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: 274

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

Mike Kandel added a discussion to the group Building Performance Institute (BPI)
Thumbnail

BPI's Home Energy Auditing Standard Published as ANSI Standard

The Building Performance Institute, Inc. (BPI) is proud to announce that BPI-1100-T-2014: Home…See More
7 hours ago
Mike Kandel posted a discussion

BPI's Home Energy Auditing Standard Published as ANSI Standard

The Building Performance Institute, Inc. (BPI) is proud to announce that BPI-1100-T-2014: Home…See More
7 hours ago
Hal Skinner posted a discussion
7 hours ago
Todd St.Clair 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
10 hours ago
Todd St.Clair replied to Jim Falakos's discussion Treat Software in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"How long ago did you buy this, if it was good for 5 months? And how much would you take for this."
10 hours ago
Bud Poll replied to Bud Poll's discussion Basing air exchange on house volume??
"Hi Sean, yes I am struggling with this and that is why I opened the discussion, so a definite…"
12 hours ago
Lynda Wright is now a member of Home Energy Pros
12 hours ago
Sean Lintow Sr replied to Bud Poll's discussion Basing air exchange on house volume??
"Sorry Bud but I think you need to clarify your issues with using volumes to calculate ACH As for…"
23 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service