Improvement of variable refrigerant flow system performance using energy saving control strategy and chilled water storage

Abstract

Variable refrigerant flow system is a popular building air conditioning solution. Modern variable refrigerant flow systems such as multi-functional variable refrigerant flow systems can also provide space cooling, space heating, and water heating to the building simultaneously. The performance improvement of variable refrigerant flow system is a key research topic. In the current article, energy saving potentials of two measures: A new energy saving control strategy and a new variable refrigerant flow system with chilled water storage are theoretically investigated. The energy saving control strategy changed the evaporating temperature based on ambient temperature. The new variable refrigerant flow system utilizes the water storage component in current multi-functional variable refrigerant flow systems as a chilled water storage unit. Simulation is carried out on a validated thermodynamic variable refrigerant flow model in EnergyPlus. The seasonal energy saving potentials of both measures are calculated in four cities: Miami, Houston, Baltimore, and Chicago. The energy saving control strategy can achieve seasonal energy saving as high as 10.8% in cooling season and 15.4% in heating season. The performance of the new system is also compared to baseline variable refrigerant flow system and the seasonal cooling energy saving could reach 12.5%.

Nomenclature

Abbreviations

AC	=	= air conditioning
COP	=	= coefficient of performance
CWS	=	= chilled water storage
EEV	=	= electronic expansion valve
HRU	=	= heat recovery unit
HPVRF	=	= heat pump variable refrigerant flow
HRVRF	=	= heat recovery variable refrigerant flow
IU	=	= indoor unit
MFVRF	=	= multi-functional VRF system
OU	=	= outdoor unit
VRF	=	= variable refrigerant flow
WHU	=	= water heating unit

Symbols

F	=	= compressor frequency
Q	=	= cooling/heating capacity
Te	=	= evaporating temperature
Tc	=	= condensing temperature

Additional information

Funding

The authors gratefully acknowledge the financial support of the Center for Environmental Energy Engineering (CEEE) at the University of Maryland, and System Air Conditioning Laboratory at LG Electronics Inc.