These must be dissipated to keep away from a buildup of heat. Evaporative cooling is a standard and environment friendly means of reducing thermal masses and relies on the principle that, when water is evaporated, power is absorbed from the surrounding surroundings, thus lowering its temperature. The power required to change water from one state to a different – about 2,430 KJ (around kwh) is used to evaporate 1 litre of liquid water to vapour at 30 C. Cooling towers use this principle. They cool water to a temperature decrease than the ambient air dry-bulb temperature with very little power input compared with refrigerated systems. Because of this, they are often used to dissipate large thermal hundreds in business and to cool large refrigeration or air-conditioning systems (e.g. to cool a large enclosed building or a building housing digital gear that produces heat because it operates). Evaporative condensers, such as these utilized in a refrigeration unit, use the identical evaporative cooling effect of water to straight cool the coils within the unit. This makes the system compact and extra vitality efficient. Nevertheless, cooling towers and evaporative condensers require important portions of make-up water to compensate for losses associated with evaporation, drift (or mist) and blowdown (or purge). Water might even be utilized in ancillary feedwater therapy processes, comparable to softening. Hidden prices Reducing water consumption in cooling towers and evaporative condensers can save more than the worth of the water alone. Understanding the true price of water is vital. Make-up water is usually pre-treated before use (e.g. softened) and, in keeping with Well being and Safety Fee (HSC) Authorized Code of Observe and Steerage (L8), may have conditioning chemicals added to it to regulate legionella. Each of those water-remedy steps provides considerably to the general price of the water.
2 2 Reducing water use in cooling towers and evaporative condensers Typical prices for make-up water are: UK mains provide /m three Softened water /m 3 Reverse osmosis (RO) treatment /m three Demineralised/deionised water /m 3 1 UK mains provide based on customary 2010/11 tariffs 2 Notice this does not include capital prices (together with membrane alternative, and so on) which could be vital for RO plant Remember that extra costs will even be incurred for disposal of any water to sewer (e.g. reject water, blowdown or purge), sometimes between 0.54 and a pair of.67/m 3. Action 1. If not already known, determine the worth of water used in your cooling towers and evaporative condensers. Understanding the place water is used Many businesses do not know how much water is being utilized by their cooling towers and evaporative condensers (via evaporation, blowdown or every other loss, similar to drift). There might even be water losses at the water treatment plant. Monitoring the quantity of water used in each step of the method allows the water effectivity of the cooling towers and evaporative condenser installations to be determined. It also permits malfunctions or reductions in efficiency to be identified, significantly if the water make-up consumption is plotted on a graph. Putting in meters is a straightforward, effective and inexpensive method of measuring water use at each step in the process. A easy 30 mm water meter with a pulsed output costs round seventy five-ninety five, excluding fitting. Determine 1 highlights some potential areas for investigation in a typical evaporative cooling tower. These would be comparable for evaporative condensers. Determine 1: Potential areas for water effectivity enhancements in a typical evaporative cooling tower Water treatment Incoming cold water M1 1. Assessment M1 M2 M3 M4 M5 Regeneration water to drain M2 three. Overview water remedy to: Treated water Feedwater or water tank Feedwater 4. Assessment Cooling demand Cooled water Warm water Cooled water Air Air M5 Key Chilly water M3 M1 Heat water Meter location 2. Evaluation blowdown M4
3 Lowering water use in cooling towers and evaporative condensers three In this example, installing meters in the urged areas would enable the next to be calculated: Determine 2: Sophisticated pipework round cooling towers and evaporative condenser plant illustrates the significance of labelling pipework M1 – M2 = M3 – M4 = water used (loss) at water treatment plant evaporation and drift loss across the cooling tower With cooling towers, it is price checking whether the water really used is in steadiness with what should be used. A water balance for a cooling tower may be summarised as: Make-up water (M) = Evaporation loss (EL) + Blowdown (BD) + Drift loss (DL) While BD will be measured simply, EL and DL are more difficult to measure, however they can be estimated. The theoretical water consumption of a cooling tower may be calculated utilizing the following steps: Step Calculation Image Unit Components 1a Thermal load A kw A = Circulation x four.2 kj/kg C x (Temp water in Temp water out ) Where four.2 kj/kg C is the particular heat of water 1b Cooling load attributable to airflow B kw B = Airflow x 1 kj/kg C x [Temp air (Temp water in – three)] the place 1 kj/kg C is the particular heat of air Note: B could be unfavorable 1c Evaporative load C kw C = A + B 1d Evaporation loss EL kg/s EL = C/2,430 kj/kg the place 2,430 kj/kg is the latent heat of evaporation of water at 30 C 2 Blowdown quantity BD litres/s BD = EL 3 Drift loss (estimate only) N 1 The place N = focus ratio in the tower (typically 1.5 :1 for very onerous water, 2:1 for onerous water, 3:1 for soft water and higher than 6:1 for deionised/reverse osmosis water) DL litres/s DL = x recirculation fee round tower (litres/s) one hundred Word: 0.005% loss is for an excellent, modern, drift eliminator four Make-up quantity M litres/s EL + BD + DL If the actual water consumption (indicated by your water meters) is considerably better than the theoretical consumption, further investigations ought to be taken to find out why. Doable causes include better thermalload dissipation than used in the calculations, leakage from the system, the blowdown valve is stuck or the system is malfunctioning. There are sometimes many pipes round cooling towers and evaporative condenser plants (see Determine 2). Unless they’re straightforward to observe, it can be tough to grasp what flows the place, making water management tougher. Labelling pipework to point the contents and stream course will make this much easier, and may be particularly helpful in an emergency. 1. Evaluation the place water meters are put in around cooling towers and evaporative condenser installations. If crucial, set up more meters to observe water use successfully. 2. Examine your precise water use in opposition to theoretical use and examine discrepancies. Three. Label pipework to point the contents and movement direction.
4 four Decreasing water use in cooling towers and evaporative condensers Blowdown or purge Optimising blowdown is commonly the best alternative to scale back water consumption in cooling towers and evaporative condenser installations. The focus of whole dissolved solids (TDS) will increase within the closed-loop system as the water evaporates. Bleeding off the system water by blowdown or purging is normally needed to forestall scale constructing up in cooling towers and evaporative condensers, which may impair effectivity or structurally harm the unit. Usually, TDS concentrations within the cooling water needs to be not more than 2,000 three,000 mg/litre, but this will depend upon specific working situations. Blowdown can be managed manually, by timer or routinely. Automatic strategies are normally based on conductivity measurement, which is proportional to TDS concentration. Using an automatically managed system is preferable as a result of TDS concentrations are monitored continuously, resulting in smaller volumes of water being blowdown extra steadily to maintain the concentration inside the desired range, minimising the overall amount of water discharged. The quantity of blowdown water required will be estimated using the make-up water TDS focus and desired maximum TDS focus in the cooling water. For instance, for water with a median TDS focus of four hundred mg/litre and a required most TDS within the cooling water of 2,000 mg/litre: Blowdown required (%) = TDS of feedwater (mg/litre) Most increase in x one hundred concentration of TDS (mg/litre) 400 = x one hundred 2, = 25% of make-up water move Blowdown is normally discharged to drain, however there may be an growing pattern to re-use this water supplied water quality permits. 1. Test if the blowdown water volumes are known. If not, try to measure or calculate them. 2. Decide if blowdown volumes could be decreased, possibly by bettering remedy of the make-up water. Three. Investigate whether or not blowdown will be automated. Four. Examine the potential for blowdown water to be re-used. Treatment of make-up water Blowdown will be minimised if the concentration ratio (CR) or cycle of focus (COC) is excessive. CR (or COC) = TDS focus in cooling water TDS focus in make-up water Focus ratios of around 3:1 5:1 are typical for a lot of cooling tower and evaporative condenser installations, however these will depend on feedwater high quality and optimal TDS or specific ion (e.g. chloride) ranges. To prevent scaling and minimise blowdown, most make-up water could have some type of pre-treatment, which include: softening (altering the chemical composition of a number of the dissolved salts) to scale back scaling; and demineralisation or reverse osmosis to remove the majority of TDS. The blowdown required may be considerably lowered by bettering the remedy course of for make-up water to cut back the TDS of the feedwater and increasing the CR/COC. Typical financial savings in make-up water that can be achieved by enhancing water remedy to increase CR/COC are shown in Table 1.
5 Lowering water use in cooling towers and evaporative condensers 5 Table 1: Volume of make-up water (%) saved by increasing the focus ratio New focus ratio Initial focus ratio % 44% 50% 53% fifty six% fifty eight% 60% 61% sixty two% sixty three% 64% 2 17% 25% 30% 33% 38% 40% 42% 43% forty four% 45% % sixteen% 20% 25% 28% 30% 31% 33% 34% three 7% 11% 17% 20% 22% 24% 25% 26% 3.5 5% 11% 14% 17% 18% 20% 21% four 6% 10% 13% 14% 16% 17% 5 four% 7% 9% 10% eleven% 6 3% 5% 6% 7% Source: North Carolina Department of Setting and Pure Resources, Division of Pollution Prevention and Environmental Help Subsequently, bettering water treatment to reduce TDS can significantly enhance the water efficiency of cooling tower and evaporative condenser installations. Keep in mind that the type of water-therapy process used might also supply a possibility to enhance water effectivity. If an ion change process is used, equivalent to softening or demineralisation, the ion trade beds would require periodic regeneration. These regeneration processes not solely use water and chemical reagents, but in addition generate effluent, all of which incur prices. Enterprise a every day regeneration process, or an identical time-dependent foundation, no matter the quantity of water that has been treated, can result in extra frequent regeneration than is critical. Using automated systems primarily based on volume of water treated or a measured worth (e.g. conductivity breakthrough) might be far more efficient and minimise the number of regenerations required. If reverse osmosis is used, a permeate stream and reject water (or concentrate) stream is produced. The permeate is basically pure water and will likely be used to supply the make-up water. The reject water can usually account for 30% of the incoming movement and, despite the fact that this can have elevated salt concentrations, it remains to be likely to be appropriate for recovery and re-use elsewhere on site. Drift Water, within the form of small droplets, is often lost in the airflow leaving cooling towers and evaporative condenser installations, and known as drift, also called mist (see Figure 3). Drift eliminators are often fitted to prevent this loss, however it’s normally still current to some degree. Relying on the design of the eliminator, water losses through drift will be zero.05% zero.2% of water movement via cooling towers and evaporative condensers. Good tower and drift eliminator design may reduce this significantly. Losses on trendy items are typically around zero.005% however will be as low as zero.001%. Motion 1. Examine your tower for drift losses and, if crucial, set up drift eliminators. Figure 3: Evaporative losses from a cooling tower 1. Calculate the CR/COC and assess if any watertreatment improvements would increase the CR/COC and what make-up water financial savings could possibly be achieved. 2. If softeners or demineralisation processes are used, check whether or not the frequency of the regeneration cycles will be lowered. Three. If reverse osmosis treatment is used, assess the potential to re-use the reject water elsewhere on site.
6 6 Lowering water use in cooling towers and evaporative condensers Losses and leaks Determine 4: Leaking pipes can have important value implications if they aren’t repaired Though cooling towers and evaporative condensers are relatively simple gadgets of plant, they are often massive and should have a big pipework system. The most common leaks are from the enclosure of the cooling tower or evaporative condenser itself, faulty pump glands, pipework flanges and joints, all of which needs to be repaired as soon as doable (see Determine four). The waste by even a small leak may be excessive and dear as cooling towers and evaporative condensers are normally in constant operation. Sticking or poorly sealing blowdown valves can lead to a steady stream of blowdown water. In addition to utilizing quite a lot of water, this can even lead to the excessive use of chemicals within the therapy regime for the cooling tower. Blowdown valves must be routinely checked and corrective action taken if any are found to be defective. 1. Undertake routine surveys of cooling towers and evaporative condensers for leaks and losses, and take remedial motion as quickly as possible. 2. Restore or substitute poorly working blowdown valves promptly. 3. Test overflows (e.g.