Energy Solutions

B O N N E V I L L E P O W E R A D M I N I S T R A T I O N

VRF Energy Modeling Savings Estimates

Regional Technical Forum Variable CapacityHeat Pump Sub-Committee Meeting

August 31, 2011

Energy Solutions


2

Outline

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• Requested Analysis

• Modeling Parameters

• Assumptions

• Results


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Requested Analysis

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• Model VRF energy savings for buildings in Seattle and Spokane using EnergyPro 5• Based on SCE analysis• Mitsubishi VRF heat pump and heat

recovery systems • Small office

• 7,200 sf• Medium office

• 41,500 sf


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Baseline Systems

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• Small office • Packaged rooftop air conditioner with gas

furnace and constant volume fan• ASHRAE system type 3• 4 units, 6-8 tons each, fixed temp economizer,

1080 cfm of OSA• Modeling software included conductive duct

losses for electric cooling• Fan energy increased to compensate for duct

leakage

• Packaged rooftop heat pump and constant volume fan• ASHRAE system type 4• 4 units, 6-8 tons each, fixed temp economizer,

1080 cfm of OSA• Modeling software included conductive duct

losses for both electric cooling and heating• Fan energy increased to compensate for duct

leakage


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Baseline Systems

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• Medium office • Packaged rooftop VAV with gas boiler

reheat• ASHRAE system type 5• 6 units, 19-26 tons each, fixed temp economizer,

6015 cfm of OSA• Increased electric cooling energy to compensate

for conductive duct losses• Fan energy increased to compensate for duct

leakage

• Packaged rooftop VAV with electric resistance reheat• ASHRAE system type 6• 6 units, 19-26 tons each, fixed temp economizer,

6015 cfm of OSA• Increased electric cooling energy to compensate

for conductive duct losses• Fan energy increased to compensate for duct

leakage


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VRF Systems

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• Small office • VRF heat pump system with DOAS

• 2 units, 10 to 12 tons each, no economizer, 1080 cfm of OSA

• VRF heat recovery system with DOAS• 2 units, 10 to 12 tons each, no economizer, 1080

cfm of OSA

• Medium office • VRF heat pump system with DOAS

• 6 units, 12 to 16 tons each, no economizer, 6015 cfm of OSA

• VRF heat recovery system with DOAS• 6 units, 12 to 16 tons each, no economizer, 6015

cfm of OSA

• No duct conductive losses or leakage


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Modeling Parameters

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• ASHRAE 90.1 - 2007 Baseline• Small office – Packaged RTU w/ gas heat or

heat pump• Separate baseline models created using 90.1

parameters• Base case had 4 total zones and 4 rooftop units• VRFs were modeled with 8 zones and 2 outdoor

units• Baseline equipment was modeled on typical

sizes, VRFs were based on actual Mitsubishi equipment in EnergyPro

• Medium office – VAV w/ boiler or electric reheat• Used standard VAV energy models auto-

generated by EnergyPro for the VRF simulation baselines

• Program assigned the same number of VAV air handlers as VRF outdoor units – 6 total; more AHUs than normal for capacity

• Baseline VAV capacities were sized by EnergyPro to satisfy peak block loads for assigned zones; capacities did not fall into typical VAV size categories


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Modeling Parameters

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• Energy savings • Baseline energy use: cooling, electric

heating, fans, and pumps• VRF and DOAS system energy use: cooling,

heating, fans, and branch selector boxes

• Peak demand analysis• Evaluated summer and winter, comparing

total building peak demand between measure and base


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Assumptions

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• 28% increase in electric heating and cooling energy to account for duct losses1

• Not included for VAV electric reheat

• 37% increase in fan energy due to air leakage from ducts2

1. Fisk, William J, et al., Duct systems in large commercial buildings: physical characterization, air leakage, and heat conduction gains, LBNL-42339, page 110, November 1999

2. Diamond, Rick, et al., Thermal Distribution Systems in Commercial Buildings, LBNL-51860, page 12, May2003


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Energy Usage – Small Office

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VRF Heat PumpCooling (kWh) Heating (kWh) Fans (kWh) Total (kWh)

Seattle 8,959 5,164 5,195 19,318Spokane 9,712 11,338 5,865 26,915

VRF Heat Recovery

Cooling (kWh) Heating (kWh) Fans (kWh)Branch Box

(kWh) Total (kWh)Seattle 9,511 5,498 5,195 310 20,514

Spokane 10,283 12,219 5,865 303 28,670

RTU Gas Furnace

Cooling (kWh)Heating (therms) Fans (kWh) Total (kWh)

Seattle 5,158 339 46,366 51,524Spokane 8,308 913 46,953 55,261

RTU Heat PumpCooling (kWh) Heating (kWh) Fans (kWh) Total (kWh)

Seattle 5,158 4,108 46,364 55,630Spokane 8,308 13,213 46,932 68,453


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Energy Usage – Medium Office

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VRF Heat PumpCooling (kWh) Heating (kWh) Fans (kWh) Total (kWh)

Seattle 52,759 17,252 22,320 92,331Spokane 55,515 34,124 24,510 114,149

VRF Heat Recovery

Cooling (kWh) Heating (kWh) Fans (kWh)Branch Box

(kWh) Total (kWh)Seattle 53,069 9,439 22,320 1,956 86,784

Spokane 52,075 29,633 24,510 1,917 108,135

VAV Gas Boiler Reheat

Cooling (kWh)Heating (therms) Fans (kWh) Pumps (kWh) Total (kWh)

Seattle 87,880 3,400 53,437 618 141,935Spokane 89,446 4,938 61,871 902 152,219

VAV Electric ReheatCooling (kWh) Heating (kWh) Fans (kWh) Total (kWh)

Seattle 85,708 58,628 52,853 197,189Spokane 86,970 84,725 60,665 232,360


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Results – Small Office

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VRF Heat PumpPackaged RTU w/ Gas Heat Base Case - ASHRAE system type 3

Packaged RTU Heat Pump Base Case - ASHRAE system type 4

Normalized Savings Savings

Demand Reduction

Gas Heat Offset


DemandReduction

(summ)

DemandReduction

(wint)(kWh/SF) (kWh/ton) (kW/ton) (therms) (kWh/SF) (kWh/ton) (kW/ton) (kW/ton)

Seattle 4.47 1464 0.45 339 5.04 1651 0.45 0.45

Spokane 3.94 1288 0.45 913 5.77 1888 0.45 1.95

Average 4.20 1376 0.45 626 5.41 1769 0.45 1.20

VRF Heat RecoveryPackaged RTU w/ Gas Heat Base Case - ASHRAE system type 3

Packaged RTU Heat Pump Base Case - ASHRAE system type 4


Demand Reduction

Gas Heat Offset


DemandReduction

(summ)

DemandReduction


Seattle 4.31 1410 0.45 339 4.88 1596 0.45 0.45

Spokane 3.69 1209 0.41 913 5.53 1808 0.41 1.91

Average 4.00 1309 0.43 626 5.20 1702 0.43 1.18


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Results – Medium Office

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VRF Heat PumpVAV w/ Gas Boiler Reheat Base Case - ASHRAE system type 5

VAV w/ Electric Reheat Base Case - ASHRAE system type 6


Demand Reduction

Gas Heat Offset


DemandReduction

(summ)

DemandReduction


Seattle 1.20 620 0.44 3400 2.53 1311 0.43 0.70

Spokane 0.92 453 0.61 4938 2.85 1407 0.58 0.87

Average 1.06 537 0.52 4169 2.69 1359 0.50 0.78

VRF Heat RecoveryVAV w/ Gas Boiler Reheat Base Case - ASHRAE system type 5

VAV w/ Electric Reheat Base Case - ASHRAE system type 6


Demand Reduction

Gas Heat Offset


DemandReduction

(summ)

DemandReduction


Seattle 1.33 689 0.41 3400 2.66 1380 0.39 0.81

Spokane 1.06 525 0.58 4938 2.99 1479 0.56 0.89

Average 1.20 607 0.50 4169 2.83 1429 0.47 0.85


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Savings Summary

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VRF Heat Pump% Electricity Savings over Baseline with Gas Heat

% Electricity Savings over Baseline with Electric Heat

Medium Office Small Office Medium Office Small Office

Seattle 34.9% 62.5% 31.5% 65.3%

Spokane 25.0% 51.3% 42.5% 60.7%

Average 30.0% 56.9% 37.0% 63.0%

VRF Heat Recovery% Electricity Savings over Baseline with Gas Heat

% Electricity Savings over Baseline with Electric Heat

Medium Office Small Office Medium Office Small Office

Seattle 38.9% 60.2% 33.2% 63.1%

Spokane 29.0% 48.1% 44.7% 58.1%

Average 33.9% 54.2% 38.9% 60.6%

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