Also on this theme, the Danish eFlex project (Dong Energy, 2012) tested the ability of heat pumps to provide turn-down DSR in response to price or wind-generation signals (or a combination of both), while participants could choose to optimize for cost or comfort. Participants only overrode turn-down events (lasting 1–3h)1%ofthe time, or approximately once in three months, leading the report authors to conclude that ‘the customers’ comfort zone has not been seriously challenged’ (p. 36).