H U MI D I F I CA T I O N SYS T E M D E S I GN G U I DE from the Humidification Experts
For more information www.dristeem.com sales@dristeem.com DRI-STEEM Humidification System Design Guide DRI-STEEM Humidifier Company A subsidiary of Research Products Corporation U.S. Headquarters: 14949 Technology Drive Eden Prairie, MN 55344 800-328-4447 952-949-2415 952-229-3200 (fax) European office: Bell Place, Bell Lane Syresham, Brackley NN13 5HP, UK +44 1280 850122 (voice) +44 1280 850124 (fax) E-mail: 106277.1443@compuserve.
Table of contents Introduction Introduction to the Design Guide . . . . . . . . . . . . . . . . . . . . . . . . 1 Load Calculating humidification load Using inch-pound units of measure . . . . . . . . . . . . . . . . . . . . 4 Using SI (Système International) units of measure . . . . . . 13 Reference tables for calculating load Steam loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Heat gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction to the Design Guide Your guide to humidification system design Let us know what you think! Welcome to DRI-STEEM’s Design Guide. In tandem with our product catalogs, this guide gives you all the information you need to design a humidification system using DRI-STEEM® products. The Design Guide covers generic humidification issues such as calculating load, determining absorption distance, and laying out piping. Use this guide to help you understand general humidification system design issues.
Table 2-1: The tools you need — DRI-STEEM's educational resources Tool Purpose Description Location Case studies Humidification education Application-specific stories about installed humidification systems. Recent topics include: • Mercy Medical Center; absorption case study • Waterloo Testing Facility; energy savings case study • View, print, download pdf file, or order a preprinted copy at www.dristeem.
Table 2-1 (continued): The tools you need — DRI-STEEM's educational resources Tool Purpose Description Location Installation, Operation and Maintenance manuals (IOM) Product-specific operation and maintenance information Available for the following products: • View, print, or download pdf CRUV DRANE-KOOLER™ GTS file, or order a preprinted copy at LTS Steam Injection STS www.dristeem.
Calculating humidification load using inch-pound units of measure Important notes about calculating load • When outside air is 10% or less, it is wise to calculate the load twice. The first calculation should be made on the basis of air changes due to mechanical ventilation; the second should be based on the natural ventilation method. Use the larger of the two results for determining the load.
Sample Problem 1 Calculate the humidification load for a printing plant where: • The desired conditions in the space are 70 °F and 50% RH. • The outside entering conditions are 10 °F and 45% RH. • The dimensions of the building are 120' × 80' × 12' (length × width × height). • Air changes per hour = 1 Solution to Sample Problem 1 using the natural ventilation method 1.
Table 6-1: Pounds of moisture per hour per 100 cfm at sea level Air temp. Percentage of saturation °F 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 80% 90% 100% -20 0.00 0.014 0.022 0.03 0.035 0.043 0.05 0.057 0.064 0.071 0.078 0.085 0.093 0.099 0.114 0.13 0.14 -10 0.012 0.025 0.037 0.05 0.06 0.074 0.085 0.097 0.11 0.121 0.134 0.147 0.159 0.171 0.20 0.22 0.24 0 0.02 0.04 0.06 0.081 0.102 0.121 0.142 0.162 0.184 0.204 0.223 0.
Mechanical ventilation method The following example shows how to calculate load using the mechanical ventilation method. This method works best when the percentage of outside air volume is at least 10%. Sample Problem 2 Calculate the humidification load for a printing plant where: • The desired conditions in the space are 70 °F and 50% RH. • The outside entering conditions are 10 °F and 45% RH. • A mechanical ventilation system circulates air at 9,000 cfm, of which 25% is outside air.
Figure 8-1: Typical economizer control system Outside air Damper Damper arms Mixed air controller set at 55 ˚F Damper motor Mixed air 55 ˚F Return air Economizer cycle method Many year-round air conditioning systems use economizer cycle control. Economizer cycles use cool outside air instead of mechanical cooling to maintain building temperature when the outside temperature is moderate (typically spring and fall).
Sample Problem 3 Determine the outside air quantity in an economizer cycle system where: • • • • The outside air is 20 °F. The return (room) air is 70 °F. The mixed air is 55 °F. The total air is 12,000 cfm. Solution to Sample Problem 3 using the economizer cycle method 1. A = 55 °F – 20 °F = 35 °F 2. B = 70 °F – 55 °F = 15 °F 3. VAH = 12,000 cfm 4.
Notes about economizer cycle method Sample Problem 4 Economizer “free cooling,” provided by using outside air, is not always cost effective. The operating cost advantage of ambient cooling may be lost when certain operating conditions prevail, such as: Determine the maximum humidification load for an economizer system located in Minneapolis where: • The indoor relative humidity requirements are in a fairly high range (40% RH or greater). • Electricity is used to heat water into steam for humidification.
Table 11-1: Average daily minimum % RH for year and extreme daily minimum % RH for year, by location (U.S.
Table 12-1: Calculation table from economizer cycle method Sample Problem 3 (inch-pound units) Outside temp. H (space) °F lbs/hr/100 cfm -20 2.4 – 0.072 = 2.328 x 17 x 12,000 ÷ 100 = 47.49 -10 2.4 – 0.124 = 2.276 x 19 x 12,000 ÷ 100 = 51.89 0 2.4 – 0.208 = 2.192 x 21 x 12,000 ÷ 100 = 55.24 10 2.4 – 0.338 = 2.062 x 25 x 12,000 ÷ 100 = 61.86 20 2.4 – 0.545 = 1.855 x 30 x 12,000 ÷ 100 = 66.78 30 2.4 – 0.856 = 1.
Calculating humidification load using SI (Système International) units of measure DRI-CALC software will calculate load for you The easiest way to calculate humidification load is to use DRI-CALC, DRI-STEEM’s humidification system sizing and selection software. The software not only sizes loads, but also selects equipment, writes specifications, creates equipment schedules, and provides as-configured installation instructions for DRI-STEEM products.
Sample Problem 1 Calculate the humidification load for a printing plant where: • The desired conditions in the space are 21 °C and 50% RH. • The outside entering conditions are -10 °C and 45% RH. • The dimensions of the building are: 40 m × 25 m × 4 m (length × width × height). • Air changes per hour = 1 Solution to Sample Problem 1 using the natural ventilation method 1.
Table 15-1: Grams of moisture per m3/h at sea level Air temp. Percentage of saturation ˚C 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 80% 90% 100% -30 0.02 0.03 0.05 0.07 0.09 0.10 0.12 0.14 0.15 0.17 0.19 0.20 0.22 0.24 0.27 0.31 0.34 -25 0.03 0.06 0.08 0.11 0.14 0.17 0.19 0.22 0.25 0.28 0.31 0.33 0.36 0.39 0.44 0.50 0.56 -20 0.04 0.09 0.13 0.18 0.22 0.27 0.31 0.36 0.40 0.44 0.49 0.53 0.55 0.62 0.71 0.80 0.89 -15 0.07 0.
Mechanical ventilation method The following example shows how to calculate load using the mechanical ventilation method. This method works best when the percentage of outside air volume is at least 10%. Sample Problem 2 Calculate the humidification load for a printing plant where: • The desired conditions in the space are 21 °C and 50% RH. • The outside entering conditions are -10 °C and 45% RH. • A mechanical ventilation system circulates air at 15,000 m3/h, of which 25% is outside air.
Reference tables for calculating load: Steam loss Steam loss in lbs/hr/ft2 Table 17-1: Steam loss in lbs/hr/ft2 of duct area or ULTRA-SORB face area at 55 °F duct temperature for all ULTRA-SORB panels and for RAPID-SORB, Multiple-Tube, and Single-Tube evaporative dispersion units Duct air velocity Tube centers or duct height with Single-Tube 3" 6" 9" 12" 18" 24" 36" 48" 60" fpm lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 lbs/hr/ft2 500 1.
Steam loss in kg/h/m2 Table 18-1: Steam loss in kg/h/m2 of duct area or ULTRA-SORB face area at 13 °C duct temperature for all ULTRA-SORB panels and for RAPID-SORB, Multiple-Tube, and Single-Tube evaporative dispersion units Duct air velocity Tube centers or duct height with Single-Tube 76 mm 152 mm 229 mm 305 mm 457 mm 610 mm 914 mm 1219 mm 1524 mm m/s kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 kg/h/m2 2.54 9.28 5.37 3.71 3.08 2.54 2.30 1.71 1.27 0.98 3.
Steam loss in lbs/hr/ft2 Table 19-1: Steam loss in lbs/hr/ft2 of duct area at 55 °F duct temperature for MAXI-BANK™, Multiple-Tube, and Single-Tube jacketed steam injection humidifiers Tube centers or duct height with Single-Tube Duct air velocity 6" 9" 12" 18" 24" 36" 48" 60" Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated 500 0.86 1.50 0.
Steam loss in kg/h/m2 Table 20-1: Steam loss in kg/h/m2 of duct area at 13 °C duct temperature for MAXI-BANK, Multiple-Tube, and Single-Tube jacketed steam injection humidifiers Duct air velocity Tube centers or duct height with Single-Tube 76 mm 152 mm 229 mm 305 mm 457 mm 610 mm 914 mm 1219 mm Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated 2.
Steam loss in lbs/hr/ft2 and kg/h/m2 Table 21-1: Steam loss in lbs/hr/ft2 and kg/h/m2 of duct area at 55 °F or 13 °C duct temperature for MINI-BANK® jacketed steam injection humidifiers 3" or 76 mm tube centers Duct air velocity Insulated Noninsulated fpm m/s lbs/hr/ft2 kg/h/m2 lbs/hr/ft2 kg/h/m2 500 2.5 1.0 5.1 2.0 9.8 750 3.8 1.4 6.7 2.8 13.5 1000 5.1 1.6 7.9 3.0 14.4 1250 6.4 1.6 7.6 3.1 15.0 1500 7.6 1.7 8.1 3.3 16.0 1750 8.9 1.7 8.5 3.5 16.9 2000 10.2 1.
Steam loss in lbs/hr/ft2 and kg/h/m2 Table 22-1: Steam loss of interconnecting vapor hose, tubing, and pipe Description Steam loss Nominal hose, tubing, or pipe size Insulation thickness Noninsulated Insulated inches DN lbs/hr/ft kg/h/m lbs/hr/ft kg/h/m inches mm 11⁄2 40 0.15 0.22 N/A N/A N/A N/A 2 50 0.20 0.30 N/A N/A N/A N/A 11⁄2 40 0.11 0.16 0.020 0.030 2.0 50 2 50 0.14 0.21 0.025 0.037 2.0 50 3 80 0.20 0.30 0.030 0.045 2.5 64 4 100 0.26 0.39 0.
Reference tables for calculating load: Heat gain Heat gain in °F Table 23-1: Heat gain in °F at 55 °F duct temperature for all ULTRA-SORB panels and for RAPID-SORB, Multiple-Tube, and Single-Tube evaporative dispersion units Duct air velocity Tube centers or duct height with Single-Tube 3" 6" 9" 12" 18" 24" 36" 48" 60" fpm °F °F °F °F °F °F °F °F °F 500 3.41 1.98 1.37 1.13 0.93 0.84 0.63 0.47 0.36 750 2.87 1.68 1.20 1.08 0.84 0.72 0.54 0.41 0.30 1000 2.52 1.59 1.
Heat gain in °C Table 24-1: Heat gain in °C at 13 °C duct temperature for all ULTRA-SORB panels and for RAPID-SORB, Multiple-Tube, and Single-Tube evaporative dispersion units Duct air velocity Tube centers or duct height with Single-Tube 76 mm 152 mm 229 mm 305 mm 457 mm 610 mm 914 mm 1219 mm 1524 mm m/s °C °C °C °C °C °C °C °C °C 2.54 1.90 1.10 0.76 0.63 0.52 0.47 0.35 0.26 0.20 3.81 1.60 0.93 0.67 0.60 0.47 0.40 0.30 0.23 0.17 5.08 1.40 0.88 0.62 0.50 0.42 0.
Heat gain in °F Table 25-1: Heat gain in °F at 55 °F duct temperature for MAXI-BANK, Multiple-Tube, and Single-Tube jacketed steam injection humidifiers Tube centers or duct height with Single-Tube Duct air velocity 6" 9" 12" 18" 24" 36" 48" 60" Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated 500 1.6 2.7 1.1 1.9 0.9 1.6 0.7 1.3 0.7 1.
Heat gain in °C Table 26-1: Heat gain in °C at 13 °C duct temperature for MAXI-BANK, Multiple-Tube, and Single-Tube jacketed steam injection humidifiers Duct air velocity Tube centers or duct height with Single-Tube 76 mm 152 mm 229 mm 305 mm 457 mm 610 mm 914 mm 1219 mm Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated Insulated Noninsulated 2.5 0.86 1.50 0.63 1.04 0.
Heat gain in °F and °C Table 27-1: Heat gain in °F and °C of duct area at 55 °F and 13 °C duct temperature for MINI-BANK jacketed steam injection humidifiers 3" or 76 mm tube centers Duct air velocity Insulated Noninsulated fpm m/s °F °C °F °C 500 2.5 1.87 1.04 3.63 2.01 750 3.8 1.66 0.92 3.32 1.84 1000 5.1 1.45 0.81 2.90 1.61 1250 6.4 1.12 0.62 2.22 1.23 1500 7.6 1.00 0.55 1.97 1.09 1750 8.9 0.90 0.50 1.78 0.99 2000 10.2 0.82 0.46 1.64 0.91 2250 11.4 0.
Reference tables for calculating load: Air duct pressure loss Air duct pressure loss in wc and Pa Table 28-1: Air duct pressure losses for all ULTRA-SORB panels and for RAPID-SORB, Multiple-Tube, and Single-Tube evaporative dispersion units Tube centers or duct height with Single-Tube (without airflow stabilizer panel) Duct air velocity 3" 76 mm 6" 152 mm 9” and greater 229 mm and greater wc Pa fpm m/s wc Pa wc Pa 250 1.3 0.010 2.5 0.005 1.2 500 2.5 0.020 5.0 0.010 2.5 750 3.8 0.
Air duct pressure loss in wc and Pa Table 29-1: Air duct pressure losses for MAXI-BANK, Multiple-Tube, and Single-Tube jacketed steam injection humidifiers With insulated jackets: Tube centers or duct height with Single-Tube Duct air velocity 6" 152 mm 9" 229 mm 12" 305 mm 18" 457 mm 24" 610 mm fpm m/s wc Pa wc Pa wc Pa wc Pa wc Pa 500 2.5 0.02 5.0 0.02 5.0 0.01 2.5 0.01 2.5 0.01 2.5 1000 5.1 0.08 20.0 0.06 15.0 0.04 10.0 0.03 7.5 0.03 7.5 1500 7.6 0.18 45.
Select energy source Choices when using on-site steam Choose energy source wisely Using on-site steam for humidification can be a good economic choice. Pressurized steam can be injected directly into the airstream, or passed through a heat exchanger to heat potable, softened, or DI/RO water for humidification steam. A pound of water requires approximately 1,000 BTUs to vaporize.
• Choose isothermal electric humidification for application flexibility. Electric element humidification systems easily integrate into existing systems. They are available in a wide range of sizes, capacities and options, allowing them to meet the humidification demands of virtually any environment.
Table 32-1: DRI-STEEM products by energy source DRI-STEEM product ELECTRICITY Maximum capacity lbs/hr kg/h RH control capability* 4,000 1,814 ±1% Shortest absorption available No unnecessary heat gain Double-header design Pre-assembled MINI-BANK • • • • Short to moderate absorption distance Suitable for medium capacity systems Sized for small ducts Pre-assembled 84 38 ±1% • • • • • Short to moderate absorption distance Suitable for large capacity systems Fits small ducts to large air handler
Humidifiers and water type Water type affects humidifier performance, maintenance, vapor quality, and efficiency Water is often called the universal solvent because almost everything is soluble to some degree in water. This property causes water to become contaminated by virtually any material it contacts, with the mix of contaminants varying greatly from one location to another.
• Dissolved organic material comes from three major sources: Figure 34-1: How a water softener works Highly soluble ions Sodium (does not form scale) exchanged here for Slightly soluble ions Calcium and magnesium (minerals that form scale) – The breakdown of naturally occurring organic materials (plant and animal matter) – Domestic and commercial chemical wastes (agricultural and urban runoff, or leaching from contaminated soils) – Chemical reactions that occur during water treatment processes (from disi
High purity water yields high purity humidification for critical process environments Figure 35-1: Single tank (mixed bed) DI system Semiconductor, pharmaceutical, and electronics manufacturers, as well as laboratories, industrial clean rooms, and healthcare facilities often require high purity humidification. To avoid water contaminants that can be carried into the air with water vapor, these types of environments use highly processed – and very pure – water in their humidification systems.
How water type affects humidifier performance Isothermal systems — systems that boil water to make steam (vapor) — typically maintain relative humidity (RH) levels within 1%-5% of an established set point, with the ability to maintain a specific level of control directly dependent on the system's ability to respond to changing environmental conditions.
semiconductor manufacturing). Hard water can be used in isothermal humidifiers with the understanding that these systems require regular inspection and cleaning and that RH performance will fluctuate. But the easiest and most cost-effective way to reduce maintenance requirements is to soften the fill water. Direct injection of boiler steam affects indoor air quality Boiler steam is often directly injected into the air through steam dispersion units to provide humidification.
Table 38-1: How fill water type affects performance, maintenance, steam quality, and efficiency in isothermal humidification systems Fill water type/ conductivity Skimming required? (Y/N) Potable (minimum conductivity 100 µS/cm) Y System with a manual drain: Humidifier typically drains one time per season, but may need to increase drain and flush frequency based on quarterly inspections, especially with water over 12 gpg (205 mg/L).
Evaporative system components and operation Components are part of a humidification system 1. Create steam (STS humidifier) Creating humidity with a DRI-STEEM evaporative humidification system is a three-step process: 1. Create steam. A DRI-STEEM humidifier with an evaporating chamber (such as VAPORSTREAM or GTS) boils water to create steam. 2. Control.
Typical evaporative system configurations Figure 40-1: Multiple evaporating chambers and an ULTRA-SORB dispersion panel installed in an AHU Figure 40-2: Evaporating chamber and a RAPID-SORB dispersion unit installed in a duct Figure 40-3: Evaporating chamber and a single dispersion tube installed in a duct Page 40 • DRI-STEEM Design Guide
Typical evaporative system configurations (continued) Figure 41-1: Evaporating chamber and a Space Distribution Unit installed in a finished space Figure 41-2: Evaporating chamber with a Space Distribution Unit installed directly above Space Distribution Unit (SDU) Evaporating chamber Figure 41-3: Evaporating chamber and an AREA-TYPE fan DRI-STEEM Design Guide • Page 41
Evaporative system components Figure 42-1: VAPORSTREAM electric system 8 1. Control cabinet 9 If a humidifier has a separate control cabinet, it can be mounted either on the humidifier or remotely. Some humidifiers, like the VAPORMIST, have control components integrated into the humidifier cabinet. Systems using VAPOR-LOGIC control also have a keypad (see Figure 42-2). 7 4 5 3 1 8 2 Figure 42-2: VAPOR-LOGIC3 keypad 2.
6. Valve (heat exchanger systems) Upon a call for humidity, valves allow steam (STS), hot water (LTS), or an air/gas mixture (GTS) to enter the heat exchanger. Figure 43-1: STS Steam-to-Steam system 2 8 9 7. Temperature sensor Systems with VAPOR-LOGIC3 have a temperature sensor mounted on the evaporating chamber enabling: • Over-temperature protection (electric systems) • Freeze protection • Preheating, allowing rapid response to a call for humidity 7 5 6 4 3 8.
Evaporative system principle of operation Figure 44-1: Standard water systems Conductivity probe detects water level 1. When the system is first activated, the fill valve opens and the evaporating chamber fills with water to the operating level. 1 4 3 2 2. On a call for humidity, the heating elements are energized, causing the water to boil. The fill valve opens and closes as needed to maintain the operating water level. 3.
Evaporative system water level control Figure 45-1: Standard water systems Standard water systems require conductive water DRI-STEEM’s standard water evaporating chambers (found in DRI-STEEM evaporative humidifiers with model numbers that do not end in “DI”) require fill (makeup) water to have conductivity of at least 100 µS/cm (2 grains/gallon). These systems use a conductivity probe to measure water levels and, therefore, will not operate with DI/RO water (which is demineralized and not conductive).
Figure 46-1: Hose connection Figure 46-2: Threaded pipe connection Figure 46-3: Flange connection Page 46 • DRI-STEEM Design Guide Evaporative system steam outlet connections Outlet sizes and connections vary by model. See product catalogs for availability. See also Table 65-1: Maximum steam carrying capacity and length of interconnecting vapor hose, tubing, and pipe on Page 65 of this document.
Steam injection system components and operation Direct injection of boiler steam DRI-STEEM’s steam injection humidifiers use steam from an external source, such as an in-house boiler, an unfired steam generator, or a district steam system. Basic operation and components are described in this section. For more complete information, see the steam injection catalog.
Steam injection components 1. Steam jacket The steam jacket is a steam-filled chamber surrounding the inner dispersion tube to keep it warm and eliminate condensation and dripping. 2. Steam separator The steam separator removes entrained water droplets and slugs of condensation. 3. Deflector plate The deflector plate directs water inside the separator toward the drain. 4. Multi-baffle plate The multi-baffle plate allows only steam to rise into the upper region of the separator.
5. Internal drying tube The internal drying tube excludes any remaining moisture particles, allowing only dry steam to leave the separator. 6. Steam valve The steam valve controls the amount of steam allowed into the dispersion tube. 7. Dispersion tube The dispersion tube provides uniform steam dispersion across the duct width. 8. Thermal-resin tubelet Unique tubelets extend into the center of the dispersion tube so only the driest steam is discharged into the air.
Steam injection principle of operation 1. Boiler steam with entrained water enters the humidifier and flows through a chamber surrounding the inner dispersion tube, jacketing it with steam to eliminate condensation and dripping. 2. The steam with entrained water slows from entering the larger space of the separator and from hitting the perimeter deflector plate, and then begins to spin and separate. 3.
Humidifier maintenance considerations Water hardness determines maintenance requirements Softened water reduces maintenance When choosing a humidification system, keep in mind that the more minerals in your supply water, the more maintenance your system will require. The easiest way to avoid maintenance in a standard water system is to use water with low levels of hardness.
Controlling DRI-STEEM humidifiers Application determines acceptable RH control range Controlling relative humidity (RH) in commercial and industrial environments can be easy or challenging, depending on the level of control required. RH fluctuations of 5% to 7% are common in commercial or office building environments where the purpose of providing humidification is primarily to improve occupant comfort and health.
Isothermal humidifier basics Isothermal humidifiers use an energy source to boil water into steam for dispersion either directly into an occupied space or through an HVAC system. All isothermal humidifiers have a makeup water fill valve, a drain valve for periodic and/or end-ofseason draining, and a water level control mechanism. Our systems also have a water surface skimmer for reducing particulates at the high-water level.
Output control basics On-off control On-off control is the simplest control scheme and does exactly what its name implies: the output device turns fully on, then fully off. Residential furnaces and air conditioners often use this type of control. In a humidification system, an on-off humidistat has a differential between the on and off switch points. The differential is established at a range sufficient to prevent output short cycling.
where it begins time-proportioning modulation control – that is, the burner system turns on for a period of time and then turns off for a period of time. With a high quality valve and responsive control at low demand, a gas humidifier should be able to provide steam output rangeability at a ratio of 40 to 1 and, especially in a large capacity system, can yield RH control to ±1%.
Achieving RH control with DRI-STEEM equipment Table 56-1: RH control comparison RH control capability* Application Energy source DRI-STEEM product Energy modulation Water type Steam Injection: ULTRA-SORB MINI-BANK MAXI-BANK Multiple-Tube Single-Tube Industrialgrade control valve Pressurized steam Electricity VAPORSTREAM SSR modulation with PID control DI/RO Hot water LTS Industrialgrade control valve DI/RO Gas GTS Valve with high turndown ratio DI/RO Pressurized steam STS Industrialg
How to design for proper humidification steam absorption Drip-free dispersion is possible HVAC engineers often express concerns about steam condensation on internal duct elements when specifying humidification systems. And these concerns are valid, for if severe enough, water accumulation from condensation can leak through ducts to cause damage below. This is an immediate — and easily noticeable — problem.
be present. Solid objects at duct air temperature, such as coils, dampers, fans, etc., downstream of this dimension will remain dry. When installing upstream of high-efficiency filters, visible condensed steam wisps entering the filter bank can result in a wetted filter. If you need to install upstream of high-efficiency filters, consult your representative or DRI-STEEM directly for special recommendations.
Humidification system components placement Determine humidifier placement A humidification system generally consists of a vapor or steam generator and a dispersion assembly. The proper placement of these two components is crucial for successful system operation. Usually, there is no single correct placement for a humidifier. Much depends on system design and application. However, the following paragraphs and dispersion assembly placement examples are presented as guidelines for common situations.
Placing a dispersion assembly near an elbow (see Figure 60-1) • Location A is the best choice. Better absorption occurs on the downstream side of an elbow than on the upstream side. • Location B is the second-best choice. Installing upstream of an elbow can cause wetting at the turning vanes. In cases where it is structurally impossible to avoid Location B, use a multiple tube dispersion unit to ensure complete absorption.
Placing a dispersion assembly in a primary/secondary system (see Figure 61-1) This type of system is commonly applied to facilities where most of the building requires one level of humidity (typically to meet comfort requirements) and part of the building requires additional humidity. In Figure 61-1, the primary humidification system is within the main air handling unit. The secondary humidification system is located close to the point of steam discharge into the secondary area.
A This is the ideal sensing location because this placement ensures the best uniform mix of dry and moist air with stable temperature control. B This location is acceptable, but the room environment may affect controllability such as when the sensor is too close to air grilles, registers, or heat radiation from room lighting.
Piping an evaporative humidification system The drawing below shows a typical piping configuration for an evaporative system. For detailed information about how to pipe a specific DRI-STEEM evaporative humidifier, see the Installation Guides available by product in DRI-CALC.
Table 64-1: Pitch of dispersion tube(s) and interconnecting piping for Single- or Multiple-Tube evaporative dispersion units Condensate drain Diameter of dispersion tube and interconnecting piping Type of interconnecting piping 11⁄2" (DN40) Vapor hose 2" (DN50) Pitch of interconnecting piping Tubing or pipe 2" (DN50) 11⁄2" (DN40) Vapor hose 2" (DN50) With drain 2"/ft (15%) toward humidifier No drain 1/8"/ft (1%) toward condensate drain 1⁄4"/ft (2%) toward floor drain or toward humidifier if humidi
Table 65-1: Maximum steam carrying capacity and length of interconnecting vapor hose, tubing, and pipe* Copper or stainless steel tubing and Schedule 40 steel pipe Vapor hose††† Hose I.D.
Piping a steam injection system Pressurized steam piping guidelines • Size piping in accordance with ASHRAE recommendations. • The humidifier’s steam supply should be taken off the top of the steam main (not the side or bottom) to ensure the driest steam. The main should be dripped and trapped (in accordance with ASHRAE recommendations). • The humidifier steam trap(s) must drain by gravity to the return main having little or no back pressure.
degradation of steam quality, and heat transfer capability. Install drip legs at all low points and natural drainage points in the system, such as at the ends of mains and at the bottoms of risers, and ahead of pressure regulators, control valves, isolation valves, pipe bends, and expansion joints. On straight horizontal runs with no natural drainage points, space drip legs at intervals not exceeding 300' (91.4 m) when the pipe is pitched down in the direction of the steam flow and at a maximum of 150' (45.
maximum lift of 2.5' (0.76 m). Do not attempt lifts in excess of 5' (1.5 m). • Steam trap. When lifting condensate, use an inverted bucket type steam trap. Float and thermostatic (F&T) traps are more prone to water hammer damage with a flooded trap, which may occur when lifting condensate. • Pipe size. The size of the vertical portion of the piping should be 1⁄2" (DN15) pipe thread. • Check valve (swing type). Install a low-pressure differential swing check-valve adjacent to the trap.
eliminates heat gain during the “off” humidification periods only (see Figures 68-1 and 69-1). The jacketing steam valve should be a two-position type, with a minimum Cv of 5, and set to the fullopen position prior to opening the modulating valve. In Figure 68-1, all of the steam (for jacketing and humidification) must pass through the jacket steam valve, and it must do so with very little or no pressure drop across the valve, or maximum capacity will be reduced.
Summary Designing a humidification system is a straightforward process of: • • • • • • • • Calculating load Selecting the energy source Choosing a water type Understanding humidifier maintenance requirements Defining control requirements Selecting humidification equipment Placing dispersion assemblies to ensure complete absorption Piping the humidification system In tandem with a product catalog, this Design Guide has hopefully given you the information you need to design a DRI-STEEM humidification syste
Glossary of humidification terms Numbers and symbols 3PDT — three-pole, double throw µS/cm — microSiemens per centimeter, a measure of conductivity A A — ampere, amps, amp ac — alternating current adiabatic humidifier — uses heat from air to convert water into vapor AGA — American Gas Association AHU — air-handling unit ANSI — American National Standards Institute aquastat — thermostat designed for use in water ASCII — American Standard Code for Information Interchange ASHRAE — American Society of Heatin
check valve — a valve allowing fluid flow in one direction only cold-snap offset RH transmitter — during periods of very cold weather, this window-mounted temperature transmitter lowers the RH control point to permit maximum room RH without condensation on windows condensate — in humidification, water condensed from steam condensation — change of state of a vapor into a liquid by extracting heat from vapor conductivity — ability to carry electrical current contactor — electromagnetic switching device cont
E EEPROM — electrically erasable programmable read-only memory EMI — electromagnetic interference entrained condensate — water droplets transported by steam flow EOS — end of season EPDM — ethylene propylene dienemonomer ETL — Electrical Testing Laboratory F °F — degrees Fahrenheit F&T trap — float and thermostatic trap flue piping — Type B: Double-wall construction with aluminum inner wall and galvanized steel outer wall Type B-W: Same as Type B except fabricated in an oval shape Type L: Same as Type B e
humidistat — a regulatory device, actuated by changes in humidity; used for automatic control of relative humidity humidity transmitter — a monitoring device that senses humidity level and provides an output signal based on humidity level HVAC — heating, ventilation, air conditioning hygrometer — an instrument responsive to humidity conditions of the atmosphere Hz — hertz I IAQ — indoor air quality ID — inside diameter in — inch, inches in2 — square inch(es) in3 — cubic inch(es) IOM — Installation, Oper
LP — liquefied petroleum LTS humidifier — Liquid-to-Steam humidifier M mA — milliampere max — maximum MB — megabyte mb — millibar MBh — one thousand Btu per hour micromho — one-millionth of a mho. The micromho is the practical unit of measurement for conductivity, and is used to approximate the total dissolved solids content of water.
R RFI — radio frequency interference RH — relative humidity S SCR — silicon-controlled rectifier SDU — space distribution unit SI — Système International D’unités (International system of units based on the meter, kilogram, second, ampere, Kelvin, candela, and mole) SSR — solid state relay SST — stainless steel STS humidifier — Steam-to-Steam humidifier T T — temperature TDS — total dissolved solids TP — time-proportioning U UL — Underwriters’ Laboratories V VA — volt-ampere Vac — volts alternating cur
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