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: 317

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.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Green Training USA posted an event
Thumbnail

Proctor’s Without Borders at Online

July 29, 2015 to August 7, 2015
Complete your training at your own pace and take exams when you want and where you want. No…See More
3 hours ago
Gar Swaffar commented on Gar Swaffar's blog post Cost of using a BPI QCI?
"Ip.s., I would presume there will be a difference between the Left Coast and nearly everywhere else."
22 hours ago
Gar Swaffar posted a blog post

Cost of using a BPI QCI?

I'd like to find out if there is a consensus on a rule of thumb cost of a QCI onsite for…See More
22 hours ago
Gar Swaffar is now a member of Home Energy Pros
22 hours ago
Colin Genge posted an event

Infiltration and Duct Leakage with BPI at Online

July 30, 2015 from 1pm to 2pm
Blower door and duct test requirementsCalculating resultsCertification optionsTest preparation and…See More
23 hours ago
Stacy Hunt posted an event

Volunteers needed for the upcoming U.S. Department of Energy Solar Decathlon in Irvine, CA at Orange County Great Park

October 8, 2015 at 11am to October 18, 2015 at 7pm
Volunteer for the upcoming U.S. Department of Energy Solar Decathlon 2015, taking place Oct. 8-18…See More
yesterday
Kim Tanner posted videos
yesterday
Don Fitchett posted a blog post
Monday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service