Author Topic: Home Energy Auditor Training  (Read 1960 times)

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Dan 04617

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Home Energy Auditor Training
« on: November 15, 2008, 02:17:54 PM »
I'm in the middle of a two week course to become a Certified Home Energy Auditor here in Maine.  The course is put on by the state.  It's split into two parts, and this last week was the classroom stuff.  Next week is fieldwork, estimating natural pressure air flow rates in houses by depressurizing them with a blower door and measuring flow, and looking around with an infrared camera while the fan runs to find the worst leaks.


In addition to keeping the heat in, a house needs fresh air.  Typically, houses get enough, even plenty, even way too much, by leaks in the structure.  Many of these are not, as would be supposed, around windows and doors, but through basements and leaky walls and attic floors.  The design standards, below which people start to feel sick, mold tends to grow on damp walls, and your pilot light makes your head spin, is either .35 air changes per hour (ACH), or 15 cubic feet per minute (CFM) per person, minimum 5 people.  


You could argue that your special architecture is efficiently designed for one person, or maybe two, and you don't need air flow for five.  I like to play house design games and work small, and one of my favorite designs is only 16' square. Why does this house need air for five?  The ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) standards assume that at some point, five people will get crammed into even a small house, so there they are.


Anyway, the point at which .35 air changes per hour and 15 CFM per person intersect is a 1600 square foot house, 8' ceilings.  When designing a small efficient house, this might be a good target size: 24x36, two stories, or 24'square, three stories. Story count includes all conditioned space, so if your basement is heated, count it in.  Any smaller and you could save on building materials and surface heat loss, but not on natural pressure ventilation heat loss.


15 CFM times five persons is 75 CFM, 4500 CF per hour.  In my coastal Maine, 7500 heating degree day climate, that's 146 gallons of heating oil (70% efficient~100kBTU/gal) just to heat the air I have to change back and forth.  Or 14,600 cubic feet of natural gas, or 4300 kWh of electricity, or a cord of softwood, 2/3rds to half a cord of hardwood.  (Somebody check my math. Ignore rounding errors.)  That doesn't include heat loss by conduction through walls and radiation out your windows.


If your house has more air exchange than that, you're letting too much heat go.  One air change per hour is not unusual in many houses.  That's about an extra 275 gal tank of oil per year (at $3 a gallon) in a 1600 sq ft house. Excess air leakage is often the biggest, and often most easily controlled, methods of heat loss.  You can control it largely by sealing air leaks through basement walls and attic floors, often unfinished spaces where you can get access without tearing out the plaster.  Always put the moisture/airflow barrier on the warm side, and put the insulation right up against it.


Now on to insulation.  People know more about insulation than air flow, so I won't say so much.


The insulation that saves you most is the first inch.  Some is good, more is better, but there comes a point where 30" isn't much more help than 29".  Fiberglass lets air move through.  It only works well when enclosed tightly on all six sides.  Fiberglass in well ventilated attics (and attics must be ventilated or they'll rot the framing!) lets air move through the insulation, greatly reducing it's value.  Putting a few inches of cellulose, which restricts air movement much better, over the fiberglass, gives you back the full value of the fiberglass, plus the value of the cellulose.


On my leaky old farmhouse, the ideal would be to rip off the exterior of the walls, spray an inch of R-7 closed cell foam, finish off with three inches of fiberglass, board it back up, and replace the siding.  This works only because I need to replace siding in places anyway.  The foam would seal the wall better than any other insulation, but it's not necessary or necessarily economical to do the whole wall full thickness with it.  This foam costs about a dollar per board foot. It's value is as both an insulator and a sealant.  If I could do the walls and the basement ceiling, then fix the worst spots in the attic (chimney and plumbing chases) this house could be sealed reasonably tight.  I'd still get some ventilation through the ductwork coming out of the basement and by door and window leakage.  I like the idea of ripping off the exterior better than the interior because it puts less plaster dust in the living space, and electrical stuff has to be fussed with less.



Should be a Diary..

« Last Edit: November 15, 2008, 02:17:54 PM by (unknown) »