Faqs: Evaporative Cooling And Humidification Systems

Transcript

FAQs Evaporative Cooling and Humidification Systems FAQs: Evaporative Cooling and Humidification Systems APPLICATION CONTROLS WATER SUPPLY AND WATER TREATMENT PUMP STATION DISPERSION INSTALLATION OPERATION MAINTENANCE __________________________________________________________________________________________________________________________________ APPLICATION What kinds of industries are using these systems? • We’ve found data centers to be our primary market. After that, manufacturing, electronic, clean rooms, printing facilities, and some comfort applications. • Anywhere cooling and humidification are needed year round are the optimal applications. Can you do indirect cooling with these systems using a sensible or enthalpy wheel, heat pipe, or air-to-air heat exchanger? Direct or indirect evaporative cooling • Yes. A very good way to indirectly cool an airstream is Heat exchanger with bypass dampers (both airstreams) with the use of a sensible wheel, heat pipe, or air-to-air Final evaporation media heat exchanger (see illustration). • An enthalpy wheel provides some value, but not as much as a sensible-only system. Dispersion location Exhaust air Filter Exhaust fan What is the cooling effectiveness of these systems? Indirect evaporative cooling • When using a High-Pressure System, more than 90% wet-bulb depression is possible. It is important to note that evaporation efficiency decreases as cooling efficiency requirements increase, affecting water usage and system sizing. • When using a Wetted Media System, cooling efficiency is determined by wetted media properties and air velocity. See the Wetted Media System Cooling Efficiency and Pressure Drop graph on the next page. Return air Direct evaporative cooling Supply fan Outside air Filter Supply air Humidification Heating coil Dispersion location Final evaporation media Cooling coil Direct evaporative cooling adds moisture to the supply air. Indirect evaporative cooling occurs in the heat exchanger without adding moisture. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 1 What are the differences between high-pressure and wetted media systems? • Although both high-pressure and wetted media systems utilize adiabatic processes, the way they deliver moisture to the air is very different. High-pressure systems break water up into very small droplets, while wetted media washes water over a vertical surface in an airstream. • Pressure drop differences are important to consider when comparing high-pressure to wetted media systems. Highpressure dispersion manifolds and nozzles add an insignificant amount to the system pressure drop, but when final evaporation media is used (installed 2’ to 4’ downstream from nozzles), its pressure drop is important to include. Wetted media panel pressure drop increases with thickness. Depending on the application, the pressure drops could be similar, but if high wet-bulb depression values are required, the wetted media thickness will need to increase, which increases pressure drop as well. Be sure to get specific pressure drop values for both systems – these values depend on material and airspeed. DriSteem uses two types of final evaporation media for High-Pressure Systems, depending on customer material and pressure requirements: a polyurethane foam for standard applications, and a stainless steel mesh for low pressure drop or all-stainless applications. DriSteem Wetted Media Systems use 12" GLASdek media, for which pressure drops can be found in the graph below. 100 0.50 95 0.40 90 0.30 85 0.20 80 0.10 75 Pressure drop (inches H2O) DriSteem Wetted Media System cooling efficiency and pressure drop Cooling efficiency (percent) • Controllability is another differentiator between highpressure systems and wetted media. Wetted media panels are intentionally kept wet to reduce mineral buildup. This means that once the system is turned on, it will be humidifying and adiabatically cooling for several minutes, regardless of when the call for humidity ends. Large panels are split into multiple stages to try to modulate demand but the lag remains. Highpressure systems modulate stages of nozzles with high-pressure solenoid valves. These solenoid valves can be cycled quickly (up to ten seconds or less) to meet a changing demand. See the “Controls” section for additional information. 0.00 100 200 300 400 500 600 700 Air velocity (fpm) Performance data courtesy of Munters Corporation • High-pressure systems are designed to use reverse osmosis treated, or better quality, water. These systems atomize water. Therefore, if used with untreated water, the dissolved solids commonly found in untreated water would be dispersed into the airstream. Wetted media systems do not require treated water because water is not aerosolized. Therefore, when used with untreated water the dissolved solids remain on the media or in the tank as scale. DriSteem's Wetted Media Systems minimize scaling and extend media life by controlling the cycles of concentration or the recirculation of water, ensuring that scaling only occurs when the systems are drying out. • Wetted media water basins require attention to reduce potential biologic growth, such as regular drain and flush sequences or chemical treatment. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 2 How do first costs and energy costs of evaporative cooling systems compare? • High-pressure system first costs are generally higher than other adiabatic systems due, mostly, to the cost of adding water treatment cost. High-pressure systems, however, are the most energy-efficient: Relative energy use comparison Adiabatic technology Energy usage High-pressure system 2.7% Centrifugal 40% Ultrasonic 53% Compressed air 100% • Wetted media systems are one of the lowest first-cost systems because the technology is simple and water treatment is not required. Wetted media system energy costs are very low and, in most cases, comparable to high-pressure systems. An application-specific energy analysis should be performed when considering a wetted media system to accurately predict energy costs. Since wetted media systems require media replacement when the media becomes clogged with minerals, there will be recurring media replacement costs. How do operating costs of a gas isothermal humidifier compare to high-pressure and wetted media systems? • In general, a high-pressure or wetted media system will have operating costs up to 80% less than a gas-fired humidifier, especially if the system is both humidifying and cooling. • The best way to calculate these costs is to give us your application, location, and site conditions and we’ll give you an estimate. CONTROLS How do high-pressure systems modulate in AHU applications? • One of the benefits of DriSteem’s High-Pressure System is its ability to control multiple zones, and also to control multiple stages within each zone. When you take into account varying space ventilation requirements, changing outside conditions, economizer cycles, and VAV applications, it is readily apparent that the ability to modulate nozzles on and off quickly is important. DriSteem High-Pressure Systems modulate stages on accumulated demand, whether that demand is from a BAS or calculated by the Vapor-logic controller. How do wetted media systems modulate? • While wetted media systems are very effective cooling supply air, they react slowly. On an initial call it takes a number of minutes to get the media wet and begin to change temperature in the airstream. When demand is removed the wetted media system will continue to cool and humidify for a significant time. The optimal applications for wetted media systems are where a wide temperature and humidity range can be tolerated in the space and where the supply air conditions can be changed quickly in order to allow the wetted media system to operate in a constant state. What are the benefits of DriSteem's High-Pressure System controller? • Tight control of water output: – Staging of nozzles allows for sections of the entire dispersion assembly to be cycled on and off to meet modulating demands – High-quality, stainless staging valves can be cycled quickly to meet low and changing demand signals. Vapor-logic controller modulates valves; low demands are met by time proportioning the smallest stage in a zone. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 3 – Recirculation of feed water increases system turndown: ∙ As demand goes down, so does pump/motor speed. When low output is required, the pump/motor is turned down to the pump minimum rpm. ∙ If lower turndown is required, the system pressure increases to 1,200 psi. At this point the high-pressure unloader valve opens to recirculate water from the outlet of the pump back to the inlet of the pump. Up to 90% of the water through the pump can be recirculated. ∙ At this level the smallest stage of a zone can be modulated up to 50% of the time. ∙ All of these measures deliver a turndown of up to 11:1 for smaller units and 20:1 for larger units. • Control example, 2- stage system: – 33% stage 1 – 67% stage 2 – 3 states Control example: 2-stage system Demand % State Stage 1 Stage 2 16.5%+ TP modulation On-off minimum 50% Off 33% State 1 On Off 67% State 2 Off On 100% State 3 On On • Control example, 3- stage system: – 15% stage 1 – 30% stage 2 – 55% stage 3 – 7 states Control example: 3-stage system Demand % State Stage 1 Stage 2 Stage 3 7.5%+ TP Modulation On-off minimum 50% Off Off 15% State 1 On Off Off 30% State 2 Off On Off 45% State 3 On On Off 55% State 4 Off Off On 70% State 5 On Off On 85% State 6 Off On On 100% State 7 On On On • Tight control is obtained in AHU applications by modulating the solenoid staging valves on and off as quickly as once every second. • System modulation by varying pump pressure is not optimal in most applications. Capacity does change with pressure, but so does droplet size. As pump pressures go down, droplet sizes get bigger. This results in lower evaporation efficiencies and more water waste. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 4 WATER SUPPLY AND WATER TREATMENT Why is RO-quality water required for the high-pressure system? • Minimal maintenance: Mineral-free water ensures a long nozzle life free of clogging. Also, the stainless steel pump operates up to 8,000 hours using mineral-free water. • IAQ: In order to have optimal indoor air quality, minerals and biologics must be removed from the supply water. Reverse osmosis technology is the minimum required to adequately accomplish this. What is the estimated life of the RO pump? • In practice, RO pumps used on the DriSteem High-Pressure System have operated for 10 years and longer without service. The pump is operated at its optimal speed and is only on when the RO holding tank needs to be replenished. This ensures that on-off cycles are minimized. What is the estimated RO membrane life? • RO membrane life is directly related to incoming water hardness. Hard water erodes membranes faster than softened water. To extend RO membrane life, DriSteem uses a particulate filter, duplex water softener, and dechlorinator to pretreat the water. • The RO pump cycles on when the pressure in the RO holding tank is below 30 psi and cycles off at 50 psi. This minimizes the number of on-off cycles on RO membranes and reduces lifetime membrane stress membranes. • Certain materials affect RO membranes more severely than others. Chlorine dissolves RO membranes, and iron erodes membranes faster than other solids. Chlorine is filtered out by the dechlorinator, and iron by the particulate filter. • DriSteem employs a back-flush feature every time the RO pump turns off. This flushes any particles that may have gotten through to the membrane and are on the supply side of the membrane, extending membrane life. • The above strategies have shown to give 2-10 years of operation before membrane replacement was required, with four- and five-year life being very common. How much water is rejected in the RO water filtering process? • Exact percentages depend on site water composition, but a rule of thumb is that between 25-40% of the water entering the RO system will be rejected to drain. • DriSteem’s reverse-osmosis system uses a recycle loop where a percentage of the concentrate from the RO membranes is recovered and sent back through. This reduces the amount of concentrate sent to drain. Why does the DriSteem High-Pressure System have an RO holding tank? • The RO holding tank is used to ensure that RO water is available for the high-pressure pump at all times. At the end of each RO cycle, pure water is used to back-flush the membranes, increasing their life. If the high-pressure pump is on during RO back-flushing, it will still have an available supply of RO water because of the holding tank. • The multi-stage pump used with the RO system is chosen for its high pressure and flow rate required for moving water through RO membranes. It is most efficiently used in a “maintenance” mode, keeping the RO holding tank between 30 and 50 psi. • If used in an on-demand mode, the RO membranes would be overly stressed due to many more on-off cycles. Fewer, longer cycles extend the life of the RO membranes. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 5 Does DriSteem require an application water analysis, and when? • Yes. To allow us to properly size system components, the earlier DriSteem receives a water report the better. What we look most for in a water report are contaminants like iron, radioactivity, or anything requiring additional filtering equipment. Most jobs don’t require this; however, what we’re most concerned with is sizing the water softener correctly. If the softener is too small it regenerates too often. We aim for at least two days between regeneration cycles. Does DriSteem provide water treatment with the high pressure pump station on a single skid? • Yes. Placing water treatment and the high-pressure station on one skid, with connections made at the factory, means an installing contractor will have only one or two connections to make. This is offered as an option. Can condensate from the dispersion system be returned to the water treatment system to meet water rationing requirements? • Yes. Collect condensate in the air handler, pump it to a holding tank and return it to the beginning of the water treatment process. What are the water quality requirements for wetted media systems? • Wetted media systems do not require water treatment. The harder the water the more water will be drained away during use to minimize scaling and extend media life. PUMP STATION What are the benefits of DriSteem’s high-pressure pump station? • Low maintenance requirements: – All stainless-steel, high-pressure pump. Cooled and lubricated by the water used for -humidification. • Low energy usage: – The high-pressure pump motor uses the majority of the energy of the system. DriSteem’s High-Pressure Systems use a high-efficiency motor with a direct-coupled pump to maximize system efficiency. – Utilizing a variable-frequency drive to turn down motor speed as demand decreases reduces energy usage. • Design for installation: – The pump station has point connections for inlet water, high-pressure water, and power. – Interconnecting piping from the pump station to the dispersion manifolds is easy-to-connect stainless steel tubing using compression fittings. There are no pitch requirements, and since there is little pressure drop with water, the pump station can be located far away from the dispersion manifolds (for example, up to 150 ft for Model 500). See the recommended distances and pressure drops in the submittal section of the DriSteem website. – Pumping station with water treatment is available on a single skid with factory connections to ease installation. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 6 What are the benefits of the Danfoss high-pressure pump? • Maintenance-free operation: – This pump is cooled and lubricated by the water used for humidification/cooling. – The motor is directly coupled to the pump so there are no belts to replace. • Quintuple-piston, positive-displacement pump design. This pump has higher pump efficiencies and less pulsation forces (which eliminates the need for a pulsation dampener) than centrifugal and triplex positive-displacement pumps. • All stainless steel construction. This is the best pump to use with reverse osmosis and demineralized water. • Its construction is consistent with DriSteem’s indoor air quality requirements for the most hygienic, safe systems. Why choose the Danfoss pump over a brass pump? • Stainless steel does not react with high purity water. Since DriSteem uses only RO or higher quality water with our High-Pressure Systems, a pump designed for these types of water is a must. • No maintenance. Brass pumps are lubricated with oil and need to have their oil changed every 500 hours of service. Brass pumps also require belt changes because the motor is not directly coupled to the pump. • It is the right pump to use when a variable frequency drive (VFD) is used to control the speed of the pump. This is most common in AHU and duct applications where multiple stages will be turned on and off at different times. When demand is low the pump turns slowly. With the stainless steel pump this is not an issue because the water for humidification flows through the pump to cool and lubricate it. Brass oil-lubricated pumps require internal oil dispersion to properly lubricate internal components. At low speeds the oil can’t lubricate all these components and premature failure will occur. • The Danfoss pump has a minimum rpm requirement to ensure long life. Above this minimum, piston faces on the Danfoss high-pressure pump ride on a sheet of water and do not touch the mating surface. • Ceramic-coated plungers used on brass pumps are susceptible to cracking when there is an elevated temperature difference between the plunger and water. • The Danfoss pump produces negligible pressure pulsation, so there is no need for pulsation dampers. • Brass, oil-lubricated pumps have the following additional components not necessary in the Danfoss pump: – 6 check valve kits and seals – 3 oil seals – 3 piston guides – Crankcase with 3 piston cranks and 3 piston rods – 2 crank bearings and seals FAQs: DriSteem® Evaporative Cooling and Humidification Systems 7 What is the expected life and time until service of the Danfoss high-pressure pump? • Maximum expected pump life is 45,000 hours, approximately 10-12 years. • The Mean Time Between Failure (MTBF) value has been based on many years of laboratory lifetime testing and analysis of customer feedback from the market. The MTBF evaluation is based on the fact that the pumps are run within the recommended conditions, but at the same time, the MTBF value is based on the assumption that the pump is being run in the worst-case scenario within the recommended conditions. If the pump runs in better conditions, then the MTBF value will improve. Danfoss states the pump will, at a minimum, last 8,000 hours. Their evaluation is that 0.5% of the pumps will fail before the 8,000 hours. This gives a failure rate of 0.625 per million hours, which is equivalent to a MTBF of 1.6 million hours. A pump can, on average, be serviced five times in the pump’s life. When a pump has been serviced and wear parts have been changed, then the 0.5% will be valid for the next 8,000 hours. The pump can either be serviced by Danfoss (recommended in the beginning) or by a customer who has participated in a pump service program. If the pumps are being serviced more frequently (i.e., every 6,000 hours) then that will improve the MTBF value. • At the 8,000-hour interval, the system should be monitored to ensure that proper pump pressure is reached during operation. Compare actual pump pressure to pump pressure set point, and, if lower, schedule maintenance for the pump. Alternatively, the pump can be disassembled and inspected for wear. • Running the pump without water is the main reason for premature pump failure. Always ensuring that properly treated and filtered water is supplied to the pump is the best way to extend the life of the pump. What is the noise level of DriSteem’s High-pressure System? • The noise level of the system depends on pump/motor speed. At maximum speed, the noise level is 74-76 dBA measured at 1 meter from the pump. At low speed the noise level is 68-70 dBA. How does the pumping package work on DriSteem wetted media systems? • DriSteem’s Wetted Media System uses one pump per stage of media plus one pump to recirculate water through the UV system and keep tank water constantly moving, which increases the effectiveness of the drain for removing debris. • Multiple pumps also provide redundancy, for if one pump is down the others will still supply water to their stages. • Multiple small pumps are more efficient that one large pump. This ensures that DriSteem Wetted Media Systems use the least amount of energy. DISPERSION What are the benefits of the nozzles used with DriSteem’s High-Pressure System? • DriSteem nozzles produce extremely small water droplets (90% of droplets are less than 10 microns). Water droplet size is one of the most important factors affecting evaporation. Nozzle orifice size determines capacity and affects droplet size. Integral to the nozzle is a micro-turbine that is hydraulically suspended and rotated by water, breaking the water up before it is ejected from the nozzle orifice. This ensures the smallest droplets possible. • There are no external impaction pins or other methods of droplet manipulation that would require annual replacement. • An integral check valve shuts off water supply to the nozzle at 100 psi, ensuring low-pressure water does not drip out of the nozzle. • A particulate filter at the base of the nozzle protects the nozzle from debris that may be in the piping. • Reverse-osmosis water treatment process removes dissolved solids that become white dust when sprayed in the AHU or space. Viruses and bacteria removed by reverse osmosis process. • Stainless-steel piping and nozzles are corrosion resistant FAQs: DriSteem® Evaporative Cooling and Humidification Systems 8 How long is nozzle life? • Supplying reverse-osmosis treated (RO) or better-quality water allows the nozzles to operate for the life of the system. Nozzle clogging is caused by debris in either the water or the piping, or by supply water with total dissolved solids (TDS) of 30 ppm or greater. Every time demand is removed and the nozzle shuts off, any water that is in the nozzle orifice at that time remains. Once that water evaporates, if there are dissolved solids they will stay behind. After an amount of time — related to the water quality — the orifice will become clogged by hard water deposits. • Erosion of the nozzle orifice is negligible with RO or better quality water. Why use 1000 psi at the nozzles for atomization? • As water pressure increases at the nozzle, water droplet size decreases. Smaller droplets evaporate more quickly than larger droplets. We have found that 1,000 psi is the optimal pressure at the nozzle outlet. The pump station can supply 800-1200 psi water to allow for some flexibility between output and interconnecting piping pressure loss. • At very low pressures, water is not broken up into droplets but exits the nozzle in a stream. This is the reason why the nozzles have an integral check valve that stops water from entering the nozzle at 100 psi or less. What size are the water droplets after leaving the nozzle? • Over 90% of the droplets leaving the nozzle are less than 10 microns. The maximum size is less than 50 microns. These values are valid for a pressure range of 800-1,200 psi, with sizes getting smaller as pressure increases. What is the expected life of the solenoid staging valves? • DriSteem uses Danfoss high-pressure solenoid valves for manifold staging. These valves have been tested to operate for at least one million cycles. Given a typical 2,000-hour humidification season, if the valves cycle, on average, once a minute, this equals 120,000 cycles. With a more than one-million-cycle life span, the solenoid staging valves have at least a ten year expected life. How do wetted media systems put water into the air? • Saturating the media creates a large area of water for the supply air to come in contact with as it passes through the system. Keeping the media continually saturated when there is a demand is key to minimizing scale accumulation. INSTALLATION Should there be a back-flow preventer on the water supply line? • Install a back-flow preventer per local code requirements. DriSteem does not supply a back-flow preventer. OPERATION What happens with a High-Pressure System when all zones are closed? Where does the pressure go? • There is an unloading valve after the high-pressure pump. If pressure exceeds 1,200 psi, water is bypassed to the particulate filter on the pump station and back through the pump. This continues until the pump shuts off when the controller determines there is no demand for cooling or humidity (30 seconds to a minute). • Recirculating water when there is no demand signal keeps the pump cool and lubricated. FAQs: DriSteem® Evaporative Cooling and Humidification Systems 9 MAINTENANCE Do evaporative cooling and humidification systems require much maintenance? • Both high-pressure and wetted media systems are extremely easy to maintain and are the lowest maintenance evaporative cooling systems available. • DriSteem High-Pressure Systems have a stainless-steel pump that is lubricated by water and doesn’t require maintenance for 8,000 hours, provided the water treatment system is kept in good working order (vs. an oillubricated pump, which requires maintenance after 500 hours). • High-pressure systems use RO-treated water, so there are no mineral buildup issues or clogged nozzles. • Wetted media systems do not require water treatment but the media does need to be replaced every few years depending on water quality and usage. • Compressed air and water systems use compressed air, and compressors require significant regular maintenance. • Ultrasonic systems require reverse osmosis treated water, as well as maintenance/replacement of the piezoelectric discs. • Systems with water treatment require maintenance that includes making sure the water softener has salt, changing the RO filter when indicated by sensor, and changing the particulate filter annually. • Evaporative systems have no boiling tank to clean as do isothermal (steam) systems. Do evaporative cooling and humidification systems go through a blowdown during winter to prevent freeze-up? • These systems should not be installed where there is a possibility of freezing. • High-pressure systems goes through an automatic system flush when, after 72 hours without a demand signal, the RO tank drains, flushes, cleans the membranes, and refills to maintain water cleanliness. At this time, the supply and depressurization valves open and water flushes the dispersion lines by zone through to floor drains. Because the dispersion lines are depressurized, no pressurized water enters the airstream. • A DriSteem Wetted Media System tank drains after a default 72 hours of inactivity. The lines from the pump to the media are open to atmosphere so they never hold water unless they are operating. DriSteem Corporation A subsidiary of Research Products Corporation An ISO 9001:2000 certified company U.S. Headquarters: 14949 Technology Drive Eden Prairie, MN 55344 800-328-4447 or 952-949-2415 952-229-3200 (fax) European office: Marc Briers Grote Hellekensstraat 54 b B-3520 Zonhoven Belgium +3211823595 (voice) +3211817948 (fax) E-mail: [email protected] www.dristeem.com © 2014 Research Products Corporation Form No. EC_FAQs_0114 FAQs: DriSteem® Evaporative Cooling and Humidification Systems 10