How Contractors Design Portion (CDP) Fills in the Gap

Contractors have many roles to play and many services to take care of during building construction, and one of the seldom acknowledged services they provide is that of the contractor’s design portion, or CDP. The CDP is critically important to the smooth functioning of the building’s services, as it fills in the gap between the functionality of installation drawings and as-built drawings. It provides additional design drawings for AV, security and sound masking in a building. In short, it mops up the work of the remaining design services.

Just what are installation and as-built drawings?

Installation drawings typically include the data required by trades to install most parts of the MEP systems, such as plant rooms, data centres, ventilation systems, underfloor heating, etc. These drawings are created by consultants, contractors or subcontractors from coordinated drawings and are then submitted for approvals. They generally consist of:

• Detailed plans
• Sections
• Elevations
• 3D BIM models with components, installation information

Data in installation drawings includes:

• Precise positioning
• Supports and fixings
• Manufacturers’ shop drawing data
• Space allowances for installation
• Builders work in connection, eg. cutting and sealing holes, chasing block and brickwork for conduits or pipes, lifting and replacing floors, constructing plinths, etc.
• Plant or equipment requirements
• Service connection requirements
• Access space for operation/maintenance requirements
• Access requirements for access panels, decking, platforms, ladders, handrails

As-built Drawings

Changes, both minor or significant, are inevitable during construction, due to changing circumstances on site. Clients may ask for updated drawings, created from as-built surveys. Thus, as-built drawings (also known as record or ‘as constructed’ drawings) are developed, during or after construction, to record what has actually been built. As-built drawings are also required for the Health and Safety file and the operations/maintenance file presented to clients.

Contractor use red ink to mark-up changes to the ‘final construction issue’ drawings on-site, which can be used to create record drawings for the completed project. One of the specific details that MEP contractors record is under-floor cabling. Tenants tend to cut off and leave in earlier cables and then add their own cabling. In the absence of cabling records, later tenants will find the situation quite challenging.

Record drawings must be updated by facilities management teams regularly, including any modifications made to the building. If a BIM (Building Information Modelling) model was developed, it must be appropriately updated with changes before handing it over to clients.

What is CDP and how does it fill the gap?

Contractor’s design portion, or CDP, is a contract, assurance or agreement by the main contractor to take responsibility to design certain parts, or portions, of the building. Either using in-house talent or outsourcing design work to trade subcontractors, the main contractor must ensure that all the designs are coordinated.

Typically, the CDP is required when consultants cannot or have agreed not to provide BIM models for audiovisual (AV) systems, security, sound masking, etc. Main contractors need to fill the gap themselves or have specialist consultants proved electrical design services or other services and then coordinate them with existing MEP systems design.

General CDP Process

• Main contractor acquires building regulations approval for subcontractor designs
• Design consultants decide when and how much of their design is entrusted to subcontractors for completion
• Clear communication of requirements from subcontractors, including function, form and quality
• Main contractors to include trade contractor design (scope, program, cost) as part of tender bid
• Subcontractors provide BIM models of audiovisual (AV) systems, security, sound masking, etc.

What Main Contractors Need from Subcontractors

Different subcontractors need to provide different services to the main contractor, who then incorporates these services into the final as-built drawings. The common services are:

AV (audio-visual) Design Services

• Develop AV functional capabilities, designs and budgets
• Define project requirements, with written specifications and bid form
• Coordinate AV system design with the project team
• Develop complete system design package, with system drawings, specifications, equipment lists, etc.
• Create AV room layout and elevation drawings with dimensions 
• Create connection-level drawings for video, audio, control, LAN
• Configure sound reinforcement systems
• Design cabinet layouts, equipment rack elevations, jack field layouts
• Test and commission AV systems for system functionality
• Prepare and follow up on punch list documents
• Provide and record client/user training assistance
• Coordinate networked AV devices with the client’s IT team
• Identify electrical circuiting, conduit and architectural work requirements as part of the final design

Details of equipment, engineering, project management and AV Integrator installation services must be given to the main contractor.

Using BIM technology can enhance the feedback of security system functioning. The BIM models can be used to locate specific system devices and coordinate them with other devices, so that every system device is properly placed, connected and can be analysed for performance. Security systems can be integrated with the building’s other operating systems for the main contractor to analyse how the security system functions in its space and with relation to the people in that space.

Security (CCTV/Access Control) Design Services

• Provide bid documents, supporting drawings, a bid form
• Develop proposals evaluations, with comparative bid analysis, recommendations
• Create shop drawing submission reviews

Sound Masking Design Services 

• Determine sound masking system requirements with the project team
• Develop sound masking floor plans and drawings
• Create bid documents, supporting drawings, with bid form
• Create shop drawing submission reviews

In addition to coordinating with each subcontractor individually, the main contractor must ensure that the subcontractors coordinate with each other. For example, the MEP subcontractor must be aware of the grid system and a suspended ceiling’s fixings positions, while the ceiling subcontractor must be aware of the plant details above the ceiling for access purposes.

To conclude, the contractor’s design portion ties up all possible loose ends nice and tight. Technically certified and experienced electrical design services providers can enhance and ease the work of main contractors by providing accurate and timely design and drafting services. From moving seamlessly to fill the gap between installation drawings and as-built drawings to providing AV, security and sound masking services design, CDP makes a crucial contribution to the longevity and effectiveness of a building and its services.

XS CAD has valuable experience providing BIM MEP services, mechanical CAD drafting services and electrical design and drafting services for global firms.  Our range of services for building services contractors across the world include MEP drafting, electrical drafting and public health system drafting. 

For further details, contact info@xscad.com

Why Is Power Factor Correction So Important for Green Buildings?

Going ‘green’ is an ideal concept that is fast becoming a necessity, rather than a preferred option. In the global construction industry, there is an increasing drive to find means to integrate ‘green’ practices into building services. One of the prime areas where this can occur is in the field of building power consumption. In addition to using various alternative power sources, the efficient functioning of electronic appliances is critical. The extent of efficiency in electronic appliance functioning is further dependent on power quality, which is improved by power factor correction. With precise electrical design services, specifically electrical drafting services, and the use of active harmonic filters, smart MEP (M&E) engineering design for building services can contribute to the longevity of electronic equipment, resulting in decreased power consumption and reduced costs.

So, what is power factor correction?

Typically using capacitors to offset inductive loads, such as those produced by motors, power factor correction (PFC) tries to improve power factor and thus power quality. Ideally, a system should use all the power drawn from its source to perform useful work. This can happen if the current is in phase with the voltage. If a variation exists between the two, some of the energy from the AC mains is lost and does not perform work.

A measure of the effectiveness of using incoming power in electrical or electronic equipment is known as power factor. The technique of PFC attempts to achieve a power factor of 1 for any system, although most appliances will function effectively at a power factor of 0.95 also. Power factor is also known as the ratio of Real to Apparent power, terms which can be defined as follows:

• Real power – power used to actually run equipment, perform work
• Reactive power – power required by certain equipment, such as motors, relays, transformers, to create a magnetic field for the operation of the equipment, but does not perform work
• Apparent power – vector sum of Real and Reactive power, total power needed to run the equipment

The efficient functioning of the power supply is increased with the use of PFC systems, resulting in cost savings on electrical consumption and supporting green architecture.

There are a number of reasons why the process of PFC may be needed, such as:

• Failure of motors
• Failure of electrical or electronic equipment or appliances
• Continuous overheating of transformers, switchgear and cabling
• Continuous and random tripping of fuses/circuit breakers
• Equipment operation that is unstable
• Increasing and undetermined high energy use and costs

Electrical equipment can become unstable and fail to work when the power factor is deemed poor. A system with a power factor of less than 90 percent will need power factor correction. Systems with poor power factors incur heavy energy costs, as an increased amount of current is needed to execute the same amount of work. Thus, improving power quality reduces power distribution system loads, reduces load on switching gear and cables, reduces costs.

To maintain systems that require power factor correction, the following levels should be regularly monitored, ideally every 6 months:

• Power load reduction
• Voltage levels
• Harmonic content
• Equipment condition
• Functional operation

Now, traditionally, PFC equipment used a bank of capacitors to help reduce the total amount of electrical demand. The capacitors would offset an inductive load, or it would offset reactors in case of capacitive loads.

Enter the harmonic filter. A harmonic filter eliminates unwanted harmonics in electrical systems produced by non-linear loads, thus improving the performance of the equipment and reducing energy costs. Harmonic filtering is useful when the following situations occur:

• Transformers, motors and conductors overheat
• Generators show instability
• Capacitors fail
• Fuses and circuit breakers keep tripping
• Drive failure/damage of sensitive electronic equipment
• Increase in energy costs

Non-linear loads, such as uninterrupted power supplies (UPS), low-energy lighting and switched mode power supplies in personal computers, cause unwanted harmonic voltages and currents. By drawing current in short pulses, rather than a smooth wave-like manner, non-linear loads generate electrical harmonics, which create currents of varying frequencies that are reflected into the system, thus twisting the AC waveform.

It is in this way, by reducing the system’s efficiency, that harmonics reduce the power quality, leading to a lower power factor and ultimately higher energy costs. Harmonic filters sieve out a system’s electrical harmonics, reducing equipment overheating, tripping of fuses and breakers, improving power quality and thus reducing energy costs. By installing resonant circuits in series or in parallel, the harmonic currents are blocked or minimised, reducing harmonic voltage distortion.

The three main types of harmonic filters are:

Passive

• Used in industrial sites with non-linear loads more than 500kVA
• Used in sites needing power factor correction, reduced voltage and current distortion
• An LC circuit is installed in parallel with the non-linear load. The circuit absorbs the harmonics, eliminating it flowing into the network.

Active

• Used in industrial sites with non-linear loads less than 500kVA
• Installed at sites that need reduced current distortion
• Systems with power electronics are installed in series or parallel with non-linear loads, compensating harmonic voltage or current drawn by the load.

Hybrid

• Combine the performance of active and passive filters

Harmonic filters thus contribute to ‘green’ buildings by improving power quality, improving power factors, reducing power consumption and, thus, helping leave a small carbon footprint and enabling low acquisition and life cycle costs. To enable construction to achieve a green building star rating, construction firms need to employ trusted engineering design services who are able to provide technically accurate electrical CAD drafting services. Rather than train and use in-house personnel, Western companies tend to seek cost-effective M&E services overseas. India, with its vast bank of qualified electrical engineers, is quickly becoming a preferred destination to seek expertise in power factor correction and other cutting-edge electrical design services that support green buildings.

How Building Orientation Can Help Curb Power Consumption in Commercial Buildings

Commercial buildings are not the bad guys. We need them all the time. They provide a sizeable proportion of our urban needs and services, but commercial buildings typically consume a large chunk of urban power. Studies in America have shown that the power consumed in commercial buildings account for up to 30 per cent of the total electricity consumed annually.* Reducing power consumption in commercial buildings is one of the prime objectives of green architecture, and in the last several years, various approaches have been formulated on how to achieve this. One of the more basic means to do so is to plan a building’s orientation to optimise heat gain in relation to the sun’s path and consider wind direction, thus reducing the heating/cooling load on power consumption, increasing the efficiency of building services. With the right HVAC mechanical engineering consultants and electrical design services working on an intelligently oriented building, a significantly effective energy-efficient building design can be formulated.

When we talk about commercial buildings, we refer to office buildings, hotels, hospitals, shopping malls or other buildings used for retail. In general, these buildings are multistoried and use power continuously throughout the day and sometimes through the night, contributing to greater power consumption.

Typically, commercial buildings are oriented to make the best use of street appeal, view scenic surroundings or for drainage considerations, but skyrocketing energy costs mean that designers and builders must attempt to incorporate the benefits of free solar energy into building design, with the result of reducing carbon footprints and increasing the building’s marketing value. At the same time, occupants experience the same, expected indoor comfort with reduced energy bills.

The orientation of a building affects the heating, cooling, lighting, daylight access, ventilation and views of occupants. Variations in the usage of power is determined by solar gains impacting cooling and the effect of daylight affecting the use of artificial lighting. Considering climate, low-E coatings on glazing can regulate solar heat gain. Cold climates may need passive solar gain, while hot climates may need a reduction in solar gain.

Orientation towards certain directions is advantageous during some climates. In cold climates, buildings-oriented west of north will result in increased solar gains in the afternoon, and buildings-oriented east of north will be warm during the mornings. At locations with warm climates, buildings-oriented east of north will be better positioned to capture cooling breezes. In commercial buildings, therefore, it must be determined early in the design stage when more warmth would be beneficial, depending on occupancy rates.

For commercial buildings in the Northern Hemisphere, orientation towards the sun requires the largest side of the building to face south and have the most windows, as the sun rests longer on a building’s southern walls. When windows face east or west, they allow the entry of excessive heat, making air conditioners work long and hard during the summer. They also cause issues with glare in commercial buildings. During winters, maximum exposure to daylight provides passive heat, reducing HVAC system dependency.

It’s easy to see that building orientation is ideally based on the geographical location of the building and the local climate for most of the year.

Orientation for Passive Cooling

When commercial buildings are oriented well and decisions are taken to incorporate landscape design and shading elements, passive cooling can be achieved fairly simply. Proper orientation can exclude bright, hot sun and hot winds while accessing cool breezes in certain climates. Hot, humid climates should ideally have buildings that are protected from direct sunlight and heat from nearby buildings (radiant heat). This can be achieved if landscape and adjacent buildings funnel beneficial breezes and shading is provided to all or most external walls.

How the sun travels, or its solar path, influences a building’s heat gain to a large extent. Intelligent building orientation can be crucial in passive solar construction. According to research, a ridgeline running east-west on a rectangular building is ideal. This will maximise the length of the southern side of the building, and several windows on the south will help. Due to the intensity of the summer sun, the northern side of the building ideally should have fewer windows. Of course, directions should be considered as a solar reference and not magnetic north, which varies considerably.

So, what really happens on the sun’s path?

The Truth about the Sun’s Path

Every child will tell you that the sun rises in the east and sets in the west. If we want to be strictly accurate, this happens only on 2 days of the year, the autumnal and vernal equinoxes. During the rest of the year, things are slightly different. The Earth’s tilt on its axis means that the sun rises and sets slightly south of east and slightly south of west during the winter, and slightly north of east and slightly north of west during the summer. The angle is slight and depends on the season and how far the observer is from the equator.

What this means is that the winter sun lives in the southern sky and the summer sun lives in the northern sky, in general. For those living in the Southern Hemisphere, these directions are reversed, which means that for those in Oceania, most of South America, almost half of Africa and some parts of Asia, the winter sun rises in the northeast and sets in the northwest, and the summer sun rises in the southeast and sets in the southwest.

Confusing? Not really. Building engineering designers and architects need to consider these directions, locations and seasons for best results.

Having a south-facing orientation results in shading from the summer sun, reducing solar gain but still accessing sufficient daylight to reduce energy loads associated with artificial lighting. Summer sun angles are high, while winter sun angles are low, enabling the easy entry of light and heat to a building. When buildings are oriented to the north as well, they receive sufficient amounts of indirect daylight, and solar gain, direct light and direct glare are reduced. These factors are more difficult to control if building facades face east or west, as they will then deal with the full intensity of the rising or setting sun, respectively.

In addition to the solar path, building orientation can also harness wind movement for optimum results, even having the potential to utilise wind turbines to generate power. Also, winds and wind patterns can help regulate heat gain. Prevailing winds in a geographical area are winds that blow predominantly from a certain general direction over that location. Studying, analysing and calculating wind data for certain locations can help design commercial buildings that can use summer breezes for passive cooling or protect the interiors from strong wintry winds. These calculations can even possibly prevent the pile-up of snow outside entrances.

In general, chilling winter winds originate in the north and the west. For coastal areas, breezes typically originate from onshore directions, and cold breezes blow down from the mountains to the valleys. Insulated glazing on the building’s sides can limit the effects of these winds.

What happens when builders are unable to choose building orientation?

Building orientation must be fixed on certain plots, especially if they are commercial buildings. The orientation cannot be chosen or planned. If the climate is hot and does not require heating, the site can be developed so that surrounding buildings and trees shade the walls and can channel cool breezes inside.

Excluding photovoltaic collectors and areas deliberately exposed for solar power generation, roofs can be shaded as much as possible. Windows facing east and west should be minimised or eliminated, and those that can’t be avoided should be well shaded. Unwanted heat enters through unprotected glass, so shading the glass can reduce heat gain.

Tips to Regulate Heat Gain through Orientation

Sometimes, builders can use these simple tips to regulate heat gain, depending on the climate:

• Solar-oriented floor plan – Individual floor plans in multi-storey buildings can face the sun for maximum heat gain.
• Tall trees for shade – Evergreen trees on the north side of the building will provide shade during the summer. However, trees can pose certain dangers, so builders must consider age, species, growth rate and canopy cover before deciding to plant new or retain existing trees on the building lot.
• Sufficient number of windows – Too many windows can drain heat from the interior during the winter, and they can allow the entry of more heat to the interiors during the summer. 
• Angled glass – It’s not always necessary to have vertical glass. When glass is sloped to match the sun’s angle, reflection can be minimized. Insulation effects are reduced with angled glass, but possible solar gains need to be balanced with heat loss to the outdoors. 

Currently, software tools can accurately calculate location-specific solar gain and seasonal thermal performance. They can rotate and animate 3D graphical models of commercial buildings with regard to the solar path.

Though street appeal and lot dimensions may ultimately limit a building’s orientation to benefit from passive solar approaches, innovative designs by HVAC mechanical engineering consultants and efficient electrical design services can result in operational energy reduction. Commercial buildings will use less energy for heating and cooling, curbing power consumption, if they are properly oriented according to their geographical location and climate. This will then result in lower power costs without compromising indoor comfort.