Stefan jensen high performance energy low charge nh3 systems_160403

Low Charge NH3 Refrigeration Systems

Stefan S. Jensen B.Sc.Eng. FIEAust, CPEng, NER, RPEQ, F.AIRAH

[email protected] Scantec Refrigeration Technologies Pty. Ltd.

HVACR Energy efficiency Seminar 2016


Options Paper – Review of the OPSGG Management Programme, October 2015

“A reduction in hydrofluorocarbon (HFC) emissions is an important part of Australia’s commitment. Australia will fast track work to reduce domestic HFC emissions by 85 per cent by 2036, in line with the most ambitious phase-down proposals under the Montreal Protocol.”

The Hon Greg Hunt MP Minister for the Environment

The HFC situation


Where to from here? Low GWP refrigerants Synthetic or natural refrigerants? What are natural refrigerants?

Ammonia (NH3) or R717 Carbondioxide (CO2) or R744 Hydrocarbons (HC) Air or R729 Water (H2O) or R718


Natural or synthetic?

- Are the two refrigerant families distinguishable by flammability?

- Are the two refrigerant families distinguishable by toxicity?

NO – low GWP refrigerants are all flammable excepting water, CO2 and air (R718, R744, R729)

NO – many low GWP refrigerants are toxic and/or have toxic combustion products excepting water, CO2 and air (R718, R744, R729)


Business case If you have one of these:

Industry standard, single stage HFC based, air cooled refrigeration plant

and can continue to pay this every month for this:


you can own one of these:

State of the art low charge NH3 refrigeration system

IN FIVE YEARS PAID FOR WITH ENERGY COST SAVINGS

Business case

and pay this per month after that:

for this


- Estimated SEC reduction from 143 to 38 kWh/m3*a - Annual cost savings A$400,000 (energy & maintenance)

- Retrofit from multiple air cooled HFC units to central low charge NH3 plant with glycol loop for medium temperature - Investment ~A$1,900,000 (refrigerated volume ~21,000 m3)

- Current monthly electricity account A$43,000-A$48,000 Simple pay-back k$1900/k$400 < 5 years

Business case


$42,000/month

$13,500/month Conversion cost $2,000,000

ROI = (42,000-13,500)*12/2,000,000*100=17%

Business case


Source: California Energy Commission 2008

Tamworth

Perth

Energy Efficiency


NH3 versus NH3

33.3 m Low charge

NH3


Plant Annual energy consumption

[MWh]

Recording period

Refrigerated volume

[m³]

Spec. energy consumption (SEC)

[kWh/m³*a] Low NH3 410 1.7.14-

30.6.15 9,474 43.2

Screw 1,135 1.7.14-30.6.15

10,748 105.6

Notes:

- Both building layouts ~identical

- Energy consumption is for entire facility not only NH3 plant

NH3 versus NH3


- Single stage compression - Twin screw compressors in parallel with economizer - No compressor speed control - No floating condensing pressure - Medium temperature serviced from low temp. segment - Superheat controlled NH3 injection for medium temp. - Poor material selection for medium temp. DX NH3 coolers

Floating condensing pressure reduced SEC by approximately 1/3.

- Refrigerant feed retrofit

What’s wrong?


43 kWh/m3*a 106 kWh/m3*a $8,000/mth. $22,000/mth.

NH3 low charge, dual stage, reciprocating compressors with VFD’s

NH3 flooded, single stage economized screw compressors

NH3 versus NH3


What’s the message?

Use of natural refrigerants does not guarantee superior energy performance

What does?

System design for energy efficiency or “Energy Efficiency Engineering”


Item Energy conservation factor Impact [%]

1 Selection of compressor type 15-25 2 Evaporator fan speed control 15-25 3 Evaporator design 5-25 4 Compressor capacity control 10-20 5 Quality of match between compressor turn-down ratios and heat load

variations 0-15

6 Condenser size, condenser fan speed control and condenser efficiency 5-10 7 Liquid injection control into the evaporators 5-10 8 Elimination of liquid within suction lines 2-4 9 Use of low friction loss 304SS schedule 10 refrigerant pipe lines in lieu

of carbon steel 1-2

Factors influencing efficiency?


What’s new here?

- Overall charge reduction from 3.5-4 kg/kW to 1.0-1.2 kg/kW; NH3 inventory in air coolers 30-50 times less than LR; potential NH3 concentration in warehouse <200 ppm - Specific energy consumption values in kWh/m3*a are 0.45 to 0.60 times the values recorded by CEC in 2008 (163 RDC’s) - Quality based refrigerant injection control (0.95 < x < 0.99) - High pressure liquid based oil separation combined with automatic oil return; oil content < 1 ppm - Hot gas defrost sequence with two hot gas supplies


What’s new here?

- Internal surface enhancement promoting capillary action - Conventional, Küba style and tank distributors - Interconnecting 304SS pipe lines with reduced absolute roughness - Infiltration and frost management - Variable frequency drives on everything

- Injection control based on evaporator exit quality enabling exceptionally low entering temperature differences

- Modern reciprocating compressors with low oil carry-over


What is SH/X control?

Electronically controlled refrigerant injection based on refrigerant quality at evaporator exit

Quality or “x” sensor

The dielectric spectroscopy (capacitance) measurement method uses the difference in dielectric properties of gases and liquid


System charge 480 kg; LT/HT≈ 170/250 kW Low charge: 1-1.2 kg/kW Conventional liquid overfeed: 3-4 kg/kW

304SS

NH3 charge reduction


- NH3 “inconveniences” gradually minimized/eliminated (oil drainage, moisture, operators, specialist maintenance) - Low charge NH3 costs about the same as NH3 liquid overfeed

- ~20% return for retrofits of HFC plants with new low charge NH3 (based on unit electrical energy cost $200-$300/MWh) - ~30-50% return on Δ investment between new low charge NH3 and new industry standard HFC (HFC=0.6*NH3)

- Lower than expected energy bills drive market acceptance

“ONCE YOU GO AMMONIA YOU NEVER GO BACK”

Discussion


QUESTIONS?

Presentations & Public Speaking

Stefan jensen high performance energy low charge nh3 systems_160403