With summer on its way, Gareth Holden offers advice on keeping the heat off through deployment of a critical cooling systems strategy.
7 May 2015 | By Gareth Holden
Buildings requiring critical cooling, including data centres, production facilities and office complexes, can pose difficult issues for FM professionals.
In some circumstances, system resilience may seem at odds with ever-mounting sustainability and energy targets.
This should not be an issue for newer plants and buildings, but that assumes that the original design parameters or occupancy of the building has not changed. When new, cooling systems provide sufficient cooling capacity, in reality site conditions often mean that it is difficult to maintain the required temperatures, which puts the whole installation under pressure. Summer temperatures are due - how can systems struggle to meet demand?
In older buildings, the issues are likely to be more pronounced. The cooling load of the building may well have changed and, over time, the efficiency of the cooling system will have declined. Although chiller replacement can be both costly and disruptive, it is not the only answer.
In data and call centres, substantial improvements to efficiency are possible. In 50 per cent of the chillers we survey, straightforward retrofit solutions can deliver 25 per cent energy savings. With a typical return on investment of two years, these will tick both the resilience and sustainability boxes.
The starting point for any work must be a detailed understanding of the system to reveal where the weaknesses lie, with data logging of energy use and cooling capacity for chillers and associated infrastructure. Analysis and modelling of the system as it stands and how it will operate once modified, can then be produced. This stage is most useful to building service managers who might be nervous about planned interventions and to FM staff who will need to make the business case to upper management when capital expenditure is required.
Often chillers or dry coolers are where issues are found. These can be disguised because of the high redundant capacity in a critical cooling installation, the temperature of the building may be maintained but, owing to reduced cooling capacity, considerably more energy than necessary is being used. Poor heat rejection is often the root of the problem. This can be caused by a number of issues, many of which can be either rectified or significantly improved.
Hot air recirculation, where heat rejected from the condenser is not able to escape and is drawn back into the condenser inlet, is a big factor. This can be caused by the proximity of taller neighbouring buildings, the screens that are designed to hide the chillers from view, or by subsequent construction developments.
This is frequently exacerbated when the chillers are fitted with low-speed fans that are unable to 'throw' the hot air far enough to avoid being recycled.
The effect of this will typically increase air temperature entering the chiller by 5°C to 10°C, in turn reducing chiller efficiency by 15 to 25 per cent. It also means that fans inevitably run longer, drawing more power and increasing wear.
Replacing condenser fans
An answer is to replace the existing condenser fans with high-efficiency EC (electronically commutated) fans. The advanced aerodynamic blades move a far greater volume of air and ensure that it does not recirculate - they also use much less energy. In addition, the constant magnet motors are speed-controllable between 0 to 100 per cent, which allows accurate and efficient control of discharge pressures to be maintained, which improves overall chiller coefficient of performance.
Condenser fouling is another factor. Cleaning is necessary, but it's a time-consuming exercise usually requiring safety handrail to be erected. Often the easily accessible visible surfaces are the only ones effectively cleaned and interior surfaces remain dirty. The issue may only become apparent during high ambient conditions, but the chillers will have been operating at reduced efficiency throughout the year.
Deep cleaning of condensers in the opposite direction to airflow will remove compacted. It is a time-consuming process, but is economical if carried out when the fans are removed for an EC fan upgrade. The installation of an electrostatic filter on the face of the condenser ensures that they do not become fouled and future cleaning is a straightforward maintenance task that can be undertaken without the need for costly access equipment.
Another way to increase chiller cooling capacity during the summer is to use adiabatic condenser cooling, an affordable way of prolonging your cooling infrastructure's life. Instead of the harmful practice of spraying water directly onto the condenser, it is sprayed onto a mesh and air passing through is then cooled by as much as 10°C - turning a 35°C day into a 25°C day.
With the right approach, it is possible to improve chiller efficiency and system resilience long-term without wholesale replacement while improving cooling efficiency and reducing energy consumption - a win-win for FM professionals and their clients.
Gareth Holden is managing director of Excalibur Energy