Realistic Expectations and "The Occupied Zone"

How many times as a technician have you gone out to the same customer's home because of unrealistic expectations?  Some homeowners expect air-conditioners to work like an ice box, want you to size them for their big party on Fourth of July weekend, and expect you to show up at the drop of a dime when it doesn't meet their impossible notion.  Of course, this could be avoided by establishing a standard during the sales process or a little customer education.  I liked to talk about "The Occupied Zone" and work in a little Radiant Asymmetry, using more layman's terms of course.

Occupied Zone - ACCA Manual RS

  The occupied zone is a concept used in the design process to properly heat and cool spaces without a customer feeling drafts.  As you can see in the picture taken from ACCA Manual RS: Comfort, Air Quality, and Efficiency By Design, the zone is 2' inwards from all walls and ceilings.  ACCA Manual J: Residential Load Calculation, states the occupied zone is only 6.5' in height.  This area near walls and ceilings is use to mix conditioned air with room air.  In fact, this mixing is what cuts down on occupants feeling convective currents or drafts in the heating season.

ASHRAE Standard 55

  Not only will occupants feel drafts, but they will feel what is termed as radiant asymmetry.  This is the phenomenon (not really, just to a homeowner) of a warm or cold temperature.  If the wall is colder than you are, the wall will be pulling radiant heat from you.  This makes you feel cold, even if it is 70F in the room, hence the statement "a cold 70F".  The best example I ever heard of this is the temperature at an ice rink.  It feels cold when on the ice, but the air temperature hovers around 65F!  Anyhow, have you ever wondered how much asymmetry is too much?  ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy was nice enough to spell this out for us.  As you can see, a warm ceiling is the number one device that occupants will find uncomfortable with only a 10-20F difference.  This would of course happen during the cooling season, and with any luck on Friday afternoon just before that Summer, holiday weekend/family reunion, right?  I can see this happening more often in Cape style homes since there are more ceiling/roof combinations and occupants are more than likely outside of the occupied zone.  The only answer to this issue is proper home air sealing and insulation.  It does not matter how oversized your air-conditioner is, it will not be able to overcome the laws of physics and radiation.  This is just another reason to peer into the attic during your sales calls to verify the weatherization of the home and the thermal boundary.  Don't set your install up for failure, and certainly establish some basic expectations with the homeowner.  You don't want to leave this up to your technician on a holiday weekend, getting paid double-time for warranty work!

http://excessair.blogspot.com/2012/05/realistic-expectations-and-oc...

Views: 277

Comment

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

Join Home Energy Pros

Comment by Bob Blanchette on May 14, 2012 at 5:16pm

Contractors need to discuss humidity control and how going with a huge A/C unit will make the house feel muggy. Also temperature swings and noise levels should be mentioned. Comfort is not just about maintaining a certain setpoint regardless of conditions.

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Casey Gesell replied to Casey Gesell's discussion Looking for home improvement companies to join our dealer network!
"Hi Patrick, I'd be glad to have a conversation with you about the details on our program. What…"
2 hours ago
Amina Lang posted an event

19th International Passive House Conference at Congress Center Leipzig

April 17, 2015 at 9am to April 18, 2015 at 6pm
The Passive House Standard enables every building owner to benefit from the energy revolution, with…See More
4 hours ago
Don Hynek replied to Luis Hernandez's discussion Non-continuous exterior insulation
"This is a matter of far more than R-values. Average exterior temp, heating load vs. cooling load,…"
20 hours ago
Patrick Michaelyan replied to Luis Hernandez's discussion Non-continuous exterior insulation
"Don, I'd like to ask you specifically about your comments on putting the structure at great…"
yesterday
Patrick Michaelyan replied to Casey Gesell's discussion Looking for home improvement companies to join our dealer network!
"Casey, Time frame for relocating is late spring to early summer. I am considering both counties…"
yesterday
Dennis Heidner replied to Patrick Michaelyan's discussion Vinyl Siding with Integral Insulation
"The observation about rot is important.   I agree. One of my complaints with some of the…"
Friday
Jennifer Schenk added a discussion to the group Job Board
Thumbnail

Job Opening - Energy Programs Manager - Frisco, CO

Energy Programs Manager - High Country Conservation CenterJob DescriptionGeneral Description of…See More
Friday
Jennifer Schenk joined Diane Chojnowski's group
Thumbnail

Job Board

This group is for posting jobs related to all aspects of the home performance industry including…See More
Friday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service