Master's Thesis Emilie Duval


Optimum design and operation of air handling units

Balancing area of LCC analysis of air handling unit Copyright: EBC Balancing area of LCC analysis of air handling unit

Efficient air handling units supply more and more buildings with conditioned air. In order to ensure comfort in buildings the energy-intensive processes of heating, cooling, humidifying and dehumidifying are performed. Compared to their investment costs, air handling units (AHU) have high demand-related costs (electricity, heat ...). So it is relevant to ask how they should be optimally designed with regards to life cycle costs (LCC) for given boundary condition

I developed functions thanks to an object-oriented programming tool to determine the life cycle costs and the primary energy consumption of AHU with a high degree of details. This model includes various heat and cold generators, various components of AHU that treat the air and the modelling of heat exchanger working based on their design water temperatures and volume flow or on real geometry data. Furthermore, I implemented the calculation of hydraulics with different hydraulic supply and control concepts including the calculation of pump energy consumption.

This tool is used to determine and compare results on LCC from individual subsystems and from the complete AHU for specified conditions. I build a simple optimization using evolutionary algorithms in order to find the best AHU configuration for given boundary conditions. This optimization take into consideration the choice and arrangement of components that treat the air, the type of generators used for heat and cold generation and their temperature regimes and the dimension of the heat exchanger that determines the dimension of the AHU. Then, the different hydraulic systems are evaluated. By using evolutionary algorithms, this optimization process enables to find a good AHU configuration for given conditions.

I found that the optimum AHU configuration use an adiabatic humidifier to provide humidification. Indeed I noticed a gas consumption reduction of 5% by using an adiabatic humidifier with enthalpy control instead of a steam humidifier. Furthermore condensing boilers are more advantageous than heat pumps regarding to their LCC, by using a condensing boiler the annuity costs are of 4747€ whereas the annuity costs are of 7578€ with an air/water heat pump for an AHU with a design air volume flow of 4500 m3/h. Moreover, I noticed that a reduction of the design air velocity leads to costs and energy savings.