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Minimum Equipment Performance Standard

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:
Electrical energy used to condition (cool and dehumidify) incoming ventilation air and infiltration represents about 25% of electrical energy used for all building cooling loads in Abu Dhabi (Figure, Ali 2011).

Current practice in UAE is to provide conditioned ventilation air by a conventional rooftop air-handling unit (AHU) containing a cooling coil, fan, and electric reheat. The need to dehumidify ventilation air determines the temperature of chilled water required for an entire building. Separation of ventilation AC (VAC) and main building cooling plants is almost never done. Similarly, design enhancements that can reduce VAC-AHU coil loads by passive means or transfer sensible cooling loads to a more efficient main chiller are rarely considered by MEP’s and suppliers.

Modeling and simulation results from the EAA research project GCC-Optimized Ventilation Equipment show that, because of the UAE’s long and severe cooling season, such enhancements are highly cost-effective and can result in ventilation AC energy savings on the order of 50%.

Efficiency levels achieved by these cost-effective AHU designs can serve as a target minimum equipment performance standard.

The intent of a MEPS is not to prescribe a specific equipment design but to mandate a performance level that will bring down life-cycle operating costs. Manufacturers are free to adopt elements of the case-study designs shown to be life cycle cost-effective but they are not prevented from meeting the standard by employing their own innovative designs and efficiency measures instead.

Two types of equipment must be covered by separate efficiency standards: ventilation AC for building pressurization and VAC with balanced supply/exhaust air streams. Buildings that meet a leakiness standard of <1 ACH@50Pa (and dedicated exhaust less than 20% of minimum occupied ventilation rate) wouldn’t require a separate pressurization system. Note that commercial kitchens generally have separate evaporatively-cooled make-up air systems; their exhaust streams are therefore not included in the 20% factor.

References:

  • Ali, M.T., M. Mokhtar, M. Chiesa, P.R. Armstrong, 2011, A cooling change-point model of community-aggregate electrical load, Energy and Buildings, 43(1):28-37
  • Sarfraz, O., and P.R. Armstrong, 2015. Optimal control of heat wheel and enthalpy wheel effectiveness to achieve closed DOAS, ASHRAE Trans. 121(2) (in review)
  • Ali, M.T., and P.R. Armstrong, 2015. Computationally efficient heat pump model to accommodate complex load-side conditions or configurations, ASHRAE Trans. 121(2) (in review)
  • Zakula, T. (2013, June). Model Predictive Control for Energy Efficient Cooling and Dehumidification. Massachusetts Institute of Technology, Massachusetts, USA.
  • Zakula, T., L.K. Norford, P.R. Armstrong. Model Predictive Control for Energy Efficient Cooling and Dehumidification. IBO Workshop, Boulder June 20-22, 2013.
  • Gayeski, N., T. Zakula, P.R. Armstrong, L.K. Norford, 2011. Empirical modeling of a rolling-piston compressor heat pump for predictive control in low-lift cooling, ASHRAE Transactions, 117(2)