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

2. 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

3. The Importance of Design Conditions

4. 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

5. 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

6. 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

7. 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

8. 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.

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

10. 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

11. 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

12. 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

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

14. 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

15. 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?

16. 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

17. Humid Ventilation Air (The Largest Moisture Load)
ASHRAE Standard 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.

18. 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

19. Design Conditions

20. Vapor Permeation

21. Products & Packaging

22. Equilibrium Moisture Content of Material

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

24. No-Load Elements

25. Door & Airlock Openings

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

27. Moisture In Fresh Air (The Largest Load)

28. The Load Summary