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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Temperature control schemes for buildings with a PCM-composite envelope




Abstract

Phase change materials (PCMs), embedded in building envelopes, have been considered to reduce the energy demand and cost associated with heating and cooling buildings. Their reversible melting and freezing during the course of a day reduces and delays the thermal load on the building. One must also wonder if the HVAC control schemes currently used (e.g., on-off control) are still appropriate for buildings with envelopes containing such thermally active PCMs. This study compares various indoor temperature control schemes for a single room with a microencapsulated PCM-composite wall exposed to diurnal thermal load typical of Los Angeles, CA. The control schemes considered included on/off, proportional, and model-predictive control (MPC) schemes. Their performance was compared in terms of daily cooling energy consumption and electricity cost accounting for time-of-use electricity pricing. Compared with a plain concrete envelope, the addition of 20 vol.% microencapsulated PCM to the room envelope combined with on/off or proportional control schemes decreased the energy consumption and the associated cost by about 24 and 32%, respectively. In addition, the formulation of a MPC algorithm was adapted to account for phase change in the PCM-composite wall. It was designed to either minimize total daily energy consumption or electricity cost. These MPC schemes achieved energy and cost savings of around 34 and 43%, respectively. Overall, MPC schemes appear to offer the largest reduction in energy consumption and/or cost when the building envelope contains embedded PCMs. These results can design of energy-efficient buildings with PCM-composite envelopes.

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