Floating Head Pressure for Refrigeration Single Compressor Systems

Michele Friedrich, PE – Sr. Engineer

Dustin Bailey – Engineer

PECI

11/2/2010

Acknowledgements

We would like to thank the following for their support:• Avista Utilities• Bonneville Power Administration• Puget Sound Energy• RTF refrigeration subcommittee

Purpose

Approval for new deemed measures for floating head pressure on refrigeration single compressor systems

4

AgendaProposed Measures

Technology Overview

Calculation Methodology

Cost

Effective Useful Life

Market Potential

Program Specifications

Program Summary

Proposed Measures

Measure Application

Energy Savings (kWh/yr-

HP)EUL

(yr)

Measure Cost ($/HP )

Benefit Cost Ratio

Floating head Pressure Single- Med Temp Condensing Unit

757 15 307.51 2.6

Floating head Pressure Single- Low Temp Condensing Unit

855 15 270.76 3.4

Floating head Pressure Single- Med Temp Remote Condenser

473 15 206.73 2.4

Floating head Pressure Single- Low Temp Remote Condenser

685 15 157.34 4.6

Technology Overview

• Current measure for FHP on multi-plex systems excludes single compressors.

• Two types of Single Compressor systems: Condensing Units (~85-90%) & Remote Condensers.

• Allows condenser to operate at a lower temp. and pressure depending on ambient conditions.

• Lower condenser temperature = less compressor work due to lower compression ratio.

Head Pressure Control

Technology Overview

Refrigeration System Diagram

Technology Overview

• This measure requires using adjustable head pressure control valve which is adjusted to equivalent pressure of 70F saturation. Replaces fixed valve set at 180 psig by factory (~94.3F for R22).

• Expansion valve is retrofitted to balanced port valve or a device is installed to supplement refrigerant feed at lower condensing pressures.

Calculation Methodology

• eQUEST model

1. Set at “typical” specifications for convenience store refrigeration system.

2. Condensing Unit modeled as 1 compressor and 1 condenser with fan ON when compressor is ON. Min Condensing P set by flood-back control valve (head pressure control valve).

3. Remote Condenser modeled as 4 compressors and 4 fans that are controlled to come ON staged with Outside Air Temperature (OAT). Minimum Condensing P set by flood-back control valve (head pressure control valve).

Calculation Methodology

• eQUEST model

4. Conduct sensitivity analysis for each type of Single Compressor system: Condensing Unit and Remote Condenser.

a) Condensing Unit highest sensitivity to Compressor efficiency and Compressor/condenser over-sizing (split into LT and MT before sensitivity analysis).

b) Remote Condenser highest sensitivity to condenser set point and suction temperature.

Calculation Methodology

• Presented to RTF refrigeration subcommittee for direction and input.

• Condensing Set Point: fixed head pressure control valve set at factory to 180 psig +/- 5 psig. For R22 this is 94.3oF +/- 1.8oF. Assume that there are as many at – 5 psig as at +5 psig.

• Suction Temperature: Split into LT and MT measures

• Compressor/Condenser over sizing: used refrigeration schedules for single compressor systems to find median value of compressor and condenser over sizing

Calculation Methodology• Weighted for compressor motor efficiency for

Condensing units by weighting by motor size (efficiency a function of size for 0.5 HP to 7.5 HP). Motor size from GrocerSmart database audits in PNW for single compressor systems.

• Weighted for climate zone (different savings for east vs. west side of cascades) using store population in GrocerSmart in PNW.

• Remote Condenser picked 1 HP fans (0.5 HP fans are quieter, 1.5 HP fans are cheaper: designers pick in between.) Picked # fans per condenser from catalogue after condenser size was found. Refrigeration schedule review median value for # fans was 3.5.

Cost• $164.64 per evaporator

– Balance Port Valve and labor

• $585.55 per condenser– Adjustable head pressure valve, filter drier, bypass valve and

labor.

• Unknown extended life on compressor from lower operating hours.

*Cost data from Grainger, Sporlan and HVAC/R wholesaler

Effective Useful Life

15 yearsSame as FHP on Multiplex.Equipment life = 15 years.

Market Potential

100% penetration of PNW GrocerSmart audited stores with Single Compressors = 1.8 aMW

Program Specifications• Install adjustable head pressure control valve (flood-back control valve) to lower minimum condensing head pressure. Field calibrated to pressure equivalent of 70 F saturated temperature or lower using NIST certified calibration of +/- 5 PSI pressure gauge or transducer.• Measure applicable only to refrigeration systems having single compressor systems of 1 HP motor or larger either in condensing unit or in remote condenser. • Must install either balanced-port valve or EEV that is sized to meet the load requirement at 70 degree condensing temperature, if not currently installed, or install device to supplement refrigerant feed to each evaporator attached to condenser that is reducing head pressure. 

Summary

Measure Classification and PropertiesMarket Sector CommercialMarket Segment Grocery

Measure CategoryFloating Head Pressure Controls on Single Compressor Systems

Measure Description

Add an adjustable condenser head pressure control valve (i.e. "floating head pressure controls") and balanced port valves to refrigeration systems with single compressors. Head pressure control (flood back) valve must be set to 70 degrees F or lower. Compressor must be 1 HP or larger.

Primary Workbook GroceryFHPCSingleCompressor_v1_03.xlsLinked WorkbooksNumber of Measures, and UES Components 4 measures with a single UES component

SummaryIdentifier Possible Values Further Explanation and Sources

Measure Type (See UES Table Below)

Floating Head Pressure Controls on Single Compressor Systems - Condensing Unit;

Floating Head Pressure Controls on Single Compressor Systems - Remote Condenser

Case TemperatueMedium Temperature (MT);

Low Temperatures (LT)

Parameter Possible Values Further Explanation and Sources

Motor Size Weighting(Condensing Unit)

Varies (see "Cond Unit Weighting Savings" tab)Based on data collected from GrocerSmart Database for PNW

R22 stand alone compressor systems (N=344 for MT; N=512 for LT)

Climate Weighting Varies (see "CondUnit Weighted Savings" and "Remote

Weighted Savings" tabs)Based on data collected from GrocerSmart database for stores in

the Pacific Northwest. (N = 5496 stores)

Condenser Fan ControlsUnitary Condenser: On/Off with Compressor

Remote Condenser: Staged with OA drybulb TFor Remote Condenser systems, fan OAT control is usually 1 fan ON always, 2nd fans at 60F, 3rd fans at 70F and 4th fans at 80F

Compressor COP Condensing Unit: Varies depending on compressor

horsepower; (LT: 0.94 to 1.51; MT: 2.0 to 3.1)Remote Condenser: LT: 1.45; MT: 2.49

Condensing Unit: Median value of manufacturers' data for 3 to 6 models per size category.

Remote Condenser: Median of Copeland catalog data for R22 units.

Compressor Oversize Factor1.21 for Condensing Units

1.13 LT and 1.17 MT for Remote Condensers

Median value, based on refrigeration schedules from 6 stores consisting of 21 condensing units and 6 stores consisting of 26

compressors in remote cond.

Other eQuest Inputs variesInputs not listed in the "Summary" tabs were generated using manufacturer's data and analyst's judgment. More detail on

inputs can be found throughout the measure workbook.

Measure Identifiers

Constant Parameters

Summary

Measure Type UES Component Analysis approach Primary Parameter / Adjustment Factor

Floating Head Pressure Controls on Single Compressor Systems

only one UES component

Energy savings were determined via eQuest modeling.

Motor size and Climate Weighting: Multiple motor sizes were modeled in Portland's climate to determine the motor size that resulted in savings that most closely matched the motor size weighted average savings for Portland. This analysis was performed for both medium temperature and low temperature scenarios. These representative motor sizes were modeled for the respective LT and MT scenarios in multiple climates and weighted by climate.

Head Pressure Controls - Floodback Control Temperature Setting

Unit Energy Savings (UES) Estimation Method, Parameters and Sources

Proposed Measures

Measure Application

Energy Savings (kWh/yr-

HP)EUL

(yr)

Measure Cost ($/HP )

Benefit Cost Ratio

Floating head Pressure Single- Med Temp Condensing Unit

757 15 307.51 2.6

Floating head Pressure Single- Low Temp Condensing Unit

855 15 270.76 3.4

Floating head Pressure Single- Med Temp Remote Condenser

473 15 206.73 2.4

Floating head Pressure Single- Low Temp Remote Condenser

685 15 157.34 4.6