Homogeneous computing systems are reaching their limits with the growing demands of current applications. Accelerating compute-intensive applications ensures manageable computing times and boosts energy efficiency, which is an important lever as part of ongoing efforts to tackle global climate change. Field Programmable Gate Array (FPGA) accelerators are well-known for increasing throughput and, in particular, energy efficiency for many applications. FPGA accelerators connected directly to the data center high-speed network are ideal for integration into a heterogeneous data center, avoiding the energy and resource overhead of a carrier system. The standalone Network-attached Accelerators (NAAs) further benefits from low latency and predictable line-rate network throughput, as well as an interoperable communications interface. For selected use cases, we compare a heterogeneous computing cluster extended by NAAs with a homogeneous CPU-based cluster not only in terms of computing performance and energy efficiency, but also considering resource efficiency. For this purpose, we perform a Life Cycle Assessment (LCA) for both systems based on the Key Performance Indicators for Data Center Efficiency (KPI4DCE) indicator set, which takes into account the manufacturing phase in addition to the usage phase. The KPI4DCE tool has been extended to include modeling of NAAs. This allows us to show that NAAs are not only more energy-efficient, but also more resource-efficient for the selected applications, leading to a strong improvement of the environmental impact of the manufacturing phase.