Compare Energy Use in Variable Refrigerant Flow Heat Pumps Field Demonstration and Computer Model Page: 1 of 9
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Compare Energy Use in Variable
Refrigerant Flow Heat Pumps Field
Demonstration and Computer Model
Chandan Sharma Richard Raustad
Member ASHRAE MAmber ASHRA!
Variable Refrigerant Flow (VRF) heat pumps are often regarded as energy efident air-conditioning systems which offer electridty savings
as well as reduction in peak electric demand while providing improved individual done seipoint control. One of the key advantages of VRF
systems is minimal duct losses which provide significant reduction in energy use and duct space. However, there is Limited data available to show
their actual performance in the field. Since VRF systems are increasingy gaining market share in the US, it is highy desirable to have more
actualfield performance data of these systems. An effort was made in this direction to monitor VRF system performance over an extended period
of time in a US national lab testfadlty.
Due to increasing demand by the energy modeling community, an empirical model to simulate VRF systems was implemented in the
building simulation program EnergyPlus. This paper presents the comparison of energy consumption as measured in the national lab and as
predicted b~y the program. For increased accurag in the comparison, a customized weather file was created b~y using measured outdoor temperature
and relative humidity at the test farit yy. Other inputs to the model included building construction, tVRF system model based on lab measured
performance, occupant! of the building, lighting/plug loads, and thermostat set-points etc. Infiltration model inputs were adjusted in the beginning
to tune the computer model and then subsequentfield measurements were compared to the simulation results.
Differences between the computer model results and actual field measurements are discussed. The computer generated VRF performance
closey resembled the field measurements.
Due to increasing emphasis on energy efficient operation of the buildings, various HVAC technologies are emerging
in the market. Variable refrigerant flow (VRF) system is one such technology which is an enhanced version of ductless
multi split air-conditioning system. Some of the key advantages offered by VRF systems are simultaneous heating and
cooling operation in heat recovery mode, minimize duct space, and improved zone setpoint control etc. VRF system
technology, benefits and market acceptance issues are discussed in . While the VRF systems were increasingly gaining
market share in the US, a dynamic simulation tool to simulate their performance was missing. Several simplified VRF
models were developed initially [2-4]. Due to increasing demand by the energy modeling community a more detailed VRF
heat pump model was implemented in EnergyPlus . This current paper focuses on validating this detailed VRF model
with field measured data. A customized weather file was created to facilitate fair comparison between measured and
simulated data. Also, building construction, lighting/plug loads of space, and thermostat set-points etc were fed to the
Chandan Sharma is Associate Research Engineer at the Florida Solar Energy Center / University of Central Florida. Cocoa, FL. Richard
Raustad is Senior Research Engineer at the Florida Solar Energy Center / University of Central Florida. Cocoa, FL.
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Sharma, Chandan & Raustad, Richard. Compare Energy Use in Variable Refrigerant Flow Heat Pumps Field Demonstration and Computer Model, article, June 1, 2013; United States. (digital.library.unt.edu/ark:/67531/metadc831612/m1/1/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.