HEATING AND VENTILATION
cooling towers, and approximately 2% of that 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. This is especially important for Trusts tasked with reducing water consumption, 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 1000 kW unit – an adiabatic cooler consumes 92 m3
of water,
compared with a hybrid cooler, which requires 8,647 m3
, and a conventional
cooling tower, with a figure more in the region of a staggering 28,032 m3
.
Latent heat of evaporation dictates that for every kW of heat that a cooling tower dissipates, it must evaporate 1.6 kg of water. In addition, in order to stop cooling tower base tanks from being clogged with the residual scale left over from the evaporation process, an additional amount of water must be bled off and replenished from a mains water supply. This means that the total water consumed is 3.2 kg per kW of cooling. For a typical 1,000 kW cooling system this gives a cooling tower water consumption of 3,200 kg every hour. In contrast, adiabatic coolers, designed with water conservation in mind, would typically consume 350 kg every
Noise-reducing technology for optimum patient comfort Patient comfort is paramount in any hospital or care setting, and specifying plant which is as quiet as possible can assist in keeping general noise levels low. Out of the three technologies discussed – cooling towers, wetted surface hybrid coolers, and adiabatic technology – cooling towers emit the most noise, requiring water silencers in low-noise environments because the splashing of the water can be the dominant sound. Hybrid coolers do boast some noise- reducing technology, such as fan speed modulation, but often have to run all fans
hour, and only for 3% of the year, rather than 100% of the year.
at full speed due to having to run at 100% speed in low ambient temperatures. Adiabatic coolers have traditionally used stage-controlled fans, which are switched on and off (usually in pairs) at full speed according to operational requirements. In other words, if more cooling power is required, two more fans would be turned on at full power, consuming large amounts of energy and creating unnecessary noise. Background noise is expected in a hospital environment, but stage-controlled fans create highly noticeable stops and starts in environmental noise levels which can be highly distracting for resting patients. Market-leading adiabatic manufacturers are now using variable speed fan controls, which match cooler capacity with load
Comment from HEJ’s technical editor
HEJ’s technical editor, Mike Arrowsmith, said: “The HSE’s HSG 274 Part 1 contains advice on wet evaporative cooling systems, and flags up ‘wet-mode’ of operation. It should also be noted that if such systems are to be considered, there must be a thorough discussion with the Water Safety Group, and an appropriate risk assessment.
“When warmer weather appears to be approaching, estates personnel should keep a look-out for portable or room, self-contained humidifiers having a water supply that is sprayed/atomised into the room. A decision on the use of these in clinical/patient areas should rest with the Infection Prevention & Control team. See also Safety Notice NHSE SN (96)06 – ‘Evaporative type cooling fan’.”
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October 2018 Health Estate Journal 47
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