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I guess you missed the part where I said "with 2 equally built houses".
The subject was which one is more energy efficent, not ins and outs of making one more efficient.
I don't give a rats ass about any rating system, I need to look at one thing, KW.
these homes are using the same exact construction techniques and materials to accomplish the ratings which are based on how much energy the homes are using. the HERS rating system and the energy star rating systems are not just construction standard rating systems, the energy star system is used on ANYTHING that uses electricity.
I design these homes for a living. We are consistently noticing that there is a definite threshold of what is efficient, and what is NOT efficient, smaller homes tend to fare worse than mid size homes in the ratings which is a VERY good way to gauge how efficient the home actually is.
The ratings also give an estimated pay based on your local power companies.
here is some information for you to read through to see why us professionals are using these two systems to rate new and existing construction
What is the HERS Index? : ENERGY STAR (http://www.energystar.gov/index.cfm?c=bldrs_lenders_raters.nh_HERS - broken link)
a net 0 house uses no grid power at ALL, while a hers rated house of 100 adheres to the 2006 IECC (energy codes). A home that falls under 80 is energy star certified and the dependency gets less the lower the number is.
not necessarily. We are noticing a trend when trying to get our HERS and energy star ratings on some of our designs, the larger homes start out at a MUCH better energy rating than the smaller ones, the large homes are also easier to get numbers down in terms of HERS rating to achieve a 5 star energy rated home. the smaller homes are VERY hard to get the points to get it down enough.
our 4500 sqft. homes are much cheaper to get down to a HERS rating of 10 which is very close to a NET Zero home than our 1700 sqft. homes.
Can you explain why this would be so? It does seem to fly in the face of the intuitive conclusion. Why does it take less energy for a larger house than a smaller one?
Can you explain why this would be so? It does seem to fly in the face of the intuitive conclusion. Why does it take less energy for a larger house than a smaller one?
I am still trying to work that one out myself. From what we have learned the more volume in the house the better it tends to do in the model analysis. as an example, we had a 6000sqft. home put into the software based on current insulation values, your standard forced air heating and cooling system really nothing special at all about the way the house is sealed, initially it hit an 80 on the HERS index which is energy star compliant right off the bat.
we just finished the model of a 1750 sqft home doing the same thing, of course the furnace and cooling systems were rated with less BTU's due to the lack of need for oversizing the system, it rated right off the bat at a 135 on the HERS index. I am still fighting tooth and nail to get the thing even down to 100 without using any "green" items like SIP panels, CIP block, geo thermal, or PV panels and it is just not getting there.
All of these numbers are based on the homes energy usage, the use of the materials gets washed out since the house is designed to last longer than a lifetime, and all wood used during construction will have regrown. (yes wood is a renewable resource)
Also the biggest factor in energy use is the people who are residing in the house.
My electric bill last month was $26. I live in a 930 square foot apartment built in the 70's.
A person can have the most efficient house in the world, but if they constantly leave things on and run the heck out of the AC with the windows open for fresh air, they are not accomplishing anything as far as energy conservation is concerned.
And again, I look at the final product which is KW used.
Also the biggest factor in energy use is the people who are residing in the house.
My electric bill last month was $26. I live in a 930 square foot apartment built in the 70's.
A person can have the most efficient house in the world, but if they constantly leave things on and run the heck out of the AC with the windows open for fresh air, they are not accomplishing anything as far as energy conservation is concerned.
And again, I look at the final product which is KW used.
yes a big factor is definatly the lifestyle of the person living in the house. The ratings do give a KW/year projected use if, and I say if the family living in the house are living is living within reason.
Another thing I forgot to add in my last post. The smaller houses do tend to fare much better at upgrades to items when it comes to gaining HERS points for the ratings. a PV array will drastically change how well a smaller house preforms over a large house. But homes constructed as they are using standard construction methods end with mid size homes doing better than very small to small homes in energy efficiency.
yes a big factor is definatly the lifestyle of the person living in the house. The ratings do give a KW/year projected use if, and I say if the family living in the house are living is living within reason.
Another thing I forgot to add in my last post. The smaller houses do tend to fare much better at upgrades to items when it comes to gaining HERS points for the ratings. a PV array will drastically change how well a smaller house preforms over a large house. But homes constructed as they are using standard construction methods end with mid size homes doing better than very small to small homes in energy efficiency.
Being a pathologically analytical person, this has me very curious. Is the 6000 sq ft house compared to the 1750 sq ft house got the same number of stories, more open areas, etc? Is it comparing a rabbit warren design with lots of rooms that obstruct air flow to large open spaces? Is it based on a per person energy use with the 6k house having more people to divideinto the total house energy use, thus getting a lower rating?
I would think that a rating system must use a basic model with assumptions on per person use of energy - otherwise you wouldn't be comparing how the structures fare, but rather on the wild-cards of personal behavior.
Being a pathologically analytical person, this has me very curious. Is the 6000 sq ft house compared to the 1750 sq ft house got the same number of stories, more open areas, etc? Is it comparing a rabbit warren design with lots of rooms that obstruct air flow to large open spaces? Is it based on a per person energy use with the 6k house having more people to divideinto the total house energy use, thus getting a lower rating?
I would think that a rating system must use a basic model with assumptions on per person use of energy - otherwise you wouldn't be comparing how the structures fare, but rather on the wild-cards of personal behavior.
It is hard to see how this works.
both are ranch style houses, of course the 6000 sqft home has more volume, and moves much more air through the structure. The model is based on the house only, not the occupants that may inhabit the structure.
since you are interested, here is a link to the site that provides the software. Of course you cannot download the rem/rate software unless you sign a lease with them, but it might have more information you could use
AEC - REM/Rate Home Energy Rating Tool (http://www.archenergy.com/products/rem/rem_rate/ - broken link) RESNET: Residential Energy Services Network | Setting the Standard for Quality
To be honest I do not know how it is making its calculations based on the information we plug into the software. We have been looking into since we have started using this software. We are just as supprised as you are lol.
This is really very interesting and a bit educational. Could the issue be the surface to volume ratio? I'm going to read up on your links.
that could definatly be part of it. There is also a wall to window ratio that is important to keep track of as well. You want 20% or less of your walls to have glazing (windows) within it. At 20% the numbers start to get bad very quickly.
the one thing that is extremely limited in the software in which I wish they would have spent more time developing is the orientation of the house to the lot. This does play a role in the efficiency of the house, but is not reflected that well in the software.
Last edited by Noahma; 06-20-2008 at 10:56 AM..
Reason: more info
After just sitting down with our HERS rater for a bit of time, I have to shift my position just a little. We went through the 1700sqft home again with a fine tooth comb, looked at every single aspect of the model and changed a few things. What we came up with was that the 1700 sqft home preformed much better than initially thought. It did not however preform better than the larger home with similar construction. It was just about on par, with the difference being 2 HERS points. Our 6000 sqft home rated at 80 and the ranch at 82. So I guess I have to humbly say that smaller homes and large homes are very close in efficiency out of the box using standard construction methods. The smaller home is more flexible when adding such things as PV arrays and other "Green" items. Adding the same size solar array to the 6000 sqft home did not change the initial numbers much, but with our small 1700 sqft home it dropped from 82 down to 62.
with the larger homes it seems to be more of an offset balance, it may use more energy to run the home, but if it uses it very efficiently you get the good ratings. Larger homes defiantly have less leeway than smaller homes that can afford to waste a bit of energy before the points start to shift from good to bad.
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