How local control saves energy
Heating unoccupied areas of buildings just to ensure that occupied areas are heated is wasteful. Steven Henry of Chalmor looks at the benefits of very localised control of heating.
Variations in use and unpredictable patterns of occupancy can provide real challenges for energy efficiency. The effectiveness of even the best-performing HVAC system can be undermined if heating or air conditioning is supplied to unoccupied spaces. In many ways, these problems have become more pronounced over the last decade.
Changes to working practices, such as hot-desking and 24-hour call centres, have extended hours of occupancy and made usage patterns more difficult to predict in many commercial properties. The same applies to many public-sector buildings. Student accommodation blocks and university libraries with 24/7 access, for example, typically have to be heated throughout, irrespective of occupancy levels. As a result, building owners can struggle to achieve their desired carbon-reduction commitments.
In sites without a BMS, problems can occur when the centralised plant does not have the capability for zone-by-zone control. This can lead to an ‘all-or-nothing’ scenario, with heating having to be supplied to the whole site to meet the needs of any space within it. This scenario can, of course, be much improved by a BMS that can facilitate zone-by-zone control across a site. Typically, however, this does not provide control at a room-by-room or radiator-by-radiator level — where the real potential to reduce energy waste lies.
In the last 12 months, advances in smart room-control technology have made it possible for HVAC system designers to address this problem from the opposite end of the system by using intelligent radiator valves to save energy.
The technology is designed for bolting-on to existing system designs without complex integration. The Chalmor eTRV+, for example, enables individual radiators to be set to operate timed programmes to suit predictable schedules.
Reducing temperature at a radiator level signals to the central plant that supply to the space needs to be reduced. Where the central plant room has variable-speed capability and a BMS, this reduces loading on energy-consuming equipment such as pumps, boilers, chillers and air-handling units. The overheating of radiators can be avoided and, in buildings without a BMS, the ‘vicious circle’ of heating and cooling components of the system are working in opposition can be broken.
Another development in this technology area is occupancy sensing to enhance energy saving in areas with intermittent or variable use. For example, the eTRV+ has an optional PAIR (passive active infra-red) sensor and timer to automatically reduce heating when areas are unoccupied. If occupants return to the space, the radiator is automatically triggered to return the room to the set temperature.
The University of Bristol has installed eTRV intelligent radiator valves to reduce energy wastage in the Hawthorns Building — a 53-room hall of residence. The energy team set the valves to provide heating in the mornings and evenings when students are in their rooms. During the day, the eTRV reduces the temperature setting. Overnight, heating is kept at a lower level. If a student returns to their room and feels a little cool, a manual push-button boosts the temperature for one hour. Heating bills in the Hawthorns Building were reduced by 30%, representing a payback period of just a year.
The University of Bristol has since installed 204 eTRVs into the Churchill and Wills Halls.
In a separate project, a leading London university installed eTRV+ models to replace traditional TRVs in the corridors and kitchens of its halls of residence. In addition, eTRV+ with PAIR replaced traditional TRVs in bedrooms to detect occupancy. These reduce room setpoints to a lower setting (16°C) if the room is unoccupied for longer than one hour. A ‘sleep’ facility provides the option to reduce heating further during longer periods of vacancy. For example, the heating can be set to switch off 24 hours after a student leaves their room, making savings when they are away over weekends or holidays.
By matching demand more closely to actual occupancy, the university has achieved energy savings of 30%. Temperature reduction in unoccupied rooms is identified by the university’s BMS which, in turn, reduces loading on variable-speed pumps and boilers, saving energy across the system. Complex scheduling is avoided and, as the eTRV+ has a weekly valve-exercise feature to prevent valve ‘sticking’ over the summer, maintenance requirements are also reduced.
In conclusion, even with the latest variable-speed BMS-controlled HVAC systems, there remains considerable potential for energy savings. Smart room control can help to unlock these savings.
Steven Henry is managing director of Chalmor.