Environmental Engineering Reference
In-Depth Information
Table 5.3 Summary of measured efficiencies of desiccant cooling units
Dehumidification efficiency
Humidification efficiency
Heat recovery efficiency
Control Strategy Modelling
The goal of the simulation was to determine the influence of the control strategy on
the system performance and to establish whether different sizing or orientation of
the collector field could improve the solar fraction and reduce the auxiliary energy
demand. The model can work with building cooling loads Q cool calculated using dy-
namic simulation tools or from measured loads obtained from the supplied cooling
energy (calculated using the supply air volume and the measured enthalpy differ-
ence between room exhaust and supply air). For each time step, the programmed
system controller calculates the required supply air temperature to cover the cool-
ing demand of the room for a given supply volume flow. To save electrical power,
the supply air volume flow is first set to 50% of its nominal value. If the resulting
supply air temperature is too low or if the cooling demand cannot be covered by
this reduced volume flow, the flow rates are gradually increased up to the nominal
Q cool
c p V supply
T required = T exhaust
The controller then switches on each of the components subsequently (first either the
exhaust air humidifier plus rotating heat exchanger for the Mataro control strategy or
the supply air humidifier for the Althengstett strategy) and calculates the supply air
temperature. If this temperature is still higher than the required temperature, the next
component is switched on, that is the next humidifier. Finally the sorption wheel starts
operating and if temperature levels are still not sufficient, auxiliary heating or cooling
takes place, depending on the system configuration.
Simulation Results
Using measured July data from the Althengstett system with a time resolution of
5 minutes, the model can be validated. Inputs to the model are the global horizontal
irradiance, ambient temperature and humidity. Room and supply air temperature and
the supply volume flowwere used for the cooling load calculation, which the controller
needs as an input.
The component switch-on times of the simulation model and measured results
in general correspond well (see Figure 5.40). The real component operating times
Search WWH ::

Custom Search