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All commercial and domestic buildings require ventilation - this involves the removal of stale air from the interior of a building and replacing it with fresh air from the outside. In the majority of cases the inside of the building is warmer than the outside, thus the ventilation of these buildings causes a gradual heat loss; warm air is replaced by cold air.
Dynamic insulation systems work by drawing outdoor air into the building through a permeable insulation layer. Heat which would normally be lost is recovered in the incoming ventilation air - in essence the incoming ventilated air is pre-heated, thereby recovering heat which is typically lost by the conduction and the cooling effect of ventilation.
For such a system to work, and to maximise the benefits of the dynamic insulation, the insulation used must be porous and a pressure differential between the inside and outside of the building is required to drive air through the dynamic insulation.
One of the first dynamically insulated buildings in the UK was a house built in Aberdeen in 1996. This particular project wasn't the most successful due to problems with excessive air leakage, the project found it difficult to achieve the air tightness required for successful dynamic insulation to operate efficiently.
A more successful project was the 'McLaren Community Leisure Centre' at Callander, opened in 1998. This was the first major building in the UK to incorporate a dynamic insulation system which worked effectively. A dynamically insulated ceiling was used in this building, not only pre-heating fresh air, but also preventing any condensation from building on the ceiling or around the roof space.
Achieving the benefits
To maximise the benefits of dynamic insulation, certain consideration need to be made, firstly it should only be used in buildings that require constant ventilation; the intermittent use of such system would cause moisture to migrate into construction, resulting in the degradation of materials.
A suitable air pressure difference between the inside and outside of the building is required to cause the air to flow in the desired direction through the dynamic insulation, without this differential in pressure no air will flow. A pressure differential of between 5 to 15 Pa is recommended. There are two ways to achieve this, under pressure in the building or by a balanced ventilation system.
Figure : Modes of generating a suitable pressure difference across a dynamically insulated ceiling
In order to prevent any unwanted air leakage, the airtightness of the building should be a top priority and finished to the highest standard. The aim is to prevent any air leakage obstructing/preventing the airflow through the dynamic insulation. In under pressure systems, the airtightness of the building below the ceiling needs to be monitored closely; on the contrary, in balanced systems the roof void must be airtight. Generally balanced systems are used for buildings where doors and windows are opened throughout the day.
Material selection for dynamic insulation systems is highly important. The materials must be permeable enough to let the ventilated air enter the room at a reasonable pressure difference across the building envelope, but at the same time being airtight enough to avoid problems from disturbed airflow (air leakage in most cases)
Extensive testing may be required to select the membrane used to control the airflow resistance of the insulation.
As previously mentioned, in order for dynamic insulation to operate effectively, the ventilated air must be able to flow into the building without restriction. The ceiling system used in the 'McLaren Community Leisure Centre used air-permeable ceiling tiles. This is rather simple to achieve. On the contrary problems can arise in a wall system, generally a permeable wall liner is used on the interior of the building, this however cannot be decorated like you typical wall. Precaution must be taken with the placement of furniture near the permeable wall, and surfaces can be tedious to clean.
This problem can be rectified however, a normal plasterboard liner (which is impermeable to air) can be attached to batons so that there's a small cavity between the plasterboard and the dynamic insulation, airflow can then be drawn through the dynamic insulation and distributed into the room under the window sill or through gaps at the top and bottom of the plasterboard.
A simple dynamic insulation design system would be as follows-
Exterior wooden cladding allowing air flow through 6mm gaps in the wooden cladding, i.e. Rainscreen cladding.
Timber framing with pearmable insulation sandwiched in between framing.
Inner liner sheet (double skin construction)
Plasterboard Liner attached to battons with small cavity allowing for air flow to occur.
Describe and critically evaluate the different ways in which hemp can be used in building.
Hemp in Buildings
Hemp is a very versatile material to work with; it is a fibrous and strong plant that is used to make anything from paper and clothing to bags and even houses. It grows naturally, being able to grow virtually anywhere without the use of herbicides or insecticides and with that, it can produce up to 4 tons of hemp per year on an acre.
In the construction industry this versatile fibre allows for hemp to me manufactured into an array of products including fibreboard, wallboard, roofing tiles, insulation, panelling and blocks can even be made from the compressed hurds
Foundations can also me made from compressed hurds, often referred to as "Hempcrete" this is a mix of hemp hurds, lime, sand, plasters and stone cement. The foundations will set in a day and dry in a week.
"Hempcrete" is reportedly half as light, seven times stronger and three times more pliable than traditional concrete. Its superior strength and flexibility makes it an ideal building material. Its resistance to rot, insects, fireproofing and waterproofing, as well as being self-insulating are additional benefits.
As shown hemp has an array of uses in the construction industry, here three applications are looked at in more detail, areas looked at include-
Hemp insulation is suitable for use as both thermal and acoustic insulation in roof spaces, walls and floors. Slabs of the insulation are made from hemp and recycled cotton fibres, the material is very workable, easy to trim and handle with easy. It is a thermally efficient material; durable; fire resistant; good acoustic performance, environmentally friendly.
The hemp insulation is made from a natural hemp fibres, it is 100% pollutant-free in the majority of cases, ruling out risks to health and providing a totally natural and healthy living environment.
During the growing process the hemp absorbs significant levels of Co2. It also benefits the ground soil as it leaves the ground loose and weed free (without the need for herbicides/pesticides). These are additional benefits to the environmental performance of the material.
Hemp insulation has extremely high thermal resistance and offers outstanding fire protection, it has the ability to absorb & release moisture without affecting this thermal performance. It's a very lightweight material, flexible and convenient to install.
No chemical protection required during growth
Hemp is a natural raw material
It is not affected by mould growth or insect attack as the fibre does not contain proteins
It does not cause irritation
No chemical additives
It has high acoustic properties
It has a high thermal mass
Hemp lime plaster
Hemp lime PlasterÂ is made from a high calcium lime (also known as a fat/air/putty LimeÂ or non-hydraulic lime) blended with the hemp fibres and a pozzolan to aid the set.
Exposure to carbon dioxide is required in the presence of moisture, this allows the hemp lime plaster to harden and set, it can be applied in thicker coats than conventional lime plasters making it easier and quicker to use.
Non-hydraulic lime products are generally extremely flexible and breathable, and hemp lime plaster is no exception. This quality makes the hemp lime plaster suitable for use in restoration projects of old 'solid wall' buildings. It is also suitable in ecological new builds as it can be applied to a variety of substrates e.g. wood fibre boards, wood wool boards, straw bale.
As with most products which hemp is applied to, the addition of hemp in plaster improves the strength and flexibility of the product, as well as increasing thermal performance of the plaster.
The application of hemp lime plaster can also assist with the airtightness of old buildings; this improves the comfort of the rooms and offers energy savings,
Made from a natural, renewable plant fibre (instead of depleting a natural aggregate resource).
As it requires fewer coats and less tending, it can make significant labour savings.
Has aesthetic value - the coarse/medium plaster gives a soft textured finish otherwise the fine hemp or ordinary finish plaster can be used for a smoother finish.
Is breathable and therefore helps to safeguard the functioning and health of the building as well as helping to regulate humidity which makes for a healthier internal environment, this make it ideal for use in older buildings.
Hemp blocks are based upon a cast or spray-on technology that has been around for some time. The blocks come in two formats, either load-bearing or non-load bearing. The blocks are manufactured using similar methods to the makeup of Hempcrete foundations; the hemp is blended with lime and a cement binder. The block has a bio-composite nature, offering unique environmental benefits such as carbon sequestration in the building.
The thermal conductivity of a hemp block is generally 0.36 (structural) and 0.11 (thermal) W/mK The Hempcrete blocks are factory produced to traditional conventional sizes of building blocks (215mm x 440mm).
Hemp is a natural material that locks in carbon as it grows. This makes hemp blocks the perfect sustainable masonry solution as part of a zero carbon house.
The non-structural blocks have superior thermal performance and a negative carbon footprint. This means they can be used as a method of offsetting carbon from other areas of a building's construction. Hempcrete structural blocks also offer better thermal insulation than conventional dense blocks.
In addition, they have the ability to absorb and hold heat (thermal mass) during sunny periods when heat is not needed for internal living or work spaces. Instead, the heat is released when it is required, such as during overcast periods or at night, to provide substantial energy and cost savings.
Hempcrete blocks prove that traditional raw materials, such as hemp and lime, can offer one of the best value materials for low impact, sustainable construction.
Hemp is a renewable material
Very good insulating properties.
High thermal mass
'Carbon negative' through sequestration of CO2 during plant growth.
Reusable if dismantled carefully.
Hygroscopic - provides a degree of humidity control.
Government plans to tackle climate change through the building of more sustainable, zero-carbon homes; Hemp blocks are certainly a sustainable block in many aspect.
There is Increased pressure on the construction industry to use materials that will reduce COÂ²emissions; again Hemp blocks offer a solution to this.
Using case studies evaluate how the environmental performance of buildings can be enhanced by the inclusion of an atrium.
During Roman times, the atrium was a central open area of the house; today the term atrium is generally associated with commercial or public buildings. The development of strong, cheap panes of glass allowed the courtyard to be glazed over and transformed into the modern atrium.
Atrium design often involves skylights and generous glazing areas that provide an infusion of natural light which make them a prominent building areas well suited to serve ceremonial and social functions.
Atria are built for three main reasons;
They fulfil an architectural role in unifying a large building by providing a hub or focus. In a similar way an atrium between buildings can give them a shared sense of identity.
They provide a view from adjoining spaces. If the sky or patches of sunlight are visible then there is also a link with the outside world. This is a major force in some commercial developments where lettable values may be considerably higher for rooms with a view
They are a passive solar feature which can save energy.
The incorporation of an atrium into a building provides people in the building with a connection to the outside. The atrium allows natural lighting into the interior giving an outdoor feeling. The inclusion of an atrium can also be beneficial in terms of space and floor areas; they generally offer larger floor areas than conventional buildings.
Atriums provide more desirable work environments by providing more space with a connection to natural daylight and the outside environment. Many believe that access to natural full spectrum lighting creates a more healthful and productive environment. There have been several studies that support this view; two cases will be looked at further on.
Benefits of incorporating an Atrium
To provide natural light and a view to adjoining spaces. This can greatly increase lettable values.
To act as a passive solar feature which can save energy.
To play a role in the natural ventilation strategy of a building
The biggest environmental benefit an atrium offers is allowing natural lighting into a building.
Numerous scholarly papers and research studies have shown that the indoor environment of a building affects the quality and well being of occupants more significantly than originally thought, the inclusion of natural lighting can benefit worker productivity.
A frequently cited report is the Heschong Mahone Group study "Day lighting in schools," which was conducted on behalf of the California Board for Energy Efficiency. The researcher's analyzed test scores for 21,000 students in 2,000 classrooms in Seattle; Orange County, Calif.; and Fort Collins, Colo. In Orange County, students with the most day lighting in their classrooms progressed 20% faster on math tests and 26% faster on reading tests in one year than those with the least day lighting. (The Atrium, 2010)
Below are two case studies showing the environmental effects an atrium has on the performance f a building.
Case Study A.
Plaza of the Americas, Dallas, Texas
The Plaza of the Americas in Dallas, Texas is an example of the bridging atrium, a complex form which utilizes the atrium to connect several buildings.
The building allows natural light into the atrium space through a set of full height glazing at the side walls between the buildings being connected. Skylights are also present in the roof allowing more light in. The atrium even incorporates prisms suspended in the side wall glazing, these produce varying colours and patterns along the interior atrium surfaces.
Floor to ceiling glass allows light entering the atrium to be transmitted to additional buildings; exterior glazing is heavily tinted to prevent too much solar gain
Designers chose to orientate the building with its long axis north-south. Atrium space is climatically tempered as opposed to controlled; this saves energy costs in the building, as well as adjacent buildings.
Designers chose to landscape the interior of the atrium with small planting areas as well as numerous potted plants giving the appearance of continuous planters. Palm trees and plants of varying species can be found recessed into the lower level floor. The planting scheme again offers an outside feel, improving air quality as well as improving the well being of workers.
The case study shows that environmental benefits can be achieved using atrium. The improvement in natural lighting as well as additional space and interior landscaping enhances the building, this is all due to the atrium.
Case Study B
Parque EXPO building, Lisbon
The Parque EXPO building is located at an urban area of Lisbon near the Tagus River. This building was designed to house the headquarters for the administration of Parque Expo. It was conceived as a low energy consumption building and its design employs a number of passive techniques. (Intelligent Energy Europe, N.D)
The building itself is composed of two blocks, a rectangular shaped building is situated in the east whilst, a v-shaped building in plan situated to the west. A full height atrium links the two buildings. The enclosed atrium space is protected from the exterior by a glazed roof and walls.
Due to the large amount of glazing solar gain is reduced with the use of external shading. Each facade is fitted with a set of perforated plates. These plates cut out direct radiation from the sun whilst allowing reflected light in for radiation. A shading device attached to the top of atriums roof can be controlled giving the occupants the ability to allow more or less light in.
An externally insulated envelope results in a reduction of heat gain during summer, but reduces heat loss in winter. Materials of high thermal mass are used inside the atrium to allow the use of night-cooling by natural ventilation.
Natural and mechanical ventilation is used in the building. A HVAC system which operates when either heating or cooling is used when insufficient natural ventilation is occurring. Air is extracted at the ceiling to the atrium via ducts built into the concrete structure of the floor above.
The natural ventilation system is provided by cross ventilation of each space, using windows and openings in the atrium. Occupants manually control these. Automatic control of the mechanical ventilation system ensures that this does not operate when there is sufficient natural ventilation. Natural ventilation is driven both by wind and the stack effect provided by the warmer air in the atrium.
The second case study shows how natural ventilation can work in harmony with mechanical ventilation. Again many improvements were made to the interior environment of the building, partly due to the atrium.