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GCC-spec Air Handling Unit

Principal Investigators:
Dr. Afshin Afshari, Professor of Practice, Engineering Systems and Management, Masdar Institute
Dr. Peter Armstrong, Associate Professor in Mechanical Engineering, Masdar Institute

Brief:
Aggregate cooling load in Abu Dhabi is almost 80% sensible load (responding to conduction, solar, internal gains, and sensible cooling of ventilation air) and over 20% latent load (removing moisture generated by occupants and that enters with ventilation air) [Ali, 2011].

Of the latent load, ventilation air comprises the majority. Ventilation air conditioning loads can be reduced cost-effectively by transferring heat and moisture from incoming air to exhaust air (Mumma, 2012) in a process called enthalpy recovery. Enthalpy recovery can be implemented in constant volume (CV), variable air volume (VAV) and dedicated outdoor air systems (DOAS).

Commercial DOAS systems with enthalpy recovery are currently being demonstrated in Masdar Block 6 (B^) and the Masdar Field Station (MFS). However the use of enthalpy recovery is a fairly new technology that and has not been well optimized for local conditions. Abu Dhabi represents an extreme case in terms of annual wet-bulb degree days and year-round humidity. There is consequently an opportunity for significant energy savings by developing DOAS and other enthalpy recovery designs specific to GCC conditions.

Objectives:
The project will develop ventilation enthalpy recovery designs and specifications that condition ventilation air by enthalpy recovery to the greatest cost-effective extent. This will not only reduce the total vapor compression cooling load but will also enable more aggressive chilled water reset schedules that will improve COP for the remaining load. A component-based enthalpy-recovery AHU model is being developed that can include various enthalpy wheel designs, run-around heat exchangers (wheel, heat-pipe, or counterflow finned tube types) and dehumidification coils (chilled water and DX types) or liquid desiccant dehumidifier elements.

The model will be validated against MFS and B6 DOAS equipment. DOAS enhancements like high-effectiveness enthalpy wheel and variable-speed DX dehumidification coil will be tested at Masdar Institute’s Field Station. A market transformation plan will be developed.

Relevance:
Latent cooling represents over 20% of aggregate cooling energy use in Abu Dhabi. Of this, savings of over 80% can be achieved with properly optimized ventilation air conditioning equipment, i.e. 0.2*0.8=16% of total cooling energy.

If we add the savings on the sensible cooling side due to enabling of high temperature chilled water another 5% (by simply changing the chilled water temperature reset schedule) to 20% (by converting to radiant or chilled beam) savings can be achieved.