Australia has a number of unique challenges it must overcome to comply with the Paris climate agreement and the global HFC phasedown, according to Scantec Refrigeration managing director, Stefan Jensen.
Delivering a presentation at the International Congress of Refrigeration (ICR) in Montreal, Canada, this month, Jensen said that between 2019 and the end of 2036, HFC importation into Australia is scheduled to reduce gradually from 8,000 tonnes CO2e to < 2,000 tonnes CO2e.
At the same time, Jensen said the year 2018 was the third warmest year ever recorded for the Australian continent.
In January 2019, he said 15 of the hottest locations in the world were in Australia with the highest night time temperature of 35.9°C recorded at Noona in central New South Wales.
This has led to many refrigerated warehouses in the major urban centres of Australia now being designed to accommodate ambient dry bulb temperatures >45°C for three consecutive days with a peak of up to 48°C within that three day period.
“Leapfrogging low global warming potential, synthetic refrigerant blends in new Refrigeration, Air Conditioning and Heat Pump (RACHP) installations raises special challenges in Australia,” Jensen said.
“It's not just about the high ambient temperatures but a low level of awareness when it comes to natural refrigerant-based solutions and the upcoming proliferation of flammable working fluids.
“Several solution providers in Australia offer imported transcritical CO2 based packaged systems for retail and refrigerated warehouse applications.
“But in jurisdictions with high ambient temperatures, these solutions do not deliver energy efficiencies significantly better than the HFC solutions they replace, if at all.”
Jensen said to comply with international treaties, Australia must implement RACHP solutions that not only eliminate dependence upon HFC refrigerants, but also reduce energy consumption and reduce indirect emissions at the same time.
“One solution that can achieve this is low charge, central type, NH3 based refrigeration systems with dry expansion (DX) refrigerant feed,” he said.
To demonstrate his point, he presented a case study which involved the retrofit of an older, industry standard, air-cooled R404A refrigeration system with electric defrost which was replaced with a modern centralized, low charge NH3 system (LC NH3).
When older HFC systems are replaced with transcritical CO2 (TC CO2) systems, Jensen said the improvement in annualized energy performance in Australia is somewhere between 0 and 20% depending on the jurisdiction.
With this LC NH3 system the recorded specific energy consumption (SEC) for that cold storage facility was reduced by 57 to 59% measured in kWh/m3*a.
“This presents a very serious challenge to the proponents of TC CO2 systems, because LC NH3 beats the energy performance of those by about 40%.This is recorded and there is no CO2 equator here,” Jensen said.
“The extra capital cost of the LC NH3 system compared with TC CO2 will be returned in about four years based on energy savings alone. In addition, the LC NH3 plant has twice the technical life of a TC CO2 system.
“What is of particular interest here is that the investment in a new LC NH3 system to replace an older HFC system is often cash flow positive from day one. This is because the value of the energy cost savings exceed the finance costs.
“All the investor needs is a balance sheet that is acceptable to the financier. If the investor can continue to pay the same off on the loan for the new LC NH3 plant that he/she paid per month for electricity consumed by the old plant, then the new LC NH3 system will be fully owned after 5-7 years depending on the size of the system and the unit electricity cost,” he said.
“This means that those who own a dilapidated HFC plant can get out of HFC’s and increase profits from day one by investing in LC NH3. That is like someone paying you to replace your old air conditioner with a new one.”
The plant that is the subject of Jensen's case study was a relative small dual stage, ammonia refrigeration system servicing a refrigerated storage/distribution facility owned and operated by a food service company.
In the first instance, Jensen said a decision was made to remove the wall between the two freezer rooms and relocate the air coolers.
“Prior to this decision, air circulation between the two freezer rooms by mechanical means was planned but with the removal of the wall, this became unnecessary,” Jensen said.
Secondly, the dividing wall between the two segments of the Chiller were also removed; this was in order to limit the number of air coolers required in that particular area to one.
“The prefabricated dual stage, central ammonia plant room was located immediately adjacent to the freezer evaporators to keep NH3 pipelines relatively short.”
The warehouse is situated in Mackay, North Queensland and the highest recorded dry bulb temperature for the region is 36.9°C.
The HFC based refrigeration plant servicing the facility ceased operations in 2015.
Discussions commenced in the fourth quarter of 2017 to replace the plant with the new installation completed in August, 2018.
Jensen said the previous system comprised a number of low temperature Bitzer air cooled condensing units suitable for outdoor installation and one medium temperature condensing unit of unknown make. These were connected to 10 matching commercial evaporators with the low temperature units arranged for electric defrost.
“The refrigerant was R404A in the low temperature segment. The refrigerant used in the medium temperature segment is unknown,” Jensen said.
He said the subfloor heating system used under the freezer floors was electrically powered and comprised two independent resistance heating circuits for redundancy.
The subfloor temperature is thermostatically controlled by switching the power supply on/off.
“We tested the subfloor heating system prior to the plant modifications commencing and it worked and was retained,” he said.
“More energy efficient heating options exist and are indeed used in new installations, but replacement of the subfloor heating system was considered too disruptive and too capital intensive in this case.
“The total peak power consumption of this plant excluding the power absorbed by the subfloor heating system and the drain/door heaters was 118 kW with all defrost heaters operational.”
The replacement refrigeration system is a central type, dual stage, low NH3 inventory refrigeration plant with dry expansion refrigerant feed for the low temperature freezer evaporators and a propylene glycol loop for the medium temperature services.
Jensen said the total NH3 inventory is approximately 200 kg. He said the glycol/NH3 plate heat exchanger for the secondary refrigerant loop is gravity flooded using the intercooler as the surge vessel.
“The plant employs three open industrial reciprocating compressors all fitted with variable frequency drives,” Jensen explained.
One compressor is a dedicated booster, one compressor is a dedicated second compression stage machine and the third compressor is connected for dual duty capability. Two compressors can service the estimated heat loads whereas the third is for redundancy. There are no ammonia pumps.
“A closed circuit water cooling segment incorporated within the evaporative condenser services the compressor top and side cooling. This closed loop includes a duty and a standby cooling water circulation pump,” he said.
“The freezer evaporators are controlled using the combined superheat/quality control principle.
“The entire engine room including base frame, weatherproof enclosure, electrical control system, motor control centre, ventilation systems, pressure vessels, oil management system, glycol pump and NH3/glycol heat exchanger was manufactured off site.
“All interconnecting NH3 pipelines are 304 stainless steel for durability and low friction.”
Jensen said the technical life of the plant is identical to what can be anticipated for larger industrial ammonia refrigeration systems i.e. about 30-40 years.
To make the transition from HFC refrigerants, Jensen said it is important to not only consider the elimination of direct emissions, but also the minimization of indirect emissions.
“These are the CO2 emissions associated with electricity generation by means of combusting fossil fuels,” he said.
“The eagerness with which direct emission reductions pertaining to HFC refrigerants are sought can often drown out the significantly more important minimization of indirect emissions.”
When buying replacement systems with low GWP working fluids, decisions are based on capital cost minimization.
“The owner (and the environment) may then be stuck with a replacement system that has failed to fully explore the maximum energy conservation potential during the replacement process,” he said.
“Excessively high indirect emissions for the life of the plant are therefore a real possibility in this scenario. Aside from increasing the energy consumption costs to the plant owner unnecessarily, this also violates the intent of the Paris Climate Treaty.
“Practical energy performance comparisons between central, low NH3 inventory refrigeration systems of the capacity range described here and equivalent transcritical CO2 systems for tropical jurisdictions are very rare.
“Such comparisons are nevertheless important to enable fully informed procurement decisions to be taken. They are also important to prevent the HFC phasedown from literally transferring us from the ashes into the fire.”