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 12-19-2009, 11:17 AM   #16
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000
Default

Manual J


Quote:
Originally Posted by Yoyizit View Post
Right sizing, or confirming Manual J
This won't work with a variable output furnace.

Toff = 65F, when you don't need heat.

Tper is the 97.5 percentile cold temp, depending on your area, when your furnace is running all the time.

The Slope = (Tper-65)/100

Tout = the average of 5 or 10 outside nighttime temps. Taking the average cancels out the effect of rain, snow, wind, clear weather, etc.

The furnace Duty Cycle in percent at Tout = 100(on time/(off time + on time)) = (Tout-Toff)/slope
Average this over a few cycles.

E.g.
Tper = 5F
so the slope is (5-65)/100 = -0.6

Tout = 29F
so the DC is 100(29-65)/(-0.6) = 60%
If your furnace has this duty cycle at this outside temp. it is right sized.
only works on boilers

__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 12-19-2009, 02:06 PM   #17
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,554
Rewards Points: 2,788
Default

Manual J


Quote:
Originally Posted by hvaclover View Post
Shill and conflict of interest!
He pays to advertise that program here.
beenthere is offline   Reply With Quote
Old 12-19-2009, 02:33 PM   #18
Member
 
tk03's Avatar
 
Join Date: Sep 2008
Location: PA
Posts: 167
Rewards Points: 150
Default

Manual J


Here is another place for the heat loss.
http://www.comfort-calc.net/home-page.html
tk03 is offline   Reply With Quote
Old 12-19-2009, 02:57 PM   #19
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

Manual J


Quote:
Originally Posted by hvaclover View Post
only works on boilers
Why?
I used
an always off [zero duty cycle] outside temp. for a furnace at 65F,
and an always on [100% duty cycle] for the design cold temp.

Excel calculates the slope of the temp/duty cycle line with the SLOPE function.

Then you know the duty cycle at any intermediate temp. for a perfectly matched house & furnace & climate by using the equation
Outside Temp = SLOPE x (Duty Cycle) + 65F
or
DC = [Outside Temp - 65F]/SLOPE



T
65.0 < enter Toff
36.0 < enter Tout

DC in %
0 < enter duty cycle
25 < enter duty cycle

-1.16 = calculated slope
65.0 = intercept

100.0 >enter DC
-51.0 = calculated Tout


Tdesign cold temp for Dist. Of Col. Is +14F, not -51F, so my furnace is oversized.

The furnace BTU output doesn't enter into the equation.

If your monthly avg. duty cycle and your monthly avg. outside temp. doesn't match these answers your furnace is undersized or oversized.

Last edited by Yoyizit; 12-19-2009 at 03:12 PM.
Yoyizit is offline   Reply With Quote
Old 12-19-2009, 03:38 PM   #20
Member
 
hvaclover's Avatar
 
Join Date: Oct 2008
Location: Suburbs of Detroit Mi
Posts: 3,704
Rewards Points: 2,000
Default

Manual J


Quote:
Originally Posted by Yoyizit View Post
Why?
I used
an always off [zero duty cycle] outside temp. for a furnace at 65F,
and an always on [100% duty cycle] for the design cold temp.

Excel calculates the slope of the temp/duty cycle line with the SLOPE function.

Then you know the duty cycle at any intermediate temp. for a perfectly matched house & furnace & climate by using the equation
Outside Temp = SLOPE x (Duty Cycle) + 65F
or
DC = [Outside Temp - 65F]/SLOPE



T
65.0 < enter Toff
36.0 < enter Tout

DC in %
0 < enter duty cycle
25 < enter duty cycle

-1.16 = calculated slope
65.0 = intercept

100.0 >enter DC
-51.0 = calculated Tout


Tdesign cold temp for Dist. Of Col. Is +14F, not -51F, so my furnace is oversized.

The furnace BTU output doesn't enter into the equation.

If your monthly avg. duty cycle and your monthly avg. outside temp. doesn't match these answers your furnace is undersized or oversized.
The latent hydro electron cyclic nature of the hydrogen atom in the water requires a a correction factor of Pi x Hy/7 xy.
__________________
Just slow, not stupid.
hvaclover is offline   Reply With Quote
Old 12-19-2009, 04:42 PM   #21
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

Manual J


Quote:
Originally Posted by hvaclover View Post
The latent hydro electron cyclic nature of the hydrogen atom in the water requires a a correction factor of Pi x Hy/7 xy.
I knew I left something out!

I have to fix this right-sizing-confirmation method.

If you know

your monthly HDD and
your monthly gas usage and
your outside design temp and
your furnace/boiler max input BTU/hr

you can check if your furnace is right sized for your house and climate.

If you know your furnace efficiency
at its monthly avg. duty cycle
you can calc. your house avg. heat loss.


Last edited by Yoyizit; 12-20-2009 at 11:45 AM.
Yoyizit 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
Manual transfer switch to power an existing sub-panel joestewart Electrical 10 11-23-2009 02:30 PM
Thermostat from Manual to Digital trinamillersmit HVAC 5 07-02-2009 09:21 AM
manual J question drewhart HVAC 2 01-31-2009 04:45 PM
needing manual HandyMac Landscaping & Lawn Care 2 07-03-2008 02:26 PM




Top of Page | View New Posts

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