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Variable Capacity Heat Pump RTF Sub-Committee November 16 , 2011. Mira Vowles, P.E., CEM Emerging Technology Project Manager BPA Energy Efficiency. Meeting Agenda. EnergyPro Correction Small Office Baseline Model Differences Small Office VRF Heat Pump Model Differences

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variable capacity heat pump rtf sub committee november 16 2011

Variable Capacity Heat Pump RTF Sub-CommitteeNovember 16, 2011

Mira Vowles, P.E., CEM Emerging Technology Project Manager

BPA Energy Efficiency

slide2

Meeting Agenda

  • EnergyPro Correction
  • Small Office Baseline Model Differences
  • Small Office VRF Heat Pump Model Differences
  • VRF Model Best Practice
  • Revised Definitions

If we have time:

  • Discuss M&V best practice & standard protocol
  • Discuss compiling list of PNW VRF installations
slide3

Seattle Small Office Energy Use Correction

* Corrected to include duct loss adjustment

slide4

Energy Solutions Small Office Model

7,200 square foot office modeled using EnergyPro 5

  • Baseline: Packaged rooftop air conditioner with gas furnace and constant volume fan
    • ASHRAE system type 3
    • 4 units, 6-8 tons each, fixed temp economizer, 1,080 cfm of OSA
    • Included 28% cooling increase to account for conductive duct losses
    • Included 37% fan energy increase to compensate for duct leakage
  • VRF heat pump system with DOAS
    • 2 Mitsubishi units, 10 to 12 tons each, no economizer, 1,080 cfm of OSA
slide5

Energy Solutions & PECI Small OfficeRTU Gas-Pack Model Differences

  • Energy Solutions used EnergyPro and PECI used eQuest
  • Energy Solutions included significant Baseline duct losses

3. PECI included two-speed fans (fan at 35% when no heating or cooling loads)

4. PECI included server room which requires minimal heating

slide6

Energy Solutions & PECI Small OfficeVRF Heat Pump Model Differences

  • Energy Solutions used EnergyPro Mitsubishi VRF performance modules

2. PECI used the eQuest “BSUG method” (PVVT model with compressor VSD and post processing heat recovery analysis)

3. PECI’s model doesn’t include refrigerant pipe losses

4. PECI included ventilation fan with 2.5” static pressure, while Energy Solutions used DOAS with unknown static pressure

slide12

Building Simulation Program Issues

  • Due to the complexity of VRF systems (both VRF HR and VRF HP), building simulation programs are needed to estimate site-specific savings;
  • How can the accuracy of the building simulation programs be verified?
  • What are the important metrics?
    • Monthly energy use and average monthly temperature
    • Other?
  • Can building simulation programs provide these important metrics for verification purposes?
slide14

Modeling VC HP with TRACE

TRACE can explicitly model VC HP, both heat pump and heat recovery systems:

  • Algorithms are based on Daikin empirical model
  • Inputs based on first generation Daikin VRV equipment
    • modify to match current generation equipment or other manufacturer
    • Heating COP or Cooling KW/ton
    • Condensing Fan power consumption KW/ton
    • Select unloading curve, compressor power consumption curve, condensing fan curve and cycling point as appropriate

Based on April 15, 2009 BSUG meeting presentation

slide15

Modeling VC HP with TRACEcontinued

TRACE airside simulation

  • When space temperature rises above the cooling setpoint, the cooling coil supplies air at a constant, cooling-supply-air-temperature until the setpoint is met; rejected heat is supplied to the refrigerant condenser loop.
  • When space temperature drops below the heating setpoint, the heating coil supplies air at a constant, heating-supply-air-temperature until the setpoint is met, and the heat is removed from the refrigerant condenser loop. The default minimum reheat is 10%, or it can be entered on a room by room basis.
  • When the heating and cooling coils are inactive, the minimum supply airflow at the mixed-air temperature is assumed; fan heat is , included.

Based on April 15, 2009 BSUG meeting presentation

slide16

Modeling VC HP with eQUEST

Model as PVVT Water Source Heat Pump system

  • Zone the building in the same manner as the design for representative heat recovery modeling
  • Select a water cooled condenser with a condenser water loop
  • Create one system per zone
  • Create separate condenser water loops for each VRF condenser and zero out the pump energy
  • Change the fan efficiency ratio and electric boiler EIR to reflect VRF efficiencies

Based on April 15, 2009 BSUG meeting presentation

slide17

Modeling VC HP with eQUESTcontinued

Model as PVVT Air CooledHeat Pump

  • Create one system per zone
  • Change to variable compressor speed
  • Label systems and zones to according to which condenser each zone is connected to
  • Create hourly reports with total heating and cooling energy use for each system
  • Use spreadsheet to find simultaneous heating and cooling for each system, and sum the savings
  • This methodology is felt to be a conservative approach, which has been accepted by the USGBC on the Portland Mercy Corp LEED building
  • DOE-2 VRF system curves need to be developed

Based on April 15, 2009 BSUG meeting presentation

slide18

How Accurate are Baseline and VC HP Models?

  • PNW EUI’s
  • EnergyPro EUI’s
  • eQuest EUI’s
  • How can we verify model accuracy?
slide21

Small Office Baseline EUI Comparison

Whole building Mean EUI = 75 (kBtu/SF), with a Standard Deviation of 13 (kBtu/SF)

slide22

Medium Office Baseline EUI Comparison

Whole building Mean EUI = 67 (kBtu/SF), with a Standard Deviation of 25 (kBtu/SF)

slide23

Small Office VRF HP & Getting to Fifty EUI Comparison

Whole building Mean EUI = 48 (kBtu/SF), with a Standard Deviation of 13 (kBtu/SF)

slide24

Small Office VRF HPHVAC EUI Comparison

HVAC EUI Mean = 9 (kBtu/SF), with a Standard Deviation of 1 (kBtu/SF)

slide25

Medium Office VRF EUI Comparison

Whole Building EUI Mean = 43 (kBtu/SF), with a Standard Deviation of 8 (kBtu/SF)

slide26

Small Office VRF Savings Comparison

Savings EUI Mean = 13 (kBtu/SF), with a Standard Deviation of 12 (kBtu/SF)

slide27

Medium Office VRF Savings Comparison

Savings EUI Mean = 11 (kBtu/SF), with a Standard Deviation of 3 (kBtu/SF)

slide28

Office Building Definition

  • A building used primarily for office functions, including desk-work, reading and light equipment (computer, copier, printer, telephone, etc.) use.
  • Office occupancies are further defined by
    • overall occupant densities between 50 and 300 square feet per person,
    • overall lighting power densities up to 1 watt per square foot, and
    • overall equipment plug loads up to 1.5 watts per square foot.
slide29

VRF System Definition

Variable refrigerant flow (VRF) systems, either heat-pump or heat-recovery styles, providing heating and air-conditioning, and typically consisting of:

  • Outdoor unit(s) with inverter driven compressor(s) and condenser fan providing improved part-load and low-ambient performance,
  • Multiple indoor units with multi-speed fans, electronic expansion devices, integrated zone temperature controllers and no electric resistance heating capacity,

3. Refrigerant piping between the outdoor and indoor units,

5. Ventilation provided by either natural ventilation or a dedicated outside air system (DOAS).

slide30

VRF System M&V Best Practice?

  • Meter baseline and VRF system electricity use for representative period, project to annual savings
  • Use calibrated Building Simulation model to predict annual savings and monthly electricity use
  • Verify savings by comparing actual monthly electricity use to predicted monthly electricity use
slide31

VRF System M&V Standard Protocol?

  • Use whole building regression analysis spreadsheet with representative period pre- and post- monthly electricity billing data and hourly average OSA temperature,
  • if savings are temperature dependant, over 15% of whole building electricity use and there are no other significant changes to electricity use, the whole building regression analysis spreadsheet can provide an 80-20 confidence interval for savings
slide34

Use Whole Building Analysis for VRF ROB Electricity Savings M&V?

  • Energy Solutions EnergyPro model predicts monthly electricity savings ranging between 21 and 33%
  • For the Small Office (7,200 SF) the monthly electricity savings ranging between 1,900 and 2,200 kWh

Next Step: use whole building regression analysis spreadsheet, using EnergyPro model predicted monthly electricity use and Seattle hourly average OSA temperature

slide35

Next Meeting

  • Scheduled for 12/21/11 at 9 am
  • Move to 12/14/11 at 9 am?

Potential Topics:

  • Compare actual RTU annual fan kWh/SF to models
  • Develop VRF savings estimates (IEER plus fan?)
  • Compile list of PNW VRF installations & brainstorm how to “mine” for useful information
  • Develop M&V best practice and standard protocol
  • Develop research plan to verify model accuracy
  • NEEA RTU Replacement Discussion
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