Page 30 - Climate Control News September 2019

Natural Refrigerants
temperature segment is unknown,” Jensen said. Jensen 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 re- placement of the subfloor heating system was considered too disruptive and too capital inten- sive in this case.
“The total peak power consumption of this plant excluding the power absorbed by the sub- floor heating system and the drain/door heaters was 118 kW with all defrost heaters operational.”
“TWO COMPRESSORS CAN SERVICE THE ESTIMATED HEAT LOADS WHEREAS THE THIRD IS FOR REDUNDANCY.”
NEW SYSTEM
The replacement refrigeration system is a cen- tral type, dual stage, low NH3 inventory refrig- eration plant with dry expansion refrigerant feed for the low temperature freezer evaporators and a propylene glycol loop for the medium tempera- ture services.
Jensen said the total NH3 inventory is approx- imately 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 re-
ciprocating 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 con- nected for dual duty capability. Two compres- sors 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 evap- orative 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 princi- ple. “The entire engine room including base frame, weatherproof enclosure, electrical control system, motor control centre, ventilation sys- tems, 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 in- dustrial 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 re- ductions 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 cap- ital cost minimization.
Energy consumption at the cold storage facility dropped by 59%.
“The owner (and the environment) may then be stuck with a replacement system that has failed to fully explore the maximum energy con- servation potential during the replacement pro- cess,” he said. “Excessively high indirect emis- sions for the life of the plant are therefore a real possibility in this scenario. Aside from increas- ing 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 refrigera- tion systems of the capacity range described here and equivalent transcritical CO2 systems for tropical jurisdictions are very rare.
“Such comparisons are nevertheless impor- tant to enable fully informed procurement deci- sions to be taken. They are also important to pre- vent the HFC phasedown from literally transferring us from the ashes into the fire.”
Plant room interior, pressure vessels in the background. Freezer evaporators.
CLIMATECONTROLNEWS.COM.AU
30