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Energy Efficiency definition including actual use of the building

asked 2018-05-28 04:45:28 -0600

AadriaanW gravatar image

updated 2021-11-20 12:41:06 -0600

I am part of a group of architects and engineers that is thinking about a definition for a Real Energy Neutral Building definition. As many of you will know there are many different definitions and adding one to the list might lead to more confusion, so we try to have a holistic approach and find a definition that might incorporate several other definitions as well. This is still in a concept phase, and it is more a philosophical discussion than a technical one. Nevertheless I would appreciate input for what I have written below. Perhaps someone else has already thought of it and it would be a waste to re-invent the wheel.

Of course many will say that energy neutral means that the energy bill at the end of the year is 0, or something similar. But if a building is not used, or only partly used, it does not or not fully serve its purpose whilst the energy consumption can come pretty close to that 0, especially with on-site energy generation. We started to think about how the use of the building can be encouraged more whilst still saying it is (close to) an Energy Neutral Building.

Basically the idea is this: The "Definition" is a standardized method for determining the energy efficiency indicator based on the real energy use of the building. The energy efficiency is not just defined as energy consumption per m2/ft2 but it also incorporates the amount of time the building is actually used. In my opinion an unused building is simply a large and expensive piece of art with no real purpose other than to look pretty (or not, depending on your taste). If we take the amount of hours that a building is used for normal office hours and use that as a baseline (lets say 65 hours/m2 per year) a building with an energy consumption of 1,386,000 kWh and floor area of 12.000 m2 will have an energy use intensity of 115,5 kWh/m2. This would be the traditional EUI. But if we incorporate the use of the building as a correction factor we might see a different picture. Let's say the total number of hours the building is used is 100h/m2/year. The same energy use intensity would be different: 115.5 / (100/65) = 75 kwh/m2/year. In some simulations we have run we could see the total energy consumption going up when buildings were used more intensively, but the "Definition" that we used showed that it dropped or stayed the same.

This may be quite different from the way we are used to measure the EUI, but with this "Definition" the energy is not just used for creating a healthy/comfortable indoor climate but also incorporates how effectively we actually use the building. It also uses the actual data of the building and the way it is used. It is therefor not exactly a simulation methodology, but I think the people ... (more)

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Your use of commas and periods for the numbers you are using for an example seem inconsistent. And could you explain the units 65 hours/m2 per year. I'm not sure how the m2 is being used.

JasonGlazer gravatar image JasonGlazer  ( 2018-05-29 06:38:20 -0600 )edit

Apologies for the confusion. The 65 hours/m2 per year is defined by taking 2.600 hours per year per person, divided over an average of 40/m2 of floor area per person. With this definition decreasing the floor area (increasing the amount of people) or having longer working hours will show a more utilized building and as such a lower EUI in this new format.

AadriaanW gravatar image AadriaanW  ( 2018-05-29 14:48:52 -0600 )edit

What is the driving force behind creating this definition? You divisors may change quite drastically depending on the aim. Are you more interested in energy cost? cost per person? carbon emissions? personal comfort? GDP/economic productivity per energy used? transmission/grid intensity? These are different goals that would suggest different metrics. In particular, annual zero energy is becoming obsolete as a goal with more renewables on the grid; it is helpful to use more energy when there is an oversupply, and curtail use at peak times. An aggregate annual value doesn't capture this.

mdahlhausen gravatar image mdahlhausen  ( 2018-05-29 18:07:33 -0600 )edit

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answered 2018-05-29 07:05:57 -0600

Many reports related to the general topic of how to define zero energy buildings have been published. NREL seems to have spent a lot of time on the topic with:

A Common Definition for Zero Energy Building https://www.energy.gov/sites/prod/fil...

Zero Energy Buildings: A Critical Look at the Definition https://www.nrel.gov/docs/fy06osti/39...

Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options https://www.nrel.gov/docs/fy10osti/44...

I think your idea is interesting since it accounts for the utilization of a building and rewards buildings that are utilized more but I think the difficulty you would find is how to clearly define the number of hours a building is used. That is often a soft number. An office building can say that it is open 6am to 8pm even though most employees only work 9am to 5pm. Someone will work until 8pm, does that mean the building is really being utilized all those extra hours? How about an apartment building? Does it have 24 hour operation even though for many hours of the day only a fraction of the peak number of occupants are present. I think you will find that almost no buildings have a clearly defined hours of occupancy.

Further, for rating purposes, the owner of the building will argue that the building is open and available to be used for many more hours than it might be just because the want to lower this metric. Allowing the owner to have direct control over part of the metric, other than energy use, seems like it is fraught with problems.

Overall, I think this approach has some potential but defining the number of hours is going to be difficult.

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answered 2018-05-29 15:00:29 -0600

AadriaanW gravatar image

Thank you for the reports! I will have a look at them and see if there are any similarities. It would indeed be a challenge to have the right hours. Right now we only focus on non-residential, non-industry buildings. The idea now is that we look at the hours the building is being used with the option of going deeper and looking at the number of people as well. If you have a security access card system the access to the building can already be defined much easier. It is also our goal to set it up as a certification system where the building owner or user will have to live up to certain criteria preventing "cheating" when the building is used.

Another way to verify if people are present is if the HVAC systems are used with certain setpoints, or with a certain air quality. In this case the residential part could be made more automatised and has (I think) the best chance of coming close to reality.

In the early and late hours less people will be present yes, but this would also be seen in the energy consumption. HVAC and lighting will be on, but the cooling loads will be less because of less people and in most if not all climate zones also a lower outdoor air termperature. Of course in winter the energy consumption will be higher, but this is also the reality right?

Again, this is just a concept that is far from finished. The goal is to make building owners aware of how efficient their building is being used in relation to the real and anticipated energy consumption and also as a verification of a certain ambition that has been set when the building was designed and built, but with leaving room for a different use for the building than was initially assumed.

Here in the Netherlands our governmental energy calculation method is static and far from accurate. An assumption is made for all building types in usage and capacity etc. Building simulations are not uncommon for offices and the like, but they are also not common and definitely not standardized. I think that is part of the reason why this discussion has started, since the market is not used to calculating it in such detail as with simulations. Quite a shame really...

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Please use the add a comment feature for comments rather than the answer section.

MatthewSteen gravatar image MatthewSteen  ( 2018-05-29 15:56:24 -0600 )edit

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Asked: 2018-05-28 04:45:28 -0600

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Last updated: May 29 '18