Sustainable Zero-Energy Buildings

According to Denmark’s State of Green, 40% of Denmark’s CO2 emissions come from buildings and with the use of existing technologies it is possible that the renovation of existing buildings and the construction of energy-efficient new buildings could reduce energy consumption for heating by 80% – corresponding to 30% of the country’s total energy consumption. It’s no wonder why investing in sustainable buildings is an area Copenhagen intends to focus on as part of the city’s initiative to become carbon neutral by 2025. It by no means will be a small investment – the published Copenhagen 2025 climate plan estimates that sustainable new construction and retrofitting of existing buildings will require total investments of up to DKK 180 bn ($31.4 billion) up to 2025.

During the USM energy study tour of Denmark we were lucky enough to be able to observe first hand one of Denmark’s answers for ‘Green Growth’. We took a short city bus trip out of Copenhagen to the city of Birkerod to meet Christian who kindly gave us a tour of one of the Trelleborg zero-energy houses. The name “zero-energy house” can be a bit misleading, it’s not a house that doesn’t use any energy, it is a house that provides as much energy as it consumes. Perhaps a better name for the house would have been “net-zero energy”.

Visiting the zero-energy house in Birkerod, Denmark.

Christian giving us some information on the zero-energy Trelleborg House in Birkerod, Denmark.

Trelleborg is a Danish prefabricated house company with the stated goal of being a leader in the production and construction of energy efficient homes. Trelleborg was able to develop the zero-energy house by using existing technologies, such as insulation, air tightness, ventilation, energy-efficient heating systems and renewable energy sources such as solar energy. The most significant feature of the home that has the greatest impact on the home’s energy usage is the building envelope. Trelleborg zero-energy homes are constructed with a lot of quality insulation, high quality three-layer energy efficient windows, and a ventilation system with a counterflow heat exchanger that recovers 90% of heat in the exhaust-air. When utilized effectively a Trelleborg zero-energy house rarely requires direct heating when outside temperatures are above freezing. Trelleborg boasts that one of their homes provides energy performance 10 times better than the European average.

Trelleborg zero-energy house

The back-side of the Trelleborg zero-energy house, showing the solar panels on the roof.

While doing some research for this blog I was pleased to learn that Maine does have a company that is in the business of constructing new zero-energy homes. The company is called Island Carpentry and they are located on Georgetown Island in Midcoast Maine. One of their most recent projects is a zero-energy four-story apartment on Portland’s Cumberland Avenue and you can learn more about the details on their website

While zero-energy houses such as the ones manufactured by Trelleborg and Island Carpentry have been gaining popularity with today’s focus on minimizing global energy consumption they come with a hefty price tag which is indisputably the number one barrier as to why zero-energy homes have not taken off. The best sales pitch for trying to convince someone that the additional cost for an energy efficient home is worth while is to think of it like you are paying for all future energy upfront and therefore the overall cost of continued ownership will be lower and the initial investment will be recuperated in the form of energy savings over a number of years. Apparently people paid too much attention in school when learning about the time value of money and the idea that “a dollar today is worth more than a dollar in the future” because that sales pitch doesn’t appear to be working very effectively, at least in Maine.

So are these zero-energy or low-energy homes worth it? I decided to dig a little deeper into some of the pros and cons of purchasing a zero-energy house.

One of the most noted advantages of a zero-energy home as mentioned previously is the reduced total cost of ownership due to improved energy efficiency. Other advantages include that investments in energy savings are said to have relatively short pay back periods and by owning a sustainable building that produces as much energy as it consumes the building owners are protected from future energy price increases. Zero-energy homes are also known for being reliable and comfortable with better air quality due to the constant ventilation. It is most often more cost effective to implement energy saving techniques during new construction compared to an afterthought retrofit and if legislative restrictions and carbon emission taxes are in the future it may be better to proactively build now than expensively retrofit later. Then there are also the environmental benefits of reduced CO2 emission and energy consumption. It is also believed that living and working in sustainable buildings influences and inspires people to make more climate/carbon conscious decisions in other areas of their life.

The largest disadvantage to the zero-energy houses is that the initial costs are higher. There are also a limited number of designers/builders in Maine that build these homes so it makes shopping around less effective. As with any investment there is risk that you made a bad bet –new more efficient and affordable green technology could be developed in the future that will reduce renewable energy prices and lessen the value of the capital invested in the existing green technology, or worse – your job could get relocated and you have to move out of your new home before reaping the benefits. One of the cons that I found particularly interesting was that while the individual house may use an average of net zero energy over a year, it may demand energy at the time when peak demand for the grid occurs. In such a case, the capacity of the grid must still provide electricity to all loads. Therefore, a zero-energy house may not actually reduce the required power plant capacity. Also part of the energy efficiency of the house still comes down to occupant behavior. The energy used in a building can vary greatly depending on the behavior of its occupants. The acceptance of what temperature is considered comfortable varies widely along with varying levels of lighting and hot water needs, and the amount of miscellaneous electric devices used. Living green may take more than buying an expensive house, it will also require somewhat of a lifestyle change.

As with any major purchasing decision there are a number of advantages as well as disadvantages to consider before making an ultimate decision to buy. It is up to the individual to weight the items that are most important to them and this is one of the major areas where I think Mainers and Danes differ. Mainer’s and I think American’s in general don’t think green in the same sense that Danes do. Americans think money green when making large purchases such as building a new home and Danes are more likely to think environment green. This is probably why zero-energy homes are more successful in Denmark than in Maine.

As first time home buyers two years ago, my husband and I decided to design and build a home. I would like to think that if we were to build our home now after taking this energy study tour to Denmark and knowing what I know now that I would have designed it differently, but the truth is it probably wouldn’t be all that different. Maybe it’s because we are a couple of narrow-minded accountants but a lot of the design decisions that we made were money driven – even the ones that are better for the environment. We put in energy star appliances and light bulbs and have a high efficiency on-demand propane heater but those were relatively small investments and we did it all for the sole purpose of saving money on energy and heating bills. We did have a conversation about increasing the insulation and tightening up the house, which lead to a conversation about ventilation and heat exchangers, and then before we knew it we were out of our price range and had to back down. We wanted to feel like we were getting the most for our money and as a result we selfishly opted for a larger home instead of a more efficient one. I don’t think we are all that different from any other typical American.

If low or zero-energy houses are going to be embraced by the American public beyond the early-adopters and the wealthy then it might be necessary to adopt some market forces that will increase demand. Some ways to achieve this in the near term may be to offer more government incentives and tax credits, enforce a stricter building code which essentially takes the options out of the decision-making process, or significantly increase the price of the alternative conventional energy options that will make the zero energy investment worth-while. However, seeing as the economy is still somewhat fragile, the quick and dirty method for early implementation may not be the best answer. Increasing the cost of fossil fuels which could potentially make everything more expensive would greatly threaten the economy and economic growth. A better answer would be to make green energy so easy and affordable that everyone will want it and need to have it. What that means is that there needs to be more privately funded investments in R&D to innovate affordable and effective solutions for the future.

Works Cited

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4 Responses to Sustainable Zero-Energy Buildings

  1. CPF says:

    I have a Trelleborg home in VT and it is outstanding! We built it in 1987 and it is actually (or was) far less pre-fab than you would think. Two trailers and 7 or 8 guys showed up from Denmark and it was up in a few weeks. All in all it has been a great home and it is amazingly efficient. Thank you for this post, I am looking to do a project and find more in the USA, I know of another one in Guilford, CT.

  2. Russ says:

    Hi – I also have a Trellegorg home on the Maine coast that we use as a get-away, also built in ’87. It’s been fantastic! Clean and efficient design, it’s held up wonderfully, and as a second home I where I don’t want to spend down time doing repairs and paying bills, I have almost zero maintenance and extraordinarily low heating costs . The place is exceptionally solid. Give a shout and we’ll compare notes.

  3. Ed Latson-Builder says:

    In 1985 (+/-) my wife and I stopped to visit a couple living in a Trelleborg home near Ellsworth, Maine. They were the dealer/importers for Trelleborg America. We were living in the Massachusetts Berkshires at the time and we discovered that Trelleborg was building a modest development in the Connecticut Berkshires. We stopped in to visit the job-site and got to talk with a number of the Danish carpenters—while they were snapping their pop-tops on their Tuborg beer at lunch time. The houses were very well thought out; made with extremely durable materials and all the shipping containers were filled with every last nail and screw for a completed house. I was dumbstruck at the time with the overall efficiencies of design, materials and workmanship. Hurrah to Danish hygge!!

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