How to implement optimum start control

Transcription

1 How to implement optimum start control Introduction Optimum start controllers vary the start times of building heating systems depending on the weather and the heat retained within the building. In milder weather, a building s heating start times will be delayed, thereby saving energy. The replacement of existing fixed start time control with optimum start/stop control can generate 10% energy savings for heating systems operating single shifts. In addition to delivering energy savings, optimum start control will substantially improve comfort by preventing under-heating at time of occupancy and by shutting down the heating system during the day if the external temperature rises. Optimum start controls have the capacity to greatly improve the environment and comfort within the building and deliver substantial carbon and cost savings. The technology The warm-up time required for building heating systems depends on: the outside air temperature the residual temperature within the building Optimum start controllers continually measure these temperatures (using sensors), and vary the heating start times accordingly. To allow this the end-user programmes in the occupation times of the building and the internal space temperature required. The optimum start controller will vary by the heating start time to ensure that the required internal temperature is achieved by the start of occupancy. Additionally, most optimum start controllers can be configured to: turn off the heating system during the day if the outside air temperature rises above a set level (called Day Economisation ) turn the heating off early, if the prevailing conditions mean that the internal space temperature will not fall excessively by the end of occupancy (called Optimum Off )

2 The following diagram illustrates the optimum start control effect: Optimum start controllers may be stand-alone devices or may be combined with other control functions, such as weather compensation. Many optimum start controllers also have data interface communication capability, allowing them to be connected into larger site-wide Building Energy Management Systems (BEMS). The standard, stand-alone, optimum start controller is a simple control box that replaces the timeswitch and hence is relatively straight forward for your heating contractor, or your maintenance staff to wire in, just replacing the existing time control. The only addition to this is that there will be internal and external temperature sensors that will generally need to be wired to the controller. The connection of the internal and external sensors is generally via simple 0.5mm 2 two-core cable and has no special protection or sheathing requirements. For smaller heating systems, it is also possible to obtain radio frequency communication from the temperature sensors to the control box to prevent the use of wiring and ease the installation. This is recommended for smaller heating systems where the temperature sensors are within 30m range of the optimum start control box.

3 Specification check list The following table lists the key parameters that you will need to define in order to specify an appropriate optimum start controller. Item No. Parameter Comments 1 Optimum start required? Essential 2 Optimum off required? Recommended 3 Day economisation required? Recommended 4 Requirement to be combined with another control function (e.g. weather compensation)? 5 Requirement to interface/communicate with other controllers (e.g. a Building Management System)? 6 Need for wireless sensors? Commissioning procedure The set-up of an optimum start controller is critical to its successful functioning and the following should be adhered to: The set time for the optimum start controller should be your occupancy time without any preheat. This combines with the setting of your desired temperature e.g. 19 or 20 o C, so that the optimum start controller can start your heating system each morning to achieve your desired temperature in time for occupancy. It is generally unnecessary to heat the building for security, cleaning or maintenance staff commencing their shift at an earlier time, however this may need to be negotiated. It will take the optimum start controller a week or two to fully bed-in, since it is trying to learn how long the building takes to warm up and cool down. You will need to bear with this, with the knowledge that once it has learned the response of your building to the heating systems that it will provide accurate monitoring and starting and stopping of your heating system to match your heating needs. Recognise that building occupants will need to be told that the heating system is now being controlled via an optimum start controller, since it will switch off the heating during warmer afternoons when the building temperature is satisfied.

4 Common problems The location of the sensors is critical, the external sensor that will monitor the environment needs to be placed on a North facing wall, so that it does not see the sun at any point of the day. The internal temperature sensor needs to be placed internally in a representative location in a colder (but heated) area of the building. Avoid direct sunlight through windows, heat gains from process equipment, office equipment, draughts from doors and windows or placing it in an office where the occupants like to open the windows or switch off their heating systems in the winter. When programming the start time, it is important not to build in any pre-heat time. The programmed start time should be the start of occupancy the optimum start controller will bring the heating on some time in advance of this, as necessary. Finding a supplier Optimum start controllers should be fitted by a reputable heating or controls contractor. If you do not already know suitable contractors, try contacting a recognised trade association for details of their membership, for example: The Heating and Ventilating Contractors Association (HVCA) Tel No: The Energy Systems Trade Association (ESTA) Tel No: The business case The costs for a stand-along optimum start controller are in the order of depending on the model and sophistication chosen. Typically, it will require a half day visit to your site for the installation and hence charges should be no more than one day s work for a turnkey project to install an optimum start controller. Savings are typically around 10%, providing a payback on most installations of less than 5 years.

5 The Carbon Trust is funded by the Department for Environment, Food and Rural Affairs (Defra), the Department for Business, Enterprise and Regulatory Reform, the Scottish Government, the Welsh Assembly Government and Invest Northern Ireland. Whilst reasonable steps have been taken to ensure that the information contained within this publication is correct, the authors, the Carbon Trust, its agents, contractors and sub-contractors give no warranty and make no representation as to its accuracy and accept no liability for any errors or omissions. Carbon Trust trademarks, service marks or logos used in this publication, and copyright in it, are the property of the Carbon Trust. Nothing in this publication shall be construed as granting any licence or right to use or reproduce Carbon Trust trademarks, service marks, logos, copyright or any proprietary information in any way without the Carbon Trust s prior written permission. The Carbon Trust enforces infringements of its intellectual property rights to the full extent permitted by law. The Carbon Trust is a company limited by guarantee and registered in England and Wales under Company number with its Registered Office at: 8th Floor, 3 Clement s Inn, London WC2A 2AZ. December 2008 CTL035