VRF for Lodging Application

This emerging technologies field evaluation was conducted by Southern California Edison (SCE) to evaluate the ability of a Variable Refrigerant Flow (VRF) system to meet heating load at zero or subzero temperatures. The primary objective of this field evaluation is to gauge the ability of a VRF system to provide comfortable room temperature under cold outside conditions while maintaining the set temperature. VRF refers to the ability of the system to control the amount of refrigerant flowing to each of the indoor units or evaporators. This technique enables simultaneous heating and cooling in different zones, heat recovery from one zone to another, and allows the system to use several evaporators with different capacities for heating or cooling demand. These capabilities allow greater individual comfort control. Most VRF condensers use variable frequency drives to control the flow of refrigerant to the evaporators. Refrigerant flow control is the key to many advantages of a VRF system, permitting more evaporators to be connected to each outdoor unit and providing additional features such as simultaneous heating and cooling and heat recovery. Heat recovery can be accomplished by transferring/exchanging heat between the pipes providing refrigerant to the cooling and heating evaporator units based on the demand of each unit. One way is to use heat an exchanger to extract superheat from the unit operating in cooling mode and route it into refrigerant entering a heated zone. This technology was tested at a two-story guest lodge (representing the hotel/motel market segment) located in climate zone 16 within SCEs service territory. The VRF system installed at the test site included seventeen 8,000 British thermal unit (Btu) heat pump air handlers with thermostats, a branch controller, a sub branch controller, and two 72,000 Btu condensers twinned together (totaling 144,000 Btu). Condensate pumps were installed for all of the air handlers on the upper floor to a common drain and gravity fed condensate drains were installed for the lower floor To evaluate the performance of a VRF system, its performance was compared to two baselines. Baseline 1 consists of electric resistance heaters. Electric heaters were the original system at the facility and hence have been used as Baseline 1 in this project. Baseline 2 is an all-electric Package Terminal Air Conditioning system that is commonly found in hotels/motels nowadays and provides a more accurate savings estimate when compared to a VRF system. During this field evaluation, various data points such as temperature, relative humidity, and demand and energy consumption were collected for the VRF system. In addition, weather data was collected to benchmark the performance of the system in cold weather conditions. Since the test site is a remote location and not used often, the evaporators of the VRF system were turned “ON’ for three rooms to emulate thermal load in those rooms. The temperature set point for these rooms varied between 68 and 74 degrees Fahrenheit (°F) depending on outside weather conditions. The set temperature was varied using unit control system TG2000. The field data for this set-up was recorded from winter 2010 to spring 2012.