Harnessing the UK weather for better cooling system performance

HVAC systems are often identified as one of the main areas of improvement when it comes to maximising building efficiency. But did you know that it is the larger plant, often situated on or around the exterior of the building, which could unlock the largest return?

Here, Tim Bound, Director for Transtherm Cooling Industries, leading manufacturer of ambient cooling technologies, explores how we can harness the UK weather to improve cooling system performance and deliver impressive reductions in energy consumption; including free cooling and the potential of rainwater harvesting.

Cooling plant such as hybrid cooling equipment, cooling towers and more modern adiabatic technologies are regularly specified to dissipate heat from Trigeneration and water-cooled chiller systems at healthcare, education and industrial sites as well as district cooling schemes.

Despite having the potential to communicate with building management systems (BMS) or remotely to a central control point via 3G, and deliver substantial energy reductions, this externally located plant is often overlooked by energy managers seeking to create a facility which is as energy efficient as possible.

The cooling market is rife with innovation and technology which can utilise UK weather patterns to maximum effect when it comes to dissipating heat from essential HVAC applications. Specifying cooling technology in accordance with relevant weather data is rapidly becoming best practice and should be a key consideration in any new or retrofitting project.

Making the most of cooler UK temperatures

Even in the very early stages of specification, decision makers can narrow down which cooling technologies they should tender by arming themselves with some basic weather data for the UK.

For example, we know from a variety of sources including the MET office that the average daily temperatures in the south west of England range from 5°C in January to 16.4°C in August, giving an average temperature across the year of around 10.3°C. Using this as a threshold, specifiers can make an informed choice for the selection of cooling technology that performs the most efficiently in that region. It is important to remember also, that technology which leverages cooler UK temperatures can reduce reliance on water-hungry evaporative cooling.

Most impressively, adiabatic technology can work efficiently in its more efficient, dry cooling mode for 97% of the year when operating in colder climates like the UK – only switching to evaporative cooling when temperatures exceed 21-23°C, which in mission critical environments that work around the clock equates to a tiny 3% of the year.

Free cooling

Free cooling can generate substantial cost and energy savings across a multitude of manufacturing and processing applications where water cooling is essential.

Free cooling is a process which uses cold air from outside to cool water within a chilled water system. Whilst it is not a direct replacement for HVAC systems with refrigerated compressor units, it offers an energy and cost-saving alternative for up to nine months of the year when the outside air is cool enough – preventing or reducing the need for energy consuming systems when the external conditions allow.

Thanks to the extremely high energy efficiency of market-leading air blast coolers, operators can take advantage of low ambient air temperatures wherever possible throughout the year, totally or partially offloading the refrigerated chiller as appropriate.

For businesses in the UK, where even spring and autumn can be particularly cool, payback on a system of this nature can be as short as four to six months, with substantial cost savings after that. Free cooling systems can also be retrofitted to most pre-existing water cooling equipment to prevent the need for a full cooling system overhaul, which means even more businesses can benefit from this trend as it continues to become best practice.

Reduce reliance of evaporative cooling for better water efficiency

When it comes to energy management, how important is water preservation for your facility?  Water is, of course, a natural resource and governments worldwide are beginning to regulate its usage and set targets for personal and commercial consumption.

It is worth remembering that adiabatic coolers, in addition to offering low energy consumption, can also deliver a reduction of between 8.5M and 17M litres of water per 1MW of cooling/annum at a cost saving of between £19k and £39k per 1MW of cooling/annum.

As a general rule hybrid cooling plant uses evaporative cooling methods for around 50% of the year, only switching to dry mode in temperatures lower than 9.6°C, most commonly between January and April and then again in November and December. Meaning such technology relies heavily on the consumption of water in order to deliver effective cooling results.

Adiabatic technology can work efficiently in dry cooling mode for 97% of the year when operating in colder climates like the UK – only switching to evaporative cooling when temperatures exceed 21-23°C, which in mission critical environments that work around the clock equates to a tiny 3% of the year. Given this advanced dry cooling capability, it should be no surprise that adiabatic coolers consume approximately 2% of the water used by wetted surface hybrid dry coolers. Even when operating in wet mode, adiabatic systems automatically employ a pulsed spray operation to minimise water usage delivering much improved Water Usage Effectiveness (WUE).

If we examine those figures more closely, as water consumed in cubic meters over a one-year period for a 1000kW unit, an adiabatic cooler consumes 92m³of water, compared to a hybrid cooler which requires 8,647m³ and a conventional cooling tower which is more in the region of a staggering 17,310m³.

Running on such a small amount of water means adiabatic systems can even work efficiently when fed by a rainwater harvesting tank or even a building-wide grey water management system; a benefit which simply cannot be matched by alternative, evaporative cooling systems.

Rainwater harvesting systems can be used specifically to feed adiabatic coolers, or, for building-wide water efficiencies, a ‘grey water’ system which recycles water from showers, baths and wash-hand basins to supply a number of water-consuming facilities including toilet flushing, laundry and irrigation systems. For buildings which are already utilising a grey water management system to good effect, onsite adaptations can be made to enable new or existing adiabatic technology to receive recycled water from this system rather than a cold mains feed.

The feasibility of feeding ambient cooling technology from rainwater is supported by the latest MET office statistics which show that in 2017, the UK was subjected to more than 10 days of rain, every month for ten out of the 12 calendar months. An average of 1,372mm of rainfall was recorded for the year, which represents a typical figure for the UK when compared to statistics from the last decade.

It is vital to remember that careful consideration should be given to the filtering, storing and hygiene of such systems and relevant experts should be consulted when considering rainwater harvesting or a grey water recycling scheme as a primary water source for adiabatic cooling technology.

For more information on how weather data can aid energy efficient specification of water cooling equipment, speak to Transtherm or visit www.transtherm.co.uk