Topical Article: How do you make your Heat Pumps and Chillers Operate as you Planned?

Based on 40 years of experience from troubleshooting and optimisation of heat pump/chiller installations, the question often comes up: “how hard can it be to get things right.” But the fact is that without the right information and clear responsibilities with monitoring of performance, systems will not be efficient. And it is often documented that 20-30% of the energy is wasted due to faults and lack of optimisation. Therefore, optimisation of existing plants is a “low hanging fruit” when it comes to the reduction of carbon emissions. The lack of focus on performance is a result of the structure of the property market and how HVACR systems are purchased.

It has been extremely rare that the specification of Measuring and Verification (M&V) delivers the information required to ensure that systems operate as intended over varying conditions. If a system is operated to specified temperatures without tripping, it is assumed that the system operates as specified. It is becoming common to specify to check winter and summer conditions, but this is less fruitful than to continuously log information in a structured way. It is cost-effective to ensure that data is collected in a structured way on all sites.

The industry needs to improve specification of design as well as that M&V is a part of proper commissioning and maintenance. It is not a question of adding many expensive sensors; it is to follow “good practice” for what sensors are used and how they are mounted and verified. To track energies, it is preferred to store hourly data together with outdoor conditions, whereas it is totally useless to have hourly averages on temperatures and pressures in a heat pump/chiller that can have started and stopped several times in that hour.

When the distribution systems are balanced, the largest “electricity consumer” – the refrigeration process remain unattended. In fact often 60% of the energy is neglected when the heat pump/chiller is assumed to work as rated. This leaves a huge, number of possible faults unattended and system efficiency and reliability reduced. It is necessary to ensure that the heat pump/chiller itself is in good shape and have the best operation conditions possible, including (a) Correct refrigerant charge, (b) Correct superheat, (c) No compressor problems, (d) Evaporator efficiency, (e) Condenser efficiency. Common practice for maintenance inspections do not verify performance, and it is virtually impossible to do that during a service inspection as system is highly unlikely to operate stably at the time inspection is carried out.

One of the most obvious and easiest energy-saving measures is to use “floating set points” on both the cold and warm sides; single set points based on design conditions on the cold and warm side increases electricity consumption by 20-40%.

The future is to implement guidelines such as those elaborated by IEA HPT Annex 52 and monitor systems 24/7 with state-of-the-art analytics to detect any deviation in performance. To pinpoint the cause instead of going to site on a schedule and handle failures when they happen.

Klas Berglöf, Head of R&D, ClimaCheck Sweden AB
The text has been shortened by the HPC team

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