Brian Wallingford, Applications Engineer Controlling Dehumidification Systems Brian Wallingford, Applications Engineer

Dehumidification System Design Process 1. Define the purpose of the project 2. Establish control levels and tolerances 3. Calculate heat and moisture loads 4. Select and position components 5. Select and locate controls

Controls Misc Humidity Control Temperature Control Airflow Control Face and Bypass Reactivation Energy Modulation Humidistat Humidifier Temperature Control Electric (Reactivation or Process Heating) Steam (Reactivation or Process Heating) Direct and Indirect Gas (Reactivation or Process Heating) Water or Glycol (Process Heating or Cooling) Ammonia (Process Cooling) DX (Process Cooling) Misc Airflow Control

Methods of Humidity Control Humidistat On / off control Space control +/- 5% of control level Small volume of make up air Face and bypass Modulating control End of duct or space control +/- 2% of control level Make up air volume not an issue Most energy efficient Reactivation energy modulation Slow response time Higher energy consumption

Passive Storage- Archival The purpose of the project is to prevent the fading of organic dyes in color film, and to prevent mold. Control level recommendations from Kodak include: 0°F, 35% rh for 500-year storage 55 to 70°F, 30 to 40% rh for prevention of major damage At 70°F, 35% rh, the moisture load profile looks like this:

Typical System for Archival Storage Independent humidity and temperature control Thermostat and humidistat control DX or chilled water cooling

Product Drying- Candy Pan Coating Purpose: To produce coated candy as quickly during the summer as during the winter, as with as high a level of quality. Ideal control level is unknown—trouble starts in spring Customer establishes delivered air condition and 50F and 50% RH At 50°F, 50% rh, the load profile looks like this:

Typical Product Drying Schematic End of duct control for humidity and temperature Face and bypass for tight humidity control Control valves for discharge temperature control Chilled water preferred over DX for end of duct temperature control

Product Drying- Other Considerations Often, product drying requires heat—post-cooling not always needed In this case, air returning from pans is humid and sugar-laden—purging makes sense. In another case, recirculation may save money In this case, DX cooling is used. When chilled water is used, be sure to add freeze-protection on weather air coils In many product drying applications, air velocity at product surface is critical. Easy in pan coating, more difficult in large rooms. Consider adding simple circulation fans in the space.

Industrial HVAC System Pharmaceutical Tableting Room Purpose: To prevent powders regaining moisture, which clogs presses, slows production and makes poor tablets Powders absorb based on rh, but to design a system, the engineer must define the humidity ratio: 10% rh is maximum based on input from R&D Comfort tolerance allows temperature to swing between 70 and 73°F Engineer selects lowest temperature: 70°F, 10% = 11 gr/lb At 70°F, 11 gr/lb, the load profile looks like this:

10% RH Room- Typical Schematic Room control for humidity and temperature Face and bypass for tight humidity control Control valves for discharge temperature control Differential pressure sensor controls make up air

10% RH Rooms- Other Considerations Less margin for error. Temperature control often as critical as humidity. Sensible heat load and uniformity needs may determine system air flow volume. The lower the humidity, the more critical the load calculations. Be sure to specify air leak rates in construction specs. When exhausting from low humidity room, air balance is absolutely critical.

Controls Summary Design condition and tolerance (50°F , +/- 5%) Dew point or humidity control Humidistat or humidity controller Sensor Location Tolerance of Sensor