HOW TO ACHIEVE ZERO UNMET HOURS
(1) COMPLETENESS
After discovering that not all HVAC components had been
installed yet and adding missing components, amount of unmet hours was reduced.
(2) CONSISTENCY
temperature setpoints, and temperature schedules must be consistent,
and temperature differences between in- and outflows must be adequate
to enable the system to provide sufficient heating and cooling power.
(3) VOLATILITY AND INERTIA
Source of highly dynamic change may be solar radiation, or EMS controls,
while the building and the HVAC system may react with inertia.
Performance can be improved e.g. by dynamic shading to avoid extremes
from solar radiation gains, by switching to dynamic (EMS controlled) natural
ventilation (infiltration), and by programming EMS controls with hystereses
in the ON-OFF criteria.
(4) CONVERGENCE AND ERRORS
convergence problems (e.g. due to highly dynamic changes in some zones or HVAC components)
may lead to increased unmet hours results, which partly may be eliminated by steps under paragraph (3).
In one case it was possible to eliminate a convergence problem by increasing thermal mass
of affected zone(s) by cross-mixing, which anyway were not truely separated in reality,
(in EnergyPlus separated only by "air wall") but together constituted a non-convex thermal
zone. Checking (severe) error messages may also help to improve performance.
(5) NECESSITY
It was found that not for all zones the same heating and cooling setpoints need
to apply. Relaxing e.g. the cooling setpoint for a bathroom (which essentially did not need
cooling), finally produced the desired result: ZERO unmet hours during occupied hours.
