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HVAC SYSTEMS


n Poor integration of low carbon technologies: Hysopt stresses that the performance and


effectiveness of low carbon technologies (condensing boilers, CHP, heat pumps, and heat recovery) are all sensitive to correct hydraulic design, and precise and stable controls. ‘Efficiency comes from correct hydraulic integration and system design’.


n Poor component selection: Correct selection of pumps and valves is an iterative process due to the interdependency of one component over another. For large systems, this can require more than a million calculations, which is ‘impossible to do manually’.


Heating pumps in the boiler house.


to assist in cooling the building in the summer.


n Commissioning by trial and error:A recent study by TNO in the Netherlands suggests that >60% of installations are not commissioned properly.


The system in use at Southend Hospital The proof of any system’s effectiveness is best demonstrated in a real-world setting. One of a number of healthcare organisations to have seen the software in action is Mid and South Essex NHS Foundation Trust, which has ambitious targets to decarbonise its building stock by at least 10 per cent over the next five years. The focus of its first use of the Hysopt software is a clinical building at Southend Hospital – a 700-bedded acute healthcare facility serving a population of around 340,000. The hospital had already gone out to market seeking a heat pump solution to produce hot water and cooling for its three-storey Cardigan Building – which houses facilities including maternity services, operating theatres, wards, and an Intensive Care Unit – as a low carbon demonstrator project. The Hysopt software was used to validate the proposed heat pump installation.


Creation of a ‘digital twin’ The Hysopt software was used firstly to create a ‘digital twin’ of the existing installation; this indicated high operating temperatures, low delta Ts, and high pump consumption due to the constant flow set-up and hydraulic imbalances. The building’s boilers and chillers were consequently cycling on and off, resulting in increased wear and tear and regular small leaks. Hysopt then reviewed the Trust’s proposed heat pump solution by implementing the planned installation into the digital model. Analysis showed that: n Only about one-third of the cooling rejected from domestic hot water production could be usefully recovered


n The overall seasonal COP of the system was calculated at 3.3, ‘much lower than the anticipated COP of >5 suggested by the supplier’, identifying ‘a clear performance gap’ between the promised and likely actual performance.


n While the heat pump solution would achieve a 14% overall carbon and cost reduction for the heating and cooling installation, the hefty investment cost would mean a payback period of 36 years.


Hysopt said: “Importantly, the reason behind this lower performance is not the heat pump itself – but the way it was planned to be hydraulically implemented into the existing heating and cooling installation.”


Alternative options


Using the digital twin already created, Hysopt and the Trust also considered alternative solutions. The option of upgrading the heating installation from


Hysopt emphasises, however, that the conclusion was not that the Trust should not invest in heat pumps for decarbonising its building stock, but that the first step – improving the existing installation – was the logical first stage to achieve carbon savings with a finite availability of capital. It added: “By taking the steps outlined first, the Cardigan Building is being optimally prepared for a future integration of heat pumps due to significantly lower operating temperatures. These will make it possible to not only integrate heat pumps for its domestic hot water, but also for its space heating, thereby creating an opportunity to save a lot more carbon.”


The low loss header in the Cardigan Building boiler house.


Supplier and end-user experience The potential carbon and energy savings identified by the Hysopt software for the Cardigan Building are clear, but to gain a better insight into its use at Southend Hospital, I recently spoke to both Chris Davis, Hysopt’s UK Sales manager, and to his end-customer, John Henry, director of Specialist Services at Mid and South Essex NHS Foundation Trust.


September 2020 Health Estate Journal 75


constant to variable flow was modelled, and a range of optimisation options offered. The resulting analysis showed that this optimisation could generate a 16% carbon saving, and a 21% annual energy cost saving, while with lower initial capital expenditure, payback could be achieved in just over five years. Hysopt said: “This solution requires significantly lower Capex, and will entail only changing a range of pumps and valves, and reprogramming the building’s building energy management system, giving a much more attractive payback period of 5.2 years.”


The headline figures In summary: n The Cardigan Building currently consumes 3 GWh of gas and 177 MWh of electricity annually for its heating and cooling – this ‘equates’ to annual CO2 emissions of 684 tons, and an energy bill (for heating and cooling only) of £106,000.


n The suggested heat pump solution would reduce the gas bill by 15%, while the electricity bill would remain the same – giving an overall carbon and cost saving of 14%, but high investment costs mean a payback of 36 years.


n By not deploying the heat pump, and first concentrating on tackling the existing heating installation, annual carbon savings of 16% and a 21% energy cost reduction should be possible, with payback in just over five years.


©Mid and South Essex NHS Foundation Trust


©Mid and South Essex NHS Foundation Trust


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