Pathfinder - St. Dympna's Hospital, Carlow

Objective

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. 

A feasibility study was carried out which identified four options for upgrade of the energy facilities.  Replacement of the existing boilers was the benchmark for all recommendations made in the report.  Energy, carbon and financial savings and costs for each option were calculated.  The option yielding the highest carbon savings coupled with the shortest payback period for energy savings was selected. 

Background

St. Dympna’s Hospital is an old building with origins on site back as far as 1832.  It was taken over by the Department of Health in 1970.  In 2008, Kelvin Grove, a residential unit for adult clients with learning difficulties, was opened.  A local district heating network provided space heating and domestic hot water (DHW) to the Hospital, Kelvin Grove and Sacred Heart Hospital, a long-stay residential and day care unit. 

Heat to the district heating network was supplied by two Hoval ST-Plus boilers, with space heating in buildings by means of radiators.  A CHP unit was also installed but was out of service and hydraulically disconnected from the district heating network at the time of the feasibility study.  The study concluded that the heat demand on site was incompatible with CHP operation and did not recommend recommissioning of the unit, which had been out of service for some time. 

Project Description

The programme of works carried out in this project included replacement of the end-of-life boilers, and the installation of heat pumps to supply space heating and DHW to Kelvin Grove, and DHW to Sacred Heart. 

The old boilers were replaced with new, smaller modulating condensing gas boilers, to supply space heating and DHW to St. Dympna’s and space heating to Sacred Heart.  Removing DHW supply to Sacred Heart from the district heat network allowed the new boilers to weather compensate and to reduce operating temperature, thus increasing operating efficiency of the system. 

Performance

The original programme scheduled works to commence in April 2021, with project completion by August 2021.  Very significant equipment delivery delays resulted in an extended programme, with the Sacred Heart DHW heat pump, the last stage of the installation, commissioned in late 2022.  Long lead times for this heat pump with a four-month delivery delay were compounded by an incorrect model being initially delivered, adding a further 9 months to the programme as the correct model was supplied. 

Baseline data was taken from 2019 as a comparison case, thus avoiding potential data anomalies associated with Covid lockdowns in 2020 and 2021.  Comparing 2023 performance with baseline consumption, there was an increase of ~273MWh in electricity consumption, and a 1,267MWh reduction in gas consumption. 

Gas consumption in a given year is heavily dependent on ambient temperatures experienced during the heating season.  To allow a like-for-like comparison, a heating degree day (HDD) analysis of gas usage in the baseline year was carried out.  This demonstrated excellent correlation between gas consumption and HDD, which was used to predict expected gas usage in 2023 with the original heating system (i.e. quantity of gas which would have been consumed if the project had not been carried out).  2023 gas usage compared to expected usage if the project had not been undertaken is shown in Figure 3, together with a chart comparing monthly electricity usage in 2023 with the baseline. 

Electricity consumption was 28% higher than the baseline, while gas consumption was 14% lower than the baseline, resulting in an overall reduction in total final consumption (TFC) of 7%.  The feasibility study estimated electricity increases in the order of 12% relative to the baseline, and gas savings in the order of 40%;therefore overall savings achieved by the project are lower than those outlined in the feasibility study.  The purpose of the feasibility study estimates was to provide a broad comparative tool to allow alternative options to be compared and evaluated.  Predictions were based on assumed percentage savings achievable and, in the absence of submetering data, generic assumptions regarding the heat demand in different facilities.  This would result in considerable uncertainty around the predicted savings figures. 

In addition, from operating experience at other sites, actual seasonal coefficient of performance figures for the heat pumps are likely to be lower than the figures assumed in the feasibility study (3 for space heating heat pump, 2.5 for DHW heat pump).  While sufficient to allow a comparison of different options, absolute savings estimates need to be treated with caution. 

Notwithstanding the fact that overall energy savings are lower than estimated from the feasibility study, the project has nonetheless resulted in a significant reduction in overall total final consumption and carbon emissions. 

Insights

The divergence between estimated potential savings outlined in the feasibility study and those logged post-installation highlight the uncertainties around estimating potential savings. The purpose of the savings estimates in the feasibility study was to allow various retrofit options to be evaluated. In circumstances where an accurate estimate of savings to be achieved is required in order to inform a decision regarding the viability of a project, it may be necessary to undertake additional submetering of energy uses across a site in advance of the works, both to validate the assumptions made, and to avoid the use of generic percentage saving assumptions associated with individual proposed measures