Heating, ventilation and air conditioning (HVAC)

Heating, ventilation and air conditioning (HVAC)

HVAC systems directly influence productivity through the health of the occupants and so are a major factor in the operation of both the building and business. This has been achieved both by the introduction of improved direct digital control (DDC) technology, distributed processing and more adaptive spatial planning in general. Systems have been developed that deliver HVAC using both the traditional approach, where the ducting is installed in the plenum space and air is directed downward, and in floor-ducted systems that supply air in an upward direction. Personal environmental control systems that integrate technologies to deliver cooling/heating to the individual are also available and are impacting greatly on the development of future HVAC systems.

The distribution of control zones and hence the number of zones that can exist on each floor is aligned with the type of HVAC system used (Table). This may pose difficulties if a broad distribution of functional zones is created in the process of providing the desired work places, thus limiting the opportunity to align building system control zones with

Table: Attributes and types of HVAC systems used in intelligent building

HVAC attribute

·     Horizontal distribution: air, water, none

·     Horizontal distribution: ceiling, floor, furniture supply/return

·     Environmental load management and load balancing

·     Split ambient and task conditioning: individual controls

·     All air systems and mixed mode systems

·     High performance systems

·     Air quality management and energy management

·     Chilled ceilings

·     Geothermal ground water systems

Capabilities of the intelligent building

Capabilities of the intelligent building

The overriding function of the intelligent building system is to support the capabilities inherent . Clearly it is necessary to consider an intelligent building as a single entity unifying objectives of the owner in delivering the building’s desired capabilities with the adaptability and functionality desired by the occupants.

As with the systems present in the intelligent building it is possible to list the capabilities. They include:

·     sensing human presence and/or occupancy characteristics in any part of the building and controlling the lighting and HVAC systems based on appropriate pre-programmed responses

·     performing self-diagnostics on all building system components

·     alerting security and fire alarm systems and monitoring the location of occupants in case of emergencies

·     sensing the intensity and angle of light and solar radiation, temperature and humidity, and adjusting the building’s envelope according to the desired interior performance levels

·     monitoring electrical outlets for malfunctioning equipment

·     monitoring access to the building and individual building spaces

·     detecting odors and pollutants and responding by increasing ventilation rates

·     distributing electric power to computers on demand or in accordance with a preset priority schedule and automatically activating reserve batteries or back-up systems

·     selecting the least cost carrier for long distance telephone calls

·     activating ice-making or heat storage systems when the utility signals that discounted rates are in effect

·     providing better acoustic privacy by activating white noise systems to mask background noise.

Intelligent building systems

Intelligent building systems

Developments in intelligent buildings have not been limited to advances in technology in the areas of computers, communications and building engineering. Changes in societal attitudes that reflect a higher standard of living have highlighted issues associated with the provision of a healthy working environment. This is being reflected in an increasing demand for high quality office space, spread across all classes of buildings, and a need for advanced information processing and communications systems. The technologies and services that are part of the intelligent building infrastructure.

The technologies and services that form part of the intelligent building infrastructure

Infrastructure	Services
Enclosure	·     load balancing ·     solar control ·     heat loss control ·     day lighting ·     passive and active ventilation ·     passive and active solar heating
Interior	·     spatial quality ·     thermal and air quality, visual quality ·     acoustic quality in the individual workstation ·     new workgroup concepts ·     shared services and amenities
Telecommunications	·     external connectivity and command centers ·     vertical chases and satellite closets/rooms ·     horizontal networks and horizontal plenums ·     service hubs and shared equipment ·     conference hubs, connectivity
Site	·     transport ·     streetscape, public access and thoroughfares ·     relationship with the community

Developers of building systems of all types have been challenged to deliver on these demands. The successes to date have created a new opportunity for adding value to the capabilities already inherent in the building. Intelligence has become ‘distributed’ enabling micro zones to exist independently of the rest of the building. For organizations, this is an important consideration. Organizations modify space to suit business needs. People, by their nature, tend to modify their work environment to suit personal tastes and corporate identities. The ability of building systems to interact using distributed intelligence enables a successful outcome to be achieved.

Intelligent architecture

Intelligent architecture

Describes intelligent architecture as architecture that is responsive. That is, the architectural components of the building can be replaced and/or modified as the building’s use changes.

Buildings have become products of well-established practices and principles. Most do not challenge the status quo, being designed for the ebb and flow of marketability. Investors, developers, architects, engineers, occupiers and the community all influence the supply and demand to varying degrees, influencing the design and specification of the building. Each group has a competing interest that depends on the form of value it seeks to extract from the development process. The identifiable aspects of these buildings are not limited to external appearance or internal fit-out but also include building environments, both internal and external.

Buildings cost money but only function can add value. Minimizing design costs and time has created an environment that is not conducive to adding value. The design of intelligent buildings has value enhancement at its core. To achieve added value, integrated design that enhances functional and physical effectiveness is needed.

Sustainable construction

Sustainable construction

There is increasing pressure on all who are concerned with construction, including developers, designers (including engineers of various disciplines) and contractors, to work towards achieving a sustainable construction industry. Major areas of concern are energy use in buildings, selection of materials, resource depletion and waste management. These concerns are being addressed by researchers in many countries with particular emphasis on reducing operational energy in buildings (e.g., energy used for heating, cooling and lighting) and reducing the amount of waste generated during construction and demolition that is disposed of to landfill.

Advances in computer modeling of building performance have made possible substantial reductions in the energy needed to run buildings, with an increasing number of non-residential buildings being constructed with smaller mechanical plant, or none at all. Daylight is utilized more effectively, reducing the need for artificial lighting, while natural ventilation systems based on sophisticated modelling of airflows in and around buildings are becoming more common.

The effect of these developments on building value will become apparent as environmental controls tighten and the environmental costs associated with energy production and use are progressively internalized through the introduction of measures such as carbon taxes (which are already in place in some countries).

Concrete Admixtures and the Environment

Concrete Admixtures and the Environment

Concrete admixtures are liquid or powder additives. They are added to the concrete mix in small quantities to meet specific requirements:

·     To increase the durability

·     To improve the workability

·     To change the setting or hardening reaction of the cement

The effect of admixtures is always to improve the concrete. In quantity terms, super plasticizers (high range water reducers) and plasticizers (water reducers) as a group make up about 80% of all of the admixtures used today.

How much do concrete admixtures leach, biodegrade or release fumes?

Super plasticizers should be non-toxic, water-soluble and biodegradable.

Tests on pulverized concrete specimens show that small quantities of super plasticizers and their decomposition products are leachable in principle. However, the materials degrade well and do not cause any relevant ground water pollution. Even under the most extreme conditions, only small quantities of organic carbon leaches into the water.

·     Conclusion of test: The air is not polluted by super plasticizers.

To summarize: How environment-friendly are super plasticizers?

Concrete admixtures are appropriate for their application and when correctly used are harmless to man, animals and the environment.

The technical benefits of super plasticizers for clients and construction professionals outweigh the occurrence of low, controllable emissions during use. Concrete admixtures merit being rated environment-friendly because they create negligible air, soil or ground water pollution.

See the following publications:

·     “Environmental Compatibility of Concrete Admixtures” Report by the Association of Swiss Concrete Admixtures Manufacturers (FSHBZ)

·     EU Project ANACAD Analysis and Results of Concrete Admixtures in Wastewater Final report BMG Engineering AG Zürich

Concrete Curing Period

Concrete Curing Period

The curing period must be designed so that the areas near the surface achieve the structural strength and impermeability required for durability of the concrete, and corrosion protection of the reinforcement.

Strength development is closely connected to the concrete composition, fresh concrete temperature, ambient conditions, concrete dimensions and the curing period required is influenced by the same factors.

As part of the European standardization process, standardized European rules are being prepared for concrete curing.

The principle of the European draft is incorporated in E DIN 1045-3. Its basis is that curing must continue until 50% of the characteristic strength fck is obtained in the concrete component. To define the necessary curing period, the concrete producer is required to give information on the strength development of the concrete. The information is based on the ratio of the 2 to 28 day average compressive strength at 20°C and leads to classification in the rapid, average, slow or very slow strength development range. The minimum curing period prescribed according to E DIN 1045-3 is based on these strength development ranges. The table below shows the minimum curing period as a factor of the strength development of the concrete and the surface temperature.

Concrete Curing Methods

Concrete Curing Methods

Protective measures against premature drying are:

·     Applying liquid curing agents

·     Leaving in the forms

·     Covering with sheets

·     Laying water-retaining covers

·     Spraying or “misting” continuously with water, keeping it effectively submerged and

·     A combination of all of these methods

Liquid curing agents can be sprayed onto the concrete surface with simple tools (e.g. low pressure, garden type sprayers). They must be applied over the whole surface as early as possible: on exposed concrete faces immediately when the initial “shiny” surface of the fresh concrete becomes “matt”, and on formed faces immediately after striking. It is always important to form a dense membrane and to apply the correct quantity (in g/m²) as specified, and in accordance with the directions for use. Several applications may be necessary on vertical concrete faces.

Leaving in the form means that absorbent timber formwork must be kept moist and steel formwork must be protected from heating (i.e. by direct sunlight) and from rapid or over-cooling in low temperatures.

Careful covering with impervious plastic sheets is the most usual method for unformed surfaces and after striking of formwork components. The sheets must be laid together overlapping on the damp concrete and fixed at their joints (e.g. by weighing down with boards or stones) to prevent water evaporating from the concrete.

Concrete Curing

Concrete Curing

For high durability, concrete must not only be “strong” but also impermeable, especially in the areas near the surface. The lower the porosity and the denser the hardened cement paste, the higher the resistance to external influences, stresses and attack. To achieve this in the hardened concrete, measures have to be taken to protect the fresh concrete, particularly from

·     Premature drying due to wind, sun, low humidity etc.

·     Extreme temperatures (cold, heat) and damaging rapid temperature changes

·     Rain

·     Thermal and physical shock

·     Chemical attack

·     Mechanical stress

Protection from premature drying is necessary so that the strength development of the concrete is not affected by water removal. The consequences of too early water loss are:

·     Low strength in the parts near the surface

·     Tendency to dusting

·     Higher water permeability

·     Reduced weather resistance

·     Low resistance to chemical attack

·     Occurrence of early age shrinkage cracks

·     Increased risk of all forms of shrinkage cracking

Concreting Operation

Concreting Operation

In general, when concreting it is important to ensure that the release agent suffers as little mechanical stress as possible. If possible the concrete should not be poured diagonally against vertical formwork to prevent localized abrasion of the release film. The pour should be kept away from the form as much as possible by using tremies/pipes etc. When compacting, make sure that the poker vibrators do not come too close to the form work skin or touch it. If they do, they exert high mechanical stress on the form surface, which can result in abrasion of the release agent and later to localized adhesion (non-release) of the concrete.

Summary

The concrete industry cannot do without release agents. When correctly selected and used with the right formwork and concrete quality, they contribute to visually uniform and durable concrete surfaces. Inappropriate or wrongly selected release agents, like unsuitable concrete raw materials and compositions, can cause defects and faults in and on the concrete surface.

Sprayed Concrete with increased Fire Resistance

Sprayed Concrete with increased Fire Resistance

A sprayed concrete has increased fire resistance if it is improved with polypropylene fibers. In the event of fire, the PP fibers melt and leave pathways free for the incipient vapour diffusion, preventing destruction of the cement matrix due to the internal vapour pressure. Suitable aggregates are essential for increased fire resistance. Their suitability must be verified by preliminary tests.

·     Granulometry                         0–8 mm

·     Cement type                           CEM III / A-S

·     Cement content                               425 kg/m³

·     Polypropylene fibers                2.7kg/m³, according to type

Sulphate resistant Sprayed Concrete

Sulphate resistant Sprayed Concrete

A sprayed concrete with a standard cement content of 400–450 kg/m³ has high sulphate resistance when it uses:

·     Cement combined with water reducer

·     a standard Portland cement combined with water reducer and added at > 5% or

·     a CEM III-S

Requirement: w/c < 0.50

Recommended mix design for wet sprayed concrete:

·     Granulometry                         0–8 mm

·     Cement content                        425 kg/m³        

Steel Fiber reinforced Sprayed Concrete

Steel Fiber reinforced Sprayed Concrete

Definition

Steel fiber reinforced sprayed concrete, like conventionally reinforced sprayed concrete, consists of cement, aggregates, water and steel. By using and adding steel fibers, the sprayed concrete is homogeneously reinforced. 

Reasons for using steel fiber reinforced sprayed concrete:

·     Saving on the costs for installation of steel mesh reinforcement

·     Reduction in slump due to higher early strengths

·     Elimination of “spray shadow” when spraying onto reinforcing mesh

·     Due to its homogeneity, steel fiber reinforced sprayed concrete can withstand forces of various kinds in various directions at any point on its cross-section. 

Additional notes:

·     The cement content may have to be increased because the fines content of steel fiber reinforced sprayed concrete must be higher than in standard wet sprayed concrete, to anchor the fibers.

·     Adding Silica fume helps to achieve the target values of the sprayed concrete because it also improves anchorage of the fibers.

·     improves the pump ability considerably.

·     The minimum diameter of the pump line should be at least double the maximum fiber length.

Test Methods of Sprayed Concrete

Test Methods of Sprayed Concrete

Determination of early strengths

To determine the very early strengths (in the range 0 to 1 N/mm²), the Proctor or Penetrating needle is used.

The following methods are well established for compressive strength testing between 2 and 10 N/mm²:

·     Kaindl/Meyco: Determination by the pull-out force of bolts.

·     HILTI (Dr. Kusterle): Determination of the impression depth (I) and pull-out force (P) of nails shot with a HILTI DX 450L shot bolt machine (load and nail size are standard).

·     Simplified HILTI method (Dr. G. Bracher, Sika):Determination of the impression depth (I) of nails shot with a HILTI DX 450L shot bolt machine (load and nail size are standard). Determining the required early strength by this method should be accurate to ±2 N/mm².

Concrete Spraying Process

Concrete Spraying Process

Dry spray process 

In the low build dry spray process (blown delivery), the semi dry (earth moist) base mix is pumped using compressed air, then water is added at the nozzle together with an accelerator (as required) and this mixture is spray applied.

The inherent moisture content of the aggregates in the base mix should not exceed 6%, as the effective flow rate is greatly reduced by clogging and the risk of blockages is increased.

Cement content

For 100 liters dry mix

28 kg of cement is added to 80 liters of aggregate.

For 1250 liters dry mix

350 kg of cement is added to 1000 liters of aggregate.

Wet spray process

There are two different wet spray processes, namely “thin” and “dense” stream pumping. In the thin stream process, the base concrete is pumped in a dense stream to the nozzle with a concrete pump, then dispersed by compressed air in a transformer and changed to a thin stream. The accelerator is normally added into the compressed air just before the transformer. This ensures that the sprayed concrete is uniformly treated with the accelerator.

With thin stream pumping, the same base mix is pumped through a rotor machine, as with dry spraying, with compressed air (blown delivery). The accelerator is added through a separate attachment to the nozzle with more compressed air.

Assuming that the same requirements are specified for the applied sprayed concrete, both processes – dense and thin stream application –require the same base mix in terms of granulometry, w/c, admixtures, additives and cement content.

Sprayed Concrete

Sprayed Concrete

Sprayed concrete is a concrete which is delivered to the point of installation in a sealed, pressure resistant hose or pipe, applied by “spraying” and this method of application also compacts it simultaneously.

Uses

Sprayed concrete is mainly used in the following applications:

·     Heading consolidation in tunnelling

·     Rock and slope consolidation

·     High performance linings

·     Repair and refurbishment works

Quality Sprayed Concrete Requirements

·     High economy due to rebound reduction

·     Increase in compressive strength

·     Thicker sprayed layers due to increased cohesion

·     Better waterproofing

·     High frost and freeze/thaw resistance

·     Good adhesion and tensile bond strength

Depth of Penetration of Water under Pressure

Depth of Penetration of Water under Pressure

Principle

Water is applied under pressure to the surface of hardened concrete. At the end of the test period the test specimen is split and the maximum depth of penetration of water is measured.

Test specimens

The specimens are cubes, cylinders or prisms with a minimum edge length or diameter of 150 mm.

The test area on the specimen is a circle with a 75 mm diameter (the water pressure may be applied from above or below).

Conditions during the test

·     The water pressure must not be applied on a smoothed/finished surface of the specimen (preferably take a formed lateral area for thet est). The report must specify the direction of the water pressure in relation to the pouring direction when the specimens were made (at right angles or parallel).

·     The concrete surface exposed to the water pressure must be roughened with a wire brush (preferably immediately after striking of the specimen).

·     The specimens must be at least 28 days old at the time of the test.

Test

During 72 hours, a constant water pressure of 500 (±50) kPa (5 bar) must be applied.

The specimens must be regularly inspected for damp areas and measurable water loss.

After the test the specimens must be immediately removed and split in the direction of pressure. When splitting, the area exposed to the water pressure must be underneath.

If the split faces are slightly dry, the directional path of penetration of water should be marked on the specimen.

The maximum penetration under the test area should be measured and stated to the nearest 1 mm.

Density of hardened Concrete

Uses of Cement

Principle

The standard describes a method to determine the density of hardened concrete.

The density is calculated from the mass (weight) and volume, which are obtained from a hardened concrete test specimen.

Test specimens

Test specimens with a minimum volume of 1 liter are required. If the nominal size of the maximum aggregate particle is over 25 mm, the minimum volume of the specimen must be over 50 D3, when D is the maximum aggregate particle size.

Example: Maximum particle size of 32 mm requires a minimum volume of 1.64 liters.)

Determining the mass

The standard specifies 3 conditions under which the mass of the specimen can be determined:

·     As a delivered sample

·     Water saturated sample

·     Sample dried in warming cupboard (to constant mass)

Determining the volume

The standard specifies 3 methods to determine the volume of a specimen:

·     By displacement of water (reference method)

·     By calculation from the actual measured masses

·     By calculation from checked specified masses (for cubes)

Determining the volume by displacement of water is the most accurate method and the only one suitable for specimens of irregular design.

Test result

The density is calculated from the specimen mass obtained and its volume:

D=m/V       D=density in kg/m³

              m=mass of specimen at time of test in kg

              V=volume determined by the relevant method in m³

The result should be given to the nearest 10 kg/m³.

Development of Hydration Heat

Development of Hydration Heat

When mixed with water, cement begins to react chemically. This is called hydration of the cement.

The chemical process of hardening is the foundation for the formation of the hardened cement paste and therefore of the concrete. The chemical reaction with the mixing water produces new compounds from the clinker materials —->hydration.

Viewing under an electron microscope shows three distinct phases of the hydration process, which is strongly exothermal, i.e. energy is released in the form of heat.

Hydration phase 1

Generally up to 4 to 6 hours after production

The gypsum in the plastic cement paste binds the tricalcium aluminates (C3 Al) to form trisulphate (ettringite), a water-insoluble layer which initially inhibits the conversion process of the other components. The gypsum addition of 2–5% therefore has a retarding effect.

The longer “needles” which are created in this phase bind the separate cement particles together, causing the concrete to stiffen.

Hydration phase 2

Generally between 4 to 6 hours after production and up to one day

After a few hours comes the start of vigorous hydration of the clinker materials, particularly the tricalcium silicate (Ca3Si), with the formation of intertwined long-fiber calcium silicate hydrate crystals which further consolidate the structure.

 Hydration phase 3

From about one day

The structure and microstructure of the cement matrix are initially still open. As hydration progresses, the interstices are filled with other hydration products and the strength is further increased.

Concrete Flexural Strength

Concrete Flexural Strength

Concrete is basically used under compressive stress and the tensile forces are absorbed by reinforcement bars. Concrete itself has some tensile and flexural strength, which is strongly dependent on the mix. The critical factor is the bond between aggregate and hydrated cement. Concrete has a flexural strength of approximately 2 N/mm²  to 7 N/mm²

Influences on flexural strength

Flexural strength increases

·     As the standard cement compressive strength increases (CEM 32.5; CEM 42.5; CEM 52.5)

·     As the water/cement ratio falls

·     By the use of angular and broken aggregate

Applications

·     Steel reinforced fiber concrete

·     Runway concrete

·     Shell structure concrete

Test methods

Principle:- A bending moment is exerted on prism test specimens by load transmission through upper and lower rollers.

·     Prism dimensions:

Width = height = d

Length > 3.5 d

Two test methods are used:

·     2-point load application

Load transfer

above through 2 rollers at a distance d (each one ½ d from centre of prism).

The reference method is 2-point load application.

·     1-point load application (central)

Load transfer above through 1 roller, in centre of prism.

In both methods the lower rollers are at a distance of 3 d (each one 1½ d from centre of prism).