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.

Building Assessment Project – Building Enclosure Class

We presented this project yesterday in the Building Enclosure Class and the purpose of it was to inspect one of the IIT campus buildings (our group project was Engineering Building). The outcomes of the project included a critical assessment of the building enclosure as well as a list of suggested improvement for increased energy and/or moisture performance that could be applied. The tool used for the assessment includes: visual inspection, photographs, infrared thermal images, notes on orientation and external driving forces. THERM was used to calculate the U value and evaluate the thermal bridges in the existing walls and then another model was constructed in Apache, IES VE with a correction factor to resemble a similar assembly as the one calculated in THERM.

Figure (1) Thermal Imaging – E1 the south entrance

During this process we were able to identify many construction details that have caused poor performance of the building envelope. The majority of heat loss was from the windows and steel columns and a little heat loss occurring through the roof per thermal imaging. Single pane windows were the largest source of heat loss. Thermal bridging structural steel through exterior walls was second largest cause of heat loss. Several poor construction details which cause moisture infiltration.

Figure (2) Proposed Glazing assembly shows the isothermal lines at window wall Jamb

Using all of the information we gathered in our inspections, we were then able to create a dynamic thermal modeling Using IES Virtual Environment and create a proposed list of improvements to the building enclosure.  Walls were improved by adding continuous insulation inside the brick wall which also covers steel and the proposed wall assembly showed a slight improvement in R‐value. Glazing was improved by adding a double pane argon unit to the in front of the existing  glass and insulation over the aluminum mullions. The proposed glazing improvements showed a large improvement in R‐Value. The overall energy performance simulations show a reduction of loads and an energy usage reduction of 20% and the occupant comfort level was increased by these improvements.

Click on the link below to access the full report 

IIT Campus Building Assessment Project

Bubble Facade

Many new studies and projects are adopting the concept of the ventilation within the building envelope. This concept appears in different names like breathing walls, ventilated double façade or skin that breathes. An ingenious idea to renovate an old building in the center of Shanghai was developed by covering the existing windows with an inflatable exterior skin made of white antibacterial technical outdoor nylon. Building with inflatable material is not a new approach and is usually used for temporary structures however the idea of covering an existing building with these materials involve some environmental aspects. The big air cavity between the old façade and the new skin will increase the overall thermal resistance of the building envelope.

The designers described this cavity as a microgreen house that exchange air with the interior spaces to provide fresh air and circulate it through the green area within the bubbles. In order to decrease the energy required to circulate the air, an automated system was designed to control the ventilation by making it works at its minimum capacity when the interior spaces are empty. When the people are in the office, the exterior will be fully inflated to keep the ventilation at its high levels. The main problem of this structure is the lack of the view since the bubbles cover the entire façade. The bubble skin is an attempt to find an alternate for the double skin façade that is built from two layers of rigid curtain walls and making it more flexible and interactive with the interior space.

http://www.archdaily.com/tag/3gatti-architecture-studio/

Smart Shading

Shading element is one of the important components of the skin façade and the effectiveness of the building enclosure depends on the shading configuration of the entire system. However, the shading system increases the cost of the construction and maintenance; and in case of double skin façade it requires a wide cavity in order to contain the blades and a space for cleaning and maintaining these devices that make the Architects very careful before making a decision on using the shading in their design. One of the purpose of the double skin facade is to provide a shell for the shading elements especially in the high rise buildings where the wind add a significant load on the shading system otherwise a sturdy structure to protect the system should be used in case of using the single skin façade.

The traditional assumption that the facade should be static with rigid walls or curtain wall is no longer valid, the homeostatic facade examines the possibility of using a responsive system to the environment. With the emergence of smart shading, an interest in using creative building systems and the need to build durable double skin facade with dynamic elements, the building enclosure can be more sensitive to the environment.

Using Shape Memory Alloy as blinds is one of the ideas to create a shading system that react automatically with the temperature variance without the need of any mechanical equipment or power of any kind and the vent ratio and air flow is determined by the properties of the material. Each blind is composed of two separate layers of different metal joined together which expand at different rates as they are heated. Therefore, when they are heated one reacts more quickly and bends in one direction, then when they cool down they go back to their original position. Bi­metal is commonly used today in thermostats as a measurement and control system and in electrical controls as a component in mechanical systems therefore instead of using it as sensor that regulates the blinds opening why they cannot become the shading element itself. Nevertheless, we are talking about flexible and very thin strips, compared with the typical blinds that have firm structural frames. Therefore, using the bimetal blinds on the exterior face of the building façade make them vulnerable to the outside conditions. As a result we cannot think of this system without integrating it into a double skin facade.

Smart shading has many areas that can be developed depending on combining different technologies to achieve the goal of built an efficient building enclosure. New materials and different configurations can be tested that lead to alterna­tive connection details. Bimetal applications on the building façade and the DSF are both serve to create an interactive façade with the temperature changes as wells as the direction of the sunlight and since the external solar protections are more effective than internal shading devices. In the case of the double-skin facade, the bimetal sheets can be integrated in the cavity. It is thus protected from the bad weather and pollution. Solar protection can remain in place even in the event of important wind, which represents an undeniable advantage for DSF of the high rise buildings.

In the last years, more public interest in sustainable design, energy conservation and zero-emission building design has provoked the designers to find alternative solutions. With the revelation of new smart materials, the evolution of digital technologies and the availability of mass-customization methods, Reacting with outside temperatures, has the potential to develop self-actuating intake or exhaust for facades.

http://www.archdaily.com/101578/

Passive houses

Passive house is a well-insulated building that needs no heating or cooling systems and the term came from German word passivhaus where the haus means any building that can be a school or office, etc.  This kind of enclosure reduces the energy consumption by a huge amount and it is widespread in Europe where the energy prices are higher than in US. These building are heated by passive solar gain that generated from the greenhouse effect usually called a sun room which it is more like a double skin façade. Also, the heat from the people and electrical equipment consider a source of heat in this case since the heat transfer from inside to outside is in its minimal values. In some cases, a heating source is needed and usually it is very small. In summer the heat gain is avoided by the efficient design, building orientation and windows location also by using shading elements.  High performance enclosure, triple glazed, double skin façade, avoiding thermal bridges and ultra thick layers of efficient insulation make an unusual reduction in energy consumption.

For decades few passive houses were built in the US comparing with Europe, In McKeesport, Pa., a YMCA existing building is converted to a passive house. Pennsylvania got the first certification from the Germany based international passive house institute.

Some critics for this building type is high cost of the material used compared with the payback amount. Also, it may face some problems with the unstable climates and there is still a need for an energy source no matter how the enclosure is sealed then it should be called the net zero energy homes.   

http://www.rockymounttelegram.com/features/life/energy-efficient-passive-homes-gain-ground-2182637

 

Bioreactor Façade

Renewable energy is receiving increased global attention as a potential sustainable. Algae bio-fuel is an alternative to fossil fuel that uses algae as its source of natural deposits. Many research study how to use this resource in industry as a sustainable energy and few months ago the first building covered with algae panels was unveiled in Germany.

The bio-reactor panels that are mounted on an existing building are like storage contain algae that continuously supplied with liquid nutrients and carbon dioxide via a separate water circuit running through the facade. With the aid of sunlight, the algae can photosynthesize and multiply in a regular cycle until they can be harvested. They are then batch separated and transferred as a thick pulp to the technical room. There they are fermented in an external bio-gas plant, so that they can be used again to generate bio-gas. The whole building is intended to be completely self-sufficient.

The algae panels are 8′ by 2′, with a total surface area of 2152 square feet at a yield of 15 g dry weight per square meter per day for the conversion of biomass into bio-gas, a net energy gain of approximately 4,500 kWh per year can be achieved. In comparison, a family of four consumes about 4,000 kWh per year. The algae facade could thus supply the entire household of the family with bio-electricity! However the system seems to be prohibitive due to the high cost and time needed to assemble also the maintenance but this kind of projects will be more efficient in the future when the fossil fuel will be depleted.

 

http://www.algaeindustrymagazine.com/algae-powered-building-to-open-in-germany/

New Form of Cooling Panels Using Nanotechnology

A research team in Stanford University designed new panel that can cool structures even under direct sunlight. This panel is made of nanophotonic materials and has a maximum reflectance keeping the building from heating, therefore it reflects as much of sunlight as possible and also it achieves minimal absorption throughout the solar spectrum. From an engineering standpoint the building must radiate heat back into the space as much as possible; as a result this will reduce the heat transferred into the interior spaces of the building. When this panel accepts the incident solar energy, it changes the frequency band to be less transparent to the atmosphere and it radiates it more efficiently that from a normal black body spectrum.

The new panel achieves both goals, it is an effective reflector for solar light and it also emits thermal radiation very effectively. According to the research, the new panel is capable of saving 100 watts per square meter and their study give an example of a typical one – story, single house with just 10% of its roof covered by radiative cooling panels could offset 35% its entire air conditioning needs during the hottest hours of the summer. Although, it is too early to predict how successful these panels are in the market and how competitive are compared with the other products.

http://engineering.stanford.edu/news/new-type-solar-structure-cools-buildings-full-sunlight

Some materials that have similar properties: silver teflon radiator coating material, “gold” thermal blanket and black thermal blanket

 

This picture is for spacecraft covered with the golden blanket. However, I do not think someone will use it to cover the building and save some energy.

More Efficient Duct System

Energy losses through ducts are crucial regarding building efficiency. There are two main ways of these losses: air leakage and by conduction. Typical systems lose 25% to 40% of the energy passes through them. The duct efficiency varies from area to another. Chicago as an example of cold area  has 63% for heating and 83% for cooling while Orlando/ Florida which is in hot climate has 74% for heating and 65% for cooling. Most of the duct are located in spaces that are not heated or cooled that result in a significant amount of energy losses when the air passes through there spaces. The duct system affects the equipment efficiency so when the losses through the ducts are high, the equipment is overloaded and make them running at low capacity. In order to achieve a high performance of the duct system of an existing building, an evaluation should be made by inspecting the duct if there is any leaking or un-insulated ductwork. Then the ducts system should be repaired and sealed. In the traditional duct sealing method, the workers need to find leaks manually and then seal them one by one, for this reason it was important to find more effective way for sealing the ducts. Aerosol sealing method require to seal the grills of the cooling/ heating system attaching the duct sealing device to single point and measuring the leakage before and after blowing sealant into the system.

http://www.youtube.com/watch?v=J6UZfXKTIlI

http://www.nrel.gov/docs/fy05osti/30506.pdf