Forums | Home Repair | Home Improvement | Painting | Interior Decorating | Remodeling | Landscaping


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-07-2011, 09:42 AM   #31
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Share |
Default

sizing choice on system upgrade


Yes, icicles and ice dams... we get those down here sometimes after a big snow dump followed by a long cold spell. My TH has cathedral ceilings and the insulation is OK but not up to those extreme situations. There are also a couple of square warm spots that melt where it looks like there may be no or little insulation. Can't get to it to inspect or correct the issue. The icicles can become a little scary. Got to look up and run to the car quickly! Luckily we don't see something like this every year... but every 5 years or so it happens.

Gotta love Bob and Doug, eh?

Quote:
Originally Posted by yuri View Post
NO JOKE. You can tell the poorly insulated houses by looking at the roof. If all the snow has melted and you see huge icicles hanging down then you know the guy has no attic insulation.

raylo32 is offline   Reply With Quote
Old 08-07-2011, 09:43 AM   #32
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,350
Default

sizing choice on system upgrade


It is not as easy as it sounds. In order to have a STABLE flame, proper ignition etc the burners have to be extremely well tuned so they cannot alter the firing rate too much w/o creating other problems. Then there is the problem of not enough temp rise and condensation in the primary heat exchanger and corrosion etc etc etc.

Bob and Doug and also the Trailer Park Boys are my heroes. Google both of them to find some hilarious You Tube vids.
Attached Images
 
__________________
"Cut it twice and it is still too short".
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by yuri; 08-07-2011 at 09:47 AM.
yuri is offline   Reply With Quote
Old 08-07-2011, 09:50 AM   #33
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


I am just talking about having it operate well within the firing rates/blower speeds it is capable of with the corresponding design blower speeds and temp rises. Just have some profiles that have different max firing rates for installs that might not need the full rated burn. Seems simple enough.

Quote:
Originally Posted by yuri View Post
It is not as easy as it sounds. In order to have a STABLE flame, proper ignition etc the burners have to be extremely well tuned so they cannot alter the firing rate too much w/o creating other problems. Then there is the problem of not enough temp rise and condensation in the primary heat exchanger and corrosion etc etc etc.

Bob and Doug and also the Trailer Park Boys are my heroes. Google both of them to find some hilarious You Tube vids.
raylo32 is offline   Reply With Quote
Old 08-07-2011, 09:55 AM   #34
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,350
Default

sizing choice on system upgrade


I agree but there would have to be a lot of $$ spent on research and testing to make sure it works well from Texas to Anchorage under a huge variety of temps etc and they don't want to do that yet. I worked with full blown Siemens bldg automation systems and chillers with VFDs etc and modulating high pressure steam boilers and know what can be done with controls.
__________________
"Cut it twice and it is still too short".
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
yuri is offline   Reply With Quote
Old 08-07-2011, 10:00 AM   #35
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 23,532
Default

sizing choice on system upgrade


Quote:
Originally Posted by raylo32 View Post
Just another thought on the whole sizing discussion... With the flexibility of the modulating systems I wonder why mfgs don't have adjustments to tweak the algorithms... like Beenthere and I were discussing the choice between 60k and 80 BTUH furnaces and I understand the importance of getting the correct size, esp with old "dumb" equipment. But since a mod furnace can run in a very wide BTUH range why not have a couple of selectable profiles that could fine tune the algorithm? Say you could choose an algorithm for an 80 K BTUH nominal unit to not go above 65K, 70K, or 75K BTUH, or whatever. Seems something like that could be easily accomplished in firmware and allow fewer sizes of furnaces to cover a wider range of applications. Less parts inventory, more fine tuned operation... all accomplished with a few changes in the firmware.
It would cost more in parts. The 80,000 would need to have 2 different boards, since it comes in 2 different blower sizes.

There are only 4 sizes of furnaces in the York Mod line. And i think all other brands that have a mod also only have 4 sizes.

Its best to just find out what size the house really needs, and use that size. Instead of trying to change the design of the unit.
beenthere is offline   Reply With Quote
Old 08-07-2011, 10:33 AM   #36
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


Exactly... we talk a lot about getting the "right size" equipment but it comes in 20K increments. That's a pretty big range but understandable from the mfgs perspective to not want to have too many models.

And if you have the capability to fine tune that further, to improve the match between furnace output and actual heat losses (that you will understand better in actual use than from any calculation) with simple firmware tweaks, why not build that in??

I guess I don't see that it would be that big a deal to have a few profiles built into the board and using them wouldn't be any more difficult to than the using the jumpers to match blower speed with A/C tonnage. If I was designing it I would try to work something like that in.


Quote:
Originally Posted by beenthere View Post
It would cost more in parts. The 80,000 would need to have 2 different boards, since it comes in 2 different blower sizes.

There are only 4 sizes of furnaces in the York Mod line. And i think all other brands that have a mod also only have 4 sizes.

Its best to just find out what size the house really needs, and use that size. Instead of trying to change the design of the unit.
raylo32 is offline   Reply With Quote
Old 08-07-2011, 10:35 AM   #37
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,350
Default

sizing choice on system upgrade


Quote:
Originally Posted by raylo32 View Post
Just another thought on the whole sizing discussion... With the flexibility of the modulating systems I wonder why mfgs don't have adjustments to tweak the algorithms... like Beenthere and I were discussing the choice between 60k and 80 BTUH furnaces and I understand the importance of getting the correct size, esp with old "dumb" equipment. But since a mod furnace can run in a very wide BTUH range why not have a couple of selectable profiles that could fine tune the algorithm? Most of the cowboy techs we have out there can barely understand a simple 2 stage furnace let alone a mod furnace. Have them try to understand what a "profile" is and they will go into "thought overload" and then they need to see a Doctor cause their head hurts.Say you could choose an algorithm for an 80 K BTUH nominal unit to not go above 65K, 70K, or 75K BTUH, or whatever. Seems something like that could be easily accomplished in firmware and allow fewer sizes of furnaces to cover a wider range of applications. Less parts inventory, more fine tuned operation... all accomplished with a few changes in the firmware.
.....
__________________
"Cut it twice and it is still too short".
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by yuri; 08-07-2011 at 10:46 AM.
yuri is offline   Reply With Quote
Old 08-07-2011, 10:49 AM   #38
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 23,532
Default

sizing choice on system upgrade


Quote:
Originally Posted by raylo32 View Post
Exactly... we talk a lot about getting the "right size" equipment but it comes in 20K increments. That's a pretty big range but understandable from the mfgs perspective to not want to have too many models.

And if you have the capability to fine tune that further, to improve the match between furnace output and actual heat losses (that you will understand better in actual use than from any calculation) with simple firmware tweaks, why not build that in??

I guess I don't see that it would be that big a deal to have a few profiles built into the board and using them wouldn't be any more difficult to than the using the jumpers to match blower speed with A/C tonnage. If I was designing it I would try to work something like that in.

Many home owners think all the manufacturer would have to do is "just" this and that.

If it was that easy, they would have done it already.

I can show you many VS blowers that weren't set up right, because the installers didn't know how to set the blower "profile" right.


Since no manufacturer is going to suddenly change how their furnace works for you this week, or this year. just do a load calc on your house to find out what size you need.

Then after its installed and working great. You can spend you time resigning the firmware for them.
beenthere is offline   Reply With Quote
Old 08-07-2011, 10:53 AM   #39
Hvac Pro
 
Join Date: Nov 2008
Location: Winnipeg, Canada
Posts: 8,350
Default

sizing choice on system upgrade


throw in another factor. VS blowers are not perfect and CANNOT compensate for undersized ductwork. They will seriously overspeed/hunt/cavitate if they have to run wide full out due to too much resistance. the newer ones can stop or slow down the motor when that happens but it still won't get you air where you want it. therefore the manufacturers cannot design a one size fitz all unit.
__________________
"Cut it twice and it is still too short".
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by yuri; 08-07-2011 at 12:40 PM.
yuri is offline   Reply With Quote
Old 08-07-2011, 11:09 AM   #40
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


I agree with you guys fully that there is no way to make a "one -size fits all" unit. But you are missing my point. I am not saying have radically different profiles. Keep the "profile" the same. All I am saying is have selector jumpers that limit the max output in the usual profile to the multiples of 5k in between the nominal max output down to the next smaller unit. Then when someone gets a load calc that says 67k they don't have to choose between 60 and 80. The 80 may be "close enough" but when you can do better, why not do better? Like get the 80 nominal max unit and and set the jumper for 65 which is well within the normal range of outputs when it modulates. Then if you later find in practice that you need 70 or 75, swap the jumper and there you go.

Anyway, I'd be surprised to not see something like this in the future. Actually, I am surprised to not see it now. The equipment can handle it. Seems crazy not to take advantage of the capabilities.

Quote:
Originally Posted by yuri View Post
throw in another factor. VS blowers are not perfect and CANNOT compensate for undersized ductwork. They will seriously overspeed/hunt/capitulate if they have to run wide full out due to too much resistance. the newer ones can stop or slow down the motor when that happens but it still won't get you air where you want it. therefore the manufacturers cannot design a one size fitz all unit.
raylo32 is offline   Reply With Quote
Old 08-21-2011, 01:11 PM   #41
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


Getting a little deeper into this... My current furnace Bryant Model HAD394 -042086, 87K input, 67K output, 1/3 HP PSC fan. Manual linked below.

According to the manual the system nominal CFM are: Cooling-1360 and heating-1170. I do not find my ducts to be objectionably loud. In fact they are very quiet in heat mode. So I am thinking that the 1279 for the 80K York units at high fire will really not be all that loud and fall in between my current heating and cooling flow noise. And any time spent at lower modulated levels will be much quieter. And during milder days I expect the unit might satisfy the call without ever getting into high fire.

Anyway, I am leaning towards the 80K after doing some load calcs (results vary a lot with assumptions, of course) and and seeing the specs for my current furnace and with my happiness with the existing sizing. Also your info that the 60k York mod unit moves only 960 CFM. That seems too litttle for my setup. In fact, the load calcs showed that heat loss approached the total 58K output under the worst conditions.

I think I have the venting nailed down. Lots of work to do on that before moving forward on the system.

http://www.xpedio.carrier.com/idc/gr...94had.50.3.pdf



Quote:
Originally Posted by beenthere View Post
Weather a 4 ton or 3 ton blower(1600 or 1200 CFM) makes no difference in heating mode. They will both run the same CFM in heating mode.

Doubt your current furnace is moving as much air as a 60,000 BTU 3 ton blower Mod will at high fire/heat.

A VS blower will speed up to move set CFM. Your current PSC blower can't do that. So an over sized mod can make your duct system very loud when it has to use its higher firing rates.

At 38,000 BTU output, a 80,000 BTU and a 60,000 BTU 95% mod will both be moving 640 CFM, if set to maintain a 55F temp rise.

At full input, the 60,000 will want to move 960 CFm for a 55 degree temp rise, and the 80,000 at full input will want to move 1,279 CFM to maintain a 55 degree temp rise.

Very good chance your current furnace is only moving between 1000 to 1100 CFM in high blower speed in cooling mode(maybe less).

many people have found out the hard way that their duct system is under sized, after they got a VS blower.

Last edited by raylo32; 08-21-2011 at 01:32 PM.
raylo32 is offline   Reply With Quote
Old 08-21-2011, 04:13 PM   #42
Member
 
Join Date: Nov 2008
Posts: 278
Default

sizing choice on system upgrade


Quote:
Originally Posted by raylo32 View Post
I know that. My OLD furnce is the old air sucker. The new one will save me from heating all that cold air infiltration.
I'm thinking you get a few static shocks during heating season. A direct vent (piped) furnace should eliminate virtually all of that stuff (assuming your house isn't a sieve).

V
veesubotee is offline   Reply With Quote
Old 08-21-2011, 04:29 PM   #43
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


That is surely one of the goals. House isn't a sieve but still gets pretty dry even though I have a good humidifier (Aprilaire 700 flow through). It runs 100% of the time the furnace runs and never has to cycle off due to reaching the humidity setpoint. With a direct vent furnace I certainly hope to do better.

Quote:
Originally Posted by veesubotee View Post
I'm thinking you get a few static shocks during heating season. A direct vent (piped) furnace should eliminate virtually all of that stuff (assuming your house isn't a sieve).

V
raylo32 is offline   Reply With Quote
Old 08-21-2011, 06:18 PM   #44
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 23,532
Default

sizing choice on system upgrade


Your old PSC blower is probably not moving as much air as you think. A VS blower speeds up to move its set CFM, a PSC motor can 't do that.

The 60,000 Would be the better choice. Its easier to seal a house a little more to make it require less heat, then it is to enlarge duct work to make it quiter.

Don't size for worse case conditions, that makes the furnace over sized too much.

The size of the house doesn't determine how many CFM are needed. The BTU loss and gain does that.
beenthere is offline   Reply With Quote
Old 08-21-2011, 06:36 PM   #45
Member
 
raylo32's Avatar
 
Join Date: Nov 2006
Location: Maryland (DC 'burbs)
Posts: 1,024
Default

sizing choice on system upgrade


Yes, the CFM numbers surprised me when I saw them in the Bryant manual. My Bryant blower motor is only 1/3 HP as compared to the York 1/2 HP in the 1.5-3 ton B cabinet models. So how exactly does it put out more CFM? Were the testing and rating standards different back in the early 1990s when these were made? Did they rate CFM based on essentially no backpressure?

The 60K York would be better in many ways... more run time which would also run the humidifier more. Might only be a little weak in zero degree conditions that don't happen that often. I will prob go with the 60K... worst case is that I have to upgrade it to the 80K if it proves to be inadequate.

I was headed that way (the 60K unit) until I saw the numbers in the Bryant manual. OK, I'll think about it some more... But I think the 60K will work. Of course, until I actually pull the trigger I may change my mind again. :-/

One thing York did that was smart was to make the furnaces compact (33" height) so that with the new taller high SEER evap coils the systems will fit into an existing installation without modifying the supply plenum. That will save a lot of work. I see alot of folks getting upgrades where the contractor sells them equipment that necessitates major plenum revisions. Totally unnecessary if you pick the right components.


Quote:
Originally Posted by beenthere View Post
Your old PSC blower is probably not moving as much air as you think. A VS blower speeds up to move its set CFM, a PSC motor can 't do that.

The 60,000 Would be the better choice. Its easier to seal a house a little more to make it require less heat, then it is to enlarge duct work to make it quiter.

Don't size for worse case conditions, that makes the furnace over sized too much.

The size of the house doesn't determine how many CFM are needed. The BTU loss and gain does that.

raylo32 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Permit For Fire Sprinklers letnes Plumbing 18 10-14-2010 05:23 PM
New HVAC System Recommendations shwank HVAC 14 10-12-2010 02:15 AM
Water Purification System - Maintenance Qs cjcocn Plumbing 1 11-18-2008 07:31 AM
Size A/C system properly 70stang HVAC 1 03-26-2006 07:22 PM
Replace furnace, coil and duct system sps123 HVAC 2 01-07-2006 10:56 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.