Literature review summaryVRF ASRAC Working Group Meeting

November 15-16 2018

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Our take …Recap from Oct 15-16 presentation – our lab and field data demonstrated:

1. EER95 is more representative of average field performance than IEER as rated in the current version of AHRI 1230

2. Performance drops off at high and low outside air temperature3. The current AHRI 1230 test does not capture native controls, and therefore has

the potential for incorrectly rating VRF systems

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Goal of today’s presentation is to demonstrate that: • Our findings are consistent with many other lab, field studies• VRF systems do outperform baseline systems but not by more

than ~50%

Literature suggests VRF systems outperform conventional AC

VRF systems use ~20-50% less energy than conventional AC

Study

Energy reduction vs. baseline system

FSEC, EPRI 2013 45%

ORNL 2016 30 - 47%

EPRI 2009 9 - 48%

IEER to EER95 ratio for VRF systems ~1.3 – 1.5

Study IEER vs. EER95

Watanabe et al,

20091.5 (est’d)

PG&E 2014 1.3 (est’d)

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EERs 22-41% higher for VRF systems than conventional AC

StudyEERVRF vs. EERsplit

EPRI 2009 9 - 48%

Aggregate of literature suggests VRF systems outperform

baseline systems by roughly 10 to 50%

Literature SummaryTitle Year Journal

1 Modeling Variable Refrigerant Flow Heat Pump and Heat Recovery Equipment in EnergyPlus 2013 DOE report

2 Evaluation of Variable Refrigerant Flow Systems Performance and the Enhanced Control Algorithm on Oak Ridge National Laboratory’s Flexible Research Platform

2016 Oak Ridge National Laboratory (ORNL)

3 Performance Assessment of a Variable Refrigerant Flow Air Conditioner with Ice Storage System 2009 Electric Power Research Institute (EPRI)

4 Evaluation of Annual Performance of Multi-type Air-conditioners for Buildings 2009 Journal of Thermal Science and Technology

5 Field Analysis of Commercial Variable Refrigerant Flow Heat Pumps 2014 PG&E’s ET Program

6 Research and Development of Innovative Energy-saving Controls of Next-generation Multi-Split type Air-Conditioning Systems for Buildings

2013 SHASE

7 Development of high efficiency VRF systems under partial heat load for commercial buildings 2012 2012 JSRAE Annual Conference Technical Program

8 Investigation on effects of piping on heating performance of multi-split variable refrigerant flow system

2017 Department of Building Science, Tsinghua University, Beijing

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2013 study found annual energy usage by VRF system ~45% less than for traditional AC

Title: Modeling Variable Refrigerant Flow Heat Pump and Heat Recovery Equipment in EnergyPlus

Year: 2013

Journal: DOE Final Report

Authors: Florida Solar Energy Center, EPRI

Efficiency features developed:

• 24-ton VRF system with 28-tons indoor unit served 10,425

sf in a school in Mobile, Alabama

• VRF system used 45% less energy over one year compared to baseline traditional split systems

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2016 field study suggests much lower

IEER for system rated at IEER of 22.7

Title: Evaluation of Variable Refrigerant Flow Systems Performance on Oak Ridge National Laboratory’s Flexible Research Platform: Part 1 Cooling Season Analysis

Year: 2016

Journal: Oak Ridge National Laboratory (ORNL)

Authors: Piljae Im, PhD (ORNL)

Mini Malhotra, PhD (ORNL)

Jeffrey D. Munk (ORNL)

Key findings:

• 12 ton VRF system compared with RTU-VAV system

serving 3200 sf two-story building

o AHRI rating for VRF 11.2 EER and 22.7 IEER

• Energy savings for VRF vs. RTU for the cooling season estimated to be 30, 37, and 47% under 100, 75, and 50% load conditions, respectively

• Average cooling COPs for VRF were 4.2, 3.9, and 3.7 (EER

~ 14.3, 13.3, 12.6) under 100, 75, and 50% load

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EER95 EER81.5 EER68 EER65

14.3 13.3 12.6 12.6 est’d

Estimating IEER as follows:

IEER ~ 0.02*14.3 + 0.617*13.3 + 0.238*12.6 + 0.125*12.6

~ 13

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2009 study found VRF reduced energy usage by 9 - 48%

Title: Performance Assessment of a Variable Refrigerant Flow Air Conditioner with Ice Storage System

Year: 2009

Journal: Electric Power Research Institute (EPRI)

Authors: C. Trueblood (EPRI), T. Geist (EPRI), J. Robinson (EPRI); R. Domitrovic (Redwood Electric); R. Radermacher (University of Maryland), T. Aynur (University of Maryland)J. Muehlbauer (University of Maryland)

Study Details:

• EPRI studied 10-ton VRF system with and without an attached ice storage unit; compared with a ducted split systemo AHRI Standard 1230 was not yet in place

• Pseudo-steady state system capacity measured using air-enthalpy method

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Key Findings: For 3 four-hour periods, VRF system used 9-48% less energy than split system

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2009 study found EERs 22-41% higher for VRF vs. split system

Average EER for VRF 22-41% better than split system

System performance relatively flat from ~68F to ~80F

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US EER ~ 10.2

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Partial load test method• For fixed compressor speed tests:

– An inverter is used to control the rotational speed of the compressor motors. Rotational speed of compressors was specified by the manufacturer

– The temperature of indoor air was controlled not by the tested air-conditioner but by the air-conditioning unit equipped in the testing apparatus

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• Partial load test method:– Indoor thermal load BLc was changed from 25% to 100% of the rated cooling capacity of the tested air-conditioner for each

outdoor temperature– Sensible heat factor (SHF) was set at 0.85– Temperature in the indoor test room was controlled at 27°C (80.6F) by the tested air-conditioner itself– Air flow rate of the fan in the indoor unit was set at the maximum value

• Performance of the air-conditioner, pressure and temperature of refrigerant, rotational speed of compressors, etc. were measuredafter ascertaining the steady-state operation of the air-conditioner

• Note: In a low thermal load condition, intermittent operations of the compressors were observed. In this case, we confirmed that a periodicity appeared in the operations of the compressors and COP was calculated based on the average in one cycle

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Partial load test method suggests IEER/EER95 of ~1.5

10COP partial load vs. COP at 100% load, 35C (95F)

EER95

EER68

• Performance peaks at 50% load

• Max ratio of EER68/EER95 < 2

• Estimated IEER/EER95 ~ 1.5

EER95 EER81.5 EER68 EER65

1 1.45 1.9 1.2

Estimating EER/EER95 as follows:

IEER / EER95 ~ 0.02*1 + 0.617*1.45 + 0.238*1.9 + 0.125*1.2

~ 1.52

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2014 field study found IEER / EER95ratio of ~1.3 vs. ~1.6 for AHRI ratings

Title: Field Analysis of Commercial Variable Refrigerant Flow Heat Pumps

Year: 2014

Journal: PG&E’s Emerging Technologies Program

Authors: Peter Biermayer (PG&E)Harshal Upadhye (EPRI)

Key findings:

• 24 ton VRF system serving 13 zones, 8466 sf of conditioned space in CZ 11

• Estimated IEER, EER95 based on binning field measurements by ambient temperatures 16.2, 12.6 vs AHRI rating of 18.2, 11.3

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• System outperformed EER95 rating by ~11%

• Calculated IEER was ~11% lower than AHRI rating

• Ratio of IEER to EER95~ 1.3 for field measurements vs. ~1.6 for AHRI ratings

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VRF controls can improve part load performance

Title: Research and Development of Innovative Energy-Saving Controls of Next-generation Multi-Split type Air-conditioning Systems for Buildings

Year: 2012

Journal: Proceedings 2012 JSRAE Annual Conference, C311-C313

Authors: Kasahara S et al

Key findings:

• The energy efficiency of conventional VRFs degrades under low heat load conditions

• VRF systems in commercial buildings are mostly operated under less than 50% heat load conditions through a year

• Field study results:

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• For conventional VRF systems, EER / COP tends to peak around 50% heat load ratio and drop off at higher and lower load ratios

• New controls can extend high part-load performance down to 20% heat load ratio

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2012 study evaluated technologies to improve efficiency of VRF systems

Title: Development of high efficiency VRF systems under partial heat load for commercial buildings

Year: 2011-2012

Journal: 2012 JSRAE Annual Conference Technical Program

Authors: Daikin, Mie University, Chubu Electric Power Co. Inc

Efficiency features developed:

• Capacity optimization controlo In conventional VRF systems, indoor units controlled

independently of outdoor unito Compressor speed of outdoor unit controlled to keep

the evaporation or condensation temperature of the refrigerant, at a target value

o Te and Tc usually fixed irrespective of the operating condition of the air conditioner

o Under low heat load conditions, the high-low pressure difference of the refrigerant is excessive relative to the heat load conditions, and the energy consumption of the compressor cannot be decreased

o Mismatch arises between the controls of the indoor and outdoor units, and consequently the air conditioner repeats operations with surplus capacities and stops causing degradation of EER/COP

• Optimized compressor• Crank case heater control 13

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2012 study found ~22% uptick for EER68 vs EER95 for conventional systems

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95F68F 95F68F

US EER ~14.5 US EER ~11.9

US EER ~25.6

US EER ~11.9

Rated cooling capacity: 45 kW (153 kBtu/h)

Source: “Development of high efficiency VRF systems under partial heat load for commercial buildings”, 2012 JSRAE Annual Conference Technical Program

Conventional VRF systems tested

had ~22% uptick for EER68 vs EER95

21.8%

Large improvements in EER required capacity optimization control

Testing without ”as shipped and

installed” controls does not

differentiate equipment with and without this

capability

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System operation with & without optimized controls

Conventional VRF operation With capacity optimization controls

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Rated cooling capacity: 45 kW (153 kBtu/h) Source: “Development of high efficiency VRF systems under partial heat load for commercial buildings”, 2012 JSRAE Annual Conference Technical Program

Conventional VRF repeats start-up/shut down operations, and then EER gets worse and the room temperature

fluctuates

With new VRF, operation is stabilized and the room temperature almost keeps a constant value

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2017 study found that pipe lengths have significant impact on heating performance

Title: Investigation on effects of piping on heating performance of multi-split variable refrigerant flow system

Year: May 16, 2017

Journal: Department of Building Science, Tsinghua University, Beijing

Authors: Ziai Li

Key findings:

• (1) Lengthening of horizontal pipe will reduce COP apparently in heating mode even under part-load conditions

• (2) Height difference in range from -50 m to 50 m had low effect on COP but it would affect the available pressure drop of EEVs

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Given impact of pipe length on performance we suggest using the same pipe lengths for

ducted and unducted systems?

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In Conclusion1. VRF is found to consistently

outperform conventional systems by 20-50% (FSEC, EPRI 2013)

2. Literature review suggests a mismatch between rated and field measured IEER; no study found rated IEER to under-predict field performance (PG&E 2014)

3. Identical VRF hardware can perform radically different depending on control sequence used (Daikin 2012)

4. EER95 may be a better predictor of annual performance than IEER as currently written (ORNL 2016)

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1. 2.

3. 4.

Pseudo—steady state approach• For pseudo-steady-state testing, both systems were forced to operate over a short period of time (<1 hour) to gather steady-

state operating data at a known and relatively constant set of indoor and outdoor ambient air conditions– When operating the VRV system in this mode all nine indoor units were on at the same time to enable measurement

of the fully loaded system capacity and efficiency– When testing the split-system performance, both ducted split systems were run together

• Test description:1. Tests were begun by turning off all air conditioning to the nine areas and allowing all rooms to reach a desired starting

indoor temperature, ranging from ~70°F - 80°F2. After the rooms reached the desired temperature range, all units (either VRV or split-system) were started. Set points

for the system under test were set sufficiently low to allow the full system to remain on for the duration of the test3. System remained on until the indoor temperatures were cooled through the range of interest and approximately 10-15

minutes of pseudo-steady-state data was collected4. All rooms were not at the same temperature during the cool down process, so an average of all room sensors was

designated the “indoor ambient test temperature.” The VRV system required ~15-20 minutes to reach a full-power state where power consumption peaks and system pressures, temperatures, etc., reach a steady-state

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Illustration of pseudo—steady state approach

Title: Evaluation of Annual Performance of Multi-type Air-conditioners for Buildings

Year: 2009

Journal: Journal of Thermal Science and Technology

Authors: Choyu Watanabe, Ei-Ichiro Ohashi, Masafumi Hirota, Katasuaki Nagamatsu, Hiroshi Nakayama

Key findings:

• JIS B8616: 2006 (Japanese standard for estimating annual electricity consumption of package air-conditioners) generally overestimates COP under relatively low thermal load operations

• Partial load test (dynamic rated capacity load based test) more closely matches actual performance

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Left axis: Ratio of measured and

simulated efficiency vs.

100% efficient system

System capacity tested: 56 kW (191 kBtu/hr) cooling; 63kW (215 kBtu/hr) heatingApproach: air-enthalpy method

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Additional references on effect of pipe length on performance

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