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CARBON AND ENERGY SAVING


Stage 1 – Immediate to short term Many acute hospital sites will be at a stage whereby good work may well already have been undertaken with lighting replacements and other demand-side reduction measures, but primary heat infrastructure will not have changed significantly for many years. Some sites may have already adopted combined heat and power (CHP) in an effort to achieve revenue savings. At these sites it is common to see the utilisation of centralised gas-fired boilers with high temperature heat distribution (steam and MTHW) to serve the various parts of the hospital estate.


The response to this typical scenario is likely to need consideration to the ongoing viability of the primary heating plant and associated high temperature heat distribution, since this represents the biggest influence on the ability to reduce the site’s carbon emissions going forward. If gas-fuelled CHP has already been deployed, it will already have reduced a proportion of the heat load and associated losses from the high temperature heat distribution side, through utilisation of CHP engine jacket heat recovery, to provide some low temperature heat distribution instead. While when these sorts of solutions were originally conceived the carbon savings opportunity would have been significant, due to ‘the greening’ of the electricity grid, they will now be less likely to show carbon-saving persistence beyond a few years, unless further measures are undertaken to build upon the concepts started.


Stage 2 – Short to medium term The next stage is one where significant investment may be needed to move into a position where a site is ready for the future and where, if CHP is still operated, it is done so in a way that saves carbon, rather than making emissions worse. Stage 2 solutions need to be laying the foundations for heat delivery that can use the best available technology now, and will also be able to accept future


Projected CO2 2000 e savings: tCO2 e/year, based on ‘greening’ the National Grid


1500


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–500


–1000


2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 Year


Figure 2: A typical existing unoptimised (electricity-led) gas CHP potential carbon- saving performance in the future – based on assumed continuing decarbonisation of the UK National Electricity Grid.


technology as it comes to commercial maturity.


Most high temperature heating distribution systems lose a great deal of heat from higher exhaust temperatures, poor insulation levels, and in the case of steam, through low levels of condensate recovery, unreliable steam trap operations, and large standing losses. In a recent study, one 500-bed hospital had a standing loss of 300 kW from its steam system. While the level of heat transferrable by steam may be much higher than that conveyed by low temperature heat distribution (LTHW), these inefficiencies usually outweigh the case for their continuance when compared with more efficient LTHW incorporating variable flow pumping and lower heat losses.


Replacing gas-fired steam boilers Initially, gas-fired steam boilers can usually be replaced with modern part condensing LTHW gas boilers, embedded in a new LTHW heat network. These may in turn ultimately be replaced with electric heat pumps, which in the next few years


will be able to deliver the temperatures needed to work even more efficiently with LTHW networks, resulting in increased transfer of heat generation away from fossil fuel boilers over to low carbon electricity.


For CHP, when the focus is on prioritising carbon saving, we find solutions that once drove down carbon now need to be re-optimised, as otherwise they start to deliver detrimental results in a low-carbon electricity grid landscape. An inappropriately sized or unoptimised gas CHP will generate more carbon than it saves over its life, based upon a continuing fall in grid electricity carbon intensity. There are arguments that say it is fairer to judge CHP fuelled by natural gas against the time of day and seasonal variance in electricity grid carbon content, rather than the annual average carbon, which is the norm for reporting protocol. However, gas CHP solutions tend to operate at the same output all year round to maximise financial savings. Unless they are modulated against available renewable content on the grid at any one time, then


June 2020 Health Estate Journal 43


Carbon saved per annum against baseline tCO2


e


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