The UTSS has two main modes of operation - charging and cooling.
Factors leading to high efficiency can be categorized as either inherent to the UTSS system itself, or emergent as a result of integration to the DX system.
The UTSS was designed to operate with refrigerant as the heat transfer fluid for both charge and discharge modes.
The UTSS cooling cycle capacity is not a function of ambient temperature, and this becomes an important source of efficiency gains for the UTSS/DX system as a whole.
UTSS designed for DX systems benefit from night/day temperature swings.
The UTSS control strategy for the charge mode also includes a delayed start time for charging.
Performance penalties associated with high daytime rooftop temperatures are also eliminated with UTSS operation.
The UTSS utilizes evaporator coils designed for liquid overfeed.
UTSS systems reduce the impact of over-sizing on energy efficiency.
UTSS systems also provide dehumidification without negatively impacting the efficiency of the overall system.
The UTSS employs a refrigerant pump and avoids the compressor cycling problem completely, both for itself and the DX system: the UTSS starts the charging module compressor exactly once a day, for a minimum loss, and the DX compressor does not run (or cycle) during peak hours, reducing the number of DX cycles by 50% or more.
There are many challenges involved with measuring and predicting the energy efficiency of a DX system designed with UTSS.