Cause and resolution of uneven temps
Last Post 17 Mar 2014 07:30 PM by stickman. 16 Replies.
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stickmanUser is Offline
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12 Mar 2014 05:06 PM
Hello, I had a 4 ton ClimateMaster 27 split installed last fall in my approx. 1700 sq' split level house. I am trying to resolve a big difference in heating temperature between the upper floors (above ground) and the two lower levels (ground level and basement, both on concrete floors). I have only one zone on my system, and have had the installer out several times checking on the system. They tell me system is operating fine. I have checked air temps at registers (90 degrees) and at the one return grille on top floor (approx. 72 degrees). I am in the process of correcting some questionable flex duct work, such as replacing bends off the distribution box with rigid metal elbows. This has helped air flow somewhat. The thermostat is located on the top floor in the hallway where the return grille is in the ceiling. What I'm noticing is that when the system is running, the temps on all floors gets pretty close to equal. However, in between cycles, the temp on the lower floors drops very quickly, almost 10 degrees before the next cycle on. I'm sure some of this is due to cold air infiltration in areas I know need improving. But beyond that, is my 1-zone system capable of attaining close to level comfort across all floors? Is zoning necessary? Would moving the t-stat downstairs help? Thank you in advance.
Eric AndersonUser is Offline
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12 Mar 2014 07:24 PM
Stickman,
Concrete floors have very high mass and are slow to absorb heat. When the unit is running, the AIR is getting up to temp, but the thermal mass is not. When the active heat stops, those areas cool much more quickly as you have a large cold mass under foot.  Poor airsealing exacerbates this as cold outside air flows into the lower portions of the house due to stack effect. Splitting into an upper and lower zone would help, but figuring out how to insulate and airseal the concrete walls and floors is the more likely cure. This is not a geothermal system problem, more likely a building shell problem.

Cheers,
Eric
Think Energy CT, LLC Comprehensive Home Performance Energy Auditing
mtrentwUser is Offline
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12 Mar 2014 09:08 PM
Slab-on-grade, crawl-space, or basement? I am amazed at how much a difference my home comfort changed by air sealing the rim joists in my crawl-space with a half dozen cans of spray foam. Night and day in certain cold/drafty areas.
stickmanUser is Offline
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12 Mar 2014 09:50 PM
Slab on grade. House was built in 1954. Understood about the air sealing. Part of my geothermal job was a home energy audit. Got a blower door test, was told a few things, but felt it wasn't thorough enough. I thought a thermal imaging would have been very helpful. I would definitely like to address the house envelope, but I will be relying on a contractor to give good advice. Any suggestions on what services I should make sure to get in an audit?
stickmanUser is Offline
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12 Mar 2014 09:52 PM
Sorry - to clarify the type of construction: my split level home has a basement with living space above it and a den level which is on a slab, with living space above also.
joe.amiUser is Offline
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13 Mar 2014 09:03 AM
Split level is different and often difficult to repair. However thermal imaging would be a good start. Also since you mention that the temperature is even when the system is running, a low speed constant fan might help.
Is there an opp to insulate the edge of the slab?
Joe Hardin
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ICFHybridUser is Offline
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13 Mar 2014 09:45 AM
but I will be relying on a contractor to give good advice.
Good luck with that. You would have much better luck getting an energy consultant. At least make sure they have a strong interest in greenbuilding and energy efficiency.
stickmanUser is Offline
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13 Mar 2014 01:49 PM
I guess I could leave the fan set to "on" instead of "auto" on those borderline days where the heat pump does turn off frequently - good thought. Insulating slab edge is not possible unless some serious excavation is done - not eager to do that. I did read some good articles on air sealing the rim joists, and thought I'd give that a try.
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13 Mar 2014 01:50 PM
After my post I realized I left myself open to a reply like this about relying on a contractor! I did mean an energy consultant. Just need to find a good one in my Long Island, NY area.
BergyUser is Offline
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13 Mar 2014 03:05 PM
The blower in your unit is an ECM motor. Running this motor 24/7 on low constant fan should cost about $8/month.

Bergy
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13 Mar 2014 03:38 PM
Will just putting the t-stat fan selection to "on" have it run in low speed? I would think so, until the compressor goes into 2nd stage. Correct?
G.O. JoeUser is Offline
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14 Mar 2014 07:24 AM
Posted By Bergy on 13 Mar 2014 03:05 PM
The blower in your unit is an ECM motor. Running this motor 24/7 on low constant fan should cost about $8/month.

Bergy


The OP has a split unit. We don't know what he has for an air handler or blower motor. Even if it is an ECM, we don't know what speeds it is programmed for. Stickman can you get us info on your air handler?
stickmanUser is Offline
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14 Mar 2014 07:46 AM
The air handler is a ClimateMaster TAH model. It is a variable speed / ECM unit. I would think any speed control would need to be done on the board, not the t-stat.
G.O. JoeUser is Offline
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14 Mar 2014 05:11 PM
A fan on at thermostat will give you the lowest fan speed. This will be good for more even temperatures. Some thermostats have a recirc or programmed fan cycles that turns the fan on based on time or percentage of time.

1st stage, 2nd stage and Aux programmed speeds are considerably higher.
jonrUser is Offline
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14 Mar 2014 06:21 PM
Moving room temperature air around is surprisingly ineffective at moving heat around.
engineerUser is Offline
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15 Mar 2014 12:49 AM
Do or have done a room-by-room manual J load calculation, then compare that with measured air flow supplied to each room (need a flow hood).

Both those tasks should be able to be completed by an "energy consultant".
Curt Kinder <br><br>

The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
stickmanUser is Offline
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17 Mar 2014 07:30 PM
I do have the manual j from the installer. Not a flow hood though. I have already discovered bad flex duct practices and am starting to resolve them. Also working on air sealing lower levels where I can. I think I need to resolve these things and take it from there.
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