Toronto, ON - When maintenance costs started to soar for the aging humidification system in the City of Toronto’s 70,000-square-foot municipal office building, city engineers turned to Toronto, ON-based HTS Engineering for a solution. The problem was that the existing electrode humidifiers in the 7-story building were nearing the end of their useful life. In addition, these humidifiers used disposable cylinders, and annual cylinder replacement costs for the 12 electrode humidifiers were running more than $300 for each unit each season - and this didn’t include labor costs.
“We recommended that the city replace each of the existing units with DRISTEEM VT Series electric humidifiers in order to reduce maintenance costs and improve humidity control,” says Kevin Little, general manager of HTS Engineering, Toronto. “As water evaporates from electrode units, the cylinders get clogged with deposits and need to be replaced every season. The DRISTEEM VT Series humidifier has a durable, stainless steel boiling tank with electric elements that resist mineral build-up. The tank removes easily for quick cleaning, and is then reused for another season, so there are no annual cylinder replacement costs.”
Design Conditions Started with Cold Winters
Winters in Toronto have an average low temperature of about -5 degrees F. (-20 degrees C.), and commercial facilities usually humidify to an indoor relative humidity (RH) of 30 to 35 percent for 6 months out of the year, according to Little. Based on the volume of the building, the amount of public traffic, and the number of people occupying each of the floors, HTS Engineering recommended installing 12 DRISTEEM Model VT-16 electric humidifiers - two for each of the occupied floors. Each unit produces up to 48 pounds of steam per hour (22 kg/h) and can maintain RH within 5 percent of set point.
The new DRISTEEM humidifiers were installed in small mechanical rooms to operate with dedicated ventilating systems for each building floor. Although VT Series humidifiers are capable of demand-signal control from a central command location, in this installation, each humidifier operates independently. “Individual control of each unit allows the building owner a lot of flexibility,” says Little. “Each floor may have a different humidity load. For example, the ground floor has entrance doors that permit a lot of dry, outside air to come in, requiring more humidification. Upper floors may have a high population density, and since people add moisture to the air, those floors require less humidification.”
Advanced Controls Ensure Proper RH Level and Minimize Maintenance
Advanced controls on DRISTEEM VT Series humidifiers are designed to minimize maintenance and improve accuracy and reliability. The built-in controller on each unit automatically controls the water level in the tank and shuts down if the water level gets too low. Periodic automatic tank draining significantly reduces scale buildup, and end-of-season automatic draining prepares the unit for inspection and any necessary cleaning. The onboard display panel indicates operating status (filling, making steam, or draining), and has a simple on/off switch.
When the humidistat senses that the RH level has dropped below set point, the VT Series humidifier unit turns on and automatically begins the process of creating humidification steam. The fill valve opens and closes as needed to maintain the correct operating water level, and the heaters automatically turn on to boil water into steam. Steam flows through a vapor hose to the dispersion assembly in the duct, where it is discharged into the airstream and absorbed. When the humidistat senses that the RH level has risen to set point, the humidifier stops making steam until the RH level drops again.
“We also provided two important safety controls as standard accessories in this installation,” says Little. “One was a high-limit humidistat mounted near the dispersion assembly. The other was an airflow proving switch mounted inside the ventilation duct. If the humidity gets too high in the duct, the high-limit humidistat will shut the humidifier down. Similarly, if the ventilating fan fails for some reason and there is no airflow in the duct to disperse the moisture, the humidifier will also shut down. These two safety devices prevent saturated air and wet ducts,” he says.
Designed for Cost-Effective Maintenance
The design of the DRISTEEM VT Series humidifier significantly lowers maintenance costs, according to Little. The biggest problem with humidifiers is scale build-up from minerals left after water evaporates, but DRISTEEM's design thoroughly addresses this problem. First, constant thermal expansion and contraction of the heating elements continually sheds mineral build-up, extending heater life. Second, the humidifier drains periodically to remove precipitated minerals from the tank before they have a chance to build up as scale. And third, the stainless steel tank removes easily for cleaning. Reusing the cleanable stainless steel tanks rather than purchasing replacement cylinders, as required for electrode systems, keeps maintenance costs low. In addition, if operated using softened water, the VT Series humidifiers may need no maintenance for the first 3 years. The Toronto installation is operating on regular city tap water, which is of medium hardness, but Little doesn’t anticipate that the build-up of scale will present any significant maintenance issues.
“When humidity isn’t called for after a period of 72 hours,” says Little, “the units automatically assume it is the end of the humidification season and shut down. After the tanks have cooled, they automatically drain, eliminating the need to drain the tanks manually. At that time, the tanks can be inspected and cleaned if necessary and then the units are ready for the next heating season.”
The City of Toronto’s electrode humidifiers had a useful life of about 15 years, after which maintenance costs began to climb. Little says that the DRISTEEM VT Series humidifiers should have a significantly longer useful life due to a rugged design, use of non-corrosive materials, the ability to resist mineral build-up, and a cleanable tank. With reduced maintenance requirements and costs, a longer operating life, and more accurate humidity control, the City of Toronto has a new, high-performance, cost-effective humidification solution.
DRISTEEM, a subsidiary of Research Products Corp., designs and manufactures humidification systems and accessories for commercial, industrial, and institutional applications. Their engineering and design expertise, proven performance, and local representative network guarantees a humidification system designed to meet any application. To find a local DRISTEEM representative, or to learn more about the VT Series electric humidifier, visit (www.dristeem.com/vt) or call (800) 328-4447.