I am participating in a DOE Better Buildings  program in southwest Ohio that is in its infancy stages. During discussions while setting the technical standards of the program, the topic of proper sizing vs 2 stage equipment came up.  Many of the "seasoned HVAC contractors" involved in this conversation including the director of operations for the program adamantly were advocating for the standard to be" 2 stage trumps sizing".  Meaning if you cant find a 2 stage piece of equipment in the correct size as specified by your manual j then go to the next available size.  (Most 2 stage equipment is not available in 1/2 ton sizes.)   For reasons discussed in this and other threads, I was in favor of forgoing the 2 stage piece of equipment for the piece of equipment closer to the proper size.  I was hoping I could get some input from this thread on reasoning for or against up-sizing in this situation especially taking in to consideration our geographic location.

Views: 157

Replies to This Discussion

Keep in mind that the MAJORITY of operation time is going to be at part-load conditions. More than likely, the larger unit running on its first-stage would be more appropriately sized, for more operating hours, that the "correctly" sized machine in a single-stage model (it would only be properly sized under the design conditions).

 

Manual-S states that the equipment selected must be able to satisfy both the sensible and latent loads. If you're wanting the benefit of a 2-stage machine (lower power consumption during part load conditions, ability to zone more effectively, etc.), you should just pick the smallest size that is available which also meets the design load. The first stage will handle the part-load conditions with the occasional help from the second stage. If an aggressive Manual-J is done, and the house effectively manages moisture, this should not be problematic.

 

If you use a program like Wrightsoft, you can look at the BIN data reports to see the number of estimated operating hours on first/second stages to help you make a decision like this.

RSS

Discussion Forum

HVAC integration – the past, the present, and the future

Started by Igor Mitbarg. Last reply by Lucifer Prescott Apr 11. 1 Reply

Target superheat formula

Started by Miguel Orduno. Last reply by John Proctor Feb 18, 2015. 6 Replies

Now for Something Different

Started by John Porterfield. Last reply by John Porterfield Jan 12, 2015. 2 Replies

Groups

Latest Activity

Alfie Davis posted a blog post
17 hours ago
Profile IconSam Compton, Cameron Home Insulation, Seth Shoneman and 2 more joined Home Energy Pros
yesterday
Home Energy Magazine's blog post was featured
yesterday
Eric Kjelshus replied to Gregory Cisco's discussion Abandoning under-slab HVAC ductwork which fills with groundwater seasonally.
"In Kansas City a lot of "cardboard" for supply was used in slab on grade.  1950-1970…"
Friday
Richard L. Rue replied to Sonja Persram's discussion Energy Savings Guarantee for single family dwellings in cold climate??
"Try EnergyWise Structures (www.energywisestructures.com) They are a NASA spin-off company that has…"
Friday
Debra Little commented on Home Energy Magazine's blog post NREL Research Finds That 22% of New Homes Completed in the U.S. in 2016 Were HERS Rated
"The avg scores are interesting. Are there comparative numbers for previous years? I thought they…"
Friday
Home Energy Magazine posted a blog post
Friday
Robert Zockoff replied to Gregory Cisco's discussion Abandoning under-slab HVAC ductwork which fills with groundwater seasonally.
"Public water systems regularly "reline" the interior of existing 50 year old water mains…"
Friday

Photos

Loading…
  • Add Photos
  • View All

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service