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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
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
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
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)
HVACR Energy efficiency Seminar 2016
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:
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
- 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
HVACR Energy efficiency Seminar 2016
$42,000/month
$13,500/month Conversion cost $2,000,000
ROI = (42,000-13,500)*12/2,000,000*100=17%
Business case
HVACR Energy efficiency Seminar 2016
Source: California Energy Commission 2008
Tamworth
Perth
Energy Efficiency
HVACR Energy efficiency Seminar 2016
NH3 versus NH3
33.3 m Low charge
NH3
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
- 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?
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
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”
HVACR Energy efficiency Seminar 2016
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?
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
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
HVACR Energy efficiency Seminar 2016
- 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
HVACR Energy efficiency Seminar 2016
QUESTIONS?