The Sussex Kidney Centre, a part of The Royal Sussex County Hospital, is a relatively new building which first opened in 2004. Its HVAC systems are based upon chilled beams fed by 8 Hoval boilers and two Carrier chillers located in a roof plant room.
The unit, comprising two floors contains a mix of consultant’s offices, wards for patients who need overnight stays and day only wards for kidney dialysis patients.
Since first opening, the building had suffered problems, particularly in areas where kidney dialysis patients are treated, of areas being too hot or too cold. This generated numerous complaints from patients and staff alike. The system was initially found by us with the 8 air handlers which supply the building running at an output temperature setpoint of 23°C. Following some research in O & M manuals and designer’s specifications as well as discussions with site staff it was discovered that this setpoint had been increased from the design value of 15°C by them.
This was in an attempt to alleviate some of the problems experienced in the building where condensation was found to drip from chilled beams onto patient’s heads when the beam was in cooling mode. By raising the setpoint at the air handler, humidity was decreased and the chilled beams condensation issue was resolved but with a major negative effect on energy consumption. This unfortunately resulted in all areas being heated although some did not require it and many others required additional cooling to maintain reasonable conditions. This happened particularly in areas where a lot of heat emitted from medical equipment is present such as in dialysis wards where the dialysis equipment emits large quantities of heat. These hot areas were calling for chilling thus wasting energy by bringing on the chillers even on the coldest day of the winter.
Another drawback was the controls that manage the boilers, chillers and chilled beams which were unstable and poorly designed leading to instability and heating fighting cooling in both air handlers and chilled beams alike. This was apparent when a thermal survey was undertaken in the building and temperature mapping undertaken with our logging equipment.
Due to the inability of the York BMS system to provide adequate trend information, a North Systems Obsys system was installed and linked to the BMS outstation controlling the building.
This system confirmed that the 8 boilers, 8 AHUs’, 2 chillers and the 90+ chilled beams in the building were poorly controlled by an inadequate control strategy and a substantial control strategy redesign was required.
Initially, it was agreed with the Trust that a controls re-design would be implemented in a “Model Area” only. The model area comprised of a single AHU feeding several dialysis wards, nurses’ stations and consultants’ offices on one floor of the building.
The model area strategy was implemented and once sufficient data had been collected to give confidence in the new control strategy the Trust agreed to implement it throughout the building. The new software was then installed to the Trend control system for every AHU and each chilled beam and proven to work effectively.
All eight AHU output setpoints were reduced to 15°C as required by the building design specification. As 50% of the building was unoccupied during evenings and throughout Sundays, the BMS schedules were set to reflect this on appropriate air handling equipment supplying them and these were switched off for the first time ever.
Using a combination of thermal imaging, Obsys data and gas and electricity consumption data, it was possible to prove to site engineers that, once the revised control strategy was implemented, the system functioned as it had been designed to do.
Data from the metering system confirmed the annual savings which were:
Gas savings of £21,115 or 428,874 kWh and 78.6 tonnes of CO2.
Electricity savings of £5,385 or 54,804 kWh and 28.7 tonnes of CO2.
An added bonus has been the complete elimination of complaints about air conditioning in the building from staff and patients as the improved controls maintain the building environment effectively in the comfort zone as designed.
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