Numbers

I recently gave a presentation to the Super Insulation class at Yestermorrow Design/Build School about building and living in our house. This presented a convenient opportunity for me to take stock of the building process, consider our experience living in the house so far, and to put together some performance numbers. We've been in the house just under two years and have established a track record for firewood consumption and are starting to get some reliable numbers on our propane and electric costs.

When our home was completed Efficiency Vermont (the state energy conservation organization) tested and evaluated our house for energy performance and determined a HERS number, which was presented as a part of their evaluation. HERS stands for Home Energy Rating System and is the standard methodology for comparing performance across buildings and regions. Many factors go into the rating system, including air-tightness, window performance, efficiency of the appliances, lighting and heating systems, as well as design specs like insulation R-Values and so on. The rating is adjusted for climatic conditions in a given location.

This is a generic chart showing the HERS rating scale. The "This Home 65" has nothing to do with our home.

In the above chart, 100 equals the energy use of a new home built to conventional standards in 2006. This is used as a base line by which to evaluate the spectrum of performance across buildings.  A rating of zero means the house requires no energy at all, while a rating over 100 means the house is sub-par in relation to current norms.

Our home earned a HERS rating of 38, which is a "5 star +" in the star rating shown below.  The scale somewhat curiously goes from 1-5 stars and then has a + category.  (Maybe they needed to add a new category as more efficient homes are being built -- I don't know.)

The HERS rating laid out estimated energy use predictions for our home as follows (calculated in 2011):  

             26.6 MMBtu heat  $990

             10.1 MMBtu hot water  $375

             17.9 MMBtu lights & appliances  $704

             HERS estimated annual energy cost:   $2,188

Based on our actual usage, these are our costs:

           $100-$150/yr firewood

           $750 propane hot water/cooking

           $768 electric

           Our actual annual energy cost:   $1,668

In the nearly two years we've been living in the house, we have only heated by wood. There is the radiant system in place should we ever choose to use it, but for now we like heating by wood; it's easy and feels good.

Although we know from experience that our heating expenses are tiny, it is useful to see them laid out together with the other home energy requirements. We plumbed the house in preparation for installing a solar hot water system, and seeing these numbers is a good motivator for costing out the completion of that project. It would feel good to bring the hot water energy numbers down. 

A tale of two bulbs

A standard "Edison-base" lamp mount on the left and a "pin-base" lamp holder on the right.

Today we had our final visit from Efficiency Vermont which is the organization that encourages, measures, and rewards efforts towards energy efficiency in Vermont businesses and homes. Although we were attentive to meeting the required standards put forth to qualify for Energy Star rating and meet the requirements for the various incentives, I must admit I didn't actually hone in on what we needed to do to meet these points until fairly late in the game, basically confident in the knowledge that the standards to which we were building would far and away exceed their minimums.

Lighting was the one area that I struggled a bit with. In order to meet the standards set for our home we needed to have a minimum of 10 pin-based light fixtures in main living areas. "Pin-based" means what it implies, and ensures that the only lights that will work in it are florescent bulbs, guaranteeing reduced electrical consumption because you can't just throw in an incandescent bulb if you feel like it.

Early on Nancy and I went to a couple of lighting stores with "pin-based" fixtures in mind to look at the selection and were quite underwhelmed. I would say that maybe 1 or 2 percent of the available fixtures were of this type, usually housed in some neglected back alcove. As long time readers will recall, soon after this experience I became fixated on building my own light fixtures and discovered that I could build almost any light fixture with a pin-base, and so many of the lamps throughout the house now feature this type of lamp base.

Additionally, we purchased some LED recessed down-lights for the living room and a series of mini-florescent bulb-fixture combinations that are mounted in the track over our counters in the kitchen.

In advance of the visit from Efficiency Vermont I knew we were in pretty good shape, but I was a little uncertain if groups of lights would count as "a light" or as individual units, so I made sure we had the required minimum, even by conservative measures.

In the end we passed the needed minimums just fine. The irony is that we would be using mostly florescents even if we weren't incentivized to do so and the light bulbs that fit pin-based lamps are actually more expensive than the Edison-based florescents that you frequently see for sale.

The expectation is that in a few years the pin-based requirement will be outdated because you will not be able to buy incandescents any longer, so there will be no need to require a special mounting base. I suspect that as the pin-based bulbs die out I will rebuild the fixtures so that we only need to have one type of bulb on hand.

You might be interested to know that we expect to receive somewhere in the neighborhood of $3000 in various incentives, rebates, and rewards for meeting the required guidelines. We will also be given what is known as a HERS rating, which stands for Home Energy Rating System and is a standardized number that allows comparison with other buildings and buildings in other regions. More about this later.