GORD COOKE. issues associated with humidification and dehumidification systems. In this article, humidification

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1 humidification BY GORD COOKE OPTIONS IN STEAM Since the thermal comfort of occupants in buildings is dependent on the amount of moisture in the air, HVAC contractors need to understand proper sizing, installation and operational issues associated with humidification and dehumidification systems. In this article, humidification in general and specifically, the merits of steam humidifiers will be explored. Dry indoor air conditions in winter will often result in cool air complaints along with the additional common complaints of dry skin, sore throats and increased thirst and static electricity. Cool air complaints stem from the fact that up to one third of the total heat loss from the human body (at rest in normal indoor environments) is via evaporation from the skin and respiration. The lower the humidity level in the air, the greater the evaporation rate from the occupant and the less comfortable they feel. HEALTH ISSUES The amount of moisture in the air can affect other aspects of air quality. High relative humidity (RH) levels are, of course, associated with mould and other fungal growth. Low RH levels can exacerbate symptoms associated with some chemical contaminants. There is also evidence that some airborne viral and bacterial infections will remain viable longer in dry air. Thus, proper sizing and operation of humidification equipment is important to both the comfort and the health of building occupants. Proper sizing and operation of humidification equipment will result in a moisture balance to maintain an RH high enough for occupant comfort but low enough to avoid any surface condensation on windows, cool foundation walls, and so on. While many design manuals would suggest a humidity range of 40 to 60 per cent RH, this may be too high for older building surfaces during the coldest winter temperatures. In addition, recent studies have shown that if all other airborne contaminants are kept at a low level then occupants will still feel comfortable at RH levels of 30 to 35 per cent. The amount of moisture in building air is a function of the moisture generated by the occupants and their activities, plus any moisture producing process equipment and humidification equipment, minus the drying effect of mechanical ventilation and natural air infiltration (air leakage). Moisture loss due to mechanical ventilation is easily determined from a psychrometric chart or other engineering manuals. For example, with outside conditions of -10C and 100 per cent RH (snowing) and inside conditions of 20C and 40 per cent RH, for every 100 l/s (200 CFM) of ventilation, a humidification capacity of approximately 2.8 kg/hr would be required to maintain a moisture balance. Moisture loss due to natural air infiltration is more difficult to measure. It is a function of building tightness, building height (stack effect), wind exposure STEAM INJECTION HUMIDIFIER Steam Trap Strainer Pneumatic Actuator Steam Condensate and building activities (operation of doors and windows). Contractors will have to rely on the experience of humidification equipment suppliers and engineers for determining the load due to natural infiltration. In general, in properly ventilated commercial and institutional buildings, the mechanical ventilation load will determine the humidification design load. SYSTEM SELECTION In cases where supplemental humidification is required, systems must be properly sized and installed to eliminate potential issues related to the task of adding moisture to air. That is, from an air quality perspective, humidifiers add to the complexity of maintaining warm, dry surfaces throughout the building. Standing water, damp surfaces in ductwork, controls that require adjustment but are inaccessible to occupants, regular maintenance requirements and the potential for water leaks, are of concern to indoor air quality (IAQ) control. There are at least five types of humidifiers available and at least four or five major brand names under which they are Inlet Steam Valve Cross Sectional View of Distributor Steam CONTINUED ON PAGE 30 Steam Jacket Dispersion Tube Support Bracket Dispersion Tube Steam Jacket Graphic NORTEC Air Conditioning Limited 28 HPAC JANUARY/FEBRUARY 2006

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3 humidification CONTINUED FROM PAGE 28 marketed. For commercial and institutional applications and for large houses with high humidification loads (due largely to high air leakage rates), the system of choice should be steam humidification for the following reasons: Steam humidification injects water in vapour form into the air stream. This reduces the cooling effect in the air stream caused by the need for evaporation of water droplets inherent in other types of humidifiers. With steam, the air temperature in the duct is maintained. This improves comfort and reduces potential for condensation in the duct. By definition, steam humidifiers are injecting boiled water into the air 30 HPAC JANUARY/FEBRUARY 2006 stream. This means there is reduced potential for introducing water borne contaminants into the air. (Not withstanding the issue of steam boiler chemical additives noted below). Steam systems have higher humidification capacities for a given duct size, air flow and plenum temperature. In many commercial/institutional applications use of wet media type humidifiers would be impractical due to capacity limitations. In general, in properly ventilated commercial and institutional buildings, the mechanical ventilation load will determine the humidification design load. Refrigeration Analyzer testokool 523 Simplifies complex functions in the field like real-time superheat and subcooling, plus trending with laboratory accuracy. Smart Features include: 35 built-in refrigerant P/T charts with more FREE via the Internet Built-in two-way manifold Up to 725 PSI Resolution of 0.1 PSI Saves 1,000 sets of values User selectable units *Available in kits with line temp probe & PC software Call today for more information and our FREE white paper A Digital Window Into Refrigeration Systems Circle #21 Atomizing humidifiers that sling or spray water droplets into the air may approximate the capacity of steam humidifiers but the cooling effect and problems with mineral fallout, particularly in hard water situations, are an issue. New pricing from $749! DIRECT STEAM HUMIDIFIERS In buildings with steam boilers, boiler steam may be simply dispersed into the ductwork of air handling equipment using a direct steam humidifier. There are a couple of methods of injecting the steam. Sometimes a simple pot or pan is attached under the duct and steam is injected into the side of this receptacle and the steam rises into the duct. Provisions must be made for condensate to return to the boiler and care must be taken to ensure condensate doesn t splash into the duct. A more sophisticated device known as a steam injection humidifier uses single or multiple injection tubes surrounded by a jacket of steam to ensure condensate free steam is injected into the air stream. The biggest drawback of direct steam humidifiers is that the neutralizing chemicals required in steam boiler systems to eliminate acid buildup in piping can be released into the air stream. These chemicals can cause a wide range of symptoms for occupants, including skin rashes, eye and throat irritation and nausea. From an air quality perspective this type of humidifier should not be used unless the steam generation system is free of chemical additives. An option for steam boiler systems is to use a steam-tosteam heat exchanger, with the steam to be used for humidification isolated from the boiler steam. SELF-CONTAINED STEAM HUMIDIFIERS Self-contained devices generate steam with either an electric element submerged in a water chamber or an electrode-type heating element in a sealed plastic container. The steam is delivered to the air stream of a duct system via short piping and a dispersal tube. Both methods use safe potable water. LOOKING FOR HUMIDIFIERS visit

4 The actual energy consumption of steam humidifiers is offset by the reduction in energy required to maintain comfort. The simple electric element units can use pretreated or softened water to minimize scale build up. Pretreatment of the AN IAQ PERSPECTIVE When selecting humdifiers the following decision criteria should be considered: Capacity sized to the demand The potential for leaks or breakdowns that may cause wetting events The potential for standing water and the introduction of water borne pollutants into the air stream Scaling and overall maintenance requirements Control strategies water for sealed electrode type humidifiers is counterproductive as the demineralized water becomes less conductive and heating performance is poor. For electrode type humidifiers, typically sealed containers and electrodes are replaced regularly to resolve the build up of minerals in the tanks. Both of these humidifiers require relatively large electrical service inputs and this may be an installation issue. The actual energy consumption of steam humidifiers is offset by the reduction in energy required to maintain comfort that is, lower air temperature setpoints can be used when the RH is in a comfortable range. In summary, steam humidifiers are the best alternative for the high capacity requirements of large houses and commercial buildings. They offer reliable operation with straightforward maintenance for HVAC contractors. In all cases humidification systems must be carefully planned and installed so as to avoid problems with leaks or wetting of ductwork or other building materials. Proper humidification can increase occupant comfort and indoor air quality and, in some cases, reduce energy consumption. Gord Cooke, P.Eng., is president of Air Solutions Inc., Cambridge, ON. Contact him at , gcooke@airsolutions.on.ca or visit for more information. RATE THE ARTICLE! Will this information be useful? Please circle the appropriate number on the Reader Postcard. Thank you. VERY USEFUL USEFUL NOT USEFUL Circle #22 JANUARY/FEBRUARY 2006 HPAC 31

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