Motor control centers (MCCs) are present in many industrial facilities, and typically require active space conditioning to ensure that excess heat generated from the electrical equipment is removed from the center. The cooling load can be viewed as a low-temperature heat resource, and be used to offset low-temperature thermal demand at the industrial facility. This post discusses a project which utilized water source heat pump (WSHP) equipment to serve the MCC cooling load while lowering both electricity and fuel consumption of the overall facility.
Facilities with thermal demands can often utilize low-temperature heat to pre-heat makeup air or water for either process or boiler use. The facility discussed here has a constant boiler makeup water demand drawn from an on-site water source or the municipal water supply. By replacing the existing conventional vapor-compression equipment with WSHP units, the waste heat from the MCC is used to pre-heat boiler makeup water, ultimately reducing boiler fuel consumption and greenhouse gas emissions.
In addition to boiler fuel savings, this project also realizes electric consumption savings. The existing cooling system utilized conventional vapor compression cooling equipment, which accepts heat within the MCC room at a low temperature and rejects heat to ambient air outside the MCC room at approximately ambient temperature. The WSHP equipment which replaced the existing cooling equipment accepts heat within the room at the same low temperature, but uses the makeup water for heat rejection at a temperature below that of ambient air, providing more efficient operation compared with the existing cooling system. The WSHP units were also specified to be provided with economizer units which allow for direct heat exchange between the makeup water and the MCC room air, eliminating energy consumption other than fan use of the WSHP units during times when temperatures are conducive to this operation. Operating at a higher efficiency and also allowing use of economizers provides electrical savings to the facility.
The table below presents the estimated electric and boiler fuel consumption and cost savings this facility will realize as a result of this project, using an assumed $0.10/kWh electric price, and $8.00/mmBtu boiler fuel price. With grid electric and natural gas as boiler fuel offset, this project is estimated to realize over 120 metric tonnes of carbon dioxide equivalent emissions reductions per year in addition to the monetary savings.
This type of approach could be implemented at any facility with a low-temperature thermal demand such as pre-heating air or water and an MCC room which requires cooling. Feel free to contact us if you would like to discuss this as it relates to your facility.