A suite of energy saving recommendations associated with the control and operation of the heating system at St. Mary’s Hospital were identified and implemented.


The 2023 Climate Action Plan reaffirmed several targets for public bodies that had been originally introduced in previous iterations of the plan.  These include a requirement that all public bodies must reduce their GHG emissions from burning fossil fuels by 51% by 2030, compared to a 2016-18 baseline.  They must also reduce their electricity emissions in line with anticipated supply-side reductions.  SEAI’s pathfinder programme has been working collaboratively with public sector organisations to develop scalable solutions to meet these targets, for benefit across the public sector and the wider non-domestic sector. 

Under the OPW’s Optimising Power @ Work programme, a Preliminary Energy Audit and Building Management Survey, carried out by Powertherm Consulting Engineers in conjunction with HSE personnel, identified a suite of energy saving recommendations associated with the control and operation of the heating system at St. Mary’s Hospital.  The BMS recommendations were implemented under this Pathfinder project, together with lighting, fabric and pump upgrades, and the installation of a PV system. 

  • Electricity savings

    730,500 kWh/y
  • Gas Savings

    2,339,000 kWh/y
  • C02 Savings

    664 tonnes/y (2022 emissions factors)
  • Abatement Cost

    €1,820/tonne C02 (single year's C02 savings)


The building to become St. Mary’s Hospital was founded in 1769 as the Royal Hibernian Military School and did not see medical purpose until it was handed over to the Irish Government in 1922.  In 1948, the hospital was transferred to the Dublin Health Authority, and in 1964 it took on the role it provides today.  The 100-bed unit and day hospital were built in 2008, with the 50-bed unit added in 2009. 

The hospital provides residential long stay care and day care services to older persons.  In addition, the hospital has 75 short stay beds, including a 10-bed stroke rehabilitation unit, a 12-bed unit for young persons with physical and sensory disability, a Healthy Aging Clinic, which provides diagnostics and education services, an Ambulance Training Centre, and an Addiction Clinic.  There is also a pharmacy on site that is not part of the hospital.  The site is approximately 32 acres in size. The hospital runs 24/7 and has a large demand for hot water, heating and electricity.  A range of gas-fired boilers and a combined heat and power (CHP) unit supply space heating demands across the campus, with a number of separate boilers meeting domestic hot water (DHW) demand. 

Project Description

The programme of works carried out in this project included modifications to the building management system (BMS) associated with the 50-bed and 100-bed units, commissioning/replacement of the existing BMS for Phoenix Hall, and connecting the three BMS to a front end located in the Maintenance Office.  Alongside this scope, LED lighting upgrades, advanced boiler load control, solar photovoltaic (PV) installations on the 100- bed residential unit and Phoenix Hall building, site-wide cold water and hot water pump upgrades and external insulation wrap of Phoenix Hall were also implemented. 

100 bed unit

The energy audit identified that the BMS in Keltoi / Phoenix Hall had not been commissioned properly, and that all plant in this area was running in manual mode.  These areas are a significant energy user on campus, responsible for ~10% of total gas consumption on site.  Recommissioning of the BMS was identified as a priority, with likely payback in a very short period, particularly as Phoenix Hall has a Monday to Friday usage profile.  The lack of heating control was likely to have contributed significantly to the overheating issues which were frequently observed in these areas also; project works are expected to result in improved comfort levels for occupants, in addition to energy and emission savings. 

Advanced on-boiler load control was implemented across the campus for the purpose of reducing energy lost to redundant tasks such as dry cycling, short cycling, and responding to hydraulic short circuiting.  Controllers were specified to be compatible and integrate seamlessly into the new BMS interconnected system for the hospital.  Additionally, the control systems were designed with a means of data acquisition to monitor the resulting energy impacts.


Table 1 shows a comparison of projected energy savings compared to actual performance.  Results indicate annual savings of 703,500 kWh of electricity, and gas savings of 2,339,000 kWh gas.  Projected savings were conservative, with actual savings achieved exceeding predictions. 

Two measures in particular delivered significantly higher savings than projected.  Predicted savings associated with advanced boiler control were calculated by a supplier based on the typical savings associated with boiler load control systems.  Actual savings achieved were almost double those projected.  The very high savings are associated with the highly inefficient operation of the boilers before the works were completed; the boilers that were upgraded did not have any controls prior to the works, and were either on, or off and dry cycled regularly, leading to very high wastage.  Therefore, the savings achieved at this site were higher than typical savings associated with these control systems. 

Project AreaElectricity SavingsGas Savings
  Projected kWh/y Measured KWh/y Projected kWh/y Measured KWh/y
LED Upgrade 1 90,000 95,620    
LED Upgrade 2 180,000 198,870    
LED Upgrade 3 35,000 39,520    
Pump Upgrade 80,000 84,530 10,000 10,000
Advanced Boiler Load Control     500,000 996,290
BMS Works     50,000 852,580
Solar PV 220,000 285,000    
Phoenix Hall External Insulation     480,000 480,000
Total 605,000 703,540 1,040,000 2,338,870

Gas savings attributed to BMS works are more than an order of magnitude higher than projected.  While the initial scope of works was being undertaken, it was uncovered that a very large number of controllers and other parts associated with the heating systems were broken, resulting in massive energy wastage.  This led to an internal project with an expanded scope where the house maintenance team worked to ensure the control equipment (valves, actuators, controllers) were in proper working order, thus enabling proper BMS control of the system.  The internal maintenance effort alongside the enhanced controls contributed to the vastly improved gas savings. 


This project demonstrates the very significant savings which can be achieved through advance boiler load control and appropriate BMS control of heating plant, with the additional benefit of improved comfort levels for building occupants. In particular, it highlights the considerable levels of energy wastage which may be associated with poorly controlled plant. Payback periods associated with works to replace or repair valves, actuators and controllers which were not working were very short, yielding energy savings in excess of those achieved via fabric and lighting upgrades. Targeted audits focussing on BMS settings and controls can often yield significant low cost savings.

Learn more about the Pathnfinder Programme