Posted by: greenpinkies | September 1, 2010

The Nitty Gritty

Wonderful, Wonderful! We have received the report from Gary and William at Home Energy Consultants. We can now start sharing some numbers and really meaty information about energy efficiency with you.

First off, the report was incredibly comprehensive as to the current state of the house, and projected cost of heating and cooling, as is. Amazingly, the house has a HERS index of 118. (Most older  homes are in the HERS, 150 range). Gary and William included suggestions for modifications which can bring the HERS down to 50-55. This means that the house can be made about 50% more efficient than it currently is.

Stop!! Here’s where we get really bogged down in the terminology going on out there. So, I will now attempt a layman’s explanation of what language these green experts are speaking. They appear  to be speaking not one language, but  about three languages.

1. The National Home Builders seem to be favoring a HERS index to measure energy efficiency in a home.

2. The Mayor of Fayetteville’s Residential Energy efficiency program is rating homes according to their “Manual J” load calculation.

3.  The Electric Cooperatives of Arkansas’ Energy Efficiency Makeover Contest seems to be using ‘Air exchanges per hour” as a major criterion in determining energy efficiency. (See Rural Arkansas publication September 2010).

So, what is the connection between “HERS index”, “Manual J” and “Air exchanges per hour”?  Are they all a sort of scale that interfaces with each other? Or, are all these well meaning programs diverging in different directions only to ‘divide and conquer; some of them to eventually disappear (Something like Cassettes vs. 8-track tapes in the ‘80s)?

Here’s the scoop as understood by a very average, math challenged person:

HERS Index or “You should never take more than you give” (Circle of Life, Elton John)

How many of us have had to deal with “needy people’?  You know the kind, they are always needing help or comfort, nothing you can do for them is enough. These types are never satisfied and they sap the energy and patience out of even the best of us, right?

Well, the higher a HERS index is, for a house, the more demanding and “needy’ it is. It sucks the energy and is never satisfied.  The leaks in a house to the outside are the number one contributor to ‘needy’. A house full of air leaks, either from uncaulked windows, or loose fitting ducts, too low insulation, is a very unsatisfied house. And like the demands of a needy friend, you will never keep up.

The scale of the HERS index is from 0 to 100 and above. (100 being the ‘set point’ of a 2006 average home). Ideally a HERS rating of 0 means ‘all that you are taking in, equals what you are putting out.’

Therefore, the lower a HERS index, the more satisfied and non demanding your house is. (To qualify to be an “Energy Star Home” this index must be somewhere around 80-85).

Manual J or “the psychiatrist”

Manual J is actually not a measurement scale. Rather, it is the calculation of load (demand) that the house is making on the heating and air conditioning system. Using the illustration above, this is the caregiver to the very needy friend.

Those math gurus in the air conditioning/heating industry, who are trying to figure out what is the problem with the needy house, are taking into account many variables as to why the house is so hard to please.  Again, there are some people, who might be really ornery based on emotional ‘baggage’ they are carrying that we do not see. Just as these people need a psychiatrist to sort them out, the house needs a Manual J load calculation to sort it out.

The neediness of the house is influenced by location, orientation, climate, surfaces inside the house, as well as sweaty humans and what they are doing in there.

Do not become an enabler:  putting in the biggest system of heating and cooling in a house will not solve all its problems any more than giving a spoiled person everything they want will make them satisfied.

An oversized system will cool too quickly and cycle off without running long enough to reduce the humidity.  This leaves the house cold and clammy. The constant short bursts of ons and offs will drive you nuts. O.K. you are saving money on energy, but your house is ‘owning’ you.

( The latest theory is to do a manual J calculation and then actually buy a unit 20% under the recommended rating).

Air changes per hour or ‘the breath of life’

‘Air changes per hour’ is actually the breath of life in your house’.  It is a measurement scale and the government has guidelines. A house too tightly wrapped to breath correctly will negatively impact the occupants. (Incidentally, a person, ’too tightly wrapped to breath correctly’ is also a negative and stressed individual). No less than 4 air changes per hour are allowed in a residential building.

But, hey, what if you are working out in your home, or singing or otherwise breathing more? Same with the house, it must breathe more too. More exchanges per hour are needed.

That is why federal guidelines have different requirements for different places:

Some interesting guidelines:  30 air exchanges per hour for bars. (lots of hot air in there).  8 to 15 air exchanges per hour for churches (I guess depending on whether they’re  ‘rollin’ or ‘sittn’ ).  40 for kitchens…you get the picture.

By now you are also seeing that there is a happy interplay between how much a house needs to breath but how much it does not need to leak. Air is good but not too much air. Sort of like conversation.

The R-Value or think: ‘Potholder”

The amount of insulation your house is carrying to protect it from the elements is the R-Value. Fur, blubber, haybales…all of them have an R-value. The R-value is simply how impervious to heat and cold transfer the material is.  If you grab a hot pot, the heat goes instantly into your hand, there was no resistance to the heat, you get burned. No R-Value. Use a cotton crocheted potholder made by your 5 year old granddaughter and you might have 10 seconds before you are burned. That potholder has a higher R-value.  Use one of those shiny, ‘yuppie’ mitts from Bed, Bath and Beyond and you could probably walk twice around your house and to the neighbor’s without feeling the heat.  That mitt has a very high R-value.

The R-Value is calculated per inch of thickness of the material. That is why it is better to have outside walls made of 2×6” studs, than 2X4” studs, you can put in 6 inches of whatever material you choose. (Blubber might be hard to work with.)

Note for misers;   If you think like me, you are thinking, ‘if I take a six inch thick bat of fiberglass rated at R19 but then squish it down and pack in a second strip of R-19 on top of that, I should get an R-38 insulation in my wall.’ WOW, and cheap at that!  Think again, the math doesn’t work. Why? Because you squished both strips from 6” down to 3” and R-value is based on thickness. You still have only 6” of the material. You didn’t double the R-value. But you did just increase cost of insulation.

The interplay: ‘talk the talk’

The R-value of the exterior walls as well as ceiling and floor should be determined first. This will affect the HERS index score, (the neediness). This number will influence the calculations of the Manual J and therefore what kind of heating and cooling should be put in the house to meet the need.  Air exchange needs to be provided, either by mechanical or opening a window, and R-value will affect this too.

But now comes another variable ouch!! Without affecting the heat and cool transfer through a wall, we do want it to breathe air and vapor in and out depending on many factors. So now we get into thermal barriers and vapor barriers…

But this blog is way too long and my brain is fried. More later.


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