Energy Performance Certificates

1. Energy Performance Certificates Building Services - Controls PRESENTED BY

2. LEVEL 3 BUILDING SERVICES TRAINING Control Systems  Effective control of boilers is a significant factor in achieving good energy efficiency. Inadequate or incorrect application of boiler control can add 15–30% to fuel consumption.   The following points should be noted: • The control of multiple boilers is often poor • The reduced standing losses and improved part load efficiency of modern well insulated, low water content boilers normally allows very simple hydraulic arrangements to be used for multiple boilers • Simple layouts do not require the use of individual boiler pumps, or automatic isolation valves, which are the cause of many problems associated with the control of multiple boilers

3. LEVEL 3 BUILDING SERVICES TRAINING Optimum Start Controls These have a control centre which computes the building internal temperature and the external air temperature. This is used to programme the most fuel efficient time for the boiler and associated plant to commence each morning and bring the building up to temperature ready for occupation. The system may also have the additional function of optimising the system shutdown time

4. LEVEL 3 BUILDING SERVICES TRAINING Compensated Circuit This system also has a control centre to compute data. Information is processed from an external thermostat/sensor and a heating pipework immersion sensor. The principle is that the boiler water delivery temperature is varied relative to outside air temperature. The warmer the external air. the cooler the system water and vice versa. The capital cost of equipment for these systems can only be justified by substantial fuel savings. For large commercial and industrial buildings of variable occupancy the expenditure is worthwhile. particularly in the intermediate seasons of autumn and spring, when temperatures can vary considerably from day to day.

5. LEVEL 3 BUILDING SERVICES TRAINING Weather Compensator Commonly referred to as a variable temperature circuit, the compensator can be used in both warm air and wet systems. Its role in life is to vary the heat input to a building with respect to the outside temperature.It is used as an economical solution to controlling the heat input to a building or a zone in a building to provide comfort conditions in the space with fuel economy.The most effective means of controlling the space temperature is for each room to have its own temperature controller. The capital costs to installing such a system are usually prohibitive; this gives rise to the heating design engineer selecting a less expensive method of control.

6. LEVEL 3 BUILDING SERVICES TRAINING In low-pressure hot water system with radiators a heating design engineer will calculate the size of the plant required (boilers, pumps, radiators etc.) in order to achieve comfort conditions within the space with a boiler flow temperature of 82DegC when the outside temperature is -1DegC.It therefore follows that when the outside temperature is above -1DegC, comfort conditions can be achieved with a boiler flow temperature of less than 82DegC. The compensator achieves this by monitoring the outside temperature, comparing this to the set parameters and adjusting the final control element (valve or boiler) until the water flow temperature achieves the desired temperature.

7. LEVEL 3 BUILDING SERVICES TRAINING It must be remembered that the compensator is a compromise between economical installation costs and comfort control. It is true that the outside temperature acts on the whole building and if the system is properly balanced reasonable control can be achieved. However no account is taken of local heat gains from people, computers, machines, solar radiation etc. and without further localized control (e.g. thermostatic radiator valves) some variation in temperature can be expected across the building.

8. LEVEL 3 BUILDING SERVICES TRAINING It is common nowadays to include a room temperature sensor to act with the compensator. This should only be used to vary the calculated water temperature slightly and usually not more than by 3DegC for every 1DegC that the actual space temperature differs from the required comfort condition. This is because it is usually very difficult to decide where to situate the room sensor. If the room sensor had a dramatic effect on the heat input any local heat gains or losses in this area would adversely affect the other areas of the building. A compensator can be used to modulate a 3 port mixing valve, directly switch a boiler on and off or drive a step controller to switch a number of boilers in sequence.A mixing valve is used when there is more than one zone or when the boiler is used to provide domestic hot water as well as heating.

9. LEVEL 3 BUILDING SERVICES TRAINING Energy management systems can vary considerably in complexity and degree of sophistication. The simplest timing mechanism to switch systems on and off at pre-determined intervals on a routine basis could be considered as an energy management system. This progresses to include additional features such as programmers. thermostatic controls. motorised valves, zoning. optimum start controllers and compensated circuits. The most complex of energy management systems have a computerised central controller linked to numerous sensors and information sources.

10. LEVEL 3 BUILDING SERVICES TRAINING These could include the basic internal and external range shown schematically. Along with further processed data to include: the time. the day of the week, time of year. percentage occupancy of a building, meteorological data, system state feedback factors for plant efficiency at any one time and energy gain data from the sun, lighting, machinery and people.

11. LEVEL 3 BUILDING SERVICES TRAINING Controlling multiple boilers in sequence: Matches the number of boilers firing to suit the load Minimises the number of boilers firing, thus, maximising overall efficiency Avoids short cycling of burner operation and, therefore, enhances energy efficient and stable operation Is normally carried out with respect to boiler circuit return temperature, although flow temperature can be used. Sequence control will not operate correctly where the flow varies as a result of individual boiler pumps or automatic isolation valves.

12. LEVEL 3 BUILDING SERVICES TRAINING Burner Controls Single-stage, two-stage and modulating burners are available. Two-stage high/low burners provide more stages and therefore improved part load efficiency compared with single-stage burners. Where high/low boilers are more efficient at low fire (e.g. with a flue damper) then the sequence should gradually bring them all on at low fire before bringing any on at high fire. Modulating burners provide the most efficient part load operation as air/fuel ratios can be maintained across the output range, ensuring high combustion efficiency. LTHW boilers with modulating burners are now becoming more widely available, providing a means of matching the load more accurately across the full output range. In larger boilers this offers the opportunity for oxygen trim control to further optimise the air/fuel ratio. Oxygen trim control can provide savings from 2% for a well maintained boiler, up to 5% for older boilers with hysteresis in linkages, etc

13. LEVEL 3 BUILDING SERVICES TRAINING Directly compensated boilers Direct compensation of non-condensing boilers is normally of little benefit with modern high efficiency boilers due to their low standing losses and the need for separately pumped secondary circuits.. However, directly compensating the primary circuit is an ideal way of achieving low return water temperatures and therefore high efficiencies with condensing boilers. Where heating and hot water are being supplied from a common plant then compensation must be overridden when hot water is required, possibly resulting in overheating of the space. Use a separate hot water supply where possible.

14. LEVEL 3 BUILDING SERVICES TRAINING Time controls Time controls should be provided to automatically control the number and duration of operating periods, with provision for day omissions. Programmers with separate weekday/weekend settings are now cheap and easy to install. Programmable room thermostats can be a cheap and flexible means of providing both time and temperature zone controls.

15. LEVEL 3 BUILDING SERVICES TRAINING Fixed Time Controls A time switch provides a simple, robust and easily understood means of saving energy and should have a resolution of 15 minutes or less for effective operation. ‘Run-back’ timers giving a fixed additional period of operation are useful where occupancy is particularly unpredictable or where extensions to the normal heating period are needed. They are particularly useful in offices and shops where evening work is sometimes carried out, and in function rooms where occupancy is unpredictable.

16. LEVEL 3 BUILDING SERVICES TRAINING Temperature Controls Good control of space temperature is required for energy efficient operation. Control of space temperature can often be achieved at low cost using TRVs. Reducing the room temperature by 1 °C can reduce the fuel use by around 10%. Distribution systems should be weather compensated unless constant temperature is absolutely necessary (e.g. air heater batteries or domestic hot water). This reduces system losses and provides basic space temperature control, although it will not react to internal gains etc.

17. LEVEL 3 BUILDING SERVICES TRAINING Multiple compensated circuits are ideal for zoning a building to allow for different occupancy patterns. etc. Where different emitters are used, or parts of the building are better insulated, the compensator schedule can be set to reflect the differing zonal temperature requirements. Zone Controls Heating is often required at different times, temperatures and areas of a building. A successful control system will satisfy these different requirements on a zone by zone basis. A zone may be regarded as a part of the building the heating system of which is capable of independent control, in terms of time, temperature, or both.

18. LEVEL 3 BUILDING SERVICES TRAINING Thermostatic Radiator Valves Thermostatic radiator valves (TRVs) provide a low cost method of local temperature control on individual emitters, particularly where there are high incidental gains. TRVs are normally two-port and should be used in association with variable speed pumps to provide good control Lockable tamper-proof heads are also recommended. These can either be completely locked on one setting, or provide a minimum level of control for the adjacent occupants.

19. LEVEL 3 BUILDING SERVICES TRAINING Motorised valves and room thermostats   Motorised valves and room thermostats can be used to provide temperature and/or time control of a zone. This method is probably best used in areas with a small group of emitters, say totalling over 5 kW.   Sensing locations are better than TRVs and a wider range of emitters can be controlled. Reset of space temperature for unoccupied periods can also be more easily achieved. Further energy savings can be achieved by installing time control in zones using two-port motorised valves, room thermostat and time control independent from the main heating time control.

20. LEVEL 3 BUILDING SERVICES TRAINING Programmable room thermostats are a convenient way of achieving this as they combine the roles of time switch and electronic room thermostat, e.g. by varying the room temperature at different times of the day in an elderly persons’ day centre. Larger zones should also be weather compensated, particularly where a boiler supplies a number of buildings or to allow for solar gains on different facades. Multiple secondary circuits should normally be connected in parallel across a common header so that each one has the full heat source available to it. This system is relatively simple and allows good control to be achieved. More sophisticated space temperature control systems are also available including occupancy sensing.

21. LEVEL 3 BUILDING SERVICES TRAINING End of Section