ENERGY PERFORMANCE OF PASSIVE HOUSE ENVELOPE

The passive house is defined by high energy standards and each of its characteristic effects differently on the overall energy saving. Nowadays modern technologies allow engineers to improve thermodynamic performance of the external enclosure using high thermal resistances for the wall, the roof and well insulated windows with low-e triple glazed. On the other hand these structures use some technologies to benefit from the natural resource like geothermal energy to capture heat from and/or dissipate heat to the ground and other used natural process that help trapping the heat from the sun to decrease the heating loads like the sunrooms. The paper presents some of the passive house technologies with focusing on the building enclosure and its effect on the general energy performance of the passive house in Chicago climate through investigating the results of energy balance at each element of the enclosure and its thermal characteristic. A comparison simulation between a typical building and a passive house in Chicago is performed to find out the building enclosure contribution to the overall energy saving for a passive house using eQUEST.

The high performance enclosure can help the passive house building to approach nearly zero-energy demand. Despite the fact that ASHREA Standard 90.1 has been a benchmark for commercial building energy codes in the United States, PHIUS standards seems to be more restrict to achieve the goal of energy efficient buildings. Increasing the thermal resistance of the envelope is an effective way to decrease the heat losses in the passive house and it mainly affects the heating loads during the cold months in Chicago. The saving in energy due to decreasing the heating loads was about 49% however this percent seems less when it is converted to cost. Since most of the heating systems in Chicago are operated by gas which has low prices relatively comparing to the electricity, the demand of more efficient building is increasing with the world will run out of fossil fuels, or it will become too expensive to retrieve those that remain. In addition to the calculated saving many characteristics of the passive house have been ignored in this study. There are many other standards that should be achieved in order to meet the criteria of a passive house like building orientation and how it is related to the window locations, also using shading devices and the interior configuration of the spaces. The saving percent performed in this paper does not include the energy generated by some of the passive house technologies such as the ground heat exchanger which may add more saving in energy. Therefore other research should achieve separate simulation for these systems in order to find their contribution in the energy efficiency. The paper discussed the air infiltration in the passive house and the air quality problem in it and how it should be provided with an appropriate vapor barrier and a mechanical, balanced ventilation system with heat recovery, which assures superior air-quality and comfort by continually exchanging the indoor air.

Current Energy Codes and Office Renovations

 In my research paper, ASHRAE 90.1-2010 and IECC 2012 were compared in the context of Chicago urban tenant fit-outs.  IECC 2012 was concluded to be the better option under the specific case study of a downtown Chicago office building with a 30,000 SF floor plate, steel frame, and infill window wall with 47% glazing.  Envelope, Electrical, and Mechanical sections of each code were compared to see what the baseline codes call for to reduce the waste in Office building energy usage.

 

 

In terms of the envelope, the area was fixed (8,030 SF) and the design temperature differences were also fixed (summer=18F and winter=82F).  This left the U-value as a variable for the heat flow equation.  ASHRAE calls for 0.45 U and IECC calls for 0.38 U for glazing, which is the dominant envelope material for Offices.  This seemingly small change decrease in ASHRAE’s resistance leads to 4.8% more gains in the summer and 15.5% more losses in the winter.  Looking beyond glass at the total UA value, we get 1,434 btu/hrF (IECC) and 1,698 btu/hrF (ASHRAE).  Simply due to window U-value the ASHRAE assembly allows 13% more flow.  Lastly, in terms of infiltration, ASHARE allow more flow through the windows which brings in pollutants or unwanted air directly into the occupant’s breathing zone.

 

 

For Mechanical systems, we can estimate total loads for an office.  The total heat losses in the winter come to an average of 145,000 btu/hr between the codes.  Relatively speaking, the internal heat gains are greater than this when considering the people, lighting, and equipment gains of 186,000 btu/hr.  This leads to a net heat gain so the systems are cooling throughout the year.  For equipment efficiency, a packaged terminal air conditioner should have a 15.9 EER (IECC) and 19 EER (ASHRAE).  Here, ASHRAE will save 25% more energy on cooling the spaces.  For demand control ventilation, IECC call for the system when 25people per 1,000 SF are present.  This will create a more efficient space such as a conference room so that ventilation is only brought on if needed.  ASHRAE only calls for this control when 40people per 1,000 SF exist.

 

In terms of electrical controls, ASHRAE calls for 50% of the power receptacles to be switched off automatically either when not in use or after-hours.  Typically, in an office building the computers are the main energy user and they are plugged into the critical receptacles which stay on 24/7 to avoid data loss.  Due to this, the power auto-off requirement will not save much more energy than typical.  Monitors, appliances, and some others may be turned off after-hours.  As for lighting controls, IECC has slightly better lighting power density (LPD) numbers.  LIghting is the number one user of energy in office buildings.  They are densely spaced and on very often.  Both codes maximize the use of daylighting through various controls.

LEED vs cost and energy

Over the past few years there have been discussions about green construction and making buildings more efficient.  Leadership in Energy and Environmental Design (LEED) was devised to keep track and rate how efficient a building is. When LEED came out in 1998, many people were not sure and questioned whether this new way of building would actually work.  The best economical way to see how much energy a building will use is to model it on a computer.  The accuracy of modeling energy consumption can vary depending on the level of detail.  The more detail the more expensive it will be and depending on which software is used it may not be as accurate as one might think.  Looking at the image below, we can also see that LEED buildings pretty much all group together. There are a few that perform better than expected and a few worse, but majority are 20-30% efficient.

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An article by John H. Scofield looked into seeing if LEED buildings actually do save a significant energy.  In a simple answer, “not really.”  The majority of LEED-certified offices are using less energy than their comparable non-LEED offices, but they only contribute about 10%. A small handful of big buildings contribute a lot more. This can be seen in the graph below. Big buildings account for majority of the consumption and smaller LEED buildings do little to curve the energy consumption.

leed-vs-cost

LEED is also full of regulations that can at time hurt and but restrictions on a project. A new residence hall at Carnegie Mellon University was built as LEED silver and everything was documented to see if it was worth it. At the end:

  • Cost $347,118 more (3% extra in construction cost)
    • 12% of the budget was spent on recycled material  and  9% on sustainable site
    • Larges  increase cost was forced air ventilation ($100,000)
    • Commissioning cost ($65,000)
    • Labor spent on compiling LEED data ($61,000)
  • 20.3% more energy efficient compared to similar residence hall, but uses 12% more energy compared to residence hall with heat recovery system. This increase in energy costs due to:
    • Required greater fresh outdoor air ventilation
    • Resulted in greater heating and cooling loads as well larger electrical fans
    • Green power costs more (LEED green power contract)

    case study 1

LEED seems like it is in the right direction, but with all of its regulations it seems to be doing more harm than good. LEED keeps being updated with new regulations, but these regulations are just being broadened to encompass more topics. LEED covers too many topics from site sustainability to construction, but energy only accounts for one small section. Parts of LEED seem to be working and other parts need to be looked at more closely. LEED needs to be cut back a bit and get revised to focus on more critical areas.

Adapts and Improvements on Natural Air Ventilation

My semester research project was taking a look into what is natural air ventilation and how it is used. I simply define natural air ventilation as simply just bringing outside air into the building. However wiki would define it out more as “natural ventilation is the process of supplying and removing air through an indoor space without using mechanical systems…wind-driven ventilation and buoyancy-driven ventilation.” The two systems mentioned from wiki have two key ways to design for this ventilation:

  • Wind-driven ventilation: is based on the amount of wind going through the building, if there is too much wind in the space could cause a wind-tunnel effect and would not be pleasant for the users.
  • Bouyancy-driven ventilation: is the air density difference between indoor to outdoor air or differences between rooms. This follows the concept of hot air rises and cool air falls due to the density. Stack effect or the chimney effect is used to achieve this system.

The paper also looked into ASHRAE 55 Standard: Thermal Environment Conditions for Human Occupancy to see how they define natural ventilation. This standard is a base line and gives guidelines to how base thermal comfort in spaces, but there is a few undefined areas that could leave designers confused.  Listed are a few key points.

  • Does not take into account specific locations
  • User’s response to their environments (age, health, activities, gender)
  • Thermal comfort based on a 80%  acceptable, 20% dissatisfaction based from Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD)
  • Urban conditions (pollution, security)
  • If you use any mechanical system, then you do not have natural ventilation

I searched for two case studies in the Chicago region to show the diversity of using natural ventilation with mechanical “hybrid” systems. Both are set in private universities and have similar square footage, programs, and only a year apart, but you can see with money, a proper design team, and support can develop these integrated systems. Since the perfect conditions for acceptable natural air ventilation only happen 50-60 days out of the year, the use of mechanical system to help support the natural ventilation in the off periods ,winter and summer months, is needed.

Case Study I: Harm A. Weber Academic Center at Judson University in Elgin, IL (4 story, 88,000sf). The Academic Center opened in 2007 and is one of the first in the region, especially in Chicago.

Image[1]Image[2]

Design methods:

  • Central lightwell acts like the stack/chimney effect
  • Night Flushing
  • Integrated Photo-voltaic (PV)
  • Thermal Massing

Case Study II: Richard J. Klarcheck Information Commons at Loyola University (north side campus) in Chicago, IL (4 story, 70,000sf). Opened in 2008 had one key goal in mind for this new building, a transparent effect to be able to see Lake Michigan.

Image[3]Image[4]

Design methods:

  • Double-Skin Façade (west wall for the stack effect)
  • Night Flushing
  • Radiant ceiling (for cooling)
  • Thermal Massing
  • Automated shading system

There is no wrong or right answer when it comes to natural air ventilation when it comes to the guidelines engineers have. This is not a new technology and is climate and urban sensitive on locations. When it comes to challenging standards or pushing the limits, there must be a good team (architects, multi-field engineers, stakeholders, etc.) to develop the proper combination of systems for the building. After a couple of years if the building is not performing to expectation there needs to be flexibility to the design since a lot of estimation/trial and error occur when dealing with natural air ventilation.

Sources:

[1] http://www.shalesmcnutt.com/projects/education/judson-university-harm-a-weber-academic-center/

[2] Kaiser, Keelan P., and David M. Ogoli, Ph.D, (2010) “The Harm A. Weber Academic Center

and the Greening of Judson University.” Judson University, 1-12.

[3] Image from author

[4] District Energy by Elara

Light conditions and window position

When striving for net zero buildings one of the important challenges is to reduce the energy consumption due to artificial lighting. Buildings have to be designed to utilize natural daylight as a replacement for artificial lighting. In order to do so window type and position are important factors that have to be considered.

The lighting software Relux makes is possible to predict how light from windows will be distributed throughout a room. The software calculates light distribution based on parameters such as location, sky conditions, room size, window size, window placement, reflectivity of surfaces etc. It turns out that how the window is placed very much determines how well the light is spread throughout the room. Just look at these three illustrations.

 

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All the illustrations represent an office room located in Chicago. The simulations are set to represent cloudy weather, June 1st at noon. Besides positioning of the window all other parameter are the same.

The first illustration represents a window placed in a high position, close to the ceiling. The second represents a window placed on the middle of the wall and the last one represents a window placed close to the floor. We clearly see that windows placed on the upper part of the wall are much more capable of distributing light deep into the room.  This means that allowing for windows to go all the way to the ceiling can potentially reduce the need for artificial lighting. 

LEED vs. Energy Efficiency: A Close look into LEED-Certified Building’s Energy Efficiency Data

In 2000 the Leadership in Energy and Environmental Design (LEED) rating system for building energy efficiency was launched by the United States Green Building Council (USGBC). LEED grew fast in popularity and soon it became commonly known as the leading “green energy/building” rating system. Perhaps too fast as little performance data has ever being available to confirm this allegation.

To ease the controversy, in 2006 the USGBC hired the New Building Institute (NBI) with support of the U.S. Environmental Protection Agency to generate a report on the LEED certified building energy efficiency performance thus far. The final report was published in March 2008 and concluded that: on average, LEED certifications energy use was 25-30% better than the national average (Frankel & Turner, 2008).

The New Buildings Institute Final Report

To complete the United States Green Building Council’s (USGBC) LEED study request, the New Building Institute asked all LEED-New Constriction version 2.0 certified building’s owners to submit at least a full year measured post-occupancy energy usage data for the entire LEED project. Of the eligible 552 projects only 121 (22%) contributed with their results. With the data collected from the owners, the NBI was able to validate the LEED rating system through the completion of three unrelated studies. The first assessment, and least accurate, assessed the different Energy Use Intensity (EUI) values between LEED and non-LEED buildings. The second study evaluated the Energy Star Rating of LEED buildings vs. Non-LEED. The last strategy compared the post-occupancy measured energy data to the initial modelled energy used expectations. According to the NBI the results show that LEED certified projects “…average substantial energy performance improvement over non-LEED building stock…” (Frankel & Turner, 2008).

1.   Energy Use Intensity (EUI) of LEED and national building stock according to building type.

On their first study, the MBI developed a method for paring each LEED building with one of similar characteristics from the 5215 sampled buildings analyzed on the Commercial Building Energy Consumption Survey (CBECS), a quadrennial survey of building energy performance directed by the U.S. Energy Information Administration (Birt, Mancini, & Newsham, 2009).

The New Building Institute report provided a full year of measured post-occupancy energy usage data for each of a 100 LEED certified buildings. For each one the total Energy Use Intensity (EUI) measured in KBtu/ft2/yr was derived from the sum of the total purchased energy of all fuel types (available for only 71 of the buildings). Later on, this was then compared to the initial baseline and design models in LEED submittals (Frankel & Turner, 2008).

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Figure 1:
EUI (KBtu/ft2) Distribution (Frankel & Turner, 2008).

Figure 1 distributes the results by LEED certification level and displays the Commercial Building’s EUI (KBtu/ft2/yr) for all the 100 LEED-New Construction. The median measured EUI was 69 KBtu/ft2, 24% lower than that of the CBECS national average which was measured at 91 KBtu/ft2. For the most common type: office spaces, LEED averaged a EUI of 33% below CBECS. Additionally, gold and platinum buildings shows a 50% energy saving than that of the CBECS office average. This graph omits the 21 buildings from the study with a median EUI of 238 KBtu/ft2; the NBI chose to eliminate them because these activity types (data centers, supermarkets, and labs) contain a very high energy activity levels driven by constant changing occupancy, and making their analysis more complex (Frankel & Turner, 2008).

2.   Energy Star ratings of LEED buildings

The U.S. Environmental Protection Agency’s (EPA) Energy Star program rates building’s energy use in relation to existing national building stock. The pairing is based primarily on building’s activity type, and secondarily on their location’s temperature, schedule, and occupancy respectively. The average Energy Star rating of the national building stock was 50, compared to a median rating of 68 for the LEED buildings. Figure 2 shows that one quarter of LEED certified buildings had ratings below 50, meaning they used more energy than average for comparable existing building stock (Frankel & Turner, 2008).

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Figure 2:
Energy Star Rating of LEED vs. National Building Stock (Frankel & Turner, 2008).

3.  Post-occupancy measurements vs. Initial design modelled energy used expectations.

Measured energy savings for the buildings in this study (Figure 3) average 28% compared to the energy cost budget (ECB) baselines, close to the average 25% savings predicted by energy modeling in the LEED submittals.

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Figure 3:
 Measured versus Proposed EUIs in KBtu/ft2 savings (Frankel & Turner, 2008).

At the extreme, several buildings use more energy than the projected code baseline modeling, as shown in the comparison of measured vs. estimated savings in Figure 5. The NBI justified this degree of scatter by suggesting the need for improvement in the accuracy of energy use prediction on an individual project basis (Frankel & Turner, 2008).

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Figure 4:
 Measured vs. Proposed Savings Percentages (Frankel & Turner, 2008)

Discussion of the Analysis

There is far too many flaws on the NBI’s analysis:

  • Biased results by exclusively gathering data from the LEED certified building owners.
  • Uneven results due to the comparison of two different metrics of central tendency: the median EUIof the LEED buildings to the mean EUI of all US commercial buildings.
  • NBI delivery chose to ignore the data from 21 LEED buildings with the highest EUI such as data centers, labs, and supermarkets by claiming that their analysis required more complexity and therefore only focused on the remaining 100 medium energy use buildings office buildings only.
  • Platinum signifies the maximum energy saving point system in the LEED ranking, yet the NBI study only included 2 LEED platinum buildings.
  • Failed to create a successful subgroup of non-LEED building with which to compare their LEED certified building data, and therefore failed to accurately match all LEED buildings with CBECS matches.
  • Little account between the two datasets regarding climate zone, building size or age.
  • Failed to appropriately weight for building size in calculating average LEED energy utilization intensities (EUI).
  • Focused on site energy rather than primary or source energy.

In conclusion, all of these factors raise a considerable amount of questions regarding the credibility of the LEED building rating systems. Further work needs to be done to define the authenticity of the LEED certification system.

References

Frankel, M., Turner, C. (2008). Energy Performance of LEED for New Construction Buildings-Final Report. New Buildings Institute, White Salmon, WA. Retrieved from https://wiki.umn.edu/pub/PA5721_Building_Policy/WebHome/LEEDENERGYSTAR_STUDY.pdf

Leite, F., Stoppel, C. M. (2013). Evaluating building energy model performance of LEED buildings: Identifying potential sources of error through aggregate analysis, Energy and Buildings, 65, 185-196. Retrieved from  http://www.sciencedirect.com/science/article/pii/S0378778813002521

Pérez-Lombard, L., Ortiz, J., Pout, C. (2008). A Review on Buildings Energy Consumption Information, Energy and Buildings, 40 (3), 394-398. Retrieved from http://www.sciencedirect.com/science/article/pii/S0378778807001016

Scofield, J. H. (2009). Do LEED-certified buildings save energy? Not really…. Energy and Buildings, 41(12), 1386-1390. Retrieved from http://www.sciencedirect.com/science/article/pii/S037877880900187X

 

 

 

Phase Change Materials in building science

A new innovative type of material is the PCM. Indeed, one of the advantage is their ability to store heat and release it when there is demand. This is really useful to be able to control the release of heat in order to take advantages from solar heat which is uncontinuous. PCMs are able to store the calories and release it by changing from one state to another depending on the temperature conditions without it affects the external temperature of PCM. The most interesting point about them is that this type of material can store  3 to 4 times more than traditional construction materials for the same thickness by increasing the building inertia.

In this project, I have introduce the concept of phase change materials in order to consider their performance in the construction field. In a second part, I have tried to simulate the efficiency of gypsum plasterboards with microencapsulated PCMs with the energy modeling software IES-VE.

PCMs are a type of material that enables thermal energy storage, heat or cold. One important fact is that it has to be a reversible melting/freezing cycle in order to be able to released the stored energy. The physical process in this case is latent heat because of the phase change. In this paper, I have focused on solid-liquid PCMs. For this type, the phase melting/solidifying can store a large amount of heat or cold. The advantages are the possibilities to find such PCMs with the following characteristics during the phase change: small volume change, small pressure change, constant temperature.

PCMs can be microencapsulated or macroencapsulated in order to prevent leakage of the liquid during the melting phase in other materials. There are also three types of PCMs: organic, inorganic, eutectic.

We are now aware that energy storage in building envelopes can be enhanced by the utilization of PCMs. They can fulfill two functions: thermal energy storage unit and element of construction. PCMs by increasing the thermal inertia can improve thermal comfort in summer as well as in winter.

An application of PCMs in building science that I describe in greater details in my paper can be the use of them in windows. In fact, a layer of PCM can be inserted in the glazing system and then improves its performances b absorbing solar radiation, reducing the cooling and heating demands, and enabling the daylight to be enjoyed inside of the building. There is an example of such glazing unit in this publication (http://www.sciencedirect.com/science/article/pii/S221260901300023X). This study deals with a four-pane glazed system with the insertion of a PCM layer and also a smart layer that regulate the solar transmittance. They are taking advantages of the transparent even translucent aspect of paraffin as PCM.

vertical section of four pane glass

I also describe the application of PCMs in walls and the possibility to simulate it on energy simulation software such as IES-VE.