Controls And Control Systems In Buildings Construction Essay

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Controls and control systems are an essential part of buildings, from the simple switching on and off of equipment to sophisticated building management systems (CIBSE KS4 2005). In order to provide a specification the requirement of the client for a building management system (BMS) needs to be established. The necessity for the provision of controls must also be identified (CIBSE Guide H 2009). The purpose behind a specification is to provide the role of this for the standards to be met and the roles of procurement, covering both responsibility and contractual issues. Initially this will be done from the clients brief and pre-tender brief in order to introduce potential suppliers to the contract and obtain tenders for the undertaking of the work. This will contain the following as laid down in Specifying Building Management Systems (BSRIA TN/6/98 1998).

A general description of the building to be controlled and monitored

What type of system does the client require?

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Is a full BMS system required or is a simpler system required?

What level of control do we need to include? This is based on the budget of the client.

Internal environment conditions & occupancy

What requires controlling items such as Boilers, Chillers, AHU's, & Pumps etc?

How complex is the system? Is the system based on a LAN or is it Web based.

A general outline including locations of control facilities and potential future extension or upgrade of the system.

Specific considerations to include integration and interfaces to other data/computer networks, such as fire and or entry controls

Scope

The scope of this work is to specify the client's requirements and functions of the system. In essence the full specification should describe the full scope of the contract between the client, design team, main contractor, specialist supplier and the commissioning engineer. This should be clear and unambiguous. The contractual and communication flow should be followed so as there is no confusion regarding individual responsibility. An example of a typical flow chart can be seen in Fig.1 Contractual relationships (CIBSE Commissioning Code M 2003).

Client

Principle contractor

Design team

Specialist Supplier

Commissioning Engineer

Fig.1 Contractual relationships

Communication route Contractual connection

Specification

Three types of specification can be considered Performance, Functional or Hybrid. A performance specification specifies of how it operates in strategic terms e.g. what the client requires monitoring. A functional specification details specific items of plant that require monitoring or controlling. Hybrid is a combination of the two systems (BSRIA TN 6/98 1998). Therefore a discussion with the client regarding a full feasibility assessment should be carried out prior to writing the full specification. Once the assessment has been carried then a specification for the system can be written. The minimum requirements according to the latest building regulations (L2B 2010) must include the following;

Safety monitoring

Effective and efficient energy use

Comfort control

Reduction of energy consumption

Provide feedback information to a central point

Reduce CO2 emissions

Reduce requirements for maintenance

Considering these minimum requirements the specification can go into greater detail. In addition to the minimum requirements any specification must also include compliance to EN 13646:1999: Building control systems - equipment characteristics and EN ISO 16484:2005 Building automation and control systems. The specification must also comply with a number of other regulatory, statutory acts, EEC directives and standards some of which are quoted in appendix A.

Particular Specification

This is the specification containing the requirements of the proposed project which are not covered by the other standards and are to include;

Project description and scope

Functional statements

Systems characteristics

System schedules including;

Point schedules

Operation schedules

Point Schedule

Requirements for points are described in terms of the parameters which need to be controlled or monitored along with their operating range. These points are normally inputs from sensors and measured outputs to a controlled device. A point schedule describes the number of inputs and outputs. A sample of a point schedule schematic is shown in Appendix B.

Operational Schedules

This is the description of how individual pieces of plant and equipment are controlled. The operational schedule is the logical configuration of the system, what monitoring and control routines are required from Standard Specifications for BMS (BSRIA AG 9/2001) and in general terms should include the following;

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Environmental parameters

Zoning

Initial time programmes

Alarms

Plant operating sequence

Actuators on start up and shut down

Other schedules to include equipment, reports and graphics.

Training

Staff operating the system must also be included in the design specification. Therefore at the procurement stage the training of operators should also be included (CIBSE Guide M 2008). This will include how the monitoring of any alarms is going to be achieved so that the system is effective. Onsite training is to be provided at the commissioning stage and instruction will be given as to the prime function and the method of the BMS operation. This will be in accordance with Standard Specifications for BMS (BSRIA AG 9/2001). A full description of the operators and responsibilities can be found in appendix B. This also provides the requirement for safety, supply, compatibility and quality assurance.

Testing and commissioning

The specification requires that the system is commissioned systematically by the application of a commissioning procedure. An example of this is shown in appendix D Completion of commissioning record sheets is specified as part of the verification process. Commissioning is to be undertaken by the specialist contractor and describes the testing and inspection to ensure all specification requirements are met and to prove correct operation. Commissioning incorporates several stages as identified in CIBSE Commissioning Code C (2001) and include the following:

Pre Commissioning checks of the components

Wiring

Sensors and actuators

Major sub assembles

Commissioning of the application software

Commissioning of the complete system including:

Checking alarms

Checking interlocks

Control loop tuning

Calibration of sensors

Performance tests to check the ability of the system to meet specified environmental performance parameters.

Guarantee and Defect Liability Period

The specification will allow time for fine tuning to be carried out by the specialist contractor before full hand over to the client. Any fine tuning work will be carried out before the commencement of any warranty defect period with a view of optimising performance of the control system. During this period the contractor will be advised of any necessary adjustments and revised settings this will form part of any testing and commissioning records. During the first twelve months (guarantee period) any hardware or software upgrades must be installed. This is to improve environment and energy performance and also optimise control loops and set points as the building response will differ throughout the year. Any defects occurring within the guarantee period are to be formally reported to the main contractor and remedial work/actions will be monitored. The specialist supplier should support the client's investment and ensure a strategy is in place to facilitate future system or building additions and expansions. This should be done in such a way as to ensure that any future additions to the system can be made with minimal cost or disruption. In addition to this a viable 10 year support period from completion of the project in accordance to Standard Specifications for BMS (BSRIA AG 9/2001) should also be put in place.

Procurement and Contractual

The procurement process chosen by the client strongly influences the way in which the control system is designed and installed. The following definitions relate to the procurement process as taken from (CIBSE Guide H 2009):

Client - the person responsible for the running and maintenance of a building.

Supplier - the company which offer design and cost control services and can be independent from any commercial interest in Installation Company.

Installer - the person responsible for installing, commissioning and handing over the completed engineering services to the client.

Normal contractual practice requires the installer, as a form of warranty, to be formally responsible for any equipment; component or operational defects that may arise of or become apparent (CIBSE Guide M 2008). The designer of the specification may have to identify the true cause of any problem. An independent opinion on the appointment of responsibility of a defect must also be provided. In the case of a fundamental defect the designers input may entail a review of the original design itself culminating in the identification of a latent defect. The guarantee period for defects within the first twelve months after completion has nothing to do with and do not include the user's responsibilities for routine maintenance. The specification allows for a twelve month contract with the installer. This has the advantage that the responsibility for first year defects and for routine operation and maintenance are vested in the same organisation. In the event of any defect arising within the first year of operation and maintenance service has been provided by an organisation independent of the installer. There is then scope for the installer to argue that maintenance attention or lack of it was contributory to the problem. This could be deemed to invalidate the installer's warranty.

Installation Warranties

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A potential downfall for the building owner regarding warranties is that the owner often assumes for one year after handover that any defect in the installation will be rectified at no extra cost. However due to the length of many projects plant installed early in a large construction project may well be out of any defect period warranty upon project completion. The specification must include who is carrying the risk and what is the procedure for the client to initiate the warranty process. The client should ensure that clear lines of responsibility are defined for assuring the safe and effective system maintenance. This should include investigate for yourself guide for basic troubleshooting before activating any call out BSRIA, BMS Maintenance Guide (2003). This will avoid contractual disputes with the system company being called out to a fault that is not related to a system fault for example a boiler alarm condition being diagnosed by the system, but it is still an unrelated boiler fault. There is no value in having a four hour call out fault for the BMS and accruing a call out cost if other mechanical services are not supported to the same level.