Analysis of a flexible steam-generating heat pump with selected control strategies and integrated heat storage by steam accumulator

To unlock emissions reduction alongside demand-side flexibility in industry, steam-generating heat pumps must ensure a continuous and steady steam supply to users during power modulation events. This study aims to understand and characterise the steam supply dynamics and off-design performance of various heat pump control strategies that could be used to enact demand-side flexibility. Dynamic simulations of a 5 MW th steam-generating heat pump reveal a significantly different power modulation range, system efficiency impact and delivered steam fluctuations of the tested control strategies. Coupling a downstream steam accumulator is shown to enable demand‑response without compromising the continuity of steam. New accumulator design charts and sizing correction factors are derived to ensure this is the case, which traditional steady‑state analyses fail to do. Through a combination of control strategies, an overall 48 to 164 % power modulation range could be spanned by the heat pump. Variable rotational speed control enables turndown to 48 % power absorption and up to 11 % higher COP compared to rated conditions, and variable inlet guide vanes yield up to 164 % power absorption with COP reductions below 13 % from rated values. Development of compressor technology with improved surge and choke characteristics, as well as co-design of steam-generating heat pumps and thermal storage, are follow-up research directions towards promoting flexibility from the integrated system considered.