Jeff Siemasko, VP Sales & Marketing - North America Moisture Load Sources Jeff Siemasko, VP Sales & Marketing - North America

Calculating Moisture Loads Choose the moisture control level Identify moisture load sources Quantify each load source Total the load & compare to the budget Adjust the calculation assumptions & recalculate Key Point: The only “correct” moisture load calculation is the one made after all parties agree on all assumptions If you give the same load calculation to 5 engineers, you will get 5 different load totals, as each person will use slightly different assumptions. Remember, this is an estimated load calc… and no answer is 100% correct

The Importance of Design Conditions

Choosing the Design Conditions Inside Conditions - How Dry? Dry enough to achieve the maximum economic benefit—and no drier Humidity control project is often the result of summer problems. So ... What is the moisture condition during the winter when no problems occur? When in doubt—test different conditions with a rental unit Weather Conditions - How Safe? How many hours can you risk being out of control? 1% of 2928 summer hours = 29 hours 2.5% of 2928 summer hours = 74 hours Extreme summer temperature DOES NOT coincide with extreme moisture ASHRAE weather data revised to reflect that fact The real message here is to select a design control level equal to what your product/process requires. Selecting a drier condition will not hurt you, but will often increase Initial Costs and Operating Costs

Moisture Load Sources Internal Loads External Loads Vapor permeation through walls, floor & ceiling Evaporation and respiration from people Desorption from moist products Evaporation from wet surfaces Vapor as a product of combustion Humid air infiltration through cracks, holes, & door openings External Loads Vapor carried into the system by moist ventilation air For the majority of industrial humidity control projects requiring low dew points, the largest load sources will be Make Up Air, People Load, Door Opening Infiltration, and Crack Load

Vapor Permeation (The Smallest Load) A lot of work to calculat, but rarely accounts for over 2000 gr/hr. Still to complete a good moisture load calculation, don’t get lazy and guess at things when the data is available

Moisture From Products & Packaging Moisture Content Since all products have different rates of releasing moisture when in a space with a lower vapor pressure, consult the chart in the DH Handbook. This can be a difficult moisture source to quantify and the Munters R & D lab can assist you when needed

Moisture From People This table uses 30 year old, conservative ASHRAE data. Applied research indicates that in low humidity environments, workers doing light work emit between 1500 gr/hr to 1800 gr/hr at 72 F. This is 50% less than the load shown here.

Moisture From Combustion Not that common, but a real source if open flame processes are in the controlled space

Moisture From Wet Surfaces Typical for investment castings or any other other application where open water tanks are present in the humidity controlled space We = H x A x (VPs - VPa) x 7000 HL

Air Leaks Through Cracks More Humid To minimze, seal with silicone or spray foam at all penetrations. Escutcheons are pretty covers that allow big leaks

Typical Air Leak Paths Air Handling System Room Construction Air duct joints upstream of blower Access panels in air handling equipment upstream of blower Ventilation louvers in doors Unused exhaust fans and back draft dampers Window air conditioners Room Construction Wall-ceiling, wall-floor joints Cracks around doors - especially at the floor Open construction above suspended ceiling tiles Wall penetrations for electrical boxes, conduits, pipes & light fixtures Vapor barrier plastic sheets....un-taped The tighter the envelope for the humidity controlled space, the lower the crack infiltration load

Humid Air From Door Openings For interior space –to-space doors, when you have no information, use 50 FPM

Humid Air From Airlock Openings May be the most conservative calculation. Why? (1.) Limit door openings = lower moisture level in the air lock (2.) If you dump dry air into the room and let it exfiltrate out, the positive pressure is helping to lower the infiltration (3.) If your controlled space is positive to the surrounding space, the lower your likely infiltration into the air lock

Humid Air Through Conveyor Openings But.. What can you do to this moisture source if you shroud the conveyor opening and make the opening small?

Ducted Openings Even with a high exit velocity, moist air can infiltrate into a dry room To minimize counter-flow infiltration, move low-pressure areas away from the room by ducting the openings With a shroud/tunnel, you limit the load to the space

Humid Ventilation Air (The Largest Moisture Load) ASHRAE Standard 62-1989 defines recommended ventilation rates for commercial and residential spaces Industrial ventilation rates are not defined by ASHRAE because of carrying contaminant levels in industrial process Assume ASHRAE Standard 62 as a minimum in the absence of industrial guidelines People To get the Make up air volume, take the time to accurately measure the exhaust air. Then add the required air volume for ventilation standards , then add make up air for space pressurization.

Glass Laminating Room Example Purpose of the project: Prevent the plastic adhesive film (Polyvinyl Butyral) from absorbing moisture, which would turn to steam in the laminating autoclave and form bubbles in the glass

Design Conditions

Vapor Permeation

Products & Packaging

Equilibrium Moisture Content of Material

Personnel Review this with Munters, as we can help you usually lower the people load

No-Load Elements

Door & Airlock Openings

Conveyor Opening Assume that the product conveyer opening will be equipped with a 2′-tunnel and plastic strips

Moisture In Fresh Air (The Largest Load)

The Load Summary