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Old 11-20-13, 02:40 PM   #11
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Quote:
Originally Posted by jeff5may View Post
...The envelope has been sealed up to "acceptable" levels...
What does this mean? "Acceptable" to who? Any numbers??

I think Daox's strategy of turning on all the exhaust fans and scouting for leaks would be a great start. A case of cans of foam, and one of those IR leak finders would come into play here.

Next, I'd recommend judicious use of bubble wrap on windows. If they're double or single hung... on the lower panes of most windows.

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Originally Posted by jeff5may View Post
Not quite energy star, but better than most "affordable" site-built homes are being constructed today in the region.
This is really interesting, because around here, the standards are such that any home built today is much better than most homes built 30+ years ago. And to see what really good homes are like, just go check out a local Habitat for Humanity project, because they really have it going on regarding insulation.

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The 80+ year old ductwork was not replaced when the HVAC system was upgraded from a fuel oil or coal burning furnace/boiler in the early 80's. As usual, the upgraded unit was upsized to push enough airflow for the ancient ductwork. From the whistling registers and vents, it is obvious that the air is just flying through the system. The ducts have been gobbed up with mastic to seal up the leaks, but not insulated. Between the high pressure drop and the exposed ductwork, the auditor estimates that duct losses are 40% or more. The HVAC gets a "D".
This part is really depressing because it reminds me of my place and the wretched old parched air heating system I formerly had. Just thinking about it is almost like post traumatic stress.

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What would you guys recommend as a starting point, assuming the homeowner can swing a couple thousand dollars or so today if it will reduce their utility bill?
So, I'd tell the young couple to do the above loss reduction strategies, and then flush the whole idea of ever retaining and improving central air, and start buying and self-installing mini-splits (not going with a multi-head unit), one at a time, as their budget allows and use the wretched parched air system (set the thermostat lower than on the mini-splits) until they have enough mini-splits to carry the house, then rid themselves of parched air, forever.

Kentucky should be a great place to use mini-splits.

-AC

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Old 11-20-13, 03:41 PM   #12
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Best,

-AC
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Old 11-20-13, 10:49 PM   #13
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AC,

I honestly didn't know I would hit so close to home with this question.

What you had is exactly the kind of duct work I was speaking of: dryer-exhaust or furnace-stack sized ducts with tight bends leading to the furthest registers in the house. Maybe 8" round ducts leading from the plenum to the first branch. No balance in airflow whatsoever; the vents closest to the air handler get the lion's share of the flow.

Kentucky is an awesome place to use mini-split heat pumps. I have seen some installed, and the owners have nothing but good things to say about them for the most part. My hacked window unit holds its own down to about 30 degF, and it will carry my heating load for the entire home 95% of the time. If I had a larger heat exchanger outdoors, it would do even better.

I honestly believe if I purchased 2 tons worth of capacity in a multi-split unit, or maybe separate units, it would carry me for all but a couple of nights a year. Even then, thermal mass would probably carry me until 3 or 4 in the morning.

Last edited by jeff5may; 11-20-13 at 11:07 PM.. Reason: More words
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Old 11-20-13, 11:37 PM   #14
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AC,

I honestly didn't know I would hit so close to home with this question.
Close to home is exactly the case... not only my home, but the homes of personal friends, who are making the same dreadful mistakes as your young couple example.

In spite of my advice, and their full knowledge of the economy and comfort of a more modern type of heating (radiant, mini-splits, GSHP, etc) they are blundering ahead same as in the past... and only perfunctory attention to sealing & insulation.

Momentum can be a terrible thing.

-AC
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Old 11-20-13, 11:50 PM   #15
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I can relate to jeff5may on post #5

"They call the local utility company and schedule an energy audit to find out where their home is on the energy-efficiency scale. What they find is confusing as heck to them."

Did this, didn't receive anything on a scale basis other than CFM.
My auditor tried to tell me that my furnace was 60% efficient which isn't true.
He argued that ACH is pointless and to ignore it.
He then took the CFM converted it to ACH and told me that I had enough natural ACH to where if I didn't seal my house that I could skip additional ventilation.
When I asked him about my "60% efficient furnace" he recommended to get it checked annually and wait until it failed a heat exchanger inspection.

He also said that my 2x4 16" on center construction wrapped in 3/4 of XPS is a "R19 wall" because "that's code for the 1980's. ...sure an R13 batt plus R3.75 of XPS makes an R19 wall.

He seemed to be all over the idea of getting a water heater blanket like it would save the world and 'pay for itself in under a year'. ..sure the 4 therms a month it used was $2.60 at the time and 12 months would be $31.20. Quite certain I'm not going to save that much in a year by buying a $20 water heater blanket, I use some of that hot water, its not all going to the basement. Water heater insulation is a good idea and is fairly easy but he made it sound like the single most important thing to do.

I asked him about sealing attic facing top plates, got no info there about attic insulation other than to seal plumbing and electrical penetrations. I'm glad I read about it here and saw S-F's pictures.

It is found during the audit that the home is "not too shabby for the neighborhood".
Mine actually thought the 2x4 design with 3/4" rigid wrap was a good idea and is 'plenty enough insulation for a house'.

"The envelope has been sealed up to "acceptable" levels and has been insulated to "above average" value."

Apparently 1500 CFM is 'plenty good', 'don't worry about it', and 'if you seal much more you'll need a ventilation system.' worthy discussion points.

"Not quite energy star, but better than most "affordable" site-built homes are being constructed today in the region."

Mine had huge thermal bypasses into the attic. I found roughly 500 sq inches or 3.5 sq ft of what were essentially holes in the attic that I've sealed up.

"During the conclusion of the audit, the homeowner sits down at the kitchen table and is given what seems to be a really expensive sales pitch. The auditor recommends to just gut the whole HVAC system and put in something new. A quick tour of the new systems on the market is given, with "good, better, best" systems of increasing estimated cost, naming major components but not much detail. A "top ten" list of local contractors is left with the report, and the auditor makes a hasty exit."

My auditor gave me the cheap fixes. Used estimates and payback periods and basically said to not do anything with only 7" of cellulose in the attic, not do anything about 1500 CFM at 50 pascals, don't consider adding additional insulation if you replace the siding, be sure to put a continuous(2 speed) bath fan in the house if you seal up the place.

I asked him about passive house insulation or at least super insulating my place and he talked about how it won't work out well for me without more thermal mass.

He left and I feel that I would have been better off with two box fans sealed in a window and renting a thermal imaging camera from Home Depot. Oddly enough, I'm looking to do that again after I have insulated, air sealed, and did everything else that I'm planning to do to this place since some of the images that I really wanted of my house during the audit, I did not get.

If you insulate well enough, I do agree with Daox though. You'll save tons more for the same amount of money by insulating and air sealing than you will on replacing the equipment. I'll save more than 26.6% of my energy with less than 1/4 the amount of a $8000 upgrade to a 96.2% efficient furnace and a 16 SEER AC. I'm thinking I'm already better off than 26.6% and I don't even have the $300 of cellulose plus blower cost in my attic yet. $140 of spray and rigid foam seems to have made a huge difference once applied to the right places.

What would you guys recommend as a starting point, assuming the homeowner can swing a couple thousand dollars or so today if it will reduce their utility bill? Bang for the buck would be to go into the attic and seal all of the wall top plates, electrical penetrations(use UL 1479 and UL 2079 rated caulking for junction boxes), and plumbing penetrations. Seal any second story or story+half knee wall holes. Pull the window trim and seal all of those gaps. Seal electrical and switch plates with the foam inserts you can get at your hardware store. Put on the thicker version of the water heater blanket. Seal the sill plates in the basement that face outside. Be sure the gaskets are good on all doors(top, bottom, and sides), check the windows too. Put on window shrink plastic, especially in the winter, but for windows you don't open in the summer, leave it on in the summer too.

After the easy bang for the buck stuff is done, return to the attic and get R60 in your attic if you are in a climate zone like mine or at the very least what the DOE recommends for ceiling/attic insulation. I was surprised that I could get just over 1000 pounds of cellulose for $250 after tax (add another $50 for blower) and will probably put me between R60-R75 from my original 7". I'm looking at about $500 with everything said and DIY done with my house and that feels super cheap to me. The next project is to add 4" of polyiso or XPS under the siding when I do DIY siding replacement on my house. That is more work and I'm less familiar, but I'll start with the easiest side first and then maybe do a side each summer until its done. A heating load calculation suggests I'm cutting my peak load by about 2.5 times and the heating bills should be reduced by even more than that. I'm planning to get solar shade screen in the summer to block out sunlight on the west side to cut the AC costs.

All of this will cost less than the $8000($6000 after government and utility rebates) for what amounts to minimal mechanical efficiency improvements in comparison to real envelope improvements. Oddly enough this makes my home even more of a candidate for ultra efficient mini-split equipment. I'm actually looking at heating and cooling my entire home to my satisfaction with one 12k mini-split heat pump and using the gas furnace on the coldest days as a backup to the mini-split or use its blower or maybe a little gas when I need a more even temperature when I have guests over. I'm particularly looking at benefits such as the super high SEER, dehumidification dry mode, local heating/cooling when I want to close the door and chill in one room on the computer or in a book all day, and long cycle benefits when cooling too.

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Old 11-21-13, 01:08 AM   #16
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...Kentucky is an awesome place to use mini-split heat pumps...
Have you done a Heating Degree calc for your location?

If you post your zip code, I can do it for you.

-AC
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Old 11-21-13, 04:32 PM   #17
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AC,
My zip code is 42701.
I have more HDD's than CDD's on paper, but the summer climate has lots of latent energy in it. It tends to be muggy and swampy here a lot. Even during heating season.
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Old 11-22-13, 08:57 AM   #18
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I have more HDD's than CDD's on paper, but the summer climate has lots of latent energy in it. It tends to be muggy and swampy here a lot. Even during heating season.
That is really an excellent point. You have correctly identified a deficiency in the terms HDD and CDD. The idea of HDD and CDD is to have a statistical, localized value to use as an aid in designing heating and cooling systems, but both HDD and CDD ignore the part that humidity plays in the design. You are right, the humidity plays a very large part. I would assume that local designers would learn from experience, and develop a 'fudge factor' to make localized corrections. But it does seem inelegant.

A few years back, I was trying to zero in on exactly what my heating requirements actually were. I was doing a study in which I was heating my house with several electric resistance heaters, and I had a Kill-a-Watt attached to each. I was logging outdoor temperatures during this time, and plotting temperature against power, expecting to get a fairly smooth curve that I could then use to precisely model heating needs of my house. I was amazed at the scattering of data points I was getting, and what I thought would be some kind of a curve, was actually a cloud of points. What you have identified, explains the scattering, because I had not accounted for variations in humidity, and the power that would be required to deal with that humidity.

But back to the HDD & CDD issue, this is a very good reason to do a concept 'upgrade' of Heating Degree Days to Heating BTU Days, HBD (with the metric equivalent being Heating Kw-h Days, or HKD) and instead of Cooling Degree Days, they would become Cooling BTU Days, CBD (ditto metric equivalent, Cooling Kw-h Days, or CKD). This would incorporate average humidity for various months.

It's an important distinction.

jeff5may, I think we should prepare to storm the halls of science...

-AC
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Old 11-23-13, 07:57 AM   #19
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Wind speed has a LOT to do with load, especially on the heating side. 20F outdoor with no wind vs. a 15MPH wind makes a HUGE difference in heat loss. Did you account for wind speed when you were plotting your heat loss?

Thermal mass of the house is another thing that needs to be accounted for. If outdoor tempatures change quickly it can take up to 24hrs before the house feels the full effect of thermal load. This is why you don't need to size AC units for peak load with high mass homes.

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Old 11-23-13, 08:01 AM   #20
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Back to the original topic, it does appear that duct losses are significant in the cycling loss calculations. Not sure hot much the 45 second burn time to heat up the exchanger costs in efficiency, and how much is recovered during the 180 second blower off delay after the burner shuts off. 90%+, 80% and old school pilot light furnaces have different cycling losses.

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