A circumstance with both heat and cold demands has emerged ubiquitously across building and urban scales. This scenario is ideally addressed by implementing a heat pump for simultaneous heat and cold production. However, ongoing challenges exist in identifying the thermodynamic effectiveness of simultaneous heat and cold production mechanisms (why) and harmonizing the time and amount of simultaneous heat and cold production with the diverse user demands (how and what). In this paper, a simultaneous heat and cold production system (SHCPS) is proposed. Three pivotal questions related to its underlying principle, design methodology, and applications are elucidated. The heat pump for simultaneous heat and cold production in this study outperforms unidirectional ones by achieving a low ratio of electricity consumption (RP) within a temperature difference of 75 ℃ between heat and cold, resulting in potential energy savings of up to 46 %. The serial-parallel configuration of the system facilitates three universal capacity sizing and operation methodologies to deal with disproportionate heat and cold production and demand: demand-based, bidirectional heat pump production-based, and balanced ratio-based strategies. In a typical supermarket scenario, the balanced ratio-based strategy can yield a 35 % occupied space reduction of storage units and attain comprehensive cost reductions in the short to medium term. The demand-based strategy holds more advantages under larger peak-to-valley electricity price ratios and in the long term. When the peak-to-valley electricity price ratio reaches 3, the investment payback period for these three strategies is within 5.2 years. The solutions to these three questions herein are anticipated to fundamentally address the practical obstacles involved in applying heat pumps for simultaneous heat and cold production, introducing novel insights into global heat and cold production patterns.