures.

If the load calc comes out to 1/2 ton less cooling and 40k less heating and the HO tells you that the system has no problem keeping up with the highest and the lowest outdoor temperatures and cycles off no matter how hot or cold it gets, then go by the load calc and do not reinstall oversized equipment. Let me repeat; new technology oversized equipment is NOT going to be forgiving the way the old technology oversized equipment was.

Now, get ready to have to read a bunch of goofy claims from airmaniacal:yes:

[Airmechanical]

yes

hey DoDobird

we had some good lessons to be learned by just opinion

don't scruff that part of this thread up with your rhetoric

you got all busted up in the pro section, what happened

gonna try here again

.

[seatonheating]

OK then! I see that airmaniacal has already trashed up this thread by tossing a bunch of crap on the wall to see if any of it would stink.....er....stick:whistle:.

Sizing of HVAC systems? Hmmmm. The down and dirty fact is that there is no pat formula for each and every application, even for dwellings that appear to be identical.

Manual J calculations are a very good base for properly sizing systems. The reason we don't upsize cooling systems any longer is because newer, higher efficient systems do not dehumidify as well as the older systems did, when installed as per manufacturer's guidelines. Therefore, we must be more cogniscent of dehumidification issues with new cooling systems.

Heating systems cannot be upsized the way they used to be because heating systems cannot take the heat....literally...that the older systems could. So, for the same amount of heat with a new system, we need a lot more air. When the ducting cannot handle the additional amount of air needed for today's heating systems, the equipment overheats and shuts down on limits.

For new construction, we should be doing "accurate" Manual J calculations with real numbers and not slightly "better" numbers, "just to make sure". If you plug in average low and high temperatures into Manual J, you can be comfortable increasing the equipment capacity to the next larger size for both heating and cooling. If you are plugging in extreme low and high temperatures, and there is more then 10k difference (for heating, 6k for cooling) between next larger capacity equipment, you should absolutely go to the next size lower capacity. Vice versa, if there is more then 10k difference (for heating, 6k for cooling) between the next lower capacity equipment, you might want to think about going to the next larger capacity equipment.

For existing homes, start with a Manual J calculation and then have an in depth discussion with the home owners about what their specific concerns and needs from an HVAC system are and how the existing system performs during extreme high and low temperatures.

If the load calc comes out to 1/2 ton less cooling and 40k less heating and the HO tells you that the system has no problem keeping up with the highest and the lowest outdoor temperatures and cycles off no matter how hot or cold it gets, then go by the load calc and do not reinstall oversized equipment. Let me repeat; new technology oversized equipment is NOT going to be forgiving the way the old technology oversized equipment was.

Now, get ready to have to read a bunch of goofy claims from airmaniacal:yes:


Good post Robo!! Those are my thoughts as well.

[just_opinion]

ICM-2 MOTOR CONTROL BOARD controls the indoor blowermotor on the XV

.

Like I said before. Those a/h had oroginal ICM motor. Those motor with square butt. It was not ICM-2. The ICM-2 was the first ROUND BUTT motor. I took the original ICM motor (square BUTT motor) out of the dead A/H and installed its in my G16 Lennox gas furnace. It is still running.

The a/h TWH739E (the leter E stand for ICM motor). And in that A/h the LVTB has R,B,T,Bk,g,y1,y2,w1,w2,w3.

Tell us which terminal that is used to vary the blower speed according to the compressor load ?? If you are so certain, then tell us what type of signal is that ? 24 volt AC, 0-10 volt dc, 4 -20 ma, etc..

[Airmechanical]

Tell us which terminal that is used to vary the blower speed according to the compressor load ?? If you are so certain, tell us what signal is that ?

motor speed is controlled by the drive output frequency

motor torque is controlled for specific requirments by varying drive output current

ok, knucklehead now what?

.

[just_opinion]

motor speed is controlled by the drive output frequency

motor torque is controlled for specific requirments by varying drive output current

ok, knucklehead now what?

.

Come on now. Stop calling name for it got you canned before. I am being nice and yearning to learn from the best acclaimed tech.

The questions were : what terminal ? What type signal ? Don't throw BS and name calling

[Airmechanical]

Come on now. Stop calling name for it got you canned before. I am being nice and yearning to learn from the best acclaimed tech.

The questions were : what terminal ? What type signal ? Don't throw BS and name calling

let's clarify something here, you are the one to have claimed/lied about working on the 2 XV's in your town

your on a mission to discredit yourself and you have asked me to help

since you insist on ruining your reputation, i can help if you must

i will do a little youtube video, with the book to repair the XV's

i will video the section of the book that shows the blower and diagnostic procedure

it may take until tommorow, but don't worry i will post a link to the video for you, where everyone can see you lied about working on them

then your lies becomes apparent to everyone

but as you wish

after this, you may want to post about stuff that you really do know about



.

[Airmechanical]

See how you get off track. It is the Bk signal. It is a PWM

so does this mean that you change your stance about the 2 xv's you lied about working on

obviously you looked at the publication i posted, to bad you did not know about it before you started your guessing!

.

[chuckcrj]

Take this:argue::argue:to the pub, children! I thought diy was against the rules!

[Stamas]

Just_, I don't care about your choices for personal hygiene and none one else here does either. Find another way to express your opinions.
This conversation shouldn't continue here, take it to Tech please.


AM, you got me going to the shelves for old manuals. Also need to check the Stat that I think I've got on the shelf for an XV.

[Airmechanical]

AM, you got me going to the shelves for old manuals. Also need to check the Stat that I think I've got on the shelf for an XV.

good, give an unbiased opinion when your done!


.

[hvac_two]

HEY!!!

I told you boys to settle down...lol

While you kids are arguing on how to deal with the customer's problem he/she is still cold and I don't think they care about how exactly the insulation fell off the Space Shuttle.....lol. JUST FIX IT already.

Gotta run...got a date with hvacpartner.

[RoBoTeq]

hey DoDobird

we had some good lessons to be learned by just opinion

don't scruff that part of this thread up with your rhetoric

you got all busted up in the pro section, what happened

gonna try here again

.
I have not been busted up anywhere and I am not the one being rhetorical.