Who among us tracks the accuracy of Manual J?

Who among us tracks the accuracy of Manual J?

I have hour meters on maybe 20 systems now.    I like to see the run time when it's "4" degrees in Kansas City.  99% rate in KC is +4' degrees.  My goal at 4' is 100% run time.   I have a super sealed home 2,100 square feet  with a 2 ton ground type heat pump R-30 walls, R-60 attic, R-8 windows & doors with 98% run time @ "+ 4' ".  When the strip heat turned on, it smelled up the home with the dirt  off the 5 KW strip, heat burned off the dust.   If you fine tune ACCA MJ  with a blower door number and infrared camera  you can get closer.   If  I find a real drafty building - I am more off.   Or building owner just turn up the heat more.  

4/5 of heat loss is at night. The wind tends to die mid-night and MJ tends to keep the wind up.  If you just run the number with Manual J I tend to get larger system sizes than needed - do not add more fudge factor. 

Views: 232

Comment

You need to be a member of Home Energy Pros Forum to add comments!

Join Home Energy Pros Forum

Comment by Eric Kjelshus on March 7, 2016 at 6:53pm

Most of the Thermostat controls I use Look at RH - humidity also  but still its just longer run time.   I am mixed very humid to dry and cold.   I have been using outside air with a damper to outside to make the building positive.  Could the outside air make 20% -30% higher fan use and higher power use?

Comment by John Proctor on March 7, 2016 at 11:25am

Eric  It is doubtful that the fan motor is using more energy, the electrical use of PSC motors is nearly constant regardless of speed. What climate are you referring to? If it is a wet climate, then you need the latent removal and should go back to 350 CFM per ton. However the lack of latent capacity should not increase the electrical usage since the thermostat controls only to temperature, not humidity.

If the duct system is not restrictive, an ECM/BPM motor would deliver the right airflow at a lower watt draw.

Comment by Eric Kjelshus on March 6, 2016 at 2:11pm

Do you see the new AC with low sensible and very large coils needing more run time?  That last 2 ton this year was just 91% Sensible and 9% Latent.   the one I took out a AC built in 1990 was 70%/30% with very small very cold coil but 350 CFM/ton now razing the CFM to 400 per ton and not the Latent removal.   I am seeing power bill go up with higher run time and more power to run the fan?   Older air handler had drives with smaller motors.   

Comment by John Proctor on March 3, 2016 at 11:06am

Proctor Engineering has done many studies on Manual J vs. true load. The short answer is the sensible load is actually 2/3 of the Manual J 7 (note 7) estimated sensible load and Manual J8 calculates an even higher sensible load. The latent load estimate varies compared to the actual latent loads. Sometimes it is too high (a tight house in a wet climate). Sometimes it is too low ( a leaky house in a wet climate).

There is a Home Energy article on all this on their website or here:

http://www.proctoreng.com/dnld/Home_Energy_Sizing_AC.pdf

Here is a letter from Trane opposing the acceptance of Manual J 8.

http://www.proctoreng.com/dnld/ACCA.pdf

Latest Activity

Michael Dunseith posted a status
yesterday
CEE posted a blog post
yesterday
Sean Lintow Sr replied to Chris Bellanca's discussion Overheating garage
"There are only two methods - block the heat before it gets in & exhaust what gets in Blocking -…"
Friday
John White posted photos
Friday
John White posted a blog post
Friday
Rob Madden posted a discussion

E&O Insurance

Any recommendations for a good E&O and general liability insurance carrier for energy…See More
Thursday
John Redmond added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

Flir I7 Infrared Camera (Barely Used)

I have been away from this site for a while, so my apologies if this is supposed to be posted…See More
Thursday
John Redmond joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
Thursday
Hannah Wood liked Quinn Korzeniecki's discussion Application Period for 2018 Energy Auditor (EA) and Quality Control Inspector (QCI) Pilots Now Open
Thursday
Quinn Korzeniecki posted a discussion

Application Period for 2018 Energy Auditor (EA) and Quality Control Inspector (QCI) Pilots Now Open

We need you!Applications are now being accepted to participate in the 2018 Energy Auditor (EA) and…See More
Thursday
Quinn Korzeniecki added a discussion to the group Building Performance Institute (BPI)
Thumbnail

Application Period for 2018 Energy Auditor (EA) and Quality Control Inspector (QCI) Pilots Now Open

We need you!Applications are now being accepted to participate in the 2018 Energy Auditor (EA) and…See More
Thursday
David Butler replied to Chris Bellanca's discussion Overheating garage
"Easy... insulate the attic ceiling. I'm not sure how much good it would do to air seal a…"
Thursday
Chris Bellanca posted a discussion

Overheating garage

Hi all, I'm looking for potential solutions to a problem at a client's house.  The south facing 2…See More
Thursday
Landon added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

Brand new retrotec blower door system $3000

Hi, I’ve got a brand new blower door system from retrotec that I got 2 months ago, and never got…See More
Thursday
John Redmond posted discussions
Thursday
David Holtzclaw replied to David Holtzclaw's discussion GSHP for domestic hot water
"Thanks John & Bill. Bill your experience is one reason why I wanted a larger heat pump with…"
Thursday
Diane Chojnowski posted events
Wednesday
Rob commented on Bob Krell's group Healthy Indoors (IAQ)
"Hello, Has anyone tried custom filtering of window AC units? Specifically concerned with…"
Wednesday
Michael Dunseith's 2 photos were featured
Wednesday
Franco Oyuela commented on Perry Ning's blog post Warnings About Portable Air Conditioners
"Here are the top five benefits of owning a portable air conditioner: 1. Low Price – All…"
Wednesday

Photos

  • Add Photos
  • View All

© 2018   Created by Home Performance Coalition (HPC)   Powered by

Badges  |  Report an Issue  |  Terms of Service