Chillers The latest in chiller technology
George Hannah looks at some of the principal technologies used in the latest generation of chillers
launch of Airedale’s chiller in 1984, systems have become increasingly advanced, delivering higher energy efficiency for footprint and capable of ever higher cooling loads, currently up to 1.4 MW. Here’s what’s available.
At conceptual stage, advanced design techniques such as computational fluid dynamics (CFD) are used to analyse a range of coil types and orientations to maximise the heat exchange area and air flow. The modular ‘V block’ arrangement and use of microchannel condensers instead of round tube plate fin alterna- tives, provides a highly efficient surface area for refrigerant heat exchange, allowing cooling capac- ities to be increased and lower condensing temperatures achieved within a smaller footprint. A further performance benefit is that these coils have a lower air side pressure drop which increases airflow; this helps to increase the total heat rejection and makes the fans more energy efficient at full and, particularly, part-load. In addition to signifi- cantly improving performance, the ‘V block’ arrangement also makes it easier to access the unit for maintenance. The variable speed control between 10- 100% allows cooling duty to be precisely matched to demand and, with tighter water set point man- agement, significant part-load efficiencies can be achieved during low load conditions or in low seasonal ambient temperatures. Being oil-free, there is virtually no vibration and fewer moving parts within the compressor, which reduces operational wear and tear and risk of downtime. In the event of a power failure, the compressor acts as a generator and powers itself down in a controlled manner. The use of flooded evaporators with built- in suction gas heat exchangers improves compressor energy effi- ciency by up to 15% particularly at part-load via the highly efficient
14 | October 2014 | HVR
method of boiling heat transfer.
with their highly efficient backward curved aerofoil impellers, EC fans reduce power in comparison with equivalent AC fans at both full and modulated fan speeds by as much as 70%. EC fans incorporate electronically commu- tated DC motor controls using control modules which respond to signals from the indoor unit. The in-built EC fan control module allows for fan speed modulation from 0-100%; in contrast, the modulating range of a standard AC fan is typically between 40 and 100% of full fan speed.
In addition to the above, current generation chillers also typically benefit from lower noise levels on compressors and fans, an important factor where chillers are situated in residential neighbour- hoods. Similarly, by removing the transient starting ‘spikes’ normally associated with screw chillers, electrical supply components do not need to be oversized on site.
Free-cooling
Free-cooling saves vast amounts of energy, particularly when room temperatures are high, and was first made available with the Ultima free-cooling chiller in 2001. To take effect, free-cooling needs a temperature difference between the outside supply and return air of only 1°C. With increasing pressures on budgets, the oppor- tunity to reduce energy costs by limiting the need for mechanical cooling can help significantly reduce operational costs.
Concurrent free-cooling Just two years on in 2013, Airedale developed the concept of ‘concur- rent’ free-cooling which further decreases energy consumption through reducing the need for mechanical (DX) cooling and maximising the part-load efficien- cies of components such as EC fans, inverter-driven pumps and centrifugal compressors. The variable speed control on such components means that load can
be very precisely matched to cool- ing duty, reducing energy con- sumption and unnecessary wear. Through the use of temperature sensors and sequencer controls, cooling can be staged, ensuring a smooth transition from mechanical to air free-cooling. Airedale’s controls logic and sequence management, for example, can configure between two and six chillers to run as master/slave and run/standby. On sites with an air cooled and free-cooling chiller, the sequencer ensures that when the ambient is low, the free-cool- ing chiller is the first to start up. The significance of free-cooling is a key influencer in the decision- making process since energy costs can often outweigh capital costs in surprisingly short periods of time. By way of example, energy costs for a traditional DX computer room
air conditioning (CRAC) system can add up to five or six times the initial purchase price over the first five years of its lifetime. In contrast, a modern free-cooling chiller is capable of operating for up to 95% of the year in concurrent free-cool- ing (cumulative hours, London, UK) significantly reducing the amount of energy used by a conventional chiller.
Free-cooling systems can there- fore easily pay for themselves with- in the first couple of years and, by the end of five years, total costs of ownership are typically significant- ly lower than those of DX systems. When free-cooling is used in conjunction with fan optimisation and elevated chilled water temper- atures the opportunity for energy savings can be increased further. // The author is the technical director of Airedale International//
BSI approved R1234ze for John Lewis
Ahead of EU targets to phase down the use of hydrofluorocarbons (HFCs) which are expected to lead to restrictions in the supply of traditional commercial cooling refrigerants like R410A and R134a by 2030, Airedale has now adopted R1234ze as the most suitable replacement. Following extensive testing and development, the first BSI approved chiller using R1234ze was installed at the most sustainable John Lewis store which opened in York in April 2014.
R1234ze is a hydro-fluoro olefin (HFO) based isomer which breaks down in the atmosphere within just 16.4 days compared with 14 years for R134a and is rated by the International Panel for Climate Change (IPCC) with a 100-year GWP lower than 1, better than CO2. In contrast, R410A and R134a have GWPs of 2088 and 1430 respectively. A further advantage, with the addition of R1234ze the Airedale
TurboChill automatically receives two BREEAM points in recognition of its low global warming impact. In contrast, R134a TurboChill TCC and TurboChill Free Cooling TCF variants receive one point for their Direct Effect Life Cycle (DELC) CO2 equivalent emissions of ≤1000 kgCO2e/kW cooling capacity and a further point for leak detection and automatic shutdown and pump-down of refrigerant.
Daily news update at
www.heatingandventilating.net
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44