Illinois Institute of Technology Entering DOE Student Home Design Challenge

GE Zero Net Energy Home Model

Among 18 other universities, Illinois Institute of Technology will be participating in a challenge that exemplifies a commitment to building energy efficient designs. Student groups will collaborate and used acquired skills to model a home that meets or exceed the DOE Challenge Home National Program Requirements.

requirements

Students will be challenged to create homes that maximize energy efficiency, show a dedication to improve indoor air quality, and making homes zero net-energy ready. In an effort to improve the awareness of environmental concerns, the US DOE and Building America Program have created this competition to direct students to building practices that help improve our world.

There are many benefits to participating in this program. Among being primarily student led, groups will learn to work in a professional environment and offer real world experiences most courses could not. Also, success in the competition would create national recognition and create many career-opening opportunities for participating students.

The DOE Student Home Design competition alternates between the DOE Solar Decathlon competitions. The design competition offers students the opportunity to learn the design phase of the building process whereas the Solar Decathlon offers the opportunity to continue onto the construction phase. Our success in the Student Home Design competition could potentially vault us into the following Solar Decathlon.

Useful technical skills will involve knowledge of modeling software such as Revit as well as building energy software tools such as THERM, Umberto, etc. All majors encouraged to join. Contact Brent Stephens for more information or visit http://www.homeinnovation.com/DOEChallengeHomeStudentDesignCompetition.

LEED Buildings and HVAC Systems

LEED buildings are built to be highly efficient, therefore quality HVAC systems are a must. In most LEED projects, HVAC systems with an efficiency of 35 percent (according to ASHRAE standards) or better are sought after. Along with traditionally used methods such as variable air volume (VAV) systems, occupancy sensors and high efficiency cooling systems,  new technologies are being used to reach high LEED ratings.

Some of these new technologies include chilled beams, which provide radiant cooling, thermal-energy storage systems, which provide cooling during peak periods, displacement ventilation and more. The key is to cut down the use of fans by separating  the ventilation system from the heating and cooling systems, thereby saving energy. Choices to use these systems are made during the design process, but these are foreign to many consultants. But this trend is changing with more collaborative design efforts.

“Integrated” design is becoming more popular in LEED and other high performance buildings. This means that decisions made in the HVAC design process are being made not only by Architectural Engineers, but Mechanical, Electrical, contractors and more. This approach is proving successful in providing fairly efficient systems. However, developing higher performance buildings and HVAC systems does not end with “integrated” design. The key is informed engineers and contractors in LEED.

In future years, HVAC systems will by more efficient than can be currently imagined with the continued use of well informed designers and new heating, cooling, and ventilation technologies.

http://www.greenheck.com/media/pdf/industryarticles/hvac&leed.pdf

Building Envelope

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In this article, I will introduce a building that stand as a great example of innovating methods in construction new building envelope and facades.  Al Bahr Towers are two twine high-rises located at the capital of the UAE. Consist of 25 floor each with a total area of 70,000 sq m and a height of 145m, they became the headquarter of the Dubai Investment council. As most of the high-rises in the world, AL Bahr Towers are covered with a glass façade which form the main envelope of the building. However, for a tall glass building in a location like UAE, where the average temperature in the summer surge to more than 40 degree Celsius, it would become unbearable to live or work in such a structure because it is subject to the green house effects.  Therefore, two options was facing the engineers either spends a lot of money on Air Conditioning systems (AC) or come up with a creative solution to solve this issue.

Building envelope or building façades is a field that is closely related to architectural engineering. Heat transfer, insulations, and thermal resistance are all topics that are related with architecture engineers. However, in high-rises such as Al Bahr Towers, engineers are constrained with the type of the materials and the thickness of the wall that they are allowed to be used because of the addition weight that it would exert of the structure and also for aesthetic reasons. As a result, the engineers and the architects in the Al Bahr Tower created a lattice screen that covers the glass façade according to the sun orientation. This lattice screen is inspired from the local traditional wooden screen that covers the windows in ancient Arabian housed as a method to prevent excessive amount of sun heat radiation from entering the building.  However, in order to control the amount of sun light entering the building, new technology was to used to create a moving sunshades that opens and closes according to the sun orientation and solar radiation.

The lattice screen was created thanks to the allocation and integration of advanced electric sensors with the moving parts of the lattice’s structure. The sensors and the moving electric components created a moving façade hat open and close in response to the sun, reducing heat gain by more than 50%. Using less air-conditioning helps reduce the towers’ carbon emissions by an estimated 1,750 tons per year, according to Times article of the best inventions of the year 2012. In addition, the façade in Al Bahar is connected by a computer-controlled system to optimize the solar and light conditions. As a result, this demonstrate how important and necessary to integrate structural envelope system with electrical system to optimize the function of the building envelope.

Al Bahr towers create a great example to understand the new innovations in building envelope and the external structural of a building. An architectural engineer, that understands the main principle of heat transfer and insulation with a solid understanding of shading and solar radiation, can create innovated building envelope and façade.

HEAT EXCHANGERS: INTERESTING APPLICATIONS: BEER

I make my own beer at home.  The end result of a brew day is a giant pot of boiling “wort,” or unfermented sugar-water.  This fluid needs to be cooled to 70 degrees Fahrenheit so that yeast can be added & fermentation can be begin.  It’s absolutely amazing how long 5 gallons of boiled wort will stay hot, even with the pot submersed in ice water.  It takes as long as 10 hours to accomplish via ice bath.  Ideally, you don’t want the wort sitting around long before adding yeast because bacteria from the air can start eating the sugars, causing bad off-flavors in the finished product.  So to demonstrate aspects of heat exchangers, show how simple they are to build, and cool my wort quickly, I built a counter-flow heat exchanger.  The one I build consists of a garden hose and inner copper tube.  The inner copper tube caries the boiling wort, and the garden hose carries tap water in the opposite direction.  On the ends are some copper fittings that seal everything up and allow connection to hoses.  Here’s a pictorial of its construction and the device in action:

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Though my first test of the heat exchanger (aka “counterflow wort chiller”)  was brewing a batch of stout (it worked great!  It cooled 5 gallons from boiling to 70 degrees in about 15 minutes, note however I had the cooling water coming from the faucet at near full blast), I did some actual tests to find epsilon, or the effectiveness of the chiller.  I measured each volumetric flow rate by measuring how long it took to fill a 2 quart pitcher:
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With this data, we can now approximate NTU, and approximate the overall heat transfer coefficient via E-NTU relationships:

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I can’t find any data to compare this “wort chiller” to.  But I think the effectiveness seems reasonable, and the the overall heat transfer coefficient seems wildly large compared to architectural materials (which are obviously designed to have low heat transfer coefficients).

HEAT EXCHANGERS: INTERESTING APPLICATIONS PART 2

HRV’s and ERV’s, which ventilate interior spaces without throwing energy out the window, are only one use of heat exchangers in buildings homes.  Another permutation keeps energy from going down the drain, and is is called drain-heat recovery.  The idea is to use hot water from a shower to preheat cold water going into the water heater.  Here’s a schematic from one manufacturer:

Drain heat 2 Drain heat 1

(imagse from gfxtechnology.com)

The design of these heat exchangers is simple, consisting of a coil of copper tubing wrapped around a typical sanitary waste pipe.  They take advantage of the fact waste water flows in a film on the inner surface of a vertical waste pipe, making for a large surface area and large convection heat transfer coefficient between the pipe’s walls and the drain water.  According to the manufacturer (GFX), this configuration can capture as much as 60% of waste heat!  This can translate into a big energy savings, especially in applications where a shower is getting a lot of use (imagine how much hot water goes down the drain in locker-room at a health club).  It’s important to note however that drain heat recovery can only occur when fresh cold water is going into the water heater at the same time hot waste water is flowing; thus if a persons in a household usually bathe, the device is rendered useless.

Another place heat exchangers find application is homes is the energy-consuming task of drying laundry.  The same concept of an HRV can be applied to a clothes dryer; the hot waste gasses heat incoming cold air, recycling heat.  In this application, large amounts of condensation form on the moisture-laden waste-gas side of the exchanger, which is collected and drained off.   Dryers of this type only recently and very briefly came to market.  They were displaced practically overnight by another even more efficient dryer design, the heat pump dryer.  Heat pump clothes dryers can be though of as utilizing a an “active” heat exchanger.  An evaporator coil recovers both sensible and latent heat from the hot waste gasses leaving the dryer, returning it via a condenser coil to the incoming cold air.  The COP of a heat pump in this configuration is very large, since it is moving heat in the same direction as a large temperature gradient.  The reason this process is more efficient than a passive fluid-fluid heat exchanger is because the evaporator coil can get very cold, thus forcing more water to condense out of the waste air and recovering much more latent heat.

Heat pump(image from http://www.winningappliancesblog.com)

What makes heat exchangers so interesting to me is that in spite of being so useful and seemingly innovative, they usually very simple and easily fabricated.  Fluid-fluid, concentric pipe type exchangers are made easily with materials available anywhere.  A great example of this obtainable utility, though not technically related to building science (forgive me), is a water pasteurizer utilizing a concentric pipe heat exchanger to regenerate waste heat.  Water pasteurization is the process of heating water to around 170 degrees Fahrenheit for a short period of time, killing virtually all microbes.  This is a very obtainable method of water treatment for developing areas of the world.  All that is needed is a large metal vessel (like a re-purposed metal drum), a heat source (this can be supplied utilizing makeshift solar arrays), and two sizes of pipe or food-grade tubing.  Water in the drum is heated to the appropriate temperature, then drained through a heat exchanger, heating the incoming water.  Here is a rough scheme for the process:

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Just to show how simple it is to fabricate a well-engineered heat exchanger, I designed and built one of my own.  It’s not for anything practical, but certainly my favorite heat-exchanger application: making beer.  See my next post for a full report and analysis.

Heat Exchangers: Interesting Applications Part I: HRV’s and ERV’s

Call me a nerd, but I actually find heat exchangers pretty cool.  My first exposure to them was in high school when my parents’ bathroom fan quit and I was tasked with purchasing and installing a new one.  When I went to a big-box home store to survey my replacement options, most of the fans were in the $50 to $150 range.  I was shocked to see one with a $500 price tag.  The unit was a “Panasonic FV-04VE1 WhisperComfortTM Spot ERV.”  The unit’s box was printed with the following image:

ERV-1(picture from http://www.panasonic.com)

It’s pretty clear from the picture what the ERV (energy recovery ventilator) does, at least regarding sensible heat.  In winter, warm air from inside a conditioned space heats fresh cold air drawn in from outside.  The reverse process occurs in summer.  This is most often accomplished by separating the fluids by a thin membrane with a very large surface area.  HRV’s (heat recovery ventilators) are units that only exchange sensible heat.  ERV’s like the one pictured above actually exchange latent heat as well,  recovering some of the energy lost due to a phase change of water.  This is commonly done via a moisture-permeable membrane separating the fluids.  Here’s a crude diagram of what’s going on:

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Both ERV’s and HRV’s are a great way to decrease indoor air pollutants in today’s tight, low-infiltration homes, while not significantly increasing space-conditioning energy use, as would traditional forced HVAC ventilation or natural ventilation would.  However ERV’s are pretty much required (when compared with HRV’s) in extreme climate conditions.  When HRV’s are used in situations with a large temperature gradient between air streams & at least one of those air streams is even slightly humidified, condensation is sure to occur in the unit, which can result in mold and actually make bad indoor air worse.  ERV’s should also not be used without considering moisture issues; some conditions may overcome a unit’s ability to exchange moisture and condensation can still occur.  A great example of ERV misuse would be the story I told before; that Panasonic ERV should have never been by the bathroom fans, since using it in that application, as a device intended to evacuate shower steam, would likely be more moisture than it was designed to cope with.

SOLAR ABSORPTION CHILLERS

Todays’ generation is faced with huge energy crises, along with increasing temperature as a result of global warming, which can all be associated with the reckless usage of natural resources and waste of fossil fuel. This crises has not only caused the contemporary generation to worry about diminishing resources, but has also resulted in mounting inflation and economy crises throughout the world. I being a Pakistani have witnessed the impact of energy crises that affect each and every Pakistani. The Times identified Pakistan, with highest recorded temperature in Asia, to be one of the 5 hottest countries of the world. With an ever growing demand of cooling system, the country faces a huge electricity crisis. Interestingly, air conditioning of buildings has been identified as one of the major reasons causing ozone depletion and greenhouse effect, reason being the huge discharge of refrigerant harmful gases from the conventional cooling systems. I was therefore quite interested in alternate energy solutions and solar cooling options caught my eye.

For over three decade now, numerous solar cooling techniques have been invented and implemented to facilitate cooling and other needs. Thus to understand and identify the most eco-friendly and suitable sustainable substitute to the currently used mechanical cooling system in Pakistan, I did some research into the available options.  Solar cooling techniques are  classified as open-cycle, closed-cycle and thermo-mechanical. Absorption and adsorption fall under the umbrella of closed-cycle, while open-cycle comprises of desiccant cooling. Absorption cooling based on thermal coefficient of performance (COP) has been referred to as the most useful, cost-effective and productive mode of energy production, as compared to the other techniques. In addition to this, desiccant cooling’s high initial cost, and small power density plus low COP for ejector and adsorption cooling techniques limits their application, making them less favorable as compared to absorption cooling technique.

This lead to a further investigation of the available solar absorption chiller options, in an effort to analyze the best and most suited one for Lahore, a central city of Punjab province, Pakistan. To understand the working of a absorption chiller, I looked at the thermodynamic cycle of a absorption chiller, working of its various parts and ways to compute the COP. A considerate of the working temperature and ways to optimize its working lead to conclude that a flat plate single effect absorption chiller would be the best solution to energy and cooling crises in Pakistan, so as to get the best results.

When deciding for the most appropriate Solar Absorption Chillers (SAC), its following main parts catch attention,

  1. The Solar Collector,

The two factors used to decide upon the solar collector are cost and efficiency. The current research on the subject suggests that expensive evacuated solar collectors should be selected when the temperature required for chiller is high or when the climate of the place is mostly cloudy or has less availability of solar radiation. Even though the comparatively cheaper flat plate collectors are less efficient then their more expensive siblings, evacuated solar collectors, given their smaller payback period and lower deployment costs the former are better suited to areas with less cloud cover and higher solar radiation such as Lahore, Pakistan.

  1. Absorption Chiller.

The Second functional part of SAC are Absorption Chillers. The two main differences between Absorption chillers and Mechanical chillers, the most prevailing type of chillers currently in use in Lahore Pakistan, are firstly, in an absorption cycle heat is used and it is a thermally driven cycle, unlike mechanical compression; and secondly a second liquid called the absorbent, other than the refrigerant, is what makes an absorption chiller different from a mechanical vapor compressor. This second absorbent liquid is very much important as the efficiency of the SAC and its usability in any given environment is directly linked to the liquid used as well as its concentrations.

SAC can further be classified on the basis of the number of stages in the cooling process and thus two types, single absorption chiller and double absorption chiller are in vogue. Double absorptions chiller have a high deployment and running cost whereas the single absorption chiller are relatively cheaper to install and run.

The introduction and implementation of SAC can cause huge energy savings along with energy-demand fulfillment in not only Pakistan but also other parts of the world. If interested in further reading here are a few links to get you started.

http://www.sciencedirect.com/science/article/pii/S0378778808001734

http://www.sciencedirect.com/science/article/pii/S0378778809002163

http://www.sciencedirect.com/science/article/pii/S0378778811005548

http://gradworks.umi.com/15/31/1531888.html