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.
Accurate predictions require sophisticated models that consider the differences in operating characteristics between a DX system and a UTSS.
Given these challenges in measuring and predicting energy efficiency, significant effort has been given to accurately model the performance of the UTSS over a range of conditions and confirm the accuracy of the model with relevant field data.
There are three methods that can be used to compare the performance of a DX system without a UTSS, to one with a UTSS.