Part 4 of my research: the homes I studied

Hi Everyone,

My last post in this series discussed some of the previously published works on net-zero and near net-zero homes. Today, I’m going to begin the process of describing the 20 homes that participated in my research.

I found roughly 60 net-zero designed or near net-zero designed homes in New England, back in the summer of 2011. I’m sure there were more, but not that many more.  I did a lot of internet searching, and also received a little help from NESEA, the Northeast Sustainable Energy Association, in publicizing my request for participants. Eventually, I had contact information for about 30 homeowners, most of whom agreed to join the project.  In the end, I had 10 net-zero homes, 9 near-net zero homes, and one control house (my own), for a total of 20.

The homes were scattered around New England, which is what I wanted. Though the six states that make up New England are relatively small in size, they make up for this in their diversity.  Thus, I had homes right on the coast of CT, where winters are relatively mild but so are the summers. I had homes in the foothills of the Green Mountains, ones in major cities, homes in the country and homes in suburbs. Here is a map:

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Part of the agreement with the homeowners was that I would never release their names or addresses.  Hence, I always refer to their letter designations, e.g., House A, House N, House R, etc.. There are three homes overlapping in the map above (A, B, and C), plus P & J overlap, too.

This set of homes, besides being geographically diverse, also varied in design and occupant characteristics–big time.  On one extreme, House O had 10,000 sq ft of finished floor area (FFA), while house G under 1000. House O was also the most expensive at $2 million dollars while House X cost only $170,000 to build. Note that building cost does not include the cost of the land/lot, just the house itself.  I’ll get much more into the costs and economics of these homes in later posts, but for now just realize that net-zero and near net-zero energy homes can come in all sizes and prices.

Most of the homes were single family, detached homes, though there were four (A, B, C and X) that were each half of a duplex.  Most were new construction, but two were full or deep energy retrofits (K and Z).  One was an apartment (W), and all were grid-tied except for House G.  The number of full time occupants ranged from 2 to 7.  The size of the photovoltaic systems ranged from 1.1 kW to a whopping (for a home) 14.4 kW.  Several homes also used solar thermal for hot water and/or space heating. One home, Q, had a PV system AND a wind turbine. Two homes did not have any PV system: House M had a large solar thermal system for heating both air and water, while House R had no on-site renewable energy system.

House R was our home. I picked it to be a “control” house for several reasons. First, it was built at about the same time as all the other homes (between 2008 and 2011). Second, it is an Energy Star certified home, meaning it is relatively energy efficient but still a few notches below the near and net-zero homes. Third, it would be easy to install energy monitors and temperature measuring devices (aka “data loggers”), since I obviously had complete access to the home. Finally, my wife and I do our best not to waste energy at home, so our habits were likely to be similar to those of the other owners.  All this would make a good apples to apples comparison for my research.  As you will see when I get to the results, the differences between our home’s performance and cost and the other homes’ are striking.  Here’s a photo of our home:

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So, remember House R is NOT a net-zero or near net-zero home, just a relatively new home built to be more energy efficient than a typical new home (it has a home energy rating system, HERS, score of 67, for those of you who are curious).

Unfortunately, I’m not going to be showing photos of any of the other homes, since I never asked permission from the owners to publish them on-line in a blog.  However, if you open up my complete thesis you will find photos of most of the homes inside (you can get to the thesis by going here: http://www.nhsolarconsulting.com, which is my “personal” webpage–not a business page).

There was also a large diversity in HVAC equipment in the homes, i.e., some used ground source heat pumps (GSHPs), aka geo thermal systems, for heating and/or cooling. Some used so-called mini-split air source heat pumps (ASHPs), while others relied on more conventional (but highly efficient) natural gas fired furnaces for heating and/or domestic hot water heating.  Here are a couple of charts that show this diversity:

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I think you get the picture (even without actual photos…) that these homes represented a wide range of sizes, costs, and systems. They also varied on construction type (traditional framed, double-walled, SIPs, etc.), number of bedrooms, finishes, size and types of electrical appliances, and so on.  This diversity was excellent, since it meant my research would expand beyond the relatively homogeneous homes from the previous works.

Next time, I’ll finish discussing the subject homes by describing what features they DID have in common, and then move on to my methodology for collecting my data.

Walter

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2 thoughts on “Part 4 of my research: the homes I studied

  1. Hi Walter, Brilliant! This is an exceptionally detailed assessment of the Energy Performance of net zero and near net zero homes. Congratulations. Have you received your Ph.D.?

    After downloading and reading parts of your study, I have a few questions regarding the Energy Modeling software that was actually used to design the home vs. its measured outcome. I am very curious to know which modeling software has been able to predict within 5% of the normalized performance of the home. Might you have some time to discuss?

    Best David

    David Burdick

    Professional Engineering (PE) Mechanical License #26503 WI Certified Energy Manager (CEM) License #19102 Certified Passive House Consultant (CPHC) License #1397 Leadership in Energy and Environmental Design – Green Associate (LEED GA), Member # 10814512 Sustainable Home Professional # 201212-5383

    Earth Harmony Habitats™ 4917 SE Aldercrest Rd. Portland, Oregon 97222-4757

    Tel & Cell: (+1) 503 654 2070 email: David@earthharmonyhabitats.org website: http://www.earthharmonyhabitats.org

    • Thanks for the compliment, David. Yes, I completed my PhD in Energy Engineering in February of this year.
      Generally, I wanted to know if homes designed to be net-zero would achieve net-zero, even in cold New England. I asked my homeowners to simply tell me what the design goal of their homes were–zero or near net-zero. I somewhat reluctantly entered the world of energy modeling, since from some prior experience, I know that proving the validity or accuracy of an energy model could be the work of an entire Ph D just on its own…

      Initially I was going to model each house in EnergyGauge, ResRate, Energy10 or some other commercial modeling software, to get an estimate or prediction for their energy consumption. However, I quickly realized that I did not have nearly enough details on each home’s specifications to really utilize any of them. (You see, I shied away from requiring complete specifications (e.g., construction drawings, schedules, etc.) because I did not want to discourage or dissuade any homeowners from participating.) Ultimately I included the output of just 5 homes from either ResRate or EnergyGauge (in table 59), but never included those predictions in any of my analysis. I simply had to make too many assumptions to fill in for missing inputs just to get an output from those programs.

      Stymied, I then,asked the homeowners to provide me–if they had them–with their architects’ or engineers’ modeling predictions (in kWh/year) for total energy consumption. These professionals certainly had access to all the necessary inputs for whatever program they were using. Only 9 out of the 20 provided me with that info, so not a very large sample. I included theses 9 homeowner-provided predictions in several figures and compared them with my own modeling results. You can go to pages 62 – 63 for my explanation on why I decided to create my own models, or wait for a future post.

      So, I’m not sure I can tell you which energy modeling software came within 5% of predicted. From all the owner-influenced variation in energy usage, plus weather variation, plus equipment malfunctions, plus any (unknown to me) changes in specifications between design and as-built, if any of the original 9 predictions were within 5% of actual consumption, I’d say that is due more to chance than the program’s performance vs. any other energy modeling program. Remember, all I had was the model output–not the program itself nor the exact inputs that were used in the models. You’ll find what I conclude about energy modeling in general on page 316 of my thesis.

      Sorry I could not answer your question more directly!

      Walter

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