屋顶单元（RTU）等成套空调设备广泛应用于小型商业建筑，约占美国商业建筑总建筑面积的52%。新的联邦法规提出了更高的效率标准，并要求新空调设备使用多速送风机。在新标准的推动下，美国的主要暖通空调制造商近年来正在推出变速RTU。本文给出了两种采用可变参数的RTU的性能评估结果- 调速技术:（1）带变速送风机的单速压缩机组；（2）带变速压缩机和风机（包括送风机和室外风机）的变速RTU。以带有定速压缩机和送风机的单速机组为基准，进行了参数分析，以了解性能对气候位置和建筑类型的敏感性。从制造商和承包商处获得成本信息，并用于改造回报分析。 评估结果表明，变速装置的年电能节约潜力最高，可达50%。根据机组类型、气候位置和建筑类型，改造投资回收期在不到一年到30年之间存在显著差异。与仅对送风机进行变速改造的机组相比，由于前期成本较高，变速机组的投资回收期一般较长。由于公用事业成本高，加州的投资回收期最短，大多不到一年。 相比之下，科罗拉多州和佛罗里达州等公用事业费率较低的电力市场由于投资回收时间较长，对变速改造不太有利。引用:2018年年度会议，德克萨斯州休斯顿，会议论文

Packaged air-conditioning equipment, such as rooftop units (RTUs), are widely used in small commercial buildings and serve approximately 52% of the total commercial building floor space in the United States. New federal regulations set forth higher efficiency standards and require multi-speed supply fan operation for new air-conditioning equipment. Driven by the new standards, the major HVAC manufacturers in the US are launching variable-speed RTUs in recent years. In this paper, assessment results are presented for performances of two types of RTUs employing variable-speed technology: (1) single-speed-compressor units with variable-speed supply fans and (2) variable-speed RTUs with variable-speed compressors and fans (both supply and outdoor fans). A single-speed unit with fixed-speed compressor and supply fan was used as a benchmark and parametric analysis was carried out to understand the performance sensitivity with respect to climate location and building type. Cost information was obtained from manufacturers and contractors and was used for retrofit payback analysis. The assessment results show that the variable-speed unit offers the highest annual electrical energy savings potential of up to 50%. The retrofit payback years show significant variation between less than a year to 30 years, depending on the unit type, climate location and building type. The variable-speed unit, in general, gives longer payback period due to the high upfront cost, compared to the unit with a variable-speed retrofit for the supply fan only. California has the shortest payback period, mostly less than a year, due to the high utility cost. In contrast, power markets with lower utility rates such as Colorado and Florida are less favorable for the variable-speed retrofits due to longer payback time.