CHILLERS Time to
think about controllability
Graham Temple, marketing manager for Mitsubishi Electric’s chiller prod- ucts, explains why it’s sensible to consider the efficiency and controlla- bility of chillers as well as capacity. And why now is a good time to think about replacing older chillers with more efficient technologies.
T
he key challenges for commercial buildings over the next twenty years are energy efficiency and carbon reduction. Whatever the outcome of the UK’s changing relationship with the EU right now, the issues of energy security and cost will still be of paramount importance in the years to come.
What’s more, the UK’s commitment to reducing carbon emissions lies outside its membership of the EU, so we must remain focused on achieving a 50% reduction in carbon emissions from 1990 levels by 2025 - a goal established by the Committee on Climate Change.
Commercial buildings continue to be large energy users, so the pressure is still on to ensure that non-dwellings optimise energy efficiency wherever possible. This is being driven by legislation and initiatives such as Part L of the Building Regulations; the Energy Saving Opportunities Scheme (ESOS); Energy Performance Certificates (EPCs) and the related Minimum Energy Efficiency Standards (MEES). This last point is particularly pressing. By April 2018 it will be illegal to let a building with an EPC rating of less than E. To put that into perspective, about 25% of the commercial buildings in London have a rating of F or G.
One of the challenges therefore for building managers is balancing this requirement for energy efficiency with occupant comfort. It is widely accepted that building services use the bulk of energy in non-domestic buildings (around 80%, according to the Carbon Trust).
It would be simple to save money by switching off air conditioning or heating - but it is guaranteed that paying tenants in a commercial building will not be thrilled by this sort of approach, no matter how much energy it saves. So finding technology that can provide robust comfort levels
40 August 2016
in an efficient way is an increasing driver for those with oversight of building services. One of the biggest energy users in a building is air conditioning - but it’s also one of the most crucial for preserving occupant comfort. Chillers remain a key technology for providing air conditioning in a range of buildings.
Generally, the key area of interest for specifiers has of course been capacity. However, given the need to balance comfort with efficiency, other aspects of chiller performance must now be given ever-closer scrutiny, for example, their performance at lower capacities.
Chillers have been developing over some years, with a view to providing building owners with the most energy efficient options. The latest chiller models are equipped with inverter drives and modulating valves to operate efficiently even when not at full capacity. These chillers only operate to meet the precise cooling demand of the building. Inverter compressor technology reduces electricity use of the chiller by up to 30% against fixed speed or mechanically modulated compressors.
Another approach for specifiers to consider when selecting chillers is the two-stage cooling circuit. Two compressors are used in a single chiller unit, with each compressor serving a separate plate heat exchanger. By modulating the evaporating temperature individually, overall system efficiency can increase by an additional 3.9%, compared to single evaporation refrigeration cycles.
There has also been a growing awareness that controlling building services equipment is central to achieving greater overall building energy efficiency. Many chillers will be delivered with their own built-in control system to manage the internal operation of the equipment. These can be used
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