  Natural draft direct dry cooling systems (NDDDCSs) combine the benefits of
two traditional dry cooling systems, air-cooled condensers (ACCs) and indirect
natural draft dry cooling systems, to offer advantages such as reduced system
complexity, high thermal efficiency, and low parasitic power losses and
operational costs. These scalable systems can potentially operate in both large
coal-fired power plants (900 MWt) and medium-scale concentrated solar power
(CSP) plants (100 MWt). While prior research focused on NDDDCS steady-state
performance, this study delves into the transient behaviour and start-up
characteristics of this cooling system, crucial for power plants with rapid
start-up requirements or load ramps during electricity demand peaks. The paper
employs a transient 1-D mathematical model to characterize the NDDDCSs'
response to start-up and load ramp conditions under no-wind, presenting results
for both large- and medium scales while identifying limiting factors.
