Time controlsTimers can be used to achieve significant energy savings. For example, building services such as heating are only needed to meet occupancy levels at certain times of the day. They can be switched on and off manually, but unless one individual has responsibility, they could be left on all day, every day. Installing time controls allows services to be switched on and off automatically.
Time switches – these switch services on or off in accordance with time settings. They can also delay switch-off in infrequently used spaces after a pre-determined time period.
Seven day programmers - good for switching services on or off at different times during the week, according to occupancy levels.
Optimum time controls – learn how quickly a building reaches its optimum temperature and switch heating on just in time to reach this temperature at the start of occupation. These controls can offer a 10% efficiency improvement compared to a well set seven day time switch.
Boost or advance controls – can be used to adjust timings without overriding existing controls. In radiator based central heating systems, boost controls switch hot water on for a limited time (usually 1 hour) outside normal control settings. Advance controls switch heating on immediately and off again at the next scheduled time.
Occupant controlsInstalling occupancy sensors can yield considerable savings by ensuring that building services only operate when there is somebody there to benefit. These controls are only suitable for fast response services such as lighting and individual ventilation fans. The main types of sensing technology available are:
Passive infra red (PIR) sensors - the cheapest and most commonly seen sensors which can only ‘see’ in direct line of sight
Ultrasonic sensors - emit and receive high frequency sound waves and can pick up smaller degrees of motion even outside their line of sight
Microwave sensors - generate and receive microwaves. Commonly used in automatic doors and able to provide good directional and spatial coverage
Combined or hybrid sensors - provide greater accuracy and improved response by combining some of the above technologies in one sensor. This does however, increase purchase costs, making them less viable for smaller spaces.
Condition controls
Energy savings and improved occupant comfort can be achieved by monitoring and adjusting building services in response to internal conditions. The conditions that are usually controlled are:
- Temperature
- Day light levels
- Humidity
- Carbon dioxide levels.
Control by temperature using room and local thermostats (e.g. radiators, hot air units). Where different systems are using separate thermostats in the same space, it is important to ensure that both systems do not operate at the same time. For example in an office, heating should switch off at no higher than 19-20°C and cooling should switch on at no lower than 24°C.
- Interlocking controls - can prevent two systems operating in competition with each other
- Compensation controls - can reduce the temperature of heating system fluid in milder weather to provide better comfort and reduce costs.
Control by daylight to reduce lighting costs by 20%. Used to control both internal and external lighting and can easily be combined with occupancy and / or time controls.
Control by humidity is useful in specific applications (eg leisure centres), particularly to control ventilation rates using a ‘humidistat’. Humidistats can switch on (or vary the speed of) fans in response to rising humidity levels.
Control by carbon dioxide levels is a form of occupancy control. Sensors switch on or adjust the speed of ventilation fans in response to rising levels of carbon dioxide. Zoning
Some areas in large buildings require different service levels of heating, cooling, ventilation and lighting. Creating 'zones' in a building allows separate time, temperature and occupancy control to be provided to these areas.
Zoning should be considered where there are:
- Different occupancy patterns
- Different temperature requirements
- A number of floors (particularly where top floors are poorly insulated).
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